Regeneration of colonic mucosa in the rat.

As part of a study of ulcer formation and healing, regeneration of colonic mucosa in rats was studied following placement of a surgical lesion. Alterations in mucosubstances and connective tissue were examined and their possible significance discussed. The sequence of events in healing was: 1) The mucosa adjacent to the lesion tipped into the lesioned area. The crypts in this mucosa became lined with cells which contained no mucus and had no striated borders. Later in the experimental period, these undifferentiated cells gave rise to cells containing carboxymucins. Cells containing sulfomucin, neutral mucin, or having striated borders arose from the carboxymucin cells. 2) An epithelial ledge of undifferentiated cells migrated onto a sulfated glycosaminoglycan, fibrous interface between necrotic and living tissue in the lesion. 3) Crypt formation began with the appearance of intraepithelial anlagen. 4) Crypts lengthened by a process of epithelial-connective tissue proliferation from the base of the crypt upwards. Following completion of connective tissue regeneration, crypts formed by invading the reestablished lamina propria. 5) The first mucous cells in the ledge contained carboxymucins. As crypt formation occurred, these cells gave rise to typical columnar absorptive cells, to cells containing sulfomucins, and to cells containing neutral mucins. 6) Lengthening of crypts ceased following the appearance of a sulfated acid glycosaminoglycan--collagenous layer deep in the submucosa.