The Healing Process of Chronic Colitis in Rats, Induced by 2,4,6-Trinitrobenzene Sulfonic Acid, with Special Reference to the Role of Fibronectin

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Abstract
The healing process of rat chronic colitis was investigated to evaluate the role of fibronectin produced by fibroblasts in the healing tissue. Chronic colitis was produced by intrarectal instillation of 2,4,6-trinitrobenzene sulfonic acid. The healing process was observed by light and electron microscopy and immunocytochemistry. Time course of fibronectin mRNA expression was measured by Northern blot hybridization. By light and electron microscopy, an abundance of young fibroblasts had gathered at the healing tissue and were involved in incorporation into the endothelium of the preexisting vessels, as vasoformative cells, and in transformation to new muscle cells in muscular regeneration. Such processes became pronounced from day 3 and persisted for 6 weeks. Immunocytochemical data showed that fibronectin, produced in the rough endoplasmic reticulum of the fibroblasts and released to the extracellular surface, played inductive roles in the movement and aggregation of such cells and in their contacts with neighboring endothelial cells of the preexisting capillaries. Northern hybridization showed that mRNA coding for fibronectin rapidly reached maximum on day 3 and gradually decreased almost to the control level at 6 weeks. These observations elucidate the role of young fibroblasts, as multipotent cells, and of fibronectin in acceleration of the healing process in this model of chronic colitis.