POSTNATAL DEVELOPMENT OF BETA-GALACTOSIDASE ACTIVITY IN THE SMALL INTESTINE OF THE RAT. EFFECT OF ADRENALECTOMY AND DIET.

1. beta-Galactosidase activity was studied in homogenates of the proximal and distal thirds of the small intestine from adult and infant rats. o-Nitrophenyl beta-d-galactoside served as the substrate. 2. Activity in suckling rats is highest in the distal part of the small intestine. 3. The pH optimum was 3.5 in the distal third of the small intestine in rats aged 5 and 15 days, whereas in the proximal third the maximum was not clearly defined. 4. Activity was higher in both thirds in newborn than in adult rats, expressed per wet wt. or per wt. of protein. In the proximal third activity continually decreases with age, whereas in the distal part there is a rise up to day 15 and then a sudden decrease. Total beta-galactosidase activity changes very little in the proximal third during postnatal development; the greatest changes occur in the distal third. 5. Adrenalectomy performed on day 15 postnatally slows down the decrease in beta-galactosidase activity, particularly in the distal part. 6. Feeding a lactose diet to infant rats from day 14 postnatally in the presence of the mother rat also slows down the decrease in beta-galactosidase activity and this is not found with a diet containing glucose and galactose instead of lactose.