Rat Milk Substitute Research Articles

Dietary Echium Oil Increases Tissue (n-3) Long-Chain Polyunsaturated Fatty Acids without Elevating Hepatic Lipid Concentrations in Premature Neonatal Rats ,

Echium oil (EO) contains notable quantities of both (n-6) and (n-3) PUFA and has not, to our knowledge, been studied in neonates. We compared growth, tissue PUFA concentrations, and liver lipid profiles in premature neonatal Sprague-Dawley rats that were fed an EO diet with those that were dam-fed (DF) or fed rat milk substitute (RMS) or a fish oil (FO) diet. EO or FO comprised 10% of dietary fat. Rats were delivered prematurely at d 21 of gestation by caesarean section and then DF or fed one of the diets for 6 d. Rats were killed and the fatty acid (FA) concentrations in brain, liver, ileum, and serum and liver lipid profiles were analyzed. All diet-fed rats had similar weight gain and tissue protein concentrations. Compared with DF rats, EO-fed rats had similar brain docosahexaenoic acid (DHA) levels, similar brain and liver arachidonic acid (ARA) levels, higher liver and ileal eicosapentaenoic acid (EPA) levels (P < 0.05), and similar ARA:(EPA+DHA) ratios in brain, liver, and serum. Compared with RMS-fed rats, EO-fed rats had lower liver triglyceride FA and cholesterol ester concentrations (P < 0.05), higher EPA and DHA levels in liver, ileum, and serum, a higher DHA level in brain, and lower tissue and serum ratios of total (n-6):(n-3) PUFA and ARA:(EPA + DHA) (P < 0.05). Compared with FO-fed rats, EO-fed rats had higher ARA levels in brain, liver, ileum, and serum. In conclusion, dietary EO increases tissue EPA and DHA without reducing ARA in brain and liver and without elevating hepatic lipid concentrations of premature neonatal rats.

Dietary Fructose During the Suckling Period Increases Body Weight and Fatty Acid Uptake Into Skeletal Muscle in Adult Rats

The suckling period is one potentially "critical" period during which nutritional intake may permanently "program" metabolism to promote increased adult body weight and insulin resistance in later life. This study determined whether fructose introduced during the suckling period altered body weight and induced changes in fatty acid transport leading to insulin resistance in adulthood in rats. Pups were randomly assigned to one of four diets: suckle controls (SCs), rat milk substitute formula (Rat Milk Substitute), fructose-containing formula (Fructose), or galactose-containing formula (Galactose). Starting at weaning, all pups received the same diet; at 8 weeks of age, half of the SC rats began ingesting a diet containing 65% kcal fructose (SC-Fructose). This continued until animals were 12 weeks old and the study ended. At weeks 8, 10, and 11, the Fructose group weighed more than SC and SC-Fructose groups (P < 0.05). At weeks 8 and 10 of age, the Fructose group had significantly higher insulin concentrations vs. rats in the SC-Fructose group. (3)H-Palmitate transport into vesicles from hind limb skeletal muscle was higher in Fructose vs. SC rats (P < 0.05). CD36 expression was increased in the sarcolemma but not in whole tissue homogenates from skeletal muscle from Fructose rats (P < 0.05) suggesting a redistribution of this protein associated with fatty acid uptake across the plasma membrane. This change in subcellular localization of CD36 is associated with insulin resistance in muscle. Consuming fructose during suckling may result in lifelong changes in body weight, insulin secretion, and fatty acid transport involving CD36 in muscle and ultimately promote insulin resistance.

