Influence of selective VIP receptor agonists in the rat gastric fundus

The receptor subtypes involved in the relaxant effect of vasoactive intestinal polypeptide (VIP) in the rat gastric fundus were investigated in vitro. The selective VIP2 receptor agonist [Ac-H-1,E-8,K-12,Nle(17),A(19),D-25,L-26,K-27,K-28,G(29,30)]VIP(cyclo21-25) (RO25-1553) induced a concentration-dependent relaxation (EC50 2.8 nM), while the selective VIP1 receptor agonist derived from growth hormone-releasing factor (GRF) [K-15,R-16,L-27]VIP-(1-7)/GRF-(8-27) had no effect up to 1 mu M. [R-16] chicken secretin, a selective VIP1 receptor agonist, induced relaxation with a potency of 4.8 nM but its maximal effect was clearly lower than that of VIP, pituitary adenylate cyclase-activating peptide [PACAP-(1-27)] and RO25-1553. This effect was reproduced by porcine secretin (EC50 2.1 nM). It is concluded that the rat gastric fundus contains functional VIP2 receptors but not VIP1 receptors, and that specific secretin receptors are also present. (C) 1998 Elsevier Science B.V. All rights reserved.