Developmental Transition of Alkaline Phosphatase from Suckling to Adult Type in Rat Small Intestine: Molecular Species and Effect of Injected Cortisone and Thyroxine1

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Abstract
Postnatal change of rat intestinal alkaline phosphatase from suckling to adult type occurred at the weaning stage (Uezato et al. (1981) Biochem. Int. 2, 561). Two distinct forms were observed in suckling rat small intestine. One was soluble and the other was membrane-bound. The ratio of the soluble to the membrane-bound form increased after birth until these forms were replaced by the adult type, which consisted of membrane-bound forms different from that of sucklings. The soluble form was demonstrated almost exclusively during the suckling period and was distributed in the distal third of the small intestine. The postnatal increase of alkaline phosphatase was enhanced by administration of hormones such as cortisone and thyroxine. On the other hand, acid β-galactosidase activity in the distal segment was reduced rapidly by the same treatment. The change of alkaline phosphatase from suckling to adult type was accelerated by the injected hormones. In the distal segment the ratio of soluble to membrane-bound activity in the homogenate prematurely decreased after administration of the hormones. Between 16 and 18 days of age, alkaline phosphatase of hormone-treated rat small intestine changed completely from fetal-suckling type to typical adult type in both the proximal and distal segments.