Clinical studies on assay for Na-K ATPase in human blood cells. I. Erythrocyte Na-K ATPase assay in patients with thyroid dysfunction and in those with chronic renal failure

Abstract

A number of erythrocyte Na-K ATPase units were measured in 22 patients with hyperthyroid Graves' disease, 3 with primary hypothyroidism, 3 with simple obesity, 13 with chronic renal failure on hemodialysis, and 20 normal controls, using ouabain binding assay as described by DeLuise et al. The number of Na-K ATPase units, derived by maximal binding of 3H-ouabain, was decreased in patients with simple obesity (Mean +/- SD, 0.26 +/- 0.07 pmol/10(9) RBC), as compared with that in normal controls (0.39 +/- 0.10), and a significant negative correlation between the number of the binding sites and the ratio of the measured body weight to the optimal body weight calculated by the modified Broca's method was observed in normal controls and patients with obesity (r = -0.51, p less than 0.05). The results agreed closely with that reported by DeLuise et al and provided validation of our estimates of the erythrocyte Na-K pump units. The maximal 3H-ouabain binding was significantly diminished in patients with hyperthyroid Graves' disease (0.28 +/- 0.07) when compared with that in normal controls, while the bindings were significantly elevated in patients with hypothyroidism (0.91 +/- 0.26). These results were in disagreement with those previously reported by animal studies where Na-K ATPase was found to be stimulated by thyroid hormones. It might be possible to partly explain this discrepancy by the degradation of Na-K ATPase in erythrocytes in addition to the apparent differences between erythrocytes and the other tissues and by the length of time that the tissue was exposed to the action of the hormones. Therefore, erythrocyte from normal controls and patients with hyperthyroid Graves' disease were divided into low and high density portions by a discontinuous 'percoll' density gradient centrifugation, and the bindings of the erythrocytes in two portions were separately measured. The bindings of erythrocyte in the higher density portion, representing relatively old-aged erythrocyte, were diminished to 92 +/- 19% of the bindings of the original whole erythrocytes in normal controls. An even more marked reduction of the maximal bindings of 3H-ouabain in old-aged erythrocytes was observed in patients with hyperthyroid Graves' disease (72 +/- 26%). Moreover, this % reduction based on aging related significantly to serum T4 concentrations in those patients (r = 0.85, p less than 0.05). These findings suggest that the number of erythrocyte Na-K ATPase units may reflect the overall peripheral metabolic state, regulated by thyroid hormone-dependent thermogenesis.(ABSTRACT TRUNCATED AT 400 WORDS)