Effect of desmethylimipramine on the canine SA node.

Abstract

Direct perfusion of the sinus node artery at constant pressure of 100 mmHg was performed in eleven canine hearts in situ. The injection of desmethylimipramine (DMI) into the sinus node artery caused an initial short deceleration followed by markedly long-lasting acceleration of the heart rate. The initial deceleration was not influenced by treatment with atropine. The secondary acceleration was inhibited by propranolol, and, furthermore, suppressed by tetrodotoxin. After the treatment with propranolol or tetrodotoxin, DMI produced only a negative chronotropic effect dose-relatedly. It was difficult to observe the blocking effect of DMI on tyramine action, because DMI alone induced marked sinus acceleration. On the other hand, tyramine action was not influenced by tetrodotoxin. Therefore, the use of both DMI and tetrodotoxin is beneficial to observe blocking effect of DMI on tyramine-like action in the in situ SA node preparation.