Biomedical subjects

Jens J Holst

Publications and source records attributed to Jens J Holst.

At least 19 recordsLinked to original sources

PubMed2026

GIP contributes to postprandial regulation of splanchnic blood supply in humans with type 2 diabetes: a randomised, single-blinded, placebo-controlled, crossover study.

AIMS/HYPOTHESIS: In healthy lean humans, endogenous glucose-dependent insulinotropic polypeptide (GIP) contributes significantly to the postprandial increase in arteria mesenterica superior blood flow. The vascular biology related to activation of the GIP receptor is markedly impaired in individuals with type 2 diabetes and is sometimes absent. In this population, we investigated the role of endogenous GIP on postprandial splanchnic blood flow by using the GIP receptor antagonist, GIP(3-30)NH2. The primary outcome of this study was the changes in blood flow in arteria mesenterica superior during oral glucose with or without GIP receptor antagonist infusion. METHODS: Ten participants with type 2 diabetes (age 20-80 years, BMI 20-35 kg/m2, and HbA1c >48 mmol/mol and <75 mmol/mol) were investigated in a randomised, placebo-controlled, crossover study. On four separate occasions, participants received the following treatment: oral glucose + i.v. GIP(3-30)NH2; oral glucose + i.v. saline (154 mmol/l NaCl); oral water + i.v. GIP(3-30)NH2; oral water + i.v. saline. Participants were randomly assigned to intervention groups using (random.org). Participants were unaware of allocation, while investigators were aware. No additional allocation concealment procedures were used. During all four interventions, splanchnic blood flow was measured using phase-contrast MRI in the arteria mesenterica superior, truncus coeliacus and vena portae during oral glucose (75 g) or water ingestion. The study was conducted at Rigshospitalet, Copenhagen. Liver volume and oxygenation, as well as gallbladder volume, were assessed. Blood samples were collected and analysed for insulin, C-peptide, GIP, glucagon and glucose. RESULTS: Oral glucose alone increased mean blood flow in arteria mesenterica superior by 57% (95% CI 26, 88) and this was 15% (95% CI -2, 32) lower during concomitant GIP receptor antagonist infusion, p=0.012. Infusion of GIP receptor antagonist during oral glucose treatment did also result in lower insulin secretion, C-peptide and C-peptide/glucose ratio compared with saline infusion, whereas glucagon levels and plasma glucose were unaffected. Oral water did not affect any outcomes. CONCLUSIONS/INTERPRETATION: Endogenous GIP contributes to postprandially increased splanchnic blood flow in people with type 2 diabetes. TRIAL REGISTRATION: ClinicalTrials.gov NCT06426823 FUNDING: This work was supported by the Novo Nordisk Foundation.

Humans↗

PubMed2026

Distal Recirculation of Enteral contents Augmented Mechanically (DREAM) Promotes Intestinal Adaptation and Restores Enterohepatic Signaling in Short Bowel Syndrome.

BACKGROUND & AIMS: Short bowel syndrome (SBS) leads to malabsorption and intestinal failure-associated liver disease. Intestinal adaptation (IA) driven by sustained enteral nutrition (EN) is essential, but EN delivery is limited after major resection. We developed DREAM (Distal Recirculation of Enteral contents Augmented Mechanically), which enables complete EN despite SBS, and enhances IA. We evaluated its efficacy in a translational large-animal model. METHODS: The study randomized 20 neonatal pigs to EN (control), SBS (75% resection), or DREAM. Growth, serum biochemistry, cytokines, intestinal morphology, barrier integrity, hepatic histology, and gene expression (quantitative polymerase chain reaction, RNA sequencing, Kyoto Encyclopedia of Genes and Genomes, and Gene Ontology enrichment) were analyzed. RESULTS: DREAM prevented hepatic and intestinal injury seen in SBS. Serum bilirubin (0.11 vs 5.14 mg/dL, P = .0008), γ-glutamyl transferase (23.2 vs 114.6 IU/L, P < .0001), and bile acids (9.7 vs 39 μmol/L, P = .0026) were significantly lower. Inflammatory cytokines (interferon-γ, P = .0296; interleukin 1β, P = .0349; and interleukin 6, P = .0189) and portal lipopolysaccharide (P = .0130) markedly improved. DREAM enhanced IA, increasing linear gut density (0.38 vs 0.209 g/cm, P < .0001), villus-to-crypt ratio (P = .0026), glucagon-like peptide 2 (P < .0001) and restored occludin and E-cadherin (P < .001). Hepatic bile salt export pump and cholesterol 7α-hydroxylase regulation were preserved (P = .0373 and P = .0034), and intestinal farnesoid X receptor, Takeda G-protein-coupled receptor 5, and epidermal growth factor signaling were reactivated (P < .01). Transcriptomic analysis confirmed improvements in metabolic, absorptive, and immune pathways. DREAM effluent demonstrated >80% macronutrient absorption within 6 hours (P < .0001). CONCLUSION: DREAM enables full EN in SBS, restoring absorption, mucosal integrity, and gut-liver homeostasis while preventing intestinal failure-associated liver disease. This approach represents a promising translational advance in SBS therapy.

