Effects of the muscarinic agonist McN‐A‐343 on responses to sympathetic nerve stimulation in the rabbit ear artery

Abstract

1 Observations were made on the effects of 4-(m-chlorophenylcarbamoyloxy)-2-butynyltrimethylammonium chloride (McN-A-343) on responses of isolated segments of the central artery of the rabbit's ear to sympathetic nerve stimulation and noradrenaline. 2 With low frequencies of nerve stimulation (2–5 Hz), McN-A-343 caused a decrease in responses to sympathetic nerve stimulation. This effect of McN-A-343 was abolished by dexamphetamine or atropine. In the presence of atropine, McN-A-343 caused an increase in responses to sympathetic nerve stimulation. 3 With high frequencies of nerve stimulation (10–20 Hz), McN-A-343 caused an increase in responses. This effect was not qualitatively changed in the presence of atropine. 4 When McN-A-343 had an inhibitory effect on responses to sympathetic nerve stimulation, responses to noradrenaline were unaffected. 5 It is suggested that McN-A-343 acts on muscarinic receptors through which noradrenaline release may be inhibited; it may also act on the cholinergic stage in adrenergic transmission postulated by Burn & Rand (1959).