Bile salt-dependent inhibition of gallbladder emptying.

Little is known about the inhibitory controls of gallbladder emptying. Since cholestyramine, a binding agent that reduces luminal concentration of bile salt, has been reported to accelerate gallbladder emptying, suggesting that bile salt is inhibitory, we hypothesized that fat-stimulated gallbladder emptying is inhibited by a bile salt-dependent mechanism. To test this idea, we compared gallbladder emptying in 10 dogs equipped with duodenal and jejunal fistulas that allowed for complete diversion of the native bile while varying concentrations of bile salt were perfused into the small intestine. In six dogs, 30 mM oleate and 5, 10, or 20 mM sodium taurocholate was perfused into the whole intestine. Since bile salt availability alters fat absorption, in a separate experiment in seven dogs we also compared gallbladder emptying while 30 mM oleate and 5 mM taurocholate were perfused between fistula and 0, 5, 10, or 20 mM taurocholate were perfused beyond jejunal fistula to separate fat from varying concentrations of bile salt. We found that intestinal taurocholate inhibited fat-stimulated gallbladder emptying in a dose-dependent fashion (P < 0.01; analysis of variance, significant linear dose effect) and that the inhibitory effect of bile salt persisted when 5-20 mM taurocholate was perfused beyond the jejunal fistula (0 vs. average of 5-20 mM taurocholate, P < 0.05, paired t-test). We conclude that fat-stimulated gallbladder emptying is inhibited by a bile salt-dependent inhibitory mechanism.

Stimulation of duodenal motility by hyperosmolar mannitol depends on local osmoreceptor control.

Duodenal motility is stimulated by hyperosmolar solution. Since intestinal distension also stimulates intestinal motility, this increase in the motility response may be due to either stimulation of duodenal local osmoreceptor control or intestinal distension resulting from osmotic equilibration. To test which mechanism is primarily responsible for this osmotically sensitive effect, we compared the number of duodenal spike bursts in five dogs equipped with duodenal fistulas that allowed for the preservation or removal of intestinal distension. The response to 300 vs. 1,200 mosM mannitol was compared under three experimental perfusion methods: 1) distension was preserved both proximal and distal to the fistula (DD); 2) distension proximal to the fistula was removed (rD); and 3) distension both proximal and distal to the fistula was removed (rr). The test solutions had access to either the whole gut (DD and rD) or only the first 10 cm of the duodenum (rr). We found that 1) there were more spike bursts after the hyperosmolar solution (dose effect, P < 0.05, analysis of variance); 2) there was no significant difference between the three experimental methods; and 3) the stimulating effect of hyperosmolar solution depended on the first 10 cm of the duodenum. Thus, since hyperosmolar solution increased duodenal motility regardless of whether intestinal distension was preserved or removed, the stimulating effect of hyperosmolar solution on duodenal motility was primarily the result of a local osmoreceptor control mechanism located in the first 10 cm of the duodenum.