Physiological assays for biological age in mice: Relationship of collagen, renal function, and longevity

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Abstract
Tests of physiological changes with age are illustrated by collagen denaturation times of tail tendon fibers and urine concentrating abilities. The tests are evaluated using the following 4 criteria: change with age, repeatability, relationship to other assays and relationship to longevity. These tests usually showed highly significant changes with age when mice of different ages were compared for 9 mouse genotypes, neither appeared to be related to subsequent longevities of individual mice. When average values for 11 mouse genotypes were compared, the mean longevities of the genotypes were not significantly correlated with their mean collagen denaturation times or mean renal concentrating abilities, tested at 2 different ages. The relationships between all 3 factors, collagen denaturation times, urine concentrating abilities and longevities were tested in the same individuals for mice of 6 different genotypes at 600-700 days of age. Only 1 marginally significant correlation appeared out of 21 tested; this probably occurred by chance. Thus, tail tendon collagen denaturation times and urine concentrating abilities change with age independently of each other; these changes are unrelated to subsequent longevities, at least when linear relationships are tested. Apparently, aging is timed by more than 1 mechanism. Strong correlations with chronological age do not necessarily indicate that independent tests will be correlated with longevity or with each other.