Systemic and coronary hemodynamic effects of glucagon

ExDerimental

Studies

Systemic and Coronary Hemodynamic

GEORGE G. ROWE, MD Madison,

Wisconsin

Effects of Glucagon

The systemic and coronary hemodynamic effects of glucagon have been studied in anesthetized mongrel dogs. Administration of this agent produced an increase in cardiac rate, a decrease in systemic arterial pressure and increases in body and cardiac oxygen consumption. Arterial hemoglobin, hematocrit and oxygen content increased as did mixed venous oxygen content, but the coronary sinus oxygen content decreased. Cardiac output and coronary blood flow increased, but peripheral and coronary vascular resistances decreased. The systemic and coronary hemodynamic effects of glucagon were similar during beta adrenergic blockade induced by propranolol. There has been considerable interest in the systemic hemodynamic effects of glucagon. Several studies have indicated that glucagon is inotropic and that it increases the cardiac output in experimental animals and in man.l-7 However, there has been no reported study on the effects of glucagon on the coronary circulation even though the drug has been infused into the coronary arteries.2 Myocaxdial glucose, lactate and free fatty acid metabolism has been studied,2 and it has been postulated that glucagon must increase cardiac oxygen consumption.*

Material and Methods

From the Cardiovascular Research Laboratory, Department of Medicine, University of Wisconsin Medical School, Madison, Wis. This work was supported in part by U. S. Public Health Service Grants HE 07754 and HE 14,928 from the National Heart Institute and by a grant from the Wisconsin Heart Association. Manuscript received June 25, 1969, accepted August 19, 1969. Address for reprints: George G. Rowe, MD, Cardiovascular Research Laboratory, Room 523, University Hospitals, 1300 University Ave., Madison, Wis. 53706.

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Fourteen anesthetized mongrel dogs were studied. In the first 4 animals, trial doses were used. Even though glucagon tends to be destroyed slowly,* our preliminary studies showed that 10 and 20 minutes after intravenous administration of glucagon (50 ,pg/kg) , repeat cardiac output and coronary flow determinations revealed that the hemodynamic effects were minimal. These preliminary studies also showed that a dose of 0.25 ‘pg/kg per min of glucagon infused continuously was inadequate to give a substantial and sustained hemodynamic response. Therefore, a single dose was given to 10 dogs and followed by an infusion as later described. The average weight of these dogs was 23 + 2.8 kg. They were anesthetized by subcutaneous administration of 3 mg/kg of morphine sulfate followed 1 hour later by intravenous administration of 0.25 ml/kg of a mixture of equal parts of veterinary pentobarbital and Dial-Urethane. [Dial-Urethane contains Dial@ (diallylbarbituric acid), 100 mg/ml; monoethylurea, 400 mg,/ml; and urethane, 400 mg/ml. Veterinary pentobarbital contains 60 mg/ml of pentobarbital.] In the following hour cardiac catheters were manipulated fluoroscopitally into the pulmonary artery, coronary sinus and right atrium, and a needle was placed percutaneously in the femoral artery. A cuffed endotracheal tube was attached to a nonrebreathing valve so that expired air could be collected in a Tissot spirometer.

