Influence of gallamine, pancuronium, d-tubocurarine and succinylcholine on adrenergic neurotransmission.

The influence of gallamine, pancuronium, d-tubocurarine and succinylcholine on adrenergic neurotransmission was studied in the isolated saphenous vein of the dog. Pancuronium increased the response of vascular smooth muscle to adrenergic nerve stimulation and to exogenous norepinephrine; gallamine, d-tubocurarine and succinylcholine had no effect. The relaxation caused by small doses of acetylcholine added during sympathetic nerve stimulation (prejunctional effect), was inhibited by pancuronium and by gallamine. In vein strips, charged with (3H) norepinephrine, acetylcholine inhibits the catecholamine-efflux evoked by sympathetic nerve stimulation. That inhibition was abolished by gallamine. This confirms that gallamine inhibits the prejunctional effect of acetylcholine on adrenergic neurotransmission. When extrapolated to the intact organism, this means that gallamine and pancuronium will augment the release of norepinephrine by acting as muscarinic antagonists also at prejunctional receptor sites in tissues exposed to combined sympathetic and vagal nerve activity. This mechanism would explain in part the cardiovascular effects of these muscle relaxants.