GLP1 and glucagon co-secreting pancreatic neuroendocrine tumor presenting as hypoglycemia after gastric bypass

Post-prandial hypoglycemia is frequently found after bariatric surgery. Although rare, pancreatic neuroendocrine tumors (pNET), which occasionally are mixed hormone secreting, can lead to atypical clinical manifestations, including reactive hypoglycemia. Two years after gastric bypass surgery for the treatment of severe obesity, a 54-year-old female with previous type 2 diabetes, developed post-prandial sweating, fainting and hypoglycemic episodes, which eventually led to the finding by ultrasound of a 1.8-cm solid mass in the pancreatic head. The 72-h fast test and the plasma chromogranin A levels were normal but octreotide scintigraphy showed a single focus of abnormal radiotracer uptake at the site of the nodule. There were no other clinical signs of hormone secreting pNET and gastrointestinal hormone measurements were not performed. The patient underwent surgical enucleation with complete remission of the hypoglycemic episodes. Histopathology revealed a well-differentiated neuroendocrine carcinoma with low-grade malignancy with positive chromogranin A and glucagon immunostaining. An extract of the resected tumor contained a high concentration of glucagon (26.707 pmol/g tissue), in addition to traces of GLP1 (471 pmol/g), insulin (139 pmol/g) and somatostatin (23 pmol/g). This is the first report of a GLP1 and glucagon co-secreting pNET presenting as hypoglycemia after gastric bypass surgery. Although pNET are rare, they should be considered in the differential diagnosis of the clinical approach to the post-bariatric surgery hypoglycemia patient.

LEARNING POINTS

pNETs can be multihormonal-secreting, leading to atypical clinical manifestations.Reactive hypoglycemic episodes are frequent after gastric bypass.pNETs should be considered in the differential diagnosis of hypoglycemia after bariatric surgery.

Glucose stimulates neurotensin secretion from the rat small intestine by mechanisms involving SGLT1 and GLUT2, leading to cell depolarization and calcium influx

Neurotensin (NT) is a neurohormone produced in the central nervous system and in the gut epithelium by the enteroendocrine N cell. NT may play a role in appetite regulation and may have potential in obesity treatment. Glucose ingestion stimulates NT secretion in healthy young humans, but the mechanisms involved are not well understood. Here, we show that rats express NT in the gut and that glucose gavage stimulates secretion similarly to oral glucose in humans. Therefore, we conducted experiments on isolated perfused rat small intestine with a view to characterize the cellular pathways of secretion. Luminal glucose (20% wt/vol) stimulated secretion but vascular glucose (5, 10, or 15 mmol/l) was without effect. The underlying mechanisms depend on membrane depolarization and calcium influx, since the voltage-gated calcium channel inhibitor nifedipine and the KATP channel opener diazoxide, which causes hyperpolarization, eliminated the response. Luminal inhibition of the sodium-glucose cotransporter 1 (SGLT1) (by phloridzin) eliminated glucose-stimulated release as well as secretion stimulated by luminal methyl-α-D-glucopyranoside (20% wt/vol), a metabolically inactive SGLT1 substrate, suggesting that glucose stimulates secretion by initial uptake by this transporter. However, secretion was also sensitive to GLUT2 inhibition (by phloretin) and blockage of oxidative phosphorylation (2-4-dinitrophenol). Direct KATP channel closure by sulfonylureas stimulated secretion. Therefore, glucose stimulates NT secretion by uptake through SGLT1 and GLUT2, both causing depolarization either as a consequence of sodium-coupled uptake (SGLT1) or by closure of KATP channels (GLUT2 and SGLT1) secondary to the ATP-generating metabolism of glucose.

Effects of sitagliptin on counter-regulatory and incretin hormones during acute hypoglycaemia in patients with type 1 diabetes: a randomized double-blind placebo-controlled crossover study

AIMS

To assess whether the dipeptidyl peptidase-4 (DPP-4) inhibitor sitagliptin affects glucagon and other counter-regulatory hormone responses to hypoglycaemia in patients with type 1 diabetes.

