Stimulative Effect of Thyroxine on Lipogenesis and Lipoprotein Synthesis by Cultured Eel Hepatocytes

Abstract

Eel hepatocytes cultured in the presence of 10-8 M thyroxine stimulated phospholipid, cholesterol, and triacylgrycerol syntheses from 14C-acetate, and the increase in phospholipid and cholesterol contents was induced in the thyroxine treated cells. The lipid efflux from the cells to the culture medium was stimulated by 143% in the thyroxine treated cells. Triacylglycerol and phospholipid contents increased significantly in the medium in which cells were cultured with thyroxine. Furthermore, in the thyroxine treated cells the incorporation of 3H-leucine into the apoproteins of the secreted lipoprotein was specifically stimulated by 2-fold compared to that in control cells, but that into other proteins except the secreted lipoprotein was not different between the thyroxine treated and control cells. The incorporation of 14C-acetate into the secreted lipoprotein was also stimulated in the thyroxine treated cells. We conclude that the primary function of thyroxine is to stimulate lipogenesis, and the increase in lipids, particularly phospholipid and cholesterol, in thyroxine treated cells seems to promote the lipoprotein synthesis and secretion.