Reduced Plasma Thyrotropin Response to Thyrotropin Releasing Hormone After Dexamethasone Administration in Normal Subjects

Abstract

In order to elucidate at which level glucocorticoids act in inhibiting thyrotropin (HTSH) secretion in man, 200µgm of synthetic thyrotropin releasing hormone (TRH) were injected intravenously in 8 normal subjects before and after oral administration of dexamethasone, 1.0 mg every 8 hr for 5 consecutive days. After dexamethasone, the mean basal plasma HTSH levels were significantly reduced, as was the plasma HTSH response to TRH: this reduced increase occurred in all subjects. The glucocorticoid did not alter significantly the serum thyroxine and triiodothyronine uptake. The data obtained are compatible with a direct inhibiting action of dexamethasone at pituitary level.