Renal water excretion before and after remission of nephrotic syndrome: Relationship between free water clearance and kidney function, arginine vasopressin, angiotensin II and aldosterone in plasma before and after oral water loading

1. An oral water load of 20 ml/kg body wt. was given to eight patients with nephrotic syndrome before and after remission of the syndrome, and to 13 healthy control subjects. Urine volume (D), free water clearance (C_water), plasma concentrations of arginine vasopressin (AVP), angiotensin II (ANG II) and aldosterone (Aldo), were determined before and three times during the first 4 h after loading.

2. D and C_water increased to a significantly lower level (P < 0.01) after water loading in patients with nephrotic syndrome than in control subjects, but D and C_water were normal after remission of the syndrome. The maximum increase in C_water (ΔC_{water max.}) was 1.07 ml/min (median) before remission and 7.93 ml/min after, compared with 8.01 ml/min in the control group.

3. Creatinine clearance (C_cr) increased significantly after remission (63 ml/min to 88 ml/min, P < 0.01), and the fractional excretion of sodium was enhanced. AVP was higher in the nephrotic syndrome both before (2.9 pmol/l) and after remission (2.9 pmol/l) compared with the control group (1.8 pmol/l). ANG II and Aldo did not change after remission and remained at the same level as in the control group.

4. The elevation in ΔC_watermax after remission was accompanied by an increase in C_cr in all patients and ΔC_watermax. and C_cr were significantly correlated (ρ = 0.600, n = 16, P < 0.05). No relationship was found between the change in ΔC_{water max.} and ANG II and Aldo.

5. AVP was significantly suppressed in patients with nephrotic syndrome before remission, but not after remission nor in control subjects, so that although AVP did not differ in nephrotic patients before and after remission, AVP cannot be excluded as a contributory factor to the reduction in C_water in the nephrotic syndrome.

6. It is concluded that patients with nephrotic syndrome excrete an oral water load slower than control subjects and that the excretion rate is normal after remission of the syndrome. It is suggested that the normalization of C_water may be attributed to an increase in glomerular filtration rate or a decrease in proximal tubular sodium reabsorption, although a possible role for AVP has not been excluded.