Effect of aging and exercise on the kidney. Anatomical and morphological studies.

The effect of short-term endurance exercise on the kidneys of C57BL/6J mice of various ages was studied. While as a function of age there was a slight increase in the ratio of kidney weight to body weight, after 6 weeks of training there was a significant hypertrophy of kidneys of old mice compared to young ones. In addition to these gross anatomical studies, light- and electron-microscopic studies were performed. Using light microscopy, semiquantitative morphological assessment of kidney damage revealed that in young animals about 66% of total glomeruli were characterized as normal. 32% of the glomeruli were singled out as slightly damaged but still functioning. These values remained basically the same for kidneys of young animals trained for 6 weeks. In old mice, on the other hand, only 37% of total glomeruli were characterized as normal morphologically, and over 60% showed various degrees of kidney sclerosis. Exercise for 6 weeks reduced the proportion of normal-appearing glomeruli to 6.25%, while the damaged glomeruli of all types increased to over 90%. Electron-microscopic pictures revealed an increased amount of mesangial damage and severe obliteration of capillary lumens in aging animals. These changes were magnified in old running mice. The results may indicate that while kidneys of young animals were not affected by 6 weeks of exercise, kidneys of old animals were adversely affected by this type of exercise regimen.