Absence of sodium and water retention in rats with severe proteinuria.

Studies with two models of immunologically mediated glomerular disease in the rat, chronic serum sickness and Heymann nephritis, show that fluid retention can be dissociated from other signs of the nephrotic syndrome (excessive proteinuria, hypoalbuminemia, hypercholesterolemia). Clinical evidence of fluid retention (increased body weight, decreased hematocrit, ascites) was only detected in severe chronic serum sickness and coincided with an abrupt drop in urinary sodium concentration and sodium excretion. Severe proteinuria was not associated with sodium and water retention in moderate chronic serum sickness and in Heymann nephritis. These observations support the hypothesis that, in conditions of severe proteinuria, an intrarenal defect in sodium excretion rather than a systemic factor, leads to fluid retention.