A possible central action of prazosin and ketanserin to cause hypotension

Cats anesthetized with chloralose were used to study the cardiovascular effects of prazosin and ketanserin infused into the vertebral artery. It was found that both drugs, when given by this route, caused hypotension at doses which were ineffective if given intravenously. Hypotensive doses of prazosin or ketanserin infused into the vertebral artery had no effect at all on the pressor response to intravenous noradrenaline. Prazosin caused a small tachycardia while ketanserin decreased heart rate. At the doses used, neither of these drugs infused into the vertebral artery caused any significant change in the cardiovascular response to bilateral carotid occlusion, 30 degrees head-up tilt, or electrical stimulation of the central end of the cut brachial nerve. It is concluded that these effects of prazosin and ketanserin, administered into the vertebral artery, do not involve direct action on vascular tissue but are probably of central origin.