Cardiovascular effects of guanazole

TOXICOLOGYANDAPPLIEDPHARMACOLOGY16,108-119(1970)

Cardiovascular JAMES

Microbiological

Effects

of Guanazole

A. VICK AND EUGENE H. HERMAN~

Associates, Inc. 5221 River Road, Bethesda, Maryland 20016 Received March 12,1969

Cardiovascular Effects of Guanazole. VICK, JAMES A., and HERMAN, H. (1970).Toxicol. Appl. Pharmacol. 16, 108-l 19. A rapid iv injection of guanazole,a potent antitumor drug, producesa sharpdrop in arterial blood pressure,an increasein right ventricular pressure,a slight decrease in heart rate, and a risein central and portal venouspressures.Thesechanges are transient, lasting 5-10 min, and can be partially amelioratedby prior treatmentwith antihistaminic,antiserotonin,andadrenergicblocking drugs. In contrast, the slowinfusion of guanazoleover a 2%minperiod causesonly a rise in right ventricular pressureand a slight drop in arterial blood pressure.These effects can be mimicked by serotonin and blocked by lysergicacid diethylamide(LSD) or propranolol. Guanazoleproducesa markedincreasein left ventricular contractile force and a sharpdrop in pump-perfusionpressurein the isolatedperfusedheart preparation. Thesechangescan be blocked by LSD. Guanazole resultsin a decreasein pulmonary vascularresistancewhich is attributable not to serotonin or histamine,but to somedirect action on the pulmonary bed. EUGENE

Guanazole,z triazole 3,5-diamino-s, has beenshown to exert strong antitumor activity against L1210 tumors in mice (Annual Progress Report, Southern Research Institute, 1968).This action is presumably due to an inhibition of DNA synthesis(Special Report, Southern ResearchInstitute, 1968).In preclinical studieswithlarger animals, suchasdogs and monkeys, guanazole has been given intravenously at varying dosesup to 1.0 g/kg for aslong as28 days (Report, South Shore Analytical and ResearchLaboratory, 1968). These dose regimens were not lethal to dogs or to monkeys and produced no marked observable symptoms other than a transient flushing seenin dogs at the highest dose levels. Clinically, such a response could conceivably produce undesirable effects in susceptiblepatients, thereby limiting the dosageof the drug. The present investigations were initiated to study the mechanism and prevention of the hypotensive action of guanazole. MATERIALS AND METHODS Fifty adult mongrel dogs anesthetized with sodium pentobarbital, 30 mg/kg, were usedin this study. Five animals were usedfor each of the testsperformed. The following physiological parameterswere monitored : systolic-diastolic blood pressure,mean blood pressure, right ventricular pressure, heart rate, electrocardiogram, and respiration. 1 Supportedby Chemotherapy, NationalCancerInstitute,NIH, ContractPH-43-68-1283. 2ObtainedfromChemotherapy, NationalCancerInstitute,NationalInstitutesof Health,Bethesda, Maryland. 108

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Blood pressure and right ventricular pressure were monitored using heparinized catheters placed in the femoral artery and the right ventricle. The electrocardiogram (ECG) was a standard lead II trace; and heart rate was determined from an integration of the spike (QRS) segment. Respiratory rate was determined through the use of a Sanborn differential pressure transducer. All recordings were made on a Sanborn Model 1122B polygraph.

FIG. 1. Effects of rapid intravenous injection of guanazole (1 g/kg) on heart rate, electrocardiogram, portal venous pressure, mean arterial blood pressure, systolic-diastolic arterial blood pressure, and respiration.

All drugs were injected through a catheter placed in the femoral vein of the dog. Guanazole was administered in a dose of 1 g/kg diluted in approximately 50 ml of saline warmed to 35”. The final pH of the drug was 7.87-7.89. Guanazole was either injected within 1 min or infused over a period of 15-25 min using a Harvard constant-infusion pump. Intravenous injections of 50 ml of saline were made in certain preparations to serve as a control. Ten isolated perfused Langendorf heart preparations (Hinshaw et al., 1957) were used to study the effect of guanazole directly on the myocardium. Adult dogs were anesthe-

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tized, and a polyethylene catheter was placed in the femoral artery to allow for the rapid removal of blood. Clotting was prevented by injection of heparin Na, 1000 USP units/kg, into the right femoral vein. Artificial respiration was maintained using a piston-type positive-pressure pump and an endotracheal tube. The chest was opened by a midline incision, and all major branches of the ascending aorta except the brachiocephalic trunk were ligated. The reservoir of the pump-oxygenator system was filled with blood

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FIG. 2. Effect of histamine 0.1 mg on heart rate, electrocardiogram, blood pressure, and respiration.

