The Failure of Physiologic Doses of Reverse T3to Effect Thyroid-Pituitary Function in Man

Abstract

Reverse T₃ (3,3′,5′-triiodothyronine, rT₃), a major product of the peripheral monodeiodination of thyroxine (T₄), was administered to normal male volunteers in doses sufficient to sustain an elevated serum rT₃ concentration similar to that frequently observed in patients with nonthyroidal illness. No changes in basal serum T₄, T₃, TSH and prolactin concentrations, nor in the T₃, TSH and prolactin responses to iv TRH were observed during rT₃ administration. These findings suggest that physiologic increases in serum rT₃ concentration probably do not inhibit T₄ to T₃ conversion or the anterior pituitary TSH and prolactin responses to thyrotropin-releasing hormone (TRH).