Glucagon-like Peptide-2 Infusion Research Articles

1982-P: Glucagon-Like Peptide-2 Inhibits Postprandial Gallbladder Emptying in Healthy Male Individuals—A Randomized, Double-Blinded, Placebo-Controlled Study

A recent study in mice has demonstrated that the gut-derived hormone glucagon-like peptide-2 (GLP-2) may be involved in the regulation of gallbladder motility and induces gallbladder refilling. This study evaluated the effect of exogenous GLP-2 on postprandial gallbladder motility in humans. On three experimental days, 15 young healthy males ([mean±SEM] age 24.3±1.9 years, BMI 22.5±0.9 kg×m-2, HbA1c 4.8±0.1% (29.3±1.5 mmol/mol)) were subjected to a 3.5-hour 300 kcal mixed liquid meal-test. Continuous 4-hour intravenous infusions of placebo (saline), low-dose GLP-2 (1 pmol×kg-1×min-1) or high-dose GLP-2 (10 pmol×kg-1×min-1) were initiated 30 min before meal ingestion. Gallbladder volume was determined by ultrasonography, and gallbladder ejection fraction was calculated. Postprandial maximum gallbladder ejection fraction during saline infusion (76.3±2.8%) was significantly reduced by low-dose GLP-2 (65.5±3.5%, P=0.026) and completely abolished during high-dose GLP-2 infusion (4.0±3.7%, P<0.0001) (Figure). Postprandial peak plasma glucose was lower during high-dose GLP-2 infusion (6.4±0.2 mmol/l) compared to low-dose GLP-2 (6.9±0.2mmol/l, P=0.0004) and placebo infusion (7.2±0.2 mmol/l, P=0.008). In conclusion, exogenous GLP-2 dose-dependently inhibits postprandial gallbladder emptying in healthy male subjects. Disclosure N.L. Hansen: None. C.C. Nexøe-Larsen: None. A. Brønden: Other Relationship; Self; AstraZeneca. A.S. Christensen: None. D.P. Sonne: None. B. Hartmann: None. T. Vilsbøll: None. J.J. Holst: Advisory Panel; Self; Novo Nordisk A/S. F.K. Knop: Advisory Panel; Self; AstraZeneca, MedImmune, Merck Sharp & Dohme Corp., Mundipharma, Novo Nordisk A/S, Sanofi. Consultant; Self; Amgen Inc., Carmot Therapeutics, Novo Nordisk A/S. Research Support; Self; AstraZeneca, Novo Nordisk A/S. Speaker's Bureau; Self; AstraZeneca, MedImmune, Merck Sharp & Dohme Corp., Mundipharma, Norgine, Novo Nordisk A/S.

Short-chain fatty acids augment rat duodenal mucosal barrier function.

What is the central question of this study? Small intestinal epithelium is exposed to high concentrations of short-chain fatty acids (SCFAs), but their role in regulating intestinal mucosal barrier function and motility is not fully understood. What is the main finding and its importance? By perfusing the duodenal segment in anaesthetized rats, we show that acetate and propionate significantly decrease mucosal paracellular permeability and transepithelial net fluid flux and increase mucosal bicarbonate secretion. Likewise, SCFAs administered i.v. decrease mucosal permeability but decrease bicarbonate secretion. Altered luminal chemosensing or aberrant signalling in response to SCFAs might contribute to symptoms observed in patients with suppressed mucosal barrier function. Short-chain fatty acids (SCFAs) are produced by bacterial fermentation in the large intestine, particularly from diets containing fibres and carbohydrates. The small intestinal epithelium is exposed to SCFAs derived mainly from oral bacteria or food supplementation. Although luminal nutrients are important in regulation of intestinal functions, the role of SCFAs in regulation of small intestinal mucosal barrier function and motility has not been fully described. The aim of the present study was to elucidate the effects of acetate and propionate on duodenal mucosal barrier function and motility. Rats were anaesthetized with thiobarbiturate, and a 30mm segment of proximal duodenum with an intact blood supply was perfused. The effects on duodenal bicarbonate secretion, blood-to-lumen clearance of 51 Cr-EDTA, motility and transepithelial net fluid flux were investigated. Perfusion of the duodenum with acetate or propionate significantly decreased mucosal paracellular permeability and transepithelial net fluid flux and significantly increased bicarbonate secretion. Acetate or propionate administered as an i.v. infusion decreased the mucosal paracellular permeability, but significantly decreased bicarbonate secretion. Luminal SCFAs changed the duodenal motility pattern from migrating motor complexes to fed patterns. Systemic administration of glucagon-like peptide-2 induced increases in both bicarbonate secretion and net fluid absorption, but did not change motility. Glucagon-like peptide-2 infusion during luminal perfusion of SCFAs significantly reduced the motility. In conclusion, SCFAs decreased duodenal paracellular permeability and net fluid flux. Short-chain fatty acids induced opposite effects on bicarbonate secretion after luminal and i.v. administration. Presence of SCFAs in the lumen induces fed motility patterns. Altered luminal chemosensing and aberrant signalling in response to SCFAs might contribute to symptoms observed in patients with suppressed barrier function.

Glucagon-Like Peptide 2 Stimulates Postresection Intestinal Adaptation in Preterm Pigs by Affecting Proteins Related to Protein, Carbohydrate, and Sulphur Metabolism.

