Synergistic effects of insulin and thyroxine on the differentiation and proliferation of epithelial cells of suckling mouse small intestine.

The interactions between insulin, cortisone and thyroxine on the functional maturation of the small intestine were investigated. 8-day-old suckling mice received one injection/day during 3 days of a single hormone or of the following hormonal combinations: insulin plus cortisone or insulin plus thyroxine. The differentiation of intestinal epithelial cells was evaluated by measuring brush border membrane hydrolytic activities and proliferation by establishing the mitotic index and 3H-thymidine incorporation into DNA. The effects of cortisone and insulin on enterocyte's differentiation are additive. Thyroxine accelerates the differentiation and has a limited action on cell proliferation. Insulin exerts a sustained effect on these two aspects of the intestinal maturation and, furthermore, acts in synergism with thyroxine. It appears that insulin, cortisone and thyroxine have their own specific effect on differentiation and proliferation of the epithelial cells and that these three hormones act in cooperation to induce the maturation of the suckling mouse small intestine during postnatal development.