Vasoactive intestinal peptide (VIP): Tissue distribution in the rat as measured by radioimmunoassay and by radioreceptorassay

This work was undertaken to study the distribution of vasoactive intestinal peptide (VIP) in the digestive tract. VIP was measured both by radioimmunoassay and by radioreceptorassay in order to determine whether immunoreactive VIP is related to a biologically active component. The effect of digestive extracts in inhibiting the binding of porcine [125I]VIP to the antibody (RIA) and to the rat liver plasma membranes (RRA) paralleled that of porcine VIP used as the standard. VIP was found throughout the digestive tract with especially high concentrations between the duodenum (1676 plus minus 186 ng/g) and the colon (1214 plus minus 214 ng/g): the maximal quantity occurred in the jejuno-ileum (11698 plus minus 687 ng/g). Less than 1 % of VIP was found in the epithelium whereas almost all VIP (>99%) was localized in the mucosal muscular tissue of the jejuno-ileum. VIP concentration in the pancreas was 180 plus minus 26 ng/g of tissue. The VIP contents of the digestive tract were similar when measured either by radioimmunoassay or by radioreceptorassay. Immunoreactive VIP was found in the brain (155 plus minus 7 ng/g of tissue) and brain extracts competitively inhibited the bonding of [125I]VIP (purified from gut) to liver plasma membranes. These results show that: 1) VIP from the overall gastrointestinal tract is a biological active molecule: 2) VIP from brain binds to receptors for intestinal VIP in liver. (author)