Exogenous glucagon-like peptide 2 (GLP-2) stimulates intestinal adaptation after resection in animal models of pediatric short bowel syndrome (SBS). It is unknown whether the molecular mechanisms of such GLP-2 effects are similar to those of postresection spontaneous adaptation. Using preterm pigs as a model, we hypothesized that GLP-2 treatment would change the intestinal proteome within the first week after resection, relative to individuals not resected or resected without GLP-2 treatment. Two-day-old preterm pigs were subjected to resection of 50% distal small intestine and fed total parenteral nutrition without (SBS) or with GLP-2 infusion (3.5 µg/kg/h, SBS+GLP-2) for 5 days. The proteome of the remnant proximal intestine was compared among the SBS, SBS+GLP-2, and unresected pigs, through gel-based proteomics. Thirty-two proteins with differential expression were identified. Ten of these proteins were affected by the resection alone (ie, SBS vs unresected pigs). Five of these resection-responsive proteins and another 22 proteins were affected by GLP-2 infusion (ie, SBS+GLP-2 vs SBS or unresected pigs). Resection alone mainly affected cellular structural proteins, while the added GLP-2 treatment affected proteins involved in protein processing and the metabolism of protein, carbohydrate, and sulphur. In the first days following resection, proteins affected by resection plus GLP-2 treatment differed markedly from those affected by the spontaneous intestinal adaptation following resection alone. Whether more long-term GLP-2 treatment may affect the intestinal proteome following intestinal resection remains unknown.

A dose-equivalent comparison of the effects of continuous subcutaneous glucagon-like peptide 2 (GLP-2) infusions versus meal related GLP-2 injections in the treatment of short bowel syndrome (SBS) patients

ObjectiveGlucagon-like peptide 2 (GLP-2), secreted endogenously from L-cells in the distal bowel in relation to meals, modulates intestinal absorption by adjusting gastric emptying and secretion and intestinal growth. Short bowel syndrome (SBS) patients with distal intestinal resections have attenuated endogenous GLP-2 secretion, which may contribute to their rapid gastric emptying, gastric hypersecretion and poor intestinal adaptation, whereas SBS patients with preserved terminal ileum and colon, who have a constantly elevated GLP-2 secretion, seem to do better in these respects. This study compared effects of continuous, subcutaneous (s.c.), exogenous GLP-2 infusion (CONT-GLP-2) versus three daily s.c. GLP-2 injections (TID-GLP-2) on intestinal absorption in SBS patients. DesignEight SBS patients (5 F, 3 M; 60±7years; remnant small bowel 111±62cm; 1 with 50% colon) were studied. In an open-label, sequential study, the 72-hour baseline admission was followed by two dose-equivalent, 21-day, dosing regimens; CONT-GLP-2, providing 1.0mg/day by a MiniMed insulin pump and TID-GLP-2, providing 0.33mg injections in relation to three meals, separated by a washout period of at least 3weeks. During admissions, the intestinal absorption was evaluated by analysing a double portion of the diet, faecal and urinary excretions. Post-absorptive plasma citrulline, reflecting enterocyte mass, was measured by HPLC. ResultsCompared to baseline, both GLP-2 dosing regimens reduced diarrhoea (CONT-GLP-2: 749±815g/d and TID-GLP-2: 877±1004g/d, p=0.01) and increased wet weight absorption (CONT-GLP-2: 19±19% and TID-GLP-2: 25±21%, p=0.003). Significant increases in plasma citrulline (CONT-GLP-2: 7.5±7μmol/L and TID-GLP-2, 12.7±8μmol/L; p=0.001) suggesting intestinotrophic effects in relation to GLP-2 treatment, are followed by increases in relative absorption of energy, carbohydrate and fat. No significant difference was seen on any of the absorptive parameters measured between the two dosing regimens. ConclusionBoth GLP-2 regimens significantly reduced diarrhoea in SBS patients, but a significant difference between continuous GLP-2 administration and TID injections could not be detected in a study of this size.

Glucagon-like peptide-2 (GLP-2) increases net amino acid utilization by the portal-drained viscera of ruminating calves

