Effects of Induced Hyperthyroidism on Steroid Metabolism in Man

Abstract

ABSTRACT Five normal men were made clinically hyperthyroid by administration of T3, 300 μg daily for three weeks. In 3 men, estradiol metabolic clearance rates and plasma concentration of testosterone-estradiol binding globulin (TeBG) were measured during the control periods, during fluoxymesterone administration, and during hyperthyroidism. Plasma LH and testosterone concentrations were determined throughout all studies in 5 men. Treatment with T3 caused a 7–8 fold increase in TeBG; a 2–3 fold increase in plasma testosterone; no change in CBG, and no change in in 2 patients and a 25% decrease in the third. The marked rise in TeBG during T3 treatment was not accompanied by a corresponding large fall in hence it is most likely that hyperthyroidism increased the rate of metabolism of estradiol. In spite of a 2–3 fold increase in plasma testosterone, plasma LH increased during T3 treatment, indicating that it is the non-TeBG-bound testosterone that determines LH release. The plasma half-life of TeBG was esti...