Neonatal Formula Feeding Leads to Immunological Alterations in an Animal Model of Type 1 Diabetes

Neonatal diet may influence the development of type 1 diabetes (T1D) in susceptible individuals through an intestinal mucosal inflammatory response, resulting in loss of self-tolerance. We tested the hypothesis that formula feeding during the neonatal period accelerates the development of T1D in diabetes-prone BioBreeding (BBDP) rats through regulation of CD4+CD25+ regulatory T lymphocytes (T(reg)) and anti-inflammatory cytokines. BBDP rat pups fed rat milk substitute (RMS) via a "pup-in-the cup" system were compared with mother-fed (MF) rats. The spleen and thymus were analyzed for Foxp3-expressing CD4+/CD25+ T cells. Multiplex enzyme-linked immunosorbent assays (ELISAs) were performed to measure cytokine-induced neutrophil chemoattractant (CINC), tumor necrosis factor alpha (TNF-alpha), interferon-gamma (IFN-gamma), interleukin (IL)-4, IL-10, and IL-18. Diabetes-free survival, time of disease onset, and T(reg)/total T lymphocyte ratios were not different. MF pups had higher ileal CINC (p < 0.001) and IL-18 (p = 0.002), but no differences in the liver. There were no differences in ileal cytokine concentrations of 75-d-old rats, but the formula-fed rats had greater liver TNF-alpha (p < 0.001), IFN-gamma, and IL-4 (p < 0.01) and lower IL-10 (p = 0.002) compared with MF animals. Formula versus maternal milk altered the hepatic cytokine profile at 75 d toward an inflammatory pattern but did not result in altered T(reg) cell frequencies or the development of T1D.

Insulin-like growth factor-I stimulates erythropoiesis when administered enterally

Background: Insulin-like growth factors I and II (IGF-I and IGF-II) are potent growth factors involved in development. IGF-I stimulates proliferation of erythropoietic progenitors and parenteral IGF-I administration stimulates in vivo erythropoiesis in animals. IGF-I and IGF-II are both present in mammalian milks and when milk-borne, are resistant to neonatal gastrointestinal degradation. Whether milk-borne IGF-I or IGF-II regulates neonatal erythropoiesis in not known. We hypothesized that physiological doses of enteral IGFs stimulate erythropoiesis in suckling rats.Methods: Eight day-old Sprague Dawley rats were artificially fed for 4 days with rat milk substitute (RMS) or RMS supplemented with physiological levels of IGF-I or IGF-II. Rats fed IGF-I and IGF-II were compared to control RMS. Blood and marrow were collected; measures of red cell mass, measures of erythropoietic stimulus, and indices of iron status were measured.Results: Rats fed IGF-I had higher hemoglobin (Hb) levels (100 ± 10 g/l), compared to those fed RMS (94 ± 9) or IGF-II (91 ± 6), p < 0.001. After IGF-I supplementation, red blood cell counts (RBC) (p < 0.04) and hematocrits (p < 0.002) were also higher. Plasma erythropoietin (Epo) levels, reticulocytes, plasma iron and erythrocyte iron incorporation were similar.Conclusion: Intact enteral IGF-I reaches distal erythropoietic tissue resulting in greater red cell mass, but not by increasing plasma Epo levels or by altering cellular iron transport.

Effects of Protein Deprivation on Growth and Small Intestine Morphology Are Not Improved By Glutamine or Glutamate in Gastrostomy‐Fed Rat Pups

ABSTRACTObjectives:Critically ill neonates often have their enteral intake severely limited shortly after birth. Whether glutamine (Gln) or glutamate (Glu) can preserve intestinal structure and function in the neonate undergoing limited enteral feeding is not clear. We hypothesize that Gln and Glu can similarly preserve intestinal structure in the developing small intestine of infant rats fed a low protein diet.Methods:Using a gastrostomy‐fed “pup‐in‐a‐cup” rat model, the effects of Gln and Glu on the developing rat small intestine were examined. Four groups of 6‐ to 7‐day‐old pups were fed rat milk substitute (RMS) via gastrostomy tube. One group was provided 100% and three were provided 25% of the protein normally received from their mothers. Two of the groups fed 25% protein received additional Gln or Glu for 6 days.Results:Pups receiving the 100% protein RMS were larger than pups receiving the 25% protein RMS with or without Gln/Glu supplementation (P &lt; 0.001). Average villus height (P &lt; 0.01) and area (P &lt; 0.01) were greater in pups receiving 100% protein RMS than in pups given 25% protein RMS formula. There was no significant difference among the groups in mucosal maltase or alkaline phosphatase activities. Tight junction protein claudin‐1 was significantly higher in the group fed 100% protein RMS diet, while occludin did not differ among the 4 groups. Neither Gln nor Glu increased claudin‐1 or occludin in rats fed 25% protein.Conclusions:These results suggest that neither Gln nor Glu supplementation can substitute effectively for whole protein in the developing rat small intestine for the outcomes that were evaluated.

