Effects of several tricyclic antidepressants on the hemodynamics and myocardial contractility of the anesthetized dogs.

Cardiovascular effects of several imipramine analogs were investigated in the anesthetized mongrel dogs. Significant reduction in the cardiac output produced by lower doses (2.5 mg/kg, i.v.) of imipramine and 2-OH-DMI was not due to a depression of myocardial contractility. In contrast, 2-OH-imipramine (1.25 mg/kg) and DMI (2.5 mg/kg) significantly reduced contractility within 10 min after i.v. administration; however, significant decrease in the cardiac output did not occur until after 60 min. Higher doses (5 mg/kg) of imipramine, DMI and 2-OH-DMI significantly attenuated cardiac rate, contractility and output within 5 min after i.v. administration. 2-OH-imipramine, 2.5 mg/kg, i.v., depressed contractility and cardiac output to a degree equivalent to that produced by 5 mg/kg of imipramine, DMI and 2-OH-DMI. 3-Chloro-imipramine (5 mg/kg, i.v.) induced decrease in the cardiac output was essentially due to a significant reduction in the heart rate since the effects of this compound on the contractility were transient in nature. 3-Cl-8-OH-metabolite of this compound had no significant effects on the cardiovascular system. The results of this investigation demonstrated that the complex cardiovascular effects of tricyclic antidepressants observed in these studies were perhaps due to a direct and/or autonomically mediated effects on the heart and vasculature. Further, the data support the conclusions that the activity of the parent compounds together with that of the metabolites contributes to overall changes observed. While all the agents are capable of reducing cardiac output, 2-OH-metabolite of imipramine appears to be most toxic on the myocardium and 3-Cl-imipramine possessed only transient effects on the contractile properties.