1. Eight patients with essential hypertension were challenged with an infusion of 32 mmol of potassium chloride in saline before and after control of their blood pressure by the angiotensin converting-enzyme (ACE) inhibitor enalapril.
2. The potassium infusion was associated with similar increases in plasma aldosterone before and during enalapril treatment, although absolute aldosterone levels were lower after enalapril treatment despite higher plasma potassium levels.
3. The handling of the potassium load was altered by ACE inhibition. The area under the curve of a plot of the increase in plasma potassium above baseline against time was greater during enalapril treatment than during treatment with placebo.
4. These observations contrast with data obtained in the dog and demonstrate that in patients with essential hypertension stimulation of aldosterone secretion by potassium is not abolished by chronic suppression of plasma angiotensin II; and although plasma aldosterone remains at a lower level, the homoeostasis of plasma potassium is only mildly impaired.