Metabolism of the heart in cardiac failure

Metabolism

of the Heart B!j

in Cardiac

Failure

JAMES SCHEUER

LTHOUGH much effort has been expended in the search for a biochemical basis of congestive heart failure, our understanding of the sequence of events that leads to decreased myocardial function is poor. Most investigations have been directed toward localizing a single defect to one of the three phases of cardiac energetics: energy liberation, energy conservation and energy utilization, as outlined in Fig. 1.’ Abnormalities have been found in all three phases of cardiac energetics in the failing myocardium. Whenever such an abnormality has been uncovered, the question arises whether this is a contributing factor in the etiology of myocardial failure or whether it is a result of failure. It now appears probable that the concept of a single biochemical lesion in heart failure is naive. The causes of heart failure are more complex than originally anticipated and may be the result of multiple defects. It seemspossible that there are structural alterations which may cause disorganization of intracellular organelle and protein relationships and thereby disrupt integrated biochemical and mechanical function. At present, biochemical changes are known to occur in nucleic acid and protein synthesis, in some of the reactions of energy utilization, and, in severe failure, in processesof energy liberation. In addition, the myocardial metabolism of catecholamines is impaired, compromising an important cardiac compensatory mechanism.

A

DEFINITION

AND CHARACTERIZATIOX

OF HEART FAILURE

Cardiac failure is considered to be that state in which cardiac output is insufficient to meet the metabolic requirements of the body.2 For the purposes of metabolic classification, heart failure has been divided into two major types. The most common is that in which an increased hemodynamic load is imposed upon the heart, such as in valvular disease, hypertension or acyanotic congenital heart disease. Less frequently, a primary metabolic defect may lead to cardiac failure. Throtoxicoses and beriberi have been thought to be examples of metabolic heart failure. It has been suggested that in hemodynamic failure a major metabolic lesion would most likely be found in the energy utilization phase of metabolism. v In metabolic failure, energy liberation would probably be abnormal. From Medical

the Division of Cardiology, Department of Medicine, University of Pittsburgh School, Pittsburgh, Pennsylvania. Work reluted to this review is supported by U.S. Public Health Service Research Grant HE 09727 and Grant-in-Aid 67 744 from the American Heart Association. JAMES SCHEUER, M.D.: Division of Cardiology, Department of Medicine, University of Pittsburgh Medical School, Pittsburgh, Pennsylvania. Dr. Scheme?- is supported by Research Career Development Award I K03 HE 15867 from the U.S. Public Health Service.

24

PROGRESSIN CARDIOVASCULAR

DISEASES,

VOL. XIII,

No.

1 (JANUARY),

1970

METABOLISM

Fig. l.-The

OF

THE

HEART

IN

CARDIAC

FAILURE

25

three phases of cardiac energetics, modified from Olson1

Many metabolic studies of heart failure have suffered from inadequate characterization of the state of myocardium as a muscle. Circulatory failure, or the failure of the heart as a pump, has usually been present, as defined by clinical and cardiac catheterization criteria. This is often expressed as diminished ventricular function (stroke work) in response to a given ventricular filling (end-diastolic) pressure. 5 The mechanical features of the heart muscle, such as the force-velocity relations, are important in defining myocardial (muscle) failure.’ In the intact heart, the relations between wall tension, volume and the rate of circumferential fiber shortening depends on the contractile state of the myocardium.’ Circulatory failure may occur without muscle failure when there is fluid volume overload” or restricted filling of the heart, as in pvricardial tamponade. On the other hand, muscle function may bc impaired in the absence of circulatory failure. Studies cf papillary muscles from cats with pulmonic stenosis demonstrate that hyp:artrophied muscles have diminished contractility, even when circulatory failure is absent.9 The h(~art compensates for muscle failure by the development of cardiac hypcrtrophy and by calling upon its FrankStarling properties. Meerson”‘-I’ has described more precisely the sequence of cardiac hypertrophy and failure. He showed that in animals with stenotic lesions of the aorta, a state of “isometric hyperfunction” is created that progresses through three phases. During the first phase, called th(b *‘damage stage of isometric hyperfunction,” there is breakdown of myocardial proteins and mitochondria. increased energy consumption, and activation of protein and nucleic acid synthesis. The greater mechanical burden imposed by the hemodynamic lesions are expressed by increased oxygen and substrate consumption per unit of myo-

cardium. There are frequently Illanif~~stations of circulatory failurr during this stage. The second stage is that of “relatively stable hyperfunction,” which may last months or years. During this stage, most measurements of circulatory function are normal, as are studies of protein turnover, energy utilization and myocardial substrate metabolism per unit of myocardial mass. The third stage is that of “gradual exhaustion and progressive cardiosclerosis.” During this stage, there is diminished protein synthesis, destructive changes in the mitochondria, degeneration of some muscle fibers, and replacement with fibrous tissue. These stages of hyperfunction described by Meerson have rough clinica counterparts. However, the sudden imposition of a sustained hemodynamic load, such as the experimental narrowing of the aorta, is not common in clinical medicine, and the “damage stage” may not be clearly delineated. Since the hemodynamic and the myocardial mechanical states are poorly characterized in many of the studies concerned with metabolism in heart failure, this review will attempt to outline the major metabolic features that have been observed. We will focus on failure due to hemodynamic overload, for that is most important clinically. Other types of failure will also be briefly rcviewed. CORONARY FLOW, OXYGEN, AND SUBSTRATE UTILIZATION The rates of oxygen or exogenous substrate uptake by the heart provide information regarding energy turnover. Oxygen consumption is stoichiometrically related to high energy phosphate formation by oxidative phosphorylation, and, therefore, is an accurate indicator of the metabolic rate. Other exogenous substrates, in addition to being catabolized for energy production, may be stored in the myocardium as glycogen or triglycerides. Studies of myocardial blood flow, oxygen, and substrate uptake have been performed during heart failure in isolated hearts, I3 in closed chest anesthetized dogs,lJ” and in humans with congestive heart failure.15-21 The majority of these studies have not demonstrated any abnormality in metabolic rates. Dogs with chronic low output circulatory failure due to right-sided valvular lesions, but with left ventricular failure, have normal coronary flow, oxygen consumption, and substrate extraction per unit of left ventricular myocardium.*114 In dogs with the recent onset of aortic regurgitation, which may effect the left ventricle more severely, coronary blood flow and left ventricular oxygen consumption are reported to be increased.?’ Coronary flow may be normal or slightly reduced in patients with congestive Oxygen extraction may be increased, but failure due to valvular disease.“-‘!‘+” oxygen consumption per gram of myocardium is normal. Because hypertrophy is present, total myocardial oxygen utilization is frequently elevated.‘” Similarly glucose, lactate, pyruvate, and free fatty acid utilization appear to be normal in patients with low output congestive heart failure.15~1f~ The many factors influencing cardiac metabolic rates in cardiac failure have recently been reviewed.“” In myocardial failure, contractility is decreased,9 and energy consumption linked to contractile work is diminished propor-

METABOLIS?d

OF

THE

HEART

IN

CARDIAC

27

FAILURE

tionately. 24 However, cardiac dilatation is frequently present, leading to greater tension requirements for generation of a given pressure.‘o The period during which tension is maintained with each beat is prolonged.‘” Since for a given contractile state, energy requirements of the myocardium are proportional to tension, the oxygen and substrate consumption for a given developed pressure or cardiac output would increase. The combined effects of increased cardiac mass and tension would probably outweigh the effect of decreased contractility on metabolic rate, and the efficiency of conversion of total cardiac chemical energy to external cardiac work would be diminished. Because of the coronary flow techniques employed in studies in humans, results are generally expressed in terms of substrate and oxygen consumption per unit of myocardium, and the efficiency espressed as external cardiac work divided by total oxygen or substrate used is not available. Since the studies in intact humans or dogs lack the precision that may be necessary to detect small metabolic changes, more carefully controlled investigations with acute valvular lesions are of interest. When acute mitral or aortic regurgitation are produced experimentally. slight increases in myocardial oxygen consumption are observed.“;,” These are associated with increased ventricular volume, greater magnitude and velocity of contractile element and fiber shortening, and peak wall tension.‘* Most of the increment in oxygen consumption can be accounted for by the increased tension. These studies emphasize the role of volume and tension changes in cardiac energetics with valvular regurgitation. In stenotic lesions, the tension demands increase markedly with proportional rises in cardiac metabolic rates. Thus, the evidence at the present time suggests that in heart failure due to hemodynamic overload, oxygen and exogenous substrate balance is normal on a per unit of myocardium basis. Changes in contractility, cardiac dimensions, tension requirements, and ventricular mass ma) alter the quantity of o.xygen or substrate consumed for a given external work. Such alterations may be difficult to demonstrate in man and intact animals, because the techniques for measuring coronary flow, ventricular volume and myocardial tension, and for arc either inaccurate 01 determining the contractile state of the myocartlium cun~l~c~rson~c~. SUBSTRATE

MKTABOLISM

AKD

ES~:RGT

KELEASE

The studies concerning substrate and oxygen consumption outlined above are concerned with the metabolic balance of these substances across the intact coronary bed. Fewer investigations have examined the endogenous substrate levels or the pathways concerned with energy liberation in tissue from failing hearts. Figure 2 shows the interconnecting pathways for the processes of energy release in the myocardium. Control over these pathways is exerted by the rates of ATP breakdown and the resultant formation of ATP, ADP, AMP, and inorganic phosphate. One way to study metabolic activity is to investigate enzymes involved in the various biochemical pathways. Post mortem analysis of myocardium from humans who died with congestive heart failure reveals a reduction in the Krebs cycle enzyme isocitric dehydrogenase.- “9 Analysis of enzyme activity of the gly-

NORMAL EXTRACELLULAR

CYTOPLASM

SPACE

i

FATTY ACIDS

j

NAD-NADH

LACTATE

GLUCOSE

MlTOCHONORlA

LAD,

j I

GLYCOGEN ’

t RED

Fig. Z.-Schematic representation of the energy-releasing pathways. Only the substrates that contribute most to energy production are shown. The rates of substrate metabolism are governed by energy utilization. The breakdown products of ATP, releasedduring energy utilization, stimulate both glycolytic and oxidative pathways. The phases of energy release and energy utilization are interdependent, and an alteration in one wiIl be reflected by changesin the others.

colytic pathway reveals aldolase to be reduced and glyceraldehyde phosphate dehydrogenase to be increased. The hexosemonophosphate shunt is relatively inactive in the intact heart0 but may be important in tissue repair.:” Some hexosemonophosphate shunt enzymes are reported to be increased in acutely overloaded guinea pig hearts3? but glucose-8phosphate dehydrogenase activity is normal in the myocardium from humans with heart failure.2s Lactic dehydrogenase ( LDH ) is an important enzyme in controlling the balance between gIycolytic and aerobic metabolism. The isoenzyme of lactic dehydrogenase which predominates in myocardium, LDH,, is particularly adapted to aerobic metabolism and is thought to be important in directing pyruvate into oxidative pathways. Total LDH activity is reported to be reduced in myocardium from failing human hearts,“!’ but normal levels of LDH were found in dogs with right ventricular hypertrophy.X3 However, there is a shift from the preponderance of LDH, toward the skeletal muscle type of LDH isoenzymc, which is better adapted for anaerobic metabolism.““-“” Although these changes in enzyme patterns might be consistent with a diminished potential for Krebs cycle oxidativc activity and enhanced glycolytic potential, they must be interpreted with caution. Only a few metabolic steps have been examined, and only by studying the integrated function of a pathway can its maximum activity be determined.

