大鼠生后早期营养状况对成年期胰岛素抵抗的影响

Effects of early postnatal nutrition on adult-onset insulin resistance in Sprague-Dawley rats

目的：通过生后早期营养干预，探讨生后早期营养环境对大鼠成年期胰岛素抵抗的影响。方法新生Sprague-Dawley大鼠于生后第2天制备生后早期营养过度（3只/窝，营养过度组）、营养正常（10只/窝，营养正常组）和营养不足（20只/窝，营养不足组）模型，每组8窝。每窝保姆鼠给予常规普通饲料喂养，至仔鼠3周龄（21 d）时断乳，每窝取3只雄性子代大鼠。按每笼3只给予常规普通饲料，喂养至16周龄。于3和16周龄取肝脏、肾周脂肪垫、附睾脂肪垫和腓肠肌，称重并记录，计算与体重比的相对质量，并提取血清标本。动态观察各组大鼠生理、生化指标和胰岛素抵抗情况（包括测定血清胰岛素水平、稳态模型法计算胰岛素抵抗指数和腹腔葡萄糖耐量试验）。采用方差分析对数据进行统计学处理。结果（1）断乳前，营养过度组自10 d起体重均明显大于营养正常组，营养不足组自7d起体重均明显低于营养正常组；断乳后，营养过度组大鼠体重仍持续大于营养正常组，而营养不足组大鼠体重则仍持续小于营养正常组（P值均＜0.05）。（2）3周龄时，营养过度组肝脏、肾周脂肪、附睾脂肪质量明显高于营养正常组，而营养不足组明显低于营养正常组；营养不足组腓肠肌质量明显低于营养正常组（P值均＜0.05）。营养过度组大鼠的肾周脂肪和附睾脂肪的相对质量明显高于营养正常组，营养不足组大鼠的附睾脂肪相对质量则明显低于营养正常组（P值均＜0.05）。16周龄时，营养过度组大鼠肝脏、附睾脂肪和腓肠肌质量高于营养正常组，而营养正常组主要组织质量均高于营养不足组；营养过度组大鼠的附睾脂肪相对质量明显高于营养正常组（P值均＜0.05）。（3）3周龄时，营养过度组大鼠空腹血糖水平明显高于营养正常组和营养不足组[（7.77±1.10）、（6.33±1.20）和（5.80±1.51）mmol/L，F=13.217， P ＜0.01]；16周龄时，营养过度组大鼠血清胰岛素水平明显高于营养正常组和营养不足组[（0.31±0.11）、（0.16±0.08）和（0.14±0.11）ng/ml，F=5.369，P=0.017]；3周龄时营养不足组大鼠稳态模型法计算胰岛素抵抗指数明显低于营养正常和营养过度组（0.09±0.01、0.25±0.01与0.31±0.05，F=25.923，P=0.005）；16周龄时营养过度组的这一指标明显高于营养正常和营养不足组（1.77±0.53、0.84±0.44与0.83±0.67，F=5.765，P=0.015）。14周龄腹腔葡萄糖耐量试验显示，营养过度组大鼠60 min血糖值和曲线下面积均高于营养正常组和营养不足组（P值均＜0.05）。（4）16周龄时，营养过度组血清白蛋白、甘油三酯和游离脂肪酸水平均高于营养正常组（P值均＜0.05）。结论生后早期营养过度可导致大鼠持续体重过重和内脏白色脂肪堆积，生后早期营养不足则与之相反。生后早期营养过度导致大鼠成年期胰岛素抵抗。应避免在这一生长发育的关键期过度营养，以防止或减少远期代谢综合征的发生风险。

Objective To explore the effects of early postnatal nutrition on adult-onset insulin resistance by an artificial nutrition intervention during the critical period. Methods On postnatal day 2, Sprague-Dawley rats were assigned randomly to overnutrition （SL）, normonutrition （NL） and undernutrition （LL） via artificially adjusting the number of pups nursed per dam. Litter size was adjusted to 3 pups/dam, 10 pups/dam and 20 pups/dam for the SL, NL and LL groups, respectively. There were eight litters for each group. All the pups were nursed by their natural dams and fed with a standard rodent laboratory chow. The pups were weaned on postnatal day 21 and three male pups from each litter were separated. After that, all male rats were housed three per cage and fed standard chow until 16 weeks old. At 3 and 16 weeks, rats were killed after overnight fasting and blood was collected. Liver, gastrocnemius muscle and perirenal and epididymal fat pads were dissected and weighed to calculate relative mass after normalization for body weight. Physiological parameters, biochemical values and insulin resistance status, including serum insulin level, homeostasis model assessment for insulin resistance （HOMA-IR） index and intraperitoneal glucose tolerance test （IPGTT）, were dynamically monitored. Analysis of variance was used for statistical analysis. Results （1） Before weaning, the body weights of SL rats were significantly heavier than NL rats after postnatal day 10, and weights of LL rats were significantly lower than NL rats after postnatal day 7. After weaning, body weights of SL rats still remained heavier and weights of LL rats continued to be lower than NL rats （P〈0.05）. （2） At 3 weeks, the weights of liver and perirenal and epididymal fat pads in SL rats were significantly heavier than NL rats, whereas LL rats were lower than NL rats （P〈0.05）. At 16 weeks, the weights of liver, epididymal fat pads and gastrocnemius muscle in SL rats were significantly heavier than NL rats. Meanwhile, the weights of all detected tissues in LL rats were lower than the NL group. The weights of epididymal fat pads after normalization for body weight in the SL group were heavier than the NL group （P〈0.05）. （3） At 3 weeks, the fasting serum glucose level of the SL group was significantly higher than the NL and LL groups [（7.77±1.10） vs （6.33±1.20） and （5.80±1.51） mmol/L, respectively, F=13.217, P〈0.01]. At 16 weeks of age, the serum insulin level in SL rats significantly increased compared to NL and LL rats [（0.31±0.11） vs （0.16±0.08） and （0.14±0.11） ng/ml, respectively, F=5.369, P=0.017]. For HOMA-IR evaluation, the index was significantly lower in LL rats compared to NL and LL rats at 3 weeks of age [（0.09±0.01） vs （0.25±0.01） and （0.31±0.05）, respectively, F=25.923, P=0.005]. At 16 weeks, the index was significantly elevated in SL rats compared to NL and LL rats [（1.77±0.53） vs （0.84±0.44） and （0.83±0.67）, respectively, F=5.765, P=0.015]. Furthermore, IPGTT was performed in all groups at 14 weeks of age. SL rats had significantly higher serum glucose levels at 60 min and a significantly increased area under the curve when compared to NL and LL rats （all P〈0.05）. （4） Serum from 16 week old SL rats was found to contain significantly higher levels of albumin, triglycerides and free fatty acids compared to NL rats （all P〈0.05）. Conclusions Early postnatal overnutrition induces persistent overweight and visceral white adipose accumulation in rats, while early postnatal undernutrition show the opposite effects. Early postnatal overnutrition may lead to adult-onset insulin resistance in rats. Avoiding overnutrition during the early postnatal period, a critical window for growth and development, may prevent or decrease later metabolic risks.