Time course effect of thyroxine on serum lipoprotein concentrations in hypothyroid subjects.

In order to analyse the time course effect of thyroxine replacement therapy on lipoprotein concentrations, 12 hypothyroid subjects were studied before and repeatedly during therapy. The substitution dose was increased gradually every fourth week until the plasma level of TSH became normal. The concentrations of cholesterol and triglycerides were analysed in whole serum and in the three major lipoprotein fractions VLDL, LDL and HDL. The main abnormality before treatment was an increased LDL cholesterol concentration. Normalization of serum LDL was established at a dose level which normalized TSH. The onset of the effect of thyroxine on LDL cholesterol was rapid and could be noted already after two weeks.