Effects of protein deprivation on growth and small intestine morphology are not improved by glutamine or glutamate in gastrostomy-fed rat pups.

Critically ill neonates often have their enteral intake severely limited shortly after birth. Whether glutamine (Gln) or glutamate (Glu) can preserve intestinal structure and function in the neonate undergoing limited enteral feeding is not clear. We hypothesize that Gln and Glu can similarly preserve intestinal structure in the developing small intestine of infant rats fed a low protein diet. Using a gastrostomy-fed "pup-in-a-cup" rat model, the effects of Gln and Glu on the developing rat small intestine were examined. Four groups of 6- to 7-day-old pups were fed rat milk substitute (RMS) via gastrostomy tube. One group was provided 100% and three were provided 25% of the protein normally received from their mothers. Two of the groups fed 25% protein received additional Gln or Glu for 6 days. Pups receiving the 100% protein RMS were larger than pups receiving the 25% protein RMS with or without Gln/Glu supplementation (P < 0.001). Average villus height (P < 0.01) and area (P < 0.01) were greater in pups receiving 100% protein RMS than in pups given 25% protein RMS formula. There was no significant difference among the groups in mucosal maltase or alkaline phosphatase activities. Tight junction protein claudin-1 was significantly higher in the group fed 100% protein RMS diet, while occludin did not differ among the 4 groups. Neither Gln nor Glu increased claudin-1 or occludin in rats fed 25% protein. These results suggest that neither Gln nor Glu supplementation can substitute effectively for whole protein in the developing rat small intestine for the outcomes that were evaluated.

O0029 ENTERAL ADMINISTRATION OF HB-EGF REDUCES THE INCIDENCE OF NECROTIZING ENTEROCOLITIS IN A RAT MODEL

Introduction: Necrotizing enterocolitis (NEC) is a devastating gastrointestinal disease of prematurely born infants. The protective role of maternal milk against NEC has been reported, however the components of milk responsible for this protection have not been identified. Previously, we have shown that epidermal growth factor (EGF) reduces the incidence of NEC in a rat model (Dvorak et al., AJP 282:G156, 2002). Heparin-binding EGF-like growth factor (HB-EGF), another member of the EGF family, has been shown to be cytoprotective for intestinal epithelial cells. Recently, the presence of HB-EGF has been detected in human breast milk. The aim of this study was to examine the effect of enteral administration of HB-EGF on survival and the incidence and severity of NEC in a neonatal rat model. Methods: Neonatal rats delivered via abdominal incision on day 22 of gestation were artificially fed with rat milk substitute for 4 days. Four diets were used in this study: growth factor-free rat milk substitute (RMS) and RMS supplemented with 5, 50, and 500 ng/ml of HB-EGF (HB-5, HB-50, and HB-500, respectively). Experimental NEC was induced by daily exposure to asphyxia and cold stress. In addition, dam fed littermates were used as a control (DF). The development and severity of NEC was evaluated in the distal ileum using our histopathological scoring system. Results: In the NEC group, 91% of animals developed characteristic pathophysiological signs of NEC in the distal ileum. Supplementation of HB-EGF into milk formula significantly reduced the incidence of NEC and improved survival of the pups in a dose dependent manner.Table 1Conclusion: Milk-borne HB-EGF provides a protective effect on the development of neonatal NEC. The mechanism by which HB-EGF prevents NEC must be further investigated on the molecular level. However, supplementation of an optimized growth factor “cocktail” into infant formula for prematurely born babies might be a feasible strategy for the prevention of neonatal NEC. Supported by the NIH Grant HD-39657 (to B.D.).

