Cholinergic enhancement by pyridostigmine increases the insulin response to glucose load in obese patients but not in normal subjects

Pyridostigmine attenuated high-fat-diet induced liver injury by the reduction of mitochondrial damage and oxidative stress via α7nAChR and M3AChR

Obesity is a major cause of nonalcohol fatty liver disease (NAFLD), which is characterized by hepatic fibrosis, lipotoxicity, inflammation, and apoptosis. Previous studies have shown that an imbalance in the autonomic nervous system is closely related to the pathogenesis of NAFLD. In this study, we investigated the effects of pyridostigmine (PYR), a cholinesterase (AChE) inhibitor, on HFD-induced liver injury and explored the potential mechanisms involving mitochondrial damage and oxidative stress. A murine model of HFD-induced obesity was established using the C57BL/6 mice, and PYR (3 mg/kg/d) or placebo was administered for 20 weeks. PYR reduced the body weight and liver weight of the HFD-fed mice. Additionally, the serum levels of IL-6, TNF-α, cholesterol, and triglyceride were significantly lower in the PYR-treated versus the untreated mice, corresponding to a decrease in hepatic fibrosis, lipid accumulation, and apoptosis in the former. Furthermore, the mitochondrial morphology improved significantly in the PYR-treated group. Consistently, PYR upregulated ATP production and the mRNA level of the mitochondrial dynamic factors OPA1, Drp1 and Fis1, and the mitochondrial unfolded protein response (UPRmt) factors LONP1 and HSP60. Moreover, PYR treatment activated the Keap1/Nrf2 pathway and upregulated HO-1 and NQO-1, which mitigated oxidative injury as indicated by decreased 8-OHDG, MDA and H2 O2 levels, and increased SOD activity. Finally, PYR elevated acetylcholine (ACh) levels by inhibiting AChE, and upregulated the α7nAChR and M3AChR proteins in the HFD-fed mice. PYR alleviated obesity-induced hepatic injury in mice by mitigating mitochondrial damage and oxidative stress via α7nAChR and M3AChR.

Association between initial in-hospital heart rate and glycemic control in patients with acute ischemic stroke and diabetes mellitus

BACKGROUND

A high resting heart rate (HR) has been associated with an increased risk of diabetes mellitus. This study explored the association between initial in-hospital HR and glycemic control in patients with acute ischemic stroke (AIS) and diabetes mellitus.

METHODS

We analyzed data from 4,715 patients with AIS and type 2 diabetes mellitus enrolled in the Chang Gung Research Database between January 2010 and September 2018. The study outcome was unfavorable glycemic control, defined as glycated hemoglobin (HbA1c) ≥ 7%. In statistical analyses, the mean initial in-hospital HR was used as both a continuous and categorical variable. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated using multivariable logistic regression analysis. The associations between the HR subgroups and HbA1c levels were analyzed using a generalized linear model.

RESULTS

Compared with the reference group (HR < 60 bpm), the adjusted ORs for unfavorable glycemic control were 1.093 (95% CI 0.786-1.519) for an HR of 60-69 bpm, 1.370 (95% CI 0.991-1.892) for an HR of 70-79 bpm, and 1.608 (95% CI 1.145-2.257) for an HR of ≥ 80 bpm. Even after adjusting for possible confounders, the HbA1c levels after admission and discharge among diabetic stroke patients increased significantly in the subgroups with higher HRs (p < 0.001).

CONCLUSIONS

High initial in-hospital HR is associated with unfavorable glycemic control in patients with AIS and diabetes mellitus, particularly in those with an HR of ≥ 80 bpm, compared with those with an HR of < 60 bpm.

Persistent exercise fatigue and associative learning deficits in combination with transient glucose dyshomeostasis in a GWI mouse model

Aims:

To characterize exercise fatigue, metabolic phenotype and cognitive and mood deficits correlated with brain neuroinflammatory and gut microbiome changes in a chronic Gulf War Illness (GWI) mouse model. The latter have been described in an accompanying paper [1].

