Effect of flosequinan (BTS 49465) on myocardial oxygen consumption

Effect of flosequinan (BTS 49465) on myocardial oxygen consumption BTS 49465 (flosequinan), a putative selective, balanced arterial and venous vasodilator, displays positive inotropic effects in doses lower than those producing vasodilation. Thus rather than unloading the myocardium, flosequinan may increase myocardial work and oxygen consumption (MV02), and may adversely affect the patient with myocardial ischemia or compromised coronary blood flow. This study compared the effects of flosequinan with milrinone, a mixed positive inotropic agent and vasodilator, and with nitroprusside (SNP), a standard direct-acting vasodilator, on myocardial d P / d T , MV02, and myocardial energetics in the normal pentobartital-anesthetized dog. The effect of flosequinan on myocardial w o r k was also evaluated in the dog with propranolol-induced heart failure (PIHF). Fifteen minutes after intraduodenal (id) administration of flosequinan (0.3, 1.0, and 3.0 m g / k g ) to seven dogs, mean myocardial d P / d T was increased by 11%, 27%, and 54%, respectively, whereas stroke MV02 was increased by 10%, 24%, and 47%, respectively. Doses of flosequinan greater than 0.3 m g / k g decreased left ventricular (LV) w o r k but LV efficiency decreased in a dose-related manner. Milrinone (0.1, 0.3, and 1.0 m g / k g , id) increased LV d p / d t by 34%, 68%, and 104% above basal values, while increasing stroke MV02 by 24%, 106%, and 249%, respectively (n = 7). LV work and LV efficiency decreased after each dose of milrinone. SNP (0.001, 0.003, and 0.01 m g / k g / m i n , intravenously) did not increase d P / d T but decreased LV work by 28%, 42%, and 46% (n = 5). In animals with PIHF, flosequinan (1 and 3 m g / k g , id) increased LV d P / d T 58% and 87% and increased LV w o r k by 58% and 76% above control values. It was concluded that (1) flosequinan is a positive inotropic agent as well as a vasodilator; (2) in the normal animal the energy cost of positive inotropic activity is less with flosequinan than with milrinone, despite the lesser vasodilating action of the former; and (3) in the animal with a depressed myocardium, flosequinan may adversely affect myocardial work and wall tension. (AM HEARTJ 1990;119:1355.)

S. Greenberg, PhD, B. Touhey, and J. Paul, BS, MS, PhD. Cedar Knolls and Newark, N.J.

Congestive heart failure (CHF) has multiple etiologies that result in differences in the hemodynamic variables associated with the disease. Some patients primarily suffer from pressure overload, while volume overload is the primary contributor toward cardiac dysfunction in others. 1-3 Some patients may have compromised coronary blood flow due to a decrease in coronary flow reserve secondary to coronary artery disease. Others may suffer from increased resting myocardial oxygen demand due to myocardial hypertrophy and increased left ventricular wall stress. 4-7

From the Department of Pharmacology, Vascular Pharmacology Research, Berlex Laboratories, Inc., and Department of Physiology, UMDNJ-New Jersey Medical School. Received for publication Aug. 25, 1989; accepted Jan. 23, 1990. Reprint requests: Stan S. Greenberg, PhD, Dept. of Physiology, UMDNJNew Jersey Medical School, H-607 Medical Science Bldg., 185 S. Orange Ave., Newark, NJ 07103. 4/1/19599

Flosequinan (BTS-49465) is undergoing clinical trials for the treatment of congestive heart failure and hypertension. T M Since flosequinan decreases blood pressure in spontaneously hypertensive rats, renal hypertensive dogs, normotensive cats, and baboons15. 16 and decreases pulmonary artery pressure and vascular resistance in the dog, 15-17 it was classified as a selective vasodilator, with balanced effects on arteries and veins. 1517 However, when left ventricular d P / d t and aortic flow were measured, flosequinan (0.3 to 3.0 mg/kg, intraduodenally) was shown to be a positive inotrope in the normal anesthetized dog and in the dog with propranolol-induced heart failure, is, 19 Flosequinan improves the hemodynamic profile in a select group of patients with low renin congestive heart failure. 9, 10 However, the myocardial oxygen cost of this improvement is unknown, since flosequinan was considered to be a pure vasodilator. This study evaluates whether the positive inotropic activity of flosequinan is associated with an adverse pro1355

June 1990

1356

Greenberg, rouhey, and Paul

AmericanHeartJournal

Table I. Initial hemodynamic parameters of anesthetized dogs

Parameter

Vehicle

SNP

Flosequinan

Milrinone

No. of dogs Body weight (kg) dP/dT (mm Hg/min) MAP(mmHg) LVEDP (mm Hg) LAP (mm Hg) CO (ml/min) CBF (ml/min) HR (beats/min) TPR (dyne 9 cm/sec • 105) CVR ([mm Hg/ml]/min) ART (02) (%) VEN (02) (%) A-V (02) (%) LV tension (mm Hg) LV work (kg 9 m/min) MVO2 (ml/min) LV efficiency (%)

6 17 • 1.2 2502 • 228 95 • 6 4.8 _+ 0.9 3.7 • 0.6 1717 + 84 33 • 5 145 • 8 4485 _+ 399 3.2 • 0.7 17.9 • 1.3 4.2 • 0.5 13.7 • 1.0 97 _+ 6 2.25 • 0.2 5.05 _+ 0.4 23.4 • 2.4

5 18 _ 0.6 2492 • 318 99• 6.4 _+ 0.5 3.8 • 0.5 1919 _+ 251 33 • 3 143 • 8 4410 • 552 3.0 • 0.3 18.2 _+ 1.0 4.3 • 0.5 13.9 • 0.7 101 • 4 2.6 • 0.4 4.45 • 0.5 30.2 • 4.8

7 17 • 1.1 2425 • 151 93 • 6 5.7 • 0.6 3.4 • 0.2 1748 • 135 37 • 4 134 • 4 4463 • 542 2.6 _+ 0.4 17.8 • 0.6 4.4 • 0.3 13.4 • 0.6 95 • 6 2.2 • 0.1 4.92 • 0.4 23.3 • 2.7

