Rat milk and dietary long arginine3 insulin-like growth factor I promote intestinal growth of newborn rat pups

Maternal low intensity physical exercise prevents obesity in offspring rats exposed to early overnutrition

Low intensity exercise during pregnancy and lactation may create a protective effect against the development of obesity in offspring exposed to overnutrition in early life. To test these hypotheses, pregnant rats were randomly assigned into 2 groups: Sedentary and Exercised, low intensity, on a rodent treadmill at 30% VO_2Max /30-minute/session/3x/week throughout pregnancy and the lactation. Male offspring were raised in small litters (SL, 3 pups/dam) and normal litters (NL, 9 pups/dam) as models of early overnutrition and normal feed, respectively. Exercised mothers showed low mesenteric fat pad stores and fasting glucose and improved glucose-insulin tolerance, VO_2max during lactation and sympathetic activity. Moreover, the breast milk contained elevated levels of insulin. In addition, SL of sedentary mothers presented metabolic dysfunction and glucose and insulin intolerance and were hyperglycemic and hyperinsulinemic in adulthood. SL of exercised mothers showed lower fat tissue accretion and improvements in glucose tolerance, insulin sensitivity, insulinemia and glycemia. The results suggest that maternal exercise during the perinatal period can have a possible reprogramming effect to prevent metabolic dysfunction in adult rat offspring exposed to early overnutrition, which may be associated with the improvement in maternal health caused by exercise.

Functional analysis of the IGF-system in milk

The development of milk during evolution is considered a more recent step to provide the neonate with adequate amounts of energy, nutrients, and specific hormonal signals thereby, granting a fast and efficient rate of postnatal growth and development. Since the insulin- or the insulin-like growth factor (IGF) systems were evolved much earlier, it can be assumed that the functionality of the IGF-system has been integrated into the novel matrix milk containing casein and whey proteins from the beginnings. In fact, IGFs and IGF-binding proteins (IGFBPs) are abundantly present in milk, which is particularly true for fore-milk or colostrum and the potential effects of milk-borne IGF-compounds on the consuming organisms have in fact been addressed by several studies. Those studies examined, if orally administered IGFs can be absorbed by the consumer's gastro-intestinal tract and thus contribute e.g. to the somatic growth of infants. A second line of studies assessed local effects of milk-borne IGFs on growth and development of the gastro-intestinal tract itself. Finally, distinct functions of isolated IGF-compounds for growth and involution of the mammary gland have also been provided in the past. While the consumption of milk seems not to represent a major source of endogenous IGFs, accumulating evidence indicates secondary effects of milk on the endogenous IGF-system, which may be mediated by micronutrients such as branched amino acids and metabolic programming. By contrast, direct effects on growth and development of oesophageal and intestinal cells have been observed if IGFs were administered orally.

Temporal changes in insulin-like growth factors I and II and in insulin-like growth factor binding proteins 1, 2, and 3 in human milk

AIM

To evaluate the postpartum time course of changes in insulin-like growth factors (IGFs) and their binding proteins (IGFBPs).

METHODS

Breast milk IGF-I and IGF-II and IGFBP-1, IGFBP-2, and IGFBP-3 levels were determined in 23 women with babies born at term, from day 4 until up to 9 months after birth.

RESULTS

The IGFBP-3 levels were highest from day 4 to day 6 and then decreased by days 10-12. In contrast, IGF-I and IGF-II and IGFBP-1 and IGFBP-2 showed little change over the first 2 weeks after birth. Subsequently, all the IGF components showed a moderate decline over approximately the first 1-3 months and then stable levels up to 9 months after birth.

CONCLUSION

Although the possibility cannot be excluded that these changes in levels of IGFs and their binding proteins in human milk represent passive loss from the mammary gland, we speculate that higher early levels of the human milk IGF system contribute to maturation of the infant gut.

