A conjugated equine estrogen with differential effects on uterine weight and plasma cholesterol in the rat.

Our purpose was to determine the effect of Premarin (conjugated estrogens) and three of its component estrogens on uterine weight and plasma cholesterol concentrations in surgically menopausal female rats. A randomized trial of Premarin and three component estrogens--estrone sulfate, 17 alpha-estradiol sulfate, and 17 alpha-dihydroequilenin sulfate--in female rats after oophorectomy. High-dose Premarin and high- and middle-dose estrone sulfate significantly increased uterine weight relative to untreated controls (high-dose Premarin, 243.34 +/- 0.15 mg; high-dose estrone sulfate, 376.1 +/- 9.36 mg; middle-dose estrone sulfate, 249.0 +/- 6.34 mg; untreated controls, 124.63 +/- 3.17 mg; for all, p < 0.05). 17 alpha-Dihydroequilenin sulfate had no effect on uterine weight relative to controls. All 17 alpha-dihydroequilenin sulfate doses markedly reduced total plasma cholesterol concentrations versus controls (34.02 +/- 3.44 mg/dl, 32.49 +/- 1.08 mg/dl, and 71.55 +/- 5.16 mg/dl vs 90.44 +/- 1.06 mg/dl; for all, p < 0.02). 17 alpha-Dihydroequilenin sulfate had a more pronounced effect on low- or very-low-density lipoprotein cholesterol than total plasma cholesterol or high-density lipoprotein cholesterol concentrations. 17 alpha-Dihydroequilenin sulfate reduced total plasma cholesterol concentrations without inducing uterine growth in rats after oophorectomy.