Direct and endothelium-linked serotonergic control of vascular tone in human uterine and umbilical arteries

Abstract: The serotonergic vascular control was investigated by in vitro pharmacology in the human uterine and umbilical arteries. The localisation of immunoreactive (IR) neuropeptide Y (NPY) and the influence of NPY on the adrenergic vascular effects in the human uterine artery were also studied. NPY-IR nerve fibres were observed predominantly at the media-adventitial border of the uterine artery. About 50% of the NPY-IR nerve fibres also contained tyrosine hydroxylase-IR. NPY potentiated the noradrenergic contraction in the uterine artery but had no effect per se. The receptors mediating the serotonergic contractile effect in the human uterine artery were of the 5-hydroxytryptamine (5-HT)2-subtype with a minor contribution of 5-HT1 receptors. The endothelium of the uterine artery secreted a vasodilating substance in response to 5-HT. This substance seemed to be a prostanoid, probably prostacylin. The endothelium-linked effect appeared to be mediated by 5-HT1 receptors. In the human umbilical artery 5-HT mediated a contraction via a mixed population of 5-HT1 and 5-HT2 receptors. The endothelium secreted a vasoconstrictive substance in response to 5-HT. This endothelium-linked effect also appeared to be mediated by receptors of the 5-HT1 subtype. It was not possible to detect the substance released by the endothelium of the umbilical artery in response to 5-HT, although endothelin could not be excluded.