Serum free triiodothyronine: determinant of the pseudohypercortisolism in obesity?

Eighteen euthyroid, grossly-obese females without characteristics of Cushing's syndrome were studied. The absolute urinary excretion rate of 17- ketogenic steroids was increased in 13 patients, whereas the excretion rate of urinary free cortisol was slightly elevated in four out of 15 patients. The urinary excretion rate of 17-ketogenic steroids was significantly (P less than 0.005) positively correlated (rs = 0.66) with the serum concentration of free triiodothyronine, whereas no correlation with the serum concentration of free thyroxine could be demonstrated. The urinary excretion rate of urinary free cortisol was not correlated with the serum concentration of free triiodothyronine or free thyroxine. The study indicates that the increased absolute urinary excretion rate of 17-ketogenic steroids in obesity is a result of increased cortisol metabolism and may be due to actions to triiodothyronine.