Cardiovascular Effects of Propranolol in Intact Puppies and Adult Dogs

Abstract

ExtractThe cardiovascular effects of propranolol (Inderal) [24] were compared in 13 adult dogs and 14 puppies. Left ventricular (LV) pressure was measured with a catheter tip manometer and myocardial contractility was assessed by LV measurements of peak rate of pressure development (LV dp/dt), LV dp/dt at 40 mm Hg LV pressure (P 40 dp/dt), and peak LV (dp/dt)/P. Cardiac output was measured by indocyanine green dye dilution. Measurements were made before and 5 min after intravenous propranolol (0.5 g/kg) administered over a period of 1 min. In the adult dog, propranolol produced a significant depression of cardiac index and peak LV systolic pressure, significant elevation of systemic resistance index and LV end-diastolic pressure, and a significant fall in indices of myocardial contractility. The changes in heart rate, cardiac index, peak LV systolic pressure, and contractility indices produced by propranolol were 2-4 times greater, on a percentage basis, in the puppies as in the adult dogs. The systemic resistance index and LV end-diastolic pressure changed similarly in both groups. The increased sensitivity of the puppies to propranolol appears to reflect a greater dependence on circulating catecholamines in the immature circulation. Speculation

The Comparative Hemodynamic Effects of Propranolol in Chronically Instrumented Puppies and Adult Dogs

“…The findings of our present study differ from these of Truccone and Levine [1973], While heart rate was reduced slightly in all three groups of animals, it did not change sig nificantly from control in any group. Also, stroke volume was reduced similarly (4-6% from control) in all three age groups of ani mals.…”

“…The difference in results between the study of Truccone and Levine [1973] and ours probably results from the different experi mental preparations. While the animals of Truccone and Levine [1973] were anesthe tized and had been subjected to surgical trauma shortly before the experiment, our preparations were awake and chronically in strumented.…”

“…At all concentrations of pro pranolol, the fetal myocardium was more de pressed than the adult. Truccone and Levine [1973] examined the cardiovascular effect of propranolol in anesthetized, acutely instru mented puppies and adult dogs. In both pup pies and adult dogs, propranolol reduced (p < 0.05) cardiac index, peak left ventricular systolic pressure, systemic resistance and left ventricular end-diastolic pressure.…”

“…There are, however, a number of reports indicating that the cardiovascular ef fects of propranolol may be different in im mature animals than in adult animals [Fried man, 1973;Truccone and Levine, 1973], While the p-blocking action of propranolol is similar in isolated myocardium from fetal and adult sheep, Friedman [1973] noted that, at any concentration of propranolol, the fetal heart was more depressed than the adult heart. Also, propranolol exerted a positive inotropic effect at low doses in adult sheep myocardium while in fetal sheep myocar dium the only inotropic effect was negative.…”

“…Also, propranolol exerted a positive inotropic effect at low doses in adult sheep myocardium while in fetal sheep myocar dium the only inotropic effect was negative. Truccone and Levine [1973] studied anesthe tized acutely instrumented puppies and adult dogs and found that the immature circulation is more sensitive to the negative chronotropic and inotropic effects of propranolol than its adult counterpart. The purpose of this inves tigation was to delineate further the develop mental differences of the hemodynamic effects of propranolol using an awake, chron ically instrumented experimental prepara tion.…”