Abstract
To determine whether the low density lipoprotein (LDL) receptor pathway is involved
in the catabolism of plasma lipoprotein (a) [Lp(a)], serum lipids, Lp(a), and LDL
receptor activity were measured in seven patients with hyperthyroidism before and
after methimazole treatment given hyperthyroidism is associated with enhanced LDL
receptor activity. LDL receptor activity in patients was estimated by the equation
using the serum concentrations of apolipoprotein (apo) B and C-II. When euthyroidism
was achieved after treatment, not only did serum total cholesterol, high density lipoprotein-cholesterol,
apo B, and LDL-cholesterol (LDL-Ch) levels rise, but Lp(a) significantly increased
and calculated LDL receptor activity significantly decreased. The changes in LDL receptor
activity were significantly correlated with the changes in LDL-Ch as expected, but
not with changes in Lp(a). These results suggest that the serum concentration of Lp(a)
is lowered in hyperthyroidism, probably by a mechanism other than the enhanced activity
of the LDL receptor, and that the LDL receptor pathway is involved in the catabolism
of Lp(a) to a limited extent.
Key words
Lipoprotein(a) - LDL Receptor - Hyperthyroidism - Apo B - Apo C-II