METHODS

We conducted a single-centre, randomized, double-blind, placebo-controlled, three-period crossover study. We studied 16 male patients with type 1 diabetes aged 18-52 years, with a diabetes duration of 5-20 years and intact hypoglycaemia awareness. Participants received sitagliptin (100 mg/day) or placebo for 6 weeks and attended the hospital for three acute hypoglycaemia studies (at baseline, after sitagliptin treatment and after placebo). The primary outcome was differences between the three hypoglycaemia study days with respect to plasma glucagon responses from the initialization phase of the hypoglycaemia intervention to 40 min after onset of the autonomic reaction.

RESULTS

Sitagliptin treatment significantly increased active levels of glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1. No significant differences were observed for glucagon or adrenergic counter-regulatory responses during the three hypoglycaemia studies. Growth hormone concentration at 40 min after occurrence of autonomic reaction was significantly lower after sitagliptin treatment [median (IQR) 23 (0.2-211.0) mEq/l] compared with placebo [median (IQR) 90 (8.8-180) mEq/l; p = 0.008].

CONCLUSIONS

Sitagliptin does not affect glucagon or adrenergic counter-regulatory responses in patients with type 1 diabetes, but attenuates the growth hormone response during late hypoglycaemia.

The glucagon-like peptide 2 receptor is expressed in enteric neurons and not in the epithelium of the intestine

Glucagon-like peptide 2 (GLP-2) is a potent intestinotrophic growth factor with therapeutic potential in the treatment of intestinal deficiencies. It has recently been approved for the treatment of short bowel syndrome. The effects of GLP-2 are mediated by specific binding of the hormone to the GLP-2 receptor (GLP-2R) which was cloned in 1999. However, consensus about the exact receptor localization in the intestine has never been established. By physical, chemical and enzymatic tissue fragmentation, we were able to divide rat jejunum into different compartments consisting of: (1) epithelium alone, (2) mucosa with lamina propria and epithelium, (3) the external muscle coat including myenteric plexus, (4) a compartment enriched for the myenteric plexus and (5) intestine without epithelium. Expression of Glp2r; chromogranin A; tubulin, beta 3; actin, gamma 2, smooth muscle, enteric and glial fibrillary acidic protein in these isolated tissue fractions was quantified with qRT-PCR. Expression of the Glp2r was confined to compartments containing enteric neurons and receptor expression was absent in the epithelium. Our findings provide evidence for the expression of the GLP-2R in intestinal compartments rich in enteric neurons and, importantly they exclude significant expression in the epithelium of rat jejunal mucosa.

Measurement of the incretin hormones: glucagon-like peptide-1 and glucose-dependent insulinotropic peptide

The two incretin hormones, glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP), are secreted from the gastrointestinal tract in response to meals and contribute to the regulation of glucose homeostasis by increasing insulin secretion. Assessment of plasma concentrations of GLP-1 and GIP is often an important endpoint in both clinical and preclinical studies and, therefore, accurate measurement of these hormones is important. Here, we provide an overview of current approaches for the measurement of the incretin hormones, with particular focus on immunological methods.

Stability of glucagon-like peptide 1 and glucagon in human plasma

To investigate the stability of glucagon-like peptide 1 (GLP-1) and glucagon in plasma under short- and long-term storage conditions. Pooled human plasma (n=20), to which a dipeptidyl peptidase 4 (DPP4) inhibitor and aprotinin were added, was spiked with synthetic GLP-1 (intact, 7-36NH2 as well as the primary metabolite, GLP-1 9-36NH2) or glucagon. Peptide recoveries were measured in samples kept for 1 and 3 h at room temperature or on ice, treated with various enzyme inhibitors, after up to three thawing-refreezing cycles, and after storage at -20 and -80 °C for up to 1 year. Recoveries were unaffected by freezing cycles or if plasma was stored on ice for up to 3 h, but were impaired when samples stood at RT for more than 1 h. Recovery of intact GLP-1 increased by addition of a DPP4 inhibitor (no ice), but was not further improved by neutral endopeptidase 24.11 inhibitor or an inhibitor cocktail. GLP-1, but not glucagon, was stable for at least 1 year. Surprisingly, the recovery of glucagon was reduced by almost 50% by freezing compared with immediate analysis, regardless of storage time. Plasma handling procedures can significantly influence results of subsequent hormone analysis. Our data support addition of DPP4 inhibitor for GLP-1 measurement as well as cooling on ice of both GLP-1 and glucagon. Freeze-thaw cycles did not significantly affect stability of GLP-1 or glucagon. Long-term storage may affect glucagon levels regardless of storage temperature and results should be interpreted with caution.

