Reversal of decreased hepatic lipase and lipoprotein lipase activities after treatment of hypothyroidism

Abstract

Plasma lipoprotein concentrations, activities of hepatic lipase and lipoprotein lipase in post-heparin plasma, and the removal rate of exogenous triglyceride were measured in 14 patients with severe primary hypothyroidism before and after 4 mo. substitution therapy with l-thyroxine. Before treatment plasma LDL [low density lipoprotein] cholesterol concentrations were markedly increased while HDL [high density lipoprotein] cholesterol and plasma triglycerides were in the upper reference range. Thyroxine substitution led to a normalization of LDL cholesterol in all patients. Plasma triglycerides and HDL cholesterol decreased moderately. Hepatic lipase and lipoprotein lipase activities were initially reduced, but increased significantly after treatment by .apprx. 170% and 55%, respectively. The increase in hepatic lipase activities was significantly correlated to the increase in serum triiodothyronine levels and also to the reduction in LDL cholesterol concentrations. The decrease in LDL cholesterol was also significantly correlated to the increase in serum triiodothyronine concentration. In 2 patients initially treated with triiodothyronine, the activity of hepatic lipase, but not that of lipoprotein lipase, increased after 24 and 48 h; however, LDL cholesterol levels decreased substantially. The reduced activities of hepatic lipase and of lipoprotein lipase are important pathogenetic factors for the dyslipoproteinemia occurring in hypothyroidism, and the low serum triiodothyronine concentration is of major importance for the alterations in lipid transport.