Levels of circulating semaglutide determine reductions in HbA1c and body weight in people with type 2 diabetes

Glucagon-like peptide-1 receptor agonists (GLP-1RA) are used for the treatment of type 2 diabetes. Whether clinically important responses and adverse events (AEs) are dependent on the route of administration has not been determined. We demonstrate that nearly identical exposure-response pharmacodynamic relationships are determined by plasma semaglutide levels achieved through oral versus injectable administration for changes in HbA1c, body weight, biomarkers of cardiovascular risk, and AEs such as nausea and vomiting. At typical exposure levels for oral semaglutide, the estimated response is 1.58% (oral) versus -1.62% (subcutaneous) for HbA1c and 3.77% (oral) versus 3.48% (subcutaneous) reduction in body weight relative to baseline after 6 months. Increased body weight is the most important variable associated with reduced semaglutide exposure for both formulations. Hence, interindividual variation in GLP-1R responsivity or route of administration are not major determinants of GLP-1RA effectiveness in the clinic.

On the role of the gut in diabetic hyperglucagonaemia

Patients with type 2 diabetes are characterised not only by compromised insulin secretion and action, but also by elevated plasma concentrations of the 29-amino acid peptide hormone glucagon, which generally is thought of as a pancreas-derived hormone (produced in and secreted from alpha cells in the islet of Langerhans). In patients with diabetes, circulating glucagon concentrations are elevated in the fasting state and fail to decrease appropriately or even increase in response to ingestion of nutrients. Glucagon is known to be a potent stimulator of hepatic glucose production, and, thus, the elevated glucagon concentrations in diabetes contribute decisively to the predominating trait of patients with diabetes namely hyperglycaemia. Interestingly, studies have shown that while oral intake of glucose results in inappropriately high plasma concentrations of glucagon in patients with diabetes, intravenous (iv) infusion of glucose does not. The mechanisms behind these differential glucagon responses to oral vs. iv glucose administration are currently unexplained. Three hypotheses were tested in the present thesis: 1) Could the inappropriate glucagon response to oral glucose ingestion in patients with diabetes be attributed to the release of glucagonotropic/glucagonostatic peptides secreted from the gut? 2) Could the inappropriate glucagon response to oral glucose ingestion in diabetes be a result of extrapancreatic glucagon secretion (possibly originating from the gut)? And 3) Does the differential glucagon responses between oral and iv glucose administration affect endogenous glucose production (EGP). The overall aim of this PhD thesis was, thus, to investigate the role of the gut in diabetic hyperglucagonaemia and hyperglycaemia. In Study I we examined the effect of the three gut-derived hormones glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide-1 (GLP-1) and glucagon-like peptide-2 (GLP-2) on glucagon secretion in patients with type 2 diabetes. We applied a 50 g-oral glucose tolerance test (OGTT), and five isoglycaemic iv glucose infusions (IIGIs) with either saline, GIP, GLP-1, GLP-2 or a combination of the three hormones. We show that these gut-derived hormones affect glucagon secretion differently and that OGTT-induced secretion of these hormones may play a role in the inappropriate glucagon response to orally ingested glucose in patients with type 2 diabetes with especially GIP acting to increase glucagon secretion. In Study II we examined totally pancreatectomised patients and non-diabetic control subjects during a 75 g-OGTT and an IIGI. We applied sandwich enzyme-linked immunosorbent assay (ELISA) and mass spectrometry-based proteomics for plasma glucagon analysis and show that 29-amino acid glucagon circulates in patients without a pancreas and that glucose stimulation of the gut results in significant hyperglucagonemia in these patients - ultimately confirming the existence of extrapancreatic glucagon secretion in humans. In Study III we examined whether the different responses of insulin and glucagon, respectively, between oral and iv glucose administration translate into differences in EGP and glucose disappearance in patients with type 2 diabetes and non-diabetic control subjects. We applied glucose tracer methodology during a 75 g-OGTT, IIGI and IIGI + iv glucagon (to isolate the effect of glucagon) and show that EGP is less suppressed during OGTT than during IIGI in both patients with type 2 diabetes and non-diabetic control subjects.

[Secretion of incretin hormones in people having risk factors for type 2 diabetes mellitus]

AIM

To study the secretion of glucagon-like peptide 1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP),and glucagon- like peptide 2 (GLP-2) in response to a carbohydrate load in people with risk factors for type 2 diabetes mellitus (DM2) in relation to the type of carbohydrate metabolic disturbances and age.

SUBJECTS AND METHODS

One hundred and twenty-seven patients having DM2 risk factors who had not previously received glucose- lowering therapy underwent an oral glucose tolerance test (OGTT). The plasma levels of glucose, insulin, glucagon, GLP-1, GIP, and GLP-2 were determined at 0, 30, and 120 minutes of the test.

RESULTS

According to the findings, the patients were divided into 3 groups: 1) normal glucose tolerance; 2) prediabetic states (impaired glucose tolerance and/or impaired fasting glycemia); 3) new-onset DM2. OGTT showed that the secretion of GLP-1 was lower and that of GIP and GLP-2 was higher in patients with DM2. GLP-1 secretion decreased with patient age.

CONCLUSION

During OGTT, there is a statistically significantly difference in the secretion of incretin hormones in persons with varying degrees of carbohydrate metabolic disturbances: the peak GLP-1 secretion is the highest in healthy individuals and lowest in the patients with DM2; on the contrary, the peak GLP2 and GIP secretions are the highest in the patients with DM2. This may suggest that GLP-1 and the two other hormones (GLP-2 and GIP) show opposite effect in the regulatory mechanisms of carbohydrate metabolism. GLP-1 secretion is decreased with age, which may be one of the reasons for the higher prevalence of DM2 among the elderly.

[Characteristics of cytokine and hormone status in patients with diabetes mellitus type 2 during alimentary exposure]

Diabetes mellitus (DM) is a main noninfectious disease, making significant influence on patients quality of life and life time. The medico-social role of diabetes is defined by wide prevalence of a disease in population and high risk of development of incapacitating complications. Therefore, considerable efforts of modern medicine focused on the study of etio-pathogenetic mechanism and the possibility of dietetic correction in this disease. In this review discusses efficacy of dietary therapy in type 2 diabetes, the role of insulin-like growth 1 (IGF-1)/insulin of pathogenesis microvascular complications. The role of inflammation in the development of microvascular complications, in the first place cytokines, act on the insulin signal pathway and affect the intracellular inflammatory kinase cascade was shown. Also, it is shown that adipose tissue inflammation modulates B-cell function and promotes progressive reduction of insulin secretion. When blood glucose levels are elevated, Glucagon-like peptide--1 stimulates insulin secretion, decrease glucagon secretion, improve B-cell function, and slows gastric emptying. It determines the necessity of fulfillment of further researches of cellular and humoral immunity in diabetes mellitus and the development of personal methods in prevention and treatment of this disease.

The peculiar processing of pancreatic hormone glucagon seen in traumatized patients

BACKGROUND/AIM

The kinetics of the pancreatic hormone glucagon in traumatized patients has not been minutely investigated as well as that of insulin, despite its significant influence on energy metabolism. In the present study, we examined the kinetics of glucagon and glucagon-related peptides assessed by radioimmunoassay, and the molecular forms of these peptides using gel filtration chromatography. In addition, we discuss glucagon processes in the pancreas and intestine in traumatized patients in the early operative days.

METHODOLOGY

Twelve traumatized patients who had undergone emergency surgery were enrolled in this study (group S). Ten healthy volunteers were also enrolled as normal control subjects (group C). The serum level of glucagon and glucagon-related peptides were assessed in the early morning fasting state in both groups, on the second postoperative day in group S, using the glucagon nonspecific N-terminal (glucagon-like immunoreactivity [GLI]) and specific C-terminal (immunoreactive glucagon [IRG]) radioimmunoassays. The molecular forms of these peptides were also estimated using the gel filtration chromatography method.

