Journal of Lipid Research, Vol 28, 828-839, Copyright © 1987 by Lipid Research, Inc.
Contraceptive steroids increase cholesterol in bile: mechanisms of action
F Kern Jr and GT Everson
Contraceptive steroids increase the risk of acquiring cholesterol
gallstones. The factors responsible include an increase in cholesterol
saturation of bile and an increase in rate of secretion of cholesterol into
bile. The goal of this study was to investigate the mechanism(s) of these
increases in biliary cholesterol. During the use of contraceptive steroids,
cholesterol saturation of gallbladder bile and the amount of cholesterol
secreted per mole of bile acid increased (P less than 0.05 and P less than
0.02, respectively). Cholesterol absorption, cholesterol synthesis,
chylomicron remnant clearance, and the concentration of plasma and
lipoprotein lipids were not altered by contraceptive steroids. Despite this
apparent lack of effect, important correlations were present during steroid
use. LDL (low density lipoprotein) cholesterol increased as dietary
cholesterol increased (r = 0.58, P less than 0.025). Cholesterol synthesis
correlated directly with VLDL cholesterol concentration (r = 0.64, P less
than 0.01), biliary cholesterol secretion (r = 0.68, P less than 0.01) and
with molar percent cholesterol in bile (r = 0.49, P = 0.06). Chylomicron
remnant clearance also correlated with cholesterol secretion (r = 0.85, P
less than 0.001). As either remnant uptake or synthesis increased, the
effect of the other source of hepatic cholesterol on biliary cholesterol
secretion diminished. These relationships were not observed in the same
subjects when they were not taking the hormones. The findings suggest that
both newly synthesized and dietary cholesterol contribute to the
cholesterol secreted in bile. This is consistent with the hypothesis that
cholesterol for secretion into bile and VLDL is derived from a common
metabolic pool of free cholesterol. It is proposed that contraceptive
steroids exert their effect on biliary cholesterol by increasing
cholesterol entering the pool and/or by inhibiting hepatic ACAT
(acylcoenzyme A:cholesterol acyltransferase) activity, a known effect of
progesterone, so that an increase in free cholesterol entering the pool
leads to an increase in output.