Interaction of GRF with VIP receptors and stimulation of adenylate cyclase in rat and human intestinal epithelial membranes

Abstract
GRF (10−8–10−5 M) is shown to inhibit competitively the binding of [125I]VIP to human and rat intestinal epithelial membranes. The affinity of GRF for VIP receptor is 700–800‐times lower than that of VIP in both species. The order of affinity of different peptides is VIP > PHI > secretin > GRF in rat, and VIP > GRF > PHI > secretin in man. The important species specificity of VIP receptors in recognizing PHI and secretin does not occur in the case of GRF. GRF stimulates adenylate cyclase through its interaction with VIP receptors in rat and human membranes. However, while GRF behaves as a VIP agonist in human tissue, it is a partial agonist/antagonist of VIP in the rat.