Gut Atrophy↗

PubMed2007

Small-molecule agonists for the glucagon-like peptide 1 receptor.

The peptide hormone glucagon-like peptide (GLP)-1 has important actions resulting in glucose lowering along with weight loss in patients with type 2 diabetes. As a peptide hormone, GLP-1 has to be administered by injection. Only a few small-molecule agonists to peptide hormone receptors have been described and none in the B family of the G protein coupled receptors to which the GLP-1 receptor belongs. We have discovered a series of small molecules known as ago-allosteric modulators selective for the human GLP-1 receptor. These compounds act as both allosteric activators of the receptor and independent agonists. Potency of GLP-1 was not changed by the allosteric agonists, but affinity of GLP-1 for the receptor was increased. The most potent compound identified stimulates glucose-dependent insulin release from normal mouse islets but, importantly, not from GLP-1 receptor knockout mice. Also, the compound stimulates insulin release from perfused rat pancreas in a manner additive with GLP-1 itself. These compounds may lead to the identification or design of orally active GLP-1 agonists.

Animals↗

PubMed2007

Hepatic autoregulation: response of glucose production and gluconeogenesis to increased glycogenolysis.

The effect of increased glycogenolysis, simulated by galactose's conversion to glucose, on the contribution of gluconeogenesis (GNG) to hepatic glucose production (GP) was determined. The conversion of galactose to glucose is by the same pathway as glycogen's conversion to glucose, i.e., glucose 1-phosphate --> glucose 6-phosphate --> glucose. Healthy men (n = 7) were fasted for 44 h. At 40 h, hepatic glycogen stores were depleted. GNG then contributed approximately 90% to a GP of approximately 8 micromol.kg(-1).min(-1). Galactose, 9 g/h, was infused over the next 4 h. The contribution of GNG to GP declined from approximately 90% to 65%, i.e., by approximately 2 micromol.kg(-1).min(-1). The rate of galactose conversion to blood glucose, measured by labeling the infused galactose with [1-(2)H]galactose (n = 4), was also approximately 2 micromol.kg(-1).min(-1). The 41st h GP rose by approximately 1.5 micromol.kg(-1).min(-1) and then returned to approximately 9 micromol.kg(-1).min(-1), while plasma glucose concentration increased from approximately 4.5 to 5.3 mM, accompanied by a rise in plasma insulin concentration. Over 50% of the galactose infused was accounted for in blood glucose and hepatic glycogen formation. Thus an increase in the rate of GP via the glycogenolytic pathway resulted in a concomitant decrease in the rate of GP via GNG. While the compensatory response to the galactose administration was not complete, since GP increased, hepatic autoregulation is operative in healthy humans during prolonged fasting.

Adult↗

PubMed2007

The antagonistic metabolite of GLP-1, GLP-1 (9-36)amide, does not influence gastric emptying and hunger sensations in man.

