SYNTHESIS ANS SECRETION OF LIPIDS BY THE LIVER OF HYPOTHYROID RATS

Publisher Summary It has been found that hypothyroidism induced in the rat by the administration of 6-propyl-2-thiouracil (PTU) causes a quantitative and qualitative alteration of plasma lipoproteins consisting of (1) decreased triacylglycerols and increased cholesterol, cholesteryl, and phospholipids in plasma, (2) decreased plasma very low-density lipoprotein concentration (VLDL), (3) increased plasma low-density lipoprotein (LDL) and high-density lipoprotein (HDL) concentration, and (4) the changes of the lipid composition particularly of VLDL and HDL. This chapter discusses a study to ascertain whether these changes reflected an altered rate of synthesis and secretion of lipids by the liver of hypothyroid. In this study, 16 male Wistar rats (8 treated with 6- N -propyl-2-thiouracil (PTU) and 8 pairfed controls) were used. The animals were kept under controlled lightdark cycle. The animals were sacrificed after 25 days of PTU treatment. Livers were rapidly removed, washed in ice cold 0.25 M sucrose, and cut into slices with a razor blade. Liver slices from each animal were incubated in duplicate in 2 ml of Eagle's basal medium at pH 7.4 in the presence of bovine serum albumin and palmitate. To investigate the ex-novo synthesis of lipids, 5 mCi of 3 H-water was added to each incubation flask. In the experiments in which the utilization of fatty acids by the liver slices was measured, 4 μCi of 3 H-palmitate bound to albumin was added to 2 ml of the incubation medium. It was found that in the hypothyroid rats, the radioactivity incorporated into total hepatic lipids was about 50% lower than that found in the control rats.