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A two-way valve was arranged in the air inflow tract to the endotracheal tube so t.hat the dog could breathe room air during determination of cardiac output or a mixture of 15 percent nitrous, oxide, 21 percent oxygen and 64 percent nitrogen during determination of the coronary flow. Cardiac output was measured by the Fick principle with air collection extended over a 5 minute period. The expired air was analyzed by the Scholander apparatus for oxygen and carbon dioxide.8 The oxygen content of femoral and pulmonary arterial blood was determined by the Van Slyke-Neil1 apparatus. Duplicate samples were required to check within 0.2 ml/100 ml of blood. The pH value of the systemic arterial and coronary sinus blood was determined with a Radiometer micro-electrode type E5021A. Hemoglobin was determined with the Coleman, Jr. spectrophotometer. Coronary blood flow was measured by the nitrous oxide saturation technique assuming a partition coefficient of 1 between blood and myocardium. The nitrous oxide content of blood was determined by the method of Orcutt and Waters? The usual hemodynamic values were calculated by standard formulas as previously described.‘O Control observations were made after all manipulations were completed and 1 hour #after the final anesthetic doses were given. Midway through the determination of coronary blood flow, specimens for oxygen and carbon dioxide were drawn from the systemic artery and from the coronary sinus in order to calculate myocardial oxygen consumption and carbon dioxide liberation; blood was drawn from the femoral artery and the coronary sinus for determinations of glucose, lactate and pyruvate levels. The methods used for glucose, lactate and pyruvatc determination were, respectively, those of Wasko and Segal et a1.l” An effort and Rice,‘l Hohorstl’ was made to replace the blood loss as it occurred by saline solution. This procedure is seldom exact because it is difficult, to quantitate the slow drip of fluid t#hrough the catheters, and there is always some small blood loss from the cutdown site in the neck. Previous experiments in this laboratory have shown that with dogs prepared and studied in this way, unless an active agent is given, duplicate sets of hemodynamic observations performed 20 minutes apart reveal no significant changes in cardiac output and coronary blood flow. Fifteen minutes after the control determination of cardiac out.put and coronary blood flow, the animals were given a 50 pg/kg dose of glucagon, intravenously; this was followed by a steady infusion of 50 (rg/kg of glucagon into a peripheral vein in the foreleg. This quantity was diluted and was administered over a period of 22 minutes, which included the time when the second determination of cardiac output and coronary blood flow was made. The second determination of cardiac output and coronary blood flow was begun 5 minutes after t.he beginning of the infusion of glucagon and was completed during the

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25, JUNE

1970

W/ml 12

EFFECTS OF GLUCAGON

GLUCOSE

I I

Id--

IO 9

‘.5-

M

FEMORAL ARTERY

W-m

CORONARY SINUS

LACTATE

1.41.31.2I.1 l.O-

O.“l

__-/

PYRUVATE

0.12

.--____/b*

0.10 1

CONTROL

CO B

CBFdl

GLUCAON s MIN.

61 T

Figure 1. The arterial and glucose, lactate and pyruvate administration. S,, Sa and s3 CBF = coronary blood flow;

SP co rlre

1 1

53 CBF ry2

T

coronary sinus blood levels of and their response to glucagon indicate time of determinations. CO = cardiac output.

next 17 minutes. Glucose, lactate and pyruvate levels were determined in blood from the femoral artery and the coronary sinus after glucagon infusion immediately before the second cardiac output determination, after the end of this dctermination-that is, just before determination of coronary blood flow and just before the end of the determination of coronary blood flow. Figure 1 shows that the myocardium continued to take up increasing amounts of glucose, lactate and pyruvate after administration of glucagon and that the myocardial arteriovenous differences tended to increase as the arterial levels of these substances rose. A reasonably steady state seemed to be reached throughout the second determination of cardiac output and coronary blood flow as indicated by recorded pressures in the systemic and pulmonary artery and the right atrium, as well as by observation of cardiac rate. Therefore, for purposes of calculation of myocardial

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ROWE

TABLE

I

Hemodynamic

Effects of Glucagon Control (Mean * SD)

Heart rate (beats/min) Blood pressures (mm Hg) Mean arterial Mean pulmonary arterial Mean right atrial Body oxygen consumption (ml/min) Body respiratory quotient Arterial hemoglobin (g/100 ml) Arterial hematocrit (%) Arterial content (ml/100 ml of blood)

Study (Mean * SD)

Change

SEM Difference

(%)

P

Value

93 * 24

155 * 50

+66.7

13.517


127 * 17 18 * 2 5.2 * 1.5 120 * 21 0.90 * 0.08 14.5 * 1.4 42 * 4 17.2 * 1.9

118 f 15 18 * 3 4.9 * 1.5 139 * 30 0.90 * 0.09 15.9 * 2.1 46 * 6 18.8 * 3.3

-7.1 0 -5.8 +15.8 0 +9.7 +9.5 +9.3

2.635 0 0.253 5.963 0 0.327 1.174 0.557


4.0 * 0.8

3.6 * 0.8

-10.0

0.388

NS

5.6 * 2.0 3.06 * 0.68 34 * 9 5.2 * 1.2 0.8 * 0.2 3,511 * 1,116

4.2 * 1.8 4.00 * 1.10 31 * 17 6.5 * 2.2 1.0 * 0.3 2,496 f 677

-25.0 +30.7 -8.8 +25.0 +25.0 -28.9

0.447 0.389 4.965 0.571 0.100 397.260

Total pulmonary resistance (CGS units) Coronary blood flow (ml/100 g per min) LV OZ usage (ml/100 g per min) Coronary vascular resistance (units) Cardiac respiratory quotient

