Effect of short term triiodothyronine administration on human leukocyte Rb(K) influx and Na efflux

The effect of short term T3 administration on leukocyte ouabain-sensitive 86Rb(K) influx and Na efflux in normal subjects was investigated. At a dose of 60 micrograms daily for 7 days, T3 induced a significant increase in leukocyte 86Rb(K) influx and a significant fall in plasma K concentrations. Plasma and intracellular Na concentrations did not change. [3H]Ouabain binding, a measure of Na-K ATPase units, did not change. A week after T3 administration, 86Rb(K) influx, Na efflux, and plasma K concentrations were normal. In a series of five hyperthyroid patients, both ouabain-sensitive 86Rb influx and [3H]ouabain binding were significantly greater than in normal subjects. We conclude that T3 stimulates 86Rb(K) influx and Na efflux by leukocytes in vivo independently of [3H]ouabain binding and that this increase is rapidly reversible. However, in hyperthyroid patients both 86Rb influx and [3H]ouabain binding are increased, probably due to prolonged exposure to thyroid hormone excess.