1. Eighteen hypertensive in-patients were studied during a period of controlled electrolyte intake and, on the basis of determinations of mid-day plasma renin activity (PRA), were classified into low, normal and high renin sub-groups.
2. The responses of systemic arterial pressure, urine sodium excretion rate and PRA to infusion of prostaglandin A1 (PGA1) at a rate of 0.4 μg min−1 kg−1 for 60 min differed among the renin sub-groups.
3. The low renin sub-group displayed the greatest fall in arterial pressure and the greatest increase in sodium excretion rate during infusion of PGA1; PRA was unaffected. The normal renin group demonstrated a lesser reduction of arterial pressure and lesser rise in sodium excretion rate during infusion of PGA1 compared with the low renin group; PRA rose significantly during infusion of PGA1. No significant change in arterial pressure occurred in the high renin group during infusion of PGA1; sodium excretion rate rose less than that observed in the other two groups. Infusion of PGA1 caused striking increases in PRA in the high renin group.
4. The changes in PRA during infusion of PGA1 may explain the differences in arterial pressure and sodium excretion rate observed in the three renin sub-groups. The results also suggest that the role of the vasodilating prostaglandins may differ in the pathogenesis of low, normal and high renin hypertension.