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

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 four 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 nine mouse genotypes, however neither appeared to be related to subsequent longevities of individual mice. When average values for eleven 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, testes at two different ages. The relationships between all three factors--collagen denaturation times, urine concentrating abilities, and longevities--were tested in the same individuals for mice of six different genotypes at 600-700 days of age. Only one marginally significant correlation appeared out of 21 tested; this probably occurred by chance. We conclude that tail tendon collagen denaturation times and urine concentrating abilities change with age independently of each other; furthermore, these changes are unrelated to subsequent longevities, at least when linear relationships are tested. These data suggest that aging is timed by more than one mechanism and demonstrate that strong correlations with chronological age do not necessarily indicate that independent tests will be correlated with longevity or with each other.