INFLUENCE OF SELECTIVE VIP RECEPTOR AGONISTS IN THE RAT GASTRIC FUNDUS

The receptor subtypes involved in the relaxant effect of vasoactive in testinal polypeptide (VIP) in the rat gastric fundus were investigated in vitro. The selective VIP2 receptor agonist A(19),D-25,L-26,K-27,K- 28,G(29,30)]VIP(cyclo21-25) (RO25-1553) induced a concentration-depend ent relaxation (EC50 2.8 nM), while the selective VIP1 receptor agonis t derived from growth hormone-releasing factor (GRF) [K-15,R-16,L-27]V IP-(1-7)/GRF-(8-27) had no effect up to 1 mu M. [R-16] chicken secreti n, a selective VIP1 receptor agonist, induced relaxation with a potenc y of 4.8 nM but its maximal effect was clearly lower than that of VIP, pituitary adenylate cyclase-activating peptide [PACAP-(1-27)] and RO2 5-1553. This effect was reproduced by porcine secretin (EC50 2.1 nM). It is concluded that the rat gastric fundus contains functional VIP2 r eceptors but not VIP1 receptors, and that specific secretin receptors are also present. (C) 1998 Elsevier Science B.V. All rights reserved.