Oral insulinlike growth factor-I stimulates intestinal enzyme maturation in newborn rats

Preterm human milk: associations between perinatal factors and hormone concentrations throughout lactation

BACKGROUND

Infants born moderate to late preterm constitute the majority of preterm births, yet guidelines for their nutritional care are unclear. Maternal milk is the most appropriate nutrition for these infants; however, its composition can be influenced by environmental factors. The present study therefore investigated perinatal predictors of human milk composition in a preterm cohort.

METHODS

Milk was collected during the DIAMOND trial (DIfferent Approaches to Moderate and late preterm Nutrition: Determinants of feed tolerance, body composition and development) from 169 mothers of 191 infants at three time-points (5 and 10 days post partum and 4 months' corrected age). Leptin, adiponectin and insulin-like growth factor-1 (IGF-1) were analysed by enzyme-linked immunosorbent assay. Generalised mixed models were used to evaluate associations between milk composition and maternal/infant/perinatal factors.

RESULTS

Most findings were independent of collection time-point. Gestational diabetes was associated with lower adiponectin. Higher adiponectin and lower leptin were associated with higher socioeconomic status, higher maternal education and ability to fully breastfeed at discharge from hospital. Higher leptin was associated with high perceived stress during hospital admission. Milk IGF-1 displayed sex-specific patterns in association with maternal social deprivation.

CONCLUSION

Maternal, infant and environmental factors during the perinatal period were associated with milk compositional profiles throughout lactation. Further clinical trials should investigate the impact of such changes in terms of long-term infant outcomes.

IMPACT

Human milk is the best nutrition for the infant. However, its composition may be susceptible to alterations determined by pathological conditions mother and infant may face throughout pregnancy and in the perinatal period. This study found that perinatal factors are associated with human milk composition from early to late lactation. If human milk composition throughout lactation is "programmed" during pregnancy or early lactation, infants who were exposed in utero to environmental insults may still be exposed to them during lactation. The impact of human milk compositional alteration on infant growth following perinatal pathological events requires further investigation.

Prolyl hydroxylase 2 silencing enhances the paracrine effects of mesenchymal stem cells on necrotizing enterocolitis in an NF-κB-dependent mechanism

Treatment options for necrotizing enterocolitis (NEC) remain inadequate. Here we examined if and how prolyl hydroxylase 2 (PHD2) silencing enhances the paracrine effects of bone-marrow-derived mesenchymal stem cells (BM-MSCs) on NEC. In this study, BM-MSCs were transduced with lentiviruses containing GFP (GFP-MSC) or shPHD2-GFP constructs (PHDMSC), followed by intraperitoneal injection of the PHDMSC-conditioned medium (PHDMSC-CM) or the GFP-MSC-conditioned medium (MSC-CM) into a rat pup model of NEC. Our results showed that systemic infusion of PHDMSC-CM, but not MSC-CM, significantly improved intestinal damage and survival of NEC rats. Such benefits may involve the modulation of epithelial regeneration and inflammation, as indicated by the regeneration of intestinal epithelial/stem cells, the regulation of Treg cells function and pro-/anti-inflammatory cytokine balance. The mechanism for the superior paracrine efficacy of PHDMSC is related to a higher release of pivotal factor IGF-1 and TGF-β2. NF-κB activation was induced by PHD2 silencing to induce IGF-1 and TGF-β2 secretion via binding to IGF-1 and TGF-β2 gene promoter. Our work indicated that PHD2 silencing enhanced the paracrine effect of BM-MSCs on NEC via the NF-κB-dependent mechanism which may be a novel strategy for stem cell therapy on NEC.

The availability of probiotics and donor human milk is associated with improved survival in very preterm infants

BACKGROUND

To determine whether the introduction of pasteurized donor human milk and probiotics for infants born < 32 weeks gestational age or < 1500 g birthweight is associated with a reduction in mortality and the incidence of necrotising enterocolitis (NEC) and sepsis.

METHODS

We performed a retrospective analysis of two cohorts: before and after the introduction of probiotics and pasteurised donor human milk. Univariate analysis of primary and secondary outcomes was performed; variables impacting outcomes were assessed using multivariate logistic regression.

