VIP and PGE1 activate adenylate cyclase in rat intestinal epithelial cell membranes via different mechanisms.

The effect of vasoactive intestinal polypeptide (VIP) and of prostaglandin E1 (PGE1) alone and in combination was tested in an adenylate cyclase (AC) preparation from rat intestinal epithelial cell membranes. AC activity increased linearly with time up to 15 min in the absence or presence of VIP or PGE1, respectively. NaF, VIP and PGE1 concentration-dependently stimulated AC activity. The dose-response curve of VIP in the presence of PGE1 was shifted to the left and the maximal effect of VIP was significantly enhanced. The dose-response curve obtained experimentally was significantly different from theoretical additive dose-response curve, indicating that PGE1 potentiates the effect of VIP on AC activity. The possible mechanisms of potentiation are discussed. The results suggest that VIP and PGE1 activate AC via two different but not entirely independent mechanisms.