OBJECTIVE: Glucagon-like peptide-1 (GLP-1 (7-36)amide) is an intestinal hormone that is released in response to meal ingestion. GLP-1 reduces postprandial gastric and exocrine pancreatic secretion and is believed to inhibit gastric emptying. Furthermore, GLP-1 may play a role in hunger and thirst regulation. In vivo, GLP-1 is rapidly (within minutes) converted into a metabolite, GLP-1 (9-36)amide, which has been shown to act as a GLP-1 receptor antagonist in vitro and in anaesthetized pigs. The purpose of this study was to assess the effect of infusion of GLP-1 (9-36)amide on hunger ratings and antral emptying of a meal. MATERIAL AND METHODS: Six healthy volunteers were tested in a double-blind, placebo-controlled fashion. Antral emptying of a liquid meal and hunger ratings were determined using ultrasound technology and visual analogue scale scoring during infusions of saline or GLP-1 (9-36)amide (5 pmol/kg body wt/min) resulting in supraphysiological concentrations. RESULTS: Infusion of GLP-1 (9-36)amide had no effect on gastric emptying or the sensation of hunger compared to saline. CONCLUSIONS: Our findings suggests that the rapid formation of the antagonistic metabolite does not influence gastric emptying and hunger ratings in humans even when it is present in supraphysiological concentrations.

Adult↗

PubMed2006

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

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

Animals↗

PubMed2006

Disassociation of bone resorption and formation by GLP-2: a 14-day study in healthy postmenopausal women.

We have previously shown that a single subcutaneous injection of glucagon-like peptide-2 (GLP-2) at 10 p.m. in postmenopausal women results in a dose-dependent decrease in the nocturnal serum and urine concentrations of fragments derived from the degradation of the C-terminal telopeptide region of collagen type I (s-CTX and u-CTX) and u-DPD, markers of bone resorption. In contrast, bone formation, as assessed by serum osteocalcin and procollagen type I N-terminal propeptide (PINP), appeared to be unaffected by treatment with exogenous GLP-2. These effects were further investigated in a 14-day study. The aim was to demonstrate that a parenteral formulation of GLP-2 is safe and well tolerated after repeated dosing in healthy postmenopausal women for 14 days. It was further investigated whether the effects on bone turnover markers were sustained throughout the study period. The study was a double-blind placebo-controlled trial with 60 postmenopausal women and 2 different doses of GLP-2 (1.6 mg and 3.2 mg GLP-2) against a saline control. The data for bone resorption revealed a similar reduction on Day 1 and Day 14, both based on time course and AUC. There were no signs of tachyphylaxis and no serious adverse reaction. Both GLP-2 doses resulted in similar and significant (p<0.001) reduction in bone resorption indicating that the maximum efficacious dose has been approached. Osteocalcin and PINP levels were unaffected at Day 1 and Day 14, suggesting a disassociation between bone resorption and bone formation during GLP-2 treatment.

Aged↗

PubMed2006

Increased postprandial responses of GLP-1 and GIP in patients with chronic pancreatitis and steatorrhea following pancreatic enzyme substitution.

We aimed to investigate how assimilation of nutrients affects the postprandial responses of glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) and to evaluate the effect of pancreatic enzyme substitution (PES) on insulin secretion in patients with chronic pancreatitis (CP) and pancreatic exocrine insufficiency (PEI). Eight male patients with CP and PEI were studied. Blood was sampled frequently on two separate days after ingestion of a liquid meal with and without PES, respectively. Eight healthy male subjects served as a control group. beta-Cell responsiveness was estimated as changes in insulin secretion rates in response to changes in postprandial plasma glucose (PG). There was no difference in the PG incremental area under curve (AUC) for patients with and without PES [406 +/- 100 vs. 425 +/- 80 mM.4 h (mean +/- SE), P = 0.8]. The response of total GLP-1 was higher after PES (AUC: 7.8 +/- 1.2 vs. 5.3 +/- 0.6 nM.4 h, P = 0.01), as was the response of total GIP (AUC: 32.7 +/- 7.5 vs. 21.1 +/- 8.3 nM.4 h, P = 0.01). Concurrently, both plasma insulin, plasma C-peptide, and total insulin secretion increased after PES (AUC: 17.7 +/- 4.2 vs. 13.6 +/- 2.9 nM.4 h, P = 0.02; 237 +/- 31.4 vs. 200 +/- 27.4 nM.4 h, P = 0.005; and 595 +/- 82 vs. 497 +/- 80 pmol.kg(-1).4 h, P = 0.01, respectively). beta-Cell responsiveness to glucose was not significantly different on the two study days for patients with CP. These results suggest that the secretion of GLP-1 and GIP is under influence of the digestion and absorption of nutrients in the small intestine and that PES increases insulin secretion.

