Elevated dietary protein intake impairs the renal hemodynamic response to hyperaminoacidemia in patients with primary glomerular diseases

We have evaluated the renal hemodynamic response to a mixed amino acid infusion in 7 control subjects and in 8 patients with primary glomerulonephritis (GN). In order to evaluate the role of dietary protein intake in this response, GN patients were maintained for 3 weeks on two separate dietary regimens providing 130 ± 5 g of protein/day (study 1) and 60 ± 3 g of protein/day (study 2), respectively. Normal subjects were studied while consuming a free diet. In GN patients, following the reduction in dietary protein intake basal RPF and GFR decreased from 589 ± 109 to 422 ± 81 ml/1.73 m2/min (p < 0.01, vs. study 1) and from 75 ± 7 to 70 ± 8 ml/1.73 m2/min (p = NS). Filtration fraction rose from 0.14 ± 0.02 to 0.19 ± 0.03 (p < 0.05). In study 1, during amino acid infusion GFR and RPF did not change significantly from baseline (75 ± 7 vs. 66 ± 8 ml/1.73 m2/min at 180 min and 589 ± 109 vs. 567 ± 102 ml/1.73 m2/min, respectively). These results are at variance with data obtained in normal controls in whom both GFR and RPF rose significantly following hyperaminoacidemia. In contrast, when dietary protein intake was reduced, a normal renal hemodynamic response to amino acid infusion was restored (GFR went from 70 ± 8 to 90 ± 18 ml/1.73 m2/min and RPF from 422 ± 81 to 517 ± 90 ml/1.73 m2/min, both p < 0.05 vs. basal), both absolute and percentage increases were similar to what was observed in controls. These results show that in subjects with primary glomerulopathies elevated dietary protein intake affects renal hemodynamics. Maintenance of dietary protein intake within the recommended dietary allowance preserves a normal renal hemodynamic response to hyperaminoacidemia in these patients.