Dietary insulin affects leucine aminopeptidase, growth hormone, insulin-like growth factor I and insulin receptors in the intestinal mucosa of neonatal pigs.

BACKGROUND: Recent studies suggest that milk-borne insulin may regulate the development of the gastrointestinal tract in neonatal mammals. OBJECTIVES: To explore the mechanism by which milk-borne insulin affects gastrointestinal tract development, we examined the effect of dietary insulin on the expression levels of leucine aminopeptidase (LAP) and insulin-like growth factor I (IGF-I), as well as its effect on growth hormone (GH), IGF-I and insulin receptors in the small intestinal mucosa of neonatal pigs. METHODS: Five piglets were anesthetized and sampled within 2-4 h after birth. They were not allowed to suckle and were used as newborn controls (group N). Ten other piglets from 5 litters were randomly divided into group M (n=5), which was fed cow's milk, and group MI (n=5), which was fed cow's milk and insulin (2.5 mg/l). Piglets in groups M and MI were artificially fed for 3 days and then sampled. Total RNA in their intestinal mucosa was extracted with Tripure reagents (Roche, USA). Reverse transcription PCR (RT-PCR) was used to semi-quantify mRNA levels of target genes and 18S rRNA was used in an RT-PCR system as an internal control. PCR products were loaded onto a 9% nondenaturing polyacrylamide gel. The gel was stained by silver staining agents. Digital photos were taken and the strength of the band areas was quantified using software. RESULTS: The results showed that the DNA contents and LAP activity in the small intestines of the piglets in group MI were higher (p<0.05) than in the piglets in group N. Compared with group M, piglets in group MI exhibited significantly increased expression levels of both insulin and GH receptor in the ileum, and LAP in the jejunum (p<0.05); IGF-I receptor expression levels in both the jejunum and ileum were significantly decreased (p<0.01 and p<0.05, respectively), while IGF-I expression was unchanged (p>0.05). CONCLUSION: Collectively, dietary insulin increased mRNA levels of insulin and GH receptor, which could help explain the effect of dietary insulin on receptor-mediated postnatal development of the small intestine. Dietary insulin suppressed IGF-I receptor expression, which may be the result of negative feedback caused when insulin binds to IGF-I receptors.

Effects of intrauterine growth retardation on development of the gastrointestinal tract in neonatal pigs.

BACKGROUND: Intrauterine growth retardation (IUGR) is a common problem in human and other species and increases the risk of death of the fetus and newborn during the perinatal period. OBJECTIVES: This study was conducted to examine the influences of intrauterine growth retardation (IUGR) on development of the gastrointestinal tract in newborn pigs. METHODS: Ten animals from five litters were divided into five piglets with IUGR and five with normal birth-weight (NW). The IUGR category comprised animals with a birth weight 2 SD below the mean birth weight of the total population, while the NW category included animals with a birth weight within one SD of the mean birth weight in the total population. Animals were anesthetized and sampled within 2-4 h after birth and without suckling. The morphological changes of intestine and stomach of IUGR piglets were compared with NW ones. The expressions of IGF-I and receptors for growth hormone and insulin in intestinal mucosa were semiquantified using reverse transcription PCR. RESULTS: The results of our study indicated that the weights of the stomach, small intestine and small intestinal mucosa were significantly lower in IUGR compared with NW piglets (p<0.01). In addition, the lengths of the small intestine and colon in IUGR pigs were also significantly less than those of NW (p<0.05). Furthermore, insulin-like growth factor-I (IGF-I) mRNA level in intestinal mucosa of IUGR piglets was increased significantly (p<0.05), and the expression mRNA levels of insulin receptor and growth hormone (GH) receptor in the mucosa in IUGR piglets showed a tendency to be lower (p=0.17 and p=0.11, respectively) than those of the NW animals. CONCLUSION: We conclude from the data that IUGR affects intestinal growth and morphology and is in associated with altered gene expression of growth-related proteins. We speculate that the morphological change and associated altered endocrine homeostasis contribute to lower growth rates of pigs affected by IUGR.