Stimulatory effects of insulin on DNA synthesis in suckling mouse colon

The influence of insulin on the postnatal development of DNA synthesis and epithelial and muscular cell proliferation has been studied in suckling mice. Daily administration of insulin (12.5 mU/g body weight) during 3 days to 8-day-old mice induced a significant increase of the incorporation of [3H]-thymidine into DNA in the small intestine and the proximal and distal halves of the colon. The esophagus and the glandular portion of the stomach did not respond. A detailed analysis of the proximal and distal colon between 4 and 30 days revealed a decrease of [3H]-thymidine incorporation into total DNA during this period. However, the establishment of the labeling indices in specific compartments such as the epithelium and the muscularis externa revealed that the epithelial cellular proliferation increased around weaning period in both segments while a drastic reduction of cellular proliferation occurred in the muscle layer. A premature rise of the circulating insulin level induced a significant increase of the epithelial labeling indices in both colonic segments but remained without effects on the muscular layer. These results suggest an important role of insulin in the modulation of the ontogenic changes in epithelial cell proliferation of the mouse colon.