Classical and post-genomic methods to study GIT function with emphasis on the pig☆
Introduction
The gastrointestinal tract (GIT) forms the contact surface between the environment and the interior of the body and acts as a dynamic interface allowing exchange of molecules but also serves as an internal barrier. Among the main roles of the GIT are the transient storage of discontinuously consumed food, the transport of chyme through the alimentary canal, and the digestion of food. During digestion food derived macromolecules are disintegrated which coincides with their absorption thereby transferring water and nutrients to the circulation where it is further utilized in adjacent tissues. Starting already in the terminal small intestine (SI) unabsorbed residues and endogenous secretions serve as substrate for the indigenous microbiota entering the intestine with the diet. In addition, the GIT has barrier functions to prevent pathogenic microorganisms, toxins and allergenic macromolecules to enter the interior space of the body. As such, intestinal function directly or indirectly affects animal health.
The timely and correct development of the GIT is a prerequisite for its proper function and adaptability to a number of challenging events during the life cycle. During transition from the fetal to the postnatal period, nutrient supply changes from the parenteral route via the umbilical cord and some swallowing of amniotic fluid to enteral nutrition with colostrum containing compounds new to the individual (e.g. fat, lactose, immunoglobulins) and protective and growth-stimulating factors (e.g. IGF-1, epidermal growth factor) (Pluske et al., 1997, Trahair and Sangild, 1997, Sangild, 2003).
The second transition refers to the change from suckling the dam, i.e. the ingestion of liquid feed, to the uptake of dry feed associated with the abrupt withdrawal of beneficial milk constituents, and a major change in the complexity of dietary carbohydrates. These alterations are accompanied by the exposure to a novel pattern of microbes or the encounter with enterotoxigenic microbes, and the social stress associated with the separation from the sow and the mixing with unfamiliar piglets (Lalles et al., 2007). It is important to recognize that enteral feed intake (i.e. luminal stimulation) in itself is a major factor influencing the function and health of the GIT (e.g. McCracken et al., 1999, Burrin et al., 2000a, Lalles et al., 2007).
During the course of the developmental genetic program and as a response to the above mentioned changes the GIT undergoes a maturational program including cellular, morphologic, digestive, absorptive, metabolic and immunological changes (Trahair and Sangild, 1997, Pluske et al., 1997). The intestinal epithelium is continuously and rapidly renewed from the stem cell population located at the bottom of the crypt to the extrusion of the terminally differentiated cells at the tip of the villus. As a consequence intestinal cells have a short life span of between 2 and 10 d (Radecki et al., 1992, Fan et al., 2001). This enables it to react quickly to changing substrate types and concentrations as well as pathogens, toxins and allergenes.
Related to the above described roles of the GIT this contribution provides an overview on classical and more recent methods applied to investigate GIT structure and functions including i) intestinal and mucosal mass and functional morphology, ii) digestive function, nutrient absorption and absorptive capacity, iii) intestinal metabolism, and iv) barrier function. The description of the principles of the methods is supplemented by examples from the experimental literature. This review is focused on in vivo functional tests of GIT function, because in vitro methods do not always describe functions in vivo completely. Due to the similarities between human and pigs GIT physiology and maturation, many of these methods have been applied in pigs as model animals for the examination of GIT development, function and disease in humans (Reisenauer et al., 1989, Sangild et al., 2002, Burrin et al., 2003, Chang et al., 2006). Especially the neonatal and infant pig is increasingly used as a model for human neonates and infants.
Section snippets
Intestinal and mucosal mass and functional morphology
One of the simplest methods to obtain information on gut development as influenced by age or diet is to measure intestinal, mucosal mass or mucosal proportion. These variables provide an approximate measure of potential digestive and absorptive mass. Also intestinal area over a specific section of the GIT or total intestinal mucosa mass can be calculated when length and circumference are obtained (Sangild et al., 2002, Adeola and King, 2006). Many researchers have shown the importance of
Digestive function, nutrient absorption and absorptive capacity
In vivo measurements of digestion or digestibility belong to the classical repertoire of animal nutrition and are important for feed ingredients evaluation and pig ration formulation (Fuller, 1991, Fuller, 2003). These methods are principally based on the disappearance of nutrients in the GIT which implies the involvement of not only digestive but also absorptive processes. The most important example is amino acid (AA) digestibility which reflects enzymatic hydrolysis, the contribution of
Intestinal metabolism
The gut is a metabolically active organ supplied by nutrients from the luminal as well as from the basolateral side and responsible for 17–25% of whole-body oxygen consumption (Cant et al., 1996). To fulfill its various roles the SI takes up a share of the nutrients provided enterally to generate ATP used for the many synthetic processes (e.g. mucin, digestive, absorptive, and transporter proteins, cell turnover). Stable isotope tracer methodologies provide powerful tools to dissect the various
Barrier function
Propulsion of food, chyme and fluid through the alimentary canal limits opportunities of opportunistic pathogens for colonization intestinal sections and bacterial translocation, decrease the contact time between toxic or cancerogenic compounds in the luminal contents (e.g. products of microbial proteolytic processes) and the epithelial surface, and thus can be considered a component of barrier function. In that way GIT infections caused by ingested pathogens leading to diarrhea can be reduced.