Aged↗

PubMed2006

Glucagon-like peptide 2 inhibits ghrelin secretion in humans.

INTRODUCTION: The growth hormone secretagogue receptor ligand ghrelin is known to play a pivotal role in the central nervous control of energy homeostasis. Circulating ghrelin levels are high under fasting conditions and decline after meal ingestion, but the mechanisms underlying the postprandial drop in ghrelin levels are poorly understood. In the present study we addressed, whether (1) exogenous GLP-2 administration decreases ghrelin levels and (2) what other endogenous factors are related to ghrelin secretion under fasting conditions. PATIENTS AND METHODS: Fifteen healthy male volunteers were studied with the intravenous infusion of GLP-2 (2 pmol l(-1) min(-1)) or placebo over 120 min in the fasting state. Plasma concentrations of glucose, insulin, C-peptide, glucagon, intact GLP-2 and ghrelin were determined. RESULTS: During the infusion of GLP-2, plasma concentrations of intact GLP-2 increased from 10.0+/-1.5 pmol/l to steady-state levels of 207.7+/-8.3 pmol/l (p < 0.0001). Administration of GLP-2 led to an approximately 10% reduction in ghrelin concentrations, whereas placebo administration was without an effect (p < 0.001). After cessation of the GLP-2 infusion, ghrelin levels returned to baseline values, and were no longer different from those in the placebo experiments. There was a strong inverse linear relationship between the fasting concentrations of ghrelin and the respective levels of glucose, insulin and C-peptide (r = 0.49, p < 0.01; r = 0.55, p < 0.01 and r = 0.59, p < 0.001, respectively). In contrast, there was no detectable association between fasting ghrelin levels and the ambient concentrations of glucagon or intact GLP-2. CONCLUSIONS: GLP-2 inhibits ghrelin secretion in humans at plasma levels of approximately 200 pmol/l. However, the physiological importance of this effect appears to be minor compared to the actions of insulin and glucose.

Adult↗

PubMed2006

Effect of single oral doses of sitagliptin, a dipeptidyl peptidase-4 inhibitor, on incretin and plasma glucose levels after an oral glucose tolerance test in patients with type 2 diabetes.

CONTEXT: In response to a meal, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP) are released and modulate glycemic control. Normally these incretins are rapidly degraded by dipeptidyl peptidase-4 (DPP-4). DPP-4 inhibitors are a novel class of oral antihyperglycemic agents in development for the treatment of type 2 diabetes. The degree of DPP-4 inhibition and the level of active incretin augmentation required for glucose lowering efficacy after an oral glucose tolerance test (OGTT) were evaluated. OBJECTIVE: The objective of the study was to examine the pharmacodynamics, pharmacokinetics, and tolerability of sitagliptin. DESIGN: This was a randomized, double-blind, placebo-controlled, three-period, single-dose crossover study. SETTING: The study was conducted at six investigational sites. PATIENTS: The study population consisted of 58 patients with type 2 diabetes who were not on antihyperglycemic agents. INTERVENTIONS: Interventions included sitagliptin 25 mg, sitagliptin 200 mg, or placebo. MAIN OUTCOME MEASURES: Measurements included plasma DPP-4 activity; post-OGTT glucose excursion; active and total incretin GIP levels; insulin, C-peptide, and glucagon concentrations; and sitagliptin pharmacokinetics. RESULTS: Sitagliptin dose-dependently inhibited plasma DPP-4 activity over 24 h, enhanced active GLP-1 and GIP levels, increased insulin/C-peptide, decreased glucagon, and reduced glycemic excursion after OGTTs administered at 2 and 24 h after single oral 25- or 200-mg doses of sitagliptin. Sitagliptin was generally well tolerated, with no hypoglycemic events. CONCLUSIONS: In this study in patients with type 2 diabetes, near maximal glucose-lowering efficacy of sitagliptin after single oral doses was associated with inhibition of plasma DPP-4 activity of 80% or greater, corresponding to a plasma sitagliptin concentration of 100 nm or greater, and an augmentation of active GLP-1 and GIP levels of 2-fold or higher after an OGTT.