METABOLISM

OF

THE

HEART

IN

CARDIAC

29

FAILURE

Evidence for alterations in pathway activity can be derived from evaluating levels of endogenous substrates and rates of conversion of substrates to lactate (for glycolysis) or CO, (for oxidative metabolism). Although endogenous glycogen stores are reported to be high in physiologic hypertrophy,“‘; low levels have been found in acute failure”; or in the transient breakdown stage of cardiac hyperfunction.” Myocardium from failing dogs is reported to have increased glycolytic rates when exposed to anoxic conditions,“” and lactate production by the heart is increased throughout the three phases of hyperfunction.15 Myocardial homogenates from guinea pig hearts with failure due to aortic constriction have normal rates of oxidation of glucose or succinate suggesting a normal oxidative potential.:” Thus, the glycolytic and oxidative capacity appear not to be diminished in failing myocardium. Studies of the lipid content of hypertrophied myocardium arc inconsistent. A decrease in the total lipid concentration, mainly due to a decline in the triglyceride fraction, has been reported.“!’ On the other hand, diminished phospholipids have been found in cardiac hypertrophy,“’ and in the failing rat heart in a heart-lung preparation. ‘I Since phospholipids play a major role in membrane integrity and function, their loss would be consistent with some of the defects in ion transport and calcium binding that have been suggested to be causally related to myocardial failure. The capacity for fatty acid metabolism by homogenates from the myocardium of guinea pigs with chronic heart failure is dinGnished.“s This appears to be related to depressed myocardial levels of camitine. The addition of camitine, which serves as a carrier of fatty acid into the mitochondria for osidation, corrects the defect in fatty acid oxidation. The results of tissue analysis demonstrate that in cardiac hypertrophy and congestive heart failure, there are some changes in enzyme balance, and at times cndogcnous myocardial substrate stores may bc diminished. The transport of fatty acid into the mitochondria may bc limited by decreased carnitine availability, but the glycolytic and osidative capacities of the myocardium are not diminished. Defects in the substrate catabolic pathways appear not to be primarily responsible for myocardial failure. THE

MITOCHONDRIA

AND

OXIDA.TIVE

PHOSPHORYLATION

Since the mitochondria are responsible for oxidation of the products of carbohydrate and lipid metabolism and for the conversion of their chemical energy into the high energy phosphate form, much attention has been focused on this organclle as the possible site of a metabolic defect in myocardial failure. Several studies of experimental hypcrtrophy and failure have reported changes in mitochondrial morphology. Myocardial hypertrophy has been associated with increased size of the mitochondria and widening of the membranes of the mitochondrial surface. the cristac, and the space between the cristae.*‘.*” Small mitochondria with a decrease in total mitochondrial mass have also been reported in dogs with congestive heart failure.” Meerson et aI42 reported that during the early damage stage of hyperfunction. the mitochondria increase in

Fig. 3.-The electron transport (cytochrome) chain. In the presence of adequate supplies of reduced flavin and nicotinamide adenine dinucleotides and oxygen, the availability of ADP regulates the electron flow, and, therefore, the rate of oxygen consumption. size and show a decreased number of cristae. Soon thereafter some of the mitochondria are destroyed. During stable hyperfunction, the mitochondria remain large, but do not take up proportionately as much space as during the breakdown phase. Very large mitochondria remain during the gradual exhaustion phase, but the area that they occupy is less than in the normal state. The enlargement of the mitochondria during the early damage stage may be related to the increased oxidative metabolic requirements for tension and for protein an d nucleic acid synthesis. The decrease in relative mass during exhaustion and the diminution in the number of cristae are thought to limit high energy phosphate availability during this stage. Mitochondria from failing human hearts are reported to show no alteration in size or structure.4G One of the most controversial areas in metabolic studies of congestive heart failure is whether there is a defect in mitochondrial oxidative energy production. Figure 3 illustrates the cytochrome chain and oxidative phosphorylation side reactions. The integrity of mitochondrial metabolism is evaluated by introducing one of the Krebs cycle intermediate compounds into a mitochondrial preparation and measuring the rate of oxygen uptake (q0,). In addition, the molar ratio of phosphate or ADP consumed to the q0, can be measured (P/O ratio). The stimulation of oxygen consumption with the addition of ADP is also an indication of mitochondrial integrity. This is called respiratory control. Several groups have reported diminished mitochondrial qO,, P/O ratios, and respiratory control in the failing heart.“7-51 In these studies, the physiologic state was either acute failure or failure soon after production of a surgical lesion. In a study of dogs with aortic constriction and myocardial hypertrophy, analysis of mitochondria one to 2% years after surgery demonstrated decreased q0, and P/O ratios.4c: In addition, the Krebs cycle enzyme malic dehydrogenase was diminished in proportion to the loss of mitochondrial cristae.“” In these hearts, maximum ATP synthetic rates would be approximately one-half of normal, suggesting that decreased ATP synthesis could be a significant factor in initiating and perpetuating myocardial failure. All of the above studies were performed with older techniques, in which the adequacy of the metabolic state of the mitochondria could be questioned. Using newer techniques of isolation and analysis, Lindenmayer et al.“’ recently reported diminished oxygen consumption, respiratory control and P/O ratios in failing hearts from guinea pigs with aortic constriction.

METABOLISM

OF

THE

HEART

IN

CARDIAC

FAILURE

31

Studies in several species, including the human, indicate that mitochondrial function may be normal in cardiac failure.11~*6~53-j6These studies have included normal oxidative phosphorylation, P/O ratios, go,, respiratory control, and mitochondrial adenosine triphosphatase ( ATPase) activity. In a study by Sobel et a1.,55 not only was circulatory failure documented, but the intrinsic myocardial contractile state was also shown to be decreased, demonstrating that mitochondrial function can be normal when myocardial failure is present. The reasons for the discrepant results concerning mitochondrial function are not clear. Sobel et al.“” suggested that the faulty methods for removal of the hearts, or for isolation and incubation of the mitochondria might have led to the abnormalities observed in some studies. However, this does not explain why the mitochondria from hypertrophied and failing hearts but not from controls should show the defects. In addition, Lindenmayer et a1.51 found abnormalities in mitochondrial function using techniques similar to those of Sobel et al. They suggested that the variable results may be due to studies being conducted during the different phases of hyperfunction. However, this conclusion also appears in doubt, since both normal and abnormal findings have been reported in more than one phase. It seems clear that although mitochondrial function may be abnormal at times, significant myocardial and circulatory failure may occur in the absence of such defects. It is possible that more precise techniques not now available will uncover a consistent aberration, and these conclusions will have to be modified. However, even if metabolic function per mitochondrion is normal, current evidence suggests that late in the course of failure, the mass of mitochondrial tissue is diminished. The possibility of decreased energy formation per unit of myocardium therefore exists. This aspect of the problem will have to be studied further. HIGH

EXERGY PHOSPHATE

COMPOUNDS

The adequacy of energy conservation can be evaluated by measuring the levels of high energy phosphates in the myocardium. These levels represent the net result of high energy phosphate formation and breakdown. Figure 4 demonstrates the pathways involved in this balance. The contractile capability

OXIDATI\‘F. PHOSPHORYLATIOK ~;I.YcoLYsIs

ADP

)

IL ,\Ti'

->

-j 11

IIIETABOLI~ AND MECHANICAL ACTIVITY

hlgokmase

Fig. 4.-This diagram shows the reactions that influence ATP levels. The constant regeneration of ATP by oxidative phosphorylation, the creatine phosphokinase reaction and the myokinase reaction balance the rate of utilization, so that ATP levels remain quite constant in cardiac muscle.

0”

JAMES

SCHEUER

of muscle is dependent on the availability of ATP, and, therefore, diminished myocardial levels of the compound might be responsible for cardiac failure. Diminished myocardial high energy phosphate levels are reported in studies of acute or subacute myocardial failure.““~“‘~5sIn a more chronic study of dogs with right sided valvular lesions, ventricular hypertrophy was associated with normal levels of creatine phosphate and creatine, but in those animals that demonstrated circulatory failure, ATP, CP, and creatine ww decreased.‘” Nomral cardiac levels of total high energy phosphates or ATP have been reported in many studies of cardiac hypertrophy and failure,‘,“,““-“’ including those patients with congestive heart failure due to tricuspid or mitral regurgitation. CP levels may be diminished, while ATP remains normal in failing myocardium.62,F’ However, creatine concentrations are also lowered, so that the CP to creatine ratio is normal. Thus, a defect in creatine metabolism, but not in its phosphorylation, may be present in cardiac hypertrophy and failure. The conflicting results regarding high energy phosphate compounds may he related to studies being conducted during different phases of hyperfunction. Meerson”’ found that ATP is reduced only during the early damage and the late exhaustion phases, although myocardial CP levels are diminished throughout most of the period of hyperfunction. The majority of studies indicate that ATP stores are adequate during periods of myocardial hypertrophy and circulatory failure. Pool et al.“A demonstrated diminished contractility in hypertrophied papillary muscles compared with controls, despite similar ATP and CP levels. This would indicate that reduced high energy stores are not the causal factor in the diminished contractility of myocardial failure. CONVERSION OF CHEWCAL

TO MECHANICAL

ENERGY

The preceding sections have presented evidence that a primary defect in energy availability is not solely responsible for the myocardial failure induced by hemodynamic overload. An abnormality in energy utilization appears probable. However, measurements of high energy phosphate levels only indicate the net result of the reactions shown in Fig. 4. They provide no information regarding the activity of any individual reactions or the r-ate of ATP turnover. One way to examine this probIem is to block the reactions that replenish high energy phosphates and examine the rate of energy utilization. Pool et al.“l blocked ATP synthesis and mcirsurcd the energy cost of contraction in papillary muscles from normal cats and cats with right ventricular failure. As in previous experiments, they found contractility and total work performed by the muscles from failing hearts to be depressed. High energy phosphate consumption was ASO decreased, so that the efficiency of the conversion of chemical to mechanical energy was not lowered. These studies demonstrate that under in vitro conditions conversion of chemical to mechanical energy in failing myocurdium is normal. The findings imply that the earlier observations of diminished efhciency of oxygen utilization for external vvork’“.‘” must be related to the efficiency with which contractile work is converted to uscbfulcastema work.

METABOLISM

OF

THE

HEART

1S

TRANSVERSE

CARDIAC

33

FAILURF

TUBULE \

CELL

SURFACE

CISTERNA

Fig. 5.-This diagram modified from Gertz et al. 7o illustrates a current concept of how calcium ion concentrations in the cell are controlled. Two terminal cisternae and an intervening transverse tubule make up the triad that is frequently found adjacent to the 2 line of the sarcomere. The solid arrows indicate passive movement, and the open arrows indicate active transport of calcium across the cell and sarcoplasmic reticular membranes.

MYOCAFDIAL IONS AND

EXCITATION-C• XTRACTIONCOUPLING

Intracellular calcium is an important mediator of excitation-contraction coupling. 66Figure 5 shows diagramatically certain features of the calcium control mechanism as it is currently visualized. The excitation wave is thought to pass along the transverse tubule and activate contraction at the sarcomere level.“‘@ The terminal cistemae of the sarcoplasmic reticulum and longitudinal tubules appear to be important in the release and binding of intracellular calcium which is associated with contraction and relaxation. Calcium release is caused by electrical activation, and calcium uptake is dependent upon ATP.6” The activity of this system probably regulates the concentration of calcium in the cytoplasm and the intensity of the contractile state. Although many investigators have speculated upon the possible role of calcium in the pathogenesis of cardiac failure, studies regarding a possible relationship are few. Gertz et al. TOfound that the rate of calcium uptake was reduced in an isolated sarcoplasmic reticulum fraction from a spontaneously failing dog heart-lung preparation. Diminished myocardial calcium concentrations have also been reported in acute failure.‘l Sodium and potassium are intimately involved with the electrical properties of the heart and also may alter calcium movements across the cell membrane and within the ce11.66,72 Magneisum is important as a co-factor for myosin ATPase in the contractile process.‘3 Decreased myocardial concentrations of potassium and magnesium and increased contents of sodium, chloride, phosphate and water have been the most frequent findings in chronic congestive heart failure.71~7~-7”Sodium and calcium appear to compete for sites in the sarcoplasmic reticulum.“’ Increased intracellular sodium therefore might reduce the capacity of the sarcoplasmic reticulum to control cytoplasmic calcium concentration. These few studies do not permit any conclusions regarding the role alterations in cardiac ions might play in the pathogenesis of myocardial failure. The

34

Fig. 6.4chematic structure of the myocardial cell and the sarcomere. Myofibrils are arranged longitudinally in the cell. The periodic myofibrillar structure is due to the regularly arranged sarcomeres. The velocity, strength and intensity of contraction may be related to the numbers of cross bridges interacting at one time and the speed with which they contract, break and form new cross bridges along the sliding protein filaments.

