Control of plasma renin activity in chronic stable renal disease

Plasma renin activity (PRA) was determined on 70 subjects in clinical salt and water balance with stable glomerular filtration rate (GFR) ranging from 4 to 189 ml. per minute. Average 24-hour urine sodium excretion was obtained for 3 to 5 days prior to the study. The relationship between PRA and daily sodium excretion present in the low GFR group (GFR less than 80 ml. per minute) was similar to that obtained in the high GFR group (GFR greater than 80 ml. per minute). Hypertensive and normotensive subjects also demonstrated a relationship between PRA and daily sodium excretion although the values for PRA tended to be lower in the hypertensive subjects. In 32 subjects, following water hydration, a hypotonic saline load was administered. PRA values fell in 26 subjects, remained unchanged in 5, and increased in 1 subject. The decrease in PRA was not related to the level of GFR and was similar in the normotensive and hypertensive low GFR group. The level of PRA before or after the saline load did not relate to the level of distal sodium supply as estimated by CH2O/GFR + CNA/GFR. In subjects with chronic stable renal disease PRA responds appropriately to variations in daily salt intake and acute volume expansion with saline. Hypertensive subjects with impaired renal function appear to be able to vary PRA levels as do normotensive subjects with impaired renal function.