The effects of hypothyroidism and replacement therapy on cholesteryl ester transfer.

To characterize further the impact of thyroid dysfunction on the transport of cholesterol in plasma, we studied plasma lipids and cholesteryl ester transfer (CET) in 10 hypothyroid women before and 3 months after thyroid replacement therapy. CET, estimated as the net mass transfer of CE from HDL to the apolipoprotein B-containing lipoproteins (very low density and low density lipoproteins) was significantly decreased at 4 h (P < 0.05) and 6 h (P < 0.001) when the patients were hypothyroid (T4, 2.01 +/- 1.4; TSH, 55.5 +/- 39.9 microIU/mL) and increased to normal levels after hormone replacement and restoration of eumetabolism. Plasma lipid levels in the hypothyroid state closely resembled those in a female reference group, although total plasma cholesterol fell significantly [pretreatment, 218 +/- 36 vs. posttreatment, 192 +/- 49 (P < 0.025); control, 218 +/- 28 mg/dL (mean +/- SD)] after treatment. Concentrations of cholesteryl ester transfer protein (CETP) were unchanged (pretreatment, 2.35 +/- 0.83 vs. posttreatment, 2.30 +/- 1.19 mg/dL). The results of recombination studies using different lipoprotein fractions suggest that decreases in CET during hypothyroidism may be secondary to acceptor lipoprotein (low density and very low density lipoprotein) changes in the hypothyroid state and not to changes in the concentration of CETP itself.