Glomerular cell number and labeling index. A: Increased glomerular cell number in 30-month-old mice. (**, P < 0.01 vs. 5 months or 22 months). B: No significant change of glomerular cell number in 2.5-month-old and 20-month-old uninephrectomized mice. C: Representative area of renal cortex showing BrdU staining (from 30-month-old mouse, ×250). Positive nuclear staining is seen within glomeruli (shown with arrow), tubules, and interstitium. D: Increased BrdU labeling of glomerular cells in 30-month-old mice. (**, P < 0.01 vs. 5 months or 22 months). E: Increased BrdU labeling of glomerular cells in uninephrectomized mice. (##, P < 0.01 vs. respective age-matched controls).