Fecal short-chain fatty acids of very-low-birth-weight preterm infants fed expressed breast milk or formula.

OBJECTIVES: In preterm infants, the metabolic responses of gastrointestinal (GI) bacteria to different diets are poorly understood despite the possible effects on GI health. Therefore, we tested the hypothesis that diet influences bacterial metabolism by measuring short-chain fatty acids (SCFAs) in stool samples from very-low-birth-weight (VLBW) preterm infants without GI disorder as surrogate biomarkers of bacterial metabolism. METHODS: Ion chromatography was used to measure fecal SCFAs (acetate, formate, propionate, butyrate, and isobutyrate), lactate, and chloride in fresh stool samples collected from 32 preterm infants (without major congenital anomalies, GI disorders, or a recent history of antibiotic administration and on full feed of either expressed maternal breast milk [EBM; n = 13] or a formula for preterm infants [Similac Special Care Formula; preterm formula, PTF; n = 19]). RESULTS: The mean birth weight was 972 g, the mean gestational age was 27 weeks, and the mean postnatal age at first stool sample was 36 days. When adjusted for gestational age, the stools of EBM infants had higher concentrations (micromoles per gram of stool) of total SCFA (128 vs 68; P = 0.002), acetate (41 vs 13; P = 0.005), propionate (15.1 vs 4.4; P = 0.003), and chloride (21,814 vs 10,652; P = 0.02). Interactions between postnatal age and diet were detected for lactate (P = 0.05), propionate (P = 0.03), and butyrate (P = 0.03). CONCLUSIONS: Diets fed to VLBW preterm infants influence fecal SCFA profiles, and hence the metabolism of the GI bacteria, and potentially the health of preterm infants. The responses of bacterial metabolism to diet are influenced with postnatal age and gestational age at birth.

Sucrose concentration in blood: a new method for assessment of gastric permeability in horses with gastric ulceration.

A urine sucrose test has recently been reported to be a reliable method of detecting gastric ulcers in horses; however, technical difficulties associated with urine collection have limited the practical value of the test. The objective of this pilot study was to determine whether gastric sucrose permeability, as evaluated by serum sucrose concentration, could be used to detect gastric mucosal injury in horses. Twelve adult horses with naturally acquired gastric ulceration were studied. After a 20-hour nonfeeding period, each horse was dosed with 250 g of sucrose via nasogastric intubation. Blood samples were collected at 0, 15, 30, 45, 60, and 90 minutes, and horses underwent gastroscopy 4 hours later. The severity of gastric ulceration in each horse was defined by means of a 4-point ulcer-scoring system, and the relationship with serum sucrose concentration was analyzed by means of a linear mixed-effects model. Serum sucrose concentration was measured by liquid chromatography operating in tandem with electrospray mass spectrometry. After nasogastric administration of table sugar, horses with moderate to severe gastric ulceration had significant increase in serum sucrose concentration at 30, 45, 60, and 90 minutes, relative to earlier times (P < .05). Peak sucrose concentration was observed at 45 minutes, and was correlated with ulcer severity (Spearman's rank correlation coefficient = 0.898, P < .05). These data indicate that determination of sucrose concentration in equine serum may be a useful test for identifying horses with endoscopically visible gastric ulceration and has potential use as a noninvasive method for screening and monitoring horses engaged in racing training and other performance-related disciplines.

Dietary supplement of neosugar alters the fecal flora and decreases activities of some reductive enzymes in human subjects.

The influence of dietary fructooligosaccharide (neosugar) on the fecal flora and activities of reductive enzymes was studied in 12 healthy, adult human subjects fed a controlled diet for 42 d and given 4 g neosugar/d between days 7 and 32. Fecal samples were collected before, during, and after supplementation with neosugar to enumerate total anaerobes, aerobes, bifidobacteria, and enterobacteria, and to assay for beta-glucuronidase, nitroreductase, and glycocholic acid hydroxylase. Although the controlled diet caused an increase in total anaerobes and bifidobacteria, the highest densities occurred during supplementation with neosugar. Total aerobes and enterobacteria were less affected by diet and neosugar. Neosugar caused beta-glucuronidase and glycocholic acid hydroxylase activities to decrease 75% and 90%, respectively; both increased after supplementation with neosugar was stopped. Nitroreductase activity declined 80% after the control diet was started, but was not affected by neosugar. These findings indicate that 4 g neosugar/d alters the fecal flora in a manner perceived as beneficial by decreasing activities of some reductive enzymes.