Glucagon-like peptide-2 (GLP-2) increases small intestinal mass and blood flow in ruminant calves, but its impact on nutrient metabolism across the portal-drained viscera (PDV) and liver is unknown. Eight Holstein calves with catheters in the carotid artery, mesenteric vein, portal vein and hepatic vein were paired by age and randomly assigned to control (0.5% bovine serum albumin in saline; n = 4) or GLP-2 (100 μg/kg BW per day bovine GLP-2 in bovine serum albumin; n = 4). Treatments were administered subcutaneously every 12 h for 10 days. Blood flow was measured on days 0 and 10 and included 3 periods: baseline (saline infusion), treatment (infusion of bovine serum albumin or 3.76 μg/kg BW per h GLP-2) and recovery (saline infusion). Arterial concentrations and net PDV, hepatic and total splanchnic fluxes of glucose, lactate, glutamate, glutamine, β-hydroxybutyrate and urea-N were measured on days 0 and 10. Arterial concentrations and net fluxes of all amino acids and glucose metabolism using continuous intravenous infusion of [U13-C]glucose were measured on day 10 only. A 1-h infusion of GLP-2 increased blood flow in the portal and hepatic veins when administered to calves not previously exposed to exogenous GLP-2, but after a 10-day administration of GLP-2 the blood flow response to the 1-h GLP-2 infusion was substantially attenuated. The 1-h GLP-2 infusion also did not appreciably alter nutrient fluxes on either day 0 or 10. In contrast, long-term GLP-2 administration reduced arterial concentrations and net PDV flux of many essential and non-essential amino acids. Despite the significant alterations in amino acid metabolism, glucose irreversible loss and utilization by PDV and non-PDV tissues were not affected by GLP-2. Fluxes of amino acids across the PDV were generally reduced by GLP-2, potentially by increased small intestinal epithelial growth and thus energy and amino acid requirements of this tissue. Increased PDV extraction of glutamine and alterations in PDV metabolism of arginine, ornithine and citrulline support the concept that GLP-2 influences intestine-specific amino acid metabolism. Alterations in amino acid metabolism but unchanged glucose metabolism suggests that the growth effects induced by GLP-2 in ruminants increase reliance on amino acids preferentially over glucose. Thus, GLP-2 increases PDV utilization of amino acids, but not glucose, concurrent with stimulated growth of the small intestinal epithelium in post-absorptive ruminant calves.

GLP‐2 receptor deficiency in the mouse brain impairs glucose homeostasis

In response to food intake, glucagon-like peptide-2 (GLP-2) with GLP-1 is co-secreted from enteroendocrine L cells in the gut. GLP-2 receptor (GLP-2R) is expressed in the hypothalamus, a key tissue to integrate energy signals to regulate energy balance and glucose homeostasis. However, the physiological role of brain GLP-2R has not been defined. Our objective was to critically test if brain GLP-2R activation is essential for glucose homeostasis. [1] We found that icv infusion of GLP-2 increased glucose tolerance with increased expression of POMC gene in the hypothalamus. [2] We showed that GLP-2 (100 nM) increased firing rate by 79%, but decreased membrane potential (Control: −38.4 ± 2.2 vs GLP-2: −32.1 ± 1.9 mV) of POMC neurons on hypothalamic slices using the whole-cell patch clamp. [3] Using our newly generated POMC-specific glp2r knockout (CKO) mice, we demonstrated that glucose intolerance increased by 42% in the CKO mice. Moreover, glucose infusion rate decreased in the CKO mice during hyperinsulinemic euglycemic clamp (WT: 6.46 ± 0.27 vs CKO: 4.54 ± 0.24 mmol/kg/h). During the clamp, hepatic glucose production increased (WT: 3.54 ± 0.34 vs CKO: 4.30 ± 0.35 mmol/kg/h) with increased fraction of gluconeogenesis by 47% and mRNA abundance of G6Pase & PEPCK by 200% in the CKO mice. We conclude that GLP-2R deficiency in POMC neurons impairs glucose homeostasis by decreasing insulin sensitivity, suggesting that brain GLP-2R activation is important for maintenance of glucose homeostasis at high postprandial insulin.

The separate and combined impact of the intestinal hormones, GIP, GLP-1, and GLP-2, on glucagon secretion in type 2 diabetes

Type 2 diabetes mellitus (T2DM) is associated with reduced suppression of glucagon during oral glucose tolerance test (OGTT), whereas isoglycemic intravenous glucose infusion (IIGI) results in normal glucagon suppression in these patients. We examined the role of the intestinal hormones glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide-1 (GLP-1), and glucagon-like peptide-2 (GLP-2) in this discrepancy. Glucagon responses were measured during a 3-h 50-g OGTT (day A) and an IIGI (day B) in 10 patients with T2DM [age (mean ± SE), 51 ± 3 yr; body mass index, 33 ± 2 kg/m(2); HbA(1c), 6.5 ± 0.2%]. During four additional IIGIs, GIP (day C), GLP-1 (day D), GLP-2 (day E) and a combination of the three (day F) were infused intravenously. Isoglycemia during all six study days was obtained. As expected, no suppression of glucagon occurred during the initial phase of the OGTT, whereas significantly (P < 0.05) lower plasma levels of glucagon during the first 30 min of the IIGI (day B) were observed. The glucagon response during the IIGI + GIP + GLP-1 + GLP-2 infusion (day F) equaled the inappropriate glucagon response to OGTT (P = not significant). The separate GIP infusion (day C) elicited significant hypersecretion of glucagon, whereas GLP-1 infusion (day D) resulted in enhancement of glucagon suppression during IIGI. IIGI + GLP-2 infusion (day E) resulted in a glucagon response in the midrange between the glucagon responses to OGTT and IIGI. Our results indicate that the intestinal hormones, GIP, GLP-1, and GLP-2, may play a role in the inappropriate glucagon response to orally ingested glucose in T2DM with, especially, GIP, acting to increase glucagon secretion.

