Ischemia and reperfusion injury: jejunum versus ileum. (2002)

The article by Takeyoshi et al. (1) has been read with much interest. However, their conclusions that prolonged preservation of canine intestine caused more damage in the ileum and that the ileum regenerated more slowly compared with the jejunum aroused much concern. These findings may affect the decision of using ileum as a segmental graft, although the article by Takeyoshi et al. did not suggest that the ileum should not be used as a graft. The use of intestinal grafts from live donors could potentially reduce the severity of rejection responses by better tissue matching and increase the donor pool. Gruessner and Sharp (2) first reported in 1997 a standardized surgical technique to use the 200 cm of distal ileum with the vascular pedicle of ileocolic artery and vein. Since then, the results of live-donor intestinal transplantation achieved with the ileum have justified its use. Our previous finding that the ileum is more resistant to ischemia and reperfusion (I/R) than the jejunum has led us to identify that nitric oxide, which is present in higher levels in the ileum than jejunum, has a protective effect on intestinal I/R (3). Benchimol et al. (4) verified that 65% of complications could be attributed to the use of jejunal graft. The resulting vascular thrombosis following mesenteric anastomosis for revascularization of the jejunum invariably led to death. Even after removal of the jejunal part of the graft, the ileum has been proven experimentally and clinically to be able to maintain the functions of the small bowel because of its ability to adapt and even acquire new functions (4). Thompson and co-workers (5) also confirmed the greater adaptation capacity of the ileum compared with the jejunum. Using a rat model, they performed a resection of 50% of the small bowel followed by either jejunal or ileal transplantation. Ileal-transplanted rats showed better weight gain than those that had jejunal transplantation. Wang and co-workers (6) have discovered a novel cDNA putative protein of 254 amino acids that is up-regulated in the remnant ileum following major small bowel resection. The following are comments and concerns regarding the study by Takeyoshi et al. (1). Intestinal I/R injury follows a specific pattern of changes (7), and this pattern has been graded by Chui et al. (8). However, the grading system was not used in the study. This made comparison between the degrees of injury in the jejunum and ileum difficult. A double-blinded study of the histological specimens would have been preferable. Furthermore, normal ileum and jejunum have different histological appearances—the jejunal villi are longer and narrower than those of the ileum (Fig. 1). Figure 1: Photomicrograph of pig jejunum (J) and ileum (I). The villi of the jejunum are longer and narrower than that of the ileum (magnification × 6).A high mortality in the preservation group of dogs (30%, 10/34) was observed. This may have affected the actual results of the study. In addition, there may be morbidities that are of sufficient severity to affect the results. Even if the results were not affected by morbidity and mortality of the surgery, severe damage of the ileum may have been caused by mechanical forces generated during the intraluminal flushing of the bowel before preservation. Gitter and co-workers (9) pointed out that the conventional Ussing chamber technique does not differentiate between epithelial and subepithelial tissue functions. They suggested that epithelial and subepithelial tissues should be examined separately with regard to mucosal damage, particularly in studies of prolonged preservation injury in the small bowel. Thompson et al. (10) discovered the presence of bacterial overgrowth of fecal flora in the transplanted bowel. The regeneration of the ileum may also have been affected in that it is usually loaded with bacteria from the large bowel. This is especially significant as the transplanted ileum was anastomosed close to the colon in the present study. In general, clinicians should be aware that much data exist to support the use of the ileum as a segmental graft. The observation of more severe damage and delayed regeneration in the ileum, compared with the jejunum observed in the dog model after prolonged preservation with orthotopic small bowel graft, requires further evaluation, and any future study should take into consideration the factors mentioned above. K. L. Chan, MD