A CYTOLOGICAL STUDY OF INTESTINAL ABSORPTION IN SUCKLING RAT

The distal small intestine of the albino rat has the capacity to absorb protein and particulate matter during the suckling period. Ultrastructural and cytochemical aspects of this absorptive phenomenon were examined in the ileum. Soon after the initial ingestion of milk, a large, yellow, smooth membrane‐limited, protein body appears in the immediate supranuclear region of ileal absorptive cells and, also, many small vacuoles and membrane‐limited droplets arise between this body and the microvilli. Exogenous protein enters an elaborate superficial tubular system and is segregated in membrane‐limited vacuoles and droplets and, then, appears in the supranuclear body. The body and adjacent membrane‐limited droplets are basophilic, periodic acid‐Schiff positive, and rich in hydrolytic enzymes (acid phosphatase, ATPase, thiamine pyrophosphatase, alkaline phosphatase, esterase). The results suggest the presence of a highly developed lysosomal system during the period of protein absorption. Additional cytological features of the absorptive cells are presented. Ileal absorptive cells are normally free of lipid droplets. When emulsified lipid is introduced into the neonatal ileum, it enters into the cytoplasmic smooth membrane system, including the supranuclear body, and later appeas in the lacteals. This suggests both that the uptake of material may be non‐selective and that similar intracellular pathways may be used in transporting protein and lipid through the epithelium. Copyright © 1969 Wiley‐Liss, Inc.