Glucagon-like peptide-2 (GLP-2) increases small intestinal blood flow and mucosal growth in ruminating calves

Glucagon-like peptide-2 (GLP-2) increases small intestinal mass and blood flow in nonruminants but its effect in ruminants is unknown. Eight Holstein calves with an ultrasonic flow probe around the superior mesenteric artery and catheters in the carotid artery and mesenteric vein were paired by age and randomly assigned to treatment of a control (0.5% of BSA in saline; n=4) or GLP-2 (50 μg/kg of body weight of bovine GLP-2 in BSA; n=4) given subcutaneously every 12h for 10 d. Blood flow was measured on d 0 (acute) and d 10 (chronic) and included 3 periods: baseline (saline infusion), treatment (infusion of BSA or 1,000 pmol of GLP-2/kg of body weight per h), and recovery (saline infusion). On d 11, calves were killed 2h after injection of 5-bromo-2′-deoxyuridine (BrdU). Gastrointestinal tissues were weighed and epithelial samples were obtained to determine villus height, crypt depth, and BrdU staining. Infusion of GLP-2 increased superior mesenteric artery blood flow to 175% of baseline on d 0 but to only 137% of baseline after chronic treatment. Compared with that of the control, GLP-2 increased small intestinal mass by 24% by increasing epithelial mass in the jejunum and ileum. Additionally, GLP-2 increased villus height, crypt depth, and BrdU-labeling in small intestinal segments. These results demonstrate that GLP-2 induces similar increases in small intestinal blood flow and growth in ruminants to those observed in nonruminants. Furthermore, GLP-2 increases small intestinal blood flow in ruminants but this response is attenuated after 10 d of GLP-2 administration. In cattle, GLP-2 may be an important hormone in the regulation of intestinal blood flow and epithelial growth.

Sustained glucagon-like peptide-2 infusion is required for intestinal adaptation, and cessation reverses increased cellularity in rats with intestinal failure

Glucagon-like peptide-2 (GLP-2) is a nutrient-dependent, proglucagon-derived hormone that is a proposed treatment for human short bowel syndrome (SBS). The objective was to determine how the timing, duration, and cessation of GLP-2 administration affect intestinal adaptation and enterocyte kinetics in a rat model of human SBS that results in intestinal failure requiring total parenteral nutrition (TPN). Rats underwent 60% jejunoileal resection plus cecectomy and jugular vein cannulation and were maintained exclusively with TPN for 18 days in these treatments: TPN control (no GLP-2); sustained GLP-2 (1-18 days); early GLP-2 (1-7 days, killed at 7 or 18 days); and delayed GLP-2 (12-18 days). Body weight gain was similar across groups, and plasma bioactive GLP-2 was significantly increased with coinfusion of GLP-2 (100 μg·kg⁻¹·day⁻¹) with TPN. GLP-2-treated rats showed significant increases in duodenum and jejunum mucosal dry mass, protein, DNA, and sucrase activity compared with TPN control. The increased jejunum cellularity reflected significantly decreased apoptosis and increased crypt mitosis and crypt fission due to GLP-2. When GLP-2 infusion stopped at 7 days, these effects were reversed at 18 days. Sustained GLP-2 infusion significantly increased duodenum length and decreased 18-day mortality to 0% from 37.5% deaths in TPN control (P = 0.08). Colon proglucagon expression quantified by real-time RT-qPCR was increased in TPN controls and attenuated by GLP-2 infusion; jejunal expression of the GLP-2 receptor did not differ among groups. In summary, early, sustained GLP-2 infusion reduces mortality, induces crypt fission, and is required for intestinal adaptation, whereas cessation of GLP-2 reverses gains in mucosal cellularity in a rat model of intestinal failure.

Whey protein potentiates the intestinotrophic action of glucagon-like peptide-2 in parenterally fed rats

Glucagon-like peptide-2 (GLP-2) is a nutrient-regulated intestinotrophic hormone derived from proglucagon in the distal intestine. Enteral nutrients (EN) potentiate the action of GLP-2 to reverse parenteral nutrition (PN)-induced mucosal hypoplasia. The objective was to determine what enteral protein component, casein, soy, or whey protein, potentiates the intestinal growth response to GLP-2 in rats with PN-induced mucosal hypoplasia. Rats received PN and continuous intravenous infusion of GLP-2 (100 microg/kg/day) for 7 days. Six EN groups received PN+GLP-2 for days 1-3 and partial PN+GLP-2 plus EN for days 4-7. EN was provided by ad libitum intake of a semielemental liquid diet with different protein sources: casein, hydrolyzed soy, whey protein concentrate (WPC), and hydrolyzed WPC+casein. Controls received PN+GLP-2 alone. EN induced significantly greater jejunal sucrase activity and gain of body weight, and improved feed efficiency compared with PN+GLP-2 alone. EN induced greater ileal proglucagon expression, increased plasma concentration of bioactive GLP-2 by 35%, and reduced plasma dipeptidyl peptidase IV (DPP-IV) activity compared with PN+GLP-2 alone, P < 0.05. However, only whey protein, and not casein or soy, potentiated the ability of GLP-2 to reverse PN-induced mucosal hypoplasia and further increase ileal villus height, crypt depth, and mucosa cellularity compared with PN+GLP-2 alone, P < 0.05. The ability of whey protein to induce greater mucosal surface area was associated with decreased DPP-IV activity in ileum and colon compared with casein, soy, or PN+GLP-2 alone, P < 0.05. In conclusion, whey protein potentiates the action of GLP-2 to reverse PN-induced mucosal hypoplasia in association with decreased intestinal DPP-IV activity.

