Reversal of Decreased Human Adipose Tissue Lipoprotein Lipase and Hypertriglyceridemia after Treatment of Hypothyroidism

Abstract

To determine whether adipose tissue lipoprotein lipase (LPL) plays a role in the regulation of triglyceride (TG) metabolism in hypothyroidism, the activity of the enzyme was measured in the subcutaneous adipose tissue of six hypothyroid patients before and during therapy with L-thyroxine. The activity of the activated form of the enzyme, measured as heparin elutable LPL, was lower in hypothyroid patients (1.54 ± 0.93; mU/10⁶ cells; mean ± SD) than in controls (3.26 ± 1.49; P < .02) and increased (163 ± 89%; P < .01) with treatment to levels comparable to the controls. The total activity of LPL, measured in ammonium hydroxide extracts of acetone ether tissue powders, was in the low normal range in the hypothyroid patients (0.68 ± 0.42), but not significantly different from normal (1.10 ± 0.58) and did not increase significantly (92 ± 105%), with treatment. Plasma post heparin lipolytic activity (PHLA) was low in hypothyroidism and increased (111 ± 78%; P < .05) with treatment. These increases in PHLA correlated with the increases in the activity of heparin elutable LPL (r = .88, P < .05). In all patients fasting plasma TG levels decreased (–43 ± 25%; P < .02) after treatment. Serial determination of heparin elutable LPL activity, PHLA, and plasma TG during L-thyroxine treatment revealed a correlation between the per cent changes in PHLA and heparin elutable LPL activity (r = .68, P < .05), an inverse correlation between plasma TG levels and heparin elutable LPL (r = −0.53, P < .05) and no correlation between plasma TG and PHLA (r = −0.05). These results suggest that the low PHLA and hypertriglyceridemia of hypothyroidism are related to low adipose tissue LPL activity. All these parameters return to normal after treatment with Lthyroxine and attainment of euthyroidism.