Lecithin: cholesterol acyl transfer rate in hypothyroidism and hyperthyroidism.

The initial rate of lecithin: cholesterol acyl transferase and serum concentration of lipids were determined in euthyroid, hypothyroid and hyperthyroid subjects. In hyperthyroid subjects, the serum levels of total and free cholesterol were significantly lower than in normal subjects and the fractional lecithin: cholesterol acyl transfer rate was significantly higher than in normal subjects. The molar lecithin: cholesterol acyl transfer rate was also higher than in normal subjects, but not significantly. The free cholesterol/total cholesterol ratio in hypothyroid females and the serum levels of triglyceride and free fatty acid in hypothyroid male were significantly higher than in normal subjects. The fractional lecithin: cholesterol acyl transfer rates in hypothyroid females were significantly lower than in normal females. After treatment of the thyroid disease the fractional and molar lecithin: cholestorol cholesterol acyl transfer rate approached the normal values. There was a positive correlation between fractional and molar lecithin: cholesterol acyl transfer rate and thyroxine. These results suggest that thyroid hormone influences the cholesterol esterification through the activation of lecithin: cholesterol acyltransferase.