RESULTS

Serum IRG in group S was significantly high compared with that of group C (P < .05). Serum GLI was not significantly different between both groups. In all 12 patients in group S, a peculiar glicentin-like peptide (GLLP: MW approximately 8000 Da) other than pancreatic glucagon was seen on gel filtration chromatography, which was not seen in group C.

CONCLUSIONS

The kinetics and processing of glucagon in traumatized patients was different from those of healthy subjects. In traumatized patients, the peculiar processing of glucagon was processed in the intestine, which is different from the ordinary glucagon processing either in the pancreas or the intestine, generating a peculiar glicentin-like peptide (GLLP).

Inappropriate glucagon response after oral compared with isoglycemic intravenous glucose administration in patients with type 1 diabetes

Hyperglucagonemia following oral glucose ingestion in patients with type 1 diabetes (and type 2 diabetes) has been claimed to result from impaired intraislet insulin inhibition of glucagon. We looked at plasma glucagon responses to the oral glucose tolerance test (OGTT) and isoglycemic intravenous glucose infusion (IIGI) in patients with type 1 diabetes. Nine patients without residual beta-cell function [age: 25 +/- 9 yr; body mass index (BMI): 24 +/- 2 kg/m(2); fasting plasma glucose (FPG): 9.5 +/- 2.1 mM; Hb A(1c): 8.4 +/- 1.2% (mean +/- SD)] and eight healthy subjects (age: 28 +/- 5 yr; BMI: 24 +/- 3 kg/m(2); FPG: 5.3 +/- 0.2 mM; Hb A(1c): 5.0 +/- 0.1%) were examined on two separate occasions: 4-h 50-g OGTT and IIGI. Isoglycemia during IIGIs was obtained using 53 +/- 5 g of glucose in patients with type 1 diabetes and 30 +/- 3 g in control subjects (P < 0.001), resulting in gastrointestinal-mediated glucose disposal [100% x (glucose(OGTT) - glucose(IIGI)/glucose(OGTT))] of -6 +/- 9 and 40 +/- 6% (P < 0.01), respectively. Equal glucagon suppression during the two glucose stimuli was observed in healthy subjects, whereas patients with type 1 diabetes exhibited less inhibition in response to OGTT compared with IIGI (AUC: 1,519 +/- 129 vs. 1,240 +/- 86 pM.4 h; P = 0.03). This difference was even more pronounced during the initial 40 min with paradoxical hypersecretion of glucagon during OGTT and suppression during IIGI (AUC: 37 +/- 13 vs. -33 +/- 16 pM.40 min; P = 0.02). These results suggest that the inappropriate glucagon response to glucose in patients with type 1 diabetes occurs as a consequence of the oral administration way, suggesting a role of the gastrointestinal tract, possibly via glucagonotropic signaling from gut hormones (e.g., glucose-dependent insulinotropic polypeptide), in type 1 diabetic hyperglucagonemia.

Effect of fatty acid chain length on suppression of ghrelin and stimulation of PYY, GLP-2 and PP secretion in healthy men

We have evaluated the effects of fatty acid chain length on ghrelin, peptide YY (PYY), glucagon-like peptide-2 (GLP-2) and pancreatic polypeptide (PP) secretion and hypothesized that intraduodenal administration of dodecanoic ("C12"), but not decanoic ("C10"), acid would decrease plasma ghrelin and increase PYY, GLP-2 and PP concentrations. Plasma hormone concentrations were measured in seven healthy men during 90-min intraduodenal infusions of: (i) C12, (ii) C10 or (iii) control (rate: 2 ml/min, 0.375 kcal/min for C12/C10) and after a buffet-meal consumed following the infusion. C12 markedly suppressed plasma ghrelin and increased both PYY and GLP-2 (all P < 0.05) compared with control and C10, while C10 had no effect. Both C10 and C12 increased PP concentrations slightly (P < 0.05). We conclude that the effects of intraduodenal fatty acids on ghrelin, PYY and GLP-2 secretion are dependent on their chain length.

Human duodenal enteroendocrine cells: source of both incretin peptides, GLP-1 and GIP

Among the products of enteroendocrine cells are the incretins glucagon-like peptide-1 (GLP-1, secreted by L cells) and glucose-dependent insulinotropic peptide (GIP, secreted by K cells). These are key modulators of insulin secretion, glucose homeostasis, and gastric emptying. Because of the rapid early rise of GLP-1 in plasma after oral glucose, we wished to definitively establish the absence or presence of L cells, as well as the relative distribution of the incretin cell types in human duodenum. We confirmed the presence of proglucagon and pro-GIP genes, their products, and glucosensory molecules by tissue immunohistochemistry and RT-PCR of laser-captured, single duodenal cells. We also assayed plasma glucose, incretin, and insulin levels in subjects with normal glucose tolerance and type 2 diabetes for 120 min after they ingested 75 g of glucose. Subjects with normal glucose tolerance (n=14) had as many L cells (15+/-1), expressed per 1,000 gut epithelial cells, as K cells (13+/-1), with some containing both hormones (L/K cells, 5+/-1). In type 2 diabetes, the number of L and L/K cells was increased (26+/-2; P<0.001 and 9+/-1; P < 0.001, respectively). Both L and K cells contained glucokinase and glucose transporter-1, -2, and -3. Newly diagnosed type 2 diabetic subjects had increased plasma GLP-1 levels between 20 and 80 min, concurrently with rising plasma insulin levels. Significant coexpression of the main incretin peptides occurs in human duodenum. L and K cells are present in equal numbers. New onset type 2 diabetes is associated with a shift to the L phenotype.

Plasma concentrations of glucagon-like peptide-2 in adult patients with treated and untreated coeliac disease

BACKGROUND

Coeliac disease is a common chronic inflammatory enteropathy characterized by villous atrophy and crypt hyperplasia in the small intestine. The mechanism of the intestinal damage in coeliac disease remains unclear. Glucagon-like peptide (GLP)-2 is an enterotrophic peptide that causes crypt hyperplasia and intestinal cell proliferation. We postulate that GLP-2 may be involved in the mucosal changes found in coeliac disease.

OBJECTIVES

To study plasma concentrations of GLP-2 in untreated patients with coeliac disease and determine the response to a gluten-free diet (GFD).

METHODS

A 440 kcal gluten-free test meal was given to seven controls and 12 coeliac patients at three time intervals: (1) before commencing a GFD; (2) 3 months after a GFD; and (3) 9 months after a GFD. Serial blood sampling was performed over a 2-h period. Each sample was analysed using radioimmunoassay for GLP-2, GLP-1, N-terminal glucagon (N-glucagon) and C-terminal glucagon (C-glucagon).

RESULTS

Untreated coeliac patients had significantly higher basal and peak GLP-2 and N-glucagon plasma concentrations compared with controls. After 3 months on a GFD, there was a significant decrease in basal GLP-2 plasma concentrations. There was no significant difference between GLP-1 or C-glucagon in untreated coeliac patients compared with controls.

CONCLUSION

This is the first reported study of GLP-2 in coeliac disease. After a GFD there is recovery of the intestine and a reduction in the GLP-2 trophic response. Our findings support the theory that GLP-2 may be part of the mucosal healing and maintenance mechanisms in coeliac disease.

