Morphological study of the regeneration mechanism of acetic acid-injured colon crypts in the rat.

The regeneration mechanism of injured rat colonic mucosa with 1% acetic acid was certified in this study. The injured colons were studied periodically on experimental days 1, 3, 5, 7, 15, and 20 with light and scanning electron microscopy. Specimens were examined in paraffin sections stained with hematoxylin and eosin; crypts were isolated with the HCl digestion method; and three-dimensional stromal collagen tissue was prepared with the NaOH cell maceration method. Damage to the mucosal and submucosal layers peaked between the 1st and 3rd days with edema, regeneration, necrosis, and inflammation. The edema and inflammation subsided, and mucosal atrophy and crypt reduction remained at around 1 week. At 2 weeks the mucosa became thick, and crypts showed many branches in their lower two-thirds; and by 3 weeks the mucosa had recovered to almost normal. The ratio of number of crypts at the base and surface was almost 1.5 on the 15th day and 1.0 on the 20th day, suggesting that each branch progresses upward to create an independent crypt. We believe that the fission mechanism plays an important role in crypt repair after acetic acid injury of the colonic mucosa. As the proliferative zone of the colonic crypt is localized at the crypt base, fission of the crypt starting at the base and progressing up to the surface is the most reasonable and efficient mechanism for repair by increasing the number of crypts.