Multipotent stem cell (CFU-S) numbers and circadian variations in aging mice

The multipotent stem cell (CFU-S) numbers were studied in aging female C3H mice (16, 21 and 26 months old, respectively) versus young controls (3 months old). Using the spleen colony technique, the d-8 CFU-S numbers were measured every 3 h during the 24-h period at three different times of the year. Prominent circadian variations were found in young mice. The peak and trough values were significantly different also in aging mice, although the peak-trough differences were declining. When comparing young and old mice at different times of the 24-h period, the CFU-S numbers were sometimes significantly different, but often not. The 24-h mean values were consistently declining during aging. Young mice had different circadian variation patterns and 24-h mean values when examined at different times of the year. It is concluded that the d-8 CFU-S numbers decline in aging mice. Conflicting reports may partly be due to neglect of physiological variations.