RESULTS

There were 1791 infants: 1334 in the pre-donor milk/probiotic cohort and 457 in the post-donor milk/probiotic cohort. On univariate analysis, mortality (7.6 vs. 2.4%, P < 0.001) and incidence of sepsis (6.2 vs. 3.5%, P = 0.028) were statistically significantly lower in the post-donor milk/probiotic group. NEC (2.8 vs. 1.5%, P = 0.14) and non-NEC associated gastrointestinal perforation (1.6 vs. 0.4%, P = 0.052) were lower in the post-donor milk/probiotics cohort, but these were not statistically significant. The difference in mortality remained statistically significant on multivariate analysis in the post-donor milk/probiotic cohort compared to those in the pre-donor milk/probiotic cohort (odds ratio 0.31, 95% confidence interval 0.16-0.61). The decrease in the incidence of NEC was consistent with previous observational studies but the difference was not statistically significant.

CONCLUSION

The availability of probiotics and pasteurised donor human milk is associated with a reduction in mortality in very preterm infants.

Effect of human milk formula with bovine colostrum supplementation on bone mineral density in infant cynomolgus macaques

Insulin-like growth factor 1 (IGF1) is a regulator of human growth during infancy and childhood, known to promote bone and muscle growth as well as lipid accumulation. This study aimed to investigate the effects of formula milk with or without IGF1 supplementation (in the form of pure IGF1 or bovine colostrum) on growth and body composition in infant cynomolgus macaques during the first 6 months of life. Three groups of infants were nursery-reared and received formula milk with or without IGF1 or bovine colostrum supplementation for 4 months, and a fourth group consisting of breast-fed infants was included for comparison (n=6 for each group). Ranked-based analysis of covariance was used to detect differences between adjusted means for sex. No differences in weight, height, fat mass, and fat-free mass could be detected between groups. However, bone mineral density (BMD) was significantly different between groups at the end of formula feeding. Infants that received bovine colostrum supplementation displayed higher mean BMD than infants of all other groups, with no differences between the latter three groups. In conclusion, our results suggest that supplementation with bovine colostrum can enhance BMD in formula-fed infants, an effect that apparently does not depend on IGF1. Bovine colostrum supplementation could be beneficial for long-term bone health in infants with suboptimal bone growth.

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.

Nutritional interventions to prevent and rear low-birthweight piglets

Selection for hyperprolific sows, as a means of increasing litter size and profit, has resulted in an increased number of low-birthweight (LBW) piglets. These LBW piglets might suffer from increased morbidity and mortality during the early neonatal period. In addition, they show reduced growth performance, meat and carcass quality, which leads to an important economic loss for the farmer in the post-natal period. Therefore, nutritional interventions can be undertaken to prevent and rear LBW piglets. In the first part of this review, the preventive strategies at the sow level will be discussed. Approaches in preventing LBW piglets are to optimize the intrauterine environment via supplementing the sow during gestation. In the second part of this review, the interventions at the piglet level will be described. To increase the survival and growth rates of LBW piglets, one must focus on ensuring adequate colostrum and milk intake. Interventions include supplementing piglets, split nursing, split weaning and cross-fostering. Additional interventions increasing the probability of optimal post-natal food intake will be discussed.

Effect of breast milk on hospital costs and length of stay among very low-birth-weight infants in the NICU

PURPOSE

Care of the very low-birth-weight (VLBW) infant is associated with prolonged hospitalization and increased hospital costs. Specific complications of prematurity, including necrotizing enterocolitis (NEC), late-onset sepsis (LOS), and feeding intolerance, contribute to increased cost and length of hospitalization in this population. The provision of breast milk to VLBW infants has been associated with decreased incidence of NEC and LOS as well as fewer days required to achieve full enteral feedings. The purpose of this study was to determine the impact of breast milk on length of hospitalization and hospital costs among VLBW infants in the neonatal intensive care unit (NICU).

SUBJECTS

A total of 80 infants weighing less than 1500 g, born prior to 32 weeks' gestation and who remained in the home hospital until discharge.

DESIGN

This descriptive comparative study examined cost of hospitalization and length of stay between 2 groups of VLBW premature infants fed either exclusively formula (n = 40) or at least 50% breast milk (n = 40) during their hospitalization.