Adaptive changes in ileal mucosal nutrient transport following colectomy and endorectal ileal pull-through with ileal reservoir.

To study ileal mucosal function when used in an ileal reservoir or ileostomy, eight dogs underwent colectomy and endorectal ileal pull-through with creation of a lateral ileal reservoir. Ileal mucosal biopsy specimens were obtained at the initial operation, from the ileostomy and dormant ileal reservoir at the time of ileostomy closure, and from the reservoir 3 months later. Rates of uptake for four different substrates were determined by radioactive absorption techniques. Absorption of carbohydrates, amino acids, and bile acids was markedly decreased and of short-chain fatty acid mildly reduced in ileal reservoir mucosa compared with normal ileum, largely owing to a decrease in reservoir absorptive surface area from flattened villi. Reservoir uptake of the substrates evaluated within 3 months after operation was similar to that for normal colonic mucosa. Uptake of all measured substrates from ileostomy mucosa approximated that of normal ileum. The use of short ileal reservoirs and the avoidance of stasis may favor reduced bacterial growth and increased nutrient absorption.

Effects of soybean meal and salinity on intestinal transport of nutrients in Atlantic salmon (Salmo salar L.) and rainbow trout (Oncorhynchus mykiss).

Groups of fresh- and seawater-adapted Atlantic salmon (Salmo salar L.) and rainbow trout (Oncorhynchus mykiss) were fed diets with (SBM diet) or without (control diet) extracted soybean meal (30% of protein substituted with SBM) for 3 weeks. Average fish size per group ranged from 597 to 1763 g. One tank or net pen per species, dietary group and water salinity was used. In vitro nutrient transport (D-glucose, the L-amino acids aspartate, lysine, methionine, phenylalanine and proline, and the dipeptide glycyl-sarcosine) was measured using intact tissue (everted sleeve method) from the different postgastric intestinal regions. The dimensions of the different intestinal regions were also measured for each treatment group. Results indicate that SBM causes decreased carrier-mediated transport and increased permeability of distal intestinal epithelium for the nutrients, and the capacity of this region to absorb nutrient was diminished. Salinity may also affect the relative contribution of carrier-mediated and independent uptake to total nutrient absorption.

Influence of fermentable fiber on small intestinal dimensions and transport of glucose and proline in dogs.

OBJECTIVE: To determine whether intestinal dimensions and nutrient absorption are influenced by different types of dietary fiber. ANIMALS: 10 adult Beagles of both sexes. PROCEDURE: Dogs were randomly assigned to 2 groups and fed a diet with fermentable fibers (beet pulp and oligofructose) or a nonfermentable fiber (cellulose) for 6 weeks. Effects of the diets on small intestinal dimensions were measured, and transport rates for glucose and proline were determined. Kinetics of glucose and proline uptake were defined in the proximal and middle regions of the small intestine, respectively. RESULTS: Small intestines of dogs fed fermentable fiber had 28% more nominal surface area and 37% more mucosal mass, were 35% heavier, and had 95% higher capacity for carrier-mediated glucose uptake than those of dogs fed a diet with cellulose. Differences were more pronounced in the proximal portion of the intestine. CONCLUSIONS AND CLINICAL RELEVANCE: Diets containing fermentable fibers increase small intestinal dimensions and the capacity for nutrient absorption in dogs. These changes may reduce the risk of enteric infections or aid in treatment of intestinal diseases, particularly those involving reduced nutrient absorption.

The gastrointestinal bacteria of mink (Mustela vison L): influence of age and diet.

Total numbers of aerotolerant and anaerobic bacteria, and densities of Enterobacteriaceae, lactobacilli, staphylococci, salmonella and shigella, and campylobacteria were enumerated in the contents of the stomach, small intestine (and the associated mucosa), and colon of mink beginning at 2 weeks of age to adulthood, and in adults that were fed diets with different levels and types of fiber or food deprived. Highest densities of all bacterial groups were found in the colon at all ages (up to 10(8) cfu per g for total anaerobes), but were 2-4 orders of magnitude lower than those of other mammals. When all regions were pooled, significant age-related increases (p < 0.05) were detected for anaerobes, aerobes, and staphylococci, and these coincided with the dietary shift at weaning. Enterobacteriaceae did not vary with age. Lactobacilli were never common isolates, but were detected more often after weaning, particularly in adults fed diets containing the 2 sources of fiber. Campylobacteria were detected only at 2 weeks of age, and salmonella and shigella were not isolated from any of the experimental mink. Total bacterial densities, the relative proportions of the bacterial groups, and age- and diet-related effects differ from those known for other mammals, which may be related to the carnivorous diet and rapid movement of digesta through the GIT.

