A Model of Intestinal Ischemia in the Neonatal Rat Utilizing Superior Mesenteric Artery Occlusion and Intraluminal Platelet-Activating Factor

Abstract

The human premature newborn is susceptible to necrotizing enterocolitis (NEC) in the first 1 to 3 weeks of life, a time when the gastrointestinal tract is structurally and functionally premature. Studies of NEC are hampered by the lack of a standard, reproducible model in newborn animals. The purpose of this study was to produce a model for intestinal ischemic injury in newborn rats. On Days 14, 18, 22, and 26 of life, newborn rats (10/day) were subjected to 1 hr of superior mesenteric artery occlusion with a microaneurysm clip. Platelet activating factor (PAF, 50 μg/kg) was injected into the lumen of the proximal small intestine after occlusion was initiated. Control animals (10/day) underwent sham laparotomy on Days 14, 18, 22, and 26. Animals were autopsied upon demise (7.6 ± 0.7 hr) or at 24 hr. The intestine was inspected for gross ischemic changes and samples were taken for histology and myeloperoxidase (MPO, an index of neutrophil infiltration). Ischemic injury was graded in a blinded fashion, by a pathologist, using a scale from 0 to 4 (0, no injury; 4, full-thickness necrosis). All animals in the experimental groups had evidence of histologic injury (mean ± SEM) on Days 14 (l.0 ± 0.0), 18 (2.5 ± 0.5), 22 (3.6 ± 0.3), and 26 (3.1 ± 0.5). The sham-operated control animals had no injury ( P < 0.0001). MPO levels (U/g protein) on Days 18 (27.2 ± 1.7 vs 13.9 ± 2.3), 22 (40.9 ± 5.4 vs 7.6 ± 0.8), and 26 (29.3 ± 4.4 vs 7.6 ± 1.0) were significantly higher in experimental groups vs controls ( P < 0.001). We conclude that this model produces consistent and reproducible ischemic injury in the newborn rat intestine and could serve as a model for necrotizing enterocolitis.