Inhibitory actions of serotonin on vascular smooth muscle

Serotonin (5-hydroxytryptamine, 5-HT) is a potent vasoactive agent possessing both constrictor and dilator properties. The vasoconstrictor properties of the monoamine include activation of serotonergic and adrenergic receptors on smooth muscle cells and an ability to amplify contractile responses to other agents. The vasodilator effects of serotonin, which are the focus of this review, are complex and include; (a) direct inhibition of vascular smooth muscle contraction; (b) inhibition of adrenergic neurotransmission; (c) enhanced release of the endothelium-derived relaxant factor (EDRF) and; (d) release of other vasodilator substances such as vasoactive intestinal polypeptide. In the intact animal responses to serotonin may be mediated by a combination of the compound's peripheral and central nervous system actions.