Glucagon-like peptide-2 acutely increases proximal small intestinal blood flow in TPN-fed neonatal piglets

Glucagon-like peptide-2 (GLP-2) is a gut hormone that is secreted in response to enteral feeding and stimulates small intestinal mucosal growth. We have previously shown that GLP-2 infusion acutely increases portal venous blood flow in TPN-fed piglets. The aim of this study was to localize the vasoactive effect of GLP-2 within the gastrointestinal tissues and other visceral organs in TPN-fed piglets. Tissue blood flow rates were quantified using fluorescent microsphere deposition in anesthetized TPN-fed piglets given intravenous infusion of GLP-2 at either 500 pmol·kg−1·h−1 (low GLP-2, n = 7 pigs) or 2,000 pmol·kg−1·h−1 (high GLP-2, n = 8 pigs) for 2 h. Compared with baseline, the low and the high GLP-2 treatment significantly increased the blood flow rate in the duodenum (+77%) and jejunum (+40% and 80%), respectively, but blood flow to the distal small intestine and colon (−15%) was unchanged or slightly decreased. Baseline mucosal blood flow was five-fold higher than serosal blood flow; however, high GLP-2 treatment increased serosal (+140%) to a larger degree than mucosal blood flow (+73%). The high GLP-2 dose increased pancreatic flow (+34%) but decreased blood flow in the kidneys (−14%) and stomach (−12%), whereas the spleen and brain were unaffected. These findings suggest that the acute GLP-2-mediated stimulation of portal blood flow in TPN-fed piglets occurs principally via increased blood flow through the superior mesenteric artery to the proximal small intestine, a tissue region where the GLP-2R mRNA abundance and trophic GLP-2 effects are greatest.

Glucagon-like peptide-1 reduces the pulsatile component of testosterone secretion in healthy males

BACKGROUND

Glucagon-like-peptide-1 (7-36) amide (GLP-1), a potent regulator of glucose homeostasis, has been implicated in the control of hypothalamic-pituitary function. In vivo it is a relevant neuroendocrine modulator of gonadotropin-releasing hormone release, suggesting its possible role as a metabolic signal to the reproductive system. The present study was undertaken to establish its effect on luteinizing hormone (LH) and testosterone secretion in nine healthy male volunteers.

MATERIALS AND METHODS

Each subject underwent an oral glucose tolerance test to establish LH, testosterone, and GLP-1 responses to glucose. Euglycaemic clamp experiments (6 h) were performed on two occasions with saline or with a constant infusion of GLP-1 (0.4 pmol kg(-1) min (-1)). Blood samples were drawn at 10-min intervals to measure the pulsatile pattern of LH and testosterone secretion.

RESULTS

Ingestion of oral glucose resulted in a reduction in plasma testosterone levels at 30 min compared with baseline (P < 0.004) despite unaltered LH levels (P = 0.5). Constant GLP-1 infusion resulted in no change in LH (P = 0.83), testosterone (P = 0.96), follicle stimulating hormone (FSH) (P = 0.86) and leptin levels (P = 0.3). Pulse analysis revealed no significant difference in the number (P = 0.1) or median absolute amplitude (P = 0.3) of the LH pulses. However, there was a significant decrease in the number (3.0 +/- 0.6 vs. 1.3 +/- 0.4; P < 0.05) and a tendency for increased duration of testosterone pulses (97.4 +/- 16.7 vs. 170 +/- 27.1 min; P = 0.06).

CONCLUSION

Oral glucose ingestion and intravenous GLP-1 infusion reduce the pulsatile component of testosterone secretion by a mechanism independent of LH release.

Teduglutide (ALX-0600), a dipeptidyl peptidase IV resistant glucagon-like peptide 2 analogue, improves intestinal function in short bowel syndrome patients

BACKGROUND AND AIMS

Glucagon-like peptide 2 (GLP-2) may improve intestinal absorption in short bowel syndrome (SBS) patients with an end jejunostomy. Teduglutide (ALX-0600), a dipeptidyl peptidase IV resistant GLP-2 analogue, prolongs the intestinotrophic properties of GLP-2 in animal models. The safety and effect of teduglutide were investigated in SBS patients with and without a colon in continuity.

METHODS

Teduglutide was given subcutaneously for 21 days once or twice daily to 16 SBS patients in the per protocol investigational group, 10 with end jejunostomy (doses of 0.03 (n = 2), 0.10 (n = 5), or 0.15 (n = 3) mg/kg/day), one with <50% colon in continuity (dose 0.03 mg/kg/day), and five with > or = 50% colon in continuity (dose 0.10 mg/kg/day). Nutrient balance studies, D-xylose tests, and intestinal mucosa biopsies were performed at baseline, on the last three days of treatment, and after three weeks of follow up. Pre-study fasting native GLP-2 levels were determined for the five patients with > or = 50% colon in continuity.

RESULTS

Pooled across groups and compared with baseline, teduglutide increased absolute (+743 (477) g/day; p<0.001) and relative (+22 (16)%; p<0.001) wet weight absorption, urine weight (+555 (485) g/day; p<0.001), and urine sodium excretion (+53 (40) mmol/day; p<0.001). Teduglutide decreased faecal wet weight (-711 (734) g/day; p = 0.001) and faecal energy excretion (-808 (1453) kJ/day (-193 (347) kcal/day); p = 0.040). In SBS patients with end jejunostomy, teduglutide significantly increased villus height (+38 (45)%; p = 0.030), crypt depth (+22 (18)%; p = 0.010), and mitotic index (+115 (108)%; p = 0.010). Crypt depth and mitotic index did not change in colonic biopsies from SBS patients with colon in continuity. The most common side effects were enlargement of the stoma nipple and mild lower leg oedema. The improvements in intestinal absorption and decreases in faecal excretion noted after treatment had reversed after the drug free follow up period. A controlled study with a more robust design is ongoing in order to determine the optimal dosage of teduglutide for SBS patients to achieve the maximal effect and utility of this drug in clinical practice.

CONCLUSION

Teduglutide, at three dose levels for 21 days, was safe and well tolerated, intestinotrophic, and significantly increased intestinal wet weight absorption in SBS patients with an end jejunostomy or a colon in continuity.

Subcutaneous oxyntomodulin reduces body weight in overweight and obese subjects: a double-blind, randomized, controlled trial

This study investigated the effect of subcutaneously administered oxyntomodulin on body weight in healthy overweight and obese volunteers. Participants self-administered saline or oxyntomodulin subcutaneously in a randomized, double-blind, parallel-group protocol. Injections were self-administered for 4 weeks, three times daily, 30 min before each meal. The volunteers were asked to maintain their regular diet and level of physical exercise during the study period. Subjects' body weight, energy intake, and levels of adipose hormones were assessed at the start and end of the study. Body weight was reduced by 2.3 +/- 0.4 kg in the treatment group over the study period compared with 0.5 +/- 0.5 kg in the control group (P = 0.0106). On average, the treatment group had an additional 0.45-kg weight loss per week. The treatment group demonstrated a reduction in leptin and an increase in adiponectin. Energy intake by the treatment group was significantly reduced by 170 +/- 37 kcal (25 +/- 5%) at the initial study meal (P = 0.0007) and by 250 +/- 63 kcal (35 +/- 9%) at the final study meal (P = 0.0023), with no change in subjective food palatability. Oxyntomodulin treatment resulted in weight loss and a change in the levels of adipose hormones consistent with a loss of adipose tissue. The anorectic effect was maintained over the 4-week period. Oxyntomodulin represents a potential therapy for obesity.

Peripheral oxyntomodulin reduces food intake and body weight gain in rats

Oxyntomodulin (OXM) is a circulating gut hormone released post prandially from cells of the gastrointestinal mucosa. Given intracerebroventricularly to rats, it inhibits food intake and promotes weight loss. Here we report that peripheral (ip) administration of OXM dose-dependently inhibited both fast-induced and dark-phase food intake without delaying gastric emptying. Peripheral OXM administration also inhibited fasting plasma ghrelin. In addition, there was a significant increase in c-fos immunoreactivity, a marker of neuronal activation, in the arcuate nucleus (ARC). OXM injected directly into the ARC caused a potent and sustained reduction in refeeding after a fast. The anorectic actions of ip OXM were blocked by prior intra-ARC administration of the glucagon-like peptide-1 (GLP-1) receptor antagonist, exendin(9-39), suggesting that the ARC, lacking a complete blood-brain barrier, could be a potential site of action for circulating OXM. The actions of ip GLP-1, however, were not blocked by prior intra-ARC administration of exendin(9-39), indicating the potential existence of different OXM and GLP-1 pathways. Seven-day ip administration of OXM caused a reduction in the rate of body weight gain and adiposity. Circulating OXM may have a role in the regulation of food intake and body weight.