Conflict of Interest
I declare that there is no actual or potential conflict of interest including any financial, personal or other relationships with other people or organizations within 3 years of beginning the submitted work that could inappropriately influence, or be perceived to influence.
References (124)
- et al.
Contribution of intestinal microbial lysine to lysine homeostasis is reduced in minipigs fed a wheat gluten-based diet
Am. J. Clin. Nutr.
(2002) - et al.
Intestinal atrophy has a greater impact on nitrogen metabolism than liver by-pass in piglets fed identical diets via gastric, central venous or portal venous routes
J. Nutr.
(1999) A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein–dye binding
Anal. Biochem.
(1976)- et al.
Minimal enteral nutrient requirements for intestinal growth in neonatal piglets: how much is enough?
Am. J. Clin. Nutr.
(2000) - et al.
Parenteral nutrition results in impaired lactose digestion and hexose absorption when enteral feeding is initiated in infant pigs
Am. J. Clin. Nutr.
(2003) Method for assay of intestinal dissacharidases
Anal. Biochem.
(1964)- et al.
Effect of direct fed microbial and antibiotic supplementation on gastrointestinal microflora, mucin histochemical characterization, and immune populations of weaning pigs
Livest. Sci.
(2007) - et al.
The preparation and properties of two new chromogenic substrates of trypsin
Arch. Biochem. Biophys.
(1961) - et al.
Characterization of brush border membrane-bound alkaline phosphatase activity in different segments of the porcine small intestine
J. Nutr. Biochem.
(1999) - et al.
Postnatal ontogeny of kinetics of porcine jejunal brush border membrane-bound alkaline phosphatase, aminopeptidase N and sucrase activities
Comp. Biochem. Physiol. A Mol. Integr. Physiol.
(2002)
Exocrine pancreatic secretions in growing pigs fed diets containing fish oil, rapeseed oil or coconut oil
J. Nutr.
Morphometry and cell proliferation in endoscopic biopsies: evaluation of a technique
Gastroenterology
Alterations in piglet small intestinal structure at weaning
Res. Vet. Sci.
Influence of creep feeding and weaning on brush border enzyme activities in the piglet small intestine
Res. Vet. Sci.
Starch digestion in normal subjects and patients with pancreatic disease, using a 13CO2 breath test
Gastroenterol.
Extensive gut metabolism limits the intestinal absorption of excessive supplemental dietary glutamate loads in infant pigs
J. Nutr.
Intestinal immunoglobulin absorption and enzyme activity in neonatal pigs fed colostrum, plasma or milk replacer
J. Nutr.
The small intestine proteome is changed in preterm pigs developing necrotizing enterocolitis in response to formula feeding
J. Nutr.
Nonstarch polysaccharide hydrolysis products of soybean and canola meal protect against enterotoxigenic Escherichia coli in piglets
J. Nutr.
A milk diet partly containing soy protein does not change growth but regulates jejunal proteins in young goats
J. Dairy Sci.
A simple, rapid and sensitive DNA assay procedure
Anal. Biochem.
Specific regulation of the gene expression of some pancreatic enzymes during postnatal development and weaning in the calf
Biochim. Biophys. Acta
Inulin alters the intestinal microbiota and short-chain fatty acid concentrations in growing pigs regardless of their basal diet
J. Nutr.
The aminopeptidase from hog intestinal brush border
Biochim. Biophys. Acta
Weaning anorexia may contribute to local inflammation in the piglet small intestine
J. Nutr.
Contribution of microbial amino acids to amino acid homeostasis of the host
J. Nutr.
Onset of small intestinal atrophy is associated with reduced intestinal blood flow in TPN-fed neonatal piglets
J. Nutr.
Factors influencing the structure and function of the small intestine in the weaned pig: a review
Livestock Prod. Sci.
Effect of energy and purines in the diet on proliferation, differentiation, and apoptosis in the small intestine of the pig
Metabolism
Folate absorption in alcoholic pigs: in vivo intestinal perfusion studies
Am. J. Clin. Nutr.
