CHANGES IN SERUM LIPOPROTEIN(A) AND LIPIDS DURING TREATMENT OF HYPERTHYROIDISM

Because of suggestions that thyroid hormones modulate serum lipoprotei n(a) [Lp(a)] concentration, we evaluated prospectively the serial chan ges of serum ip(a), measured as apolipoprotein(a) [apo(a)], and other lipoproteins in 40 subjects with hyperthyroidism treated with radioact ive iodine (RAI) therapy. Hyperthyroid patients had lower (P <0.001) c oncentrations of apo(a), total cholesterol CTC), low-density lipoprote in cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), and apo B, but higher apo A-I concentrations compared with age-matched controls [geometric mean (range)]; apo(a) 81 (17-614) vs 187 (17-1808 IU/L): TC 4.07 +/- 0.8 vs 5.22 +/- 1.00 mmol/L (mean +/- SD); LDL-C 2 .47 +/- 0.89 vs 3.40 +/- 0.88 mmol/L; HDL-C 1.05 +/- 0.33 vs 1.24 +/- 0.34 mmol/L; apo B 0.66 +/- 0.23 vs 1.13 +/- 0.34 g/L, and apo A-I 2.0 7 +/- 0.42 vs 1.46 +/- 0.28 g/L, respectively. Euthyroidism was associ ated with normalization of serum TC, LDL-C, and apo B within 1 month o f treatment. However, apo(a) required 4 months to normalize, and HDL-C and apo A-I were still abnormal 6 months after RAI. Serum apo(a), TC, LDL-C, and apo B were negatively correlated with serum thyroxine (T-4 ), free thyroxine index, and triiodothyronine (T-3) and positively cor related with thyrotropin during the transitional period from hyperthyr oidism to euthyroidism. Parallel changes of these lipoproteins and thy roid hormones were also observed after treatment of hyperthyroidism. I n conclusion, thyroid hormones do modulate lipoproteins, particularly Lp(a). The delay in normalization of apo(a) but not LDL suggests an ef fect on apo(a) production rather than on LDL removal.