Metabolic changes in lipids of rat plasma and hepatocytes induced by 17α-ethynylestradiol treatment

Abstract Cultured hepatocytes isolated from livers of 17α-ethynylestradiol-treated rats were used to investigate the change of lipid metabolism induced by administration of 17α-ethynylestradiol. Treatment with 17α-ethynylestradiol caused a decrease of rat plasma lipids (free cholesterol, cholesterol ester, triacylglycerol and phosphatidylcholine). No difference in the ability of urea nitrogen synthesis could be demonstrated between cultured hepatocytes isolated from livers of 17α-ethynylestradiol-treated rats and propylene glycol-treated rats (control). Total cholesterol and cholesterol ester contents of cultured hepatocytes isolated from livers of 17α-ethynylestradiol-treated rats were increased in comparison with those of the control. Triacylglycerol content of cultured hepatocytes was not affected by 17α-ethynylestradiol treatment. There was no difference in the composition of lipid content between liver tissues and cultured hepatocytes. These results suggest that hepatocytes isolated from livers maintain the character of livers treated with 17α-ethynylestradiol or livers treated with propylene glycol. Free cholesterol and cholesterol ester synthesis from [ 14 C]acetic acid by cultured hepatocytes isolated from livers of 17α-ethynylestradiol-treated rats were decreased to about 30% of the control. Triacylglycerol and polar lipid (phospholipid) synthesis from [ 14 C]acetic acid were not affected by 17α-ethynylestradiol treatment. Microsomal hydroxymethylglutaryl-CoA reductase activity of rat liver treated with 17α-ethynylestradiol was decreased to about 50% of control. The secretions of free cholesterol, cholesterol ester, triacylglycerol, phosphatidylcholine, apolipoprotein B L and B S by cultured hepatocytes isolated from livers of 17α-ethynylestradiol treated rats were not decreased when compared with the control. Because lipid and apolipoprotein secretions from cultured hepatocytes treated with 17α-ethynylestradiol were not decreased and cholesterol contents of liver tissues and cultured hepatocytes treated with 17α-ethynylestradiol were increased and hepatic microsomal hydroxymethylglutaryl-CoA reductase activity was decreased by 17α-ethynylestradiol treatment, it is suggested that the liver plays an important role in hypolipidemia induced by 17α-ethynylestradiol by increasing the plasma lipid uptake mediated by an increased amount of lipoprotein receptors of liver membranes.