Does maternal nicotine exposure during gestation increase the injury severity of small intestine in the newborn rats subjected to experimental necrotizing enterocolitis

Background/Purpose

The aim of this study was to evaluate the effects of maternal nicotine exposure during gestation on injury severity of small intestine in the newborn rats subjected to hypoxia-reoxygenation and cold stress.

Methods

A total of 21 Sprague-Dawley pregnant rats were divided into 3 equal groups. The groups were labeled as group 1, control group; group 2, hypoxia-reoxygenation group; and group 3, nicotine-hypoxia-reoxygenation group. The rats of group 3 were exposed to nicotine via subcuticular injection for the last week of gestation (2 mg/kg/d). Newborn rats were collected immediately after birth to prevent suckling of maternal milk (40 rat pups in group 1, 43 rat pups in group 2, and 41 rat pups in group 3). Litters in groups 2 and 3 were stressed twice daily with asphyxia followed by cold (4°C for 10 minutes) stress to induce hypoxic intestinal injury which is relevant to human necrotizing enterocolitis. Breathing 100% CO₂ for 10 minutes in a chamber followed by 10-minute 100% O₂ breathing was the asphyxia model repeated twice daily. After hypoxia-reoxygenation and cold stress, newborn rats were returned to their mother's cages. This protocol was repeated for the following 2 days, and the rat pups were decapitated on the third day. Using this protocol of asphyxia and cold stress, all of neonatal rats developed clinical and pathological signs of hypoxia-induced intestinal injury. The entire gastrointestinal tract was removed and examined macroscopically. A 2-cm section of distal ileum from each animal was taken for histopathological and biochemical examinations. Histological changes in ileal architecture were scored and graded from 1 to 5. The remaining intestinal tissues of the animals were used for lipid peroxidation analysis.

Results

Typical signs of hypoxia-induced intestinal injury were observed in the 2 experimental groups (groups 2 and 3) macroscopically. There were more grades 3 and 4 injuries in group 3 (P < .05). The malondialdehyde levels were elevated in groups 2 and 3 (P < .001). The malondialdehyde levels of the group 3 were also significantly higher than group 2 (P < .01).

Conclusions

Maternal nicotine exposure during gestation results in higher grade histological injury in newborn rats subjected to hypoxia-reoxygenation and cold stress.