Renin-angiotensin-aldosterone system, plasma
atrial natriuretic peptide (PANP), and blood volume (BV) have been investigated in 20 nephrotic patients with normal renal function and with (group 1; n = 12) or without (group 2; n = 8)
sodium retention. Patients of group 1 had a
plasma albumin (PALB) concentration < 1.7 g/dl, low BV and PANP levels, a reduced fractional excretion of
lithium (FELi), and high plasma
angiotensin II levels. Patients of group 2 had PALB > 1.7 g/dl, and the other parameters were normal. The spontaneous intake of
dietary sodium was lower in group 1 than in group 2. In all patients the BV was directly correlated with PALB, and the plasma
renin activity (PRA) was inversely correlated with both BV and PALB. A nonlinear inverse relationship was present between plasma
aldosterone (PALD) levels and fractional excretion of
sodium (FENa). The acute expansion of the BV in patients of group 1 normalized PRA, PALD, PAII, FENa, and FELi and increased PANP. The administration of
spironolactone to the patients of both groups had variable effects on FENa, did not modify PRA and PALD, and reduced
body weight, PANP, and FELi, thus suggesting that the reduction of BV induced by the
drug increased the proximal reabsorption of
sodium. Three additional patients who had
sodium retention, PALB of 2.3-2.4 g/dl, normal PRA and PALD, elevated urinary excretion of
aldosterone, and a slightly low PANP showed a spontaneous normalization of urinary
aldosterone and PANP associated with natriuresis and
weight loss, but thereafter urinary
aldosterone increased, PANP decreased, and the
sodium retention began again. Our data suggest that in nephrotic patients with severe
hypoalbuminemia, contraction of BV plays a major role in promoting the
sodium retention through the activation of compensatory hormonal mechanisms. On the other hand, when PALB is not severely reduced, the patients have normal BV, but they are very sensitive to small changes of BV which are better evidenced by modifications of the urinary excretion of
aldosterone and PANP rather than by the profiles of PRA and PALD.