Abstract
The receptor subtypes involved in the relaxant effect of vasoactive intestinal polypeptide (VIP) in the rat gastric fundus were investigated in vitro. The selective VIP 2 receptor agonist [Ac-H 1,E 8,K 12,Nle 17,A 19,D 25,L 26,K 27,28,G 29,30,T 31]VIP(cyclo21-25) (RO25-1553) induced a concentration-dependent relaxation (EC 50 2.8 nM), while the selective VIP 1 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 μM. [R 16] chicken secretin, a selective VIP 1 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 (EC 50 2.1 nM). It is concluded that the rat gastric fundus contains functional VIP 2 receptors but not VIP 1 receptors, and that specific secretin receptors are also present.
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