ISO-ONCOTIC VOLUME EXPANSION IN THE NEPHROTIC SYNDROME

1. In previous studies we found that albumin infusions caused only a m odest natriuresis in the nephrotic syndrome, suggesting that hypovolae mia played no part in the sodium retention of these patients. However, this finding was inconclusive, since the hyperoncocity of the infused albumin probably opposed sodium excretion. 2. In the present study, w e examined the effect of sustained (68 h) plasma volume expansion (+18 %), by means of iso-oncotic albumin infusions, on renal function, bloo d pressure, humoral factors and sodium balance. 3. Plasma atrial natri uretic peptide levels increased almost threefold and renin-angiotensin system activity was suppressed. Glomerular filtration rate remained u nchanged, whereas estimated renal plasma flow increased, resulting in a further decrease in filtration fraction. 4. The increase in plasma v olume expansion was accompanied by a modest increase in sodium excreti on, which, however, was less than the amount of sodium daily infused w ith the albumin solutions and consumed with the diet, so that net sodi um was retained. 5. This observation supports the concept that an intr insic renal defect causes the sodium retention in the nephrotic syndro me, and argues against the therapeutic use of albumin infusions.