METHODS

A retrospective chart review was used to collect information concerning patient demographics, discharge information, and nutritional variables. Information regarding hospital costs was obtained from the hospital's patient accounting office.

MAIN OUTCOME MEASURES

Independent t tests were used to compare demographic data, length of hospitalization, and cost of care between the 2 groups.

PRINCIPAL RESULTS

No statistically significant differences in length of stay or cost of care were found between infants fed at least 50% breast milk and those who were exclusively formula fed. Descriptive data concerning length of stay and cost of care for VLBW infants and those infants weighing less than 1000 g are presented.

CONCLUSION

This article presents a descriptive comparative study on the effect of providing at least 50% breast milk feedings compared with formula feeding on days to discharge and cost of hospitalization in VLBW infants in the NICU. It also provides information concerning cost of care and length of stay in VLBW and infants weighing less than 1000 g.

Human milk consumption and full enteral feeding among infants who weigh </= 1250 grams

OBJECTIVE

Establishing enteral feeding is an important goal in the care of very low birth weight infants. In such infants, receipt of >/=50 mL/kg per day human milk during hospitalization has been associated with shorter time to full enteral feeding. The objective of this study was to determine whether high proportions (>/=50%) of human milk during feeding advancement are associated with shorter time to full enteral feeding and improved feeding tolerance.

METHODS

This was a prospective cohort study of very low birth weight infants (n = 127) who were grouped into low (<50%; n = 34) and high (>/=50%; n = 93) human milk consumption groups according to their human milk proportion of enteral feeding during the time of feeding advancement. The primary outcomes of interest were ages at which 100 and 150 mL/kg per day enteral feedings were achieved.

RESULTS

The high human milk group reached 100 mL/kg per day enteral feeding 4.5 days faster than the low human milk group. The high human milk group reached 150 mL/kg per day enteral feeding 5 days faster than the low human milk group. After adjustment for gestational age, gender, and respiratory distress syndrome, times to reach 100 and 150 mL/kg per day were significantly shorter for those in the high human milk group. Infants in the high human milk group had a greater number of stools per day; other indicators of feeding tolerance were not statistically different.

CONCLUSION

In infants who weighed </=1250 g, enteral feeding that contained at least 50% maternal human milk was associated with fewer days to full enteral feedings.

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.

Effects of Oral Administration of Insulin-Like Growth Factor-I on Circulating Concentration of Insulin-Like Growth Factor-I and Growth of Internal Organs in Weanling Mice

Insulin-like growth factor (IGF)-I is a polypeptide that mediates the growth-promoting action of growth hormone in postnatal animals. The present study was conducted to examine whether orally administered IGF-I would be absorbed into the general circulation and also whether ingested IGF-I would enhance the growth of whole body as well as internal organs, and tissues in 3-week-old ICR-strain female weanling mice. In experiment (Exp) 1, a total of 70 mice received IGF-I orally at 1 microg.g-1 in 0.2-ml PBS or the vehicle alone. Concentrations of IGF-I and glucose in heart blood were measured after killing 5 animals in each group every fourth hour during a 24-hour period. In Exp 2, a total of 40 mice received oral IGF-I administration at 1 microg.g-1 or vehicle every third day beginning from day 0 for a 13-day period. Half the animals were killed at day 7 and the other half at day 13. Weights of whole body and organs/tissues (small intestine, liver, thigh muscle, and brain) were measured every day and at slaughter, respectively. In Exp 1, following the oral IGF-I administration, serum IGF-I concentration increased at hour 4 (p<0.01) and returned to the hour 0 level by hour 8, whereas glucose concentration was lowest at hour 4 and returned to the hour 0 level by hour 16. In the PBS-fed group, neither IGF-I nor glucose concentration changed during the 24-hour period. In Exp 2, weight of small intestine increased (p<0.05) in response to the oral IGF-I, whereas weights of liver and thigh muscle of the IGF-I-fed group were greater (p<0.01) and tended to be greater (p=0.06), respectively, than those of the PBS-fed only at day 13. However, brain weight and serum concentrations of IGF-I and IGF-II were not affected by oral IGF-I administration. Results suggest that although orally administered IGF-I mainly acts at the intestine, a portion of ingested IGF-I is absorbed into the general circulation to enhance the growth of selective organs/tissues in weanling mice.

