Effects of early postnatal nutrition on adult-onset insulin resistance in Sprague-Dawley rats / 中华围产医学杂志

ABSTRACT

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.