Alteration of large intestinal electrolyte transport by vasoactive intestinal polypeptide in the rat

Vasoactive intestinal polypeptide (VIP) alters fluid and electrolyte movement in the small intestine. These studies were designed to evaluate the effect of VIP on Na and Cl transport across isolated large intestinal epithelia of the rat under short-circuited conditions since some evidence suggests that this intestinal hormone may not affect colonic ion transport. An increase in short circuit current and potential difference was produced by the addition of VIP to the serosal media at concentrations as low as 10^-9 M, and maximal increments were observed at 10^-7 M. In control mucosa J(Na/net) was 4.93 ± 0.52 μEq per hr.cm². The addition of VIP (6 x 10^-7 M) resulted in a decrease in J(Na/net) (0.87 ± 0.46 μEq per hr.cm²), a reversal of Cl absorption to Cl secretion (-2.42 + 1.12 μEq per hr.cm²) and an increase in short circuit current. Decreases in J(ms) were the predominant changes in unidirectional Na and Cl fluxes. The changes produced by VIP were identical with those induced by 10 mM theophylline. Furthermore, the effect of VIP plus theophylline on J(Na/net) and short circuit current were undistinguishable from those of VIP alone and theophylline alone. VIP also increased mucosal cyclic AMP content. These studies indicate that VIP alters large intestinal ion transport; these changes are most likely mediated by increased mucosal levels of cyclic AMP.