Plasma cholesteryl ester transfer protein activity is high in infants and is not affected by thyroid hormones

We investigated the effects of thyroid dysfunction on cholesteryl ester transfer protein (CETP) by studying plasma CETP activity in hypothyroid infants before and after they were rendered euthyroid by L-thyroxine (LT4) replacement therapy. To exclude environmental factors possibly affecting plasma CETP activity, we selected hypothyroid infants to study plasma CETP activity. Plasma CETP activity was measured as the rate of radiolabeled cholesteryl ester transfer from high-density lipoprotein (HDL) to serum apolipoprotein B (apo B)-containing lipoproteins in plasma from 14 hypothyroid infants before and 2 months after LT4 replacement, 23 normal infants, and 61 normal adults. Relationships between CETP and thyroid hormones were examined separately in the 14 hypothyroid infants and 32 euthyroid infants, including the 14 above-described hypothyroid infants and an additional 18 treated hypothyroid infants. Serum levels of thyrotropin (TSH), free thyroxine (FT4), and free triiodothyronine (FT3) were also determined on an autoanalyzer system in our hospital. In contrast to previous reports, we found no differences in plasma CETP activity between hypothyroid infants and age-matched normal infants. LT4 substitution did not cause any changes in plasma CETP activity after therapy. Plasma CETP activity showed no correlation with serum TSH, FT4, and FT3 levels. Both hypothyroid and normal infants were found to have significantly higher plasma CETP activity than normal adults. From these results, we conclude that in infants thyroid hormones do not affect plasma CETP activity, and normal infants have high plasma CETP activity, compared with normal adults. Copyright (C) 2000 by W.B. Saunders Company.