Hepatocyte growth factor regulates angiotensin converting enzyme expression

Hepatocyte growth factor (HGF) is a mitogen, morphogen, and motogen that functions in tissue healing and acts as an anti-fibrotic factor. The mechanism for this is not well understood. Recent studies implicate somatic angiotensin-converting enzyme (ACE) in fibrosis. We examined the effects of HGF on ACE expression in bovine pulmonary artery endothelial cells (BPAEC). Short term treatment of BPAEC with HGF transiently increased both ACE mRNA (3 h) and activity (24 h), as determined by ACE protease assays and reverse transcription-PCR. Incubation of BPAEC with HGF for longer periods suppressed ACE mRNA (6 h) and activity (72 h). In contrast, phorbol ester (PMA) treatment produced sustained increase in ACE mRNA and activity. We examined the short term molecular effects of HGF on ACE using PMA for comparison. HGF and PMA increased transcription from a luciferase reporter with the core ACE promoter, which contains a composite binding site for SP1/3 and Egr-1. Immunocytochemistry and electrophoretic mobility shift assay showed that both HGF and PMA increased Egr-1 binding. HGF also increased SP3 binding, as measured by EMSA. However, HGF and PMA increased the cellular activity of only Egr-1, not SP3, as measured by luciferase reporter assays. Deletion of the Egr-1 site in the reporter construct completely abrogated HGF-induced transcription but only approximately 50% of PMA-induced activity. Expression of dominant negative Egr-1 and SP3 blocked up-regulation of the ACE promoter by HGF but only reduced up-regulation by PMA. These results show that HGF transiently increases gene transcription of ACE via activation of Egr-1, whereas PMA regulation involves Egr-1 and additional factor(s).

Nutritional and physiologic significance of human milk proteins

Human milk contains a wide variety of proteins that contribute to its unique qualities. Many of these proteins are digested and provide a well-balanced source of amino acids to rapidly growing infants. Some proteins, such as bile salt-stimulated lipase, amylase, beta-casein, lactoferrin, haptocorrin, and alpha1-antitrypsin, assist in the digestion and utilization of micronutrients and macronutrients from the milk. Several proteins with antimicrobial activity, such as immunoglobulins, kappa-casein, lysozyme, lactoferrin, haptocorrin, alpha-lactalbumin, and lactoperoxidase, are relatively resistant against proteolysis in the gastrointestinal tract and may, in intact or partially digested form, contribute to the defense of breastfed infants against pathogenic bacteria and viruses. Prebiotic activity, such as the promotion of the growth of beneficial bacteria such as Lactobacilli and Bifidobacteria, may also be provided by human milk proteins. This type of activity can limit the growth of several pathogens by decreasing intestinal pH. Some proteins and peptides have immunomodulatory activities (eg, cytokines and lactoferrin), whereas others (eg, insulin-like growth factor, epidermal growth factor, and lactoferrin) are likely to be involved in the development of the intestinal mucosa and other organs of newborns. In combination, breast-milk proteins assist in providing adequate nutrition to breastfed infants while simultaneously aiding in the defense against infection and facilitating optimal development of important physiologic functions in newborns.

Insulin-like growth factor-I and its binding proteins in colostrum compared to measures in serum of Holstein neonates