/

/

\\

/ /’

\

\

SARCOMERE

interrelationships between transmembrane action potential, monovalent ion shifts, calcium exchange and contractility in myocar&aI failure wouId appear to be potentially fruitful areas for further investigation. STRU~~~~RAL CIWNCES OF THE CONTRACTILE APPARATUS The organizational aspects of the muscle cells are shown diagramatically in Fig. 6. The myocardial fibers are discrete cells, and the intercalated discs are specialized cell borders which probably serve as impulse conduction pathways between cells. The sarcomere is the fundamental unit of myocardial contraction. During activation it is thought that angulated cross bridges form between the thin and thick filaments. When the cross bridges shorten, the two filaments slide over each other causing shortening of the sarcomere. It is probabIe that caIcium and magnesium control the number or frequency of cross bridge interactions for which ATP provides the energy. During contraction ATP is hydrolyized by myosin ATPase. Investigations into the histological and biochemical aspects of the hypertrophied and failing myocardium have centered around the following questions: (1) Is all myocardial growth due to cellular hypertrophy, or does hyperplasia occur? (2) Does the myocardium outstrip its capillary supply and become hypoxic? (3) Is the structure of the sarcomere changed, so that the thick and thin fiIaments may not be able to interact with their normal intensity? LinzbachsO has reported that in physiological hypertrophy, such as that seen in athletes, heart weights of up to 500 Gm. are encountered. This is due to muscle cell hypertrophy. In pathological hypertrophy, where heart weights exceed 500 Gm. he found no further increase in fiber size, but increased numbers of fibers and nuclei. Capillaries were present in proportion to fibers so that the distance across which nutrients must travel in the estravascular space

METABOLISM

OF

THE

HEART

IS

CARDIAC

FAILURE:

35

is probably the same in physiologic and pathologic hypertrophy, but may be greater than in the normal myocardium. Other reports do not support the concept of muscle cell hyperplasia. Meerson” found that the ratio of muscle nuclei to tissue diminishes throughout the three stages of hyperfunction. Several studies have demonstrated an increase in desoxyribonucleic acid (DNA) in myocardial hypertrophy, suggesting the addition of nuclei.82-y” However, this finding has not been invariable.s6 Some of the DNA increase appears to be due to polyploid nuclei, but studies with radioactive DNA precursors identify most of the mw DNA in connective tissue and blood vessels.sl,s’ Electron microscopic studies of myocardial hypertrophy demonstrate that the number of myofibrils per cell is increased, but the usual uniform array of the myofibrils and 2 bands are often disrupted, and the intercalated discs are &storteda4j,hg.!“l Th e cross-sectional geometric relationship of thick to thin filamcuts are not altered. Thick filament diameter and myosin structure also appear normal in myocardial hypertrophy. o”,91 The disarray of adjacent sarcomeres or fibers could possibly lead to slippage or asynchrony of contraction, but this remains to be proven. -4lthough the distance between Z lines of the sarcomere is increased in acute cardiac dilatatioqQ2 stretching of the sarcomere is not apparent in hypertrophied and dilated diseased hearts. 8o Although this finding must be confirmed, it suggests that if sarcomere stretching is a factor in cardiac failure, it is probably involved only in the end stage of cardiac exhaustion. PROTEIN

SYNTHESIS

The mechanisms of protein synthesis are schematically outlined in Fig. 7. The nucleus is probably the site of all ribonucleic acid (RNA) formation. DNA dependent messenger RN-4 (mRNA) synthesis is under the control of the enzyme RNA polymcrase. mRNA transfers the genetic information to

Fig. 7.-Schematic representation of protein synthesis. During hemodynamic overload of the heart, nuclear and nucleolar stimulation of RNA synthesis initiate the hypertrophic response,

36

JOIES SCHEUER

ribosomes. An aggregate of ribosomes, the polyribosome, which contains enzymes, ions, high energy phosphate compounds and mRNA, assembles sRNAlinked amino acids into proteins. The ribosomes arc found in the microsomal ultracentrifugational fraction of cardiac muscle. Increased amino acid incorporation into protein occurs as early as three hours after a pressure load is imposed on the isolated heart,93 and is regularly found during the acute damage stage of hyperfunction.S1+9G During stable hyperfunction the rate of amino acid incorporation somewhat diminishes compared with the damage phase, and the turnover of protein is normal. During the phase of exhaustion, protein synthetic rates are diminished. Several steps in the protein synthetic pathway have been in\.estigated. Although muscle cell DNA does not increase in hyperfunction, DNA-linked RNA polymerase increases within 24 hours of aortic banding in rats.“: Actinomyocin D, an inhibitor of DNA dependent RNA synthesis, blocks the qnthetic responses to overload,“S indicating that the DNA-mRNA step is obligatory. Numerous workers have detected increased myocardial RNA or increased incorporation of precursor bases into RNA in myocardial hypertroSl-R-I.SF,96.97,99 MeeTSOnS found that the number of nucleoli responsible for phy. rRNA synthesis increases during the damage stage of hyperfunction. Kakug6 reported increased synthetic rates for mRNA, nuclear RN,4, mitochondrial RNA, and microsomal, mitochondrial and cytoplasmic protein during the first 3 weeks after aortic constriction in rabbits. With failure, mRN-4 synthesis remains high, but synthesis of other fractions returns to normal. Increased ribosomal and microsomal activity during hypcrtrophy arc reported to bc due to greater numbers of these structures in the n~yocardium,lOO but there is also elevated microsomal activity per unit of protein.“” Microsomal protein synthetic rates rise after only one hour of increased cardiac 1oad.‘0’,‘02 The evidence then supports the conclusion that protein synthesis is stimulated very early in the course of cardiac hypcrfunction. Protein synthetic rates are highest early in the acute damage phase, but may remain tale\-atcd during stable hyperfunction. During exhaustion of the myocurdium, protein synthesis is diminished. Stimulation of protein synthesis in overloaclrd hearts depend on the DNA-RNA system. Because protein synthesis is an energy-consuming process, this adds a further burden to the energy release mechanisms in the hemodynamically overloaded heart. FACTORS INFLUEWING

THE IXITIATION

AND MAIR‘TESANCE

01; H~PEKIROPIIY

The observation that increased pressure load rapidly stimulates protein synthesis suggeststhat tension may be a controlling factor in development of cardiac hypertrophy. The mechanism by which increased pressure is translated to the hypertrophic stimulus is not known, but it has been proposed by Badeerlo than an increased metabolic rate per beat is the determining factor. Hormonal support appears to bc necessary for the development of myocardial hypertrophy. Hypertrophy does not develop in hypophyscctomized animals with aortic constrictionl”‘JO” unless growth hormone is administered. Thyroid stimulating hormone, while not effective by itself, seemsto potentiate the effect of growth hormone. 106Although adrenalectomy results in decreased myo-

METABOLISM

37

OF THE HEART IN CARDIAC FAILURE:

cardial mass in the normal animal, the presence of adrenal hormones does not appear to be necessary for hypertrophy to occur.‘07 Insulin and male hormones have also been identified as factors in the response of the heart to stimulation of hypertrophy. 81Although hormonal balance is important for the development of hypertrophy, the initiation of protein synthesis is not dependent upon hormonal factors, for increased protein synthesis can be stimulated by overloading isolated hearts. .Q3~101~10Z PHYSICAL CHEMISTRY

OF COKI-RACTILE

PROTEISS

Actomyosin bands and glycerol extracted fibers from failing hearts have diminished contractility when compared with extracts from normal hearts,l’Jh~‘os suggesting that a specific defect may be present in the contractile proteins. Physicochemical properties of actomyosin and myosin from failing hearts have been reported to have abnormalities in viscosity, ultracentrifugational sedimentation patterns, and diffusion and light-scattering properties.‘l”-llZ The more recent physicochemical studies report no differences between actomyosin and myosin from control and failing hearts.““-” At present there appears to bc no good evidence for a physicochcmical alteration in the contractile proteins in the failing myocardium. CONTRXXILE

PROTEIX

,%TPAsE

One of the key enzymatic propertics of the myosin molecule, particularly of the H meromyosin portion, is that it acts as a magnesium dependent ATPase. The activity of this enzyme system. which is probably responsible for the breakdown of ATP during contraction, correlates well with contractility.72~1’8 In 1963, Alpert and Gordon’l” reported that the ATPase activity is reduced in myofibrils extracted from hearts of patients with cardiac failure. This finding has been confirmed in further studies of failure in human heartslZU and cats with right ventricular failure.l?l Myofibrillar ATPase was found to be depressed in proportion to contractility in papillary muscles from normal cats, cats with right ventricular hypcrtrophy, and cats with hypertrophy and circulatory failure. Left ventricular myofibrillar ATPasc was also rcduccd when faihue was induced by puhnonary artcry stenosis. Earlier studies of actomyosin or myosin from failing hearts reported that ATPase activity was not deprcsscd.1’1.3’4More recmtly ATPase has been found to be lowered in both preparations from failing hearts.11T,1”.123 The reduction in contractile protein ATPaso activity in myocardial failure may prove to be a finding of major importance. It indicates a distinct metabolic defect at the contractile protein level. which has implications regarding the conversion of chemical to mechanical energy. However, studies have not been conducted to establish whether this defect is a result or a cause of myocardial failure. Furthermore, the possibility exists that it is only one abnormality in a chain of metabolic abnormalities at the contractile protein lc~el. C~TECHOLA~IINES

IS ~~YOCARDWL

HWI~:RTROPHY

ASD FAILURE

Sympathetic stimulation and exogenous and cndogenous catecholamines are important in influencing both thr inotropic and chronotropic responsesof the

heart. Increased catecholamincs pro\idc important compensatory ruecllanisn~s in cardiac failure, particularly during cxercise.l”‘.‘X’ The mechanism by which catecholamines influence contractility is not understood, but they may affect intracellular and cytoplasmic calcium level~.~ X- *“’ The adcr~yl cyclasc, cyclicAMP system may also be invo1ved.12”~1:“’ The myocardium can extract and store catecholamines from pclrfusing blood, and it also contains the necessary enzymatic pathways for their synthesisl,‘-‘:‘,’ Myocardial synthesis of norepinephrine accounts for approximately SO per cent of that substance present in the heart. 13’ Endogenous catecholamines are released after stimulation by sympathetic nerves or by pharmacologic agents such as tyramine. In 1963, Chidsey et a1.13” reported that the concentration of norepincphrine is diminished in atria1 appendages removed at surgery from patients with congcstivc heart failure. Since then, dccreascd myocardial norepinephrinc stores have been found in many animals with cardiac failure.“~“‘~‘“‘‘-“” Norepinephrine concentration has also been reported to be low in hypertrophicd myocardium in the absence of failure., S,1R9There appears to be a correlation between the contractile potential and norcpinephrine stores in myocardial fnilurc.“‘” The myocardial responsiveness to exogenous catecholamines is retained,“,“‘7 but endogenous catecholamines arc not available for release b\. tyran~inc,l:‘fSJ37 and presumably by sympathetic nerve stimulation. Furthcrmore, exogenous norepinephrinc absorbed bv the myocardium is not stored in sites accessible to normal release mechanisms. I u Norepinephrine uptake by the myocardium is diminished in myocardial uptake may be norhypertrophy and failurc,‘4’ although in mild hypertrophy a rate limiting enzyme in the synthesis of mal.‘“” Tyrosinc hydroxylase, norepinephrine,‘,‘4 is reduced in myocardial hypertrophy and failure.‘:” This enzyme is found in sympathetic nerve endings. Another enzyme found in nerve endings, monoamine oxidasc, is decreased in failing myocardium.l”o Catcchol O-methyl transferasc levels do not appear to change.‘4” It has becn reported that adrencrgic nervcb endings adjacent to myocardial fibers disappear in proportion to norepinephrinc depletion in the failing heart,l”” and that nerve endings and myocardial norepinephrine content arc restored to normal when failure subsides. It is possible that the destruction of nerve endings can explain most of the myocardinl catecholaminc abnormalities in cardiac failure. Thcsc structures arc important both in catccholaminc~ synthesis and storage. Recently, it has bc\cn reported that adcnyl cyclascb, the membrane enzyme system that generates cyclic-AMP formation, is reduced in failing myocardium.l’j Phosphodiesterase, the cnzymc that breaks down cyclic-AMP, is normal. This implies that synthetic rates may bc low and degradation rates normal in the failing myocardium. The significance of this finding awaits further study. The findings regarding myocardial catccholaminc metabolism in cardiac failure are highly important, especially in terms of compensatory mechanisms. This has been confirmed by the observation that the inotropic and chronotropic response to sympathetic nerve stimulation is markedly reduced in dogs with

METABOLISM

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CAHDIAC

39

FAILURE

cardiac failure and myocardial norepinephrine depletion.‘“‘; The question of whether these abnormalities are causally related to the onset of myocardial failure cannot be answered. The findings that norepinephrine depletion seems to follow the course of failurc’4:3 would suggest, but does not prove, that catecholamine depletion does not have a primary role in causing the myocardium to fail. THI'ROTOXICOSIS

Circulatory failure may occur in humans with thyrotoxicosis in the absence of other apparent cardiac disease.14’ Failure can be produced in dogs by the administration of exogenous I-thyroxine. 14y However, most studies of the effects of increased thyroid state on the heart have been conducted in the compensated state. Increased myocardial respiratory rates,14”~1so decreased glycogen StoreS,‘w”’ and a shift toward lipid metabolism have been reported.15”.1”4 In humans with thyrotoxicosis, increased myocardial blood flow and oxygen consumption per beat are present.155 In dogs with thyrotoxic circulatory failure, a marked increase in myocardial blood flow and oxygen consumption are observed, accompanied by decreased uptake of exogenous substrates.l”” Oxidative phosphorylation is reported to be normal in mitochondria from these hearts, and the myocardial levels of high energy phosphates are the same as in control animals. Thus. energy liberation does not appear to be limited in hyperthyroid hearts. Preliminary reports on energy utilization in isolated papillary muscles from hyperthyroid cats indicate that both oxygen consumption and high energy phosphate utilization per unit of contractile work may be increased, suggesting that conversion of chemical to mechanical energy is inefficient.1”6~“~ In hearts from hyperthyroid animals without failure, contractility is increased’ib*l”” and myosin ATPasc activity is elcvated.lr.‘! Catecholamine binding and catecholamine stores are also high.“;‘~“;’ These mechanical and biochemical features are opposite to those reported in myocardial failure due to hemodynamic overload. Similar measurements have not bec~nmade in hearts from animals with thyrotoxic cardiac failure. Several features of thyrotoxicosis may contribute to the development of circulatory failure. The first is the increased cardiac output which results in chronically increased cardiac work. The second is the increased metabolic rate per beat, which fits with the concept of Badeer’o” as a determinant of myocardial hypertrophy. This is related to the third factor, that of the elevated inotropic state of the muscle, which may be wasteful in terms of efficiently converting chemical energy to mechanical energy. Fourth is the possibility that chemical-mechanical coupling at the sarcomcrcslevel is inefficient out of proportion to the inotropic state. The relative importance of these factors \vill have>to be evaluated by further studies. CARDIAC