7 18 _+ 1.1 2470 • 170 98_+ 5 6.3 • 0:9 5.0 • 0,6 1472 _+ 108 30 • 4 138 _+ 6 5568 • 586 3.7 • 0.6 19.0 • 0.6 4.8 • 0.4 14.2 • 0.4 100 • 5 2.0 • 0.1 4.25 • 0.5 25.2 _+ 3.2

dP/dt, Rate of pressure development of the left ventricle; MAP, mean arterial pressure; LVEDP, left ventricular end-diastolic pressure; LAP, left atrial pressure; CO, cardiac output; CBF, coronary blood flow; HR, heart rate, TPR, total systemic vascular resistance; CVR, coronary vascular resistance; ART (O2), arterial oxygen content; VEN (02), venous oxygen content; A-V (02), arteriovenous oxygen difference; SNP, nitroprusside; MVO2, maximum venous oxygen consumption; LV, left ventricular.

file o n m y o c a r d i a l work, o x y g e n c o n s u m p t i o n , a n d c o r o n a r y b l o o d flow i n t h e n o r m a l p e n t o b a r b i t a l a n e s t h e t i z e d dog a n d i n t h e dog w i t h p r o p r a n o l o l - i n duced heart failure (PIHF). METHODS Preparation and administration of drugs. Flosequinan

(0.3, 1, and 3 mg/kg, intraduodenally), milrinone hydrochloride (0.1, 0.3, and 1.0 mg/kg, intraduodenally), and sodium nitroprusside (SNP) (1, 3, and 10 #g/kg/min, intravenously) were prepared as described previously in detailJ s Vehicle consisted of three injections of 5 ml of deionized water intraduodenally (n = 5 dogs) or 0.05, 0.15, and 0.5 m l / m i n of 5% dextrose in water (D5W), intravenously (n = 2 dogs). The hemodynamic responses were observed for 30 minutes prior to administration of the next higher dose of drug or vehicle. No differences existed in the stability of the animals receiving water or those receiving D5W, so that all the vehicle control data were pooled for statistical comparison with the data from the t r e a t m e n t groups receiving drug. The rationale for intraduodenal administration of flosequinan has been described in detailJ s Briefly, this route of administration allows flosequinan to undergo first-pass hepatic metabolism and generate the metabolites that may affect hemodynamics and myocardial energetics, as they would in m a n J 3 SNP was used since it is the most balanced of the vasodilators currently available for the clinical t r e a t m e n t of heart failure. Experimental procedures. Twenty-six mongrel dogs, unselected for sex or age (15 to 19 kg in body weight), were allocated to one of four experimental groups with the aid of a computer and a random n u m b e r generator: vehicle (n = 7), nitroprusside (n = 5), flosequinan (n = 7), milri-

none (n = 7). On the day of the experiment, a dog was anesthetized with pentobarbital sodium (35 mg/kg intravenously) and maintained under surgical anesthesia with supplemental injections of pentobarbital sodium (1 to 3 mg/kg/hr) as required, is Body temperature was maintained with a water circulating heating blanket under the animal. The animals were i n t u b a t e d with Murphy endotracheal tubes (U.S. Hospital Supply, Newark, N.J.) and were ventilated with positive pressure using room air and were prepared for recording of arterial pressure, left ventricular end-diastolic pressure (LVEDP), heart rate (HR), and cardiac o u t p u t (CO), as described previously in detail. 18 In addition, coronary artery blood flow was measured with an electromagnetic flow probe placed around the left circumflex coronary artery. Polyethylene cannulas were also placed into the great coronary vein and coronary ostium for sampling and collection of venous and arterial blood. All pressures and blood flow rates were recorded continuously on a Sensormedics R-611 dynograph (Sensormedics Corp., Anaheim, Calif.) All wounds were covered with moist pads after completion of the instrumentation of the animal. The animals were allowed to stabilize for 60 minutes before baseline values of the hemodynamic parameters were obtained. After the 60-minute equilibration period, each of the measured and computed hemodynamic variables were sampled at 5-minute intervals over the next 120 minutes. Coronary arterial and venous oxygen samples were obtained at 15 and 30 minutes before, immediately prior to, and at 15 and 30 minutes after the intravenous or intraduodenal administration of each of three doses of test compound or vehicle. The oxygen sample obtained immediately before administration of the first dose of vehicle or

Volume 119 Number 6

drug was used for calculation of percent changes of the myocardial energetic parameters. The blood samples, collected in ice-cold polyethylene syringes, were immediately placed on ice and read within 5 minutes on a LEXo2CON T L (Hospex I n s t r u m e n t s Inc, Waltham, Mass.). P r o p r a n o l o l - i n d u c e d h e a r t f a i l u r e . Nine mongrel dogs, unselected for sex or age (15 to 22 kg in body weight), were allocated to one of two experimental groups vehicle (n = 4) or flosequinan (n = 5) and were anesthetized with pentobarbital sodium (35 mg/kg intravenously) as described above. At the end of the equilibration period, cardiac contractility was decreased by infusion of propranolol (0.5 mg/kg/min, intravenously) until left ventricular d P / d T was reduced 50 % to simulate acute heart failure. Heart failure was maintained by the infusion of propranolol (0.02 to 0.08 mg/kg/min, intravenously) for the remainder of the experiment.is, 20 After a 60-minute equilibration period, each animal received a single dose of either saline or flosequinan (1 mg/ kg, intraduodenally). The hemodynamic parameters were observed continuously and were measured every 5 minutes for 30 minutes. A second dose of saline or flosequinan (3 mg/kg, intraduodenally) was then given and the hemodynamic parameters were monitored for an additional 30 minutes. The level of each hemodynamic variable obtained immediately before the first dose of vehicle or flosequinan was considered the control value for that parameter, and was used for calculation of the percent changes of that variable. Hemodynamic parameters. The hemodynamic parameters measured included left ventricular pressure (LVP), systemic arterial pressures, left atrial pressure (LAP), LVEDP, and coronary arterial (CBF) and aortic blood flows (CO). Heart rate (HR) was obtained from the electronic addition of the aortic flow pulses. Left ventricular d P / d t was obtained by computer sampling and differ. entiation of the u n d a m p e n e d LVP pulse signal. Cardiac contractile index, obtained by on-line computer analysis of LVP and diastolic arterial pressure, was taken as d P / d T / P at 40 mm Hg. Coronary arterial resistance (CVR) was calculated as the quotient of the difference between mean arterial pressure (MAP) and LAP divided by CBF.mCoronary arterial oxygen supply (CAS), myocardial oxygen consumption (MVO2), stroke MVO2, relative left ventricular wall tension (LVTEN), work, stroke work, and contractile efficiency were calculated by established formulas21, 22 as follows: CAS (ml O2/min) = [Art02] x CBF; MVO2 (ml 02/min) = AVO2 x CBF; and Stroke MVO2 (ml O2/beat) = MVO2/ HR. The pressure equivalent of L V T E N (in millimeters of mercury) was calculated from the following equation: LV tension (mm H g ) = (MSAP-LAP) and MSAP (mm Hg) = SAP - I/3 (SAP-DAP), where MSAP is mean systolic arterial pressure (in millimeters of mercury), SAP is systolic arterial pressure (mm Hg), and DAP is diastolic arterial pressure (in millimeters of mercury]. LV work (kg 9 ms/min) = L V T E N x CO x 0.0136 and stroke work (kg 9 m/beat) = LV work/hr, where CO is cardiac output

