ANALYSIS OF THE CONTRACTILE RESPONSE TO SEROTONIN AND TRYPTAMINE OF ISOLATED DOG CEREBRAL, FEMORAL AND MESENTERIC ARTERIES

Abstract

In helically-cut strips of cerebral arteries isolated from dogs, serotonin, tryptamine, 5-hydroxytryptophan and tryptophan caused a dose-related contraction. The potency was in the order of serotonin>tryptamine>5-hydroxytryptophan=tryptophan. In femoral arterial strips, only serotonin and tryptamine produced contractions. In cerebral arteries, the dose-response curve for serotonin was shifted to the right and downward by treatment with cinanserin, whereas in femoral and mesenteric arteries, the curves were shifted to the right. The contractile response of cerebral arteries to tryptamine was attenuated by cinanserin in concentrations above 10−7 M; however, 10−5 M was required to significantly reduce the response of femoral arteries. Phentolamine reduced the contractile response of femoral arteries to tryptamine, but not the response of cerebral arteries. It may be concluded that the different antagonism of cinanserin against the serotonin action on cerebral and femoral arteries is due to the ability of high concentrations of serotonin to induce relaxations of cerebral but not femoral arteries or to the different nature of receptors. Tryptamine appears to elicit contractions of cerebral arteries via a stimulation of tryptamine receptors, but elicit those of femoral arteries via stimulation of both alpha-adrenergic and tryptamine receptors. Whether or not receptors for serotonin and tryptamine are the same was not determined.