Adrenergic and peptidergic (substance P and vasoactive intestinal polypeptide) innervation of the rat portal vein.

The adrenergic innervation of the rat portal vein is subdivided into two plexuses: the adventitial and the medial. Nerve fibres containing immunoreactive substance P (SP) are present in the adventitial and medial plexuses, and extend into the longitudinal and circular muscle layers. Vasoactive intestinal polypeptide (VIP) immunofluorescence is restricted to the adventitial plexus. The catecholamine modulation of the intrinsic rhythmical contractions of the portal vein may be complemented by SP released from intramural nerves and VIP released from the adventitial nerves.