The comparative hemodynamic effects of isoproterenol in chronically instrumented puppies and adult dogs.

Although isoproterenol is the sympathomimetic amine used most often to augment cardiovascular function in infants and children, little is known about the hemodynamic effects of this drug on the immature cardiovascular system. To compare the hemodynamic effect of isoproterenol in the young animal with that in the mature animal, we infused the drug into 11 puppies of 12-38 days of age, 12 puppies of 56-89 days of age and 10 adult beagle dogs. The animals were chronically instrumented and nonsedated during the study. Isoproterenol was infused in doses of 0.05, 0.125, 0.25 and 0.5 microgram/kg/min. Isoproterenol decreased systemic arterial mean blood pressure, increased heart rate and had no effect on renal blood flow in all three groups of animals. While cardiac output was increased and systemic vascular resistance decreased in the adult dogs, neither changed in puppies. Stroke volume increased slightly in adult dogs, but decreased in puppies. This refractoriness to change of cardiac output in immature dogs may be a function of elevated resting cardiac output, developmental changes of contractility or ventricular compliance or developmental changes of vascular smooth muscle responsiveness.