OXYGEN CONSUMPTION AND THYROXINE DEIODINATION BY HUMAN LEUKOCYTES*†

Abstract

Homogenates of white blood cells from 31 euthyroid persons, 16 thyrotoxic patients and 3 hypothyroid patients were incubated with labeled thyroxine. Respiration and deiodination of thyroxine were measured. The oxygen consumption of white-cell homogenates from 31 euthyroid subjects ranged from 0.150 to 0.545 and averaged 0.334[plus or minus] 0.1 ul. O2/1O6 cells/hour. Oxygen consumption by leukocytes from thyrotoxic patients was significantly increased, and in 16 thyrotoxic subjects ranged from 0.21 to 0.76 and averaged 0.444[plus or minus] .15 [mu]l. O2/1O6 cells/hour. The oxygen consumption by leukocytes from 3 hypothyroid subjects averaged 0.313 [mu]l. O2/IO cells/hour. Deiodination of labeled thyroxine by cells from 10 euthyroid women ranged from 7 to 39 per cent of the total radioactivity and averaged 19[plus or minus].16 per cent. Deiodination by cells from 7 thyrotoxic women was significantly greater, and ranged from 15 to 57 per cent, averaging 44+14.5 per cent. The average deiodination by leukocytes from 3 hypothyroid patients was only 7.3 per cent[long dash]below the euthyroid mean. The deiodinase of human leukocytes is active at physiologic pH 7.4, is thermolabile (being decreased by heating to 60-70[degree] C for thirty minutes), and is aerobic (being inactive in an atmosphere of nitrogen). It is inhibited by 10-3 NaCn and 0.1 M HgCl2, and requires both ATP and DPN for maximum activity. The use of the leukocyte as a test organ may permit direct studies of peripheral thyroid hormone metabolism in man.