Age-related changes in the D-aspartic acid content of the cranial bones in senescence-accelerated mice (SAM).

We measured the age-related changes in the D/L-aspartic acid ratio (D/L ratio) of cranial bones in two different sublines of senescence-accelerated mice (SAM/Iw): SAMP2/Iw (SAM, prone 2/Iwate) and SAMR1/Iw (SAM, resistant 1/Iwate). In SAM/Iw under 9 months of age, the D/L ratio in SAMP2/Iw was higher than that in SAMR1/Iw (p<0.001). However, in all 12-month old SAM/Iw, whether SAMP2/Iw or SAMR1/Iw, the D/L ratio was higher in males than in females. There were minor differences in the age-related changes in the D/L ratios between different types of cranial bone. In 1-month old SAM/Iw the rectal temperature was similar in both males and females. However from the age of 2 months, there was a divergence, with the rectal temperature measurement in SAMP2/Iw reaching a peak 2 months of age, whereas SAMR1/Iw had the highest temperature readings at 6 months of age. In both SAMP2/Iw older than 2 months, and SAMR1/Iw older than 6 months, the temperature readings tended to gradually decrease with age in both males and females. These results suggest that the differences in D/L-aspartic acid ratios were dependent on the age, gender, and strain of SAM/Iw, but were not dependant on the type of cranial bone studied. It seems likely that these differences may be related mainly to changes in body temperature.