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

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.