An analysis of cosecretion and coexpression of gut hormones from male rat proximal and distal small intestine

Gut endocrine cells are generally thought to have distinct localization and secretory products. Recent studies suggested that the cells are highly related and have potential to express more than one hormone. We studied the coexpression and cosecretion of gut hormones in separate segments of rat small intestine. We measured secretion of glucagon-like peptide-1 (GLP-1), peptide YY (PYY), neurotensin, glucose-dependent insulinotropic polypeptide (GIP), and cholecystokinin (CCK) from proximal and distal half of the small intestine, isolated from male rats and perfused ex vivo. Hormone secretion was stimulated by bombesin, the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine, and peptones. Furthermore, tissue samples collected along the intestine were analyzed for expression, hormone content, and cell densities including colocalization. Most hormones responded to all three stimuli (but no GIP response to bombesin). GLP-1 secretion was similar from proximal and distal intestine, whereas PYY was secreted only from the distal half. CCK and GIP were mainly secreted proximally, whereas neurotensin was equally secreted from both parts. Cell densities, hormone concentrations, and expression patterns were generally parallel, with increasing values distally for GLP-1 and PYY, an exclusively proximal pattern for CCK, even distribution for neurotensin and GIP except for the most distal segments. PYY nearly always colocalized with GLP-1. Approximately 20% of GLP-1 cells colocalized with CCK and neurotensin, whereas GLP-1/GIP colocalization was rare. Our findings indicate that two L cell types exist, a proximal one secreting GLP-1 (and possibly CCK and neurotensin), and a distal one secreting GLP-1 and PYY. GIP seems to be secreted from cells that are not cosecreting other peptides.

Provision of Amniotic Fluid During Parenteral Nutrition Increases Weight Gain With Limited Effects on Gut Structure, Function, Immunity, and Microbiology in Newborn Preterm Pigs

BACKGROUND

Small enteral boluses with human milk may reduce the risk of subsequent feeding intolerance and necrotizing enterocolitis in preterm infants receiving parenteral nutrition (PN). We hypothesized that feeding amniotic fluid, the natural enteral diet of the mammalian fetus, will have similar effects and improve growth and gastrointestinal (GI) maturation in preterm neonates receiving PN, prior to the transition to milk feeding.

MATERIALS AND METHODS

Twenty-seven pigs, delivered by cesarean section at ~90% of gestation, were provided with PN and also fed boluses with amniotic fluid (AF; n = 13, 24-72 mL/kg/d) or no oral supplements (nil per os [NPO]; n = 14) until day 5 when blood, tissue, and fecal samples were collected for analyses.

RESULTS

Body weight gain was 2.7-fold higher in AF vs NPO pigs. AF pigs showed slower gastric emptying, reduced meal-induced release of gastric inhibitory peptide and glucagon-like peptide 2, changed gut microbiota, and reduced intestinal permeability. There were no effects on GI weight, percentage mucosa, villus height, plasma citrulline, hexose absorptive capacity, and digestive enzymes. Intestinal interleukin (IL)-1β levels and expression of IL1B and IL8 were increased in AF pigs, while blood biochemistry and amino acid levels were minimally affected.

CONCLUSION

Enteral boluses of AF were well tolerated in the first 5 days of life in preterm pigs receiving PN. Enteral provision of AF before the initiation of milk feeding may stimulate body growth and improve hydration in preterm infants receiving PN. Furthermore, it may improve GI motility and integrity, although most markers of GI maturation remain unchanged.

