Effects of chronic morphine on biliary tract responses to cholecystokinin-octapeptide in male guinea pigs.

Opioid peptides share the spasmogenic action of acutely administered morphine on the sphincter of Oddi. In this study, gallbladder function was assessed following chronic opioid administration. Implantation of morphine pellets (400 mg) in male guinea pigs depressed cholecystokinin-octapeptide(CCK)-induced emptying of gallbladder bile (monitored via a duodenal cannula). Gallbladder muscle strips, isolated from the morphine treated animals, showed depressed contractile responses to CCK. This antagonism was non-specific and indirectly mediated, as ACh contractions were also depressed, whereas CCK-induced contractions of gallbladder strips from untreated animals were unaffected by direct exposure to morphine (3 x 10(-6)M). The depression of CCK stimulation of bile flow by chronic morphine administration in male guinea pigs suggests that chronic exposure to opioids can impede gallbladder emptying.