Invited review: the preterm pig as a model in pediatric gastroenterology.

At birth, the newborn mammal undergoes a transition from a sterile uterine environment with a constant nutrient supply, to a microbe-rich environment with intermittent oral intake of complex milk nutrients via the gastrointestinal tract (GIT). These functional challenges partly explain the relatively high morbidity and mortality of neonates. Preterm birth interrupts prenatal organ maturation, including that of the GIT, and increases disease risk. Exemplary is necrotizing enterocolitis (NEC), which is associated closely with GIT immaturity, enteral feeding, and bacterial colonization. Infants with NEC may require resection of the necrotic parts of the intestine, leading to short bowel syndrome (SBS), characterized by reduced digestive capacity, fluid loss, and dependency on parenteral nutrition. This review presents the preterm pig as a translational model in pediatric gastroenterology that has provided new insights into important pediatric diseases such as NEC and SBS. We describe protocols for delivery, care, and handling of preterm pigs, and show how the immature GIT responds to delivery method and different nutritional and therapeutic interventions. The preterm pig may also provide a sensitive model for postnatal adaptation of weak term piglets showing high mortality. Attributes of the preterm pig model include close similarities with preterm infants in body size, organ development, and many clinical features, thereby providing a translational advantage relative to rodent models of GIT immaturity. On the other hand, the need for a sow surgical facility, a piglet intensive care unit, and clinically trained personnel may limit widespread use of preterm pigs. Studies on organ adaptation in preterm pigs help to identify the physiological basis of neonatal survival for hypersensitive newborns and aid in defining the optimal diet and rearing conditions during the critical neonatal period.

Prenatal gastrointestinal development in the pig and responses after preterm birth.

Despite clinical research and medical advances, care of the preterm infant remains a clinical challenge, with the immature gastrointestinal (GI) system limiting the types and amounts of nutrients that can be provided enterally to meet energy and nutrient requirements. Progress in understanding the relationship between dietary inputs and the developing GI system after preterm birth has been limited by ethical constraints of using preterm infants as experimental subjects and a lack of relevant animal models. We review development of the GI system of the pig during gestation, the similarities shared with human fetuses, and the responses to dietary stimuli. The GI systems of pigs and humans develop early in gestation, with growth and maturation accelerating during the final weeks prior to birth. As a consequence, deficits in GI digestive capacities are directly related to how early in gestation an infant or pig is delivered, thereby complicating attempts to provide adequate enteral nutrients for growth and development. Pigs differ from humans by being born with low activities of the brush border membrane carbohydrases necessary for hydrolysis of nonlactose carbohydrates. Fetuses of both species have impaired lipid digestion coinciding with lipid malabsorption after preterm birth. Protease activity, although present, may not be adequate and may limit growth potential. Undigested enteral inputs are available to the resident bacteria and the production of metabolites can influence health and nutrition. The preterm pig represents a relevant and translational animal model for understanding GI development and for identifying diet and regulatory factors that stimulate GI growth and maturation after preterm birth and thereby accelerate the transition from parenteral nutrition to full enteral nutrition.

Companion animals symposium: development of the mammalian gastrointestinal tract, the resident microbiota, and the role of diet in early life.