Administration, Oral↗

PubMed2006

Switching from insulin to oral sulfonylureas in patients with diabetes due to Kir6.2 mutations.

BACKGROUND: Heterozygous activating mutations in KCNJ11, encoding the Kir6.2 subunit of the ATP-sensitive potassium (K(ATP)) channel, cause 30 to 58 percent of cases of diabetes diagnosed in patients under six months of age. Patients present with ketoacidosis or severe hyperglycemia and are treated with insulin. Diabetes results from impaired insulin secretion caused by a failure of the beta-cell K(ATP) channel to close in response to increased intracellular ATP. Sulfonylureas close the K(ATP) channel by an ATP-independent route. METHODS: We assessed glycemic control in 49 consecutive patients with Kir6.2 mutations who received appropriate doses of sulfonylureas and, in smaller subgroups, investigated the insulin secretory responses to intravenous and oral glucose, a mixed meal, and glucagon. The response of mutant K(ATP) channels to the sulfonylurea tolbutamide was assayed in xenopus oocytes. RESULTS: A total of 44 patients (90 percent) successfully discontinued insulin after receiving sulfonylureas. The extent of the tolbutamide blockade of K(ATP) channels in vitro reflected the response seen in patients. Glycated hemoglobin levels improved in all patients who switched to sulfonylurea therapy (from 8.1 percent before treatment to 6.4 percent after 12 weeks of treatment, P<0.001). Improved glycemic control was sustained at one year. Sulfonylurea treatment increased insulin secretion, which was more highly stimulated by oral glucose or a mixed meal than by intravenous glucose. Exogenous glucagon increased insulin secretion only in the presence of sulfonylureas. CONCLUSIONS: Sulfonylurea therapy is safe in the short term for patients with diabetes caused by KCNJ11 mutations and is probably more effective than insulin therapy. This pharmacogenetic response to sulfonylureas may result from the closing of mutant K(ATP) channels, thereby increasing insulin secretion in response to incretins and glucose metabolism. (ClinicalTrials.gov number, NCT00334711 [ClinicalTrials.gov].).

ATP-Binding Cassette Transporters↗

PubMed2006

GIP-(3-42) does not antagonize insulinotropic effects of GIP at physiological concentrations.

Glucose-dependent insulinotropic polypeptide [GIP-(1-42)] is degraded by dipeptidyl peptidase IV (DPP IV), forming GIP-(3-42). In mice, high concentrations of synthetic GIP-(3-42) may function as a GIP receptor antagonist, but it is unclear whether this occurs at physiological concentrations. In COS-7 cells transiently transfected with the human GIP receptor, GIP-(1-42) and -(3-42) bind with affinities (IC(50)) of 5.2 and 22 nM, respectively. GIP-(1-42) was a potent agonist, stimulating cAMP accumulation (EC(50), 13.5 pM); GIP-(3-42) alone had no effect. When incubated together with native GIP, GIP-(3-42) behaved as a weak antagonist (IC(50), 92 and 731 nM for inhibition of cAMP accumulation elicited by 10 pM and 1 nM native GIP, respectively). In the isolated perfused rat pancreas, GIP-(3-42) alone had no effect on insulin output and only reduced the response to GIP (1 nM) when coinfused in >50-fold molar excess (IC(50), 138 nM). The ability of GIP-(3-42) to affect the antihyperglycemic or insulinotropic actions of GIP-(1-42) was examined in chloralose-anesthetized pigs given intravenous glucose. Endogenous DPP IV activity was inhibited to reduce degradation of the infused GIP-(1-42), which was infused alone and together with GIP-(3-42), at rates sufficient to mimic postprandial concentrations of each peptide. Glucose, insulin, and glucagon responses were identical irrespective of whether GIP-(1-42) was infused alone or together with GIP-(3-42). We conclude that, although GIP-(3-42) can weakly antagonize cAMP accumulation and insulin output in vitro, it does not behave as a physiological antagonist in vivo.

