Preferential Release of Adrenaline from the Adrenal Medulla by Muscarine and Pilocarpine

Abstract

HISTOCHEMICAL examination of the adrenal medulla of several species, including the cat, has revealed two distinct types of chromaffin cell, one rich in adrenaline and the other rich in noradrenaline^1,2; and with appropriate physiological stimuli it is possible to release one or the other of these catecholamines more or less selectively^3–5. Pharmacological investigations, on the other hand, have indicated that two types of ‘acetylcholine receptor’ are present in the cat's adrenal medulla. Attention was directed to this by Feldberg, Minz and Tsudzimura⁶, who found that both nicotine and pilocarpine had pressor effects when injected ‘close-arterially’ into the adrenal gland and that the effect of the former was blocked by excess nicotine while that of the latter was blocked by small doses of atropine. They were further able to demonstrate both nicotine-sensitive and atropine-sensitive components in the stimulant action of the splanchnic nerve on adrenal medullary secretion. Our purpose here is to present evidence suggesting that the two sets of phenomena are related: that, in the cat at least, pilocarpine and muscarine release adrenaline with little or no noradrenaline; while nicotine releases large amounts of noradrenaline as well as adrenaline.