Effect of vasoactive intestinal peptide on duodenal motility in the isolated perfused porcine pancreaticoduodenal block.

The peptidergic regulation of duodenal motility has not been clarified in detail. The aim of the present study was to investigate the effect of vasoactive intestinal polypeptide (VIP) on duodenal motility in the isolated perfused porcine pancreaticoduodenal block. VIP was administered arterially at 10(-7) M and motility was measured by means of the perfused side-hole technique using an intraluminal catheter. It was found that spontaneous duodenal motility was intense at the beginning of each experiment. However, the spontaneous motility diminished by time to cease after 45-90 min. VIP inhibited the duodenal motility. Thus, the frequency of duodenal contraction was decreased from 11 (8-16) to 3 (0-10) contractions per minute by VIP (p less than 0.01) and VIP also decreased the arterial perfusion pressure from 7.5 (3.5-23.2) to 5.8 (2.6-17.3) kPa (p less than 0.01). Since the same inhibitory effect has previously been demonstrated after alpha 2-adrenoceptor activation, we also examined whether alpha 1- and alpha 2-adrenoceptor agonism stimulated the release of VIP from this preparation. We then found that alpha 1-adrenoceptor agonism (phenylephrine or noradrenaline plus idazoxan) given intra-arterially stimulated VIP release (p less than 0.01). In contrast, alpha 2-adrenoceptor agonism (UK-14,304 or noradrenaline plus prazosin) had no effect. Therefore, we conclude that VIP inhibits duodenal motility in the pig but that this effect does not mediate the sympathetically induced inhibition of motility.