High muscle lipoprotein lipase activity in thyrotoxic patients.

Serum lipoprotein metabolism was studied in 7 women before and after treatment for thyrotoxicosis. Of the lipoprotein lipids, the triglyceride concentration in the low density lipoproteins (LDL) (P less than 0.01) and the cholesterol concentration in both LDL (P less than 0.01) and the high density lipoproteins (HDL) (P less than 0.05) increased significantly during treatment. These changes were accompanied by increases in apolipoprotein B (P less than 0.01) and A-I (P less than 0.05) concentrations in serum. Muscle lipoprotein lipase activity (LPLA) was increased in the thyrotoxic state by 46% (P less than 0.05) compared with the value after the patients had been rendered euthyroid, but adipose tissue LPLA was only 8% higher (ns) in the former state. The capacity for removal of exogenous fat, as determined by the fractional elimination rate (K2) at an iv fat tolerance test, was 23% higher in the thyrotoxic than in the euthyroid state (ns). It is suggested that the increase in muscle LPLA in the thyrotoxic state may be due to enhanced sensitivity to catecholamines. This may contribute to the increased capacity for plasma triglyceride turnover in thyrotoxicosis.