Abstract

Spleen volume and femoral perfusion pressure of anesthetized dogs have been recorded to illustrate any reflex changes after equal beta receptor antagonistic doses of alprenolol, bunolol and propranolol. These agents caused indistinguishable reductions in spleen volume which were induced reflexly and probably initiated by reductions in blood pressure. Unlike the other agents, alprenolol continued to cause hypotension and induce splenic changes with repeated doses or after prior doses of the other agents. After ganglion blockade or acute splenic denervation, alprenolol frequently caused splenic relaxation. These actions may be due to the beta sympathomimetic effect of alpnenolol. After guanethidine, femoral perfusion pressure of barbiturate-anesthetized dogs was increased by bunolol and propranolol, but not by alprenolol. Essentially, the same relationships were seen in chloralose-anesthetized dogs without prior guanethidine treatment. In open-chest dogs, alprenolol caused the least reduction in cardiac output and was the only agent to lower significantly diastolic blood pressure in barbiturate- and chlonalose-anesthetized dogs. These properties of alprenolol may act to lessen the reduction in pulse pressure which is a manifestation of cardiac beta receptor antagonism, and thereby attenuate a stimulus which can initiate cardiovascular reflexes.