Effects of cholecystokinin-octapeptide on the human gallbladder both in vivo and in vitro

To determine the sites and mechanisms of action of cholecystokinin-octapeptide (CCK-OP) on the human gallbladder, effects of atropine sulfate on CCK-OP-evoked contractions were studied in both in vivo and in vitro experiments. In vivo studies performed by means of real time ultrasonography in six healthy volunteers showed remarkable contractions of the gallbladder after intramuscular injection of CCK-OP (0.07 microgram/kg), which was nearly abolished by premedication of atropine sulfate (0.015 mg/kg). Atropine sulfate (10(-6) M) slightly but significantly reduced CCK-OP (10(-11) M-3 X 10(-7) M) induced contractions and the dose-response curve for CCK-OP was shifted to the right of the muscle strips of the human gallbladders. It is suggested that CCK-OP acts mainly on cholinergic neurons in vivo. On the contrary, the most sensitive sites of action of CCK-OP might be smooth muscles rather than cholinergic neurons in vitro.