Developmental changes in morphometry of the small intestine and jejunal sucrase activity during the first nine weeks of postnatal growth in pigs
J. Anim. Sci.
The effect of feed intake on ileal rate of passage and apparent amino acid digestibility determined with or without correction factors in pigs
J. Anim. Sci.
Methods compared for determining total amylase activity and amylase enzymes in serum
Clin. Chem.
Citrulline and intestinal fatty acid-binding protein: longitudinal markers of postweaning small intestinal function in pigs?
J. Anim. Sci.
Preterm birth makes the immature intestine sensitive to feeding-induced intestinal atrophy
Am. J. Physiol. Regul. Integr. Comp. Physiol.
Lipase and co-lipase activities of human small intestinal contents after a liquid test meal
Scand. J. Gastroenterol.
Ontogeny of T lymphocytes and intestinal morphological characteristics in neonatal pigs at different ages in the postnatal period
J. Anim. Sci.
Absorption of amino acids in different parts of the small intestine in growing pigs. I. Absorption of free amino acids and water
Acta Physiol. Pol.
GLP-2 stimulates intestinal growth in premature TPN-fed pigs by suppressing proteolysis and apoptosis
Am. J. Physiol. Gastrointest. Liver Physiol.
The regulation of intestinal metabolism and its impact on whole animal energetics
J. Anim. Sci.
Carbohydrate sulfation effects on growth of Pseudomonas aeruginosa
Microbiology
Serial transverse enteroplasty enhances intestinal function in a model of short bowel syndrome
Ann. Surg.
Transcriptome profiling of the small intestinal epithelium in germfree versus conventional piglets
BMC Genomics
Acidomucin goblet cell expansion induced by parenteral nutrition in the small intestine of piglets
Am. J. Physiol. Gastrointest. Liver Physiol.
Nutrition and the gut mucosal barrier
Curr. Opin. General Surg.
Substrate specificity of human pancreatic elastase 2
Biochemistry
Effect of supplementation of xylanase and phospholipase to a wheat-based diet for weanling pigs on nutrient digestibility and concentrations of microbial metabolites in ileal digesta and feces
J. Anim. Sci.
Parenteral nutrition selectively decreases protein synthesis in the small intestine
Am. J. Physiol.
Lactase synthesis is pretranslationally regulated in protein-deficient pigs fed a protein-sufficient diet
Am. J. Physiol. Gastrointest. Liver Physiol.
Enterocyte digestive enzyme activity along the crypt–villus and longitudinal axes in the neonatal pig small intestine
J. Anim. Sci.
Cited by (6)
Fermented soybean meal increases nutrient digestibility via the improvement of intestinal function, anti-oxidative capacity and immune function of weaned pigs
2022, AnimalCitation Excerpt :Because the limited number of enzymes was evaluated, these enzymes may reflect overall enzyme activities on some degree. Animal health is essential to maintain digestive enzyme activity and nutrient digestion (Metges, 2010; Campbell et al., 2013). The health issue of weaned pigs caused by various stress and infection is the major concern in swine industry.
Adding crude glycerin to nursery pig diet: Effect on nutrient digestibility, metabolic status, intestinal morphology and intestinal cytokine expression
2014, Livestock ScienceCitation Excerpt :In our experiment, there were no differences between the different treatments in the relative GIT weight and pH along the GIT. These parameters are related to the intestinal health of piglets, and their optimal development is a precondition for dealing with the challenges that arise in the post-weaning period (Metges, 2010). Note that sweet milk whey (rich in lactose) is a suitable substrate for encouraging the growth of lactic acid bacteria, which ferment lactose to lactic acid.
Artificial rearing of piglets: Effects on small intestinal morphology and digestion capacity
2014, Livestock ScienceCitation Excerpt :Therefore, the present study investigated the short-term and long-term consequences of artificially rearing piglets on formulated milk in a brooder. In addition to their growth, the morphological characteristics and digestive capacity of the small intestine were analyzed, because the latter are crucial elements in driving postnatal development, growth and health (Metges, 2010). In our study, feeding milk formula for one week inhibited the growth of the piglets by 112 g d−1, resulting in reduced body weights at 10 d of age (on average −0.818 kg).
The Effect of Combined Feed Additives on Growing Pigs' Performance and Digestive Tract Parameters
2019, Annals of Animal ScienceTerminalia Sericea aqueous leaf extract protects growing wistar rats against fructose-induced fatty liver disease
2019, Journal of Complementary and Integrative Medicine
- ☆
This paper is part of the special issue entitled “11th International Symposium on Digestive Physiology of Pigs.”