Glutamine decreases lipopolysaccharide-induced intestinal inflammation in infant rats.

Using a gastrostomy-fed (GF) rat infant "pup-in-a-cup" model, the effects of protein deprivation and supplemental glutamine (Gln) and glutamate (Glu) were examined to test the hypothesis that Gln decreases the proinflammatory response induced by LPS in the developing infant rat small intestine. Four groups of 6- to 7-day-old pups were fed a rat milk substitute (RMS), one providing 100% and three providing 25% of normal protein intake for another 6 days. Two of the 25% protein-fed groups received supplemental Gln or Glu. GF and LPS treatment blunted body growth and intestinal villus height and increased intestinal cytokine-induced neutrophil chemoattractant (CINC) mRNA in the protein-deprived, non-Gln-treated group compared with mother-fed pups (P < 0.05). Gln blunted intestinal CINC mRNA (P < 0.05), but Glu did not. Intestinal CINC peptide in the LPS-treated pups provided 100 and 25% protein was elevated approximately 13-fold compared with the mother-reared pups (P < 0.001). Gln and Glu decreased intestinal CINC peptide by 73 and 80%, respectively. GF, LPS-treated pups also had a higher level of plasma CINC peptide (P < 0.05). Gln but not Glu decreased plasma CINC peptide (P < 0.05). An approximate sixfold elevation of intestinal MPO activity in the GF, LPS-treated rats was decreased by Gln and Glu by 92% (P < 0.001) and 54% (P < 0.05), respectively. Intestinal and plasma TNF-alpha were increased in GF, LPS-treated pups (P < 0.01), and Gln and Glu both blunted this increase (P < 0.05) in the intestine but not in the plasma. The results indicate that Gln decreases the LPS-induced inflammatory response in infant rat intestine under different conditions of protein intake.

Accumulation of bile acids in ileum associated with intestinal damage rats with experimental necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is associated with the release of a variety of proniflamatory mediators in the small intestine. We have previously shown that through the enterohepatic axis, luminal ileal TNFa was significantly increased and correlated with severity of intestinal damage. Upregulation of IL-113 and TNFet reduces significantly the ileal sodium-dependent bile acid transporter (ASBT) in rats (Gastroenterology 2002; 123) and thus may lead to accumulation of bile in the terminal ileum. Increased concentrations of cytotoxic bile acids (BA) were reported to induce damage to intestinal mucosa. Objective: The aim of this study was to determine if changes in bile acid levels in the terminal ileum and serum are associated with the development of NEC. Design/Methods: Newborn rats were artificially fed cow milkbased rat milk substitute (RMS) and exposed to asphyxia and cold stress for 4 days to induce experimental NEC. Dam fed (DF) littermates were also exposed to asphyxia-cold stresses and served as controls. Total BA levels were determined in ileal flushes using an enzymatic assay (Diazyme). In addition, segments of terminal ileum were processed and evaluated histologicaly and by scanning electron microscopy (SEM). Results: Total BA were significantly increased (p<0.05) in RMS animals compared to the DF group (340 • 164 and 77 -+ 3 lg, mol, respectively). Serum total BA were not significantly different between animals with and without NEC (4.0-+ 2.3 and 3.7 + 1.7~mol, respectively). Severe morphologic changes consistent with those previously attributed to BA were observed in RMS rats. These changes were confirmed by histology. DF littermates had no ileal damage. Conclusions: Increased BA in terminal ileum may exacerbate the progression of intestinal damage. Evaluation of BA transport may lead to important advances in understanding NEC pathogenesis. Supported by NIH grants HD-39657, HD-26013 (to B.D.)

Maternal milk reduces severity of necrotizing enterocolitis and increases intestinal IL-10 in a neonatal rat model.

