Pancreatic polypeptide: a unique model for vagal control of endocrine systems

Pancreatic polypeptide revisited: Potential therapeutic effects in obesity-diabetes

Pancreatic polypeptide (PP), a member of the neuropeptide Y (NPY) family of peptides, is a hormone secreted from the endocrine pancreas with established actions on appetite regulation. Thus, through activation of hypothalamic neuropeptide Y4 (NPY4R or Y4) receptors PP induces satiety in animals and humans, suggesting potential anti-obesity actions. In addition, despite being actively secreted from pancreatic islets and evidence of local Y4 receptor expression, PP mediated effects on the endocrine pancreas have not been fully elucidated. To date, it appears that PP possesses an acute insulinostatic effect, similar to the impact of other peptides from the NPY family. However, it is interesting that prolonged activation of pancreatic Y1 receptors leads to established benefits on beta-cell turnover, preservation of beta-cell identity and improved insulin secretory responsiveness. This may hint towards possible similar anti-diabetic actions of sustained Y4 receptor modulation, since the Y1 and Y4 receptors trigger comparable cell signalling pathways. In terms of exploiting the prospective therapeutic promise of PP, this is severely restricted by a short circulating half-life as is the case for many regulatory peptide hormones. It follows that long-acting, enzyme resistant, forms of PP will be required to determine viability of the Y4 receptor as an anti-obesity and -diabetes drug target. The current review aims to refocus interest on the biology of PP and highlight opportunities for therapeutic development.

Impaired glucose tolerance is associated with enhanced postprandial pancreatic polypeptide secretion

BACKGROUND

The purpose of this study is to compare serum pancreatic polypeptide (PP), insulin, C-peptide, and glucagon in different glucose tolerance stages; analyze the influencing factors of PP secretion; and further explore the role of PP in the pathogenesis of diabetes mellitus.

METHODS

Data were collected from 100 subjects from hospital. According to the results of oral glucose tolerance test (OGTT), the subjects were divided into a normal glucose tolerance (NGT) group, an impaired glucose regulation (IGR) group, and a newly diagnosed type 2 diabetes mellitus (T2DM) group. PP and the related parameters were measured, and the area under the curve (AUC) 120 min after OGTT was calculated. AUC_pp (AUC of PP) was used as the dependent variable and the potentially influencing factors were used as the independent variable for multiple linear regression analysis.

RESULTS

Postprandial 60 min PP in the IGR group was higher than those in the NGT group (2973.80 [±547.49] pg·h/mL vs 2663.55 [±594.89] pg·h/mL, p < 0.05). AUC_pp was significantly higher in the IGR group (428.76 pg·h/mL, 95% confidence interval [CI] [41.06 -816.46], p = 0.031) and newly diagnosed T2DM group (404.35 pg·h/mL, 95% CI [5.37-803.33], p = 0.047) than in the NGT group. AUC_pp was negatively correlated with body mass index (BMI) (r = -0.235, p = 0.038) and positively correlated with postprandial 60 min blood glucose (r = 0.370, p = 0.001) and AUC_bg (AUC of blood glucose) (r = 0.323, p = 0.007). Multiple linear regression analysis indicated that there was a linear correlation between BMI, AUC_bg , and AUC_pp (p = 0.004, p = 0.001), and the regression equation was calculated as: AUC_pp  = 6592.272 + 86.275 × AUC_bg -95.291 × BMI (R²  = 12.7%, p < 0.05).

CONCLUSIONS

Compared with NGT subjects, IGR and T2DM patients have an enhanced postprandial PP secretion. In T2DMs, the secretion of PP is mainly affected by BMI and blood glucose.

Urinary Dopamine Excretion Rate Decreases during Acute Dietary Protein Deprivation and Is Associated with Increased Plasma Pancreatic Polypeptide Concentration

