1. In order to examine the potential role of atrial natriuretic factor in modulating the increased sodium excretion per nephron in chronic renal failure, we studied 12 uraemic patients on the last day of two successive 7 day periods during which their sodium intake was 100 and 20 mmol of sodium/day, respectively.
2. There was a parallel decrease from 6.31 ± 0.75 to 2.17 ± 0.32% in the fractional excretion of filtered sodium and from 234.4 ± 74.9 to 80.6 ± 20.3 pg/ml (supine position) or 140.1 ± 43.6 to 60.7 ± 14.6 pg/ml (upright position) in plasma atrial natriuretic factor. Both parameters were significantly correlated during the two periods of different sodium intake (P <0.05). The ratio of plasma guanosine 3′:5′-cyclic monophosphate to plasma creatinine changed proportionally to plasma atrial natriuretic factor. Plasma aldosterone and plasma renin activity increased during the sodium-depleted period but only plasma renin activity was significantly correlated with fractional excretion of filtered sodium.
3. The predominant role of atrial natriuretic factor compared with that of aldosterone in the renal response to varying sodium intake is suggested both by regression analysis and by the effect of 5 day's treatment with a converting enzyme inhibitor (enalapril) in six other uraemic patients on a normal (100 mmol/day) sodium intake. Such treatment, although resulting in a significant increase in plasma renin activity and a significant decrease in plasma aldosterone, at least in the supine position, did not modify the fractional excretion of sodium and plasma atrial natriuretic factor.
4. Taken together, these results suggest a role for plasma atrial natriuretic factor in promoting the adaptation of sodium excretion on chronic changes of sodium intake in patients with chronic renal failure.