T1290 Enteral Feeding in Acute Pancreatitis: A Meta-Analysis of Randomized Controlled Trials

Glucagon-like peptide-2 (GLP-2) is a nutrient-dependent, intestinotrophic hormone derived from post-translational processing of proglucagon in the distal bowel. Parenterally-fed rats showed a synergistic intestinal growth response to combination treatment with enteral nutrients (EN) and a low-dose of intravenous GLP-2 (Am J Physiol 295:R1794, 2008). Evidence suggest that whey protein may inhibit dipeptidyl peptidase-IV (DPP-IV) and prolong the half life of GLP-2. The objective of this study was to determine what enteral protein component is responsible for the synergistic intestinal growth induced by treatment with EN + GLP-2. Rats were randomized to 7 treatment groups (n=6) maintained with parenteral nutrition (PN) and continuous intravenous infusion of GLP-2 (100 μg/kg bw/day) for 7 days. The control group received only PN+GLP-2. Six treatment groups received PN+GLP2 from days 1-3 and partial PN+GLP-2 plus EN from a semi-elemental liquid diet from days 4-7 (n=6). Enteral protein was provided from different sources as follows: Casein, Soy, and 4 groups receiving different combinations of whey protein, whey protein concentrate (WPC), hydrolyzed WPC, WPC + hydrolyzed WPC, and soy + WPC + hydrolyzed WPC. The 4 groups receiving whey protein showed significantly increased mucosa growth in ileum for dry mass, protein, and DNA by approximately 20%, 22% and 30%-49% compared to Casein, Soy or the PN+GLP-2 control, respectively. All groups that received EN showed significantly greater jejunal sucrase segmental activity and gain of body weight after 7 days of PN compared to the PN+GLP-2 control. This suggests that during PN, any form of a supplemental complete enteral diet improves digestive capacity and gain in body weight irrespective of protein source. There was a significant 35% greater concentration of plasma bioactive GLP-2 in 5 out of the 6 groups that received EN, compared to the PN+GLP-2 control. All groups that received EN showed greater proglucagon mRNA expression in ileum compared to the PN+GLP-2 control. Increased proglucagon mRNA and plasma bioactive GLP-2 are consistent with nutrient regulation of GLP-2. The 3 groups receiving hydrolyzed WPC showed significantly lower plasma DPP-IV activity compared to Casein or Soy. In addition, the 4 groups receiving EN that included whey protein showed significantly decreased DPP-IV specific activity in ileum and colon compared to Casein or Soy. In conclusion, the synergistic ileal mucosa growth due to combination treatment with EN+GLP2 in rats with PN-induced mucosal atrophy is associated with intake of whey protein which may mediate this effect through decreasing DPP-IV activity.

T1289 Whey Protein Potentiates the Intestinotrophic Action of Glucagon-Like Peptide-2 in Association with Reduced Dipeptidyl Peptidase-IV Activity in Parenterally-Fed Rats

Glucagon-like peptide-2 (GLP-2) is a nutrient-dependent, intestinotrophic hormone derived from post-translational processing of proglucagon in the distal bowel. Parenterally-fed rats showed a synergistic intestinal growth response to combination treatment with enteral nutrients (EN) and a low-dose of intravenous GLP-2 (Am J Physiol 295:R1794, 2008). Evidence suggest that whey protein may inhibit dipeptidyl peptidase-IV (DPP-IV) and prolong the half life of GLP-2. The objective of this study was to determine what enteral protein component is responsible for the synergistic intestinal growth induced by treatment with EN + GLP-2. Rats were randomized to 7 treatment groups (n=6) maintained with parenteral nutrition (PN) and continuous intravenous infusion of GLP-2 (100 μg/kg bw/day) for 7 days. The control group received only PN+GLP-2. Six treatment groups received PN+GLP2 from days 1-3 and partial PN+GLP-2 plus EN from a semi-elemental liquid diet from days 4-7 (n=6). Enteral protein was provided from different sources as follows: Casein, Soy, and 4 groups receiving different combinations of whey protein, whey protein concentrate (WPC), hydrolyzed WPC, WPC + hydrolyzed WPC, and soy + WPC + hydrolyzed WPC. The 4 groups receiving whey protein showed significantly increased mucosa growth in ileum for dry mass, protein, and DNA by approximately 20%, 22% and 30%-49% compared to Casein, Soy or the PN+GLP-2 control, respectively. All groups that received EN showed significantly greater jejunal sucrase segmental activity and gain of body weight after 7 days of PN compared to the PN+GLP-2 control. This suggests that during PN, any form of a supplemental complete enteral diet improves digestive capacity and gain in body weight irrespective of protein source. There was a significant 35% greater concentration of plasma bioactive GLP-2 in 5 out of the 6 groups that received EN, compared to the PN+GLP-2 control. All groups that received EN showed greater proglucagon mRNA expression in ileum compared to the PN+GLP-2 control. Increased proglucagon mRNA and plasma bioactive GLP-2 are consistent with nutrient regulation of GLP-2. The 3 groups receiving hydrolyzed WPC showed significantly lower plasma DPP-IV activity compared to Casein or Soy. In addition, the 4 groups receiving EN that included whey protein showed significantly decreased DPP-IV specific activity in ileum and colon compared to Casein or Soy. In conclusion, the synergistic ileal mucosa growth due to combination treatment with EN+GLP2 in rats with PN-induced mucosal atrophy is associated with intake of whey protein which may mediate this effect through decreasing DPP-IV activity.

