Protein restriction influences glomerular matrix turnover and tubular hypertrophy by modulation of renal proteinase activities.

Following renal ablation, there is marked compensatory renal growth, which is associated with alterations in the activities of renal proteinases. In the present study, rats underwent 5/6 nephrectomy (5/6-NX). Sixteen weeks after surgery, glomeruli and tubules were isolated and proteinase activities were determined using fluorogenic peptidyl substrates. Following 5/6-NX, there was considerable compensatory renal growth resulting in a final weight of 1,923 +/- 46 mg for the remnant kidney as compared to 1,402 +/- 63 mg for the left kidney of SHAM animals. This hypertrophic response was associated with lower activities of tubular cysteine proteinases (cathepsin L & B: -43%; cathepsin B: -61%; cathepsin H: -53%). Significantly reduced activities were also observed for glomerular collagenase (20.2 +/- 6.2 vs. 53.4 +/- 5.7 mU/micrograms DNA) and gelatinase (24.1 +/- 5.0 vs. 130.8 +/- 8.4 mU/micrograms DNA) activities. Protein restriction (5 vs. 20% casein) considerably attenuated compensatory renal growth after surgical ablation (790 +/- 45 vs. 1,923 +/- 46 mg) and partially prevented the fall in tubular cathepsin activities. In terms of glomerular enzymes, protein restriction caused a significant increase in the activity of gelatinase from 24.1 +/- 5.0 to 66.7 +/- 9.2 mU/micrograms DNA, while collagenase remained unchanged. From these data, we conclude that compensatory renal growth is strongly influenced by the amount of protein ingested. It appears that this effect is mediated by modulation of renal proteinase activities.