Mammalian gastrointestinal (GI) development is guided by genetic determinants established during the evolution of mammals and matched to the natural diet and environment. Coevolution of the host GI tract (GIT) and the resident bacteria has resulted in commensal relationships that are species and even individual specific. The interactions between the host and the GI bacteria are 2-way and of particular importance during the neonatal period, when the GIT needs to adapt rapidly to the external environment, begin processing of oral foods, and acquire the ability to differentiate between and react appropriately to colonizing commensal and potentially pathogenic bacteria. During this crucial period of life, the patterns of gene expression that determine GI structural and functional development are modulated by the bacteria colonizing the previously sterile GIT of fetuses. The types and amounts of dietary inputs after birth influence GI development, species composition, and metabolic characteristics of the resident bacteria, and the interactions that occur between the bacteria and the host. This review provides overviews of the age-related changes in GIT functions, the resident bacteria, and diet, and describes how interactions among these 3 factors influence the health and nutrition of neonates and can have lifelong consequences. Necrotizing enterocolitis is a common GI inflammatory disorder in preterm infants and is provided as an example of interactions that go awry. Other enteric diseases are common in all newborn mammals, and an understanding of the above interactions will enhance efforts to support neonatal health for infants and for farm and companion animals.

Elective cesarean delivery affects gut maturation and delays microbial colonization but does not increase necrotizing enterocolitis in preterm pigs.

Although preterm birth and formula feeding increase the risk of necrotizing enterocolitis (NEC), the influences of cesarean section (CS) and vaginal delivery (VD) are unknown. Therefore, gut characteristics and NEC incidence and severity were evaluated in preterm pigs (92% gestation) delivered by CS or VD. An initial study showed that newborn CS pigs (n = 6) had decreased gastric acid secretion, absorption of intact proteins, activity of brush-border enzymes and pancreatic hydrolases, plasma cortisol, rectal temperature, and changes in blood chemistry, indicating impaired respiratory function, compared with VD littermates (n = 6). In a second experiment, preterm CS (n = 16) and VD (n = 16) pigs were given total parenteral nutrition (36 h) then fed porcine colostrum (VD-COL, n = 6; CS-COL, n = 6) or infant milk formula (VD-FORM, n = 10; CS-FORM, n = 10) for 2 days. Across delivery, FORM pigs showed significantly higher NEC incidence, tissue proinflammatory cytokines (IFN-gamma and IL-6), Clostridium colonization, and impaired intestinal function, compared with COL pigs. NEC incidence was equal for CS (6/16) and VD (6/16) pigs, CS pigs had decreased bacterial diversity and density, higher villus heights, and increased brush-border enzyme activities (lactase, aminopeptidases) compared with VD pigs. In particular, VD-FORM pigs showed reduced mucosal proportions, reduced lactase and aminopeptidases, and increased proinflammatory cytokine IL-6 compared with CS-FORM (P < 0.06). Despite the initial improvement of intestinal and metabolic functions following VD, gut function, and inflammation were similar, or more negatively affected in VD neonates than CS neonates. Both delivery modes exhibited positive and negative influences on the preterm gut, which may explain the similar NEC incidence.

Cortisol increases the activities of intestinal apical membrane hydrolases and nutrient transporters before weaning in mink (Mustela vison).

Glucocorticoids from endogenous and exogenous sources accelerate maturation of brush-border membrane (BBM) hydrolases in omnivorous laboratory rodents and pigs. Less is known for carnivores, and whether the route of administration (oral or systemic) has an influence. The present study examined the influence of administering cortisol (hydrocortisone succinate, 5 mg/kg-day) to mink during postnatal week 4, just prior to weaning, on small intestine glucose and amino acid (aspartate, leucine, lysine, methionine, proline) absorption and on the activities of BBM disaccharidases and peptidases. Kits treated with cortisol were smaller (P<0.05), but had small intestines that were proportionally larger (P<0.05 for length and mass per kg body weight, but not for mucosal mass) than control kits with higher rates of absorption for most nutrients, except leucine, and increased activities of most BBM hydrolases, except lactase. As a consequence, cortisol increased hydrolytic and absorptive capacities of the entire small intestine, with the responses more pronounced when the cortisol was given orally. These findings indicate administration of cortisol stimulates growth of the developing mink small intestine, but does not accelerate the postnatal declines in nutrient transport, and may be a dam-to-kit signal that prepares suckling mink to digest and absorb the adult diet.

Glucagon-like peptide 2 stimulates intestinal nutrient absorption in parenterally fed newborn pigs.

