Ouabain-binding sites of reticulocytes from guinea pigs treated with triiodothyronine

To understand the mechanism of reduced number of sodium pump units (ouabain-binding sites, OBS) of erythrocytes in hyperthyroidism, OBS of reticulocytes from guinea pigs injected with triiodothyronine (T3) were measured. Reticulocytosis was induced in 16 guinea pigs by withdrawing 6 to 10 mL of blood for 5 days followed by 2 days rest. T3 (50 micrograms/100 g body weight) was injected into seven animals on days 4 and 6, and the remainder were injected with solvent for T3. Reticulocyte-rich blood was withdrawn on day 8. Oxygen consumption determined 24 hours after the first injection of T3 was 30% higher in the T3-treated animals (P less than .001). OBS of reticulocytes from control animals were sixfold higher than that of mature erythrocytes. Reticulocytes from T3-treated guinea pigs had significantly lower OBS (P less than .01) compared with controls. We conclude that the loss of OBS induced by thyroid hormones probably occurs during the formation of reticulocytes.