Oxyntomodulin suppresses appetite and reduces food intake in humans

Oxyntomodulin (OXM) is released from the gut postprandially, in proportion to energy intake, and circulating levels of OXM are elevated in several conditions associated with anorexia. Central injection of OXM reduces food intake and weight gain in rodents, suggesting that OXM signals food ingestion to hypothalamic appetite-regulating circuits. We investigated the effect of iv OXM (3.0 pmol/kg.min) on appetite and food intake in 13 healthy subjects (body mass index, 22.5 +/- 0.9 kg/m(2)) in a randomized, double-blind, placebo-controlled, cross-over study. Infusion of OXM significantly reduced ad libitum energy intake at a buffet meal (mean decrease, 19.3 +/- 5.6%; P < 0.01) and caused a significant reduction in scores for hunger. In addition, cumulative 12-h energy intake was significantly reduced by infusion of OXM (mean decrease, 11.3 +/- 6.2%; P < 0.05). OXM did not cause nausea or affect food palatability. Preprandial levels of the appetite-stimulatory hormone, ghrelin, were significantly suppressed by OXM (mean reduction, 44 +/- 10% of postprandial decrease; P < 0.0001). Elevated levels of endogenous OXM associated with disorders of the gastrointestinal tract may contribute to anorexia.

Time-dependent intestinal adaptation and GLP-2 alterations after small bowel resection in rats

Existing data on morphological adaptation after small bowel resection are obtained by potentially biased methods. Using stereological techniques, we examined segments of bowel on days 0, 4, 7, 14, and 28 after 80% jejunoileal resection or sham operation in rats and correlated intestinal growth with plasma levels of glucagon-like peptide-2 (GLP-2). In the jejunum and ileum of the resected rats, the mucosal weight increased by 120 and 115% during the first week, and the weight of muscular layer increased by 134 and 83%, compared with sham-operated controls. The luminal surface area increased by 190% in the jejunum and by 155% in the ileum after 28 days. The GLP-2 level was increased by 130% during the entire study period in the resected rats. Small bowel resection caused a pronounced and persistent transmural growth response in the remaining small bowel, with the most prominent growth occurring in the jejunal part. The significantly elevated GLP-2 level is consistent with an important role of GLP-2 in the adaptive response.

Mediators for fat-induced ileal brake are different between stomach and proximal small intestine in conscious dogs

Our aim was to determine the mechanisms by which intraileal fat alters proximal gastrointestinal motility--the ileal brake. Five mongrel dogs with ileal Thiry-Vella fistulas were equipped with strain gauge force transducers on the upper gut to measure contractile activity. Ileal infusions of 115 mmol/L oleic acid and triglyceride were studied in dogs with extrinsically innervated and extrinsically denervated Thiry-Vella loops. Plasma concentrations of peptide YY and total glucagon-like immunoactivity were measured. Oleic acid but not triglyceride inhibited postprandial contractions in the gastric antrum in dogs with innervated and denervated Thiry-Vella loops. Postprandial duodenal and jejunal motility was inhibited by oleic acid regardless of extrinsic denervation to the loops (P <0.05), but triglyceride inhibited small intestinal motility only in dogs with innervated Thiry-Vella loops. Intraileal oleic acid but not triglyceride increased plasma concentrations of peptide YY and total glucagon-like immunoactivity in dogs with innervated and denervated Thiry-Vella loops. Intraileal oleic acid inhibits gastric and small intestinal motility possibly via increased plasma concentrations of peptide YY and enteroglucagon. Intact extrinsic innervation is necessary for intraileal triglyceride to inhibit small intestinal motility.

Oxyntomodulin inhibits pancreatic secretion through the nervous system in rats

Glicentin (GLIC), oxyntomodulin (OXM), and peptide YY (PYY) released in blood by ileocolonic L-cells after meals may inhibit pancreatic secretion. Whereas OXM interacts with glucagon and tGLP-1 receptors, OXM 19-37, a biologically active fragment, does not. The purpose of this study was to measure the effect of OXM, OXM 19-37, GLIC, tGLP-1, and PYY on pancreatic secretion stimulated by 2 deoxyglucose (2DG), electrical stimulation of the vagus nerves (VES), acetylcholine and cholecystokinin octapeptide (CCK8) in anesthetized rats. The effect of OXM was also studied in dispersed pancreatic acini. Plasma oxyntomodulin-like immunoreactivity (OLI) was measured by radioimmunoassay after the exogenous infusion of OXM and after an intraduodenal meal. OXM 19-37, infused at doses mimicking postprandial plasma levels of OLI, decreased pancreatic secretion stimulated by 2DG, VES, or CCK8. Similar effects were found with OXM and GLIC. OXM 19-37 did not change the pancreatic stimulation induced by acetylcholine in vivo, or CCK-induced amylase release in isolated acini. Vagotomy completely suppressed the inhibitory effect of OXM 19-37 on CCK8-stimulated pancreatic secretion. PYY inhibited the effect of 2DG, but not that of CCK8, whereas tGLP-1, even in pharmacologic doses, had no effect on stimulated pancreatic secretion. OXM, OXM 19-37, but not tGLP-1, inhibit pancreatic secretion at physiologic doses, through a vagal neural indirect mechanism, different from that used by PYY, and probably through a GLIC-related peptide-specific receptor.

Modulation by colonic fermentation of LES function in humans

Colonic fermentation of carbohydrate has been shown to influence gastric and intestinal motility. Our aim was to investigate the effects of colonic infusion of lactose and short-chain fatty acids (SCFAs) on lower esophageal sphincter (LES) function in humans. LES pressure (LESP), transient relaxations of LES (TLESRs), and esophageal pH were monitored over 6 h on 4 different days in 7 healthy volunteers. After 1 h of baseline recording, the effects of different colonic infusions (270 ml of isotonic or hypertonic saline, 30 g lactose, or 135 mmol SCFAs) were tested in fasting conditions and after a standard meal. Peptide YY (PYY) and oxyntomodulin (OLI) were also measured in plasma. Both lactose and SCFA infusions increased the number of TLESRs as well as the proportion of TLESRs associated with acid reflux episodes, but saline solutions did not. The postprandial fall of LESP was enhanced by previous SCFA infusion. Plasma PYY and OLI increased similarly after all colonic infusions. Colonic fermentation of lactose markedly affected LES function, and this effect was reproduced by SCFA infusion. Whether the mechanisms of this feedback phenomenon are of hormonal nature, neural nature, or both remains to be determined.

Diabetic intestinal growth adaptation and glucagon-like peptide 2 in the rat: effects of dietary fibre

BACKGROUND/AIMS

Dietary fibre influence growth and function of the upper gastrointestinal tract. This study investigates the importance of dietary fibre in intestinal growth in experimental diabetes, and correlates intestinal growth with plasma levels of the intestinotrophic factor, glucagon-like peptide 2 (GLP-2).

METHODS

Male Wistar rats were randomised to the following groups: two streptozotocin-diabetic and two control groups fed either a fibre-containing or a fibre-free diet for three weeks. Intestinal weight, length, and morphometric data (villus height, villus area, crypt depth) were measured. Blood samples were obtained after two weeks for measurement of GLP-2 and enteroglucagon (glicentin, oxyntomodulin).

RESULTS

The mean daily consumption of food in the two diabetic groups was 40% higher than in controls. In diabetic rats fed fibre, the increase in intestinal weight from day 0 to 20 was sixfold greater than that of the controls and small intestine weight per cm length was increased by 50%. In the diabetic rats fed a fibre-free diet, intestinal growth was 30% less than in diabetic rats fed fibre, and intestinal weight increased only threefold compared with controls. Morphometric data showed that the intestinal increase in diabetic rats fed fibre was due primarily to growth of the mucosal layer. Villus height and crypt depth increased 60% and 40% respectively, but by only 20% in fibre-free diabetic rats. The plasma levels of GLP-2 parallelled diabetic intestinal growth, whereas plasma levels of enteroglucagon increased regardless of the extent of intestinal growth.

