Serum bile acids and the bile acid tolerance test under oral contraception

Oral contraceptives (OC) have lithogenic properties as shown by a rise in biliary cholesterol secretion and cholesterol saturation index. Since we noted not only a rise in saturation index, but also a reduction in chenodeoxycholate (CDC) pool size and an increase in cholate (C) pool size during oral contraception (30 micrograms ethinylestradiol + 150 micrograms desogestrel), we investigated the endogenous bile acid tolerance test as a potential predictor of this effect on bile acid pool sizes using a cholecystokinin infusion of 55 min duration (1.2 U.kg-1.hr-1) as stimulus of the enterohepatic bile acid circulation in 12 healthy females before and during oral contraception for 3-5 months. Serum C and CDC conjugates were measured at 5-10 min intervals over a period of 150 min and analysed by two specific RIA's. Although no significant correlations between the serum CDC and C measurements and CDC and C pool sizes were found, a significant reduction of nearly 40% for both serum peak levels and the integrated area under the serum curve of CDC conjugates during oral contraception, but not of C conjugates was found. The reduction in serum levels of CDC conjugates during OC using the present model is best explained by both a reduction in CDC pool size and more efficient hepatic uptake of CDC conjugates (consisting of considerably more taurine conjugates during OC use), as well as by an intestinal effect on bile acid absorption under OC.