FAILURE

DUE

TO IJXIITED

ENEHCY

AVAILABILITY

Ll’hen substrate supply or energy releasing pathways arc* interrupted, cardial failure will occur.16”

myo-

40

J-4 \fk:S

SC:HI,IJI~:I~

The most significant clinical condition relating to diminished energy supplies is that of dccrcascd oxygc~u delivery to the myocardium, as is seen in ischemic heart discasc. A mom conrplete discussion of the metabolic changes in myocardial ischemia and hypoxia has recently been published.16$ Severe hypoxia of the heart is associated with an abrupt fall in the content of high energy phosphate conmouuds5~~‘G” and a shift to anaerobic metabolism. Myocardial glycogen stores decline, and a shift from lactate uptake to output occurs. The assumption has not been proven that the reduction in high energy phosphate levels is responsible for the dccrcascd contractility in myocardial ischemia. Signs of left ventricular failure occur before a detectable decline in subepicardial high cncrgy phosphate levels,166JC7 although subendocardial stores may falP due to decreased oxygen tcusion and coronary flow distribution to the subendo~~~rdium. ‘l,‘~l.‘li+ Ghangcs in high energy phosphate IC\YIS correlate well with mechanical activity in anosia, particularly when the compensatory rcleaw 0F catc~chol~~miiic~ is 1~locked.l’;~ When a portion of the heart is made ischemic, the force of contraction of that segment declines, and finally expansion occurs during systole.lG” If a large enough portion of the heart is affected, there will be a decrease in ventricular function, and failure will wsuc.170 The noncontractile portion of the heart serves as au added elastic component against which the remainder of the myocardium must contract in order to develop pressure, Each active sarcomere must shorten further in ordrr to take up this added elastic clement. In addition, dilatation of the ventricle frequently occurs. The magnitude and duration of ventricular force rcquircd for the ejection of blood are increased. Because contractile work is greater, a disproportionately large amount of energy is expended in the compensating portion of myocardium. These changes probably are responsible for the high end-diastolic prcssurc seen in angina pectoris. The most pronounced mechanical burdens of these types are seen with large myocardial infarctions”” or with ventricular ancurysms.171 Other than oxygen deprivation, failure due to limited energy sources are probably uncommon in the intact animal. In isolated hearts, glycogen and triglycerides dedinc during perfusion and may lead to a fall in high rnergy phosphate compounds.172,173 Glycog(,ir availability appears to bc an important limiting factor in cardiac function, wen when other substrates are present.lTa It has been proposed that glycogcn metabolism is directly linked to the high energy phosphate supply for contraction.“’ Diminished glycogcn stores and decreased high energy phosphate 1~~~~1sin the myocardium are detected cluring the acute damage stage of hyp’~rfunctioll.” Whether there is an element of faihrre due to decreased energy ;~\xiIability during this stage has not hcen established. EFFECTS

OF THIAMINE

DEFICIESCY

UPON

TIIE

MYOCAWIUM

Thiamine is an important component of the, oxidativc decarboxylation coenzymes in the oxidative pathways. Thus, thiamine dcficicwcy would bc cxpetted to create a block in energy liberation in thu heart. Although in vitro pyruvatc utilization in cardiac tissue diminishes in propor-

METABOLISMOFTHEHEARTINCARDIACFAILURE

41

tion to thiamine Ievels,17Gin animals with thiamine deficiency the elevated blood pyruvate levels facilitate myocardial pyruvate uptake. Total myocardial pyruvate usage may be normal, unless a severe state of deficiency is present.177 E.xperimental thiamine deficiency in animals usually does not produce failure,17’ and failure in humans with thiamine deficiency is usually associated with other contributory factors.“s-lSo Cardiac output and coronary flow are usually elevated in beriberi, and myocnrdial extraction ratios of oxygen and circulating substrates are diminislled.1T7 ‘4s failure ensues, cardiac output, coronary flow and oxygen consumption may be reductd7~“-l** In this situation myocardial glucose, lactate and pyruvate uptake may fall, and lipid utilization increase. It is probable that when heart failure occurs in the presence of thismine deficiency, the high output state and the borderline metabolic rcscrve may combine to initiate failure. In addition, multiple nutritional deficiencies mnv coexist in many of the pntionts. Trm MYOCARDIOPATFIIES Our knowledge of metabolic abnormalities in the idiopathic myocardionathies is fragmentary. Normal or diminished coronary flow and myocardial oxygen consumption have been rcported,1”-1”3 Myocardial lactate production occurs in some cases,indicating drfectivc oxidative metabolism. Enzyme lcakagc from the myocardium is also reported. 111alcoholic myocardiopath!i, &&ran microscopic studies show abnormalitics in endoplasmic reticulum, myofibrils, and mitochondria.l”* As in idiopathic myocardiopathy, leakage of mitochondrial enzymes from the heart and abnortnalitics in lactate and pyruvatc metabolism hu\c been reported.“‘~“~ Triglyceride accumulates in the myocardium, IhGin part due to alcohol-induced increased uptake of triglyceride fatty acid by the heart.lS’ This is related to activation of myocardial lipoprotein lipase.lS8Alcoholic myocardiopathy probably represents a condition that is distinct from circulatory failure found in drinkers of beer with a high cobalt content.l’g Although the cause of that condition is not known, it is thought to result from direct cobalt toxicity to the myocardium.‘90 Tlrc myocardiopathies may have an experimental counterpart in a strain of Syrian Hamsters. These animals develop a triphasic i&less characterized first by spotty myolysis of the myocardium, nest b)’ hypertrophy and cardiac dilntion, and finally by progressive circulatory failure.1g’ That this may be a disease of energy production is indicated by the increased myocardial glycolytic rates that have been reported’“’ and by findings of abnormalities in mitochondrial oxidative phosphorylation.1”2”“3 Further studies with this animal model may uncover basic mechanisms that are relevant to the myocardiopathies. DIGITALIS

GLYCOSIDES

The effects of the digitalis glycosides upon myocardial energy relationships are largely secondary to their influence upon cardiac mechanics. In isolated muscle preparations, digitalis increases both the contractile element work and the velocity of contraction. and these are associated with increased oxygen

42

JAhfES

SCHEUER

consumption and heat production.‘j”,““L”!‘” Similar mechanical and metabolic effects of digitalis have been observed in nonfailing human and dog hea,-ts.196J97 Since digitalis does not increase cardiac output in the normal heart, external work is performed at a greater oxygen cost. In the presence of a high end-diastolic volume and pressure, digitalis decreases these, so that a fall in tension balances the increased velocity of contraction, and oxygen consumption is not altered. Thus, whereas digitalis in the nonfailing heart may be associated with a drcreased efficiency of converting chemical energy to external work, in failing hearts digitalis promotes a more favorable geometry for this conversion, In humans with cardiac failure, digitalis glycosides increase cardiac output but without changes in coronary flow, myocardial oxygen consumption, or substrate extraction p”ttenls.‘“.‘““,‘!‘” Many workers have sought an independent effect of digitalis glycosides upon oxygen and substrate utilization by the myocardium. The results regarding oxygen consumption arc inconsistent. Studies with homogenized myocardial tissue, slices or resting papillary muscles have reported increased or decreased oxygen consumption in the presence of digitalis preparations.““~‘““~“” Glucose uptake, and glycolytic and oxidative metabolism are increased after the administration of digitalis glycosides in both beating hearts and isolated fissues.?O?‘?“:~ In dogs with failure, decreased extraction of glucose has been reportedUZo4 In isolated hearts, the stimulation of lipid and carbohydrate use by digitalis correlates with the increased mechanical activity of the muscle.“‘;‘,““’ Therefore, although digitalis glycosides appear to have direct effects upon energy release pathways, there is no evidence to indicate that thcsc actions are responsible for the inotropic responses of the heart. Although there are reports that digitalis glycosides increase high energy phosphate levels in the failing myocardium,“’ a decline in creatine phosphate has also been found during the positive inotropic response.“‘~““,‘“’ Several studies report no change in ATP or total high energy phosphate levels when digitalis glycosides are administered.“‘.F1”O’*‘O’ In one study,;‘O digitalis glycosides were found not to change the oxidative phosphorylation characteristics of mitochondria from the failing myocardium. Although increased turnover of ATP probably accompanies the effects of digitalis glycosides, the pharmacologic action of these agents do not appear to be due to a primary cffcct on high energy phosphate metabolism. Digitalis glycosides are reported to enhance the spiraling and shortening of contractile proteins in solution?og~Z1Oand to increase the association of pure actin and myosin.211 They increase the contractility of glycerol extracted cardiac muscle fibers or actomyosin bands, but only if calcium is present.1”“.‘Z3pZ1’ They are reported not to affect the ATPase activity of contractile proteins 117~123,212 although in one study increased actomyosin ATPase activity was found with a high dose of digoxin.?l” The inotropic effect of ouabain is associated with a proportional increase in tissue calcium exchange, but the total myocardial calcium remains constant214 The mobilization of calcium by digitalis depends upon heart rate and is not demonstrable in the noncontracting preparation.‘15Jln It has been pro-

SIETABOLISM

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FAILURE

43

that the mechanism of action of digitalis is through increasing the pool of calcium related to contraction.2’7-219 Several studies indicate that digitalis glycosides may influence the control of calcium by the sarcoplasmic reticulum. The calcium uptake by sarcoplasmic reticulum from normal hearts appears to be diminished in the presence of cardiac glycosides.s?o~??l Administered in vivo, ouabain is reported to prevent the defect in calcium uptake of sarcoplasmic reticulum of the failing heartlung preparation.7o When administered in viva, digoxin becomes localized in the sarcoplasmic reticulum.‘2”,223 Ouabain enhances-the contraction of glycerol extracted cardiac fibers only in the presence of sarcoplasmic reticulum fragmentsX2$ The effects of digitalis glycosides on other cardiac ions have been extensively reviewed.‘25,Z2” In failing hearts there is restoration of the ionic milieu toward normal, which may be in part due to the abolition of the failure state.7’:,‘!’ High doses of digitalis glycosides reduce intracellular potassium and increase sodium and chloride concentrations and cell water. Digitalis preparations cause potassium efflux into the corona? sinus.“~~2”o Although changes in potassium concentration do not appear to necessarily accompany therapeutic levels of digitalis, the effect on potassium and sodium movement may be found at (mite low extracellular digitalis concentrations.2”1.‘“’ Digitalis glycosides probably affect sodium and potassium transport by acting on the mdium and potassium sensitive membrane ATPase system. Low concentrations of glycosides may stimulate this system,2’43 while higher doses inhibit it.Z34.?‘<,Potassium efflux would probably occur only with a high concentration of glycoside at the membrane site. Some workers have proposed that tlw inotropic action of digitalis is mediatecl by its effects on sodium and potassiun~.‘:“.23” Close temporal relations between inotropic and potassium changes have been reported after cardiac glycosidesZ3’ On the other hand, the inotropic effects of glycosides can be dissociated from potassium efflux by the simultaneous treatment with diphenylhydantoirF or insulin.“3s It has been suggested that the inotropic effects of digitalis are mediated by the sympathetic neurohumoral system, because the effects of glycosides arc attenuated by pharmacologic agents that deplete or block cardiac catecholamines.2Jg However, denervated hearts with depleted catecholamine stores respond we11 to ouabain, indicating that the depressant actions of the pharmacologic agents are through mechanisms other than their effects on catecholamines,24o and digitalis glycosides must act independently. The most acceptable hypotheses now appears to be that digitalis glycosides act therapeutically through increasing the exchangeable calcium pool and enhancing calcium release from the sarcoplasmic reticulum, thereby raising the calcium concentration in the region of the contractile proteins.241 The effects of glycosides upon potassium balance may be partially responsible for the toxic arrhythmias. The toxic arrhythmias also appear to be influenced by the interrelation betvveen these agents, sympathetic stimulation, and catecholamine rc%lease. posed