502 * 106 * 11.9 * 1.29 * 0.93 *

149 29 3.8 0.39 0.08

392 * 150 141 =+=48 20.0 * 3.8 0.97 * 0.31 0.80 f 0.10

-21.9 +33.0 +68.1 -24.8 -14.0

1.926 14.069 1.682 0.141 0.049

Index of efficiency (LV work/LV O2 usage)

0.47 * 0.14

0.31 * 0.11

-29.8

0.069

NS

SD = standard

deviation;

Arteriovenous O2 difference (ml/100 ml of blood) Coronary sinus content (ml/100 ml blood) Cardiac output (liters/min) Stroke volume (ml/min) LV work (kg-m/min) RV work (kg_m/min) Total peripheral resistance (CGS units)

LV = CGS = centimeter-gram-second; SEM = standard error of the mean.

left ventricular;

utilization

pyruvate,

of

glucose,

lactate

and

it

NS = not significant;

was

that the hemodynamic state was steady throughout the second determinations and that the glucose, lactate and pyruvate levels were the average of the 11 and 16 minute values throughout the second coronary blood flow. In 2 animals, the effects of glucagon were determined during beta adrenergic blockade with propranolol. In these animals the study was performed in the same manner as in the preceding group with these exceptions: 1 ml/kg of propranolol was given 10 minutes before the control determination of cardiac output and coronary flow and followed by an infusion of 3 mg/kg of propranolol which ran continuously over the 50 minut,e period required for both determinations of cardiac output and coronary blood flow. This dose was. calculated to give a steady state of beta adrenergic blockade throughout the administration of glucagon. assumed

Results The hemodynamic results are summarized in Table I. With administration of glucagon a very significant increase in cardiac rate occurred promptly, accompanied by a decrease in systemic arterial pressure and a rise in minute volume of respiration. Both oxy-

672

RV = right ventricular;

<0.02 <0.05 NS NS NS <0.05 NS <0.05
gen consumption and the elimination of carbon dioxide were increased so that the body respiratory quotient remained constant. The arterial oxygen content rose as did the hemoglobin and hematocrit. Mixed venous oxygen content also increased with a minor and insignificant decrease in the arteriovenous oxygen difference. The increased ventilation that occurred after administration of glucagon was accompanied by a significant decrease in systemic arterial and mixed venous carbon dioxide content. During the action of glucagon the coronary sinus oxygen content decreased significantly with a significant increase in the arteriovenous oxygen difference across the myocardium. Cardiac output was significantly increased, but peripheral vascular resistance was reduced. Although left ventricular work tended to increase, the change was not. statistically significant because of the variability created by an increase in cardiac output and a decrease in systemic arterial pressure. Stroke volume was not significantly changed. Coronary blood flow was significantly increased, as was the left ventricular oxygen usage and carbon dioxide elimination. Coronary vascular resistance was significantly decreased. The index of efficiency, which

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relates left ventricular work to left ventricular oxygen usage, tended to decrease, but the change was not statistically significant. In the dogs with beta adrenergic blockade induced by propranolol a significant increase in cardiac rate and transient decrease in blood pressure occurred immediately after administration of the initial dose of glucagon. In these dogs, cardiac out.put and coronary flow levels rose while left ventricular work and oxygen consumption increased. The hemodynamic effects appeared to be similar t.o those in animals that had not received propranolol. The results of analyses for glucose, lactate and pyruvate of blood drawn from the femoral artery and coronary sinus in the control state and 4, 5, 11 and 16 minutes after the initial dose of glucagon are summarized in Table II and Figure 1. To calculate the myocardial consumption of these materials, the specimens drawn during the determination of coronary flow were averaged and multiplied by the coronary blood flow. These calculations show that the heart did not contribute to any of the rise in the arterial level of glucose, lactate or pyruvate since the myocardium extracted increasing amounts of each of these substances as the blood concentration rose. Pretreatment with propranolol did not change this pattern.

