EFFECT OF PROTEIN DIETS ON THE RENAL FUNCTION OF BABOONS (PAPIO-HAMADRYAS) WITH REMNANT KIDNEYS - A 5-YEAR FOLLOW-UP

To assess the progression of renal disease and the effects of protein intake in a species phylogenically close to humans, 14 adolescent baboons (Papio hamadryas) were subjected to infarction of one third of the left kidney and, 2 months later, to right nephrectomy. They were then randomized to a synthetic protein diet containing either 8% or 25% casein. Hemodynamic and metabolic measurements were obtained in awake animals every 4 months. Modest proteinuria developed immediately after left kidney infarction, and hypertension after right nephrectomy. Proteinuria and hypertension, however, were similar in both groups and did not progress for the next 60 months. Inulin clearance markedly increased with implementation of the synthetic diet in baboons given 25% protein, in contrast to animals given 8% protein, averaging 46.6 ± 4.7 mL/min versus 28.2 ± 2.6 mL/min, respectively, after 4 months. The glomerular filtration rate (GFR) changed little immediately thereafter and, at 1 year, averaged 43.0 ± 1.4 mL/min and 28.0 ± 4.3 mL/min, respectively. During the next 4 years, however, inulin clearance steadily decreased in baboons fed 25% protein. The inverse correlation between inulin clearance and time of follow-up was y = 48.5 - 0.36x (r = -0.879, P < 0.001) in baboons fed 25% protein and y = 29.0 - 0.11x (r = -0.625, P < 0.02) in baboons fed 8% protein. Nevertheless, after 5 years, the mean GFR was still significantly greater in animals given the 25% protein diet than in baboons fed 8% protein, averaging 29.1 ± 0.6 mL/min and 24.1 ± 1.0 mL/min, respectively (P < 0.01). No similar trend was evident when endogenous creatinine clearance was used to estimate renal function. In conclusion, a protein-enriched diet leads to a rapid and sustained increase in GFR in baboons with remnant kidneys. With time, however, the differences in GFR between baboons fed 25% protein and those fed 8% slowly and progressively abates, as GFR declines at a rate three times faster in the former group. The differences and changes in GFR observed between the two groups cannot be attributed to differences in protein excretion, hypertension, or calories, calcium, phosphorus, or lipid intake. © 1994, National Kidney Foundation. All rights reserved. All rights reserved.