Specificity and sensitivity of commercially available assays for glucagon-like peptide-1 (GLP-1): implications for GLP-1 measurements in clinical studies

AIMS

To evaluate the performances of commercially available glucagon-like peptide-1 (GLP-1) assays and the implications for clinical studies.

METHODS

Known concentrations (5-300 pmol/l) of synthetic GLP-1 isoforms (GLP-1 1-36NH2, 7-36NH2, 9-36NH2, 1-37, 7-37 and 9-37) were added to the matrix (assay buffer) supplied with 10 different kits and to human plasma, and recoveries were determined. Assays yielding meaningful results were analysed for precision and sensitivity by repeated analysis and ability to discriminate low concentrations. Endogenous GLP-1 levels in clinical samples were assessed using three commercial kits.

RESULTS

The USCN LIFE assay detected none of the GLP-1 isoforms. The active GLP-1 enzyme-linked immunosorbent assays (ELISAs) from Millipore and DRG appeared identical and were specific for intact GLP-1 in buffer and plasma. The Meso Scale Discovery (MSD) total GLP-1 kit detected all six GLP-1 isoforms, although recovery of non-active forms was incomplete, especially in plasma. Millipore total GLP-1 ELISA kit detected all isoforms in buffer, but mainly amidated forms in plasma. The Alpco, Phoenix and Bio-Rad kits detected only amidated GLP-1, but the Alpco kit had a limited measurement range (30 pmol/l), the Phoenix kit had incomplete recovery in plasma and the Bio-Rad kit was insensitive (detection limit in plasma 40 pmol/l). The pattern of postprandial GLP-1 responses in clinical samples was similar between the kits tested, but the absolute concentrations measured varied.

CONCLUSIONS

The specificity and sensitivity of commercially available kits for the analysis of GLP-1 levels vary considerably. This should be taken into account when selecting which assay to use and when comparing data from different studies.

Glucose-dependent insulinotropic polypeptide inhibits bone resorption in humans

BACKGROUND

In humans, the pronounced postprandial reduction in bone resorption (decreasing bone resorption markers by around 50%) has been suggested to be caused by gut hormones. Glucose-dependent insulinotropic polypeptide (GIP) is a peptide hormone secreted postprandially from the small intestine. The hormone is known as an incretin hormone, but preclinical studies have suggested that it may also influence bone metabolism, showing both antiresorptive and anabolic effects as reflected by changes in biomechanical measures, microarchitecture, and activity of the bone cells in response to GIP stimulation. Its role in human bone homeostasis, however, is unknown.

OBJECTIVE

To examine the effect of GIP administration on bone resorption in humans.

MATERIALS AND METHODS

Plasma samples were obtained from 10 healthy subjects during four conditions: euglycemic (5 mmol/L) and hyperglycemic (12 mmol/L) 90-minute glucose clamps with co-infusion of GIP (4 pmol/kg/min for 15 min, followed by 2 pmol/kg/min for 45 min) or placebo. The samples were analyzed for concentrations of degradation products of C-terminal telopeptide of type I collagen (CTX), a bone resorption marker. RESULTS regarding effects on pancreatic hormone secretion have been published.

RESULTS

During euglycemia, the decremental area under the curve in CTX was significantly (P < .001) higher during GIP infusion (2084 ± 686 % × min) compared to saline infusion (656 ± 295 % × min). During hyperglycemia, GIP infusion significantly (P < .001) augmented the decremental area under the curve to 2785 ± 446 % × minutes, compared to 1308 ± 448 % × minutes during saline infusion, with CTX values corresponding to 49% of basal values.

CONCLUSIONS

We conclude that GIP reduces bone resorption in humans, interacting with a possible effect of hyperglycemia.

Hyperglucagonaemia analysed by glucagon sandwich ELISA: nonspecific interference or truly elevated levels?