central venous pressure, arterial

drawn from the femoral artery. The brachiocephalic trunk was then cannulated with a short stainless steel cannula connected by tubing to the pump-oxygenator system. The descending aorta was then ligated. The heart was quickly removed from the chest cavity and placed in a chamber. It was then perfused at constant flow with autologous blood maintained at 35-37”. The perfusion pressure was continuously monitored using a needle-tipped catheter placed into the arterial limb of the pump-oxygenator system. Needle-tipped electrodes were also used to monitor ECG and heart rate. Force of ventricular contraction was measured by a Walton-Brodie strain gauge arch sutured to

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the left ventricle of the heart. All injections were made into a rubber tubing placed in the intake line of the perfusion pump. Experiments were performed using the isolated ventilated perfused lung of the dog. After removal of the lungs from the chest of the dog, the pulmonary artery was quickly cannulated and the lungs were flushed with freshly drawn heparinized whole blood. The autologous blood was maintained at 35-37” by circulation through a heated water jacket. The blood was then pumped into the lungs at a perfusion pressure of approximately 20 mm Hg. A needle-tipped catheter was inserted into the perfusion circuit to

FIG. 3. Effect of pretreatment with diphenhydramine the dog to a rapid injection of gtranazole (1 g/kg).

(10 mg/kg) on the cardiovascular response of

continuously monitor pressure.In that flow was constant, changesin perfusion pressure were reflected directly as changes in lung resistance(R = M/F). The cut trachea was also cannulated, and the lungs were inflated intermittently with a Harvard positivepressurerespirator. All drugs were injected into a rubber tubing placed in the arterial limb of the perfusion circuit. Guanazole was administered both rapidly (1 g) and by infusion over a 10min period oftime (5 g/l0 min).

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RESULTS

The effects of a rapid intravenous injection of guanazole (1 g/kg) on heart rate, ECG, portal venous pressure, mean arterial blood pressure, systolic-diastolic arterial blood pressure and respiration are shown in Fig. 1. Immediately after injection there is a decreasein heart rate of 20-30 beats per min. This is followed by a prolonged increase

FIG.

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Effect of a rapid injection of guanazole (1 g/kg) on right ventricular pressure in the anesthetized

dog.

lasting for 15-30 min. An increasein the height of the QRS segmentof the ECG is noted during the bradycardia but returns to normal or near normal at 2-3 min after injection. Portal venous pressureincreasesapproximately 5 mm Hg during this sameperiod of time. The most remarkable effect of guanazole was on blood pressureand respiration. Arterial pressurefell precipitously immediately after injection. Thishypotensive episode lasted for 3-5 min after which time pressureslowly returned to control levels. A pressure increaseabove control then persisted for 15-20 min. Both rate and depth of respiration increased.An intravenous injection of histamine (0.1 mg) produced an effect somewhat

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ACTIVITY

similar to that produced by guanazole (Fig. 2). A sharp fall in blood pressure occurred with associated slowing of heart rate. Both portal venous pressure and respiratory rate increased after histamine. The amplitude of the respiratory volume exchange decreased, however, which was not observed with guanazole. In addition, the QRS segment of the ECG decreased, rather than increased, in amplitude.

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FIG. 5. Effect of serotonin (0.05 mg/kg) on arterial blood pressure, heart right ventricular pressure, respiration, and mean arterial blood pressure.

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Diphenhydramine (Benadryl, 10 mg/kg) partially prevented the decreasein arterial blood pressure and the increase in portal venous pressure produced by the rapid injection of guanazole (Fig. 3). It is important to note, however, that some fall in arterial pressure did occur. Little or no change in respiratory rate, central venous pressureor heart rate was observed in this preparation. The QRS segmentof the ECG trace exhibited a sustained elevation. The effect of a rapid injection of guanazole (1 g/kg) on right ventricular pressureaswell asheart rate, ECG, respiration and arterial blood pressureis presented in Fig. 4. Simultaneous with the precipititous fall in arterial

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pressure was a spectacular increase in right ventricular pressure. This change occurred within 30 seconds after injection and persisted for at least 5 min, and in many studies for up to 30 min. 5-Hydroxytryptamine (serotonin) produced an increase in right ventricular pressure almost identical to that observed after guanazole (Fig. 5). Serotonin in a dose of 0.05

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FIG. 6. Effect of pretreatment with LSD (0.05 mg/kg) on the cardiovascular response of the dog to a fast injection of guanazole (1 g/kg).

mg/kg did not, however, produce either the fall in arterial blood pressureor the increase in respiratory rate noted with guanazole. Rather, there occurred a temporary period of apnea and an increasein pulse pressure.Lysergic acid diethylamide (LSD) (0.05 mg/kg), propranolol (Inderal@) (1 mg/kg) or phenoxybenzamine (Dibenzyline@) (5 mg/kg) prevented the increase in right ventricular pressureproduced by the rapid injection of guanazole (Fig. 6). Neither diphenhydramine nor atropine was capable of modifying this increasein right ventricular pressure.