CONCLUSIONS

In this review we have outlined the biochemical and nrctabolic &angcs that occur in myocardial hypertrophy and in cardiac failure. The metabolic fcatures may differ, depending upon the stage of hypcrfunction, and thcreforc, when comparing the results, the mechanical and hemodynamic status of the heart muscle and intact heart should bc known. In failure due to an increased hemodynamic load, oxygen and substrate uptake per unit of myocardium are normal or nearly normal, However, total use of these substrates may be considerably increased because of greater cardiac mass, ventricular dilatation, and elevated tension requirements for ejection of blood. The efficiency of convertin, 0 chemical energy to external work is therefore decreased. Abnormal mitochondrial function does not appear to be a necessary concomitant of myocardial failure, ahhough the mass of mitochondria may be reduced, potentially leading to diminished energy availability. However, the finding of normal ATP concentrations and normal conversion of chemical to mechanical energy at the muscle level indicate that the decreased contractile work capacity of failing cardiac muscle is not due to diminished energy availability or to a block in mechanochemical coupling. Preliminary information suggests that there may be a defect in intracellular calcium control in myocardial failure. Contractile protein ATPase activity in failing myocardium is decreased, and this appears to be proportional to the diminished contractility. Cardiac catecholamine stores, which provide important compensatory drive for the failing heart, are lowered and cardiac uptake and synthesis of norcpinephrinc arc aIso decreased. These may be rclatcd to degeneration of sympathetic nerve endings in the myocardium. The finding of mechanical and metabolic changes in the left ventricles of animals with primary hemodynamic overload of the right heart is of interest. The abnormalities that have been identified are left ventricular failure, shifts in the lactic dehydrogenase isoenzyme patterns, depressed myofibrillar ATPase, degeneration of nerve endings, and depletion of norepinephrine stores. Myocardial failure may be a diffuse cardiac condition not just localized to the portion of the heart primarily affected by an increased hemodynamic load. The important synthetic compensatory responses to hemodynamic overload have also been reviewed. Protein synthesis is activated almost immediately after an increased cardiac load is imposed. The synthetic rates differ during the phases of hypertrophy and failure. Cardiac failure in thyrotoxicosis and beriberi appear to be caused by a combination of increased hemodynamic load and intrinsic metabolic abnormalities. In thyrotoxicosis, the possibility has been raised that coupling of chemical to mechanical energy is inefficient. In severe vitamin B, deficiency, a relative blockade of oxidative metabolism may occur. Cardiac hypoxia is the most important primary metabolic cause of myocardial failure. However, even here, we lack unequivocal proof of diminished high energy phosphate availability as the cause for the failure. The many actions of the digitalis glycosidcs upon metabolism have been reviewed. Most of the changes in rates of oxygen or substrate use appear to bc

METABOLISM

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HEART

IN CARDIAC

FAILtrRE

45

secondary to the effects of the agents on cardiac mechanics. Although the mechanism of action is not known, the evidence supports the concept that digitalis glycosides influence intracellular calcium availability for contraction. The toxic effects appear to be related to potassium loss from the myocardium. In light of the facts now available regarding the metabolism and biochemistry of myocardial failure, no simple explanation based on a single biochemical defect is likely to be correct. Multiple biochemical abnormalities may be responsible. It is possible that changes in intracellular relationships of organelles, membranes, and proteins might be disturbed in cardiac failure. These relationships are important for the integration of biochemical and mechanical function. Such subtle changes would bc difficult to discover with currently available techniques. REFERENCES 1. Olson, R. E., and Piatnek, D. A.: Conservation of energy in cardiac muscle. Ann. N. Y. Acad. Sci. 72:466, 1959. 2. Stead, E. A., Warren, J. V., and Brannon. E. S.: Cardiac output in congestive heart failure: An analysis of the reasons for lack of close correlation between the symptoms of heart failure and the resting cardiac output. Amer. Heart J. 35529, 1948. 3. Wollenherger, A.: On the energy-rich phosphate supply of the failing heart. Amer. J. Phvsiol. 150:733, 1947. 4. Olson, R. E., and Schwartz, W. B.: Myocardial metabolism in congestive heart faihne. Medicine 30:21, 1951. 5. Samoff, S. J., and Mitchell, J. H.: The control of the function of the heart. In Dow, P., and Hamilton, W. F. (Eds.): Handbook of Physiology. Vol. I, Circulation. American Physiological Society, 1962, p. 489. 6. Sonnenblick, E. H.: Instantaneous force-velocity-length determinants in the contraction of heart muscle. Circ. Res. 26: 441, 1965. 7. Levine, H. J.. and B&man, N. A.: Force-velocity relations in the intact dog heart. J. Clin. Invest. 43:1383, 1964. 8. Albert, R. E., Smith, W. W., and Eichna, L. W.: Hemodynamic changes associated with fluid retention induced in noncardiac subjects by corticotropin (ACTH) and cortisone; comparison with the hemodynamic changes of congestive heart failure. Trans. Ass. Amer. Physicians 67:72, 1954. 9. Spann, J. F,, Buccino, R. A., Sonnenblick, E. H., and Braunwald, E.: Contractile state of cardiac muscle obtained from cats with experimentally produced ventricular hypertrophy and heart failure. Circ. Res. 21:

341, 1967. 10. Meerson, F. Z.: Compensatory hyperfunction of the heart and cardiac insufficiency. Circ. Res. 10:250, 1962. 11. Meerson, F. Z.: A mechanism of hypertrophy and wear of the myocardium. Amer. J. Cardiol. 15:755, 1965. 12. Meerson, F. Z.: The myocardium in hyperfunction, hypertrophy, and heart failure. Circ. Res. 25 (Suppl. 2), 1969. 13. Lorber, V.: Energy metabolism of the completely isolated mammalian heart in failure. Circ. Res. 1:298, 1953. 14. Olson, R. E.: Myocardial metabolism in congestive heart failure. J. Chronic Dis. 9:442, 1959. 15. Goodale, W. T., Olson, R. E., and Hackel, D. B.: Myocardial glucose, lactate and pyruvate metabolism of normal and failing hearts studied by coronary sinus catheterization in man. Fed. Proc. 9:49. 1950. 16. Blain, J. M., Schafer, H., Siegel, A. L., and Bing, R. J.: Studies on myocardial metabolism: VI. Myocardial metabolism in congestive failure. Amer. J. Med. 20:820, 1956. 17. Gudbjamason, S., Hyden, R. O., Wendt, V. E., Stock, T. B., and Bing, R. J.: Oxidation reduction in heart muscle: Theoretical and clinical considerations. Circulation 26 (11):937, 1962. 18. Messer, J. V., and NeilI, W. A.: The oxygen supply of the human heart. Amer. J. Cardiol. 9:384, 1962. 19. Rowe, G. G., Skoda, A., Lugo, J. E& Castillo, C. A., Boake, W., and Crumption, C. W.: Coronary blood flow and myocardial oxidative metabolism at rest and during

46 exercise in subjects with severe aortic valve disease. Circulation 32:251, 1965. 20. Levine, H. J.. and Wagman, R. J.: Encrgetics of the human heart. Amer. J. Cardiol. 9:372. 1962. 21. Lombardo, T., Rose, L., Taeschler, hf.. T&y, S., and Bing, R. J.: The effect of exercise on coronarv blood flow, mvocardial oxygen consumption and cd&c efficiency in man. Circulation 7:71, 195.3. 22. West, J. W., Wendel, H., and Foltz, E. L.: Effects of nor-tic insufficiency on circulatory dynamics of the dog: With special reference to coronary blood flow and cardiac oxygen consumption. Circ. Res. 7:685, 1959. 23. Scheuer, J., and McDonald, R. H.: Current status of myocardial mechanicalenergetic relationships. J. hlount Sinai Hosp. N.Y. (issue in honor of Dr. Alesander B. Gutman), in press. 2-l. Pool, P. E., Chandler, B. M., Spann, J, F., Sonnenblick, E. H., and Braunwald, E.: Mechanochemistry of cardiac muscle: IV. Utilization of high-energy phosphates in experimental heart failure in cats. Circ. Res. 24:313, 1969. 25. Gault, J. H., Ross, J,. and Braunwald, E.: Contractile state of the left ventricle in man: Instantaneous tension-velocity-length relations in patients with and without discase of the left ventricular myocardium. Circ. Res. 22:451, 1968. 26. Wegria, I~., hluelheims, G., Golub, J. R.. Jreissaty, R., and Nakano, J.: Effect of aortic insufficiency on arterial blood pressiire, coronary blood flow and cardiac oxygen consumption. J. Clin. Invest. 37:471, 1958. 27. Wegria, R., Muelheims, G., Jreissaty, R., and Nakano, J.: Effect of acute mitral insufficiency of various degrees on mean arterial blood pressure. coronal? blood flow, cardiac output and oxygen consumption. Circ. Res. 6:301, 1958 28. Urschel, C. W., Covell, J. W., Graham, T. P., Clancy, R. L., Ross, J., Sonnenblick, E. H., and Braunwald, E.: Effects of acute valvular regurgitation on the oxygen consumption of the canine heart. Circ. Res. 2.333, 1968. 29. Gudbjamason, S., De Schryver, C., Hunn, C., and Bing, R. J.: Changes in myocnrdial enzyme patterns in human heart disease. J. Lab. Clin. Med. 64:796, 1964. 30. Shipp, J, C., Delcher, H. K., and Crevasse, L. E.: Glucose metabolism by the hesose monophosphate pathway in the per-

JAMES

SCHtX’ER

fllwtl rat llc;~rt. Bioche~n. Bioph+ Act,1 86: 399 1 1964 . 31. (:udbjamason, s., COW.~II, (:., and Bing, 1~. J.: Increase in hexosemonophosphate shunt activity during tissue repair. Life Sci. 6:1093, 1967. 32. Nagano. hl., and Hochrein. H.: Enzymatische stonmgen in hlyokard bei belastung und insuffizienz des Herzens. Klin. Wchr. 41:792, 1963. 33. FOS, A. C., and Reed, G. E.: Changes in lactate dehvdrogenase composition of hearts with right ventriciilar hypertrophy. Amer. J. Physiol. 216:1026, 1969. 94. Sahel. B. E., Henry, I’. D., and Bloor, C. hl.: Altered myocardial lactic dehydrogenasc isoenzvmes hi experimental cardiac hypcrtrophy. Fed. Proc. 28:451, 1969. 35. Bishop. S. I’., and Altschuld, R. A.: Inerensed gl!colytic metabolism in hypertrophirtl. failing mvocardium. Circulation 37-38 (VI):43, 1968: 36. Drasnin, R., Hughes, J. T., Krause, R. I’.. and Van Liere, E. J.: Glycogen content in normal and hypertrophied rat heart. Proc. Sot. Esp. Biol. Med. 99:438, 1958. 37. Szekeres, I,., and Schein, hl.: Cell metabolism of the overloaded mammalian heart in situ. Cardiologia 3419, 1959. 38. Wittels. B., and Spann, J. F., Jr.: Defective lipid metabolism in the failing heart. J, Clin. Invest. 47:1787. 1968. 39. Nelson, G. H., Bear, D. hl., Dotson, T. O., and Krause, R. F.: Lipid changes in cardiac hv-pertrophy as measured by silicic acid chro&tograph\-. Amer. J. Physiol. 204: 297, 1963. 40. Quercio, M., Pala, V., and Gastaldi, G.: Behaviour of some lipids in experimental heart h!.pertrophy. Ital. J. Biochem. 14:402, 1965. 41. Di hlinelli, R., Panagia, V., and Sciorelli, C.: 11 contenuto in lipidi de1 miocardio in funzione de1 lavoro e dello scompenso di sperimentale (cuoro-polmoni cardiac0 ratto). Arch. Sci. Biol. 52254, 1968. 42. hlccallister, B. D., and Brown, A. L.: A quantitative study of myocardial mitochondria in experimental cardiac hypertrophy. Lab. Invest. 14:692, 1965. 43. Wollenberger, A., and Schulze, W.: Mitochodrial alterations in the myocardium of dogs with aortic stenosis. J. Biophys. Biothem. Cytol. 10:285, 1961. 44. Bishop, S. P., and Cole, C. R.: Ultrastructural changes in the canine myocardium

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LN CARDIAC

FAILURE

with right ventricular hypertrophy and congestive heart failure. Lab. Invest. 20:219, 1969. 43. Meerson, F. Z., Zaletayeva, T. A. Lagutchev, S. S., and Pshennikova, hl. G.: Structure and mass of mitochondria in the process of compensatory hyperfunction and hypertrophy of the heart, Exp. Cell Res. 36:568, 1964. 46. Chidsey, C. A., Weinbach, E. C., Pool, P. E., and Morrow, A. C.: Biochrrnical studies of energy production in the failing human heart. J. Clin. Invest. 45:40, 1966. 47. Schwartz, A., and Lee, K. S.: Study of heart mitochondria and glycolvtic metabolism in experimentally induced cardiac failure. Circ. Res. 10:321, 1962. 48. Wollenberger, A., Kleitke, B., and Raabe, G.: Some metabolic characteristics of mitochondria from chronicallv overloaded, hypertrophied hearts. Exp. Mdlec. Path. 2: 251, 1963. 49. Argus, M. F., Arcos, J. C. Vishwanath, S. hf., and Overby, J. L.: Oxidative rates and phosphorylation in sarcosomes from experimentally-induced failing rat heart. Proc. Sot. Esp. Biol. Med. 117:380, 1964. 50. Procita, I,., Schwartz, A., and Lee, K. S.: Oxidative phosphorylation in the failing dog heart-lung preparation. Circ. Res. 16:391, 1965. 51. Gertler, M. M., Murakami, K., and Guthrie, R. G.: Oxidative phosphoqdation in normal and failure liver, kidney and heart mitochondria. Proc. Sot. Exp. Biol. Med. 121:657, 1966. 52. Lindenmayer, G. E., Sordahl, L. A., and Schwartz, A.: Reevaluation of oxidative phosphorylation in cardiac mitochondria from normal animals and animals in heart failure. Circ. Rcs. 23:439, 1968. 53. Fox, A. C., and Reed, G. E.: Exchanges of nucleotide phosphates in normal and in failing canine hearts. Amer. J. Physiol. 210: 1383, 1965. 54. Brody, T. M., Pahner, J. F., and Bennett, D. R.: Phosphorylation in cardiac muscle from failing and uxrfailing heartlnny preparations. Proc. SIX. Eup. Biol. hlrd. 86:740, 1954. 55. Sobel, B. E., Spann, J. F., Pool, P. E., Sonnenblick, E. H., and Braunwald, E.: Normal oxidative phosphorylation in mitochondria from the failing heart. Circ. Res. 21::35S, 1967.

