VASOACTIVE INTESTINAL PEPTIDE (VIP): TISSUE DISTRIBUTION IN THE RAT AS MEASURED BY RADIOIMMUNOASSAY AND BY RADIORECEPTORASSAY

Abstract

This work was undertaken to study the distribution of VIP in the digestive tract. VIP was measured both by radioimmunoassay and by radioreceptor assay 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 .+-. 186 ng/g) and the colon (1214 .+-. 214 ng/g); the maximal quantity occurred in the jejuno-ileum (11,698 .+-. 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 .+-. 26 ng/g of tissue. The VIP contents of the digestive tract were similar when measured either by radioimmunoassay or by radioreceptor assay. Immunoreactive VIP was found in the brain (155 .+-. 7 ng/g of tissue) and brain extracts competitively inhibited the binding of [125I]VIP (purified from gut) to liver plasma membranes. VIP from the overall gastrointestinal tract is a biologically active molecule. VIP from brain binds to receptors for intestinal VIP in liver.