[Ultrastructural study of the colon after massive intestinal resection in rats].

The modifications suffered by the colon after massive intestinal resection (RIM) have been barely studied, especially from the ultrastructural point of view. On the basis of optical microscope studies we planned this experimental study to evaluate fundamentally the ultrastructural changes in the colonic mucosa and its cellular elements. A total of 115 Wistar rats weighing 350 to 550 grams were used. Twenty animals constituted group 0 (controls), 30 underwent intestinal section (group I) and 65 were submitted to resection of 90% of the intestine (group II). After weighing, the animals were sacrificed by groups on days 15, 30, 45 and 60 of the operation to obtain histologic samples of the ascendant colon for study by transmission (MET) and scanning (MEB) electron microscopy. All the animals resected showed statistically significant weight loss (p less than 0.001), an expression of short intestine syndrome. Groups 0 (controls) and I (intestinal section) did not evidence important ultrastructural changes. In contrast, although in the initial electron microscopic scan the colonic mucosal surface offered a normal aspect, at 45 days it presented irregularities, without the appearance of villi. Days 60 there were deep folds and the mucosal surface had acquired a foliaceous aspect similar to that of the surface of the small intestine of the rat. The abundance of microorganisms adhered to the surface, constituting clumps of bacteria, was striking. Transmission electron microscopy confirmed the greater number and height of the enterocytes, covered by well-developed apical microvilli with dimensions that increased throughout the experiment. The cellular nuclei are voluminous and occasionally have various nucleoli. The cytoplasm showed changes that affected fundamentally the mitochondria.(ABSTRACT TRUNCATED AT 250 WORDS)