Main methods:

Adult male C57Bl/6N mice were exposed for 28 days (5 days/week) to pyridostigmine bromide: 6.5 mg/kg, b.i.d., P.O. (GW1) or 8.7 mg/kg, q.d., P.O. (GW2); topical permethrin (1.3 mg/kg in 100% DMSO) and N,N-diethyl-meta-toluamide (DEET 33% in 70% EtOH) and restraint stress (5 min). Exercise, metabolic and behavioral endpoints were compared to sham stress control (CON/S).

Key findings:

Relative to CON/S, GW2 presented persistent exercise intolerance (through post-treatment (PT) day 161), deficient associative learning/memory, and transient insulin insensitivity. In contrast to GW2, GW1 showed deficient long-term object recognition memory, milder associative learning/memory deficit, and behavioral despair.

Significance:

Our findings demonstrate that GW chemicals dose-dependently determine the presentation of exercise fatigue and severity/type of cognitive/mood-deficient phenotypes that show persistence. Our comprehensive mouse model of GWI recapitulates the major multiple symptom domains characterizing GWI, including fatigue and cognitive impairment that can be used to more efficiently develop diagnostic tests and curative treatments for ill Gulf War veterans.

The Local Paracrine Actions of the Pancreatic α-Cell

Secretion of glucagon from the pancreatic α-cells is conventionally seen as the first and most important defense against hypoglycemia. Recent findings, however, show that α-cell signals stimulate insulin secretion from the neighboring β-cell. This article focuses on these seemingly counterintuitive local actions of α-cells and describes how they impact islet biology and glucose metabolism. It is mostly based on studies published in the last decade on the physiology of α-cells in human islets and incorporates results from rodents where appropriate. As this and the accompanying articles show, the emerging picture of α-cell function is one of increased complexity that needs to be considered when developing new therapies aimed at promoting islet function in the context of diabetes.

Altered autonomic inputs as a cause of pancreatic β-cell amyloid

A partial loss of β-cell mass and β-cell dysfunction in Type 2 Diabetes Mellitus (T2DM) is associated with amyloid deposition but whether it is causal or consequential is debated. Although the in vitro polymerization of amylin has been studied in detail, the exact trigger for the mechanism in vivo has not been identified. One suggestion is that an increased load on β-cells results in inefficient handling of proteins leading to misfolding and aggregation, but this hypothesis is faced with certain paradoxes. We suggest an alternative mechanism based on the assumption that polymerization is a spontaneous process. The concentration of the polypeptide in β-cell granules is shown to be sufficient to allow polymerization. However if the rate of turnover in normal cells is greater than the rate of polymerization, amyloid deposition will not be observed. If this is true, it follows that amyloid deposition could be a result of increased retention time of amylin in the β-cell granules. In T2D, the sympathetic inputs are known to increase which could result in suppression of the secretion process. The increase in the retention time due to this suppression can allow polymerization. In addition to this in a prediabetic state parasympathetic stimulation increases β-cell proliferation. This reduces the insulin demand per cell thereby increasing the mean retention time. Thus a combination of contrasting actions of sympathetic and parasympathetic systems could lead to increase in the amyloid deposition. We suggest testable predictions of the alternative hypotheses and the lines of research needed to test them.

Nogo-A downregulation improves insulin secretion in mice

Type 2 diabetes (T2D) is characterized by β-cell dysfunction and the subsequent depletion of insulin production, usually in a context of increased peripheral insulin resistance. T2D patients are routinely treated with oral antidiabetic agents such as sulfonylureas or dipeptidyl peptidase-4 antagonists, which promote glucose- and incretin-dependent insulin secretion, respectively. Interestingly, insulin secretion may also be induced by neural stimulation. Here we report the expression of Nogo-A in β-cells. Nogo-A is a membrane protein that inhibits neurite outgrowth and cell migration in the central nervous system. We observed that Nogo-A-deficient mice display improved insulin secretion and glucose clearance. This was associated with a stronger parasympathetic input and higher sensitivity of β-cells to the cholinergic analog carbachol. Insulin secretion was also improved in diabetic db/db mice treated with neutralizing antibody against Nogo-A. Together, these findings suggest that promoting the vagal stimulation of insulin secretion through the selective inhibition of Nogo-A could be a novel therapeutic approach in T2D.

