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)