Infusion of cholecystokinin octapeptide in man: relation between plasma cholecystokinin concentrations and gallbladder emptying rates

Abstract

To establish the sensitivity of the gallbladder in relation to plasma concentrations of cholecystokinin, a dose-response study was performed in 5 normal volunteers. Cholecystokinin octapeptide [CCK-O] was infused in ascending incremental dose sequence, interval blood samples taken for estimation of plasma hormone concentrations and gallbladder emptying rates monitored continuously using 99mTc-HIDA [N-(2,6-dimethylacetanilide)-iminodiacetic acid]. In 5 other volunteers, gallbladder emptying rates following a liquid fat meal were measured. Infusion rates of 0.0, 0.75 .+-. 0.2, 6.8 .+-. 0.5, 23.8 .+-. 1.6 and 66.1 .+-. 2.5 pmol cholecystokinin kg-1 h-1 produced plasma concentrations of < 3.0 (undetectable), < 3.0, 6.6 .+-. 1.8, 13.3 .+-. 1.5 and 26.9 .+-. 2.9 pmol l-1, respectively, and gallbladder emptying rates (% min-1) of 0.0, 0.0, 0.14 .+-. 0.15, 1.57 .+-. 0.38 and 4.29 .+-. 1.12. Following the fat meal, peak plasma cholecystokinin concentrations reach 30 pmol 1-1 and gallbladder emptying rates (% min-1) are 3.86 .+-. 1.01. The threshold of the gallbladder to circulating CCK-O is around 6 pmol l-1, but infusions which result in plasma levels of around 25 pmol l-1 produce gallbladder is apparently equally sensitive to endogenous and exogenous cholecystokinin, plasma concentrations observed after oral fat can probably entirely account for the gallbladder response.