Flosequinan and MV02

1357

T a b l e Ih Effect of vehicle on hemodynamic parameters of

pentobarbital-anesthetized dogs Treatment period with vehicle a 1

Parameter

2

3

(percent change from Control • SEM)

dP/dT 4.0 • 4.0 -2.5 • 5.5 -1.6 • 4.1 (mm Hg/min) MAP -2-+ 3 -2 + 4 10 • (mm Hg) LAP -0.3 • 0.2 -0.4 + 0.2 -0.2 • 0.2 (mm Hg) LVEDP 0.4 _+ 0.3 0.2 + 0.2 -0.3 • 0.2 (mm Hg) CBF -5+3 -5_+4 -7• (ml/min) HR -1 • 1 -3_+ 1 -6 • 2 (beats/min) TPR 7_+ 6 14_+ 8 31• (dyne 9 cm/sec • 105) ART (02) 4.9 _+ 1.9 6.7 + 2.1 7.0 • 1.8 (%) VEN (02) 10.6 • 4.2 20.1 +_ 4.6 23.9 • 2.5 (%) A-V (O2) 3.2 • 1.9 2.9 + 3.4 2.0 • 2.7 (%) LV work -8.4 _+ 2.4 -11.9 + 1.9 -10.5 • 2.8 (kg. m/min) SLV work -7.6 + 1.7 -10.8 • 2.8 -7.3 • 3.3 (kg. m/min) MV02 1.8 • 4.8 -2.9 • 6.6 -4.8 • 6.0 (ml/min) SMV02 1.8 • 4.7 -2.0 _+ 6.3 2.6 • 6.5 (ml/min) LV efficiency -8.1 • 5.1 -7.1 • 8.2 -5.6 • 8.8 (%) SLV efficiency -8.1 • 5.4 -5.3 • 8.8 4.4 • 10 (%) Each value represents the mean response _+SEM from six animals. Abbreviationsas in Table I. An "S" before a parameter indicatesthe per beat value of the parameter. aHemodynamicparametersbeforeand 30 minutesafter each doseof vehicle.

(L/min) and 0.0136 is the conversion factor for kg . meters per minute. Since left ventricular myocardial contractile efficiency is the quotient of LV external work and MV02, then: LV efficiency ( % ) = LV work/(MVO2 x 2.059), where 2.059 is the conversion from ml O2/min to k g . m/rain. S t a t i s t i c s . Experimental data were digitized a n d analyzed with the aid of a computer every 5 minutes and at the peak of the individual parameters. For this the blood pressure and flow rate signals were sampled for 5 seconds (one respiratory cycle) using sampling rates of 100 Hz (for blood flow rates) to 400 Hz (for LVP), and the data for all cardiac cycles/sample were averaged. The data are presented as the mean change from predrug control values (expressed as a percent or absolute change) z SEM. Data were analyzed with analysis of variance with repeated measures and means compared with Tukey's procedure and the Hotell-

June 1 9 9 0

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America.HeartJournal

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E f f e c t s of w a t e r and 5 % d e x t r o s e in water. Intraduodenal administration of deionized water and intravenous administration of D5W did n o t affect most hem o d y n a m i c parameters. B o t h ve1~icles decreased C B F and, as a result, increased the calculated par a m e t e r of CVR {Table If). Hemodynamics. T h e effects of flosequinan {0.3, 1, a n d 3 mg/kg, intraduodenally) milrinone (0.1, 0.3 and 1 mg/kg, intraadnodenally), and S N P (1, 3, and 10 #g/kg, intravenously) on arterial pressure and total

Volume 119 Number 6

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Fig. 4. Percent changes in the pressure equivalent 0f LV wall tension and tension HR index in the normal pentobarbital-anesthetized dog after increasing doses of intraduodenal flosequinan (n = 7; open triangles) and milrinone (n = 7; closed circles) and intravenous administration of sodium nitroprusside (SNP, n = 5; open circles). *p < 0.05 from predrug values; **p < 0.05 for flosequinan differences from the first, second, or third dose of SNP, respectively.

peripheral resistance were described previously 18 and are summarized in Fig. 1. This report will address the cardiac effects of these compounds. M y o c a r d i a l contractility. Flosequinan and milrinone increased myocardial cardiac contractility index (CCI) in a dose- and time-dependent manner, whereas SNP was without effect (Fig. 2). The relationship between the compounds in their effects on myocardial contractility (LV dP/dT) and preload is also summarized in Fig. 2. The positive inotropic effect of milrinone was greater than that produced by flosequinan. SNP did not affect myocardial LV dP/dT. However, the reduction in preload did not differ between milrinone and SNP, whereas flosequinan produced less of a decrease in LVEDP than either milrinone or SNP (Fig. 2). C o r o n a r y v a s c u l a r d y n a m i c s and HR. Fig. 3 shows that flosequinan (n = 7), milrinone (n = 7), and SNP (n = 5) increased CBF and HR. CBF remained ele-

vated after each dose of flosequinan, whereas H R remained elevated only after the highest dose of flosequinan. Milrinone-induced tachycardia did not differ in magnitude from t h a t of flosequinan. However, the increases in CBF were greater with milrinone than with flosequinan. The increases in CBF were highly variable and ranged from 60% to 628% and from 23% to 289%, respectively, among the seven dogs (1 SD). Analyses of the data demonstrated heteroscedasticity of variance for the effects of milrinone on CBF and MVO2 (see below). Moreover, correlation analyses of the percent change in CBF against the initial absolute values of blood pressures, LV dP/dT, CBF, MV02 or LVEDP alone, and when taken together (e.g., changes in CBF versus LV d P / d T • HR • LV dP/dT) indicated the absence of any correlation between the changes in CBF produced by milrinone and the initial values of the hemodynamic parameters evaluated. SNP also in-