Enteral nutrients potentiate the intestinotrophic action of glucagon-like peptide-2 in association with increased insulin-like growth factor-I responses in rats

Glucagon-like peptide-2 (GLP-2) is a nutrient-dependent, intestinotrophic hormone derived from posttranslational processing of proglucagon in the distal bowel. GLP-2 is thought to act through indirect mediators, such as IGF-I. We investigated whether intestinal expression of GLP-2 and IGF-I system components are increased with the mucosal growth induced by enteral nutrient (EN) and/or a low dose of GLP-2 in parenterally fed rats. Rats were randomized to four treatment groups using a 2 x 2 design and maintained with parenteral nutrition (PN) for 7 days: PN alone, EN, GLP-2, and EN+GLP-2; n = 7-9. The two main treatment effects are +/-GLP-2 (100 microg.kg body wt(-1).day(-1)) and +/-EN (43% of energy needs, days 4-6). Combination treatment with EN+GLP-2 induced synergistic intestinal growth in ileum, resulting in greater mucosal cellularity, sucrase segmental activity, and gain of body weight (ENxGLP-2, P < 0.04). In addition, EN+GLP-2 induced a significant 28% increase in plasma concentration of bioactive GLP-2, a significant 102% increase in ileal proglucagon mRNA with no change in ileal dipeptidyl peptidase-IV (DPP-IV) specific activity, and significantly reduced plasma DPP-IV activity compared with GLP-2. This indicates that EN potentiates the intestinotrophic action of GLP-2. Proliferation of enterocytes due to GLP-2 infusion was associated with greater expression of ileal proglucagon, GLP-2 receptor, IGF-I, IGF binding protein-3 mRNAs, and greater IGF-I peptide concentration in ileum (P < 0.032). Ileal IGF-I mRNA was positively correlated with expression of proglucagon, GLP-2R, and IGFBP-5 mRNAs (R2 = 0.43-0.56, P < 0.0001). Our findings support the hypothesis that IGF-I is one of the downstream mediators of GLP-2 action in a physiological model of intestinal growth.

Exogenous Glucagon‐Like Peptide‐2 (GLP‐2) Augments GLP‐2 Receptor mRNA and Maintains Proglucagon mRNA Levels in Resected Rats

Glucagon-like peptide-2 (GLP-2) is a nutrient-dependent proglucagon-derived hormone that stimulates intestinal adaptive growth. Our aim was to determine whether exogenous GLP-2 increases resection-induced adaptation without diminishing endogenous proglucagon and GLP-2 receptor expression. Rats underwent transection or 70% jejunoileal resection +/- GLP-2 infusion (100 microg/kg body weight/d) and were fed a semipurified diet with continuous infusion of GLP-2 or saline by means of jugular catheter. After 7 days, body weight, mucosal cellularity (dry mass, protein and DNA), crypt-villus height, and crypt cell proliferation (by bromodeoxyuridine staining) were determined. Plasma bioactive GLP-2 (by radioimmunoassay), proglucagon and GLP-2 receptor mRNA expression (by Northern blot and real-time reverse transcriptase quantitative polymerase chain reaction) were measured. GLP-2 receptor was colocalized to neuroendocrine markers by immunohistochemistry. Low-dose exogenous GLP-2 increased mucosal cellularity and crypt-villus height in the duodenum, jejunum, and ileum; enterocyte proliferation in the jejunal crypt; and duodenal and jejunal sucrase segmental activity. Plasma bioactive GLP-2 concentration increased 70% upon resection, with an additional 54% increase upon GLP-2 infusion in resected rats (P < .05). Ileal proglucagon mRNA expression increased with resection, and exogenous ileum GLP-2 failed to blunt this response. Exogenous GLP-2 increased ileum GLP-2 receptor expression 3-fold in resected animals and was colocalized to vasoactive intestinal peptide-positive and endothelial nitric oxide synthase-expressing enteric neurons and serotonin-containing enteroendocrine cells in the jejunum and ileum of resected rats. Exogenous GLP-2 augments adaptive growth and digestive capacity of the residual small intestine in a rat model of mid-small bowel resection by increasing plasma GLP-2 concentrations and GLP-2 receptor expression without diminishing endogenous proglucagon expression.