Changes in food intake, metabolic parameters and insulin resistance are induced by an isoenergetic, medium-chain fatty acid diet and are associated with modifications in insulin signalling in isolated rat pancreatic islets

Long-chain fatty acids are capable of inducing alterations in the homoeostasis of glucose-stimulated insulin secretion (GSIS), but the effect of medium-chain fatty acids (MCFA) is poorly elucidated. In the present study, we fed a normoenergetic MCFA diet to male rats from the age of 1 month to the age of 4 months in order to analyse the effect of MCFA on body growth, insulin sensitivity and GSIS. The 45% MCFA substitution of whole fatty acids in the normoenergetic diet impaired whole body growth and resulted in increased body adiposity and hyperinsulinaemia, and reduced insulin-mediated glucose uptake in skeletal muscle. In addition, the isolated pancreatic islets from the MCFA-fed rats showed impaired GSIS and reduced protein kinase Ba (AKT1) protein expression and extracellular signal-related kinase isoforms 1 and 2 (ERK(1/2)) phosphorylation, which were accompanied by increased cellular death. Furthermore, there was a mildly increased cholinergic sensitivity to GSIS. We discuss these findings in further detail, and advocate that they might have a role in the mechanistic pathway leading to the compensatory hyperinsulinaemic status found in this animal model.

Enhanced cholinergic response in pancreata of nonhuman primates with impaired glucose tolerance shown on [18F]fluorobenzyltrozamicol positron emission tomography

BACKGROUND

Islet cell adaptation to insulin resistance in type 2 diabetes mellitus may be due in part to increased stimulation of beta cells by the autonomic nervous system. The parasympathetic neurotransmitter acetylcholine (ACh) mediates insulin release via M3 muscarinic receptors on islet beta cells. The vesicular ACh transporter (VAChT) receptor correlates with cholinergic activity in vivo. The positron emission tomography (PET) radiotracer (+)-4-[18F]fluorobenzyltrozamicol ([18F]FBT) binds to the VAChT receptor on presynaptic cholinergic neurons and can be quantified by PET. In this study, we utilize [18F]FBT PET to demonstrate pancreatic cholinergic activity before and after dextrose infusion in nonhuman primates with normal (NGT) and impaired (IGT) glucose tolerance.

METHODS

Seven adult female vervet (Chlorocebus aethiops) monkeys were maintained on an atherogenic Western diet. They were divided into two groups: four with NGT and three with IGT. Each subject underwent [18F]FBT PET twice: first, a baseline PET under fasting conditions; and second, PET under fasting conditions but after intravenous infusion of dextrose solution. Quantitative analysis of pancreatic uptake at 60 min post-injection was performed.

RESULTS

There was no difference in pancreatic uptake of [18F]FBT on baseline scans between the two groups. Pancreatic uptake of [18F]FBT increased in every subject after dextrose infusion (P = 0.03). On post-dextrose PET scans, pancreatic uptake of [18F]FBT was significantly higher in IGT subjects compared with NGT subjects (P = 0.03). The post-dextrose to pre-dextrose uptake ratios were higher in IGT subjects (P = 0.08).

CONCLUSIONS

Acute increases in pancreatic cholinergic activity in vivo were detected in the pancreata of nonhuman primates with NGT and IGT after intravenous dextrose infusion on [18F]FBT PET. In subjects with IGT, this activity was significantly higher, suggesting increased autonomic nervous system stimulation of the pancreatic islets in insulin-resistant subjects.

Muscarinic M2 receptor is active on pancreatic islets from hypothalamic obese rat