CONCLUSIONS

Intestinal growth in experimental diabetes is strongly influenced by the presence of dietary fibre. The effect may be mediated by GLP-2.

Effect of ileojejunal transposition on gastrointestinal motility, gastric emptying, and small intestinal transit in dogs

There is speculation that enteroglucagon and peptide YY are responsible for mediating the <<ileal brake>> known as a suppressive reaction of upper gastrointestinal motility and transit that is induced by the infusion of nutrients into the ileum. We studied changes in motility and transit in dogs with ileojejunal transposition in which the distal ileum is exposed to undigested nutrients. Nine adult mongrel dogs were equipped with strain gauge force transducers placed on the gastric body, antrum, duodenum, and proximal jejunum. Measurements of gastrointestinal motility, gastric emptying, and plasma levels of total glucagon-like immunoreactivity, immunoreactive glucagon, and peptide YY were obtained both before and after either ileojejunal transposition (5 dogs) or sham operation (4 dogs). Postprandial contractions in the gastric antrum and gastric emptying were significantly inhibited after ileojejunal transposition. The inhibitory effect of ileojejunal transposition on antral motor activity was found to correlate with the rise in plasma total glucagon-like immunoreactivity and peptide YY concentrations. However, plasma glucagon levels were unaffected by ileojejunal transposition. These results suggest that hypersecretion of enteroglucagon and peptide YY induced by ileojejunal transposition inhibits postprandial gastric motor function.

Nondigestible carbohydrates and mineral bioavailability

Generally, fiber and compounds associated with fiber in cereal products (e.g., phytates) have been found to reduce the apparent absorption of minerals (such as calcium, magnesium, zinc and manganese) in humans, livestock and animal models. The effects of "soluble" forms of fiber (specifically pectins, gums, resistant starches, lactulose, oligofructose and inulin) on mineral absorption are more difficult to characterize. The addition of these soluble forms of fiber has been found in various studies to add viscosity to the gut contents, promote fermentation and the production of volatile fatty acids in the cecum, have a trophic effect on the ceca of animals and increase serum enteroglucagon concentrations. Thus it is not surprising that the addition of soluble forms of fiber to diets often has been found to improve absorption of minerals. This may reflect absorption of electrolytes from the large intestine. Future work should address the mechanisms by which ingestion of nondigestible carbohydrates improves mineral absorption in humans.

Gastrointestinal responses to a panel of lectins in rats maintained on total parenteral nutrition

Total parenteral nutrition (TPN) causes atrophy of gastrointestinal epithelia, so we asked whether lectins that stimulate epithelial proliferation can reverse this effect of TPN. Two lectins stimulate pancreatic proliferation by releasing CCK, so we asked whether lectins that stimulate gastrointestinal proliferation also release hormones that might mediate their effects. Six rats per group received continuous infusion of TPN and a once daily bolus dose of purified lectin (25 mg. rat-1. day-1) or vehicle alone (control group) for 4 days via an intragastric cannula. Proliferation rates were estimated by metaphase arrest, and hormones were measured by RIAs. Phytohemagglutinin (PHA) increased proliferation by 90% in the gastric fundus (P < 0.05), doubled proliferation in the small intestine (P < 0.001), and had a small effect in the midcolon (P < 0.05). Peanut agglutinin (PNA) had a minor trophic effect in the proximal small intestine (P < 0.05) and increased proliferation by 166% in the proximal colon (P < 0.001) and by 40% in the midcolon (P < 0.001). PNA elevated circulating gastrin and CCK by 97 (P < 0.05) and 81% (P < 0.01), respectively, and PHA elevated plasma enteroglucagon by 69% and CCK by 60% (both P < 0.05). Only wheat germ agglutinin increased the release of glucagon-like peptide-1 by 100% (P < 0.05). PHA and PNA consistently reverse the fall in gastrointestinal and pancreatic growth associated with TPN in rats. Both lectins stimulated the release of specific hormones that may have been responsible for the trophic effects. It is suggested that lectins could be used to prevent gastrointestinal atrophy during TPN. Their hormone-releasing effects might be involved.

Circulating oxyntomodulin-like immunoreactivity in healthy children and children with celiac disease

BACKGROUND

The aim of the study was to evaluate the new hormonal entity oxyntomodulin-like immunoreactivity in malabsorption states, and to assess its potential in celiac disease management.

METHODS

We measured basal and postprandial oxyntomodulin-like immunoreactivity values in 35 children divided into 3 groups: group 1 was composed of 13 children with celiac disease, either under a gluten-free diet (8 patients) or normal diet (5 patients); group 2 was composed of 8 children hospitalized for gastroenteritis or chronic diarrhea, without biological evidence of malabsorption nor abnormal jejunal mucosa; group 3 was composed of 22 control subjects.

RESULTS

Fasting and meal-stimulated levels in the control group were 71+/-10 and 130+/-26 pmol/l, respectively. Mean concentrations were elevated in patients with celiac disease (basal = 349+/-254 pmol/l, postprandial = 446+/-332 pmol/l) and in the group 2 (basal = 139+/-58 pmol/l, postprandial = 218+/-85 pmol/l), but the difference with control subjects did not reach statistical significance. In children with celiac disease, basal and stimulated values correlated with the degree of malabsorption as assessed by hemoglobin (p = 0.006 and p = 0.01, respectively) and serum folate concentrations (p = 0.03 and p = 0.02, respectively).

CONCLUSIONS

Oxyntomodulin-like immunoreactivity is noticeably higher in healthy children than previously measured in healthy adult subjects. This hormonal parameter is not an adequate diagnostic tool in celiac disease. Nevertheless, in the context of celiac disease, its elevation reflects the degree of malabsorption and may provide a quantitative approach of the extent of mucosal damage.

Fermentable dietary fibre, intestinal microflora and plasma hormones in the rat

1. Conventional and germ-free rats were fed a fibre-free elemental diet with or without the addition of fermentable dietary fibres. We have previously reported that fibre was associated with greatly increased epithelial cell proliferation, but only in the conventional group, implying that it is the breakdown of fibre by the colonic microflora that is the main determinant of mucosal proliferation in the hind gut. The relationship of these changes to various plasma hormones implicated in intestinal growth control are described in this paper. 2. The most dramatic finding was that plasma levels of enteroglucagon and peptide YY were greatly increased in the germ-free groups. The response of these rats to fibre differed in that fibre decreased levels of enteroglucagon and peptide YY in the germ-free animals, but increased them in the conventional rats. Gastrin and insulin levels were significantly lowered in the fibre-supplemented groups, but were not affected by the microflora. 3. These results corroborate our previous findings that the effects of fibre and its fermentation are dynamically complex, and demonstrate that, like proliferation, direct effects and indirect fermentation-derived effects on plasma hormones also coexist.

Effect of ageing on pancreatic hyperplasia after 90% proximal small bowel resection

The present study was performed to examine the effect of ageing on pancreatic hyperplasia observed after proximal small bowel resection (PSBR). Young and old Wistar rats were randomly assigned to two groups, which underwent either an approximate 90% PSBR or a jejunal and ileal transection (TRC). One week after the operation, the pancreatic wet weight and the protein, DNA and RNA content of the pancreas were all significantly higher in young PSBR rats than in young TRC rats. However, no differences were seen in the old rat groups. Plasma enteroglucagon levels were elevated in both young and old PSBR rats, but the ratio of increase between the PSBR and TRC groups was significantly higher in young rats. Plasma cholecystokinin and gastrin levels did not increase after PSBR in either the young or old rats. These findings suggest that pancreatic hyperplasia observed after PSBR is attenuated by ageing, probably due to an insufficient increase in plasma enteroglucagon levels.

Colonic fermentation and proximal gastric tone in humans

BACKGROUND & AIMS

Some carbohydrates escape small intestinal absorption, and their presence in the ileum can affect proximal gut motility. Carbohydrates reaching the colon can inhibit gastric and pancreatic secretions. The hypothesis of this study was that colonic fermentation products of carbohydrates (short-chain fatty acids [SCFAs]) affect proximal gut motility and especially gastric tone.

