The human leucocyte sodium pump in adrenocortical insufficiency

In view of the known effects of cortisol and related compounds on sodium balance, we examined leucocyte 22Na+ efflux in patients with adrenocortical insufficiency. The ouabain-sensitive 22Na+ efflux rate constant, which reflects sodium pump activity, was lowered in secondary hypoadrenalism (mean 1.95 +/- SD 0.25 vs 2.33 +/- 0.45 h-1, P less than 0.002, n = 6). Patients with hypoadrenalism also had higher intracellular sodium content (mean 34.9 +/- SD 3.5 vs 27.8 +/- 9.5 mmol/kg dry weight, P less than 0.008) and lower intracellular potassium to sodium ratios (mean 9.7 +/- SD 0.7 vs 12.9 +/- 3.6, P less than 0.001). These defects in cellular sodium balance were corrected following replacement therapy with cortisol, prednisolone or dexamethasone. In-vitro incubation of normal leucocytes with 5-20 nmol/l dexamethasone led to an increase in the Na+/K+-ATPase activity. The effect of cortisol and related compounds on the distribution of sodium between intra- and extra-cellular fluid may be mediated by their action on the sodium pump.