Alkaline phosphatase activity of the large intestinal principal cells in postnatal developing rats.

The localization of alkaline phosphatase activity in the large intestinal mucosa of postnatal developing rats was studied by means of light and electron microscopes. On the day after birth, alkaline phosphatase activity, as shown by the azo-coupling method was found on the microvilli and the tubulovacuolar system in the proximal part of the large intestine between the 1st and the 15th days, enzyme activity was localized on the microvilli, the tubulovacuolar system, and the supranuclear vacuole of the surface principal cells of the cecum and the ascending colon. After the 15th day, all the principal cells of the proximal large intestine were free of reaction products as were those in the full-grown rats. Before the 4th day of life, in the descending colon, the enzyme activity of the principal cells was observed, but only on the microvilli. After the 5th day, enzyme activity disappeared from the principal cells.