METHODS

Healthy volunteers were studied after oral administration of 20 g lactulose (n = 6) and intracolonic infusions of 20 g lactose (n = 7) and SCFAs (54 mmol/180 mL and 90 mmol/180 mL, respectively). Gastric tone (electronic barostat) and H2 concentrations in exhaled air were simultaneously monitored, and peripheral intestinal peptide levels were measured by specific radioimmunoassays.

RESULTS

After oral lactulose administration (but not after saline), a significant decrease in gastric tone was observed, which rapidly followed the increase in H2 concentrations. Gastric tone also decreased after intracolonic infusions of both lactose and SCFAs; the most marked effect occurred after the highest SCFA dose. No significant changes in the level of plasma oxyntomodulin-like immunoreactivity and glucagon-like peptide 1 were found, whereas the level of peptide YY increased significantly over time, but not differently after saline and test solutions.

CONCLUSIONS

Colonic fermentation of undigestible carbohydrates can inhibit gastric tone, and SCFAs may be responsible for this colonic brake. The role of intestinal peptides, if any, was not identified.

Fermentable carbohydrate modulates postprandial enteroglucagon and gastrin release in rats

We studied the effects of a fermentable sugar-alcohol (lactitol) on the concentrations of enteroglucagon and gastrin in the blood of rats for 7.5 h after feeding. The control and treatment groups were fed on semi-purified diets containing either non-fermentable cellulose or lactitol respectively, at 100 g/kg. Compared with the cellulose-fed group, the animals fed with lactitol had higher levels of enteroglucagon (5-10 times higher than control; P < 0.05) and lower serum gastrin (70-80% of control; P < 0.05) for several hours after the withdrawal of feed. In contrast, varying the level of dietary lipid (maize oil) over a range of 8-120 g/kg had no effect on the release of either peptide. These results suggest that poorly absorbed fermentable dietary carbohydrate stimulates postprandial plasma enteroglucagon and inhibits serum gastrin release in the rat. The mechanism is uncertain but an endocrine response by the colon to fermentation products seems probable.

Increased ileal proglucagon expression after jejunectomy is not suppressed by inhibition of bowel growth

After jejunectomy, a rapid and sustained increase in the abundance of proglucagon mRNA occurs in residual ileum and is accompanied by increases in plasma intestinal proglucagon-derived peptides. This response may be a component of adaptive growth, or proglucagon-derived peptides may regulate adaptive growth. To distinguish these possibilities, rats were treated with difluoromethylornithine, blocking ornithine decarboxylase activity and thereby adaptive bowel growth. Three groups fed ad libitum were compared: (1) resect: rats with 80% proximal small bowel resection; (2) resect + difluoromethylornithine: resected rats given difluoromethylornithine in drinking water; and (3) transect: transected controls. Six days after surgery, the resect + difluoromethylornithine group demonstrated inhibition of adaptive bowel growth. Abundance of ileal proglucagon mRNA in resect and resect + difluoromethylornithine groups was double that in the transect group (P < 0.02), whereas ornithine decarboxylase mRNA levels did not differ. Plasma enteroglucagon and glucagon-like peptide-I levels were greater in resect than transect groups (P < 0.002) and did not differ between resect and resect + difluoromethylornithine groups. The rise in ileal proglucagon mRNA after proximal small bowel resection is not inhibited by difluoromethylornithine despite blocking bowel growth and, therefore, is not merely a component of adaptive growth. Proglucagon-derived peptides are possible modulators of adaptive bowel but cannot stimulate growth when ornithine decarboxylase activity is inhibited.

Fermentable carbohydrates elevate plasma enteroglucagon but high viscosity is also necessary to stimulate small bowel mucosal cell proliferation in rats

Enteroglucagon is a collective term for a small family of peptides derived from proglucagon by post-translational processing in the L-cells of the distal small intestine and colon. There is evidence that it inhibits gastric secretion, and high levels of enteroglucagon occur in plasma during intestinal adaptation, which suggests that it may also function as a trophic factor for the intestine. Certain types of soluble non-starch polysaccharide (dietary fiber) stimulate the release of enteroglucagon in rats but the mechanism is unknown. In this study we explored the importance of the viscosity and fermentability of nonabsorbed carbohydrates as determinants of plasma enteroglucagon and mucosal cell proliferation in the distal ileum of rats. Replacement of cellulose (10 g/kg) with guar gum in a semisynthetic diet led to a prompt and sustained rise in plasma enteroglucagon concentrations. Our initial hypothesis that this was a consequence of delayed nutrient absorption was disproven by the fact that hydroxypropylmethylcellulose (HPMC), a viscous but nonfermentable polysaccharide, had no effect on plasma enteroglucagon under the same conditions. In contrast, the nondigestible disaccharide lactitol led to a prolonged rise in plasma enteroglucagon, similar to that observed with guar gum. Lactitol is nonviscous, but highly fermentable, and we conclude that fermentable carbohydrate is an important stimulus for the release of enteroglucagon under our experimental conditions. There was no evidence that enteroglucagon released by this mechanism exerted trophic effects on the distal small intestinal mucosa.

Release of vasodilator, but not vasoconstrictor, neuropeptides and of enteroglucagon by intestinal ischaemia/reperfusion in the rat

Reperfusion of ischaemic intestine is characterised by an initial hyperaemia with ensuing mucosal repair. This study investigated possible roles for gut vasoactive neuropeptides and trophic peptides in these phenomena. Groups of rats were monitored during superior mesenteric artery occlusion for five or 20 minutes, with or without subsequent reperfusion for five minutes. Peptide concentrations (fmol/ml) in arterial blood, were measured using specific radioimmunoassays. Intestinal ischaemia alone did not cause haemodynamic disturbance or peptide release. Reperfusion, after five minutes of ischaemia, resulted in arterial hypotension and a rise in plasma vasoactive intestinal polypeptide (mean (SEM)) (37 (3), control 11 (4), p < 0.001). After 20 minutes of ischaemia, reperfusion resulted in greater hypotension (p < 0.05) and release of both vasoactive intestinal polypeptide (31 (3), p < 0.05 v control) and the more potent vasodilator beta-calcitonin gene related peptide (49 (3), control 23 (1), p < 0.001). By contrast, the vasodilators alpha-calcitonin gene related peptide and substance P and the vasoconstrictors neuropeptide Y, peptide YY, and somatostatin were not released. Bombesin, a stimulatory neuropeptide, was released after 20 minutes of ischaemia/reperfusion (13 (2), control 7 (3), p < 0.05). Plasma enteroglucagon rose from control (51 (4)) to 110 (16) (p < 0.001) and to 158 (27) (p < 0.005) after five and 20 minutes of ischaemia/reperfusion. The potent enteric vasodilators vasoactive intestinal polypeptide and beta-calcitonin gene related peptide, unopposed by vasoconstrictors, may promote post-ischaemic intestinal hyperaemia. The rise in plasma enteroglucagon may point to diffuse mucosal injury and is consistent with the putative trophic role of this peptide.

Enteroglucagon, but not CCK, plays an important role in pancreatic hyperplasia after proximal small bowel resection

The present study was performed to examine the role played by pancreatotrophic factors, especially enteroglucagon and cholecystokinin (CCK), in the compensatory pancreatic hyperplasia observed after proximal small bowel resection (PSBR). Male Wistar rats were randomized into two groups, receiving either PSBR or transection (TRC). Five animals from each group were randomly selected for treatment with FK-480, a novel CCK antagonist. Four weeks after the operation, plasma levels of gastrin, CCK and enteroglucagon were measured. Pancreatic wet weight and protein, DNA, RNA and enzyme content were also determined. The wet weight and content of protein, DNA and RNA were significantly higher in PSBR rats than in TRC rats, regardless of whether they received FK-480. FK-480 had no suppressive effects on adaptive pancreatic growth after PSBR. Plasma enteroglucagon levels rose significantly in PSBR rats, and there were positive correlations between plasma enteroglucagon levels and pancreatic protein, DNA and RNA content. These findings demonstrated that plasma CCK was not the major trophic factor operating in the pancreas after PSBR, and showed that enteroglucagon plays an important role in the pancreatic hyperplasia that occurs after PSBR.

