Effect of a novel cholecystokinin receptor antagonist, FK480, administered intraduodenally, on pancreatic secretion in rats.

The effect of a new cholecystokinin (CCK)-A receptor antagonist, FK480, developed in Japan, on pancreatic exocrine secretion stimulated by exogenous CCK and intraduodenal casein was investigated in vivo when administered to anesthetized rats intraduodenally, and its CCK antagonistic activity was compared with that of CR 1505. Intraduodenal administration of FK480 at graded doses of 0.0016-1.0 mg/kg-h produced dose-dependent inhibition of pancreatic juice volume and amylase output stimulated by intravenous infusion of CCK-8 at a dose of 0.06 micrograms/kg-h. The half-maximal inhibitory dose (ID50) of FK480 for CCK-8-stimulated amylase secretion was 0.025 mg/kg-h, whereas the ID50 of CR 1505 was 5.2 mg/kg-h, indicating that FK480 is 208 times more potent than CR 1505. Moreover, intraduodenal FK480 (0.2 mg/kg-h) significantly suppressed pancreatic juice volume and amylase output augmented by intraduodenal infusion of casein (400 mg/h). It is concluded that FK480 administered intraduodenally has a significant, potent inhibitory action on the exocrine pancreas stimulated by exogenous CCK and intraduodenal casein.