Central effect of beta adrenergic blocking agents on arterial blood pressure

dl-Sotalol, dl-pindolol, d-propranolol and dl-propranolol were evaluated for central hypotensive activity in chloralose-anesthetized vagotomized cats. Blood pressure and average evoked potentials recorded from one postganglionic renal nerve were measured during intraventricular (lateral ventricle) or intravenous (radial vein) infusion of each agent. Potentials were evoked in the sympathetic nerve by single shocks to the sciatic nerve. Three concentrations (1, 3, 5 mM) of each compound were infused consecutively for 20 minutes per concentration. The decrease in blood pressure after intraventricular infusion of 1 mM pindolol, 5 mM d-propranolol and 3 mM dl-propranolol was significantly greater than the decrease after intravenous infusion of the same concentrations of each agent. The decrease in the average evoked potential after intraventricular infusion of the 5 mM concentration was greater than the response after intravenous infusion. Consecutive (1, 3, 5 mM) intraventricular or intravenous infusions of sotalol did not significantly change either parameter. During intraventricular infusion of 3 mM dl-propranolol blood pressures was markedly decreased at a time when the average evoked potential was unchanged; however, parallel changes were observed during infusion of the drug in vagotomized cats in which the carotid sinus baroreceptors were also denervated. The results indicate a) that intraventricular administration of d-propranolol, dl-propranolol and dl-pindolol, but not of dl-sotalol, decreased blood pressure and discharge evoked in the postganglionic renal nerve by an action on central sympathetic structures, and b) that baroreceptor activity during hypotension can overcome the depressant effect of dl-propranolol on potentials evoked reflexly in the renal nerve.