VIP nerve fibres around peripheral blood vessels

By immunocytochemistry nerve fibres containing vasoactive intestinal polypeptide (VIP) were demonstrated around many peripheral blood vessels in the cat. Such nerve fibres were particularly numerous around arteries in the upper respiratory, gastrointestinal and genito-urinary tracts. They were less numerous around large arteries and veins and seemed to be absent from the blood vessels in liver, spleen and kidney. VIP nerve fibres were few around blood vessels in skeletal muscle and absent in coronary arteries. Administration of VIP in vitro relaxed all arteries tested provided they had been given an increased tone, for instance by preincubation with PGF2 alpha. It is likely that VIP in vascular nerve fibres may participate in the regulation of systemic and local blood flow.