2008 Volume 44 Issue 3+4 Pages 129-141
The present study evaluated the effects of histamine 10-2 M on longitudinal preparations of rat portal vein. It was observed that histamine 10-2 M induced relaxation of rat portal vein preparations pre-contracted with phenylephrine 10-4 M. On the other hand, no pharmacological effects were observed in preparations not pre-contracted. The observed histamine-induced relaxing effect was absent in preparations pre-contracted with KCl (120 mM) or in the presence of depolarizing nutritive solution. However, the histamine-induced relaxation was still present in the endothelium-removed preparations. The histamine-induced relaxation also was not prevented by astemizole (10-6 M, 10-5 M and 10-4 M), cimetidine (10-5 M, 10-4 M and 10-3 M) or thioperamide (10-6 M, 10-5 M and 10-4 M), selective antagonists H1, H2 and H3, respectively. The presence of L-NAME 10-4 M or L-NAME 10-4 M plus indomethacin 10-5 M also did not prevent the histamine-induced relaxation observed in rat portal vein. Thus, the histamine-induced relaxation observed in rat portal vein appears to involve a non-endothelial hyperpolarizing mechanism independent of H1, H2 and H3 receptors.
