A study of the renal handling of water in lipoid nephrosis

Children with lipoid nephrosis were studies during clinical relapse and after complete remission. As expected, the calculated serum oncotic pressure was reduced severely from the remission value of 28.6 +/- 0.9 mm Hg to 15.4 +/- 1.1 (P less than 0.005) during relapse. Although no apparent change in plasma volume was noted using the volume of distribution of labeled human albumin, calculated plasma volume was reduced 13 +/- 8% during relapse when estimated from changes in hematocrit. After a water load, the ability to excrete water was markedly blunted during relapse. The clearance of solute-free water (CH2O) was 0.9 +/- 0.8 ml/min during relapse, compared with 3.6 +/- 0.6 ml/min during remission (P less than 0.005). In addition, there was a reduced maximal urinary concentrating ability during relapse in four of the six patients examined. Mean urine osmolality for the group during relapse was 778 +/- 82 mOsm/kgH2O and 991 +/- 71 during remission (P less than 0.05). The demonstrated alteration in nephron function during relapse of nephrotic syndrome could result from either (1) a decrease in the amount of sodium delivered to the ascending limb of the loop of Henle because of increased proximal reabsorption or (2) a change in the intrinsic characteristics for sodium reabsorption in that segment. Although this observation does not prove that proximal reabsorption is increased, it suggests a common underlying mechanism for altered nephron function in all of the major edema-forming conditions.