Enteroglucagon. A putative humoral factor inducing pancreatic hyperplasia after proximal small bowel resection

The present study evaluated pancreatotrophic factors after massive small bowel resection. Specifically, we examined the role of enteroglucagon in compensatory pancreatic hyperplasia after proximal small bowel resection (PSBR) by using rats fed a fiber-free elemental diet or an elemental diet containing pectin. PSBR increased the net pancreatic weight as well as the protein, DNA, RNA, and amylase contents, and elevated plasma enteroglucagon levels. Pectin addition to the diet provoked a further increase in these parameters and significant positive correlations were found between the plasma enteroglucagon levels and the protein, DNA, and RNA contents of the pancreas. Plasma gastrin and CCK levels were not affected by the small bowel resection. These results indicate that enteroglucagon may exert a potent trophic effect on the pancreas after PSBR.

Effect of ileal oleate on interdigestive intestinal motility of the dog

To determine the effect of ileal oleate on fasting intestinal motility, pairs of duodenal and ileal catheters and bipolar duodenal and jejunal seromuscular electrodes were surgically implanted in six dogs. The ileum was perfused with either normal saline (154 mM NaCl) or oleic acid emulsion (152 mM), while intestinal myoelectric activity was continuously monitored. For transit studies, a bolus of [3H]PEG was injected into the duodenum, and jejunal and ileal alliquots were collected every 15 min for a 6-hr study period. Plasma samples were collected for radioimmunoassays of peptide YY and enteroglucagon. Ileal oleate infusion increased the MMC cycle length and decreased the number of MMCs (P < 0.001) and the myoelectric spike-burst frequency/10 min in the duodenum (P < 0.05). Both duodenal-jejunal (P < 0.05) and duodenal-ileal transit (P < 0.01) were delayed markedly by ileal perfusion with oleic acid emulsion as compared to control studies. Ileal oleate increased plasma levels of peptide YY (P < 0.01) and enteroglucagon (P < 0.01). Ileal perfusion with oleate therefore activated the so-called "ileal brake," diminishing duodenal myoelectric spike bursts and slowing intestinal transit while concurrently increasing plasma levels of peptide YY and enteroglucagon.

Polyunsaturated fatty acids of the n - 3 series influence intestinal crypt cell production in rats

The effects of saturated and polyunsaturated dietary lipids on intestinal mucosal cell proliferation were investigated in rats. Animals were randomly allocated to three groups of 10, and fed fibre-free diets containing lipid in the form of lard, corn oil or fish oil at a level of 80 g/kg. Total energy intake was kept constant by pair-feeding. After 14 days the crypt cell production rates (CCPR) at two sites in the small intestine, one site in the caecum and two sites in the colon were determined by the metaphase arrest technique, together with circulating levels of enteroglucagon and gastrin and parameters of mucosal morphology. Consumption of fish oil led to lower CCPR compared to corn oil at all sampling positions except the caecum (Treatment approximately 50% of control values; P < 0.05). In animals fed lard the CCPR in the small bowel was not significantly different to that of animals fed corn oil but their rates were lower in the colon. Post-prandial enteroglucagon and gastrin levels were lower in animals fed fish oil compared to the other two groups. These results suggest that polyunsaturated fatty acids of the n - 3 series may support a relatively low rate of crypt cell proliferation in some regions of the alimentary tract and might thereby tend to suppress the progression of colorectal neoplasms.

Activity of oxyntomodulin on gastric acid secretion induced by histamine or a meal in the rat

Conscious rats with chronic gastric fistula were trained for drinking a 14-ml milk meal. The activity of an intestinal hormone, oxyntomodulin (OXM), was studied in this model and compared to that observed when histamine was the stimulus. Under histamine (0.25 mg.kg-1.h-1) stimulation, OXM at doses (60-120 pmol.kg-1.h-1) that induced physiological circulating levels inhibited gastric acid secretion up to 50%. Under meal stimulation, OXM reduced up to 29% acid secretion at doses (1-1.5 nmol.kg-1.h-1) inducing supraphysiological levels. We conclude that at physiological concentrations OXM cannot counteract the complex processes triggered by a meal. OXM would be a component of enterogastrone, a combination of several intestinal hormones acting in synergy. The OXM action is related to pathways recognizing the C-terminal 19-37 moiety of the molecule.

Plasma enteroglucagon levels in different models of intestinal resection in the rat

To assess the influence of the different intestinal segments on the plasma enteroglucagon level, three models of intestinal resection in the rat were studied (jejunal, ileal, 90%). The basal values for this peptide and those obtained after an infusion of intraduodenal glucose were compared. The results obtained in basal/post-glucose infusion were: 50% proximal (jejunum): 220/728 pg/ml; 50% distal (ileum): 10/233 pg/ml; and the middle 90%: 108/297 pg/ml. The glucose infusion produced a maximal response, permitting a better evaluation of the differences among the three resection models. The highest levels corresponded to the group in which the entire ileum was conserved.

Hormonal enteroinsular axis in newborn infants of insulin-treated diabetic mothers

To study whether the increased glucose levels in the amniotic fluid during diabetic pregnancies induce an early maturation of the hormonal enteroinsular axis, we measured blood glucose levels and plasma concentrations of C-peptide, pancreatic glucagon, enteroglucagon, and gastric inhibitory polypeptide (GIP) in cord blood from 18 newborn infants of insulin-treated diabetic mothers (IDM) and 18 infants of nondiabetic mothers. In addition, we studied the same parameters in 20 IDM and 12 control infants before and after their first feed comprising human milk (5 mL/kg), given by nasogastric tube at the age of 2 h. The IDM had significantly higher blood glucose levels and plasma C-peptide concentrations in their cord blood than the control infants, which was followed postnatally by a substantial fall in these levels, whereas a more modest decrease could be seen in the control infants. Circulating enteroglucagon and GIP concentrations at the age of 2 h were significantly higher than those observed in cord blood in both the IDM and the control infants, but the IDM had significantly lower blood glucose levels, higher plasma C-peptide, and lower enteroglucagon concentrations before the first feed. There was a significant increase in blood glucose levels after the feed in both the IDM and the control infants, and the concentrations 2 h after feeding were of the same magnitude in the two groups. No significant C-peptide response could be observed in either group, but the IDM continuously had higher C-peptide concentrations. A significant enteroglucagon and GIP response could be seen in the IDM, whereas the controls exhibited only a GIP response. However, no significant differences were found between the two groups in the absolute postprandial plasma concentrations of these hormones. Our results show rapid, substantial postnatal changes in circulating concentrations of enteroinsular hormones in both IDM and control infants. Enteral feeding with human milk corrects early postnatal hypoglycemia within 2 h in most IDM without causing any exacerbation of their hyperinsulinemia. The absence of any C-peptide response to the first feed and of any observed differences between IDM and normal infants in absolute concentrations of enteroglucagon and GIP after the first feed suggests that the enteroinsular axis matures postnatally in both groups of infants.

Diurnal profile of oxyntomodulin-like immunoreactivity in duodenal ulcer patients

Plasma concentrations of oxyntomodulin-like immunoreactivity, a group of intestinal peptides capable of mediating an enterogastrone signal, were measured during a 24-h period in 6 duodenal ulcer patients and compared with those of 16 age-matched controls. Each subject was submitted to 18 oxyntomodulin-like immunoreactivity determinations. Four standardized meals were given during the test. Furthermore, each patient was evaluated for peak acid output after pentagastrin stimulation. The values of the duodenal ulcer subjects were predominantly within normal acid secretion limits. Fasting levels, meal-induced variations, and nocturnal production of oxyntomodulin-like immunoreactivity were similar in the two groups. A negative correlation was observed between peak acid output and oxyntomodulin-like immunoreactivity evaluated either as nocturnal production or as maximum nyctohemeral concentration. We conclude that, taken as a whole, duodenal ulcer disease is not caused by a defect in oxyntomodulin-like immunoreactivity secretion. However, this study does not rule out the possibility of a selective deficiency of these peptides in some duodenal ulcer subgroups such as hypersecretory patients.

