Subepithelial elastic system fibers of oblique mucosal folds in the rat proximal colon.

The proximal colon of the rat is characterized by a 'herring bone' pattern of oblique mucosal folds (OMF) which are arranged in a parallel array. By light and electron microscopy the OMF exhibited rich subepithelial elastic system fibers which bound the epithelial basement membrane and the smooth muscle cells of the lamina propria together. The elastic system fibers usually consist of elastic, elaunin and oxytalan fibers. However, the subepithelial elastic system fibers of the OMF were composed of relatively thin elastic fibers with a few microfibrils, and elaunin and oxytalan fibers which were almost indiscernible. Areas other than the OMF were quite poor in subepithelial elastic system fibers. The interpositions between each of the OMF were composed of typical components: elastic, elaunin and oxytalan fibers. The composition of the subepithelial elastic system fibers of the OMF does not correspond to that of any other organs previously reported. The present study suggests that the OMF of the rat proximal colon might be equipped in such a way to resist to distension or compression.