Background: Dopamine, a key neurotransmitter in the autonomic nervous system participating in the homeostatic balance between sympathetic and parasympathetic divisions, is involved in food intake regulation. Objective: We investigated whether dopamine is altered by acute fasting or overfeeding diets with varying macronutrient content. Design: Ninety-nine healthy subjects underwent 24-h dietary interventions including eucaloric feeding, fasting, and five different overfeeding diets in a crossover design. Overfeeding diets (200% of eucaloric requirements) included one diet with 3%-protein (low-protein high-fat overfeeding-LPF: 46%-fat), three diets with 20%-protein, and a diet with 30%-protein (44%-fat). Urine was collected for 24 h and urinary dopamine concentration was quantified by high-performance liquid chromatography. Plasma pancreatic polypeptide (PP) concentration, an indirect marker of parasympathetic activity, was measured prior to and after each diet after an overnight fast. Results: During 24-h of fasting, dopamine decreased on average by ~14% compared to eucaloric conditions, whereas PP increased by two-fold (both p < 0.001). Lower dopamine during 24-h fasting correlated with increased PP (r = -0.40, p < 0.001). Similarly, on average urinary dopamine decreased during LPF by 14% (p < 0.001) and lower dopamine correlated with increased PP (r = -0.31, p = 0.01). No changes in dopamine and PP concentrations were observed during other overfeeding diets (all p > 0.05). Conclusions: Dopamine concentrations decrease during short-term fasting and overfeeding with a low-protein diet. As both dietary conditions have in common protein deficit, the correlation between dopamine and PP suggests a compensatory mechanism underlying the shift from sympathetic to parasympathetic drive during dietary protein deprivation.

Assessment of Gastrointestinal Autonomic Dysfunction: Present and Future Perspectives

The autonomic nervous system delicately regulates the function of several target organs, including the gastrointestinal tract. Thus, nerve lesions or other nerve pathologies may cause autonomic dysfunction (AD). Some of the most common causes of AD are diabetes mellitus and α-synucleinopathies such as Parkinson’s disease. Widespread dysmotility throughout the gastrointestinal tract is a common finding in AD, but no commercially available method exists for direct verification of enteric dysfunction. Thus, assessing segmental enteric physiological function is recommended to aid diagnostics and guide treatment. Several established assessment methods exist, but disadvantages such as lack of standardization, exposure to radiation, advanced data interpretation, or high cost, limit their utility. Emerging methods, including high-resolution colonic manometry, 3D-transit, advanced imaging methods, analysis of gut biopsies, and microbiota, may all assist in the evaluation of gastroenteropathy related to AD. This review provides an overview of established and emerging assessment methods of physiological function within the gut and assessment methods of autonomic neuropathy outside the gut, especially in regards to clinical performance, strengths, and limitations for each method.

Neuroendocrine Response to Exogenous Ghrelin Administration, Combined With Alcohol, in Heavy-Drinking Individuals: Findings From a Randomized, Double-Blind, Placebo-Controlled Human Laboratory Study

BACKGROUND

Accumulating evidence has established a role for the orexigenic hormone ghrelin in alcohol-seeking behaviors. Accordingly, the ghrelin system may represent a potential pharmacotherapeutic target for alcohol use disorder. Ghrelin modulates several neuroendocrine pathways, such as appetitive, metabolic, and stress-related hormones, which are particularly relevant in the context of alcohol use. The goal of the present study was to provide a comprehensive assessment of neuroendocrine response to exogenous ghrelin administration, combined with alcohol, in heavy-drinking individuals.

METHODS

This was a randomized, crossover, double-blind, placebo-controlled human laboratory study, which included 2 experimental alcohol administration paradigms: i.v. alcohol self-administration and i.v. alcohol clamp. Each paradigm consisted of 2 counterbalanced sessions of i.v. ghrelin or placebo administration. Repeated blood samples were collected during each session, and peripheral concentrations of the following hormones were measured: leptin, glucagon-like peptide-1, pancreatic polypeptide, gastric inhibitory peptide, insulin, insulin-like growth factor-1, cortisol, prolactin, and aldosterone.

RESULTS

Despite some statistical differences, findings were consistent across the 2 alcohol administration paradigms: i.v. ghrelin, compared to placebo, increased blood concentrations of glucagon-like peptide-1, pancreatic polypeptide, cortisol, and prolactin, both acutely and during the whole session. Lower levels of leptin and higher levels of aldosterone were also found during the ghrelin vs placebo session.

CONCLUSION

These findings, gathered from a clinically relevant sample of heavy-drinking individuals with alcohol use disorder, provide a deeper insight into the complex interplay between ghrelin and appetitive, metabolic, and stress-related neuroendocrine pathways in the context of alcohol use.

Cellular and systemic mechanisms for glucose sensing and homeostasis

Glucose is a major source of energy in animals. Maintaining blood glucose levels within a physiological range is important for facilitating glucose uptake by cells, as required for optimal functioning. Glucose homeostasis relies on multiple glucose-sensing cells in the body that constantly monitor blood glucose levels and respond accordingly to adjust its glycemia. These include not only pancreatic β-cells and α-cells that secrete insulin and glucagon, but also central and peripheral neurons regulating pancreatic endocrine function. Different types of cells respond distinctively to changes in blood glucose levels, and the mechanisms involved in glucose sensing are diverse. Notably, recent studies have challenged the currently held views regarding glucose-sensing mechanisms. Furthermore, peripheral and central glucose-sensing cells appear to work in concert to control blood glucose level and maintain glucose and energy homeostasis in organisms. In this review, we summarize the established concepts and recent advances in the understanding of cellular and systemic mechanisms that regulate glucose sensing and its homeostasis.