Colostral insulin-like growth factor-I (IGF-I) may be beneficial in the development of gastrointestinal tracts of bovine neonates. Thus, the purpose of this study was to examine relationships among concentrations of IGF-I and IGF-binding proteins (IGFBP) in colostrum used at two initial feedings and serum concentrations of IGF-I, IGFBP, total protein, gamma glutamyltransferase (GGT), and immunoglobulin G at 0 and 48 h after birth in Holstein neonates. Calves (n = 22) were separated from dams immediately after birth. Blood samples were taken before initial feeding and at 48 h after birth. Calves were fed 2 L of colostrum twice and milk replacer thereafter. Linear regression of serum IGF-I at 48 h and colostral IGF-I revealed a significant positive relationship (R2 = 0.204). Serum IGFBP-3 at 48 h and colostral IGFBP-3 also had a positive relationship (R2 = 0.143). However, linear regression of colostral IGF-I on the difference in serum IGF-I at 48 and 0 h was not significant. Calves were assigned to group 1 (0-h serum IGF-I < 10 ng/ml; n = 11) or group 2 (0-h serum IGF-I > or = 10 ng/ml; n = 11) for further analysis. There were no differences in serum IGF-I or IGFBP-2, -3, -4, and -5 concentrations at 48 h between groups 1 and 2. Correlation coefficients revealed negative relationships of serum IGF-I at 0 h to the difference between serum IGF-I at 48 and 0 h (r = -0.824), as well as birth weight of the calf to the amount of GGT at 48 h (r = -0.604). Females had lower birth weights than males, but sex of calf did not affect serum measures. At 0 h, but not 48 h, total serum protein was correlated to serum GGT concentrations (r = 0.573). From indirect evidence, absorption of colostral IGF-I and IGFBP-3 into systemic circulation may occur, but relative importance compared to endogenous sources is uncertain.

Oral IGF-I alters the posttranslational processing but not the activity of lactase-phlorizin hydrolase in formula-fed neonatal pigs

To determine the cellular mechanism whereby oral insulin-like growth factor I (IGF-I) increases intestinal lactase-phlorizin hydrolase (LPH) activity, we studied 2-d-old pigs fed cow's milk formula (control, n = 5), formula + low IGF-I (0.5 mg/L; n = 6) or formula + high IGF-I (12.0 mg/L, n = 6) for 15 d. On d 15, intestinal protein synthesis and lactase processing were measured in vivo in fed pigs using a 6-h intravenous, overlapping infusion of multiple stable isotopes (2H(3)-Leu, 13C(1)-Leu, 13C(1)-Phe, 2H(5)-Phe, 13C(6)-Phe and 13C(9)-Phe). Morphometry and cell proliferation also were measured in the jejunum and ileum. Neither dose of IGF-I affected the masses of wet tissue, protein or DNA, or the villus height, cell proliferation or LPH-specific activity. Oral IGF-I decreased the synthesis and abundance of prolactase-phlorizin hydrolase (pro-LPH), but increased brush-border (BB)-LPH synthesis in the ileum. The BB-LPH processing efficiency was twofold to threefold greater in IGF-fed than in control pigs. In all pigs, villus height and the total mucosal and specific activity of LPH activity were greater in the ileum than in the jejunum, yet the synthesis of BB-LPH were significantly lower in the ileum than in the jejunum. We conclude that oral IGF-I increases the processing efficiency of pro-LPH to BB-LPH but does not affect LPH activity. Moreover, the posttranslational processing of BB-LPH is markedly lower in the ileum than in the jejunum.

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.

Dexamethasone administration to newborn mice alters mucosal and muscular morphology in the ileum and modulates IGF-I localization

Glucocorticoid exposure accelerates the maturation of small bowel mucosa. We hypothesized that IGF-I, a mitogen and differentiating peptide expressed in small bowel, mediates steroid-induced change within the developing ileum. To investigate this possibility, we intraperitoneally administered 1 microg/gm/d of dexamethasone (DEX) or equal volumes of saline to litter-mate newborn mice. The animals were killed on d 1-3 of life and their ilea were harvested and prepared for microscopy. Tissue sections of ileum were examined for morphologic analyses, mucin staining, immunolocalization of IGF-I and -II, proliferating cell nuclear antigen (PCNA), terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL), and in situ hybridization for IGF-I transcripts. Morphologic comparisons showed increases in goblet cell number, total cell number, and TUNEL-positive cells within the mucosa of DEX-treated animals. In contrast, the number of smooth muscle nuclei per cross-section was unchanged with DEX treatment despite a reduction in the number of PCNA-positive nuclei and an increased bowel circumference. These findings suggest the muscularis stretches to accommodate increasing bowel diameter. IGF-I peptide was localized to the mesenchyme of all control animals. After 48 h of DEX treatment, IGF-I was detected in the epithelia whereas mesenchymal IGF-I localization appeared diminished. In situ hybridization analyses for IGF-I transcripts showed no differences in localization between the groups. We conclude that DEX administration differentially affects adjacent tissues in the newborn ileum and that the associated changes in IGF-I localization are consistent with its participation in this process.