Artificial rearing of mouse pups: development of a mouse pup in a cup model

Artificial rearing of rat pups has been used in the investigation of the neonatal gut. We propose to adapt the model of artificially rearing rat pups for use in mouse pups, thereby allowing the use of transgenic animals for our research. We hypothesized that gastrostomy catheters may be placed successfully into neonatal mouse pups and that the pups may be artificially reared without significant alterations in their growth or intestinal development. Gastrostomy tubes are placed into 5-d-old mouse pups [artificially reared (AR); n = 32], and the mice are fed rodent milk substitute. Littermate pups [maternally reared (MR); n = 22] are used as controls. After 5 d, pups are killed and their organs are harvested. Intestinal villus measurements, protein content, and DNA content are determined. Data are reported as mean +/- SEM, compared with appropriate statistical methods, and significance is determined at P < 0.05. Initial weights and lengths are not different between the two groups, but after 5 d, MR pups weigh more than their AR counterparts (5.0 +/- 0.13 versus 4.1 +/- 0.14 g, MR versus AR; P < 0.01). However, the pups' length and the intestinal villus height-to-width ratios, protein, and DNA content are not different between the MR and AR pups. To our knowledge, this is the first report of artificially rearing mouse pups. Development of this technique will permit nutritional manipulation in neonatal mice, a mammalian model wherein the genome is sequenced and transgenic mutants are available.

Key nutrients and growth factors for the neonatal gastrointestinal tract

The nutritional support of gastrointestinal growth and function is an important consideration in the clinical care of neonatal infants. In most health infants, the provision of either breast milk or formula seems to support normal intestinal mucosal growth, but the most significant advantages of breast milk may be for host defense or gut barrier-related functions that are involved in reducing infection. The specific effects of various milk-borne growth factors on key mucosal immune and barrier functions are likely to provide valuable new clues to the advantages of human milk. A substantial number of preterm, low-birth weight babies or those suffering from compromised intestinal function, however, often cannot tolerate oral feedings and instead receive TPN. The consequences of TPN on gastrointestinal function and how this contributes to morbidity of these infants warrants further study, with respect to both clinical and basic research questions. Although enteral nutrition seems to be a critical stimulus for intestinal function, the minimal amounts and composition of nutrients necessary to maintain specific intestinal functions remain to be established. The experimental tools exist to start defining the specific nutrient requirements for the infant gut and some of these nutrients are known (e.g., glutamate, glutamine, and threonine). Peptide growth factors and gut hormones clearly play a role in gut growth and in several ways mediate the trophic actions of enteral nutrition. Although a number of these growth factors are good candidates for therapeutic use, their clinical application in the management of gastrointestinal insufficiency and disease has been slow. The emergence of GLP-2 as a trophic peptide that seems to target the gut is a promising candidate on the horizon.

Feeding colostrum, its composition and feeding duration variably modify proliferation and morphology of the intestine and digestive enzyme activities of neonatal calves

We studied the effects of amounts of colostrum consumed on intestinal morphology and proliferation and digestive enzyme activities in neonatal calves. Group GrCmax calves were fed colostrum from the first milking undiluted on d 1-3 and diluted with 25, 50, 75 and 75 parts of a milk replacer on d 4-7. Group GrC1-3 calves were fed colostrum from milkings 1-6 up to d 3 and then a milk replacer up to d 7. Group GrF1-3 calves were fed a milk-based formula (containing only traces of growth factors and hormones) up to d 3 and then a milk replacer up to d 7. Calves were killed on d 8. Differences in feeding affected villus sizes and villus height/crypt depth ratios in the duodenum (GrCmax > GrC1-3), villus areas and villus height/crypt depth ratios in the jejunum (GrC1-3 > GrF1-3) and crypt depths in the colon (GrF1-3 > GrC1-3). Furthermore, different feeding protocols affected the proliferation rates of epithelial cells in the duodenum (GrC1-3 > GrCmax; GrC1-3 > GrF1-3) and the jejunum (GrF1-3 > GrC1-3; based on Ki-67 labeling). Lipase activities in the pancreas were influenced by colostrum feeding (GrC(max) > GrC(1-3)). Colostrum intake differentially affected intestinal epithelial surface and proliferation and enzyme activities. Feeding high amounts of first colostrum seemed to enhance the survival of mature mucosal epithelial cells in selected parts of the small intestine, whereas the lack of colostrum seemed to decrease epithelial growth.

Dietary regulation of intestinal gene expression

We are becoming increasingly aware of inherited genetic abnormalities as causes of disease. However, alterations in gene expression can also contribute to other disease processes. Recently it has been suggested that our environment may alter such genes and thus be a direct influence on disease. Diet is a potent mechanism for altering the environment of cells of most organs, particularly the gastrointestinal tract. This review addresses the influence of nutritional factors on intestinal gene regulation. These influences include insulin, which is not a dietary component but responds to dietary changes, and butyrate, a short chain fatty acid produced by normal intestinal flora. Manipulation of diet may be a means of treating intestinal disorders. Nutritional treatment therefore is also discussed in the light of its effect on gene expression.

