Are vascular mechanisms involved in antidepressant action?

The effects of imipramine, mianserin and trazodone on the chronotropic, inotropic and coronary vascular responses in the isolated perfused rat heart

1. The cardiovascular effects of the tricyclic antidepressant imipramine and two second generation antidepressants mianserin, a tetracyclic, and trazodone, a triazolopyridine derivative, were investigated in the isolated perfused rat heart. 2. Imipramine caused cardiac slowing and a negative inotropic effect at 2.5 microM after 30 min of perfusion. Conversely mianserin and trazodone had no effect on heart rate at 5 microM with inotropic state remaining above control values after 30 min of perfusion. 3. Varying effects on coronary flow, which appear to correlate well with the documented receptor actions of each drug, were demonstrated. Imipramine caused a decrease in coronary flow at 1.25 and 2.5 microM, followed by an increase at 10 microM. Mianserin decreased coronary flow at all concentrations between 1 and 20 microM. Trazodone elicited a marked elevation in coronary flow over the dose range of 2.5 to 250 microM. 4. The results in this model suggest that although the second generation agents appear to cause less cardiodepression all three agents elicit quantitatively different coronary vascular responses.

Effects of antidepressants on receptor-activated and Ca2+-activated contractions of rabbit isolated aorta

Helically-cut strips of rabbit aorta were used to examine the inhibitory effects of some antidepressants on the contractile responses produced by norepinephrine (NE), serotonin (5-HT) or K+. The order of potency of antidepressants in antagonizing 5-HT-induced responses was: mianserin greater than amitriptyline greater than imipramine (IMI) greater than desipramine greater than or equal to nomifensine. With NE as agonist, the order of potency was: amitriptyline greater than mianserin greater than IMI greater than desipramine greater than or equal to nomifensine. Viloxazine (10(-5) M) was ineffective on 5-HT- or NE-induced contractions. For K+-induced contraction (which is mediated by Ca2+ entry into smooth muscle cells) tricyclic antidepressants were about equipotent with mianserin; nomifensine and viloxazine were relatively ineffective. These results indicate that certain antidepressants have multiple effects on arterial smooth muscle. Such effects could underlie not only the side-effects, but also the therapeutic actions of these agents.