Effects of renal capsulectomy on kidney growth in the rat

There are theoretical and experimental indications that the renal capsule may limit compensatory renal growth, the limitation increasing with age. The experiments reported here were designed to investigate the effects of renal capsulectomy in young and old rats both on the normal kidney and on that undergoing compensatory growth following unilateral nephrectomy. Capsulectomy had no effects on kidney wet or dry weight in control animals, nor during compensatory growth. In old rats but not in young, capsulectomy increased tubular mitotic index in sham-operated and unilaterally nephrectomized rats. Capsulectomy stimulated hyperplasia in fibroblasts remaining on the kidney surface in all groups. In the young adult rats, renal capsulectomy initiates repair mechanisms in the remaining connective tissue overlying the cortex, but does not itself induce the tubular cells to divide and does not influence compensatory renal growth in the 1st week after unilateral nephrectomy. The capsulectomy-induced increase in tubular mitotic index seen in the old rats may be due to subtle injury to the renal parenchyma resulting from the relative difficulty of removing the older, thicker and more adherent capsules, or to a concomitant increase in platelet-derived growth factor generated during rupture of perforating blood vessels.