Cholecystokinin and gallbladder contraction: effect of CCK infusion.

Cholecystokinin octapeptide (CCK-8) was infused intravenously in five normal subjects. Plasma levels of CCK-8 and infusion concentrations were measured by a specific radioimmunoassay and gallbladder volumes wee monitored using ultrasound. Calculated CCK-8 infusion rates were 16.4, 32.8, and 65.6 pmol.kg(-1) hr(-1). During infusion of the lowest dose plasma concentrations rose from 8 +/- S.E. 5 to 18 +/- 4 pmol.1(-1) equivalent to normal postprandial concentrations of CCK and were accompanied by a 76 +/- 7% reduction in gallbladder volume. Infusion at the two higher rates resulted in 87 +/- 3% and 88 +/- 3% reduction of initial gallbladder volumes returned to 73 +/- 26% of initial volumes within 30 minutes. These studies are consistent with the hypothesis that CCK is the main postprandial stimulus for gall-bladder contraction.