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The slow infusion of guanazole (1 g/kg) over a period of 25 min produced only an increase in right ventricular pressure and a slight decrease in arterial blood pressure (Fig. 7). Lysergic acid diethylamide, phenoxybenzamine, propranolol, cyproheptadine (5 mg/kg), and methysergide (1 mg/kg) were capable of preventing the change in right ventricular pressure produced by the slow infusion of guanazole (Fig. 8).

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FIG. 8. Effect of LSD (0.05 mg/kg) on the response of the anesthetized dog to a slow infusion of guanazole (1 g/kg).

The effect of guanazole on the isolated perfused heart preparation is shown in Fig. 9. Doses of less than 1 g produced a sharp increase in left ventricular contractile force and an abrupt fall in pump perfusion pressure indicating a decrease in resistance in the coronary circulation. The slow infusion of guanazole into the perfusion circuit of the isolated heart resulted in a marked decrease in pump perfusion pressure and a slight transient increase in force

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of contraction. Restoration of pump perfusion pressure to control levels did result. however, in a remarkable and sustained increase in left ventricular force. The effect of serotonin on the isolated heart was much like that observed with guanazole with the important exception that perfusion pressure fell only slightly as force of contraction increased (Fig. 10). Lysergic acid diethylamide and propranolol partially

FIG. 9. Effect of guanazole (1 g) on pump perfusion pressure, heart rate, force of contraction, and electrocardiogram in the isolated perfused heart preparation.

prevented the changes produced by guanazole; however, significant decreases in pump perfusion pressure were still observed in many preparations. The effect of a rapid injection of guanazole into the isolated perfused lung was to produce a sharp fall in pump perfusion pressure lasting for 3-5 min. A slow infusion of 5 g of guanazole produced much the same effect lasting over the entire period of administration. The decrease in perfusion pressure produced by either method of administration could not be blocked by LSD. In addition, serotonin produced an actual increase in perfusion pressure of the lung rather than a drop.

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FIG. 10. Effect of serotonin (0.2 pg) on pump perfusion, heart rate, force of contraction, and electrocardiogram in the isolated perfused heart preparation. DISCUSSION

The results of this study indicate that guanazole produces peripheral vasodilatation and pulmonary congestion due primarily to its releaseof histamine and serotonin into the circulation. The drop in arterial blood pressureand the slight increasein heart rate are most probably due to the action of serotonin on the pulmonary vasculature. Previous studies confirm the observation that serotonin causes pulmonary vasoconstriction and decreasedflow of blood to the left side of the heart (Hinshaw et al., 1957). It is important to note, however, that with guanazole this action is fleeting, lasting for 5-10 min. It is equally important to point out that in conditions of impaired pulmonary function this effect might precipitate a crisis. Lysergic acid diethylamide has been shown to prevent effectively the increasein right ventricular pressure. This is in keeping with the known blocking action of LSD on serotonin. It is important to note that LSD does not prevent the action of guanazole on the pulmonary vasculature, nor

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does it completely prevent the drop in arterial pressure produced by guanazole. Likewise, pretreatment with diphenhydramine is only partially effective in blocking the hypotensive effects of the drug. It is concluded that both histamine and serotonin are released following guanazole and together result in the observed changes in arterial blood pressure. The increase in portal venous pressure further substantiates the release of histamine. It is interesting to note, however, that even after pretreatment with LSD guanazole is still capable of producing a decrease in coronary vascular resistance and may be related to some direct actions of the drug on these areas of the body. The observation that propranolol partially prevents the drop in pressure and the increase in right ventricular pressure is unexplainable at the present time. It is suspected, however, that propranolol may act to block serotonin and/or histamine. ACKNOWLEDGMENTS The authors wish to express their appreciation to Robert Farmar and Andrew Leiter for technical assistance in this study. REFERENCES Annual Progress Report to Cancer Chemotherapy National Service Center by Southern Research Institute, Birmingham, Alabama, March 29, 1968. HINSHAW, L. B., KUIDA, H.,GILBERT, R. P., and VISSCHER, M. B. (1957). Influence of perfusate characteristics on pulmonary vascular response to endotoxin. Am. J. Physiol. 191,293. ResearchReport to CancerChemotherapyNational ServiceCenterby South ShoreAnalytical and ResearchLaboratory, Inc., Islip, New York, April 19, 1968. Special Report to Cancer Chemotherapy National Service Center by Southern Research Institute, Birmingham,Alabama, September4, 1968.