Direct and sensitizing effects of serotonin agonists and antagonists on vascular smooth muscle.

Serotonin has several effects on vascular smooth muscle. In most vascular beds it causes vasoconstriction, but under the proper conditions it can cause vasodilatation. The constrictor response is a result of activation of specific receptors on the vascular smooth muscle, whereas the vasodilator response is mediated in part by the vascular endothelium. In addition to these direct effects on the vascular wall, serotonin can potentiate contractile responses to several other vasoactive agents (norepinephrine, angiotensin II, histamine, etc.). This indirect sensitizing action of the monoamine is probably mediated by activation of the S2 subclass of serotonergic receptors. These complex actions of serotonin on vascular smooth muscle may be altered in disease states such as hypertension.