Stimulation of hepatic cholesterol 7alpha-hydroxylase activity by administration of an estrogen (17beta-estradiol-3-benzoate) to female rats.

Adult female rats were given daily subcutaneous injections of 17beta-estradiol-3-benzoate, 25 mug/day for twenty days. Rats were then killed under four different experimental conditions: (1) Fasting, killed in the morning (FM), (2) Non-fasting, killed in the morning (NFM), (3) Fasting, killed at night (FN), and (4) Non-fasting, killed at night (NFN). Estradiol induced a three-fold increase in hepatic cholesterol 7alpha-hydroxylase activity in group FM and a significant increase in group NFN. Although increases in 7alhpa-hydroxylase activity might be associated with lower serum cholesterol levels (by increasing the rate of conversion of cholesterol to bile acids), serum cholesterol concentrations were, in fact, elevated in all rats given estradiol.