CENTRALLY MEDIATED PERIPHERAL HYPOTENSIVE EFFECTS OF RESERPINE AND HYDRALAZINE WHEN PERFUSED THROUGH THE ISOLATED IN SITU CAT BRAIN

¹ Department of Pharmacology, The Albany Medical College of Union University, Albany, New York

Centrally mediated peripheral hypotensive actions of reserpine and hydralazine were studied, utilizing an in situ isolated, perfused brain technique which was adapted in the form of a preparation in a single cat, composed of an extracorporeally perfused brain, which exercises reflex and/or tonic sympathetic control over the peripheral circulation of the vascularly isolated body, and an in situ isolated, perfused hindlimb. Perfusion of reserpine or hydralazine through the isolated brain produced, within minutes after the drug reached the brain, a hypotension and bradycardia in the body. Hydralazine, but not reserpine, decreased hindlimb vascular resistance. The central components of cardiovascular reflexes initiated by mechanically increasing or decreasing carotid sinus and cerebral blood flow and pressure were not appreciably affected by either drug. Norepinephrine levels in various brain areas after reserpine were significantly diminizhed only after the onset of the hypotension and bradycardia, indicating a lack of correlation between these effects and brain norepinephrine depletion. Hydralazine caused elevation of brain norepinephrine, but no temporal correlation between this action and its centrally induced cardiovascular effects was attempted. These studies are interpreted as demonstrating a significant central component to the hypotensive effects of reserpine and hydralazine.