CHARACTERIZATION OF THE VASODILATATORY RESPONSE TO SEROTONIN IN HUMANUMBILICAL ARTERIES PERFUSED IN-VITRO - THE INFLUENCE OF THE ENDOTHELIUM

In most preparations of human cord arteries perfused in vitro, infusio n of 10(-7) M of serotonin leads to a biphasic pressure response start ing with a transient minor vasodilatation followed by a dominant vasoc onstriction. In some preparations, however, the vasoconstrictive part of the response with this dose of serotonin is less pronounced or comp letely absent, whereas the dilatation is stronger and more prominent. The present study deals exclusively with experiments on cord arteries displaying the latter type of serotonin reactivity, and was undertaken in order to characterize the relaxing effect of serotonin, and in par ticular, the role of the endothelial layer. This was accomplished by s tudying the response pattern before and after treatment with different drugs or removal of the endothelium. The vasodilatatory action of ser otonin was found to be abolished following treatment with methysergide , significantly reduced after denudation (P < 0.05), slightly reduced after exposure to methylene blue or N omega-nitro-L-arginine methyl es ter (L-NAME) (non-significantly), but not affected by indomethacin. Th e results suggest that the relaxing effect is mediated by specific ser otonin receptors and that endothelium-derived substances, possibly inc luding nitric oxide, are involved. (C) 1997 Elsevier Science Ireland L td.