Hypothalamic obese rats, obtained by neonatal treatment with monosodium L-glutamate (MSG), are hyperinsulinemic, and secrete more insulin than lean ones do when stimulated by glucose, while acetylcholine insulinotropic effect decreases. The effect of acetylcholine on glucose-induced insulin secretion is attributed to muscarinic receptors of pancreatic beta cells, mainly to M(3) subtype. However, it has been observed that activation of M(2) or M(4) subtypes causes inhibition of glucose-induced insulin secretion in insulin secreting cell line. Insulin secretion was measured, stimulated by glucose in the presence of acetylcholine plus methoctramine, a muscarinic M(2) antagonist, on pancreatic islets isolated from MSG-obese and lean rats to investigate whether impairment of acetylcholine insulinotropic effect on pancreatic islets from MSG-obese rats has any relationship with muscarinic M(2) receptor function in beta cells. Insulin secretion stimulated by 8.3 mM glucose was higher in islets from obese rats than from lean ones. Insulinotropic effect of acetylcholine was reported in islets of both animals, albeit less than in obese ones. Blockage of muscarinic M(2) receptor, using methoctramine at 1; 5 and 10 microM, increased acetylcholine secretory response in islets of obese rats, while no effect has been observed in lean ones. Results demonstrate that muscarinic M(2) receptors are functioning in pancreatic islets of MSG-obese rats. The inhibitory action of muscarinic M(2) receptor may be a mechanism by which acetylcholine discloses weak insulinotropic effect in MSG-obese rats.

Islet beta cell failure in type 2 diabetes

The major focus of this Review is on the mechanisms of islet beta cell failure in the pathogenesis of obesity-associated type 2 diabetes (T2D). As this demise occurs within the context of beta cell compensation for insulin resistance, consideration is also given to the mechanisms involved in the compensation process, including mechanisms for expansion of beta cell mass and for enhanced beta cell performance. The importance of genetic, intrauterine, and environmental factors in the determination of "susceptible" islets and overall risk for T2D is reviewed. The likely mechanisms of beta cell failure are discussed within the two broad categories: those with initiation and those with progression roles.

Parasympathetic innervation and function of endocrine pancreas requires the glial cell line-derived factor family receptor alpha2 (GFRalpha2)

Vagal parasympathetic input to the islets of Langerhans is a regulator of islet hormone secretion, but factors promoting parasympathetic islet innervation are unknown. Neurturin signaling via glial cell line-derived neurotrophic factor family receptor alpha2 (GFRalpha2) has been demonstrated to be essential for the development of subsets of parasympathetic and enteric neurons. Here, we show that the parasympathetic nerve fibers and glial cells within and around the islets express GFRalpha2 and that islet parasympathetic innervation in GFRalpha2 knockout (KO) mice is reduced profoundly. In wild-type mice, neuroglucopenic stress produced a robust increase in plasma levels of islet hormones. In the GFRalpha2-KO mice, however, pancreatic polypeptide and insulin responses were completely lost and glucagon response was markedly impaired. Islet morphology and sympathetic innervation, as well as basal secretions of the islet hormones, were unaffected. Moreover, a glucose tolerance test failed to reveal differences between the genotypes, indicating that direct glucose-stimulated insulin secretion was not affected by GFRalpha2 deficiency. These results show that GFRalpha2 signaling is needed for development of the parasympathetic islet innervation that is critical for vagally induced hormone secretion. The GFRalpha2-KO mouse represents a useful model to study the role of parasympathetic innervation of the endocrine pancreas in glucose homeostasis.

Islet adaptation to insulin resistance: mechanisms and implications for intervention

Insulin sensitivity and insulin secretion are reciprocally related such that insulin resistance is adapted by increased insulin secretion to maintain normal glucose and lipid homeostasis. The relation between insulin sensitivity and secretion is curvilinear and mathematically best described as a hyperbolic relation. Several potential mediators have been suggested to be signals for the beta cells to respond to insulin resistance such as glucose, free fatty acids, autonomic nerves, fat-derived hormones and the gut hormone glucagon-like peptide-1 (GLP-1). Failure of these signals or of the pancreatic beta cells to adequately adapt insulin secretion in relation to insulin sensitivity results in inappropriate insulin levels, impaired glucose intolerance (IGT) and type 2 diabetes. Therefore, treatment of IGT and type 2 diabetes should aim at restoring the normal relation between insulin sensitivity and secretion. Such treatment includes stimulation of insulin secretion (sulphonylureas, repaglinide and nateglinide) and insulin sensitivity (metformin and thiazolidinediones), as well as treatment aimed at supporting the signals mediating the islet adaptation (cholinergic agonists and GLP-1). Both, for correct understanding of diabetes pathophysiology and for development of novel treatment modalities, therefore, the non-linear inverse relation between insulin sensitivity and secretion needs to be acknowledged.