OBJECTIVES: Parenteral nutrition is a critically important intervention for children with intestinal dysfunctions. However, total parenteral nutrition (TPN) with no enteral feeding is associated with small intestine atrophy and malabsorption, which complicate the transition to enteral nutrition. The objective of the present study was to evaluate the therapeutic potential of the intestinotrophic peptide glucagon-like peptide 2 (GLP-2), which reduces TPN-associated atrophy and maintains nutrient absorption in adult rats, for preventing nutrient malabsorption in neonates receiving TPN. METHODS: Term pigs obtained by cesarean delivery received from birth TPN alone (TPN; n = 7) or TPN with GLP-2 (25 nmol . kg(-1) . d(-1); GLP-2; n = 8) or were fed sow milk enterally (n = 7). The small intestine was removed on postnatal day 6 to measure morphological responses and absorption of glucose, leucine, lysine and proline by intact tissues and brush border membrane vesicles and to quantify the abundances of mRNA and protein for enterocyte glucose transporters (SGLT-1 and GLUT2). RESULTS: Relative to TPN alone, administration of GLP-2 resulted in small intestines that were larger (P < 0.01), had greater abundances of mRNA and protein for SGLT-1, but not for GLUT2, and had higher capacities to absorb nutrients (P < 0.01). Moreover, the intestines of GLP-2 pigs were comparable in size and absorptive capacities with those of pigs fed sow milk enterally. CONCLUSIONS: Providing GLP-2 to neonates receiving TPN prevents small intestine atrophy, results in small intestine absorptive capacities that are comparable to when nutrients are provided enterally and may accelerate the transition from TPN to enteral nutrition.

Glucagon-like peptide-2 protects against TPN-induced intestinal hexose malabsorption in enterally refed piglets.

Premature infants receiving chronic total parenteral nutrition (TPN) due to feeding intolerance develop intestinal atrophy and reduced nutrient absorption. Although providing the intestinal trophic hormone glucagon-like peptide-2 (GLP-2) during chronic TPN improves intestinal growth and morphology, it is uncertain whether GLP-2 enhances absorptive function. We placed catheters in the carotid artery, jugular and portal veins, duodenum, and a portal vein flow probe in piglets before providing either enteral formula (ENT), TPN or a coinfusion of TPN plus GLP-2 for 6 days. On postoperative day 7, all piglets were fed enterally and digestive functions were evaluated in vivo using dual infusion of enteral ((13)C) and intravenous ((2)H) glucose, in vitro by measuring mucosal lactase activity and rates of apical glucose transport, and by assessing the abundances of sodium glucose transporter-1 (SGLT-1) and glucose transporter-2 (GLUT2). Both ENT and GLP-2 pigs had larger intestine weights, longer villi, and higher lactose digestive capacity and in vivo net glucose and galactose absorption compared with TPN alone. These endpoints were similar in ENT and GLP-2 pigs except for a lower intestinal weight and net glucose absorption in GLP-2 compared with ENT pigs. The enhanced hexose absorption in GLP-2 compared with TPN pigs corresponded with higher lactose digestive and apical glucose transport capacities, increased abundance of SGLT-1, but not GLUT-2, and lower intestinal metabolism of [(13)C]glucose to [(13)C]lactate. Our findings indicate that GLP-2 treatment during chronic TPN maintains intestinal structure and lactose digestive and hexose absorptive capacities, reduces intestinal hexose metabolism, and may facilitate the transition to enteral feeding in TPN-fed infants.

Intestinal nutrient transport during ontogeny of vertebrates.

Patterns of transporter development are known for 12 species of vertebrates (2 fish, 1 amphibian, 1 bird, and 8 mammals), ranging from early gestation to adulthood. Although transporters for some nutrients (amino acids and some sugars) appear before the onset of external feeding, species differ in when and which transporters appear. Postnatal changes in the activities of different transporters are twofold: corresponding with shifts in the composition of a species' evolutionary diet, and the need to absorb ever-increasing quantities of food for growth and metabolism. The mechanisms responsible for the age-related shifts in rates of transport include changes in the densities, distribution, and types of transporters for specific nutrients and changes in the physiochemical characteristics of the intestinal brush-border membrane. The signals that trigger the age-related changes originate from internal preprogrammed sources and external sources, with both acting in concert to mediate intestinal development. Although much more is known for the brush-border hydrolases, recent studies with the pig suggest the ontogenetic development of hydrolases and transporters are regulated independently during early development.

Nutrition and ontogenetic development of the intestine.

