Modulation of albuminuria by dietary protein and converting enzyme inhibition

Both dietary protein restriction and angiotensin converting enzyme inhibitors (CEI) reduce proteinuria in experimental renal disease. To determine whether the effects of dietary protein on albuminuria (UalbV) in nephrotic rats are modified by CEI, we measured UalbV and glomerular filtration rate (GFR) in rats with passive Heymann nephritis fed 40 (HP) or 8.5% (LP) protein diets. Half of each group received enalapril beginning 2 days after injection of antibody. Enalapril prevented the greater UalbV and fractional clearance of albumin (FCalb) observed in HP (HP + enalapril, 136 +/- 44 mg/day and 0.88 +/- 0.54 X 10(-2), vs. HP, 368 +/- 60 mg/day and 4.40 +/- 2.90 X 10(-2), P less than 0.05 and P less than 0.05, respectively) but did not alter GFR significantly. Enalapril did not alter UalbV or FCalb in LP. To determine if CEI would reduce UalbV in rats after proteinuria was already present, rats fed 21% protein were studied 1 wk after the onset of proteinuria. Enalapril decreased UalbV (423 +/- 35 to 169 +/- 18 mg/day, P less than 0.001) and FCalb (3.19 +/- 0.36 X 10(-2) to 0.71 +/- 0.11 X 10(-2), P less than 0.001) after 3 days. Thus CEI reduced albuminuria in nephrotic rats fed high- or normal-protein diets without modifying GFR or serum albumin. This effect may be due to changes in glomerular hemodynamics or permselectivity.