AIM/HYPOTHESIS

Hyperglucagonaemia is a characteristic of several clinical conditions (e.g. end-stage renal disease (ESRD), type 2 diabetes, obesity before and after Roux-en-Y gastric bypass (RYGB) and vagotomy with pyloroplasty), but the molecular nature of 'immunoreactive' glucagon is poorly characterised. The specific determination of fully processed, intact glucagon requires a 'sandwich' assay employing a combination of antibodies directed against both N- and C-termini. We compared a novel assay for intact glucagon with a highly sensitive C-terminal RIA (hitherto considered specific) to determine the extent to which the hyperglucagonaemia measured in clinical samples was caused by authentic glucagon.

METHODS

We examined the performance of three commercial glucagon 'sandwich' ELISAs. The ELISA with the best overall performance was selected to compare glucagon measurements in clinical samples with an established glucagon RIA.

RESULTS

The first assay performed poorly: there was high cross-reactivity with glicentin (22%) and a lack of sensitivity for glucagon. The second and third assays showed minor cross-reactivity (1-5%) with oxyntomodulin and glicentin; however, the second assay had insufficient sensitivity for glucagon in plasma (>10-20 pmol/l). Thus, only the third assay was suitable for measuring glucagon concentrations in clinical samples. The ELISA and RIA measured similar glucagon levels in healthy individuals. Measurements of samples from individuals with abnormally high (type 2 diabetes or obese) or very elevated (post vagotomy with pyloroplasty, post-RYGB) glucagon levels were also similar in both assays. However, glucagon levels in participants with ESRD were much lower when measured by ELISA than by RIA, indicating that the apparent hyperglucagonaemia is not caused by fully processed intact glucagon.

CONCLUSIONS/INTERPRETATION

For most purposes, sensitive C-terminal glucagon RIAs are accurate. However, measurements may be spuriously high, at least in patients with renal disease. Trial Registration Samples from type 2 diabetic and normoglucose-tolerant patients before and 1 year after RYGB were from a study by Bojsen-Møller et al (trial registration number NCT 01202526). Samples from vagotomised and control individuals were from a study by Plamboeck et al (NCT01176890). Samples from ESRD patients were from a study by Idorn et al (NCT01327378).

Stimulation of intestinal growth and function with DPP4 inhibition in a mouse short bowel syndrome model

Glucagon-like peptide-2 (GLP-2) has been shown to be effective in patients with short bowel syndrome (SBS), but it is rapidly inactivated by dipeptidyl peptidase IV (DPP4). We used an orally active DPP4 inhibitor (DPP4-I), MK-0626, to determine the efficacy of this approach to promote adaptation after SBS, determined optimal dosing, and identified further functional actions in a mouse model of SBS. Ten-week-old mice underwent a 50% proximal small bowel resection. Dose optimization was determined over a 3-day post-small bowel resection period. The established optimal dose was given for 7, 30, and 90 days and for 7 days followed by a 23-day washout period. Adaptive response was assessed by morphology, intestinal epithelial cell (IEC) proliferation (proliferating cell nuclear antigen), epithelial barrier function (transepithelial resistance), RT-PCR for intestinal transport proteins and GLP-2 receptor, IGF type 1 receptor, and GLP-2 plasma levels. Glucose-stimulated sodium transport was assessed for intestinal absorptive function. Seven days of DPP4-I treatment facilitated an increase in GLP-2 receptor levels, intestinal growth, and IEC proliferation. Treatment led to differential effects over time, with greater absorptive function at early time points and enhanced proliferation at later time points. Interestingly, adaptation continued in the group treated for 7 days followed by a 23-day washout. DPP4-I enhanced IEC proliferative action up to 90 days postresection, but this action seemed to peak by 30 days, as did GLP-2 plasma levels. Thus DPP4-I treatment may prove to be a viable option for accelerating intestinal adaptation with SBS.