Parasympathetic blockade attenuates augmented pancreatic polypeptide but not insulin secretion in Pima Indians

There is evidence from animal models of obesity and type 2 diabetes that increased parasympathetic vagal input to the pancreas contributes to hyperinsulinemia. Compared with Caucasians, Pima Indians have a high risk of type 2 diabetes and exhibit marked hyperinsulinemia and elevated plasma levels of pancreatic polypeptide (PP), an islet hormone considered a surrogate marker of parasympathetic nervous system (PNS) drive to the pancreas. To test if hyperinsulinemia in Pima Indians is due to increased vagal input to the beta-cell, we examined the effect of PNS blockade in 17 Caucasian (aged 35 +/- 8 years, body fat 23 +/- 7% [mean +/- SD]) and 17 Pima Indian males (aged 28 +/- 8 years, body fat 29 +/- 5%) with normal glucose tolerance. Each participant underwent four consecutive standardized liquid meal tests (64% carbohydrate, 22% fat, and 14% protein) during which a primed infusion of atropine was administered for 120 min at the following doses: 0, 2.5, 5, and 10 micro g. kg fat-free mass (FFM)(-1). h(-1). Areas under the curve for early (AUC(0-30 min)) and total (AUC(0-120 min)) postprandial insulin and PP secretory responses were calculated. Early postprandial insulin and PP secretory responses were higher in Pima Indians compared with those of Caucasians (both P = 0.01). Secretion of insulin and PP was inhibited by atropine (both P < 0.001). Increasing doses of atropine attenuated the ethnic difference in PP (P = 0.01) but not in early insulin secretory responses (P = 0.6), an effect that was not due to differences in gastric emptying rate (acetaminophen test) and/or circulating glucose. Similar results were observed for total secretory responses. These results confirm that compared with Caucasians, Pima Indians have an exaggerated PNS drive to pancreatic F-cells that secrete PP. However, the hyperinsulinemia of this population does not appear to be due to increased vagal input to pancreatic beta-cells.

Development and validation of a liquid chromatography-tandem mass spectrometry method for the determination of pyridostigmine bromide from guinea pig plasma

An HPLC/MS/MS method was validated for the low level analysis of pyridostigmine bromide (PB) from guinea pig plasma. An advantage of this strong-cation exchange HPLC/MS/MS method was the enhancement of the ESI-MS signal by providing good retention and good peak shape of PB with a mobile phase of 70% acetonitrile. In addition, the use of 70% acetonitrile in the mobile phase allowed the direct injection of the supernant from the protein precipitated extracted sample. The assay was linear from the range of 0.1 to 50 ng/ml using only 25 microl of sample. The precision and accuracy of the assay was better than 9.1 and 113%, respectively.

Pharmacological agents that directly modulate insulin secretion

Blood glucose levels are sensed and controlled by the release of hormones from the islets of Langerhans in the pancreas. The beta-cell, the insulin-secreting cell in the islet, can detect subtle increases in circulating glucose levels and a cascade of molecular events spanning the initial depolarization of the beta-cell membrane culminates in exocytosis and optimal insulin secretion. Here we review these processes in the context of pharmacological agents that have been shown to directly interact with any stage of insulin secretion. Drugs that modulate insulin secretion do so by opening the K(ATP) channels, by interacting with cell-surface receptors, by altering second-messenger responses, by disrupting the beta-cell cytoskeletal framework, by influencing the molecular reactions at the stages of transcription and translation of insulin, and/or by perturbing exocytosis of the insulin secretory vesicles. Drugs acting primarily at the K(ATP) channels are the sulfonylureas, the benzoic acid derivatives, the imidazolines, and the quinolines, which are channel openers, and finally diazoxide, which closes these channels. Methylxanthines also work at the cell membrane level by antagonizing the purinergic receptors and thus increase insulin secretion. Other drugs have effects at multiple levels, such as the calcineurin inhibitors and somatostatin. Some drugs used extensively in research, e.g., colchicine, which is used to study vesicular transport, have no effect at the pharmacological doses used in clinical practice. We also briefly discuss those drugs that have been shown to disrupt beta-cell function in a clinical setting but for which there is scant information on their mechanism of action.

