The Effect of Hyperthyroidism on in Vivo Aging of Erythrocyte Ouabain-Binding Sites and Intracellular Sodium and Potassium

Abstract

The sodium pump activity of erythrocytes is inhibited in hyperthyroidism, whereas in all other cells it is increased. To examine the possibility that thyroid hormones cause an accelerated loss of membrane proteins during in vivo aging, we determined the number of ouabain-binding sites (OBS) in young and old erythrocytes from 13 hyperthyroid and 13 euthyroid subjects. Erythrocytes were separated according to their cell age by centrifugation. In euthyroid subjects, the median number of OBS decreased from 415 (range, 341-551; mean +/- SEM, 440 +/- 19.1) in young cells to 336 (range, 287-453; mean, 340 +/- 13.6) in old cells. In hyperthyroid subjects the median number of OBS decreased from 290 (range, 190-370; mean, 280 +/- 13.3) in young cells to 207 (range, 155-244; mean, 208 +/- 7.5) in old cells. In hyperthyroid subjects the number of OBS of erythrocytes of all ages was lower than that in euthyroid subjects. The ratio of OBS between young and old cells in hyperthyroid subjects (median, 1.27; mean +/- SD, 1.34 +/- 0.16) was similar to that in euthyroid subjects (median, 1.29; mean, 1.30 +/- 0.12). We conclude that these results do not support the hypothesis that in hyperthyroidism there is accelerated loss of sodium pump sites during the lifespan of erythrocytes in circulation.