Age-related changes in 5'-nucleotidase and alkaline phosphatase activities in mouse thymocytes

Enzymatic activities of thymocytes isolated from Swiss albino mice were studied at various ages from immediately post weaning until 100 weeks of age, approaching the life expectancy of these animals. Between 5 and 10 weeks of age, the activities of lactate dehydrogenase and alkaline phosphatase decreased to a level that was maintained throughout the remainder of the aging profile. Neutral beta-glycerophosphatase (pH 7.5) activity in a thymus membrane preparation was similar in all age groups. The activity of membrane-bound 5'-nucleotidase, that is, AMP-hydrolyzing activity inhibited by 100 microM alpha, beta-methyleneadenosine 5'-diphosphate, progressively increased as a function of age, indicating thymocyte population changes occurring very late in life. In thymocytes of the oldest mice examined (100 weeks of age), 5'-nucleotidase specific activity was approximately ten-fold greater than the activity found in 5-week-old mice. Thus, membrane-bound 5'-nucleotidase activity in thymocytes increased markedly as a function of age in Swiss albino mice; yet several other enzymatic activities, including alkaline phosphatase, remained relatively unchanged in mature mice.