GLP-1 amidation efficiency along the length of the intestine in mice, rats and pigs and in GLP-1 secreting cell lines

XXX: Measurements of plasma concentrations of the incretin hormone GLP-1 are complex because of extensive molecular heterogeneity. This is partly due to a varying and incompletely known degree of C-terminal amidation. Given that virtually all GLP-1 assays rely on a C-terminal antibody, it is essential to know whether or not the molecule one wants to measure is amidated. We performed a detailed analysis of extractable GLP-1 from duodenum, proximal jejunum, distal ileum, caecum, proximal colon and distal colon of mice (n=9), rats (n=9) and pigs (n=8) and determined the degree of amidation and whether this varied with the six different locations. We also analyzed the amidation in 3 GLP-1 secreting cell lines (GLUTag, NCI-H716 and STC-1). To our surprise there were marked differences between the 3 species with respect to the concentration of GLP-1 in gut. In the mouse, concentrations increased continuously along the intestine all the way to the rectum, but were highest in the distal ileum and proximal colon of the rat. In the pig, very little or no GLP-1 was present before the distal ileum with similar levels from ileum to distal colon. In the mouse, GLP-1 was extensively amidated at all sampling sites, whereas rats and pigs on average had around 2.5 and 4 times higher levels of amidated compared to non-amidated GLP-1, although the ratio varied depending upon the location. GLUTag, NCI-H716 and STC-1 cells all exhibited partial amidation with 2-4 times higher levels of amidated compared to non-amidated GLP-1.

Specificity and sensitivity of commercially available assays for glucagon and oxyntomodulin measurement in humans

AIM

To determine the specificity and sensitivity of assays carried out using commercially available kits for glucagon and/or oxyntomodulin measurements.

METHODS

Ten different assay kits used for the measurement of either glucagon or oxyntomodulin concentrations were obtained. Solutions of synthetic glucagon (proglucagon (PG) residues 3361), oxyntomodulin (PG residues 3369) and glicentin (PG residues 169) were prepared and peptide concentrations were verified by quantitative amino acid analysis and a processing-independent in-house RIA. Peptides were added to the matrix (assay buffer) supplied with the kits (concentration range: 1.25-300 pmol/l) and to human plasma and recoveries were determined. Assays yielding meaningful results were analysed for precision and sensitivity by repeated analysis and ability to discriminate low concentrations.

RESULTS AND CONCLUSION

Three assays were specific for glucagon (carried out using the Millipore (Billerica, MA, USA), Bio-Rad (Sundbyberg, Sweden), and ALPCO (Salem, NH, USA) and Yanaihara Institute (Shizuoka, Japan) kits), but none was specific for oxyntomodulin. The assay carried out using the Phoenix (Burlingame, CA, USA) glucagon kit measured the concentrations of all three peptides (total glucagon) equally. Sensitivity and precision were generally poor; the assay carried out using the Millipore RIA kit performed best with a sensitivity around 10 pmol/l. Assays carried out using the BlueGene (Shanghai, China), USCN LIFE (Wuhan, China) (oxyntomodulin and glucagon), MyBioSource (San Diego, CA, USA) and Phoenix oxyntomodulin kits yielded inconsistent results.

Fructose stimulates GLP-1 but not GIP secretion in mice, rats, and humans

Nutrients often stimulate gut hormone secretion, but the effects of fructose are incompletely understood. We studied the effects of fructose on a number of gut hormones with particular focus on glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP). In healthy humans, fructose intake caused a rise in blood glucose and plasma insulin and GLP-1, albeit to a lower degree than isocaloric glucose. Cholecystokinin secretion was stimulated similarly by both carbohydrates, but neither peptide YY3-36 nor glucagon secretion was affected by either treatment. Remarkably, while glucose potently stimulated GIP release, fructose was without effect. Similar patterns were found in the mouse and rat, with both fructose and glucose stimulating GLP-1 secretion, whereas only glucose caused GIP secretion. In GLUTag cells, a murine cell line used as model for L cells, fructose was metabolized and stimulated GLP-1 secretion dose-dependently (EC50 = 0.155 mM) by ATP-sensitive potassium channel closure and cell depolarization. Because fructose elicits GLP-1 secretion without simultaneous release of glucagonotropic GIP, the pathways underlying fructose-stimulated GLP-1 release might be useful targets for type 2 diabetes mellitus and obesity drug development.