47

56. Plaut, G. W. E., and Gertler, M. M.: Oxidative phosphorylation studies in normal and experimentally produced congestive heart faihue in guinea pigs: A comparison, .4nn. N. Y. Acad. Sci. 72:515, 1959. 57. Greiner, T.: The relationship of force of contraction to high-energy phosphate in heart muscle. J. Phamlacol. Exp. Ther. 105: 178, 1952. 58. Frinstein, hl. B.: Effects of experimental congestive heart failure, ouabain, and asphyxia on the high-energy phosphate and creatine content of the guinea pig heart. Circ. Res. 10:333, 1962. 59. Fox, A. C., Wikler, N. S., and Reed, G. E.: High energy phosphate compounds in the myocardium during experimental congestive heart failure. Purine and pyrimidine nncleotides, creatine, and creatine phosphate in normal and in failing hearts. J. Clin. Invest. 44:202, 1965. 60. Lee, K. S.. Yu, D. H., and Burstein, R.: The effect of ouabain on the oxygen consrmrption, the high energy phosphates ancl the contractility of the cat papillary muscle. J. Phannacol. Exp. Ther. 129:115, 1959. 61. Fruchgott, R. F., and De Gubareff, T.: The high energy phosphate content of cardiac muscle under various experimental conditions which alter contractile strength. J. Pharmacol. Exp. Ther. 124:203, 1958. 62. h,linton. P. R., Zoll. P. M., and Norman, L. R.: Levels of phosphate compounds in experimental cardiac hypertrophy. Circ. Res. 8:924, 1960. 63. Buckley, N. Xl.. and Tsuboi, K. K.: Cardiac nucleotides and derivatives in acute and chronic ventricular failure of the dog heart. Circ. Res. 9:618, 1961. 64. Pool, P. E., Spann, J. F., Jr., Buccino, R. A., Sonnenblick, E. H., and Braunwald, E.: blyocardial high energy phosphate stores in cardiac hvpertrophy and heart failure. Circ. Res. 2i:365, 1967. 65. Meerson, F. Z.: The myocardium in hyperfunction, hypertrophy, and heart failure. Circ. Res. 25 (Suppl. 2):72, 1969. 66. Langer, G. A.: Ion fluxes in cardiac excitation and contraction and their relation to myocardial contractility. Physiol. Rev. 48: 708, 1968. 67. Nelson, D. A. and Benson, E. S.: On the structural continuities of the transverse tubular system of rabbit and human myocardial cells. J. Cell. Biol. 16:297, 1963.

48 68. Huxley, A. F., and Taylor, R. E.: Local activation of striated muscle films. J. Physiol. 144426, 1958. 69. Lee, K. S., Ladinsky, II., Choi, S. J., and Kasuya, Y.: Studies on the in vitro interaction of electrical stimulation and Cat+ movement in sarcoplasmic reticulum. J. Gen. Physiol. 49689, 1966. 70. Gertz, E. W., Hess, hl. L., Lain, R. F., and Briggs, N. F.: Activity of the vesicular calcium pump in the spontaneously failing heart-lung preparation. Circ. Res. 20:477, 1967. 71. Hochrein, H. A., and Lossnitzer, K.: The interrelation between myocardial metabolism and heart failure. Ann, N. Y. Acad. Sci. 156:387, 1969. 72. Reynolds, E. W.: Ionic transfer in cardiac muscle. An explanation of cardiac electrical activity. Amer. Heart J. 67:693, 1964. 73. Hasselbach, W.: Die wechselwirkung verschiedener NukIeosidtriphosphate mit Aktomyosin im Gelzustand. Biochem. Biophys. Acta 20:355, 1956. 74. Harrison, T. R., Pilcher, C., and Ewing. G.: Studies in congestive heart failure: IV. The potassium content of skeletal and cardiac muscle. J. Clin. Invest. 8:325, 1930. 75. Wilkins, W. E., and Cullen, G. E.: Electrolytes in human tissue. III. A comparison of normal hearts with hearts showing congestive heart failure. J. Clin. Invest. 12:1063, 1933. 76. Clarke, N. E., and Mosher, R. E.: The water and electrolyte content of the human heart in congestive heart failure with and without digitalization. Circulation 5: 907, 1952. 77. Benson, E. S., Freier, E. F., Hallaway, B. E., and Johnson, M. J.: Distribution of fluid and electrolytes and concentration of actomyocin and other proteins in the myocardium of dogs with chronic congestive heart failure. Amer. J. Physiol. 187:483, 1956. 78. Yankopoulos, N. A., Davis, J. O., Cotlove, E., and Trapasso, M.: Mechanism of myocardial edema in dogs with chronic congestive heart failure. Amer. J. Physiol. 199:603, 1960. 79. Bliss, H. A., and Adolph, R. J.: Effect of experimental congestive heart failure and acetyl strophanthidin on myocardial electrolyte and water content. Circ. Res. 13:207,

JAMES

SCHEUER

1963. HO. Linzl)ach, A. J.: Heart failure from the point of view of quantitative anatomy. Amer. J. Cardiol. 5:370, 1960. 81. hlcerson, F. Z., Alekhina, G. M., Aleksautlrov. I’. IN.. irnd Bazardjan, A. G.: Dynamics of nucleic acid and protein synthesis of the myocardium in compensatory h!pcrhmction and hypertrophy of the heart. Amer. J. Cardiol. 22:337, 1968. 82. Cluck, L., Talner, N. S., Stem, H., Gardner, T. H., and Kulovich, M. V.: Experimental cardiac hypertrophy: Concentrations of RN’rl iu the ventricles. Science 144: 1244, 1964. 83. Grimm, ii. F., Kubota, R., and Whitehorn, W’. \‘.: \‘rntricular nucleic acid and protein levels with myocardial growth and hvpcrtrophv. Circ. Res. 19:552, 1966 84. Sumuer, R. G., and McIntosh, H. D.: Nucleic acid studies in experimental cardiomegaly. Circ. Res. 12:170, 1963. 85. Mcerson, F. Z., Belochapkina, ‘I’. D., Lushnikov, E. F., Leikina, E. M., Markovskaya, G. N.. and Chemyshova, G. V.: Function, structure and protein metabolism of hypertrophied m~oc~artlirun. \‘est. hknd. Med. Nauk S.S.S.R. 1827, 1963. 86. lioyle, T. C., III, Su~muer, Ii. C., ant1 McIntosh, II. D.: Nucleic acid and protein dctcnninations in the studs of experimental cardiomegalv. J. Lab. Clin. Aled. 62:632, 1963. ’ 87. Kompmann, hf.. Paddags, I., and Sandritter, W.: Feulgen cytophotometric DNA determinations on human hearts. Arch. Path. 82:303, 1966. 88. Morkin, E., and Ashford, T. P.: hlyocardial DNA synthesis in experimental cardiac hypertrophy. Amer. J. Physiol. 215: 1409, 1968. 89. Richter, G. W., and Kellner, A.: Hypertrophy of the human heart at the level of fine structure. J. Cell Biol. 18195, 1963. 90. Carney, J. A., and Brown, A. L., Jr.: hlyofilament diameter in the normal and hypertrophic rat myocardium. Amer. J. Path. 44:521, 1964. 91. Camey, J. A., and Brown. A. L., Jr.: The morphology of myosin in cardiac hypertrophy. Lab. Invest. 16:36, 1967. 92. Sonnenbhck, E. H., ROSS, J., Jr., COveil, J. W., Spotnitz, H. H., and Spiro, D.: The ultrastructure of the heart in systole and diastole. Circ. Res. 21:423, 1967. 93. Schreiber, S. S., Oratz, hf., and Roths-

METABOLISM

OF THE

HEART

IN CARDIAC

FALLURE

child, M.: Protein synthesis in the overloaded mammalian heart. Amer. J. Physiol. 211: 314, 1966. 94. Gudbjamason, S., Telerman, M., Chiba, C., Wolf, P. L., and Bing, R. J.: Myocardial protein synthesis in cardiac hypertrophy. J. Lab. Clin. Med. 63:245, 1964. 95. Gudbjamason, S., Telerman, hl., and Bing. R. J.: Protein metabolism in cardiac and heart failure. Amer. J. hvpcrtroph\ Pjlvsiol. 2oFj:294, 1963. 96. Kaku. I.: Study of the myocardial nl&ic acids and proteins metabolism in e\-perimcntally induced cardiac hypertrophy and he:ut failure. Jap. Heart J. 9:393, 1968. 97. Nair, I;. C., Cutilletta, A. F., Zak, R., M.: Biochemical Koidc~, T., nnd Rabinowitz, correlates of cardiac hypertrophy: I. Experimvntnl model; changes in heart weight, RNA content, and nuclear RNA polymerase nctivitv. Circ. Res. 23:451, 1968. 98. hleerson. F. Z., Kalebina, pi. S., Malov, C,. rZ.. Simonynn, N. T., and Romanova, L. K.: Eflec+ of actinomycin D on the development of the compensatory hyperfunction of the myocardium. kidney and liver. Acta Biol. Acad. Sci. Hung. 15:375, 1965. 99. Tomintq K.: Studies on myocardial protein metabolism in cardiac Ilypertrophy. Jnp. Heart J. 7:566, 1966. 100. Xloroz, L. A.: Protein synthetic activit\. of heart microsomes and ribosomes during left ventricular hypertrophy in rabbits. Circ. Res. 21:449, 1967. 101. Schreiber, S. S., Oratz, M., Evans, C., Silvrr. E., and Rothschild, hl. A.: Effect of acute overload on cardiac muscle mRNA. Amer. J, Physiol. 215:1250, 1968. 102. Schreiber, S. S., Oratz, M., and Rothschild, M. A.: Effect of acute overload on protein synthesis in cardiac muscle microsomes. Amer. J. Physiol. 213:1552, 1967. 103. Badeer, H. S.: Metabolic basis of cardiac hypetirophy. Prog. Cardiovasc. Dis. 11:53, 1968. 104. Hajdu, I., and Beznak, M.: Die rolle tlrr flypophyse bei der re~ulierung von Arbeitsvermogen und hlasse des Herzens. Schweiz. Med. Wchr. 75:665, 1915. 105. Beznak, M.: The effect of different degrees of subdiaphragmatic aortic constriction on heart weight and blood pressure of normal and hypophysectomized rats. Cnnad. J. Biochem. Physiol. 33:985, 1955. 106. Beznak, M.: The role of anterior pituitay hormones in controlling size, work

49

and strength of the heart. J. Physiol. 150: 251, 1959. 107. Barta, E., Sapakova, E., and Pavlovicova, H.: Participation of adrenals in morphological adaptation of the heart to elevated pressure work. Cor Vasa 7:156. 1965. 108. Kako, K.. and Bing. R. J.: Contractility of actomvosin bands prepared from normal and faGin,< human hearts. J. Clin. Invest. 37:465, 1958. 109. Benson. E. S.. Hnllawa!., B. E.. and Turbak, C. E.: Contractile properties of glycerol-extracted muscle bundles from the chronically failinS cnninc heart. Circ. Res. 6:122, 1958. 110. Benson. E. S.: Composition and state of protein in heart muscle of normal dogs and dogs with eq)erimental In\-ocardial failure. Circ. Res. 3:2X, 1953. 111. Olson. R. E.. Ellenbogen. E., and Iyengar, R.: Cardiac myosin and congestive heart fnilurc in the doq. Circlllation 24:471, 1961. 112. Nebel, hf. L., and Bing, R. J.: Contractile proteins of normal and failing human heart. Arch. Intern. hletl. 111:190. 1963. 113. Olson, R. E.: .4bnormnhties of myocardial metabolism. Circ. lies. 11-1.5 (TI):109, 1964. 114. Davis, J. 0.. Trapnsso. M., and Ynnkopoulos, N. A.: Studies of actomyosin from cardiac muscle of dogs with experimental congestive heart failure. Circ. Res. 7:957, 1959. 115. Davis, J. 0.. Carroll, W. R., Trapasse, hf., and Yankopoulos, N. -4.: Chemical characterization of cardiac mvosin from normal dogs and from dogs with chronic congestive heart failure. J. Clin. Invest. 39: 1463, 1960. 116. Conwnt-. C. l-., and Roberts, J. L.: Comparison of molecular weight of mvosin from normal and failing dog hearts. Amer. J. Physiol. 208:243, 1965. 117. Lnchi. R. J., Kritcher, E. hi., and Thyrum, I’. T.: Reduced cardiac myosin ndenosinetriphosphatase activitv in dogs with spontaneouslv occurring heart failure. Circ. Res. 24:513,. 1969. 118. Davies, R. E.: -4 molecular theory of muscle contraction: Calcium-dependent contractions with hydrogen bond formation plus ATP-dependent extensions of part of the myosin-actin cross-bridges. Kature 199: 1068, 1963.

