Na-K pump activity in erythrocytes of patients with endogenous and exogenous glucocorticoid excess.

The mechanism of glucocorticoid-induced hypertension is not clarified. Recent data suggest an alteration of active electrolyte transport systems by glucocorticoids. We therefore studied the activities of the Na-K pump by measuring the Na-K-ATPase activity in erythrocyte ghosts and the ouabain-sensitive uptake of rubidium in erythrocytes of patients with Cushing's syndrome and of patients with exogenous glucocorticoid excess after treatment with fluocortolone or ACTH. Na-K-ATPase activity was significantly increased in patients with Cushing's syndrome and in patients treated with ACTH compared to the controls. Similarly, total uptake of 86Rb and the ouabain-sensitive uptake in erythrocytes were found to be above the control range both in patients with Cushing's syndrome and in patients treated with fluocortolone. There was no difference in furosemide-sensitive uptake of 86Rb. The results demonstrate an increased maximal activity of the Na-K pump in patients with glucocorticoid excess.