Intestinal Secretion Induced by Vasoactive Intestinal Polypeptide A COMPARISON WITH CHOLERA TOXIN IN THE CANINE JEJUNUM IN VIVO

peptide (VIP) on intestinal water and electrolyte trans-port and transmucosal potential difference was inves-tigated in the dog jejunum in vivo and compared to secretion induced by cholera toxin. Isolated jejunal loops were perfused with a plasma-like electrolyte so-lution. VIP (0.08 ug/kg per min) was administered di-rectly into the superior mesenteric artery by contin-uous infusion over 1 h. From a dye dilution method, it was estimated that a mean plasma VIP concentra-tion of 12,460 pglml reached the loops. VIP caused secretion of water and electrolytes; for example, chlo-ride: control, 8,ueq/cm per h absorption; VIP, 92,eq/ cm per h secretion. A marked increase in transmucosal potential difference (control,-1.0 mV; VIP,-5.9 mV, lumen negative) occurred within 1 min after starting VIP infusion. Analysis of unidirectional fluxes showed increased plasma-to-lumen flux of sodium and chloride and decreased lumen-to-plasma flux of sodium. Chlo-ride and bicarbonate were actively secreted against an electrochemical gradient. Although sodium secretion occurred down an electrochemical gradient, flux ratio analysis suggested a component of active sodium se-cretion. VIP caused a slight increase in protein out-put into the loops; light microscopy revealed capillary dilatation and closed intercellular spaces. The effect of VIP was readily reversible. Except for the delayed onset of secretion, the effect of cholera toxin was quali-tatively similar to VIP; however, capillary dilatation and increased protein output were not noted with cholera toxin