The Mechanism of the Pressor Responses to Physostigmine in the Rat and Their Modification by Mebutamate and Amylobarbitone

Pressor responses to intravenous injections both of physostigmine and of pilocarpine were smaller in rats anaesthetized with either mebutamate or amylobarbitone than in rats anaesthetized with urethane. The response to electrical stimulation of the hypogastric nerve in the isolated hypogastric nerve-vas deferens preparation was diminished by mebutamate and by amylobarbitone, but not by urethane. Similar results were obtained with the cat isolated splenic nerve-spleen preparation. In the rat anaesthetized with urethane, pressor responses to physostigmine were only partially antagonized by hexamethonium but were completely abolished during "depolarizing" ganglionic block by nicotine or tetramethylammonium. It is suggested that, in addition to the central mechanism, there is a peripheral component in the pressor action of physostigmine and in the antihypertensive actions of mebutamate and amylobarbitone.