The clinical, morphologic, and molecular changes in the ileum associated with early postnatal dexamethasone administration: from the baby's bowel to the researcher's bench

Focal small bowel perforation (FSBP) is a life-threatening event that predominantly affects extremely low birth weight (ELBW) infants. Histopathology from surgical specimens of ileum with FSBP shows a healthy mucosa overlying a thinned muscularis with segmental degeneration. Clinical data strongly support an association between early postnatal administration of dexamethasone (EPD) and FSBP. Additional risk factors, including gestational age, administration of prophylactic indomethacin, and severity of illness, may be synergistic with EPD for the pathogenesis of perforations. Animal models of dexamethasone administration show morphologic changes in the ileum, similar to those seen in ELBW infants, including increased mucosal maturation and thinning of the muscularis. These tissue-specific differences may be mediated by a perturbation in growth factor expression or accumulation. In support of this hypothesis, dexamethasone has been associated with increased IGF-I immunolocalization in the mucosa and decreased immunolocalization in the muscularis. The known growth-promoting functions of IGF-I are consistent with the observed dexamethasone-associated changes within both the mucosa and the muscularis. Ongoing studies in this animal model are exploring the potential mechanisms by which dexamethasone might affect IGF-I availability.

Stability of insulin-like growth factor I in the gastrointestinal lumen in neonatal pigs

BACKGROUND

Insulin-like growth factor (IGF)-I is present in the milk of various species. A prerequisite for any biological activity of milk-borne IGF-I in the suckling young is to survive the gastrointestinal luminal digestion. In the present study, the stability of IGF-I was examined in the gastrointestinal lumen in neonatal pigs.

METHODS

Iodine-labeled IGF-I was incubated in the gastrointestinal luminal fluids of 3-day-old suckling and 45-day-old weaned pigs at 37 degrees C for 20 minutes. Degradation of the peptide was analyzed by trichloroacetic acid (TCA) precipitation, liquid chromatography, and receptor binding assay.

RESULTS

IGF-I remained unchanged in the gastric fluids of suckling and weaned pigs when determined by TCA precipitation. IGF-I degraded 3%, 18%, and 37% in the luminal fluids of the proximal, mid and distal small intestine in suckling piglets compared with 53%, 62%, and 54% in weaned pigs. The results were supported by the chromatography and receptor binding analysis. Porcine colostrum had a capacity to protect IGF-I from gastrointestinal luminal digestion in weaned pigs.

CONCLUSION

Milk-borne IGF-I is stable in the gastrointestinal lumen in suckling pigs and may play a role in regulating postnatal development in the suckling young.

Milk-borne epidermal growth factor modulates intestinal transforming growth factor-alpha levels in neonatal rats

Epidermal growth factor (EGF) is present in milk from various mammalian species, but its physiologic function in neonatal development remains unclear. Transforming growth factor-alpha (TGF-alpha) is a peptide structurally related to EGF, and its presence is detected in the developing small intestine of rats. The purpose of the present study was to examine the effect of milk-borne EGF on endogenous production of EGF and TGF-alpha in the small intestine of suckling rats. Neonatal rats were fed via gastrostomy either growth factor-free rat milk substitute (RMS) or RMS supplemented with EGF (100 ng/mL of RMS) from 8 to 12 d of age. Artificially reared rats were then compared with their dam-fed littermates. Animals fed the EGF-deficient diet RMS had markedly increased EGF and TGF-alpha mRNA levels in duodenum and ileum compared with dam-fed controls and significantly elevated total intestinal content of TGF-alpha peptide. Intestinal EGF content and EGF serum levels were significantly decreased in the RMS group compared with controls. The addition of EGF to the RMS diet normalized TGF-alpha mRNA levels in the duodenum and ileum, EGF mRNA levels in the ileum, and total intestinal TGF-alpha content and EGF serum levels to the levels measured in dam-fed littermates. Motility studies showed that enteral administration of EGF did not affect stomach emptying and intestinal transit. These studies indicate that exogenous milk-borne EGF modulates endogenous production of TGF-alpha in developing small intestine. It is likely that neither TGF-alpha nor EGF are solely responsible for small intestinal overgrowth of artificially reared neonatal rats.