Differential effects of motilin on interdigestive motility of the human gastric antrum, pylorus, small intestine and gallbladder

Motilin was infused in this study with the aim of examining refractory characteristics for motilin stimulation of antral phase III and fasting gallbladder emptying. Moreover, interdigestive pyloric and small intestinal motility from duodenum to ileum were studied, as these may be target organs for motilin. Eight fasting, healthy male volunteers received, on separate subsequent days, repeated infusions of 13leucine-motilin (8 pmol (kg min)(-1) for 5 min) or saline at 30 min after phase IIIs in the duodenum. Interdigestive motility of the antrum, pylorus, duodenum, jejunum and ileum was measured for maximum 10 h by using a 21-lumen perfused catheter. Gallbladder motility was measured by ultrasonography. Motilin infusions induced antral phase IIIs, but only after a preceding phase III of duodenal origin. Under this condition, time-interval to phase III at the duodenal recording site was 30 +/- 13 (SEM) min after motilin, compared with 79 +/- 14 min after saline (P < 0.01), and compared with 121 +/- 13 min for motilin infusion following an antral phase III (P < 0.001). Motilin did not affect small intestinal motility or isolated pyloric pressure waves (IPPWs). However, the number of IPPWs was significantly affected by the origin of the preceding phase III, irrespective of whether motilin or saline was infused. Gallbladder volume decreased significantly within 10 min after each motilin infusion. We conclude that this study clearly demonstrates differential regional effects of motilin. Motilin initiates antral phase IIIs, but stimulation is subject to a refractory period which is clearly prolonged after a preceding antral phase III. Motilin induced gallbladder emptying, however, is not subject to a refractory state. Small intestinal phase IIIs as well as pyloric IPPWs are not affected by motilin.