EARLY WEANING INDUCES JEJUNAL ORNITHINE DECARBOXYLASE AND CELL-PROLIFERATION IN NEONATAL RATS

Increased ornithine decarboxylase (ODC) activity is associated with ra pid cell proliferation in many cell types. The cellular effects of ear ly weaning on intestinal development are not well established. To inve stigate whether ODC is involved in intestinal growth after early weani ng, we precociously weaned suckling rats on postnatal d 15 and followe d through d 21 (6 d after early weaning). Age-matched suckling pups se rved as controls. Rat pups were killed 1, 2, 3 and 6 d after early wea ning and jejunal mucosa was assayed for ODC and sucrase activities, an d protein and DNA contents. Jejunal cell proliferation was monitored b y bromodeoxyuridine immunohistochemistry. Elevated jejunal ODC activit y 1 d after early weaning was the earliest cellular event that was det ected in the current study. ODC activity peaked at d 3 (about 15-fold greater than age-matched unweaned suckling controls). Sucrase activity was elevated at d 2 after weaning and peaked at d 3 (about IO-fold gr eater than controls). Greater bromodeoxyuridine immunostaining in earl y weaned rats occurred on d 3. Protein and DNA contents were greater i n jejunal mucosa of early weaned rats at d 6. Serum corticosterone lev els were elevated on d 1 and d 2 after early weaning compared to contr ols. To explore whether the intake of nonpurified diet played a role, we also compared the induction of jejunal ODC activity in early weaned pups and pups that were food-deprived for I d. ODC activity was not g reater in the food-deprived group compared to suckling controls while the early weaned group had 6-fold greater activity 1 d after early wea ning. Early weaning stimulates jejunal cell proliferation and differen tiation. The temporal sequence of increased ODC activity followed by i ncreases in other growth variables suggests that the induction of ODC activity may act as an early marker of intestinal growth during early weaning.