Involvement.

Purpose: The aim of the present study was to investigate a nitric oxide (NO) involvement in the mediation of a 5-HT-induced vasoconstrictions response in the rat portal vein in vitro. Material and Methods: Isolated rat portal vein preparations obtained after dissection were placed in organ baths for isometric force measurement via a strain gauge. Results: 5-Hydroxytryptamine (5-HT) in concentrations ranging from 3x10-8 M to 3x10-4 M contracted portal vein preparations (EC50= 7x10-7 M) in a concentration dependent manner. The vasoconstrictions induced by 5-HT was significantly increased in endothelium-denuded vessels. Pre-treatment with Nw-nitroL-arginine methyl Ester (L-NAME 100 μM) enhanced the contractive response to 5-HT either in intactor denuded endothelium vessels. Whereas, ketanserin (0.1 μM) abolished 5-HT-induced vasoconstrictions (EC50= 4.6x10-8 M). Furthermore, a non-selective 5HT1B/Dreceptors agonist, sumatriptan, (1x10-10 M 1x10-5 M) induced a reduction of spontaneous rhythmic contractions either in endothelium-intact or in endothelium –denuded vessels. However, 5-HTinduced vasoconstriction was unaffected by propranolol (10 μM). Conclusions: These findings are consistent with the hypothesis that the vasoconstrictor activity of 5-HT in vascular smooth muscle was mediated by activation of 5-HT1B/D and 5-HT2B receptors subtypes involving the endothelium (NO) dependent mechanism.