Necrotizing enterocolitis (NEC) is a devastating intestinal disease of premature infants. Maternal milk has been suggested to be partially protective against NEC; however, the mechanisms of this protection are not defined. The aim of this study was to examine the effect(s) of artificial feeding of rat milk (RM)-versus cow milk-based rat milk substitute (RMS) on the development of NEC in a neonatal rat model and elucidate the role of inflammatory cytokines in NEC pathogenesis. Newborn rats were artificially fed with either collected RM or RMS. Experimental NEC was induced by exposure to asphyxia and cold stress and evaluated by histologic scoring of damage in ileum. Intestinal cytokine mRNA expression was determined by real-time PCR. Cytokine histologic localization was performed by confocal microscopy. Similar to human NEC, artificial feeding of RM reduces the incidence and severity of NEC injury in neonatal rats. Freezing and thawing of collected RM did not eliminate the protective effect of maternal milk. Ileal IL-10 expression was significantly increased in the RM group compared with RMS. Increased IL-10 peptide production was detected in the RM group with signal localized predominantly in the cytoplasm of villus epithelial cells. These results suggest that the protective effect of maternal milk is associated with increased production of anti-inflammatory IL-10 in the site of injury. Better understanding of the mechanisms underlying these protective effects could be beneficial either in the prevention of NEC or in the development of future therapeutic strategies to cure NEC.

Ileal cytokine dysregulation in experimental necrotizing enterocolitis is reduced by epidermal growth factor.

Necrotizing enterocolitis (NEC) is the most common gastrointestinal disease of premature infants. We have shown in previous studies that proinflammatory interleukin-18 and interleukin-12 are up-regulated in the ileum of rats with experimental NEC and that epidermal growth factor (EGF) reduces the development of disease. Here we investigated whether the protective effects of EGF are a result of changes in ileal interleukin-18, interleukin-12 and/or antiinflammatory interleukin-10. Newborn rats were artificially fed with either growth-factor-free rat milk substitute (RMS) or RMS supplemented with 500 ng/mL EGF (RMS + EGF) and NEC was induced via exposure to asphyxia and cold stress. Cytokine expression and localization were assessed using reverse-transcription real-time polymerase chain reaction and immunohistology/confocal microscopy. Enteral administration of EGF (RMS + EGF) decreased overproduction of interleukin-18 and increased interleukin-10 production in the ileum. Furthermore, increased interleukin-10 production was associated with up-regulation of the transcription factor Sp1 in RMS + EGF rats. These data suggest that EGF may reduce NEC via increased interleukin-10 and decreased interleukin-18 and that EGF-mediated up-regulation of Sp1 may account for the increased interleukin-10.

Ileal Cytokine Dysregulation in Experimental Necrotizing Enterocolitis Is Reduced by Epidermal Growth Factor

ABSTRACTBackgroundNecrotizing enterocolitis (NEC) is the most common gastrointestinal disease of premature infants. We have shown in previous studies that proinflammatory interleukin‐18 and interleukin‐12 are up‐regulated in the ileum of rats with experimental NEC and that epidermal growth factor (EGF) reduces the development of disease. Here we investigated whether the protective effects of EGF are a result of changes in ileal interleukin‐18, interleukin‐12 and/or antiinflammatory interleukin‐10.MethodsNewborn rats were artificially fed with either growth‐factor–free rat milk substitute (RMS) or RMS supplemented with 500 ng/mL EGF (RMS + EGF) and NEC was induced via exposure to asphyxia and cold stress. Cytokine expression and localization were assessed using reverse‐transcription real‐time polymerase chain reaction and immunohistology/confocal microscopy.ResultsEnteral administration of EGF (RMS + EGF) decreased overproduction of interleukin‐18 and increased interleukin‐10 production in the ileum. Furthermore, increased interleukin‐10 production was associated with up‐regulation of the transcription factor Sp1 in RMS + EGF rats.ConclusionsThese data suggest that EGF may reduce NEC via increased interleukin‐10 and decreased interleukin‐18 and that EGF‐mediated up‐regulation of Sp1 may account for the increased interleukin‐10.

IGF alters jejunal glucose transporter expression and serum glucose levels in immature rats.

