TYRAMINE-LIKE ACTION OF SUCCINYLCHOLINE IN THE ISOLATED, BLOOD-PERFUSED CANINE ATRIUM

The mechanisms of succinylcholine-induced cardiac effects have not been fully elucidated. Accordingly, we studied the effects of succinylcholine on atrial rate and contractile force in the isolated canine atrium perfused with donor blood. The sinus node artery was perfused with heparinized blood from the common carotid artery of the donor dog at a constant pressure of 100 mm Hg. When succinylcholine in a dose range of 30-1000 mug was injected directly into the sinus node artery of the isolated atrium, increases in atrial rate and contractile force were observed in a dose-related manner. The atrial rate and contractile force were increased to 10.5% +/- 1.8% (mean +/- SEM) and 56.8% +/- 8.5% above the control values after the administration of 1000 mug of succinylcholine, respectively. After treatment with propranolol, the positive chronotropic and inotropic effects of succinylcholine and norepinephrine were significantly suppressed. Hexamethonium or tetrodotoxin pretreatment inhibited the cardiac effects of nicotine but did not Modify the succinylcholine-induced cardiac effects. The succinylcholine-induced effects were significantly inhibited by treatment with imipramine, which also suppressed the tyramine-induced effects. We conclude that succinylcholine has cardioexcitatory properties mediated by release of catecholamine due to a tyraminelike action.