Animals↗

PubMed2006

Influence of gastric inhibitory polypeptide on pentagastrin-stimulated gastric acid secretion in patients with type 2 diabetes and healthy controls.

AIM: Gastric inhibitory polypeptide is secreted from intestinal K-cells in response to nutrient ingestion and acts as an incretin hormone in human physiology. While animal experiments suggested a role for GIP as an inhibitor of gastric secretion, the GIP effects on gastric acid output in humans are still controversial. METHODS: Pentagastrin was administered at an infusion rate of 1 microg . kg(-1) . h(-1) over 300 min in 8 patients with type 2 diabetes (2 female, 6 male, 54+/- 10 years, BMI 30.5+/- 2.2 kg/m(2); no history of autonomic neuropathy) and 8 healthy subjects (2/6, 46+/- 6 years., 28.9+/- 5.3 kg/m(2)). A hyperglycaemic clamp (140 mg/dl) was performed over 240 min. Placebo, GIP at a physiological dose (1 pmol . kg(-1) . min(-1)), and GIP at a pharmacological dose (4 pmol . kg(-1) . min(-1)) were administered over 60 min each. Boluses of placebo, 20 pmol GIP/kg, and 80 pmol GIP/kg were injected intravenously at the beginning of each infusion period, respectively. Gastric volume, acid and chloride output were analysed in 15-min intervals. Capillary and venous blood samples were drawn for the determination of glucose and total GIP. Statistics were carried out by repeated-measures ANOVA and one-way ANOVA. RESULTS: Plasma glucose concentrations during the hyperglycaemic clamp experiments were not different between patients with type 2 diabetes and controls. Steady-state GIP plasma levels were 61+/- 8 and 79+/- 12 pmol/l during the low-dose and 327+/- 35 and 327+/- 17 pmol/l during the high-dose infusion of GIP, in healthy control subjects and in patients with type 2 diabetes, respectively (P=0.23 and P=0.99). Pentagastrin markedly increased gastric acid and chloride secretion (P< 0.001). There were no significant differences in the rates of gastric acid or chloride output between the experimental periods with placebo or any dose of GIP. The temporal patterns of gastric acid and chloride secretion were similar in patients with type 2 diabetes and healthy controls (P=0.86 and P=0.61, respectively). CONCLUSION: Pentagastrin-stimulated gastric acid secretion is similar in patients with type 2 diabetes and healthy controls. GIP administration does not influence gastric acid secretion at physiological or pharmacological plasma levels. Therefore, GIP appears to act as an incretin rather than as an enterogastrone in human physiology.

Adult↗

PubMed2006

Impact of incretin hormones on beta-cell function in subjects with normal or impaired glucose tolerance.

The mechanisms by which the enteroinsular axis influences beta-cell function have not been investigated in detail. We performed oral and isoglycemic intravenous (IV) glucose administration in subjects with normal (NGT; n = 11) or impaired glucose tolerance (IGT; n = 10), using C-peptide deconvolution to calculate insulin secretion rates and mathematical modeling to quantitate beta-cell function. The incretin effect was taken to be the ratio of oral to IV responses. In NGT, incretin-mediated insulin release [oral glucose tolerance test (OGTT)/IV ratio = 1.59 +/- 0.18, P = 0.004] amounted to 18 +/- 2 nmol/m(2) (32 +/- 4% of oral response), and its time course matched that of total insulin secretion. The beta-cell glucose sensitivity (OGTT/IV ratio = 1.52 +/- 0.26, P = 0.02), rate sensitivity (response to glucose rate of change, OGTT/IV ratio = 2.22 +/- 0.37, P = 0.06), and glucose-independent potentiation were markedly higher with oral than IV glucose. In IGT, beta-cell glucose sensitivity (75 +/- 14 vs. 156 +/- 28 pmol.min(-1).m(-2).mM(-1) of NGT, P = 0.01) and potentiation were impaired on the OGTT. The incretin effect was not significantly different from NGT in terms of plasma glucagon-like peptide 1 and glucose-dependent insulinotropic polypeptide responses, total insulin secretion, and enhancement of beta-cell glucose sensitivity (OGTT/IV ratio = 1.73 +/- 0.24, P = NS vs. NGT). However, the time courses of incretin-mediated insulin secretion and potentiation were altered, with a predominance of glucose-induced vs. incretin-mediated stimulation. We conclude that, under physiological circumstances, incretin-mediated stimulation of insulin secretion results from an enhancement of all dynamic aspects of beta-cell function, particularly beta-cell glucose sensitivity. In IGT, beta-cell function is inherently impaired, whereas the incretin effect is only partially affected.