Mechanisms and physiological significance of the cholinergic control of pancreatic beta-cell function

Acetylcholine (ACh), the major parasympathetic neurotransmitter, is released by intrapancreatic nerve endings during the preabsorptive and absorptive phases of feeding. In beta-cells, ACh binds to muscarinic M(3) receptors and exerts complex effects, which culminate in an increase of glucose (nutrient)-induced insulin secretion. Activation of PLC generates diacylglycerol. Activation of PLA(2) produces arachidonic acid and lysophosphatidylcholine. These phospholipid-derived messengers, particularly diacylglycerol, activate PKC, thereby increasing the efficiency of free cytosolic Ca(2+) concentration ([Ca(2+)](c)) on exocytosis of insulin granules. IP3, also produced by PLC, causes a rapid elevation of [Ca(2+)](c) by mobilizing Ca(2+) from the endoplasmic reticulum; the resulting fall in Ca(2+) in the organelle produces a small capacitative Ca(2+) entry. ACh also depolarizes the plasma membrane of beta-cells by a Na(+)- dependent mechanism. When the plasma membrane is already depolarized by secretagogues such as glucose, this additional depolarization induces a sustained increase in [Ca(2+)](c). Surprisingly, ACh can also inhibit voltage-dependent Ca(2+) channels and stimulate Ca(2+) efflux when [Ca(2+)](c) is elevated. However, under physiological conditions, the net effect of ACh on [Ca(2+)](c) is always positive. The insulinotropic effect of ACh results from two mechanisms: one involves a rise in [Ca(2+)](c) and the other involves a marked, PKC-mediated increase in the efficiency of Ca(2+) on exocytosis. The paper also discusses the mechanisms explaining the glucose dependence of the effects of ACh on insulin release.

Carbachol restores insulin release in diabetic GK rat islets by mechanisms largely involving hydrolysis of diacylglycerol and direct interaction with the exocytotic machinery

In several models of insulin resistance, cholinergically induced insulin secretion is augmented. We studied here whether this also is present in the spontaneously diabetic GK (Goto-Kakizaki) rat pancreas. Using carbachol (50 micromol/L), enhanced insulin release was elicited in perfused pancreas under normal or depolarized conditions in GK compared with control rats at 3.3 mmol/L glucose (p < 0.03). Carbachol fully normalized insulin secretion in GK rats at 16.7 mmol/L glucose through an effect abolished by atropine. Similarly, direct stimulation of protein kinase C (PKC) with the DAG-permeable compound 1-oleoyl-2-acetyl-sn-glycerol (OAG, 300 micromol/L) induced more pronounced insulin release in GK islets than in control islets. The diacylglycerol (DAG) lipase inhibitor RHC-80267 (35 micromol/L) significantly reduced carbachol effects in control and GK islets, but had no effect on OAG-induced insulin release. The enhanced insulinotropic effects of carbachol in GK islets was not accompanied by increased cyclic adenosine monophosphate (cAMP) or arachidonic acid (AA) formation in GK when compared with control islets. In conclusion, cholinergic stimulation induced enhanced insulin release in diabetic GK islets. This is largely mediated through mechanisms involving hydrolysis of DAG to AA and interaction with exocytotic steps of insulin release.

Increased insulin secretion and normalization of glucose tolerance by cholinergic agonism in high fat-fed mice

Increased insulinotropic activity by the cholinergic agonist carbachol exists in insulin-resistant high fat-fed C57BL/6J mice. We examined the efficiency and potency of carbachol to potentiate glucose-stimulated insulin secretion and to improve glucose tolerance in these animals. Intravenous administration of carbachol (at 15 and 50 nmol/kg) markedly potentiated glucose (1 g/kg)-stimulated insulin secretion in mice fed both a control and a high-fat diet (for 12 wk), with a higher relative potentiation in high fat-fed mice measured as increased (1-5 min) acute insulin response and area under the 50-min insulin curve. Concomitantly, glucose tolerance was improved by carbachol. In fact, carbachol normalized glucose-stimulated insulin secretion and glucose tolerance in mice subjected to a high-fat diet. Carbachol (>100 nmol/l) also potentiated glucose-stimulated insulin secretion from isolated islets with higher efficiency in high fat-fed mice. In contrast, binding of the muscarinic receptor antagonist [N-methyl-(3)H]scopolamine to islet muscarinic receptors and the contractile action of carbachol on ileum muscle strips were not different between the two groups. We conclude that carbachol normalizes glucose tolerance in insulin resistance.