June 1990

1360 Greenberg, Touhey, and Paul MILRINONE 0 ~ 0 FLOSEQUINAN A ~ A 300.

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in the normal pentobarbital-anesthetized dog after increasing doses of intraduodenal flosequinan (n =7; closed triangles) and milrinone (n = 7; closed circles). *p < 0.05 from predrug values; **p < 0.05 for flosequinan differences from the first, second, or third dose of SNP, respectively. The responses to the low dose of each drug are shown at 15 and 30 minutes. At 30 minutes the second dose of drug was administered, followed by the third dose of drug at 60 minutes.

creased H R and CBF, The increases in H R produced by S N P were transient and differed statistically only from those following the highest doses of milrinone or flosequinan. SNP-induced increases in CBF exceeded the increase produced by flosequinan but was less than the increase in CBF produced by milrinone. Left ventricular tension. Flosequinan, milrinone, and SNP decreased the pressure equivalents of L V T E N (Fig. 4). The changes in L V T E N did not differ between milrinone- and flosequinan-treated animals, but were less than those produced by S N P (Fig. 4). Similar results were found when the pressure equivalent of wall tension was corrected for H R (Fig.

4). Myocardial energetics. Flosequinan did not affect the A-V 02 difference of the pentobarbital-anesthetized dog (control = 72 _+ 4%; after 3 mg/kg of flosequinan = 68 _+ 5 % ; p > 0.1). In contrast to flosequinan, milrinone (0.3 and 1 mg/kg) decreased the myocardial oxygen extraction coefficient from 7 4 + 3% to 67 + 3% and 6 4 + 3%, respectively (p < 0.05). S N P (1, 3, and 10/~g/kg, intravenously) decreased the myocardial oxygen extraction coefficient from 72_+ 2% to 65 +_ 3%, 57_+ 5%, and 46 _+ 5%, respectively (p < 0.05). Fig. 5 shows that flosequinan and milrinone increased LV MVO2 in a dose- and time-related man-

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% A dP/dT Fig. 6. Relationship between percent changes in LV dP/ dT (abscissa) and LV MVO~ (ordinate) following intraduodenal administration of flosequinan (0.3, 1, and 3 mg/kg) and milrinone (0.1, 3, and 1 mg/kg) to the pentobarbital-anesthetized dog. The solid line and the dashed line are the regression lines using the method of least squares. The dotted line is the line of identity. Significant deviation from the line of identity denotes an oxygensparing or an oxygen-wasting effect, as indicated.

ner. The maximal increase in LV MVO2 produced by flosequinan was 77 + 18%, for a 54% increase in LV dP/dT; the maximal increase in LV MV02 produced bymilrinone, on the other hand, was 309 + 139%, for a 104% increase in LV dP/dT. For flosequinan the percent increases in MVO2 and LV d P / d T did not differ at each dose of compound at each time period examined. However, for milrinone the percent increases in MVO2 and LV d P / d T began to divagate after the 0.3 mg/kg intraduodenal dose of milrinone. This suggests that high doses of milrinone have direct effects on myocardial metabolism independent of the metabolic changes that accompany and support its positive inotropic effects. Fig. 6 contains Braunwald plots 21' 22 comparing percent changes in LV MV02 against percent changes in LV dP/dT. Equivalent changes in MV02 and LV d P / d T indicate that myocardial oxygen demand is primarily due to the increased contractility produced by a drug. In contrast, significant deviations above or below the line of identity are suggestive of an oxygen-wasting or oxygen-sparing effect, respectively, of a compound or pharmacologic intervention. The positive inotropic responses to flosequinan were neither oxygen-wasting nor oxygen-efficient at any level of LV d P / d T reached. In contrast, the positive inotropic response to milrinone (0.1 mg/kg, intraduodenally) was energy efficient, occurring with a lower change in MV02 than that expected from the magnitude of the change in LV dP/dT. Nevertheless, the remaining positive inotropic responses following mil-

Volume 119

Number 6

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Fig. 7. Percent changes in LV MVO2, LV work, and LV contractile efficiency in the normal pentobarbita]-anesthetized dog after increasing doses of intraduodenal flosequinan (n = 7; open triangles) and mflrinone (n = 7; closed circles) and intravenous administration of sodium nitroprusside (SNP, n = 5; open circles). *p < 0.05 from predrug values; **p < 0.05 for flosequinan differences from the first, second, or third dose of SNP, respectively.

Fig. 8. Percent changes in LV MV02, LV work, and LV contractile efficiency normalized for changes in HR in the normal pentobarbital-anesthetized dog after increasing doses of intraduodenal flosequinan ( n = 7; o p e n t r i a n g l e s ) and milrinone ( n = 7; c l o s e d circles) and intravenous administration of sodium nitroprusside ( S N P , n = 5; o p e n circles). *p < 0.05 from predrug values; **p < 0.05 for flosequinan differences from the first, second, or third dose of SNP, respectively.

rinone administration occurred at a level of L u MVO2 that far exceeded the percent change in LV dP/dT. Regression analyses of the data indicated the slope of the line for milrinone was significantly higher than that for flosequinan. The relationship between LV MVO2, LV work, and LV contractile efficiency for the vasodilator SNP and for the cardiotonic agents flosequinan and milrinone are summarized in Figs. 7 and 8. Because LV work decreased while LV MVO2 increased, the contractile efficiency of the myocardium decreased from predrug

control values after each dose of flosequinan. The effects of flosequinan on myocardial energetics were not mediated by the positive chronotropic effects of this compound, because the changes in stroke MVO2, LV stroke work, and LV stroke efficiency did not differ from those of MVO2, LV work and LV efficiency. Similarly, milrinone decreased LV work while LV MVO2 increased in a highly variable manner. Therefore the contractile efficiency of the myocardium decreased in a variable manner after each dose of milrinone. The decrease in contractile efficiency