Discussion The general systemic hemodynamic effects of glucagon were similar in this study to those produced by catecholamines and to those that have been reported previously in animals and in manl-7 It is accepted that glucagon has significant positive inotropic and chronotropic actions on t.he heart of animals and man.‘-’ The reports have indicated that the systemic vascular resistance of man responds inconsistently with increases in some subjects and decreases in others.’ In the present study the decrease in vascular resistance was consistent and significant in the systemic and coronary beds but more variable in the lungs. Generally, in subjects in a reasonable physiologic state, cardiac output is controlled not by the inotropic state of the myocardium but by the peripheral vascular resistance and the venous return. The decrease in peripheral resistance is a reasonable hemodynamic explanation for increased cardiac output. Although the venous pressure did not change in these animals, no conclusion can be drawn about venous return because glucagon is known to change the inotropic state of the myocardium,1-7 and under these circumstances even augmented venous return need not cause increased levels of venous pressure. The elevation of the hemoglobin and hematocrit levels reported here is similar to that seen with administration of catecholamines.

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TABLE

EFFECTS OF GLUCAGON

II

Effects of Glucagon on Myocardial and Pyruvate

LV glucose used LV lactate used LV pyruvate used

Uptake of Glucose,

Lactate

Control

Study

(Irm/lOOg per min)

(pm/100 g per min)

42.40 55.24 7.36

115.62 111.76 8.93

LV = left ventricular.

The coronary hemodynamic effects of glucagon are similar to those of catecholamines.1-7 These effects on the coronary circulation have been surmised” but not demonstrated before. At least a portion of the increase in flow may be due to the increase in cardiac rate since coronary flow tends to follow changes in cardiac rate.14 The increase in left ventricular oxygen consumption during administration of glucagon is striking indeed. This increase in myocardial oxygen consumption and carbon dioxide elimination is also similar to that seen after administration of catecholamines.l”,le It has been concluded17 that glucagon increases the level of cyclic adenosine monophosphate by augmenting the activity of adenyl cyclase in the liver. However, studies of t,he effect, of glucagon on the enzyme systems of the heartlR have not shown this result. Consequently, it is not known whether the mechanism of its action on the heart is secondary to adenyl cyclase effects on 3’, Ti’ adenosine monophosphate (cyclic AMP). Adenosine, adenosine triphosphate and related compounds are active coronary vasodilators. In The significant decrease in coronary sinus oxygen content, supports the ideas that coronary flow increased because it was required to sustain the increased myocardial activity and the elevated cardiac work. Previous workers have described inability of propranolol to prevent the systemic hemodynamic effect of glucagon,Svl and the inability of catecholamine depletion with reserpine to prevent the systemic hemodynamic effects of glucagon.‘,’ Our study shows that glucagon remains active in the coronary circulation during propranolol-induced beta adrenergic blockade. Clinical implications: Although administration of glucagon produces an increase in coronary blood flow, the hemodynamic effects that are seen would not encourage its use in subjects with angina pectoris since the increase in coronary flow appears to be required to supply energy to the myocardium. This requirement is a result of the increased cardiac rate,14 the increased rate of pressure rise in the ventricleszO and the increased vigor of cardiac contraction. The general hemodynamic effects of glucagon are so similar to those of catecholamines that its usefulness in

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ROWE

their stead has been widely considered, and its potential advantages have been pointed out.4 Particularly during catecholamine depletion, or extensive beta adrenergic blockade, glucagon may be an effective inotropic agent that will produce a catecholamine-like effect when commonly used agents, such as isoproterenol, are not active.

Acknowledgments The glucagon used in this study was furnished through the courtesy of Dr. Francis G. Henderson of Eli Lilly and Co., Indianapolis, Ind. Propranolol was generously supplied by Ayerst Laboratories, New York, N. Y., through the courtesy of Dr. John A. Devaney.

References 1. Farah 2.

3. 4.

5. 6.

7.

8.

9.

10.

11.

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