50 110. Alpert, N. K., zmcl Gorrltn~, \I. S.: Myofibrillar adenosine triphosphatase activit\; in congestive heart failure. Amer. J. Phvsiol. 202:940, 1962. h. Gordon, M. S., and Brown, A. L.: hlyofibrillar adenosine triphosphatase activity of human heart tissue in congestive failure: Effects of ouabain and calcium. Circ. Rrs. 18:534, 1966. 121. Chandler, B. hf., Sonnenblick, E. H., arm, J. F.. and Pool, P. E.: Association SP of depressed myofibrillar adenosine triphosphatase and reduced contractility in experimental heart failure. Circ. Res. 21:717, 1967. 122. Miyahara, M.: Studies on actomyosin of heart muscle. Jap. Circ. J. (Eng. ed.) 26: 8, 1962. l2:3. Mivahara, M., Yokoyama, M., Nagasaki. Y., and Kinjo, K.: Effect of ouabain on nctomyosin-studies on the effect of ouabain on actomyosin extracted from cardiac, both normal and failing, and skeletal muscles. Jap. Heart J. 3:46, 1962. 124. Chidsey, C. A., Braunwald, E., and Morrow, A. G.: Catecholamine excretion and cardiac stores of norepinephrine in congestive heart failure. Amer. J. Med. 39:442, 1964. 125. Chidsey, C. A., Harrison, D. C., and Braunwald, E.: Augmentation of the plasma norepinephrine response to exercise in patients with congestive heart failure. New Eng. J. Med. 267:650, 1962. 126. Hess, M. L., Briggs, F. N., Shineboume, E., and Hamer, J.: Effect of adrenergic blocking agents on the calcium pump of the fragmented cardiac sarcoplasmic reticulum. Nature 220:79, 1968. 127. Clower, B. R., Williams, W. L., and Matheny, J. L.: Effects of reserpine on calcium levels in cardiac tissue of mice. Cardiovasc. Res. 3:64, 1969. 128. Shineboume, E. A., Hess, M. L., White, R. J., and Hamer, J.: The effect of noradrenaline on the calcium uptake of the sarcopIasmic reticuIum. Cardiovasc. Res. 3: 113, 1969. 129. Cheung, W. Y., and Williamson, J. R.: Kinetics of cyclic adenosine monophosphate changes in rat heart following epinephrine administration. Nature 207:979, 1965. 130. Levine, R. A., and Vogel, J. A.: Cardiovascular and metabolic effects of adenosine 3’, 5’-monophosphate in vivo. Nature 207:987, 1965. 131. Miyahara, M.: Catecholamine metab-

olism in heart muscle. Jap. Circ. J. 26:I. 1962. 1:32. Chidsey, C. A., Kaiser, G. A., Braunwald, E.: Biosynthesis of norepinephrine in isolated canine hearts. Science 139:828, 1963. 13.3. Spector, S., Sjoerdsma, A., Nirmberg, P. Z., Levitt, M., and Udenfriend, S.: Norelnnephrine synthesis from Tyrosine-C*q in isolated perfused guinea pig heart. Science 139:1299, 1963. 134. Kopin, I. J., and (Gordon, E. K.: Origin of norepinephrine in the heart. Nature 199:1289, 1963. 135. Chidsey, C. A., Braunwald, E., Morrow, A. G.. and Mason, D. T.: Myocardial norepinephrine concentration in man. New Engl. J. Med. 269:653, 1963. 136. Chidsey, C. A., Sonnenblick, E. H., Morrow, A. G., and Braunwald, E.: Norrpinephrine stores and contractile force of papillary muscle from the failing human heart. Circulation 33:43, 1966. 137. Chidsey, C. A., Kaiser, G. A., Sonnenblick, E. II., Spann, J. I;., and Brarirrwald, E.: Cardiac norephinephrine stores in experimental heart failure in the dog. J. Clin. Invest. 43:2386, 1964. 138. Pool, P. E., Covell, J. W., Levitt, M., Gibb, J., and Braunwald, E.: Reduction of cardiac tyrosine hydroxylase activity in experimental congestive heart failure: Its role in the depletion of cardiac norepinephrine stores. Circ. Res. 20:1967. 139. Fischer, J. E., Horst, D. W., and Kopin, I. J.: Norepinephrine metabolism in hypertrophied rat hearts. Nature 207:951, 1965. 140. Krakoff, L. R., Buccino, R. A., Spann, J.: Cardiac caJ. F., and De Champlain, tech01 0-methyltransferase and monoamine oxidase activity in congestive heart failure. Amer. J. Physiol. 215:549, 1968. 141. Spann, J. F., Jr., Chidsey, C. A., and Braunwald, E.: Reduction of cardiac stores of norepinephrine in experimental heart failure. Science 145:1439, 1964. 142. Spann, J. F., Jr., Chidsey, C. A., Pool, P. E., and Braunwald, E.: Mechanism of norepinephrine depletion in experimental heart failure produced by aortic constriction in the guinea pig. Circ. Res. 17:312, 1965. 143. Vogel, J. H. K., Jacobowitz, D., and Chidsey, C. A.: Distribution of norepinephrine in the failing bovine heart. Circ. Res.

XIETABOLISM

OF THE

HEART

IN CARDIAC

24:71, 1969. 144. Levitt, hf., Spector, S., Sjoerdsma. A.. and Udenfriend, S.: Elucidation of the rate-limiting step in norephinephrine biosynthesis in the perfused guinea-pig heart. J. Phannacol. Exp. Ther. 1481, 1965. 145. Sobel, B. E., Henry, P. D.. Robinson, A., Bloor, C., and Ross, J., Jr.: Depressed adenvl cvclase activity in the failing guinea pig heart. Circ. Res. 24:507, 1969. 146. Covell. J. W., Chidse!., C. .A.. and Braunwald, I?.: Reduction of the cardiac to postganglionic slmpathetic response stimulation in experimental heart nerve failure. Circ. RPS. 19:51. 1966. I-47. Sandier. G., and Wilson. C. hl.: The natiue and prognosis of heart disease in thvrotoxicosis. J. ?rIed. (Quart.) 28:347, 19.W. 1-N. Leunissen, D. P.. and Olson, Ft. E.: Cartliac failure in the dog as a consequence of euogenous Ilyperthy~oitlism. Circ. Res. 20:242, 1967. 140. Cordon. E. S., Heming, -1. E.: The effect of thvroid treatment on the respiration of vnrions‘ rat tissues. Endocrinology 34: .35x 1944. 1.50. Ullrick, W. C., and W’itehom. 1%‘. \‘.: Influence of thyroid hormone on respiratinn of cardiac tissue. Amer. J. Physiol. 171407, 1952. lril. Moses, L. E.: hlechanism of the effect of hyperthyroidism on cardiac glycogen, Amer. J. Physiol. 142~686, 1944. 152. Shelley. W. B., Code, C. F.. and Visscher. M. B.: The influence of thyroid, dinitrophenol and swimming on the glyco,gen and phosphocreatine level of the rat heart in relation to cardiac hypertrophy. Amer. J. Physiol. 138:652, 1943. 15:3. Bressler, R., and Wittels, B.: The ell’ect of thyroxine on lipid and carhohydratca metabolism in the heart. J. Clin. Invest. 45: 1326, 1966. 1.5-I. Cold, hl., Scott, J. C., and Spitzer, J. J.: Myocardial metabolism of free fattv acids in control, hyperthyroid, and hypdth\roitl (logs. Amer. J. Physiol. 213:239, 1967. 1.53. Rowe. t:. C., Huston. steirr. A. B., Tuchman, H., and Cnunpton. C. W.: The of tbvrotoxicosis in man with encc’ to coromuy hlood flow ox!-gen rrretaholism. J. Clin. l%(i.

J. H., \VeinBrown, J. F., hemodynamics special referand myocarclial Invest. 35:272,

FAILUBE

51

156. Pool, P. E., Skelton, C. L., Seagren, S. C., and Braunwald, E.: Chemical energetics of cardiac muscle in hyperthyroiclism. J. Clin. Invest. 47:80a. 1968. 157. Skelton, C. L., Coleman, H. N.. Wildenthnl, K., and Braunwald, E.: .4ugmentation of myocarclial oxygen consumption in hyperthyroidism. Circulation 38 (Suppl. 6):181, 1968. 158. Buccino, R. A., Spann, J. F.. Jr.. Pool, P. E.. Sonnenblick, E.-H., and Braunwald, E.: Influence of the thyroid state on the intrinsic contractile properties and energ! stores of the myocardium. J, Clin. Invest. G:1669. 1967. 159. Taylor, R. R.. Covell, J. W., and Ross, J., Jr.: Influence of the thyroid state on left ventricular tension-velocitv relations in the intact, sedated do,<. J. Clin. Invest. -18:775. 1969. 1GO. Coodkind. hl. J., Dambach. (G. E.. and Luchi, R. J.: Increased mvocardial mvosin ATPase activity associated with an .increased mvocardial contractility in hyperthvroitl guinea pigs. J. Clin. Invest. 48:30a, 1969. 161. Wurtman. R. J., Kopin, I. J., and Axelrod, J.: Thyroid function and the cardiac disposition of catecholamines. Endocrinologv 7:3:6:3, 1963. 162. Coodkind, M. J.% Fram, D. H., and Roberts, M.: Effect of thyroid hormone on mvocardial catecholamine content of the guinea pig. Amer. J. Physiol. 201:1049, 1961. 163. Fleckenstein, .-1., Doring, H. J., and Kanunermeier, H.: Experimental heart failure due to inhibition of utilisation of highenergy phosphates. In: International Symposium on the Coronary Circulation and Enrrgetics of the hl\ocardium. Milan, 1966, P, 220. 164. Scheuer. J.: hlyacardial metabolism in cardiac hyl>oxi;i, .4mer. J. Cartliol. 19: 1967. 16ij. Scheuer, J., and Stezoski, S. \I\‘.: Effects of high-energy phosphate dep!etion and repletion on the dynamics and electrocardiogram of isolated rat hearts. Circ. Res. 20:319, 1968. 166. Covell, J. W., Pool, P;‘E., and Braunwald. E.: Effects of acutely induced ischemic heart failure on myocardial high energy phosphate stores. Proc. Sot. Exp. Biol. Med. 124:126. 1967. 167. Pool. I’. I-.. <:ovell. J. \I’., Chidse! ,

5.2 C. .4., and Braunwald, E.: Myocardial high energ\. phosphate stores in acutely induced hypoiic heart failure. Circ. Res. 19:221, 1966. 168. Leunissen, R. L., Piatneh-Leunisscn, D. A., Nakamura, Y., and Griggs, D. M., Jr.: Regional metabolism of the heart during reduced coronary flow. Circulation 34 (Suppl. 3): 155, 1966. 16&t. Kirk. E. S., Honig, C. R.: Nonrruiform distribution of blood flow and gradients of oxygen tension within the heart. Anrer. J. Physiol. 207:661, 1964. 1681,. Criggs. D. \I., Jr., Nakamura, Y.: E 1iri.t of coronan coirtricti~m on myocardial distribution of itloantipyrine--“’ I. Amer. J. Physiol. 215:108~, 1968. 169. Tennant, R., and Wiggers, C. J.: The effect of coronary occlusion on myocnrdial contraction. Amer. J. Physiol. 112: 351, 1935. 170. Hood, 11’. B., Jr., McCarthy, B., and Lown, B.: .Ilyocardial infarction following coronary ligation in dogs; Hemodynamic effects of isoproterenol and acetylstrophanthidin. Circ. Des. 21~191, 1967. 171. Klein, hf. D., Herman, M. V., and Gorlin, R.: -4 hemodynamic study of left 1entricular anruqsm Circrdation 35:614, 1967. 172. Dhalla, N. S., and Olson, R. E.: Correlation of endogenous fuel supply and contractile force in the isoIated perfused rat heart. Fed. Proc. 26:352, 1967. 173. Olson, R. E., and Hoeschen, R. J.: Endogenous lipid utilization by the isolated perfused rat heart. Biochem. J. 103:796, 1967. 174. Whiting, J. D., Penpargkul, S., and Scheuer, J.: Glucose utilization by the working rat heart. Proc. Sot. Exp. Biol. Med., in press. 175. Gercken, G.: Zur Theorie der energieubextragung auf das contractile Element des Herzmuskels. Pflueger Arch. 283:75, 1’965. 176. Olson, R. E., Pearson, 0. H., Miller, 0. N., and Stare, F. J.: The effect of vitamin deficiencies upon the metabolism of cardiac muscle in vitro: I. The effect of thiamine deficiency in rats and ducks. J. Biol. Chem. 175:489, 1948. 177. Hackd, D. B., Goodale, W. T., and Kleinermau, J.: Effects of thiamine deficiency on myocardial metabolism in intact dogs. Amer. Heart J. 46:883, 1953.