June 1 9 9 0

1362 Greenberg, rouhey, and Paul

AmericanHeartJournal

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was greater than that produced by flosequinan. The effects of milrinone on myocardial energetics were mediated in part by the positive chronotropic effects of this compound, since the changes in these parameters were greater than the changes in stroke MVO2, LV stroke work, and stroke efficiency. LV MVO2 was increased after the 3 ttg/kg dose of SNP. However, the effects were small and did not increase further when the highest dose of SNP was given (Fig. 7). Because LV work decreased while LV MVO2 increased, the contractile efficiency of the myocardium decreased. However, the maximal decrease in LV contractile efficiency reached a nadir after the intermediate dose of SNP and was less than the decrease in efficiency produced by the highest dose of milrinone, but greater than that produced by the intermediate dose of flosequinan. The increase in LV MVO2 was partially related to the HR, since stroke MVO2 only significantly increased after the 10 t~g/kg dose of SNP (Fig. 8). Fig. 9 is a Mohrman-Feigl plot 24 comparing percent changes in LV MVO2 against percent changes in CAS. Equivalent changes in MVO2 and CAS indicate t h a t drug-induced changes in CBF result from an autoregulatory response to an increased myocardial oxygen demand. Deviations from the line of identity are suggestive of a direct-acting coronary vasodilator

or a potential proischemic effect, respectively, of a compound, For all doses of flosequinan studied, the percent change in CAS did not differ from the corresponding percent change in LV MVO2. Thus flosequinan is not a direct-acting coronary arterial vasodilator. For all doses of milrinone tested, the percent change in CAS did not differ from the corresponding percent change in LV MVO2. However, at each dose of milrinone the oxygen demand and supply were significantly greater than those produced by flosequinan (Fig. 9). For all doses of SNP tested, the percent change in CAS was greater than the corresponding percent change in LV MV02. The slope of the regression line was shifted toward the 02 supply axis, which confirms the finding that SNP is a coronary vasodilator (Fig. 9). Propranolol-induced heart failure

Effects o[propranolol. Infusion ofpropranolol (0.5 mg/kg/min) decreased myocardial LV d P / d T from 2502 _+ 228 mm Hg/sec to 1243 _+ 153 mm Hg/sec (p <0.05) and CO from 1717 _+ 84 ml/min to 963 _+ 91 ml/min (p < 0.05),while increasing LVEDP from 4.8 _+ 0.9 mm Hg to 9.8 + 0.6 mm Hg, pulmonary artery pressure from 13 + 1 mm Hg to 19 _+ 2 mm Hg, and total systemic vascular resistance (TPR) from 4485 +_ 399 to 7190 _+ 834 dyne 9 cm/sec x 105 (p < 0.05). The effects ofpropranolol on HR (145 _+ 8 beats/min to 151 + 20 beats/min) were highly variable because the HRs of some animals were elevated by spontaneous, ectopic beats. The hemodynamic variables measured in the two groups of dogs with PIHF (vehicle and flosequinan) were comparable and did not differ. Effects of vehicle. Most hemodynamic parameters were unaffected by either of the vehicle treatments and remained within 4 _+ 2 % of P I H F control values over the time course of the experiment. MAP increased by 2 +_ 3% and T P R increased by 21% after the last dose of vehicle. Thus the hemodynamic parameters of the flosequinan-treated animals with the P I H F group were corrected for the effect of vehicle at each time period. Effects o[ flosequinan on myocardial contractility. Table III summarizes the effects of flosequinan and milrinone on myocardial dynamics in the pentobarbital-anesthetized dog with PIHF. FLosequinan (1 and 3 mg/kg) increased myocardial dP/dT. The onset of drug action was similar to that observed in normal animals. However, the 1 mg/kg dose of flosequinan increased myocardial d P / d T by the same percent as the 3 mg/kg dose in the normal animal. Thirty minutes after the administration of 1 and 3 mg/kg of flosequinan, myocardial d P / d T and the rate of myocardial relaxation remained elevated above

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Flosequinan and MV02

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Table III. Effects of flosequinan and milrinone on myocardial variables of dogs with propranolol-induced heart failure

(PIHF) Flosequinan

Milrinone

% Change Parameter M A P (ram Hg) dP/dT (mm Hg/min) CO ( m l / m i n ) CBF (ml/min) HR (beats/min) T P R ([mm Hg/[ml/min]) LV t e n s i o n ( m m Hg) LV w o r k (kg . m / m i n ) SLV wo rk (kg 9 m / b e a t )

Control 91 1310 1135 16 118 0.084 86 1.3 0.011

_+ 5 +_ 245 _+ 316 _+ 3 _+ 13 + 0.009 +_ 7 _+ 0.3 +_ 0.003

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-+ 8 _+ 101 _+ 107 _+ 1 +_ 6 _+ 0.014 _+ 8 +_ 0.2 _+ 0.002

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Propranolol-induced failure was produced by infusing 0.5 mg/kg of the S-receptor blocking agent until LV dP/dt was reduced by 50% from control values. Infusions of 0.02 to 0.08 mg/kg/min of propranolol were then given to maintain this level of dP/dt. For details, see text. Abbreviations as in Table I. An "S" before a parameter indicates the per beat value of the parameter. amg/kg, intraduodenal. *p < 0.05 from control values. ~p < 0.05 from the corresponding dose of milrinone.

that of the vehicle-treated PIHF animals as well as above predrug control values. Milrinone produced qualitatively and quantitatively similar effects on LV d P / d T to those produced by flosequinan. MAP, CO, TPR, HR, CBF, and CVR. Flosequinan (1 and 3 mg/kg, intraduodenally) produced a biphasic effect on arterial pressures. The low dose of compound increased systolic and diastolic pressures (data not s h o w n ) a n d MAP. Blood pressures increased within 5 minutes after the administration of flosequinan, reached their highest values by 20 minutes after each dose of drug, and remained elevated. Within 5 minutes after the 3 mg/kg dose of flosequinan, blood pressures returned toward control values. However, after the 3 mg/kg dose of flosequinan, blood pressures were equal to or remained elevated compared with vehicle-treated animals with PIHF (Table III). Thus the blood pressure-lowering efficacy of flosequinan was diminished in animals with P I H F when compared with normal animals (Fig. 1 and Table III). Flosequinan increased CO in a dosedependent manner (Table III). Although MAP increased with flosequinan, the larger increases in CO resulted in dose-dependent decreases in TPR (Table III). Flosequinan did not affect HR in the animals with PIHF (Table III), but increased CBF and decreased CVR in a dose-related manner (Table III). Milrinone produced effects similar to those of flosequinan, However, milrin0ne decreased, rather than increased MAP (Table III). Myocardial energetics. Flosequinan increased LV tension, LV work, and LV stroke work. In contrast,

milrinone (1 mg/kg) decreased LV tension and did not affect LV work (Table III). DISCUSSION

