A CENTRALLY MEDIATED PROLONGED HYPOTENSION PRODUCED BY OXOTREMORINE OR PILOCARPINE

Abstract

1 Oxotremorine, methyloxotremorine, pilocarpine or arecoline were given intravenously to anaesthetized cats, dogs or rats, and intraperitoneally to conscious normotensive and spontaneously hypertensive rats, pretreated with doses of methylatropine that completely blocked peripheral muscarinic receptors, to ascertain their effects on blood pressure and heart rate. 2 Oxotremorine but not methyloxotremorine produced a prolonged hypotension in cats and dogs but not in rats. Heart rate was not changed. Pilocarpine, although less potent, produced an identical effect, whereas the effect of arecoline was short by comparison. The hypotensive effect of these drugs was reversed by atropine. 3 In dogs, oxotremorine produced a prolonged hypotension with no change in heart rate or cardiac output. 4 A decrease in spontaneous sympathetic nerve activity accompanied the hypotension in cats. Both effects were reversed by atropine but could be reinvoked by large doses of oxotremorine. 5 The oxotremorine-induced hypotension in cats was not altered by decerebration but was abolished by high cervical spinal section. 6 The results indicate that the prolonged hypotension elicited by oxotremorine is mediated by an action at muscarinic receptors in the brain stem resulting in a decrease in sympathetic nerve activity and peripheral resistance but not heart rate or cardiac output.