Absorption of horseradish peroxidase by the small intestinal epithelium in postnatal developing rats.

After an intraluminal injection of horseradish peroxidase into the small intestine, the localization of peroxidase was studied in neonatal developing and adult rats by means of electron microscopy. Until around the 14th day of the neonatal period absorbed peroxidase granules in the duodenal and jejunal epithelium were abundant in the microvillous membrane, the apical tubulo-vacuolar system, and the Golgi apparatus, and on the lateral cell and basal membranes, and the luminal surfaces of the capillary cells. At the weaning period the tubulo-vacuolar system was absent in the duodenal and jejunal epithelial cells, and at that point absorbed peroxidase was observed in the same sites as in the adult rats: the microvillous membrane, the lateral cell and basal membranes, the Golgi apparatus, and the vesicles and vacuoles of the cytoplasm. During the suckling period, in the ileal epithelial cells exogenous peroxidase was found on the microvilli, in the tubulo-vacuolar system, in the supranuclear vacuole, in the Golgi apparatus, on the lateral cell and basal membranes, and also on the luminal surface of the endothelial cells of blood capillaries. When the tubulo-vacuolar system and the supranuclear vacuole were lost from the ileal cells at the weaning period, no exogenous peroxidase uptake was observed in the absorptive cell of the ileal epithelium.