Gastrointestinal proliferation and aging.

The gastrointestinal tract represents an organ system that is characterized by rapid proliferation and by cells that demonstrate differentiation from immature stem cells to terminal differentiated mature cells. Aging gastrointestinal tissues illustrate markedly different phenomena from aged post-mitotic cells. Contrary to generally held prejudices, a state of hyperproliferation, not hypoproliferation, occurs in the epithelial cells of the stomach, the small intestine, and the large intestine of stable-fed, aged rodents when compared to young mature rodents. Furthermore, abnormalities of proliferative and differentiation responses become evident when gastrointestinal tissues are stimulated by injury, or by starvation and refeeding. We speculate that such changes in proliferation and differentiation expose aging gastrointestinal epithelial cells to genotoxic effects that may increase the susceptibility to gastrointestinal cancers.