Milk-borne insulin-like growth factors (IGFs) enhance nutrient absorption in the immature intestine, which is characterized by low levels of glucose oxidation. We therefore hypothesized that feeding a rat milk substitute (RMS) devoid of growth factors to rat pups would lower serum glucose levels relative to dam-fed control rats and that supplementation of RMS with physiological doses of either IGF-I or IGF-II would normalize serum glucose levels via increased jejunal glucose transporter 2 (GLUT2) and high-affinity Na(+)-glucose cotransporter (SGLT1) expression. We found lower serum glucose concentrations in RMS-fed pups; in contrast, serum glucose levels in the IGF-supplemented pups were similar to those of dam-fed controls. RT-PCR and laser scanning confocal microscopy similarly demonstrated that IGF supplementation increased expression of jejunal glucose transporters. Further experiments demonstrated that IGF supplementation altered mRNA levels of key mitochondrial enzymes without altering jejunal lactase activity. We conclude that IGF-I and IGF-II supplementation increases serum glucose levels in the immature rat pup fed artificial formula and alters gene expression of the jejunal glucose transporters.

Epidermal growth factor reduces the development of necrotizing enterocolitis in a neonatal rat model.

Necrotizing enterocolitis (NEC) is the most common gastrointestinal disease of prematurely born infants. Maternal milk plays an important protective role against NEC development and is the major source of epidermal growth factor (EGF) for neonates. The aim of this study was to examine the effect of orally administered EGF on the incidence of NEC in a neonatal rat model. Newborn rats were artificially fed either with growth factor-free rat milk substitute (RMS) or RMS supplemented with 500 ng/ml of EGF (RMS+EGF). Experimental NEC was induced by exposure to asphyxia and cold stress. Development of NEC was evaluated by gross and histological scoring of damage in the ileum. Ileal EGF receptor (EGF-R), EGF, and transforming growth factor-alpha mRNA expression was assessed by RT competitive-PCR, and the EGF-R was localized by immunohistochemistry. EGF supplementation of formula reduced the incidence and severity of NEC in rats (13/16 RMS vs. 4/13 RMS+EGF). Ileal EGF-R mRNA expression was markedly increased in the RMS group compared with RMS+EGF. Enhanced EGF-R expression in the RMS group was localized predominantly in the epithelial cells of injured ileum. These data suggest a new potential therapeutic approach for the prevention and treatment of NEC.

Identification of soluble transforming growth factor-beta receptor III (sTbetaIII) in rat milk.

Transforming growth factor-beta (TGF-beta) is present at high concentrations in maternal milk. In milk TGF-beta2 is the predominant isoform. For function TGF-beta2 requires TbetaRIII to facilitate efficient binding to the TGF-beta receptor types I and II signalling complex. We have shown that TGF-beta receptor types I (TbetaRI), II (TbetaRII) and III (TbetaRIII) are coexpressed in the suckling rat intestine. Immunostaining for TbetaRIII was also observed in the intestinal lumen prior to weaning. TbetaRIII (or betaglycan) has been reported in serum, cell culture medium and extracellular matrix. To determine whether a soluble form of TbetaRIII is present in milk, the rat milk aqueous phase was analysed by slot-blot and Western blot. Soluble TbetaRIII was detected in milk throughout lactation. Western blot analysis of rat milk revealed a high molecular weight band of glycosylated protein of >200 kDa, with a core protein of approximately 110-120 kDa that comigrated with recombinant TbetaRIII. Immunoabsorption of soluble TbetaRIII (sTbetaRIII) from milk resulted in partial depletion of active TGF-beta from milk, suggesting that the receptor may interact with ligand in milk. In addition rat pups suckled on mother's milk demonstrated an enhanced labelling of TbetaRIII in the gut, as compared with pups fed on a rat milk substitute (RMS). These findings suggest that milk sTbetaRIII is functional, and may modulate milk-derived TGF-beta function in the developing intestine.

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.

