Effect of thyroid hormones on human mononuclear leukocyte lysosomal acid lipase activity

Lysosomal acid lipase (LAL), the enzyme which hydrolyzes lipoprotein cholesteryl esters, is under thyroid hormone regulation in experimental animals. To evaluate whether human LAL is also under thyroid regulation, we measured mononuclear leukocyte LAL activity in 31 hypothyroid, hyperthyroid, and euthyroid children under treatment. LAL activity was positively correlated with serum T3 and serum T4 levels, and was significantly higher in hyperthyroid children than in those who were hypothyroid. In another study, 5 adult euthyroid males were given 50 micrograms L-T3 every 8 h for 4 days. Their LAL activities increased significantly after treatment. The data suggest that LAL activity in man, as in experimental animals, is influenced by thyroid hormone status. Hormonal control of LAL activity may be important in the regulation of human cholesterol metabolism.