Fat-induced ileal brake in humans: a dose-dependent phenomenon correlated to the plasma levels of peptide YY

BACKGROUND

Upper gastrointestinal motility is regulated by the presence of nutrients in the distal gut. The present study evaluated whether lipid-induced ileal brake on gastric emptying (1) can be elicited by low fat concentrations; (2) is a dose-dependent phenomenon; and (3) is related to gastrointestinal peptide release.

METHODS

Seven patients were studied in the defunctionalized stage of total colectomy, on three separate occasions. On each study day, patients ate a meal labeled in the solid component; 30 minutes later, one of the following solutions was randomly infused into the ileal pouch: 0.9% saline, 2% oleic acid, and 20% oleic acid. Plasma concentrations of peptide YY (PYY), enteroglucagon, neurotensin, and motilin were measured.

RESULTS

Both oleic acid solutions slowed gastric emptying compared with saline (P < 0.001), the effect being dose dependent (P < 0.001). Ileal infusions did not modify neurotensin and enteroglucagon levels but induced a dose-dependent increase of PYY (P < 0.01) and a borderline decrease of motilin (P = 0.05) levels. Slower rates of gastric emptying were related to increased plasma concentrations of PYY (r = 0.615; P < 0.05).

CONCLUSIONS

This study shows that (1) the ileal brake on gastric emptying can be evoked by low doses of lipids in the distal ileum; (2) the delay of gastric emptying is related to the release of PYY; and (3) both phenomena are dose dependent.

Bile salt inhibition of motility in the isolated perfused rabbit terminal ileum

The effects of bile on small bowel motility were studied in isolated, perfused rabbit terminal ileum. It was proposed that bile delivery into the distal ileum would inhibit ileal motor activity, by peptide YY (PYY) release and therefore the effect of luminal bile on motor activity was examined and PYY release measured. Luminal bile and taurocheodeoxycholic acid (10 mmol) inhibited ileal motor activity. Arterial infusion of venous effluents from a bile inhibited ileum suppressed motor activity in a second isolated ileum. This shows the presence of a humoral inhibitor of ileal motor activity. Luminal bile increased venous PYY concentrations (42.5 (8.5) to 502 (46.2) pmol/l; p < 0.01) and increased bile salt values (1.7 (0.36) to 88.6 (5.6) 10 mumol/l/l; p < 0.005). Arterial infusion of taurocheodeoxycholic acid at concentrations found in the venous effluent (100 mumol/l/l) suppressed motility (p < 0.001) but infusion of PYY at concentrations in the venous effluent (500.0 pmol/l) failed to inhibit motility. Furthermore, PYY antagonist, PYX 1, failed to reverse the bile induced inhibition of motility. Luminal bile salts inhibit terminal ileal motility and this is independent of PYY release. By slowing motility, bile salts may participate in their own absorption by the 'ileal pump' and in the 'ileal brake' mechanism.

Pancreas and gut hormone responses to oral glucose and intravenous glucagon in cystic fibrosis patients with normal, impaired, and diabetic glucose tolerance

Pancreatic and gut hormone responses to oral glucose, and insulin sensitivity were studied in cystic fibrosis patients with normal (N = 14), impaired (N = 4), and diabetic (N = 12) glucose tolerance, and in 10 control subjects, and beta cell responses to oral glucose and intravenous glucagon were compared. Compared to control subjects, initial insulin and C-peptide responses to oral glucose were lower in all patient groups, and decreased with decreasing glucose tolerance. Insulin sensitivity in patients with impaired and diabetic glucose tolerance was lower than in control subjects. The 6 min post-glucagon C-peptide concentration was positively correlated with the initial insulin response to oral glucose. Fasting levels of pancreatic polypeptide, pancreatic glucagon, total glucagon, glucagon-like peptide-1 7-36 amide, and gastric inhibitory polypeptide were normal in all patient groups. Following oral glucose, pancreatic polypeptide responses were absent in all patients, suppressibility of pancreatic glucagon secretion was increasingly impaired with decreasing glucose tolerance, and gut hormone levels were normal. In conclusion, at cystic fibrosis (a) insulin secretion is impaired even when glucose tolerance and insulin sensitivity are within the normal range, (b) the glucagon test gives valid estimates of residual beta cell function, (c) pancreatic polypeptide response to oral glucose is absent, (d) glucagon suppressibility decreases with decreasing glucose tolerance, and (e) the enteroinsular axis is intact.

[Oxyntomodulin, a new hormonal marker of intestinal malabsorption syndromes]

Plasma oxyntomodulin-like immunoreactivity (OLI) concentrations were found to be significantly elevated in 6 patients with coeliac disease when compared with those observed in 38 healthy subjects. Furthermore, OLI hypersecretion is related to the degree of malabsorption. This marker could be used as a test for detection and follow-up of patients with malabsorptive disorders.

Dietary corn oil and guar gum stimulate intestinal crypt cell proliferation in rats by independent but potentially synergistic mechanisms

The effects of corn oil, guar gum and cellulose on mucosal proliferation were investigated in rats. Animals were allocated to three groups and fed a fiber-free diet or diets containing 100 g/kg of cellulose or guar gum. Each group was subdivided to receive corn oil at 40 or 80 g/kg. The crypt cell production rate (CCPR) was determined after 28 d. Consumption of guar gum or corn oil led to greater CCPR in the ileum and cecum. In a second experiment, animals were allocated to two groups and fed diets containing either cellulose or guar gum (100 g/kg). Each group was again subdivided to receive either corn oil (80 g/kg) or minimal lipid (linolenic acid, 10 g/kg). The trophic effect of guar gum occurred even in the low lipid-fed group, indicating that guar gum exerts a positive effect on cell turnover independently of any interaction with luminal lipid. However, the highest CCPR occurred in animals fed guar gum and corn oil. Postprandial enteroglucagon and gastrin concentrations were highest in animals fed both guar gum and corn oil. Thus, corn oil and guar gum exert independent trophic effects on the intestinal mucosa. The combination of effects led to a three- to four-fold increase in colon mucosal CCPR.

An experimental study on the gastric acid and gut hormone secretion after pylorus preserving duodenectomy in dogs

To clarify changes in gastric acid and gut hormone secretion after pylorus-preserving pancreaticoduodenectomy (PPPD), an experimental study was performed using a model of pylorus-preserving duodenectomy in dogs previously provided with Heidenhain pouch (HP). The duodenectomy involves resection of the duodenum and 10 cm of the proximal jejunum preserving 2 cm of juxtapyloric duodenum and round-shaped duodenal wall around pancreatic papilla. Reconstruction was done by anastomosing the rho-shaped jejunal loop to gallbladder, juxtapyloric duodenum and peripapillar round-shaped duodenal wall with ligation of the common bile duct. For these dogs, intravenous glucose tolerance test (IVGTT), oral glucose tolerance test (OGTT), meal ingestion test (TM) and histological studies of pancreatic specimen obtained at autopsy were performed investigating pancreatic, gastric acid and gut hormone secretion. Preservation of endocrine and exocrine pancreatic secretion after operation demonstrated our experimental model to be adequate for evaluation of the factor of duodenectomy in PPPD on gastric acid and gut hormone secretion avoiding the influences of changes in pancreatic secretion. Postprandial gastric acid secretion from HP did not change significantly after operation. Postprandial secretion of gastrin, glucagon, GIP and enteroglucagon did not alter significantly after operation. These results indicated that in the clinical PPPD procedure, preservation of more than 2 cm of duodenum from the pylorus produced neither postprandial gastric acid hypersecretion, which might be cause of postoperative stomal ulcer, nor any change of related gut hormone secretion.