Erythrocyte ouabain binding capacity as a possible cellular index of hyperthyroid status

Erythrocyte sodium fluxes, ouabain binding sites, and Na+,K(+)-ATPase activity in hyperthyroidism

Erythrocyte sodium pump activity, in contrast to other tissues, is decreased in hyperthyroidism. In order to examine whether the effect of thyroid hormones on erythrocytes is part of a generalized effect on other transport pathways, we measured sodium pump activity, Na+,K(+)-adenosine triphosphatase (ATPase) activity, ouabain binding sites, bumetanide-sensitive sodium potassium cotransport (SPC), sodium lithium countertransport (SLC), and ouabain- and bumetanide-insensitive passive efflux of sodium (sodium "leak") in erythrocytes from 20 healthy subjects and 18 untreated hyperthyroid subjects. Sodium pump activity (ouabain-sensitive sodium efflux rate constant), Na+,K(+)-ATPase activity, and the number of ouabain binding sites were lower and the erythrocyte sodium content was higher in hyperthyroid subjects. The rate constants of erythrocyte SPC (P less than .05), SLC (P less than .001), and sodium "leak" (P less than .05) were also significantly lower in hyperthyroidism. In 11 of the hyperthyroid subjects, sodium flux measurements were repeated after 20 weeks of treatment. Sodium pump activity, the number of ouabain binding sites, and the rate constant for SLC increased. These results suggest that the effect of thyroid hormones on the erythrocyte sodium pump is part of a generalized effect on membrane proteins, rather than a specific effect.

The haematology of hyperthyroidism: abnormalities of erythrocytes, leucocytes, thrombocytes and haemostasis

The abnormalities of erythrocytes, leucocytes, thrombocytes and coagulation that have been reported, particularly in more recent years, to be associated with hyperthyroidism are surveyed. Several areas are highlighted where further investigations could lead to clinically useful insights, improved information about the haematological processes involved or to a better understanding of thyroid hormone action.

Erythrocyte thermogenesis in hyperthyroid patients: microcalorimetric investigation of sodium/potassium pump and cell metabolism

Erythrocyte thermogenesis was studied by microcalorimetry in 11 patients before and after treatment for hyperthyroidism. Cell heat production rate and intracellular Na+ and K+ levels were measured in plasma suspensions of erythrocytes with and without specific inhibition of Na/K ATPase by ouabain. The ouabain induced change in the heat production rate (the Na/K pump thermal power); the erythrocyte intracellular Na+ content and the ouabain sensitive Na+ transport were used to estimate the Na/K pump function. The mean value for heat production rate was 131 +/- 4 mW/L erythrocytes before treatment, which is significantly higher than in euthyroid subjects. A significant decrease (P less than 0.01) to normal levels was recorded following therapy. This decrease, as determined in samples with ouabain, correlated to changes in serum levels of triiodothyronine, T3, (r = .74, P less than 0.01). The Na/K pump thermal power was 11 +/- 2 mW/L erythrocytes (8 +/- 2% of total heat production rate) before and 9 +/- 2 mW/L erythrocytes (8 +/- 2%) after treatment. These two values were not different from those obtained in euthyroid subjects. The erythrocyte Na+ content decreased from 9.9 +/- 2.1 to 4.9 +/- 0.5 mmol/L erythrocytes (P less than 0.001) following normalization of thyroid function. The decrease in intracellular Na+ concentration correlated to the decrease in serum T3 levels, but only when calculated from the data obtained in samples with ouabain (r = .60, P less than 0.05). The relative increase in intracellular Na+ concentrations following addition of ouabain was significantly lower (P less than 0.05) before than after treatment for hyperthyroidism, 37 +/- 10% and 61 +/- 5%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Alteration in activities of Na,K, ATPase, sugar transport, and insulin receptors in erythrocytes from hyperthyroid patients

To investigate the selectivity of the reduction in Na,K, ATPase activity in erythrocytes from patients with hyperthyroidism, we have assessed cytochalasin B-sensitive galactose uptake and insulin receptors as well as Na,K, ATPase-mediated rubidium uptake in erythrocytes from 11 patients with hyperthyroidism, 5 patients after treatment and 11 normal controls. There was a significant reduction in the Vmax values for rubidium uptake and the number of insulin receptors (23% and 20% below control, respectively), whereas there was a significant increase in the Vmax and Km values for galactose uptake (49% and 30% above control) and also in the average affinity of insulin receptors. The alterations both in rubidium and galactose transport activities were reversible with effective treatment of hyperthyroidism. The magnitude of alterations in the Vmax for rubidium uptake correlated inversely (r = -0.537 P less than 0.01, n = 16) and the Vmax and Km for galactose uptake correlated positively (r = 0.597 P less than 0.02 and r = 0.553 P less than 0.05, respectively) with serum T4 level. No correlation was found between the number of insulin receptors and serum IRI or T4 levels. These results suggest that the reduction in Na,K, ATPase activity observed in erythrocytes from hyperthyroid patients is not selective to this enzyme, but rather a reflection of widespread alterations of erythrocyte cell-surface proteins.