Serum lipids and apolipoproteins A-I, A-II and B in primary hypothyroidism before and during treatment.

Serum lipids and apolipoproteins (apo) A-I, A-II, and B were measured in twenty-four patients with severe primary hypothyroidism (Thyrotropin above 40 mU/l), before and during 1-thyroxine treatment. Apo A-I, A-II, and B were assayed by immunonephelometry, using monospecific antisera. The serum levels of total cholesterol (TC), of low-density lipoprotein cholesterol (LDLc), and of the major LDL apoprotein, apo B, were markedly increased in the untreated hypothyroid patients compared to the values during therapy (TC: mean +/- SD, 8.87 +/- 2.9 v. 5.48 +/- 1.6 mmol/l; LDLc: 6.66 +/- 2.6 v. 3.78 +/- 1.4 mmol/l; apo B: 1.66 +/- 0.48 v. 1.14 +/- 0.37 g/l; P less than 0.00001 for all variables). High-density lipoprotein cholesterol (HDLc) was slightly higher before than during therapy (1.58 +/- 0.7 v. 1.31 +/- 0.4 mmol/l; P less than 0.05), while the main HDL apoprotein, apo A-I, was significantly elevated (1.49 +/- 0.42 v. 1.13 +/- 0.27 g/l; P less than 0.0002). The increase of the second major HDL apoprotein, apo A-II, was less pronounced (0.33 +/- 0.1 v. 0.30 +/- 0.08 g/l; P less than 0.022). The apo A-I to apo A-II ratio, which reflects the relative concentrations of the HDL subfractions HDL2 and HDL3, was significantly higher before than during treatment (P less than 0.0006). Serum triglyceride levels were moderately elevated in the untreated hypothyroid patients (1.34 +/- 0.6 v. 0.95 +/- 0.4 mmol/l; P less than 0.002). The small decrease in body weight during therapy did not correlate with the changes of the various lipid and apoprotein parameters.(ABSTRACT TRUNCATED AT 250 WORDS)