1. Nifedipine (20 mg) was given by mouth to seven patients with moderate essential hypertension receiving a low, normal or high sodium intake. The drug produced an important hypotensive effect. Normal sodium intake enhanced the hypotensive action of the drug compared with that during the low and high sodium regimens. Blood pressure remained significantly lower 3 h after drug ingestion.

2. Increases in heart rate and plasma renin activity under all conditions reflected enhanced adrenergic activity.

3. A short-term natriuresis followed nifedipine ingestion in spite of increased aldosterone excretion during the low sodium diet and a decrease in urinary kallikrein during the low and high sodium diets.

4. Nifedipine increased urinary volume only during the high sodium intake.

5. Apart from vasodilatation, nifedipine induces important changes in neurogenic, renal and adrenal mechanisms that regulate blood pressure homoeostasis. Different conditions of sodium balance modulate most of these effects.

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