Effect of muscarine on release of catecholamines from the perfused adrenal gland of the cat.

1 The secretory effect of muscarine was studied in the perfused adrenal gland of the cat. During perfusion of the adrenal gland with Krebs-bicarbonate solution containing muscarine 480 microM, the rate of catecholamine (CA) secretion was 2.02 +/- 0.43 micrograms/2 min in the first 2 min; thereafter, CA output declined only moderately, to reach about 70% of the initial value after 10 min. Secretory responses to brief infusions of muscarine remained reproducible for at least the first 3 infusions. 2 When the adrenal gland was perfused with muscarine (480 microM), infusions of high K+, nicotine, or veratridine produced their usual responses. A 100 fold lower dose of muscarine also failed to modify these responses. 3 During perfusion with high K+, muscarine evoked a secretory response that was only slightly smaller than the response to muscarine alone. 4 It is concluded that muscarine and nicotine activate CA secretion in the cat adrenal gland by independent mechanisms and that the muscarinic response, unlike the nicotinic response, is not readily desensitized.