Red Cell Sodium and Ionic Fluxes in Patients with Hyper- and Hypothyroidism

To investigate the status of the Na(+) concentrations [Na(+)]i, K(+) concentrations [K(+)]i and ionic fluxes in red cells of human subjects with abnormal thyroid function, we measured the Na(+)-K(+) pump activity as well as Na(+)-K(+) contransport (CoT), Na(+)-Li(+) countertransport (CTT) and Na(+) passive permeability in erythrocytes of 37 normal subjects, 19 untreated hyperthyroid patients, 12 treated hyperthyroid patients and 9 hypothyroid patients with T4 replacement. The mean [Na(+)]i value in the untreated hyperthyroidism group was significantly higher than that in the normal subjects (p<0.5), but not significantly different from that in the treated hyperthyroidism group. The mean [Na(+)]i value in the hypothyroidism with T4 replacement group, however, was significantly lower than that in the normal group (p<.01). We did not find any significant difference of [K(+)]i in comparing each group. It was found that the Na(+)-K(+) pump activity in erythrocytes was significantly increased in untreated hyperthyroidism (mean; 23.4% above control, p<10(−5)), but there was no significant difference in treated hyperthyroidism and hypothyroid patients with T4 replacement. The rate constant for ouabain-sensitive Na(+) efflux in the hypothyroidism with T4 replacement group was markedly higher than that in normal subjects (p<.01), but not significantly different in the untreated hyperthyroidism group. We observed a significant increase of the Na(+) CoT value in the patients with untreated hyperthyroidism as campared with that of the normal subjects (p<.05), but there was no significant difference in the patients treated for hyperthyroidism and the hypothyroidism with T4 replacement group. However, the rate constant for Na(+)-CoT in the patients with hypothyroidism with T4 replacement was significantly higher than that in normal subjects (p<.05). We observed a marked decrease of Na(+)-Li(+)CTT value in the patients with untreated hyperthyroidism versus that in the normal group (p<.01). Passive Na(+) permeability in the patients with untreated hyperthyroidism was markedly increased (p<.05), and was markedly decreased in the patients with hypothyroidism with T4 replacement compared to normal subjects (p<.01). It can be concluded from these studies that an increase in Na(+)-K(+) pump activity in the patients untreated for hyperthyroidism might then be regarded as a secondary adaptive cellular response to higher [Na(+)]i values due to enhanced passive Na(+) permeability, rather than a direct effect of the thyroid hormone.