VIP (vasoactive intestinal polypeptide)--immunoreactive innervation of the portal vein.

Nerve fibres displaying immunoreactivity for vasoactive intestinal polypeptide (VIP) were found in the wall of the portal vein in cats, guinea pigs, rats and mice. In whole-mount preparations a sparse network of VIP fibres was seen in the vessel wall. Electrical field stimulation of the rat portal vein in vitro caused a significant release of VIP. The results suggest that VIP ergic nerve fibres play a role in the regulation of portal blood flow.