Journal of Lipid Research, Vol. 23, 1159-1166, November 1982
Copyright © 1982 by Lipid Research, Inc.

Effects of triiodothyronine and propylthiouracil on plasma lipoproteins in male rats

Henry G. Wilcox , William G. Keyes , Thomas A. Hale , Richard Frank , Douglas W. Morgan , and Murray Heimberg

Department of Pharmacology, University of Tennessee Center for the Health Sciences, Memphis, TN 38163 and Department of Pharmacology, University of Missouri School of Medicine,² Columbia, MO 65212

Hyperalphalipoproteinemia, characterized by increased plasma concentrations of apoA-I and of HDL lipid and protein, was observed in rats treated with triiodothyronine (T₃) for 7 days. The increase in the plasma HDL apoproteins was general for apoC, apoE plus A-IV, and apoA-I, as determined by isoelectric focusing. Hypotriglyceridemia, characterized by decreased concentrations of VLDL and apoB, was also observed in the hyperthyroid state. Although in the mildly hypothyroid animals (propylthiouracil-treated), hepatic metabolism of free fatty acid is shifted toward esterification to triglyceride and VLDL formation, as we reported previously, plasma HDL and apoA-I concentrations were not different from control plasma values, while the d 1.006-1.063 g/ml (IDL + LDL) lipoprotein fraction tended to be increased. In general, the proportion of apoE in the (IDL + LDL) fraction of the hypothyroid rat was greater than in controls and hyperthyroid animals, while the proportion of apoE tended to be lower in VLDL from both hypo- and hyperthyroid rats than in VLDL from controls. An enhanced release of apoA-I by perfused livers isolated from rats treated with T₃ was also observed; this enhanced output of apoA-I may explain, in part, the hyperalphalipoproteinemia observed in these rats. The depressed net output of apoA-I in vitro by perfused livers from rats treated with propylthiouracil (PTU) was not expressed in a statistically significant diminished plasma concentration of HDL or apoA-I in the intact animals. Treatment with T₃ also resulted in modification of the content of essential fatty acids in various lipid classes. Linoleic acid residues were significantly reduced and arachidonic acid content was increased in plasma phospholipids and esterified cholesterol in T₃-treated rats. However, the relative fatty acid composition of unesterified fatty acids and triglyceride fatty acids was not altered by T₃ treatment. PTU treatment had no effect on fatty acid distribution in any of the plasma lipids. Secretion of biliary lipids was increased in perfused livers from T₃-treated rats, while treatment with PTU did not affect release of lipids in the bile. These observations suggest a regulatory role for thyroid hormones that determine concentration and composition of plasma HDL and other lipoproteins.—Wilcox, H. G., W. G. Keyes, T. A. Hale, R. Frank, D. W. Morgan, and M. Heimberg. Effects of triiodothyronine and propylthiouracil on plasma lipoproteins in male rats.

Supplementary key words thyroid hormones • apolipoproteins A-I, B, C, and E • biliary lipids • fatty acids • phospholipids • cholesterol • triglycerides

Submitted on August 25, 1981
Revised on June 9, 1982

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