Effects of whole-body hypoxic preconditioning on hypoxia/reoxygenation-induced intestinal injury in newborn rats

Purpose: The precise cause of necrotizing enterocolitis (NEC) is elusive. Ischemia and reperfusion injury of the intestine has been considered to be a major contributing factor for NEC. Ischemic preconditioning is defined as one or more brief periods of ischemia with intermittent reperfusion that protects tissues against a sustained period of subsequent ischemia. Contribution of preconditioning to hypoxia/reoxygenation-induced intestinal injury in newborn rats has not been evaluated previously. Methods: The study was carried out on 1-day-old Wistar albino rat pups. Whole-body hypoxia and reoxygenation (H/R) was achieved by 10 min hypoxia using 95% N-2 + 5% CO2 followed by 10 min reoxygenation with 100% oxygen. Whole body hypoxic preconditioning (HP) cycles were performed with 3 min hypoxia and 5 min reoxygenation. Thirty-three pups were randomly allocated into 4 groups. Group 1 served as untreated controls. The pups in group 2 were subjected to H/R only. In groups 3 and 4, 1 cycle and 3 cycles of HP were performed prior to H/R, respectively. Animals were killed at the end of the protocols. Intestine specimens were obtained to determine the histological changes, as well as to measure the tissue malondialdehyde (MDA) and nitric oxide (NO) levels, and xanthine oxidase (XO) and myeloperoxidase (MPO) activities. Results: The microscopic lesions in H/R rat pups were virtually the same as those seen in neonatal NEC, with severe destruction of villi and crypts, in some cases extending to the muscularis. In both HP groups, the lesions were found to be milder. H/R resulted in a marked elevation in MDA and NO levels, and XO and MPO activities compared to the untreated controls. Both 1 cycle and 3 cycles of HP prior to H/R resulted in an obvious decrease in all biochemical parameters. Differences of the biochemical results between both HP groups were not statistically significant. Conclusion: This study revealed that whole-body hypoxic preconditioning is beneficial for hypoxia/reoxygenation-induced intestinal injury in newborn rats.