Age changes of mitochondria of rat kidney

Age-related changes of the mitochondria in the renal proximal convoluted tubules, using 2-, 12-, 18- and 25-29-month-old rats, were morphometrically examined with reference to the mitochondrial function. Mitochondrial volume per cell was significantly larger in 12- and 18-month-old rats compared with that in 2- and 25-29-month-old animals. The total volume of mitochondria in the proximal convoluted tubules was estimated to be maximal in the 18-month-old rats, and decreased significantly in the 25-29-month-old ones; the mitochondrial cristae were arranged most sparsely in the former case and became significantly compact in the latter. The number of epithelial cells in the 25-29-month-old rats was also significantly smaller than in the 18-month-old rats. From the above, in the 25-29-month-old rats, each mitochondrion seems to function more actively to compensate for the numerical loss of cells and their mitochondria.