Effect of estrogens on rat serum cholesterol concentrations: consideration of dose, type of estrogen, and treatment duration.

Abstract

Daily sc injections of estradiol (17β-estradiol-3-benzoate) were given to five groups of adult female rats in doses of 0.25 μg, 2.5 μg, 25 μg, 250 μg, and 2 mg. The rats were bled at 0, 2, 5, and 8 weeks after the initiation of hormone treatment. In a second experiment, five groups of rats received daily sc injections of mestranol (ethynyl estradiol-3-methyl ether) in doses of 0.025,0.25, 2.5, 25, and 250 μg. These rats were bled after 2 weeks of treatment. In the first experiment, estradiol produced a biphasic effect: high doses (250 μg and 2 mg) lowered serum cholesterol concentrations, whereas lower doses (2.5 and 25 μg) increased serum cholesterol concentrations. Mestranol did not elicit this biphasic response, but was found to be 100 times more potent than estradiol with respect to its cholesterol-lowering ability. Both estradiol and mestranol stimulated hypertriglyceridemia at the same dose level: 2.5 μg. At 250 μg, mestranol caused a marked lowering of serum triglyceride concentrations, which was a...