Early phase insulin infusion and muscarinic blockade in obese and lean subjects

The effect of early phase insulin on postprandial levels of insulin, C-peptide, glucose, and glucagon was investigated in lean (n = 10) and obese (n = 12) subjects. Subjects underwent four conditions during ingestion of a meal (600 kcal): 1) saline infusion; 2) 10-min insulin infusion simultaneously with meal ingestion (0.24 U bolus, 15 mU. m(-2). min(-1)); 3) atropine infusion (0.4 mg/m(2) bolus, 0.4 mg. m(-2). h for 4 h); 4) insulin and atropine infusion. Blood samples were taken for 3.5 h. Insulin infusion had no effect on postprandial insulin levels in either population but significantly reduced postprandial glucose in the obese subjects (P < 0.05). Obese subjects with elevated postprandial glucose levels in the presence of muscarinic blockade exhibited a decline in glucose with insulin supplementation. Atropine reduced postprandial insulin levels in both groups, with a greater attenuation in the obese (P < 0.01), but postprandial glucose levels were also significantly reduced, suggesting that atropine inhibited gastric emptying. Thus the effects of muscarinic blockade on postprandial insulin levels cannot be evaluated. These data suggest that insulin supplementation during the preabsorptive time period may contribute to glucoregulation in the obese population.

Muscarinic blockade inhibits gastric emptying of mixed-nutrient meal: effects of weight and gender

We compared the vagal contribution to gastric emptying in lean and obese subjects by monitoring gastric emptying of a meal during muscarinic blockade. Lean (n = 6) and obese subjects (n = 6) underwent two treatments: 1) saline infusion and 2) atropine infusion [0.4 mg/m2 bolus, 0.4 mg. (m2)-1. h-1] for 2 h, initiated 30 min before ingestion of a 600-kcal breakfast (64% carbohydrate, 23% fat, 13% protein) composed of orange juice (labeled with Indium-111), egg sandwich (labeled with Technetium-99m), cereal, milk, and banana. Anterior and posterior images were taken every 90 s for 90 min using a dual-headed camera. Atropine significantly delayed emptying of both solid (P < 0.007) and liquid (P < 0.002). Obese subjects exhibited a greater delay in liquid emptying during muscarinic blockade compared with lean subjects (P < 0.02). Female subjects exhibited a slower rate of gastric emptying and were less sensitive to atropine. These data suggest that obese subjects exhibit altered gastric cholinergic activity compared with lean subjects and that gender differences in gastric emptying rate may be due to differences in autonomic tone.

Potentiated beta-cell response to non-glucose stimuli in insulin-resistant C57BL/6J mice

Insulin secretion in response to acetylcholine receptor activation by carbachol in insulin resistance induced by 12 weeks of high-fat diet in C57BL/6J mice is exaggerated. To study whether this persists after a longer period of time and also involves other non-glucose stimuli, we fed C57BL/6J mice a high-fat diet for 24 weeks. Both hyperinsulinemia (341 +/- 33 vs. 148 +/- 15 pmol/l) and slight hyperglycemia (7.8 +/- 0.2 vs. 6.1 +/- 0.1 mmol/l) were evident at this time point. The insulinotropic response to high dose carbachol (0.53 micromol/kg; 3403 +/- 377 vs. 1595 +/- 429 pmol/l), to the glucose analogue, 2-deoxyglucose (6 mmol/kg; 2014 +/- 315 vs. 1167 +/- 200 pmol/l), to cholecystokinin-8 (15.9 nmol/kg; 499 +/- 93 vs. 119 +/- 40 pmol/l) and to glucagon-like peptide-1 (32 nmol/kg; 307 +/- 86 vs. 71 +/- 9 pmol/l), were all exaggerated in mice given high-fat diet. In contrast, the insulin response to glucose was impaired. This shows that insulin resistance is accompanied by a general islet supersensitivity to non-glucose stimuli, which persists over a long period of time.