Flosequinan is a positive inotrope in the normal dog and in the dog with PIHF, rather than a selective vasodilator with balanced effects on the artery and vein. Myocardial d P / d T and the cardiac contractile index are increased following intraduodenal administration of flosequinan, similar to the effects observed with milrinone, but unlike the selective vasodilation observed following the administration of SNP. Flosequinan is less efficacious as a positive inotrope than is milrinone. Nevertheless, the positive inotropy associated with flosequinan occurs with an increase in myocardial oxygen consumption and a decrease in myocardial contractile efficiency in the normal anesthetized dog, and with an increase in LV work in the animal with PIHF. Moreover, our data show that the positive inotropy produced by flosequinan cannot be mediated by stimulation of fladrenoceptors in the myocardium, since it persisted in animals with PIHF, The mechanism of the positive inotropy remains to be determined. Nevertheless, the data show that flosequinan, unlike the pure vasodilator SNP, stimulates the normal and failing myocardium at the cost of an increased LV MVO2. Finally, the data show that milrinone, in doses that increase LV d P / d T to levels equal to and greater than those with flosequinan, increases MVO2 disproportionately above the 1:1 ratio expected for the increase in LV dP/dT, especially with the reduction in

June 1990

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Greenberg, Touhey, and Paul

afterload.21, 22 This is in agreement with previous findings in a canine model of ischemia-induced heart failure 25 and with those observed in man with congestive heart failure (CHF). 26, 27 There are two potential limitations to this study. First, as stated by Braunwald et al., 21, 22 regional measurements of circumflex CBF and oxygen content in the great cardiac vein may not be entirely representative of energetics in the entire left ventricle. Second, our calculation of LV work and contractile efficiency is based on whole heart myocardial oxygen consumption, but regional CBF. Therefore extrapolation of results obtained with this model to man with chronic C H F must be limited in scope. However, it should be noted that the data obtained previously in this model with milrinone and other drugs 25 were consistent with the hemodynamic and energetic profiles of these agents in patients with chronic CHF. 26-29 In doses that produced positive inotropy, flosequinan increased CBF and SCBF (per beat value of CBF) while decreasing CVR. This would suggest that flosequinan was a coronary vasodilator, similar to milrinone. 3~ However, flosequinan did not decrease myocardial oxygen extraction, as did SNP, nor did it affect the coronary arterial oxygen supply/demand ratio (Fig. 9). Thus it is unlikely that flosequinan is a direct-acting coronary vasodilator. The increased CBF probably resulted from the autoregulatory response of the coronary vascular smooth muscle to the increased MVO2 of the myocardium as a result of the positive inotropic and positive chronotropic effects of flosequinan. Determinants o f MV02. The major determinants of LV MVO2 are heart rate, LV dP/dT, systolic wall stress, myocardial chamber diameter, wall thickness, and systolic pressure. LV MVO2 can also be influenced by factors directly affecting cell metabolism and the enzymatic machinery involved in energy production and utilization. 21, 22, 27.34 The factors affecting myocardial oxygen supply and demand are similar in normal experimental animals and in animals with myocardial dysfunction. The effects of cardiotonic agents on LV MVO2 in normal animals can be offset by effects of these agents on myocardial wall tension, thickness, and intraventricular chamber size in the animal with chronic cardiac dysfunction. However, the normal animal (1) allows a direct comparison of cardiotonic agents on the factors affecting myocardial oxygen supply and demand, (2) provides information on the hemodynamic profiles of the compounds, and (3) allows the investigator to predict the potential beneficial and adverse effects of cardiotonic agents on myocardial function and energetics in patients with CHF.

American Heart Journal

Flosequinan differs qualitatively and quantitatively from milrinone in the factors affecting LV MVO2. Both compounds increased H R and LV d P / dT and decreased MAP and LVEDP, with milrinone producing a greater positive inotropy and vasodilation than flosequinan. In the animal with PIHF, flosequinan increased MAP, whereas milrinone decreased MAP. 35 Moreover, flosequinan increased myocardial work, whereas milrinone did not increase it in the dog with PIHF. is, 19, 35 Increases in LV d P / dT and H R will increase LV MVO2, which should be partially offset by the decrease in MAP and LVEDP.21, 22, 25 As previously shown with atrial pacing, LV MVO2 increases approximately 1:1 on a percent basis with increases in H R and/or LV d P / dT.21, 22, 25, 29 However, MVO2 increased significantly more for equivalent increases in LV d P / d T with milrinone (despite greater reductions in MAP) than with flosequinan. Moreover, the slope of the Braunwald plot (Fig. 6), even when corrected for reductions in afterload (unpublished data), clearly show that milrinone increases MVO2 more than the increase required by the increase in H R and LV dP/dT. This finding suggests that flosequinan, by a mechanism yet to be defined, stimulates up to a 60% increase in LV d P / d T without an adverse effect on myocardial oxygen demand. The mechanism of its positive inotropy remains to be defined. The disproportionate increases in MVO2 and LV d P / d T produced by milrinone cannot be due to an increased work load imposed on the myocardium, since LV work and stroke work decreased. A previous study 25 showed that at lower levels of positive inotropy milrinone, an inhibitor of type III cAMP (cyclic adenosine monophosphate) phosphodiesterase, increased LV MVO2 by over 300 % above basal values. Grose et al. 36 showed that in patients with CHF milrinone significantly decreased MAP and right atrial pressure in doses that did not increase LV dP/dT. Milrinone significantly decreased myocardial oxygen extraction but did not change myocardial lactate extraction. Thus under conditions where preload and afterload were decreased, milrinone did not produce the expected decrease in myocardial oxygen Consumption. Similarly, inappropriate decreases or overt increases in myocardial oxygen consumption have been reported for milrinone and may account, in part, for the failure to improve survival in some classes of patients with heart failure. 26,27,37-39 These data strongly support the contention that milrinone may stimulate an inappropriately high consumption of oxygen. This would not be unexpected with a substance that increases cAMP by inhibiting its cellular metabolism.26, 2s, 39 Flosequinan undergoes hepatic metabolism that

