Effect of a single dose of dexamethasone on serum concentrations of thyroid hormones.

In ten euthyroid subjects, in whom endogenous thyroid-stimulating hormone (T.S.H.) production was suppressed by oral thyroxine (T4), a single dose of dexamethasone resulted in reduced serum-3,3'5-triidothyronine (T3) concentration and raised serum-3,3',5'-triiodothyronine (reverse T3 or rT3) concentration after 24 h. These changes were not related to changes in free hormones or binding proteins. Adrenal glucocorticoids may have a pathophysiological role in modulating the peripheral metabolism of thyroid hormones in stress.