JAhIES

SCHEUEH

178. Blnnkcnhorn, hl. A.: The diagnosis of beriberi heart disease. Ann. Intern. Mctl. 23398, 1945. 179. Wagner, P. I.: Beriberi heart disease. Amer. Heart J. 69:200, 1965. 180. Brink, A. J., Lochner, A., and Lewis, C. M.: Thiamine deficiency and beriberi heart disease. S. Afr. Med. J. 40:581, 1966. 181. Wendt, V. E., Stock, T. B., Hayden, R. O., Bruce, T. A., Gudbjamason, S., and Bing, R. J.: The hemodvnamics and cardiac metabolism in cardiomyopathies. Med. Clin. N. Amer. 46:1445, 1962. 182. Brink, A. J., Lewis, C. M., and Van Heerden, P. D. R.: Corona? blood flow and myocardial metabolism in obstructive cardiomyopathy: Observations before and after treatment with a beta adrenergic blocking agent. Amer. J. Cardiol. 19:548, 1967. 183. Brink, A. J., and Lewis, C. M.: Coronary blood flow, energetics, and myocardial metabolism in idiopathic mural endomyocardiopathy (14 patients). Amer. Heart J. 73:339, 1967. 184. Hibbs, R. G., Ferrans, V. J., Black, W. C., Weilbaecher, D. G., Walsh, J. J., and Burch, G. E.: Alcoholic cardiomyopathy: An electron microscopic study. Amer. Heart J. 69:766, 1965. 185. Wendt, V. E., Wu, C., Balcon, R., Doty, G., and Bing, R. J.: Hemodynamic and metabolic effects of chronic alcohohsm in man. Amer. J. Cardiol. 15:175, 1965. 186. Ferrans, V. J., Hibbs, R. G., Weilbaecher, D. G., Black, W. C., Walsh, J. J., and Burch, G. E.: Alcoholic cardiomyopathy: A histochemical study. Amer. Heart J. 69:748, 1965. 187. Regan, T. J., Koroxenidis, G., Moschos, C. B., Oldewurtel, H. A., Lehan, P. H., and Hellems, H. K.: The acute metabolic and hemodynamic responses of the left ventricle to ethanol. J. Clin. Invest. 45:270, 1966. 188. Mallov, S., and Cerra, F.: Effect of ethanol intoxication and catecholamines on cardiac lipoprotein lipase activity in rats. J. Pharmacol. Exp. Ther. 156:426, 1967. 189. Epidemic cardiac failure in beer drinkers. Nutr. Rev. 26:173, 1968. 190. Bonenfant, J. L., Auger, C., Miller, G., Chenard, J., and Roy, P. E.: Quebec beer-drinkers’ myocardosis: Pathological aspects. Ann. N. Y. Acad. Sci. X%3:577, 1969. 191. Bajusz, E., Baker, J. R., Nixon, C.

METABOLISM

OF THE

HEART

IN

CARDIAC

FAILURE

W., and Homburger, F.: Spontaneous, hereditary myocardial degeneration and congestive heart failure in a strain of Syrian hamsters. .%nn. N. Y. Acad. Sci. 156105, 1969. 192. Lochner. .4., Opie, L. H., Brink, A. J., and Bosman. .4. R.: Defective oxidative phosphorylation in hereditary myocardiopath! in the Syrian hamster. Cardiovasc. Res. 3297, 1968. 193. Schwartz, A., Lindenmayer, G. E., and Hariga!-a, S.: Respiratory control and calcirim transport in heart mitochondria from the cardiomyopathic Syrian hamster. Trans. N. T. Acad. bled. 30:951, 1968. 191. Coleman. N. H., III: Role of acetylstroph;unthidin in augmenting myocardial oxygen consumption. Circ. Rcs. 21:487, 1967. 195. Gihhs, C. L., and Gibson, W. R.: Ell’ect of ouabain on the energy output of rabbit cartliac muscle. Circ. Res. 24:951, 1969. .l96. hlason. D. T., and Braunwald, E.: Studies on digitalis. IX. Effects of ouahain on the nonfailing human heart. J. Clin. Invest. 42:1105, 1963. 197. Covell, J. W., Braunwald, E., Ross, J. Jr., and Sonnenblick, E. H.: Studies on digitalis. *XVI. Effects on myocardial oxygen consrm~ption. J. Clin. Invest. 45:1535, 1966. 198. Bing, R. J., hfaraist, F. M., Dammann. J. F., Jr.. Draper, A., Jr., Heimhecker, R., Daley, R., Gerard, R. and Calazel P.: Effect of strophanthus on coronary blood flow and cardiac osvgen consumption of normal
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case-Cl& utilization in the intact clog. Circ. Res. 8:188, 1960. 203. Wollenherger, A.: hletaholic action of the cardiac gltcosides: III. Influence of ouahain on the ‘utilization of C*b-labeled glucose. lactate and pvruvate by dog heart slices. Naunyn Schmiedeherg Arch. Exp. Path. Pharm. 219:408, 1953. 204. Olson, R. E., Roush, G., and Liang, M. hl. I,.: Effect of acetyl strophanthidin upon the mvocardial metabolism and cardiac work of normal dogs and dogs with congcstive heart fnilnrc. Circulation 12:755, 1955. 205. Gousios, A. G., Felts, J. hl., and Havel, R. J.: Effects of ouahain on force of contraction, oxygen consumption, and metabolism of free fatty acids in the perfused rabbit heart. Circ. Res. 21:445, 1967. 206. Kreisberg, R. A., and Williamson, J. R.: Metabolic effects of ouabain in the perfused mt heart. .4mer. J. Physiol. 207:347, 1964. 207. Rehar, J., Jr., Rehar, B. T., and Omachi, A.: Influence of digitoxin on labile and inorganic phosphates, lactate, glycogen, potassium and sodium in dog ventricle. Circ. Res. 5504, 1957. 208. Wollenherger, A.: Metabolic action of the cardiac glvcosides. II. Effect of ouahain and digoxin on the energy-rich phosphate content of the heart. J. Pharmacol. Exp. Ther. 103:123, 1951. 209. Mallov, S., and Robh, J. S.: Behavior of actomvosin threads. Fed. Proc. 8:104, 1949. 210. Bowen, W. J.: Effect of digoxin upon rate of shortening of myosin B threads. Fed. Proc. 11:16, 1952. 211. Fritz, P. J., Cho, Y., Lankford, J. C., Clark, C. E., and Hamrick, M. E.: The effect of digoxin on rat contractile proteins: 2. In vitro studies. Pharmacology 2:32, 1969. 212. Luchi, R. J., and Kritcher, E. M.: Drug effects on cardiac myosin adenosine triphosphatase activity. J. Pharmacol. Exp. Ther. 158:540, 1967. 213. Fritz, P. J., Hamrick, M. E., Lankford, J., Cho, Y., and Clark, C. E.: The effect of digoxin on rat contractile proteins. 1. In vitro studies. Pharmacology 1:303, 1968. 214. Lullmann, H., and Holland, W.: In5uence of ouahain on an exchangeable calcium fraction, contractile force, and resting

tclhal:m of gllinea-pig atria. J. I’han~rac~ol. hp. Ther. 137:186, 1962. 215. Sekul, A. A., and Holland. \\‘. C.: l’ffccts of ouabain on Ca-‘” entry in quiescent and electrically driven rabbit atria. Amcsr. J. Physiol. 199:457, 1960. 216. Cersmever, E. F.. an<1 Holland, 14’. C.: Effect of heart rate on action of mlabain on Ca exchange in guinea pig left atria. Amer. J. Physiol. 205:795, 1963. 217. Govier, W. C., and Holland. W. C.: The relationship between atria1 contractions and the effect of ouabain on contractile strength and calcium exchange in rabbit atria. J. Pharmacol. Exp. Ther. 148:284, 196Fj. 218. Crossman, A., and Furchgott, R. F.: The effects of various drugs on calcium exchange in the isolated guinea-pig left auricle. J. Pharmacol. Exp. Ther. 145:162, 1964. 219. Bailey, L. E.. and Harvey, S. C.: Effect of ouabain on cardiac 45Ca kinetics measured by indicator dilution. Amer. J. Phvsiol. 216:123, 1969. 220. Lee, K. S., and Choi, S. J.: Effects of the cardiac glycosides on the Cn* uptake of cardiac sarcoplasmic reticulum. J. Pharacol. Exp. Ther. 153:114, 1966. 221. Carsten, h1. E.: Cardiac sarcotubular vesicles: Effects of ions, ouabain and acetylstrophanthidin. Circ. Res. 20:599, 1967. 222. Dutta, S., Goswami, S., Lindower, J. O., and Marks, B. H.: Subcellular distribution of digoxin-H” in isolated guineapig and rat hearts. J, Pharmacol. Exp. Ther. 159:324, 1968. 223. Fozzard. H. A., and Smith, J. R.: Observations on the localization of tritiated digoxin in myocardial cells bv autoradiography and ultramicroscopy: With added reference to the sarcotubular system studied by cell fractionation and enzyme staining. Amer. Heart J. 69:245, 1965. 224. Lee, K. S.: Effect of ouabain on glycerol-extracted fibers from heart containing a “relaxing factor.” J. Pharmacol. Exp. Thrr. 132:149, 1961. 225. cosides 30:237,

Page, E.: The actions of cardiac glyon heart mllscle cells. Circulation 1964.

226. Weatherall. of digitalis. Brit.

M.: Heart

Ions and J. 28:497,

the action 1966.

227. Blnckmon, J. R.. Hellerstein, H. K.. Cillespir. L.. Jr., and Berne, R. M.: Effect of digitalis glycosides on the myocardial sodium and Ijotassium balance. Circ. Res. 8: 1003, 1960. 228. Regan, T. J., Talmers, F. Hellems, H. R.: Myocardial transfer

N., and of sod-

229. Samolt‘, S. J.. (:illtlorr, J. I'.. Mitclwll, J. 11.. and Rrmensmdt~r. J. P.: Potassirlm chngcs in the heart tlluing homeorrlrtric autoregulation and acrtyl strophar~thitlin. Amer. J. hletl. 34:440. 196:3. 230. Vick. R. I,., and Kahn, J, B.. Jr.: The effects of ouabain and veratridirrr cm potassium nlovement in the isolated crlirrea pig heart. J. Phnrmacol. I’:\-p. Thcr. 121: 389. 1957. 231. Schreiber, S. S.: Potassium and sodilun exchange in the working frog heart rtfrcts of overwork, external concentrations of potassium and on&in. Amer. J. Ph\.siol. 185:.337, 1956. 2:32. Aluller, P.: Ouabain effects on cardiac contraction. action potential, and celhdar potassium. Circ. Res. 17:46, 1965. 233. Lee, K. S.. and YII. D. H.: A stlldy of the sodium-and potassirunl-activated ndenosirletriphosphat;Ise activitl. of heart microsomal fraction. 234. >fatsui, II., and Schwartz. A.: Purification and properties of a highly active ouabain-sensitive Na.. KS -dependent ndenosinetriphosphatase from cardiac tissue. Biothem. Biophys. Acta 128:380. 1966. J.: The 235. Song, S. Y., and Schruer, effects of pharmacologic agents on myocardiol sodillm (Na’) and potassium (Kc) stimulated i\TPase. Pharmacology 1:209, 1968. 236. Repkc, K.: L%er den Biochemischen wirklmgsmodus van Digitalis. Klin. Wschr. 12:ll. 1964. 2:37. Schrrlag, B. J., Helfant, R. H., Ricciutti, hl. A., and Damato, A. N.: Dissociation of the efi’ects of digitalis on myocardial potassium flux and contractility. Amer. J. Phvsiol. 215:1288, 1968. 238. Regan, T. J.. Frank, M. J., Lehan, P. II., and Hellems, H. K.: Relationship of insulin ant] strophanthidin to myocardial metabolism and function. .4mer. J. Physiol. 205:790, 1963. 239. Panz, R. D.: The action of ouabain on cardiac muscles treated with reserpine and tlichloroisoproterenol. J. Pharmacol. Exp. Ther. 144:205, 1964. 240. Spann, J. F., Jr., Sonnenblick, E. H., Cooper. T., Chidsui, C. .4., \Villman, V. L., Braunwald. E.: Studies OLL digitalis XIV: InHllc~nce of cardiac norepinephrine stores on the response of isolated heart muscle to digitalis. J. Circ. Res. 1919:326, 1966. 241. \‘aylrr, W. C:.: Calcium exchange in c~rdi;~,, 11111s~.lts: A basic mechanism of dru,g xtion. .411rrr. Heart. J. 7X.379, 1967.