Alterations of the lipid profile are a well known phenomenon in thyroi
d dysfunction. Thyroid hormones regulate lipid metabolism through vari
ous mechanisms, but a key role is played by the LDL receptor pathway.
Thyroid hormone influence on Lipoprotein (a) (Lp[a]) metabolism is unk
nown; therefore we studied Lp(a) concentrations in a group of 29 hypot
hyroid patients with post-surgical hypothyroidism and in a group of 14
hyperthyroid subjects with Graves' disease before and after the thyro
id 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 tr
iglycerides decreased (from 75 +/- 22 mg/dl to 56 +/- 18 mg/dl and fro
m 182 +/- 87 mg/dl to 112 +/- 42 mg/dl respectively, p<0.001). Lp(a) s
howed minor but not significant variations (median values 80 mg/l befo
re 55 mg/l after treatment, p: N.S.). In hyperthyroid patients total a
nd LDL-cholesterol increased after methimazole treatment (from 148 +/-
49 mg/dl before to 254 +/- 67 mg/dl after and from 87 +/- 38 mg/dl be
fore to 178 +/- 51 mg/dl after, p<0.001). HDL-cholesterol increased (f
rom 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 afte
r 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.