POSTNATAL CHANGES IN β-GALACTOSIDASE ACTIVITY IN THE JEJUNUM AND ILEUM OF MICE, RABBITS, AND GUINEA PIGS

During the postnatal development of mice, intestinal β-galactosidase activity (0.001 M o-nitrophenyl β-D-galactoside as substrate) is always higher at pH 3.5 than at pH 5.5. In the jejunum a steady decrease of activity during postnatal development is evident, whereas in the ileum the activity increases temporarily and later decreases. The changes in rabbits are more complicated. At pH 5.5 there is a steady decrease of β-galactosidase activity in the ileum and jejunum, but at pH 3.5 there is a steady decrease in activity in jejunum only; in ileum, first an increase is observed and then a decrease. In guinea pigs the activity in newborn animals is relatively very low, and only a small decrease during postnatal development is found. During postnatal development, the activity decreases less at pH 3.5 than at pH 5.5. In contrast to mice and rabbits, guinea pigs showed no substantial differences between jejunum and ileum in all the age groups studied.The results are discussed from the point of view of significance of differences between the jejunum and the ileum, and the existence of several types of β-galactosidase activity.