Erythrocyte Na+/K+-ATPase is increased in subjects with subclinical hypothyroidism

In erythrocytes of patients with overt hyperthyroidism, the number of ouabain-binding sites and the activity of the Na+/K+-ATPase have been demonstrated to be decreased, whereas the opposite is true in patients with overt hypothyroidism. No information has been reported on the status of the Na+/K+-ATPase in subclinically hypothyroid (Sub Hypo) patients. design We investigated the number of ouabain-binding sites and Na+/K+-ATPase activity in erythrocytes of chronic Sub Hypo subjects. patients and methods We measured 3H-ouabain-binding sites in erythrocytes from 15 patients with subclinical hypothyroidism, and compared with those found in 17 normal subjects (N), seven with overt hypothyroidism (Hypo) and 10 with overt hyperthyroidism (Hyper). The activity of the sodium pump was assessed by measuring ouabain-sensitive 86Rb uptake in a subpopulation of the same groups. results The number of ouabain-binding sites in Sub Hypo patients (252 ± 17; mean ± SEM) was significantly higher (P < 0·02) than in Hyper (135 ± 12) and N (203 ± 10) groups, whereas it was not significant different from Hypo (293 ± 31). There was a positive correlation between the number of ouabain-binding sites and TSH concentrations (P < 0·002) when Sub Hypo and N groups were considered together. There was a negative correlation between the number of ouabain-binding sites and free thyroxine (FT4; P < 0·0001) and free triiodothyronine (FT3) concentrations (P < 0·001) when all subjects were considered. Ouabain-sensitive 86Rb uptake (picomoles 86Rb/h 106 cells) in Sub Hypo was significantly higher (4·2 ± 0·5) when compared with N (2·5 ± 0·2, P < 0·01) and Hyper (2·5 ± 0·5, P < 0·02). conclusions Erythrocytes of subclinically hypothyroid patients show a significant increase in the number of ouabain-binding sites and in ouabain-sensitive 86Rb uptake. The state of erythrocyte Na+/K+-ATPase may therefore represent a biochemical marker of subclinical hypothyroidism.