Regulation of the descending relaxation phase of intestinal peristalsis by PACAP.

The presence of pituitary adenylate cyclase-activating peptide (PACAP), a homologue of vasoactive intestinal peptide (VIP), in enteric neurons suggests that it may involved in the regulation of the descending relaxation phase of the peristaltic reflex. The role of PACAP was evaluated by measurement of PACAP release and by immuno-neutralization with specific monoclonal antibodies to PACAP-27 and PACAP-38, and an antibody to VIP. Electrical field stimulation at 4 Hz caused a 12-fold increase in PACAP release that was inhibited by 53 +/- 6% (P < 0.01) by the nitric oxide synthase inhibitor, NG-nitro-L-arginine (L-NNA). Orad stretch of colonic segments elicited descending relaxation and PACAP release in proportion to the degree of stretch. PACAP release induced by 10-g stretch was inhibited by 67 +/- 10% (P < 0.01) by L-NNA. Previous studies (Am. J. Physiol., 264 (1993) G334-G340) showed that orad stretch elicits also VIP release and nitric oxide (NO) production and that VIP release is inhibited (59%) by L-NNA. Preincubation of the segments with PACAP-27 plus PACAP-38 antibodies (50 micrograms/ml each), or with VIP antibody (1:60) inhibited descending relaxation at all degrees of stretch (inhibition with PACAP antibodies: 90 +/- 8% with 2-g and 22 +/- 5% with 10-g stretch). Preincubation with both PACAP and VIP antibodies virtually abolished descending relaxation. A similar pattern was observed with the antagonists, PACAP6-38 and VIP10-28, alone and in combination.(ABSTRACT TRUNCATED AT 250 WORDS)