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

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Abstract
Summary: 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. 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. 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. When McN‐A‐343 had an inhibitory effect on responses to sympathetic nerve stimulation, responses to noradrenaline were unaffected. 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).