Establishment and evaluation of three necrotizing enterocolitis models in premature rats

Necrotizing enterocolitis (NEC) is a gastrointestinal disease that usually affects premature infants and has high morbidity and mortality rates. Reliable animal models aid further study of the etiological factors, pathogenesis, prevention and treatment of NEC. The present study aimed to establish NEC models in premature rats using three common methods, and to determine the optimal model establishment method. The study consisted of six groups; in group A, rats were raised with simulated milk and subjected to inhalation of 100% nitrogen gas (hypoxia) for 90 sec, followed by exposure to cold ambient conditions (4˚C) for 10 min twice daily for 3 days. In group B, rats were exposed to 100% nitrogen gas for 5 min and 100% oxygen for 5 min twice daily for 3 days. Group C rats were intraperitoneally administered 5 mg/kg lipopolysaccharide. Group D and E rats did not receive any intervention. Group F rats were intraperitoneally administered 1 ml/kg physiological saline. Groups D-F served as the control groups corresponding to groups A-C, respectively. Following hematoxylin and eosin staining, intestinal tract, liver, lung and kidney tissues were observed under optical microscopy and were scored. Successful NEC induction was measured by a score of ≥2. Rats from groups A-C exhibited reduced movement, abdominal distention, diarrhea, intestinal tract expansion, and congestion to varying degrees. The pathological scores of intestinal injury in groups A-F were 3.13±0.64, 1.40±0.52, 2.00±0.42, 0.30±0.48, 0.30±0.48, and 0.40±0.52 points, respectively. Significant differences were found between the model groups and their corresponding control groups (p<0.01). Among the model groups, the histological score of group A was higher than that of groups B (p<0.01) and C (p<0.05). The morbidity rate of NEC in groups A-C was 75, 20 and 50%, respectively. There was no morbidity in groups D-F. Compared with groups A and B, injury to the liver, kidney and lung was more severe in group C. Similar symptoms were not observed in groups D-F. Compared with methods of simple hypoxia-reoxygenation or intraperitoneal administration of lipopolysaccharide, the combination of artificial feeding and hypoxia plus cold stimulation most resembles the pathological causes of neonatal NEC. This method resulted in high morbidity, reproducibility and specificity, and was therefore considered an ideal model for establishing NEC.