A possible explanation of myxedema and hypercholesterolemia in hypothyroidism: control of lysosomal hyaluronidase and cholesterol esterase by thyroid hormones.

Thyroid hormones control the levels of the lysosomal enzymes, cholesterol esterase and hyaluronidase, in rat liver, skeletal muscle and skin. Activities of these enzymes decreased to approximately 40-50% of normal levels in liver cell fractions, skeletal muscle homogenates and skin homogenates from thyroidectomized rats. Treatment of hypophysectomized rats with L-triiodothyronine increased the activities of cholesterol esterase and hyaluronidase approximately 2-fold in liver cell fractions. The low levels of hyaluronidase and cholesterol esterase in thyroidectomized rats may account for the accumulation of mucopolysaccharides in skin and for the elevation of serum cholesterol levels in hypothyroid patients.