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Flosequinan and MV02

Number 6

results in metabolites that retain the vasodilator action of the parent compound. 13,14 If a metabolite was solely responsible for either the positive inotropic effects or the blood pressure-lowering action of flosequinan, it would be evident in the hemodynamic changes observed over the time course of the experiment. We gave flosequinan intraduodenally, in solution, and monitored its hemodynamic effects for 30 minutes after each dose. This route of administration of the drug more closely reflected the clinical mode of flosequinan administration and allowed for genera: tion of metabolites as a result of first-pass hepatic metabolism.13,14 Moreover, the times of observation following the first and second doses of flosequinan were 90 and 60 minutes, respectively. In addition, flosequinan increased d P / d T in doses lower than those decreasing blood pressure. After flosequinan was given, blood pressure reached a nadir within 15 to 20 minutes and then returned toward control values, rather than decreasing more with time, which would be expected if a metabolite were solely responsible for vasodilation. Finally, flosequinan was a positive inotropic agent in vitro. Thus it is unlikely that metabolism can account for the positive inotropic or poor vasodilator responses to flosequinan. However, this study did not address the problem of chronic dosing of dogs with flosequinan. Therefore it is possible that the vasodilator effect of flosequinan may be enhanced during steady-state distribution of the compound, when a higher concentration of its active metabolite is present. Our finding that flosequinan is a mixed positive inotrope and vasodilator rather than a selective, balanced vasodilator appears to be at variance with previously published results by others, s-12' 15-17However, in those studies only blood pressure and H R were measured; CO and LV function were not reported. Moreover, significant blood pressure reduction in the dog was only observed after an oral dose of flosequinan of 10 mg/kg. 15 In both the dog and cat, the decreased blood pressure observed with doses below 10 mg/kg were of the same magnitude as we report herein. Inspection of Fig. 1 shows that flosequinan, at least ~ normal animals and, depending on the dose of flosequinan used, in animals with PIHF, could clearly be mistaken for a vasodilator unless CO and d P / d t were actually measured. Thus the results of our study and those of others are similar, insofar as they can be compared. Finally, Falotico et al. 19 recently published data in the dog clearly showing the positive inotropic effects of flosequinan in normal dogs and in dogs with PIHF. Clinical i m p l i c a t i o n s a n d c o n c l u s i o n s . Flosequinan is not a novel, selective balanced vasodilator in the dog, but rather a bivalent mixed positive inotrope and

1365

vasodilator. It is less potent as a vasodilator than is milrinone for equal levels of positive inotropy, in: addition to having lcss positive inotropy than milrinone. The positive inotropy of flosequinan is associated with an increase in LV MVO2. A controversy currently exists on the rationale and efficacy between the use of positive inotropic drugs and balanced vasodi!ators in the treatment of CHF. 1~, 17 Flosequinan, which is claimed to be a selective, balanced arterial and venous vasodilator, 1-6 is the first compound of this class to undergo clinical evaluation for efficacy in CHF. As such, the importance of flosequinan becomes magnified, because it would be the first agent to rigorously test the concept that a single, directacting balanced vasodilator has utility in the treatment of the disease. If flosequinan is not a selective balanced vasodilator, then the inferences made with this compound relative to balanced vasodilation become clouded. Flosequinan improved the hemodynamic profile in a select group of patients with low renin CHF. 9, 10 However, the myocardial oxygen cost of this improvement is unknown, since flosequinan was considered to be a pure vasodilator. In patients with CHF associated with myocardial ischemia or decreased coronary flow reserve, increased myocardial oxygen demand, which can occur with a positive inotropic agent, may exceed the vasodilator capacity of the coronary vascular reserve. This can exacerbate existing myocardial dysfunction and myocardial ischemia and initiate life-threatening ventricular arrhythmias. 4-7 Further clinical studies must be conducted to ascertain the complete hemodynamic profile of flosequinan in man. The authors thank Dr. B. Venapali, who synthesized flosequinan at Berlex Laboratories, Inc. REFERENCES

1. Kirk ES, Le Jemtel TH, Nelson GR, Sonnenblick EH. Mechanisms of the beneficial effects of vasodilators and inotropic stimulation in the experimental failing ischemic heart. Am J Med 1978;65:189-98. 2. Mikulic E, Cohn JN, Franciosa JA. Comparative hemodynamic effects of inotropic and vasodilator drugs in severe heart failure. Circulation 1977;56:528-41. 3. Nelson GIC, Verma SP, Hussain M, Silke B, Forsyth D, Abdulali S, Taylor SH. A randomized study of the hemodynamic changes induced by venodilation and arteriolar dilation singly and together in left ventricular failure complicating acute myocardial infarction. J Cardiovasc Pharmacol 1984;6:331-8. 4. Simonton CA, Chatterjee K, Cody RJ, Kubo SH, Leonard D, Daly P, Rutman H. Milrinone in congestive heart failure: acute and chronic hemodynamic and clinical evaluation. J Am Coil Cardiol 1985;6:453-9. 5. LeJemtel TH, Keren G, Reis D, Sonnenblick EH. The role of novel inotropic agents in the treatment of heart failure. J Cardiovasc Pharmacol 1986;8(suppl 9):$47-$54. 6. Alousi AA, Farah AE, Leaher GY, Opalka CJ. Cardiotonic activity of milrinone, a new potent cardiac bipyridine, on isolated tissues from several species. J Cardiovasc Pharmacol 1983;5:804-11.

