The thickness of the glomerular basement membrane in irradiated and unirradiated Wistar rats and C-57 BL mice of different age groups.

In both Wistar rats and C-57 BL mice, the thickness of the glomerular basement membrane increases progressively with age. This change, which can be measured in cohorts of manageable size, produces a measurement of biological age--if one accepts the assumption that it correlates with the viability of the organism that exhibit it. Whole-body exposure to x-rays has no observable influence on this age-related change.