A possible competition between 5'-monodeiodination of thyroxine and the respiratory burst in human granulocytes.

Thyroxine (T4) pretreatment of A 23187-stimulated human granulocytes in 10(-5)-10(-6) M concentration range inhibited the superoxide anion production of these cells. T4 increased the level of oxidized form of glutathione, whereas the intracellular level of the reduced form decreased. A similar alteration in the ratio of the oxidized to reduced forms of glutathione was detected in granulocytes during yeast cell phagocytosis. In addition, conversion of T4 to triiodothyronine (T3) was also inhibited during phagocytosis. A possible competition between 5'-monodeiodination of T4 and the oxidative burst of human granulocytes is discussed.