Glucagon-like peptide 2 has limited efficacy to increase nutrient absorption in fetal and preterm pigs

Exogenous glucagon-like peptide 2 (GLP-2) prevents intestinal atrophy and increases nutrient absorption in term newborn pigs receiving total parenteral nutrition (TPN). We tested the hypothesis that the immature intestine of fetuses and preterm neonates has a diminished nutrient absorption response to exogenous GLP-2. This was accomplished using catheterized fetal pigs infused for 6 days (87-91% of gestation) with GLP-2 (25 nmol.kg(-1).day(-1) iv; n = 7) or saline (n = 7), and cesarean-delivered preterm pigs (92% of gestation) that received TPN with GLP-2 (25 nmol.kg(-1).day(-1) iv; n = 8) or saline (n = 7) for 6 days after birth. Responses to GLP-2 were assessed by measuring intestinal dimensions, absorption of nutrients (glucose, leucine, lysine, proline) by intact tissues and brush border membrane vesicles, and abundance of sodium-glucose cotransporter mRNA. Infusion of GLP-2 increased circulating GLP-2 levels in fetuses, but did not increase intestinal mass or absorption of nutrients by intact tissues and brush border membrane vesicles, except for lysine. Administration of exogenous GLP-2 to preterm TPN-fed pigs similarly did not increase rates of nutrient absorption, yet nutrient absorption capacities of the entire small intestine tended to increase (+10-20%, P < 0.10) compared with TPN alone due to increased intestinal mass (+30%, P < 0.05). GLP-2 infusion did not increase sodium-glucose cotransporter-1 mRNA abundance in fetuses or postnatal preterm pigs. Hence, the efficacy of exogenous GLP-2 to improve nutrient absorption by the intestine of fetal and preterm pigs is limited compared with term pigs and more mature animals and humans.

Parenterally Fed Neonatal Piglets Have a Low Rate of Endogenous Arginine Synthesis from Circulating Proline

Parenterally fed neonatal piglets cannot synthesize sufficient arginine to maintain arginine status, presumably due to the intestinal atrophy that occurs with parenteral feeding. Parenteral feeding-induced atrophy can be reduced by the infusion of glucagon-like peptide 2 (GLP-2). GLP-2 infusion was hypothesized to increase the rate of endogenous arginine synthesis from proline, the major arginine precursor, in parenterally fed piglets receiving an arginine-deficient diet. Male piglets, fitted with jugular vein catheters for diet and isotope infusion, and femoral vein catheters for blood sampling (d 0), were allocated to a continuous infusion of either GLP-2 (n = 5; 10 nmol·kg−1·d−1) or saline (n = 5) for 7 d. Piglets received 2 d of a complete diet, followed by 5 d of an arginine-deficient [0.60 g·kg−1·d−1] diet. Piglets received primed, constant infusions of [guanido-14C]arginine to measure arginine flux (d 6) and [U-14C]proline (d 7) to measure proline conversion to arginine. Plasma arginine concentrations and arginine fluxes indicated a similar whole-body arginine status. Piglets receiving GLP-2 showed improvements in intestinal variables, including mucosal mass (P < 0.01) and villus height (P < 0.001), and a greater rate of arginine synthesis (μmol·kg−1·h−1) from proline (11.6 vs. 6.3) (P = 0.03). Mucosal mass (R2 = 0.71; P = 0.002) and villus height were correlated (R2 = 0.66; P = 0.004) with arginine synthesis. This study was the first to quantitate arginine synthesis in parenterally fed neonates and showed that although GLP-2 infusion increased arginine synthesis in a manner directly related to mucosal mass, this increased arginine synthesis was insufficient to improve whole-body arginine status in piglets receiving a low arginine diet.

Infusion of glucagon-like peptide 2 with an arginine deficient diet increases endogenous arginine synthesis from proline in parenterally-fed neonatal piglets

Parenteral feeding can be used to induce intestinal atrophy in piglets, and this atrophy is believed to be associated with the inability of parenterally-fed piglets to maintain arginine status via synthesis. Glucagon-like peptide 2 (GLP-2) has been shown to maintain intestinal structure and blood flow during intravenous feeding. GLP-2 infusion was hypothesized to increase the rate of endogenous arginine synthesis from proline in parenterally-fed piglets receiving an arginine deficient diet. Male piglets ( n = 10, 1.5–2.0 kg), fitted with jugular vein catheters for diet and isotope infusion, and femoral vein catheters for blood sampling (d 0), were allocated to a continuous infusion of either GLP-2 (10 nmol/kg/d) or saline into the jugular vein. Piglets received 2 d of a complete diet, followed by 5 d of an arginine deficient (0.60 g/kg/d) diet. A primed, constant infusion of [guanido- 14 C]arginine measured arginine flux (d 6), and of [U- 14 C]proline (d 7) measured proline conversion to arginine. There were no differences between groups in plasma ammonia, urea and arginine concentrations and arginine flux. Piglets receiving GLP-2 had a greater jejunal mucosal mass ( P = 0.003) and a two-fold greater rate of arginine synthesis from proline ( P = 0.03). This study indicates that the intestinal metabolism of circulating precursors may be important for arginine synthesis in parenterally-fed neonates.