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7. Steffen RP, Eldon CM, Evans DB. The effect of the cardiotonic imazodan on myocardial and peripheral hemodynamics in the anesthetized dog. J Cardiovasc Pharmaco11986;8:5206. 8. Cowley AJ, Wynne RD, Hampton JR. The effects of BTS49465 on blood pressure and peripheral arteriolar and venous tone in normal volunteers. J Hypertens 1984;2~547-9. 9. Kessler PD, Packer M. Hemodynamic effects of BTS 49465, a new long-acting systemic vasodilator drug, in patients with severe congestive heart failure. AM HEART J 1987;113:137-43. 10. Kessler PD, Packer M, Medina N, Yushak M, Gottleib S. Activation of the renin-angiotensin system limits the long-term hemodynamic and clinical responses to the direct acting vasodilator flosequinan in heart failure [Abstract]. J Am Coll Cardiol 1987;9:120A. 11. Cowley AJ, Wynne RD, Stainer K, Fullwood L, Cowley JM, Hampton JR. Flosequinan in heart failure: acute hemodynamic and longer term symptomatic effects. Br Med J 1988;297:169-73. 12. Cowley AJ, Wynne RD, Hampton JR. Flosequinan as a third agent for the treatment of hypertension: a placebo controlled, double-blind study. Eur J Clin Pharmacol 1987;33:203-4. 13. Wynne RD, Crampton EL, Hind ID. The pharmacokinetics and hemodynamics of BTS 49465 and its major metabolite in healthy volunteers. Eur J Clin Pharmacol 1985;28:659-64. 14. Sim MF, Yates DB. Method of treating heart disease. United States Patent 4,552,884. Nov. 12 1984;514/:312. 15. Sim MF, Yates DB, Parkinson DB, Cooling MJ. Cardiovascular effects of the novel arteriovenous dilator agent, flosequinan, in conscious dogs and cats. Br J Pharmacol 1988;94:371-80. 16. Smith JG, Kinasewitz GT. Effects of BTS 49465 on hypoxic pulmonary vasoconstriction. J Cardiovasc Pharmacol 1986;8:878-84. 17. Sim MF, Yates DB, Parkinson DB, Cooling MJ. BTS 49465: a novel hypotensive agent [Abstract]. International Society of Hypertension 1984;10th Scientific Meeting: A804. 18. Greenberg S, Touhey B, Wiggins, J. Positive inotrophy contributes to the hemodynamic mechanism of action of flosequinan (BTS 49465) in the intact dog. J Cardiovasc Pharmacol 1990;(In press) 19. Falotico R, Haertline B J, Lakas-Weiss CS, Salata JJ, Tobia AJ. Positive inotropic and hemodynamic properties of flosequinan, a new vasodilator, and a sulfone metabolite. J Cardiovasc Pharmacol 1989~14:412-9. 20. Greenberg S, Cantor E, Paul J. Beta-adrenoceptor blockade by diprafenone in pentobarbital anesthetized dogs. J Cardiovasc Pharmacol 1989;14:102-13. 21. Braunwald E, Ross J Jr, Sonnenblick EH. Mechanism of contraction of the normal and failing heart. Boston: Little, Brown & Company, 1979. 22. Braunwald E, Ross J Jr. Control of cardiac performance. In: Berne RM, Sperelakis N, Geiger SR, eds. Handbook of physiology. The cardiovascular system. Baltimore: The Williams & Wilkins Co, 1979:533-80.

June 1990 American Heart Journal

23. Keppel G. Design and analysis: A researchers handbook. 2nd ed. Englewood Cliffs, NJ:Prentice Hall, 1982. 24. Mohrman DE, Feigl, EO. Comparison between sympathetic vasoconstriction and metabolic vasodilation in the canine coronary circulation. Circ Res 1978;42:79-88. 25. Greenberg S, Paul J, Taggart W, Weiss S, Wiggins J. Evidence for myocardial oxygen wasting by milrinone in normal pentobarbital anesthetized dogs. Fed Proc 1986;45:658. 26. Colucci WS, Wright RF, Jaski BE, Fifer MA, Braunwald E. Milrinone and dobutamine in severe heart failure: differing hemodynamic effects and individual patient responsiveness. Circulation 1986;73(suppl):III-175-III- 183. 27. Monrad ES, Baim DS, Smith HS, Lanoue A, Braunwald E, Grossman WR. Effects of milrinone on myocardial energetics in patients with congestive heart failure. Circulation 1985;71:972-9. 28. Tada M, Katz AM. Phosphorylation of the sarcoplasmic reticulum and sarcolemma. Annu Rev Physiol 1982;44:401-43. 29. Braunwald E. Control of myocardial oxygen consumption. Am J Cardiol 1971;27:416-23. 30. Colucci WS, Jaski BE, Fifer MA, Wright RF, Braunwald E. Milrinone: a positive inotropic vasodilator. Trans Assoc Am Physicians 1984;97:124-33. 31. Jaski BE, Fifer MA, Wright RF, Braunwald E, Colucci WS. Positive inotropic and vasodilator actions of milrinone in patients with severe congestive heart failure. Dose-response relationships and comparison to nitroprusside. J Clin Invest 1985;75:643-9. 32. Ludmer PL, Wright RF, Arnold JM, Ganz P, Braunwald E, Colucci WS. Separation of the direct myocardial and vasodilator actions of milrinone administered by an intracoronary infusion technique. Circulation 1986;73:130-7. 33. Colucci WS, Ludmer PL, Wright RF, Arnold JM, Ganz P, Braunwald E. Myocardial and vascular effects of intracoronary versus intravenous milrinone. Trans Assoc Am PhysiCians 1985;98:136-45. 34. Tada M, Katz AM. Phosphorylation of the sarcoplasmic reticulum and sarcolemma. Annu Rev Physiol 1982;44:401-43. 35. Greenberg S. Effect of milrinone on cardiodynamics and myocardial energetics in dogs with propranolol-induced heart failure: effect of positive inotropy with ouabain. Can J Physiol Pharmacol (In press). 36. Grose R, Strain J, Greenberg M, LeJemtel TH. Systemic and coronary effects of intravenous milrinone and d0butamine in congestive heart failure. J Am Coll Cardiol 1986;7:1107-13. 37. Baim DS, Colucci WS, Monrad ES, Smith HS, Wright RF, Lanoue A, Gauthier DF, et al. Survival of patients with severe congestive heart failure treated with oral malrinone. J Am Coll Cardiol 1986;7:661-70. 38. Colucci WS. Positive inotropic/vasodilator agents. Cardiol Clin 1989;7:131-44. 39. White HD, Ribeiro JP, Hartley LH, Colucci WS. Immediate effects of milrinone on metabolic and sympathetic responses to exercise in severe congestive heart failure. Am J Cardiol 1985;56:93-8.