The possible involvement of hyperpolarizing mechanisms in histamine-induced relaxation of the rat portal vein

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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 (120mM) 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 H_1, H_2 and H_3, 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 H_1, H_2 and H_3 receptors.
日本平滑筋学会の論文