Growth of artificially fed infant rats: effect of supplementation with insulin-like growth factor I.

Insulin-like growth factor I (IGF-I), a potent mitogenic peptide, is present in considerable quantities in most mammalian milks, but its importance for the neonate is unknown. To test the hypothesis that milk-borne IGF-I is an important factor in the regulation of neonatal growth, as well as that of the gastrointestinal tract, rat pups were fed a rat milk substitute (RMS) devoid of growth factors via gastrostomy. These animals were compared with those given RMS supplemented with recombinant human IGF-I added at a concentration of 500 ng/ml. Animals given RMS + IGF-I gained mere weight than controls, although skeletal growth as represented by elongation of the tail was no different. Animals fed RMS + IGF-I had increased brain and liver wet weights as well as increased liver and small intestine protein contents. Serum IGF-I concentrations in the IGF-I-supplemented group were more than twofold above RMS controls and were similar to dam-fed rat pups. Semiquantification of serum IGF-binding proteins (IGFBP) in these animals documented that in IGF-I-supplemented pups the amount of 38- to 40-kDa molecular mass IGFBP species was also greater than in RMS controls. The rate of migration of enterocytes from crypts in duodenum and proximal jejunum was greater in IGF-I-supplemented animals than in rats fed RMS alone. These studies suggest that milk-borne IGF-I is important in modulation of somatic and gastrointestinal tract growth in the neonatal rat.

Effect of milk-borne epidermal growth factor on the hepatic microcirculation and Kupffer cell function in suckling rats.

Epidermal growth factor (EGF) is contained in breast milk, is transported intact across the gastrointestinal mucosa during the suckling period, retains its biological activity, and affects hepatic growth. Whether or not EGF also influences postnatal hepatic development by affecting nonparenchymal cells or by modifying intrahepatic blood is not clear. As a result, the effect of EGF on the hepatic microvasculature was studied in suckling rats fed rat milk substitute (RMS) with and without EGF (100 ng/ml, i.e. twice the normal intake in breast milk) between days 11 and 14 and compared to pups breast-fed for 14 days. The livers of anesthetized pups were examined by in vivo microscopy to determine the numbers of sinusoids with flow (SCF) in each of 10 microscopic fields and the numbers of phagocytic Kupffer cells (KC) in the same fields following an intraportal injection of fluorescent 1-micron latex particles. Phagocytic activity was expressed as the ratio KC/SCF. In pups fed RMS without EGF, SCF and KC/SCF was 75 and 45%, respectively, of that in breast-fed animals. The addition of EGF to the RMS restored SCF and KC/SCF nearly to the levels measured in breast-fed pups. Thus, the results suggest that milk-borne EGF plays a role in the development of KC phagocytic function and affects the amount of blood that perfuses the sinusoidal bed in the suckling.

Metabolism in the Artificially Reared Rat Pup: Effect of an Atypical Rat Milk Substitute

A substitute for rat milk [Messer et al., 1969 (1)] has been evaluated as a nutrient source to artificially feed rat pups from 4 days after birth. The rat milk substitute has a normal fat concentration, suboptimal protein concentration and a high carbohydrate concentration when compared to natural rat milk. Rat pups artificially reared on the milk substitute by intermittent infusion via miniaturized intragastric cannulae have: 1) atypical ketone body metabolism: lower than normal concentration and turnover of d-(-)-3-hydroxybutyrate in blood and less than normal amounts of d-(-)-3-hydroxybutyrate used for respiration, 2) atypical carbohydrate metabolism: higher than normal insulin and galactose concentrations in blood and a greater than normal amount of glucose used for respiration, and 3) atypical amino acid levels: the concentrations of several amino acids in blood were 60% or less than normal, and the concentration of taurine in plasma was negligible. We observed frequent head tremors, hyperreactivity to handling and about a 20% incidence of cataracts in rat pups reared on the milk substitute. We conclude this rat milk substitute is not suitable as a nutrient source for the developing rat pup.artificially reared rat rat milk substitute metabolism during development ketone bodies carbohydrate