Cholecystokinin receptor antagonist loxiglumide: influence on bilio-pancreatic secretion and gastrointestinal hormones in man.

We characterized the effect of the specific cholecystokinin (CCK) receptor antagonist loxiglumide (CR 1505) on gallbladder contraction, pancreatic enzyme output and plasma CCK concentrations determined by radioimmunoassay and bioassay. Gallbladder emptying and bilirubin output in response to the intraduodenal administration of a mixed liquid meal were completely inhibited by an intravenous infusion of loxiglumide (10 mg/kg/h). In contrast, meal-stimulated pancreatic enzyme secretion was diminished by only 30-40%. CCK concentrations in response to the test meal were 3-fold higher during infusion of loxiglumide, as determined by radioimmunoassay. In the absence of the antagonist, the bioassay measured CCK plasma levels identical to those determined by radioimmunoassay. In the presence of loxiglumide, CCK-like bioactivity was not detectable, indicating that the plasma concentrations of the CCK receptor antagonist were sufficient to abolish all circulating CCK-like bioactivity. We conclude that fasting volume and meal-induced contraction of the gallbladder are controlled by CCK. Postprandial pancreatic enzyme secretion, however, is mainly mediated by non-CCK-dependent mechanisms. Plasma CCK-like immunoreactivity is increased by loxiglumide, whereas plasma CCK-like bioactivity is zero in the presence of an CCK-receptor antagonist.