THE ACTIVITY OF CHOLESTERYL ESTER TRANSFER PROTEIN IS DECREASED IN HYPOTHYROIDISM - A POSSIBLE CONTRIBUTION TO ALTERATIONS IN HIGH-DENSITY-LIPOPROTEINS

The activity of cholesteryl ester transfer protein is instrumental in the distribution of cholesteryl ester between lipoproteins in plasma. We measured the activity of cholesteryl ester transfer protein in plasma, designated cholesteryl ester transfer activity, as the rate of cholesteryl ester transfer between exogenous radiolabelled low-density and high-density lipoproteins. The effect of hypothyroidism on cholesteryl ester transfer activity was investigated in 13 athyreotic patients who were studied in the hypothyroid condition and in the euthyroid state, after they had received triiodothyronine supplementation for 33 to 67 days. During hypothyroidism plasma total cholesterol, very-low- plus low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, plasma triacylglycerol, apolipoprotein A1 and B were significantly higher than in the euthyroid state. Cholesteryl ester transfer activity was 15% lower during hypothyroidism (P < 0.02), and an effect of treatment duration was observed. The changes in high-density lipoprotein total cholesterol (P < 0.02), free cholesterol (P < 0.001), triacylglycerol (P < 0.05) and the free cholesterol/cholesteryl ester molar ratio in high-density lipoproteins (P < 0.01) were inversely related to the changes in cholesteryl ester transfer activity. We concluded that thyroid hormone is involved in the regulation of cholesteryl ester transfer protein activity, and that cholesteryl ester transfer protein activity may play a role in the alterations in high-density lipoprotein lipids observed in hypothyroidism.