1. The activity of ouabain-sensitive Na+,K+-dependent ATPase and ouabain-sensitive ATPase was measured in the microsomal fractions of kidney, liver and heart tissue of Sprague-Dawley rats treated with DOCA (10 mg day−1 kg−1 for 6 days, systolic blood pressure 143 ± 13 mmHg, n = 9) or 6 α-methylprednisolone (100 mg day−1 kg−1 for 6 days, systolic blood pressure 140 ± 19 mmHg, n = 9) and of a control group (systolic blood pressure 124 ± 12 mmHg, n = 9).
2. In the kidney, the ouabain-sensitive Na+,K+-ATPase activity (μmol of phosphate h−1 mg−1 of protein) was increased in the DOCA-treated (33.0 ± 6.9) and in the prednisolone-treated groups (30.8 ± 6.9) compared with that in the control group (26.4 ± 3.4) (P < 0.05). In the liver, the ouabain-sensitive Na+,K+-ATPase activity was elevated in the prednisolone-treated animals only (4.8 ± 1.3 vs 3.1 ± 0.8 in the controls, P < 0.025). The ouabain-sensitive Na+,K+-ATPase activity in heart tissue was similar in all three groups. The ouabain-insensitive ATPase activity was not altered by DOCA or prednisolone in the tissues studied.
3. In a separate study, the activity of the ouabain-sensitive Na+,K+-ATPase in erythrocyte ghosts was found to be elevated in 10 patients with Cushing's syndrome (0.91 ± 0.35 μmol of phosphate h−1 mg−1 of protein) compared with five patients with primary aldosteronism and compared with 12 normotensive control subjects (0.38 ± 0.08) (P < 0.005).
4. These data demonstrate an increased Na-K pump activity in the kidney in mineralocorticoid-induced hypertension. Glucocorticoids in addition activate the Na-K pump in a variety of other tissues. This could partially explain the redistribution of volume from the intracellular to the extracellular space.