Epithelial renewal in protection and repair of gastroduodenal mucosa.

The constant, rapid renewal of the gastroduodenal epithelium is an important mechanism of mucosal protection because it maintains the functional integrity of the epithelium. It also is necessary for the repair of mucosal injury. Aspirin, indomethacin, and ethanol all have been shown to stimulate epithelial proliferation in the experimental setting. The stimulatory effects of these agents may be a compensatory reaction to mild injury and may contribute to the process of mucosal adaptation. On the other hand, corticosteroids, physiologic stress, and smoking appear to depress epithelial proliferation, which could render the mucosa susceptible to the effects of other ulcerogens as well as retard the healing of existing mucosal lesions. Epithelial proliferation in mucosa adjacent to active duodenal ulcers as well as from nonulcerated duodenitis is increased when compared to normal-appearing mucosa. This stimulation of epithelial proliferation may be caused by inflammation; it is not known whether ulcer patients have a defect in epithelial proliferation that precedes ulceration. Although prostaglandins (PGs) protect ulceration. Although prostaglandins (PGs) protect the gastroduodenal mucosa, the weight of evidence indicates that PGs do not have a primary effect on epithelial proliferation but rather retard senescence and loss of epithelial cells. The result is thickening of the mucosa, which may contribute to the protective effects of PGs. Ulcerogenic agents or conditions may either depress epithelial proliferation, which predisposes to ulceration or the ulcerogenic effects of other ulcerogens, or result in a hyperproliferative response, which may contribute to the process of mucosal adaptation and protection.