Lipoprotein (a) in thyroid dysfunction before and after treatment.

Alterations of the lipid profile are a well known phenomenon in thyroid dysfunction. Thyroid hormones regulate lipid metabolism through various mechanisms, but a key role is played by the LDL receptor pathway. Thyroid hormone influence on Lipoprotein (a) (Lp[a]) metabolism is unknown; therefore we studied Lp(a) concentrations in a group of 29 hypothyroid patients with post-surgical hypothyroidism and in a group of 14 hyperthyroid subjects with Graves' disease before and after the thyroid function was normalized by treatment. In hypothyroid patients total and LDL-cholesterol markedly decreased after T4 treatment (342 +/- 78 mg/dl before and 193 +/- 46 mg/dl after; 225 +/- 72 mg/dl before, 111 +/- 43 mg/dl after respectively, p < 0.001). Also HDL-cholesterol and triglycerides decreased (from 75 +/- 22 mg/dl to 56 +/- 18 mg/dl and from 182 +/- 87 mg/dl to 112 +/- 42 mg/dl respectively, p < 0.001). Lp(a) showed minor but not significant variations (median values 80 mg/l before 55 mg/l after treatment, p: N.S.). In hyperthyroid patients total and LDL-cholesterol increased after methimazole treatment (from 148 +/- 49 mg/dl before to 254 +/- 67 mg/dl after and from 87 +/- 38 mg/dl before to 178 +/- 51 mg/dl after, p < 0.001). HDL-cholesterol increased (from 39 +/- 9 to 50 +/- 15, p < 0.01) while triglycerides were unchanged. Lp(a) levels slightly rose (median values 57 mg/l before 84 mg/l after treatment, p < 0.05). These data suggest that the influence of thyroid hormones on Lp(a) metabolism is of minor entity and probably does not operate through the LDL receptor pathway.