Assay of a Circulating Sodium Pump Inhibitor in Patients with Essential Hypertension and Normotensive Subjects

The plasma levels of a sodium pump inhibitor (Na+PI) were measured by a modified method of Hamlyn et al, using dog kidney Na+, K+-ATPase. When the level of Na+PI was expressed as the % inhibition of the enzyme and compared with that of a control solution, it was found to be 9.0 ± 0.7% in 43 untreated patients with essential hypertension. This was significantly higher than 5.0 ± 0.4% for 56 normotensive subjects (p < 0.01). Male patients with essential hypertension showed the highest mean value of 10.5 ± 1.1%, disclosing an apparent sex difference in the patient group (p< 0.01). Only in female patients was there a significant positive correlation between the inhibitor's level and the mean blood pressure (r = 0.649, p < 0.01). These results provided additional evidence for increased Na+ PI in the plasma of patients with essential hypertension, which might bear an important role in the pathogenesis of the disease.