Effect of nicotine on the lower esophageal sphincter. Studies on the mechanism of action.

Intravenous administration of nicotine sulfate caused a dose-dependent reduction in the lower exophagel sphincter pressure in anesthetized opossums. The maximal reduction in pressure of 85.0 +/- 2.6% was observed with a dose of 50 mug per kg. The effect of 50 mug per kg was not antagonized by bilateral cervical vagotomy, atropine, propranolol or by catecholamine depletion with reserpine. The sphincter relaxation produced by 50 mug per kg of nicotine was antagonized during tachyphylaxis produced by a larger dose (4 mg per kg) of nicotine. Nicotine tachyphylaxis also blocked the vagal-stimulated relaxation of the sphincter. It is suggested that the main action of nicotine on the sphincter in intact animals is caused by its effect on the noncholinergic, nonadrenergic inhibitory neurons which lie in the vagal pathway to the lower esophageal sphincter.