Divergent effects of cyproheptadine and R 50 656, a 5-HT2 antagonist, on the cardiovascular response to 5-hydroxytryptamine in rats.

Cyproheptadine and R 50 656, a novel 5-HT2 antagonist, produced a dose-dependent suppression of the pressor response to 5-hydroxytryptamine (5-HT), but did not affect the depressor response. The pressor effect of 5-HT was significantly more sensitive to R 50 656 than to cyproheptadine. On the contrary, the tachycardic response to 5-HT was antagonized only with cyproheptadine. Accordingly, in rats the 5-HT receptors of cardiac tissue differ in their pharmacological properties from both the excitatory and inhibitory 5-HT receptors of vascular smooth muscle.