Lack of effect of three putative vasoactive intestinal peptide receptor antagonists on vasoactive intestinal peptide-induced secretory responses in rat colon.

We have assessed the potential usefulness of three vasoactive intestinal peptide antagonists for investigating whether vasoactive intestinal peptide has a functional role as a secretomotor neurotransmitter at the neuroepithelial junction in rat colonic mucosa. Vasoactive intestinal peptide (VIP) increases short-circuit current in muscle-stripped preparations of rat colon. The response is unaffected by tetrodotoxin and can only be obtained when the peptide is applied to the basolateral side of the membrane. Three putative antagonists were tested for their ability to inhibit short-circuit current responses to vasoactive intestinal peptide. Vasoactive intestinal peptide-(10-28) (1 microM and 3 microM), human growth hormone releasing factor (human GRF) analogue [Ac-Tyr1]human GRF-(1-40)OH (0.1 microM and 1 microM) and [Lys1,Pro2,5,Arg3,4,Tyr6]VIP (0.5 microM) produced concentration-dependent increases in basal short-circuit current but were ineffective as antagonists to vasoactive intestinal peptide.