Dietary protein restriction and glomerular permselectivity in nephrotoxic serum nephritis.

We have previously demonstrated that long-term dietary protein restriction ameliorates proteinuria and limits glomerular structural injury in rats with nephrotoxic serum nephritis. In the present study, we examined the influence of short-term dietary protein restriction on glomerular permselectivity. As compared to nephritic rats maintained on a normal protein diet, whole kidney and single nephron hemodynamics were lower in nephritic rats subjected to dietary protein restriction of three days duration (glomerular filtration rate: 0.79 +/- 0.10 vs. 1.46 +/- 0.11 ml/min, P less than 0.003; renal plasma flow rate: 2.50 +/- 0.34 vs. 3.96 +/- 0.38 ml/min, P less than 0.02; glomerular capillary pressure: 44 +/- 1 vs. 53 +/- 1 mm Hg, P less than 0.002; proteinuria: 77 +/- 15 vs. 224 +/- 14 mg/24 hr, P less than 0.01). This was associated with a rise in afferent resistance, from 2.99 +/- 0.77 to 5.45 +/- 0.94 dyn.sec.cm-5, NS. In nephritic rats maintained on 24% protein, fractional clearances were elevated above control values for neutral dextrans with molecular radii exceeding 50 A but were depressed for those with molecular radii below 30 A (P less than 0.05). Dietary protein restriction elevated the fractional clearances of dextrans with radii less than 30 A while depressing the fractional clearances of dextrans with radii greater than 50 A (P less than 0.05). The proportion of glomerular filtrate permeating the shunt pathway was elevated above control values in nephritic rats on the 24% protein diet but declined in those fed the low protein diet (NSN-24%: 0.86%; NSN-6%: 0.31%; control: 0.19%).(ABSTRACT TRUNCATED AT 250 WORDS)