Fetal, suckling, and postweaning vertebrates have distinct dietary inputs that impose different functional demands on the developing intestine. Differences between species and life-history stages in intestinal structure and functions are set by genetic determinants that reflect evolutionary diets. Dietary inputs interacting with genetic determinants influence intestinal functions by triggering the production of new enterocyte populations and (or) by reprogramming existing enterocytes. In addition to nutrients, nonnutritive components of amniotic fluid and milk, such as growth factors and hormones, are important mediators of intestinal development and in humans can exert influences at as early as 10 weeks of gestation, when fetuses begin swallowing amniotic fluid. Changes in diet composition during suckling elicit limited and apparently nonspecific responses in intestinal structure and activities of brush-border hydrolases and transporters. The ability to adaptively modulate intestinal brush-border functions develops at weaning, when diet composition begins to vary unpredictably. Hydrolytic and transport capacities of the developing intestine are matched to age-related increases in dietary inputs, are not in great excess, and may be growth limiting. Although not as extensively studied, postnatal diet also influences development of intestinal endocrine and immune functions and has a complex, poorly understood interaction with the developing microflora.

Does the natural diet influence the intestine's ability to regulate glucose absorption?

Two fish species (rainbow trout and common carp) that differ in natural diet also exhibit differences in the adaptive flexibility of their intestinal nutrient transport mechanisms in response to changes in dietary nutrient composition. When carp ingested a feed that was 24% glucose by weight, there was an increase in both the intestinal length and rates of nutrient absorption, particularly for glucose, when compared to carp fed an isonitrogenous diet devoid of digestible carbohydrate. As a result, the intestine's uptake capacity (nmol of glucose and proline absorbed per min per g body weight) was higher in carp fed the 24% glucose feed. Due to the greater increase in glucose uptake, the ratio of glucose uptake relative to proline (G/P ratio) was higher in carp fed the 24% glucose. Thus, carp are able to adapt to the quantity, and apparently also to the type, of digestible carbohydrate in the diet. In contrast, glucose uptake by trout was unresponsive to the quantity of dietary carbohydrate. Instead, the elevated glucose paradoxically resulted in a greater uptake capacity for proline and a lower G/P ratio. Hence, the adaptive capabilities of the intestinal nutrient transport processes are matched to the potential variation in the carbohydrate content of the natural diet.

Aristotle revisited: the function of pyloric caeca in fish.

The function of the pyloric caeca of fish has been uncertain since their detailed description in 345 B.C. by Aristotle. He suggested three hypotheses about their function: "to store up the food," "putrify it up," and "concoct it" (i.e., storage, fermentation, and digestion). Our results for trout, cod, largemouth bass, and striped bass support the third but not the first or second of Aristotle's theories. In all four species, the caeca prove to be a major site of sugar, amino acid, and dipeptide uptake, contributing more uptake than the entire remaining alimentary tract in trout and cod. Caecal brush-border membranes contain hydrolytic enzymes. X-ray plates taken at various times after trout had ingested radioopaque marker, and observations of trout fed blue dye plus glass beads of graded sizes, show that caeca fill and empty of food with the same time course as proximal intestine. Thus, whereas the caeca of mammals and birds serve as fermentation chambers, fish caeca are an adaptation to increase gut surface area.

Pyloric ceca of fish: a "new" absorptive organ.

The functions of the blind appendages attached to the proximal intestine of many fish, the pyloric ceca, have been disputed. Hence we recorded morphological parameters and nutrient uptake rates in the ceca and intestine of four fish species (rainbow trout, cod, largemouth bass, and striped bass) with various degrees of cecal development (the ceca contribute 70, 69, 42, and 16% of the total postgastric surface area, respectively). Proline and glucose uptake, measured in vitro, is similar in the ceca and proximal intestine. For these two solutes in these four species, and for 10 other solutes (9 amino acids and 1 dipeptide) in trout, the ceca contribute about the same percentage to uptake as to total gut area. Trout ceca and intestine have similar membrane-bound disaccharidase activity. Separate experiments with trout fed either graded glass beads or a radiopaque marker and then X-rayed show that the ceca fill and empty with particles less than 150 microns and over the same time course as the proximal intestine. Thus ceca are an adaptation for increasing intestinal surface area without increasing the length or thickness of the intestine itself. Fish ceca are entirely different from the distally located ceca of birds and mammals, which have fermentation functions.