The effect of a progestin-only oral contraceptive on biliary lipid composition in the cat

Following a control period of 5 weeks, 3 female cats with chronic gastric and duodenal fistulae were given 37.5 micrograms of the progestin D-norgestrel for 15 weeks. The study was continued for 8 weeks after withdrawal of treatment. Bile was collected via the duodenal fistula at 7-10 day intervals. During treatment the combined molar percentage of biliary cholesterol of all cats (4.2 +/- 0.4, n = 34) was significantly lower than during the control period (8.2 +/- 1.3, n = 11) [P = 0.001], and remained depressed after treatment withdrawal (5.5 +/- 1.0, n = 11) [P = 0.02]. The molar percentage of phospholipids remained unchanged in all animals, and that of total bile acids increased during treatment in one animal. As assessed by triangular coordinate plotting, the bile of each animal became less saturated with cholesterol during norgestrel administration. These results support the concept that the oestrogen component may be a major factor in the development of increased biliary cholesterol saturation in users of mixed-type oral contraceptives.