Effects of Ethynyl Estradiol and Progesterone on Triglyceride Metabolism in the Female Rat*

Abstract

Several lipase activities in adipose tissue and liver as well as triglyceride content in liver and blood were concomitantly investigated in adult female rats after 21 days of oral treatment with ethynyl estradiol (6 .mu.g daily), progesterone (5 mg daily), or the 2 steroids in combination. Treatment with ethynyl estradiol alone markedly decreased the levels of all lipase activities assayed at acid and alkaline pH levels in liver fractions. Decreases in enzyme activities were associated with a 39% increase in blood triglyceride levels. The administration of progesterone alone did not modify triglyceride level in blood or liver lipase activities. The combined regimen of ethynyl estradiol plus progesterone caused maximal decreases in hepatic lipases, a 29% decrease in the triglyceride content of liver, but no change in the level of triglycerides in blood. Studies in adipose tissue showed that treatment with ethynyl estradiol and progesterone, separately or in combination, increased lipoprotein lipase activity to a comparable extent. After treatment with progesterone alone, the increase was observed in the absence of elevated levels of triglycerides in blood. Triacylglycerol lipase activity assayed at pH 7.4 (hormone-sensitive lipase) was not affected by ethynyl estradiol or progesterone alone, but a significant decrease was observed under a combined regimen. None of these hormonal treatments modified the level of monoester lipase activity. These may be major hormonal influences on lipid metabolism in liver and adipose tissue. It cannot be assessed whether these effects are due to the direct action of ethynyl estradiol and progesterone on liver and adipose tissue lipases and/or to some other altered metabolic response(s) secondary to the intake of the steroids.