Investigation of three doses of oral insulin-like growth factor-I on jejunal lactase phlorizin hydrolase activity and gene expression and enterocyte proliferation and migration in piglets

In a previous study, oral IGF-I at 65 nM increased lactase phlorizin hydrolase (LPH) activity and villus height in piglets, however, the mechanisms were unknown. Herein, the response to a range of doses of IGF-I was investigated and we hypothesized that LPH and villus height would respond to oral IGF-I in a dose-dependent manner. Two 14-d experiments were conducted using cesarean-derived piglets. In experiment 1, piglets (n = 28) were fed formula containing 0, 33, 65, or 131 nmol/L (0, 0.25, 0.5, or 1.0 mg/L) recombinant human IGF-I. In experiment 2, 5'-bromodeoxyuridine was administered to piglets fed formula alone (n = 4) or containing 131 nmol/L IGF-I (n = 4). IGF-I did not affect body weight gain or intestinal weight or length. Jejunal villus height and LPH activity were significantly greater in piglets fed 131 nmol IGF-I/L than control piglets. Villus height and lactase activity in piglets fed the 33 and 65 nmol/L IGF-I doses were similar and intermediate between control and 131 nmol IGF-I/L. Jejunal mRNA expression and LPH polypeptide abundance were investigated in piglets receiving 0 or 131 nmol/L IGF-I. Steady state LPH mRNA abundance was significantly higher (p < 0.05) in IGF-I-treated piglets. The relative abundance of proLPH(h) was not significantly increased (p = 0.06) by IGF-I treatment. Mucosal DNA content and DNA synthesis were greater in piglets receiving 131 nmol IGF-I/L than control, however, enterocyte migration and mucosal protein content were unaffected. Thus, oral IGF-I increased jejunal LPH activity and LPH mRNA abundance and stimulated intestinal cell hyperplasia in normal piglets.

Development of intestinal transport function in mammals

Considerable progress has been made over the last decade in the understanding of mechanisms responsible for the ontogenetic changes of mammalian intestine. This review presents the current knowledge about the development of intestinal transport function in the context of intestinal mucosa ontogeny. The review predominantly focuses on signals that trigger and/or modulate the developmental changes of intestinal transport. After an overview of the proliferation and differentiation of intestinal mucosa, data about the bidirectional traffic (absorption and secretion) across the developing intestinal epithelium are presented. The largest part of the review is devoted to the description of developmental patterns concerning the absorption of nutrients, ions, water, vitamins, trace elements, and milk-borne biologically active substances. Furthermore, the review examines the development of intestinal secretion that has a variety of functions including maintenance of the fluidity of the intestinal content, lubrication of mucosal surface, and mucosal protection. The age-dependent shifts of absorption and secretion are the subject of integrated regulatory mechanisms, and hence, the input of hormonal, nervous, immune, and dietary signals is reviewed. Finally, the utilization of energy for transport processes in the developing intestine is highlighted, and the interactions between various sources of energy are discussed. The review ends with suggestions concerning possible directions of future research.

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.

Modulation of the gastrointestinal tract of infants by human milk. Interfaces and interactions. An evolutionary perspective

