Introduction of enteral food increases plasma GLP-2 and decreases GLP-2 receptor mRNA abundance during pig development

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.

Preterm birth makes the immature intestine sensitive to feeding-induced intestinal atrophy

Preterm birth and formula feeding predispose to small intestinal dysfunction, which may lead to necrotizing enterocolitis (NEC). In piglets, we tested whether the physiological and environmental transitions occurring at birth affect the response of the immature intestine to enteral feeding. Pig fetuses (106 days gestation, term = 115 days) were prepared with esophageal feeding tubes and fed either sow's colostrum (n = 8) or infant formula (n = 7) in utero. After 24 h of oral feeding, the pig fetuses were delivered by cesarean section and their gastrointestinal morphology and function were compared with those of preterm newborn (NB) littermates that were not fed (n = 8) or fed colostrum (n = 7) or formula (n = 13) for 24 h after birth. Before birth, both colostrum and formula feeding resulted in marked increases in intestinal mass, brush-border enzyme activities, and plasma glucagon-like peptide 2 concentrations, to levels similar to those in NB colostrum-fed piglets. In contrast, NB formula-fed piglets showed reduced intestinal growth, decreased brush-border enzyme activities, and intestinal lesions, reflecting NEC. NB formula-fed pigs also showed impaired enterocyte endocytotic function and decreased antioxidative capacity, whereas brush-border enzyme mRNA levels were unaltered, relative to NB colostrum-fed pigs. Our results indicate that the feeding-induced growth and enzyme maturation of the immature intestine are not birth dependent. However, with a suboptimal diet (milk formula), factors related to preterm birth (e.g., microbial colonization and metabolic and endocrine changes) make the immature intestine sensitive to atrophy and development of NEC.

Glucagon-like peptide 2: a key link between nutrition and intestinal adaptation in neonates?

This paper reviews the evidence from recent studies in young piglets to examine the hypothesis that glucagon-like peptide 2 (GLP-2) is a physiologically relevant hormonal signal linked to the intestinal adaptation associated with enteral nutrition in neonates. Observations that support the hypothesis include, 1) the GLP-2 secretory response to enteral nutrition is functional as early as late gestation, 2) parallel changes in intestinal growth and circulating GLP-2 occur in response to the quantity and composition of enteral nutrition after birth, and 3) the acute temporal changes in intestinal metabolism and circulating GLP-2 concentrations in response to enteral nutrition are generally coincident. In contrast, however, the lack of intestinal trophic responses to both pharmacological GLP-2 concentrations in the fetus and weanling pigs, and to physiological GLP-2 concentrations in neonates raises doubts concerning the physiological relevance of GLP-2 as a enterally mediated trophic signal. A more definitive test of this hypothesis will require further studies that assess the intestinal metabolic response to enteral nutrition using experimental approaches that block GLP-2 action.

Preterm as Compared with Full-Term Neonatal Calves Are Characterized by Morphological and Functional Immaturity of the Small Intestine

Intestinal diseases in neonatal calves may be due to morphological and functional immaturity. We have studied histomorphology, crypt cell proliferation rates (based on incorporation of 5-bromo-2'-deoxyuridine into DNA), presence of apoptotic cells (based on terminal deoxynucleotidyl transferase-mediated X-dUTP nick end labeling), and brush border enzyme activities in preterm calves (277 d of gestation), euthanized on d 1 (P0) or 8 (P8), and in full-term calves (290 d of gestation), euthanized on d 1 (F0) or 8 (F8). Vacuolated epithelial cells were present in ileum of P0 and F0 but not in P8 and F8. During the first 8 d, villus sizes, crypt depths, and proliferation rates of crypt cells in the small intestine of preterm calves did not significantly change. In contrast, in full-term calves during the first 8 d, villus sizes in jejunum decreased, crypt depths increased in small intestine and colon, and crypt cell proliferation increased in duodenum and jejunum. Submucosal thickness in jejunum was highest in P0, but in ileum it increased with gestational age and feeding. Gestational age x feeding interactions indicated increased activities of aminopeptidase N and reduced lactase activities only in F8 and reduced dipeptidylpeptidase IV activities only in P8. In conclusion, in preterm calves the small intestinal epithelium was immature and brush border enzyme activities differed in part from those in full-term calves.

Cell and molecular biology of the small intestine: new insights into differentiation, growth and repair

PURPOSE OF REVIEW

This paper will discuss recent research that has provided new insights into the molecular and cell biology of the small intestine.

RECENT FINDINGS

Differentiation of the epithelial cell lineages, including the enterocytes, enteroendocrine, Goblet and Paneth cells, from the stem cells is better understood. Important interactions have been demonstrated between these cells, luminal bacteria, and underlying mesenchymal tissue. Intestine-specific gene expression is regulated by transcription factors that are becoming well characterized, including CDX1, CDX2 and HNF1. The actions of growth factors such as GLP-2 and EGF are now known to be complex, demonstrating multiple effects in this tissue at a number of levels.

SUMMARY

Progress in the cellular and molecular biology of the small intestine is producing many intriguing new findings.