Adult↗

PubMed2006

Prohormone convertase 1/3 is essential for processing of the glucose-dependent insulinotropic polypeptide precursor.

The physiology of the incretin hormones, glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), and their role in type 2 diabetes currently attract great interest. Recently we reported an essential role for prohormone convertase (PC) 1/3 in the cleavage of intestinal proglucagon, resulting in formation of GLP-1, as demonstrated in PC1/3-deficient mice. However, little is known about the endoproteolytic processing of the GIP precursor. This study investigates the processing of proGIP in PC1/3 and PC2 null mice and in cell lines using adenovirus-mediated overexpression. Supporting a role for PC1/3 in proGIP processing, we found co-localization of GIP and PC1/3 but not PC2 in intestinal sections by immunohistochemistry, and analysis of intestinal extracts from PC1/3-deficient animals demonstrated severely impaired processing to GIP, whereas processing to GIP was unaltered in PC2-deficient mice. Accordingly, overexpression of preproGIP in the neuroendocrine AtT-20 cell line that expresses high levels of endogenous PC1/3 and negligible levels of PC2 resulted in production of GIP. Similar results were obtained after co-expression of preproGIP and PC1/3 in GH4 cells that express no PC2 and only low levels of PC1/3. In addition, studies in GH4 cells and the alpha-TC1.9 cell line, expressing PC2 but not PC1/3, indicate that PC2 can mediate processing to GIP but also to other fragments not found in intestinal extracts. Taken together, our data indicate that PC1/3 is essential and sufficient for the production of the intestinal incretin hormone GIP, whereas PC2, although capable of cleaving proGIP, does not participate in intestinal proGIP processing and is not found in intestinal GIP-expressing cells.

Adenoviridae↗

PubMed2006

The glucagon-like peptide-1 metabolite GLP-1-(9-36) amide reduces postprandial glycemia independently of gastric emptying and insulin secretion in humans.

Glucagon-like peptide 1 (GLP-1) lowers glycemia by modulating gastric emptying and endocrine pancreatic secretion. Rapidly after its secretion, GLP-1-(7-36) amide is degraded to the metabolite GLP-1-(9-36) amide. The effects of GLP-1-(9-36) amide in humans are less well characterized. Fourteen healthy volunteers were studied with intravenous infusion of GLP-1-(7-36) amide, GLP-1-(9-36) amide, or placebo over 390 min. After 30 min, a solid test meal was served, and gastric emptying was assessed. Blood was drawn for GLP-1 (total and intact), glucose, insulin, C-peptide, and glucagon measurements. Administration of GLP-1-(7-36) amide and GLP-1-(9-36) amide significantly raised total GLP-1 plasma levels. Plasma concentrations of intact GLP-1 increased to 21 +/- 5 pmol/l during the infusion of GLP-1-(7-36) amide but remained unchanged during GLP-1-(9-36) amide infusion [5 +/- 3 pmol/l; P < 0.001 vs. GLP-1-(7-36) amide administration]. GLP-1-(7-36) amide reduced fasting and postprandial glucose concentrations (P < 0.001) and delayed gastric emptying (P < 0.001). The GLP-1 metabolite had no influence on insulin or C-peptide concentrations. Glucagon levels were lowered by GLP-1-(7-36) amide but not by GLP-1-(9-36) amide. However, the postprandial rise in glycemia was reduced significantly (by approximately 6 mg/dl) by GLP-1-(9-36) amide (P < 0.05). In contrast, gastric emptying was completely unaffected by the GLP-1 metabolite. The GLP-1 metabolite lowers postprandial glycemia independently of changes in insulin and glucagon secretion or in the rate of gastric emptying. Most likely, this is because of direct effects on glucose disposal. However, the glucose-lowering potential of GLP-1-(9-36) amide appears to be small compared with that of intact GLP-1-(7-36) amide.

