Action of nicotine on the rabbit muscular organ (ileo-colic sphincter).

The effects of nicotine on the longitudinal muscle of the rabbit muscular organ (ileo-colic sphincter) have been studied. Nicotine in doses from 1 to 10 mug/ml. inhibits the pendular movements of the muscle. This inhibition can also be produced by acetylcholine in the presence of atropine. In both instances, the inhibitory effect can be blocked by ephedrine, hexamethonium and bretylium. Doses of hexamethonium which block the inhibitory action of nicotine reveal an excitatory action, which itself can be blocked by higher doses of hexamethonium. Bretylium blocks both actions of nicotine at the same dose level. It is suggested that nicotine produces inhibition by releasing catechol amines, the site of action being a cholinergic junction between sympathetic nerve and catechol amine store, and further that bretylium blocks the action of acetylcholine and nicotine at this site as well as at the parasympathetic ganglia.