Effect of Estradiol Benzoate on Lipid Metabolism in the Rat

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Abstract
The effect of estradiol benzoate on the concentration of lipids in the plasma, liver and heart and on the incorporation of acetate 1-14C into lipids in these tissues has been studied in adult male rats. Following the daily injection of 1.7 mg of estradiol benzoate for 5 days, estrogen-treated and control animals were injected with 14 [mu]c of sodium acetate 1-14C and killed 2, 4, 12, 24, 48 and 60 hr after the injection. There was a marked decrease in plasma free and esterified cholesterol, plasma phospholipids and the plasma cholesterol/phospholipid (C/P) ratio. The accompanying increase in liver cholesterol ester suggests that estradiol benzoate causes the transfer of cholesterol ester from the plasma to the liver. The increased turnover rate of plasma free cholesterol but lack of increase in liver free cholesterol may be due to an influx of free cholesterol from the plasma to the liver the effect of which is balanced by a decreased rate of hepatic free cholesterol synthesis. There was a decreased incorporation of acetate 1-14C into liver cholesterol ester and free cholesterol. In the plasma cholesterol ester fractions of the estrogen-treated animals there was an increase in the percentage of cholesterol oleate. The decrease in plasma phospholipids was not reflected by significant changes in corresponding liver or myocardial tissue fractions. Estradiol benzoate had no apparent effect on the concentration of tri- and diglycerides in the tissues examined but decreased the plasma monoglyceride and the liver free fatty acid (FFA) concentrations. The incorporation of acetate 1-14C into the plasma FFA was decreased in the estrogen-treated animals. There was also a decreased incorporation of the acetate 1-14C into the plasma triglycerides and the FFA liver tri-, di-and monoglycerides and phospholipids. The specific activity values for myocardial tissue were too low to determine whether estradiol benzoate might have any effect on the lipids in this tissue. There was no apparent effect on myocardial lipid concentrations.