Adult↗

PubMed2006

Wheat-fibre-induced changes of postprandial peptide YY and ghrelin responses are not associated with acute alterations of satiety.

Weight gain and risk of type 2 diabetes are inversely associated with a high intake of insoluble cereal fibres. Because nutrient-induced changes of 'satiety hormones' from the gut may play a role in this process, we evaluated the effects of purified insoluble fibres on postprandial responses of plasma peptide YY (PYY), serum ghrelin and satiety as secondary outcome measures of a study investigating effects of cereal fibres on parameters of glucose metabolism. Fourteen healthy women were studied on six occasions in a randomized, single-blind, controlled crossover design. After 24 h run-in periods and 10 h overnight fasts, subjects ingested isoenergetic and macronutrient matched portions of control white bread or fibre-enriched bread (wheat-fibre or oat-fibre) at 08.15 hours. Gut hormones and hunger scores were measured for 300 min. Basal PYY and ghrelin concentrations were not different between the test meals (P>0.15). Postprandial responses of PYY and ghrelin were blunted after the intake of wheat-fibre (total area under the curve (AUC) PYY, 177.9 (SEM 8.1) (pmol/l) min; P=0.016; ghrelin 51.0 (SEM 2.5) (pmol/l) min; P=0.003), but not after oat-fibre (PYY 226.7 (SEM 25.7) (pmol/l) min; P>0.15; ghrelin 46.2 (SEM 1.6) (pmol/l) min; P=0.127), compared to control (PYY 247.5 (SEM 25.6) (pmol/l) min; ghrelin 42.5 (SEM 1.3) (pmol/l) min). Postprandial hunger scores were unaffected by the different test meals (P>0.15). Thus, oat- and wheat-fibre consumption result in different postprandial responses of PYY and ghrelin, but interestingly do not differ in satiety effects.

Avena↗

PubMed2006

Glucagon-like peptide 2 stimulates glucagon secretion, enhances lipid absorption, and inhibits gastric acid secretion in humans.

BACKGROUND & AIMS: The gut-derived peptide glucagon-like peptide 2 (GLP-2) has been suggested as a potential drug candidate for the treatment of various intestinal diseases. However, the acute effects of GLP-2 on gastric functions as well as on glucose and lipid homeostasis in humans are less well characterized. METHODS: Fifteen healthy male volunteers were studied with the intravenous infusion of GLP-2 or placebo over 120 minutes in the fasting state, and pentagastrin-stimulated gastric acid output was assessed. Another 15 healthy male volunteers were studied with a 390 minutes infusion of GLP-2 or placebo during the ingestion of a solid test meal. Gastric emptying was determined using a 13C-sodium-octanote breath test. Plasma concentrations of glucose, insulin, C-peptide, glucagon, GLP-2, free fatty acids, free glycerol, and triglycerides were determined. RESULTS: GLP-2 administration led to a marked increase in glucagon concentrations both in the fasting state and during the meal study (P < .001). Postprandial plasma concentrations of triglycerides and free fatty acids were significantly higher during GLP-2 infusion compared with placebo (P < .01), while glycerol concentrations were similar (P = .07). GLP-2 administration caused an approximately 15% reduction in pentagastrin-stimulated gastric acid and chloride secretion (P < .01), whereas gastric emptying was not affected (P = .99). CONCLUSIONS: GLP-2 reduces gastric acid secretion but does not seem to have an influence on gastric emptying. The stimulation of glucagon secretion by GLP-2 may counteract the glucagonostatic effect of GLP-1. Changes in postprandial lipid excursions seem to reflect enhanced intestinal nutrient absorption during GLP-2 administration.

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