Comparative cardiovascular toxicity of trazodone and imipramine in the rat

Several authors have associated the cardiotoxicity of the tricyclic antidepressants with their capacity to potentiate the response to catecholamines. Trazodone is a psychotropic drug with a clinically proven antidepressant activity. It differes from the tricyclic antidepressants under several aspects (chemistry, pharmacology, mode and mechanism of action, etc.), including interactions with catecholamines. Contrary to the tricyclic antidepressants, it does not potentiate the response to catecholamines, but, instead, has an adrenolytic activity. We therefore decided to compare the cardiotoxicity of trazodone and of a tricyclic antidepressant, i.e. imipramine in the rat. The experiments were conducted on anaesthetized Long Evans rats, the drugs being administered by i.v. infusion until cardiac arrest occurred; ECG (lead II) and blood pressure (BP) were recorded at the same time. The primary effect of trazodone was its hypotensive action. ECG changes, consisting of a lengthening of the PR interval, were observed only when there was a marked drop in BP. The primary effect of imipramine, instead, consisted of disturbances in cardiac conduction. It is concluded that trazodone and imipramine produce different cardiovascular effects.