Metabolism of glucagon-like peptide-2 in pigs: Role of dipeptidyl peptidase IV

Little is known about the metabolism of the intestinotropic factor glucagon-like peptide-2 (GLP-2); except that it is a substrate for dipeptidyl peptidase IV (DPP-IV) and that it appears to be eliminated by the kidneys. We, therefore, investigated GLP-2 metabolism in six multicatheterized pigs receiving intravenous GLP-2 infusions (2 pmol/kg/min) before and after administration of valine-pyrrolidide (300 μmol/kg; a well characterized DPP-IV inhibitor). Plasma samples were analyzed by radioimmunoassays allowing determination of intact, biologically active GLP-2 and the DPP-IV metabolite GLP-2 (3–33). During infusion of GLP-2 alone, 30.9 ± 1.7% of the infused peptide was degraded to GLP-2 (3–33). After valine-pyrrolidide, there was no significant formation of the metabolite. Significant extraction of intact GLP-2 was observed across the kidneys, the extremities (represented by a leg), and the splanchnic bed, resulting in a metabolic clearance rate (MCR) of 6.80 ± 0.47 ml/kg/min and a plasma half-life of 6.8 ± 0.8 min. Hepatic extraction was not detected. Valine-pyrrolidide addition did not affect extraction ratios significantly, but decreased ( p = 0.003) MCR to 4.18 ± 0.27 ml/kg/min and increased ( p = 0.052) plasma half-life to 9.9 ± 0.8 min. The metabolite was eliminated with a half-life of 22.1 ± 2.6 min and a clearance of 2.07 ± 0.11 ml/kg/min. In conclusion, intact GLP-2 is eliminated in the peripheral tissues, the splanchnic bed and the kidneys, but not in the liver, by mechanisms unrelated to DPP-IV. However, DPP-IV is involved in the overall GLP-2 metabolism and seems to be the sole enzyme responsible for N-terminal degradation of GLP-2.

Synergistic effect of supplemental enteral nutrients and exogenous glucagon-like peptide 2 on intestinal adaptation in a rat model of short bowel syndrome

Short bowel syndrome (SBS) can lead to intestinal failure and require total or supplemental parenteral nutrition (TPN or PN, respectively). Glucagon-like peptide 2 (GLP-2) is a nutrient-dependent, proglucagon-derived gut hormone that stimulates intestinal adaptation. Our objective was to determine whether supplemental enteral nutrients (SEN) modulate the intestinotrophic response to a low dose of GLP-2 coinfused with PN in a rat model of SBS (60% jejunoileal resection plus cecectomy). Rats were randomly assigned to 8 treatments by using a 2 x 2 x 2 factorial design and maintained with either TPN or PN for 7 d. The 3 main treatment effects were the following: transection or resection (TPN alone), +/- SEN (days 4-6), and +/- GLP-2 (100 mug . kg body wt(-1) . d(-1)). The treatments induced differential growth of duodenal and jejunal mucosa. Significant differences in villus height, crypt depth, dry mass, and concentrations of protein and DNA were observed between the treatments and TPN alone (SEN: 15-59% increase; GLP-2: 14-84% increase; and SEN + GLP-2: 63-160% increase). Plasma concentrations of bioactive GLP-2 were significantly greater with GLP-2 infusion (TPN alone: 25 +/- 9 pmol/L; SEN: 29 +/- 10 pmol/L; GLP-2: 59 +/- 31 pmol/L; SEN + GLP-2: 246 +/- 40 pmol/L) and correlated with mucosal growth. Jejunal sucrase activity (in U/cm) was significantly greater with SEN than without SEN. SEN + GLP-2 induced dramatic mucosal growth and greater plasma concentration of GLP-2 (SEN x GLP-2 interaction, P < 0.0001). Resection significantly increased expression of proglucagon mRNA in colon. Combination treatment with SEN and GLP-2 induced a synergistic response resulting in greater mucosal cellularity and digestive capacity in parenterally fed rats with SBS. This shows that SEN improve the intestinotrophic response to exogenous GLP-2, possibly by stimulating enterocyte proliferation and differentiation.

GLP‐2 infusion increases endogenous arginine synthesis in parenterally‐fed piglets receiving an arginine deficient diet

Neonatal piglets fed via total parenteral nutrition (TPN) cannot synthesize sufficient arginine (ARG) to maintain ARG status, presumably due to the intestinal atrophy that occurs with TPN feeding. Glucagon-like peptide 2 (GLP-2) helps maintain intestinal structure during TPN feeding by reducing intestinal apoptosis and proteolysis and maintaining intestinal blood flow. GLP-2 infusion was hypothesized to increase the rate of endogenous ARG synthesis from proline (PRO), the major ARG precursor, in TPN-fed piglets receiving an ARG deficient diet. Male piglets (n=10, ~1.7 kg), fitted with jugular vein catheters for diet and isotope infusion, and femoral vein catheters for blood sampling (d 0), were allocated to a continuous infusion (1 mL/kg/h) of either GLP-2 (n =5; 0.4 nmol/mL) or 0.9% saline (n =5) into the jugular vein catheter for 7 d. Piglets received 2 d of complete TPN, followed by 5 d of an ARG deficient (0.60 g/kg/d) TPN. Piglets received primed, constant infusions of [guanido-14C]ARG to measure ARG flux (d 6), and [U-14C]PRO (d 7) to measure PRO conversion to ARG. Plasma ARG concentrations and ARG fluxes were similar (P > 0.05). Piglets receiving GLP-2 had a greater jejunal mucosal mass (P = 0.003) and a two-fold greater rate of ARG synthesis (μ mol/kg/h) from PRO (11.6 vs. 6.3) (P = 0.03). Maximal ARG synthesis in TPN-fed piglets is usually ~25% of that in enterally-fed piglets. This study is the first to quantitate ARG synthesis in TPN-fed neonates and show that GLP-2 infusion increases ARG synthesis. Also, second-pass intestinal metabolism may be important for ARG synthesis in TPN-fed neonates. Funded by NSERC.