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 (U(alb)V) in nephrotic rats are modified by CEI, we measured U(alb)V 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 U(alb)V and fractional clearance of albumin (FC(alb)) observed in HP (HP + enalapril, 136 ± 44 mg/day and 0.88 ± 0.54 x 10^-2, vs. HY, 368 ± 60 mg/day and 4.40 ± 2.90 x 10^-2, P < 0.05 and P < 0.05, respectively) but did not alter GFR significantly. Enalapril did not alter U(alb)V or FC(alb) in LP. To determine if CEI would reduce U(alb)V in rats after proteinuria was already present, rats fed 21% protein were studied 1 wk after the onset of proteinuria. Enalapril decreased U(alb)V (423 ± 35 to 169 ± 18 mg/day, P < 0.001) and FC(alb) (3.19 ± 0.36 x 10^-2 to 0.71 ± 0.11 x 10^-2, P < 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.