Sex steroid influence on triglyceride metabolism

Triglyceride metabolism was investigated in groups of fed and fasted rats after 21 days of parenteral estradiol (5 mug daily), progesterone (5 mg daily), or the two steroids in combination. Results were compared with control groups receiving an oil solvent alone. In rats given estradiol separately or combined with progesterone, hypertriglyceridemia was uniformly associated with increased plasma triglyceride entry, estimated with the i.v. Triton WR1339 technique. Progesterone alone had no effect on these parameters. Plasma postheparin lipolytic activity (PHLA), adipose, mammary gland, and protamine-resistant liporotein lipases (LPL) were significantly increased in progesterone-treated rats and significantly decreased in rats receiving estradiol with the exception of mammary gland LPL, which was also increased to a slight extent. The combined regimen reduced plasma PHLA and increased protamine-resistant adipose, and mammary gland LPL activity. Sex steroid treatments had minimal effects on plasma glucose and free fatty acid concentrations, but all increased plasma insulin significantly. Hyperinsulinemia did not parallel changes in body weight or other measured parameters. Linear regression analyses revealed that plasma triglyceride concentrations in all fed, treated rats correlated significantly with triglyceride entry but not very uniformly with plasma or tissue LPL activity. We conclude that estradiol, unlike progesterone, has substantial lipemic effects in the rat which relate best to triglyceride entry. Hyperinsulinemia, changes in body weight, plasma PHLA, and tissue LPL activities did not consistently predict the influence of sex steroid treatment on plasma triglyceride concentrations.