Glucagon-like peptide 2 treatment may improve intestinal adaptation during weaning

Transition from sow's milk to solid feed is associated with intestinal atrophy and diarrhea. We hypothesized that the intestinotrophic hormone glucagon-like peptide 2 (GLP-2) would induce a dose- and health status-dependent effect on gut adaptation. In Exp. 1, weaned pigs (average BW at weaning 4.98 ± 0.18 kg) were kept in a high-sanitary environment and injected with saline or short-acting GLP-2 (80 μg/(kg BW·12 h); n = 8). Under these conditions, there was no diarrhea and GLP-2 did not improve gastrointestinal structure or function. In Exp. 2, weaned pigs (average BW at weaning 6.68 ± 0.27 kg) were kept in a low-sanitary environment, leading to weaning diarrhea, and injected with saline or short-acting GLP-2 (200 µg/(kg BW·12 h); n = 11). Treatment with GLP-2 increased goblet cell density (P < 0.05) and reduced short chain fatty acid concentration in the colon (P < 0.01) but had limited effects on diarrhea. In Exp. 3, weaned pigs (average BW at weaning 6.90 ± 0.32 kg) were kept in a low-sanitary environment and injected with saline or a long-acting acylated GLP-2 analogue (25 µg/(kg BW·12 h); n = 8). In this experiment, GLP-2 increased intestinal weight (+22%; P < 0.01) and activity of brush border enzymes (+50-100%; P < 0.05). Circulating GLP-2 levels were in the pharmacological range in Exp. 3 (constant levels >20,000 pmol/L) and Exp. 2 (increases to 20,000 pmol/L for a few hours each day) while they were in the supraphysiological range in Exp. 1 (50-200 pmol/L). In conclusion, GLP-2 may improve gut structure and function in weanling pigs. However, the effects may be significant only under conditions of diarrhea and if GLP-2 exposure time is extended using long-acting analogues.

Model of influenza A virus infection: dynamics of viral antagonism and innate immune response

Viral antagonism of host responses is an essential component of virus pathogenicity. The study of the interplay between immune response and viral antagonism is challenging due to the involvement of many processes acting at multiple time scales. Here we develop an ordinary differential equation model to investigate the early, experimentally measured, responses of human monocyte-derived dendritic cells to infection by two H1N1 influenza A viruses of different clinical outcomes: pandemic A/California/4/2009 and seasonal A/New Caledonia/20/1999. Our results reveal how the strength of virus antagonism, and the time scale over which it acts to thwart the innate immune response, differs significantly between the two viruses, as is made clear by their impact on the temporal behavior of a number of measured genes. The model thus sheds light on the mechanisms that underlie the variability of innate immune responses to different H1N1 viruses.

The incretin effect does not differ in trained and untrained, young, healthy men

AIM

After both oral and intravenous glucose administration, peripheral insulin concentrations are lower in trained compared with untrained humans. Part of this is explained by an adaptation within the β-cell. The insulin secretion rate is higher after oral compared with intravenous glucose administration due to the release of glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) enhancing the glucose-induced insulin secretion (the incretin effect). Our aim was to investigate whether GIP or GLP-1 release or the incretin effect was different in trained compared with untrained humans after oral and intravenous glucose administration.

METHODS

A 3½-h oral glucose tolerance test was performed in eleven trained and ten untrained, young, healthy men. On a separate day, an isoglycaemic intravenous glucose infusion was performed matching the individual glucose concentrations obtained during the oral glucose tolerance test. Blood samples for insulin, C-peptide, GIP and GLP-1 analyses were obtained frequently during both tests, and the insulin secretion rate, incretin effect and insulin clearance were calculated.

RESULTS

Plasma GIP and GLP-1 concentrations, the incretin effect and the insulin clearance did not differ, and plasma glucose, insulin and C-peptide concentrations and the insulin secretion rate were lower in trained compared with untrained subjects during both tests.

CONCLUSION

With no difference in incretin effect and insulin clearance between the two groups, the lower plasma insulin concentrations found in trained compared with untrained, young, healthy men are most likely explained by lower β-cell sensitivity to glucose and enhanced glucose uptake in skeletal muscle in the former group.