Human milk contains agents that affect the growth, development and functions of the epithelium, immune system or nervous system of the gastrointestinal tract. Some human and animal studies indicate that human milk affects the growth of intestinal villi, the development of intestinal disaccharidases, the permeability of the gastrointestinal tract and resistance to certain inflammatory/immune-mediated diseases. Moreover, one cytokine in human milk, interleukin (IL)-10, protects infant mice genetically deficient in IL-10 against an enterocolitis that resembles necrotizing enterocolitis (NEC) in human premature infants. There are seven overlapping evolutionary strategies regarding the relationships between the functions of the mammary gland and the infant's gastrointestinal tract as follows: 1) certain immunologic agents in human milk compensate directly for developmental delays in those same agents in the recipient infant; 2) other agents in human milk do not compensate directly for developmental delays in the production of those same agents, but nevertheless protect the recipient; 3) agents in human milk enhance functions that are poorly expressed in the recipient; 4) agents in human milk change the physiologic state of the intestines from one adapted to intrauterine life to one suited to extrauterine life; 5) some agents in human milk prevent inflammation in the recipient's gastrointestinal tract; 6) survival of human milk agents in the gastrointestinal tract is enhanced because of delayed production of pancreatic proteases and gastric acid by newborn infants, antiproteases and inhibitors of gastric acid production in human milk, inherent resistance of some human milk agents to proteolysis, and protective binding of other factors in human milk; and 7) growth factors in human milk aid in establishing a commensal enteric microflora.

Transgenic hypersecretion of des(1-3) human insulin-like growth factor I in mouse milk has limited effects on the gastrointestinal tract in suckling pups

We tested the hypothesis that chronic ingestion of increased concentrations of milk-borne des(1-3) human insulin-like growth factor-I (hIGF-I) stimulates gastrointestinal growth and development in suckling mice. We used a transgenic mouse with targeted, lactation-dependent, overexpression of des(1-3) hIGF-I in the mammary gland (IGF). Pups were suckled (7 pups per litter) from birth by either IGF (n = 3-6 litters) or control (n = 3-5 litters) dams. In IGF and control pups, we measured the growth (protein and DNA content) and protein synthesis rate (3H-phenylalanine incorporation) of gastrointestinal and visceral organs in 4-, 8-, 12-, 16- and 29-d-old pups. Des(1-3) hIGF-I in milk from IGF dams was 40-200-fold higher than mouse IGF in either IGF or control dams, but was not detected in the plasma of pups suckling IGF dams. Small intestinal weight, protein and DNA content at 8 and 16 d were greater in pups suckling IGF dams than control dams; protein synthesis was also greater in IGF pups at 8 d. Total intestinal lactase activity at 8 and 12 d of age tended to be higher (P < 0.10) in IGF than in control pups. Hypersecretion of des(1-3) hIGF-I in milk ingested by suckling mice pups had limited effects on the growth and maturation of the gastrointestinal tract. Moreover, there was little evidence that milk-borne IGF-I is absorbed into the circulation and stimulates visceral organ growth. This study also demonstrates the feasibility of using mammary-specific transgenes to increase the concentration of milk-borne growth factors to examine whether they affect the growth and development of the suckling neonate.

Systemically but not orogastrically delivered insulin-like growth factor (IGF)-I and long [Arg3]IGF-I stimulates intestinal disaccharidase activity in two age groups of suckling rats

The growth mitogenic properties of IGF-I on tissues of the gastrointestinal tract are well established; however, IGF effects on enzyme maturation are less clear. To test whether IGF-I peptide administration stimulates disaccharidase activity, we administered IGF-I or the more potent analog, long [Arg3]IGF-I, at doses ranging between 2 and 12.5 micrograms g-1 d-1 to suckling Wistar rat pups by either continuous s.c. infusion or by three times daily orogastric gavage. Peptides were administered for approximately 6 d starting on d 6 or 12 postpartum with six to nine rats per group. The results of the study demonstrated that systemically but not orally administered IGF-I stimulated duodenal wet tissue weight (up to 85%) and length (up to 36%). Enzyme maturation was assessed by measuring disaccharidase biochemically in tissue homogenates. Enzyme activity was also localized histocytochemically in cryostat-sectioned duodenum. After systemic infusion of IGF-I, intestinal lactase activity increased proportional to mucosal mass in both age groups. Systemic infusion of the more potent analog, long [Arg3]IGF-I, precociously induced the decline in lactase activity and accelerated the appearance of sucrase activity in the rat pups infused during the later suckling period. These findings indicate that enzyme maturation can be accelerated by systemically derived IGF-I peptides. Orogastrically IGF-I peptides, delivered at pharmacologic doses, did not affect intestinal growth or digestive enzyme maturation in suckling rat pups treated between 6 and 18 d postpartum, indicating the efficacy of IGF-I peptides may depend on the route of delivery and postnatal age of the recipient.