Gastrointestinal peptides are known to influence the blood supply of splanchnic area; however the physiological significance and the action mechanisms of these substances are not clearly understood. The aim of this experimental study is to investigate the effect of VIP on the isolated portal vein of the sheep. In this experiment VIP caused a dose-dependent dilatatory effect on the portal vein. Using noradrenaline -which is used as an endogenous agent-resulted in contraction on the portal vein. This effect of noradrenaline was significantly potentiated by the VIP.

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