The microvasculature in aging kidneys, visualized by microcomputed tomography

In senescence there is a marked decline in nephron number and indicators of renal function. However, little is known about the microvasculature of aging kidneys. Micro‐computed tomography was used study 3‐dimensional images of 4 kidneys from young (3 month, 419 ± 12 gm; mean ± SEM) and 8 kidneys from old (21 month, 515 ± 38 gm; mean ± SEM) Sprague‐Dawley rats. The rats were anesthetized and the vasculature of the kidneys was infused via an aortic cannula first with heparinized 0.9% saline, then with 10% buffered formalin and finally with radiopaque silicone rubber (Microfil 122). The kidneys were scanned by micro‐CT to generate the 3‐dimensional images of the vasculature. Analysis of the resultant 3‐dimensional images showed that the kidneys of the young rats were significantly smaller than those of the old rats (young: 1781 ± 65, old: 2393 ± 81 μl; mean ± SEM). In comparison to the young rats, the glomeruli of old rat kidneys were significantly fewer in total number (young: 35,775 ± 329, old: 31,071 ± 191; mean ± SEM) but larger in diameter (young: 127 ± 2, old: 159 ±1 μm; mean ± SEM). Despite these changes, there were no significance differences between the old and young kidneys in the vascular fractions of the cortex, outer and inner zones of the outer medulla, or the inner medulla. These results indicate that with age there is a loss of nephrons in the kidney that is compensated by growth of remaining nephrons and peritubular vasculature. Supported in part by NIH grants EB 000305 and HL16496.