Effects of electroacupuncture on stress-induced gastric dysrhythmia and mechanisms involving autonomic and central nervous systems in functional dyspepsia

Electroacupuncture (EA) is widely used as an effective method to treat stress-related disorders. However, its mechanisms remain largely unknown. The aim of this study was to investigate the effects and mechanisms of EA on gastric slow wave (GSW) dysrhythmia and c-Fos expression in the nucleus of the solitary tract (NTS) induced by stress in a rodent model of functional dyspepsia (FD). Rats in the neonatal stage were treated using intragastric iodoacetamide. Eight weeks later, the rats were implanted with electrodes in the stomach for the measurement of GSW and electrodes into accupoints ST36 for EA. Autonomic functions were assessed by spectral analysis of heart rate variability. Rats were placed for 30 min in a cylindrical plastic tube for acute restraint stress. The involvement of a central afferent pathway was assessed by measuring c-Fos-immunoreactive cells in the NTS. 1) EA normalized restraint stress-induced impairment of GSW in FD rats. 2) EA significantly increased vagal activity (P = 0.002) and improved sympathovagal balance (P = 0.004) under stress in FD rats. 3) In FD rats under restraint stress, plasma norepinephrine concentration was increased substantially (P < 0.01), which was suppressed with EA. 4) The EA group showed increased c-Fos-positive cell counts in the NTS compared with the sham EA group (P < 0.05) in FD rats. Acute restraint stress induces gastric dysrhythmia in a rodent model of FD. EA at ST36 improves GSW under stress in FD rats mediated via the central and autonomic pathways, involving the NTS and vagal efferent pathway.

Glucose-Dependent Insulinotropic Polypeptide Is a Pancreatic Polypeptide Secretagogue in Humans

BACKGROUND

Glucose-dependent insulinotropic polypeptide (GIP) has been suggested to stimulate the secretion of pancreatic polypeptide (PP), an islet hormone thought to regulate gut motility, appetite, and glycemia.

OBJECTIVE

To determine whether human GIP1-42 (hGIP) stimulates PP secretion.

METHOD

As glycemia modulates the secretion of PP, we measured plasma PP concentrations from 2 studies in healthy men (n = 10) and in patients with type 2 diabetes (T2D) (n = 12), where hGIP1-42 had been administered intravenously during fasting glycemia, hyperglycemia (12 mmol/L), and insulin-induced hypoglycemia (targets: 2.5 mmol/L [healthy]; 3.5 mmol/L [T2D]). Porcine GIP1-42 (pGIP) was also infused intra-arterially in isolated porcine pancreata (n = 4).

RESULTS

Mean fasting plasma glucose concentrations were approximately 5 mmol/L (healthy) and approximately 8 mmol/L (T2D). At fasting glycemia, PP concentrations were higher during intravenous hGIP1-42 infusion compared with saline in healthy men (mean [standard error of the mean, SEM], net incremental areas under the curves (iAUCs)[0-30min], 403 [116] vs -6 [57] pmol/L × min; P = 0.004) and in patients with T2D (905 [177] vs -96 [86] pmol/L × min; P = 0.009). During hyperglycemic clamping, mean [SEM] PP concentrations were significantly higher during hGIP1-42 infusion compared with saline in patients with T2D (771 [160] vs -183 [117] pmol/L × min; P = 0.001), but not in healthy individuals (-8 [86] vs -57 [53] pmol/L × min; P = 0.69). When plasma glucose levels were declining in response to exogenous insulin, mean [SEM] PP concentrations were higher during hGIP1-42 infusion compared with saline in healthy individuals (294 [88] vs -82 [53] pmol/L × min; P = 0.0025), but not significantly higher in patients with T2D (586 [314] vs -120 [53]; P = 0.070). At target hypoglycemia, PP levels surged in both groups during both hGIP1-42 and saline infusions. In isolated pancreata, pGIP1-42 increased mean [SEM] PP output in the pancreatic venous effluent (baseline vs infusion, 24[5] vs 79 [16] pmol/min x min; P = 0.044).

CONCLUSION

GIP1-42 increases plasma PP secretion in healthy individuals, patients with T2D, and isolated porcine pancreata. Hyperglycemia blunts the stimulatory effect of hGIP1-42 in healthy individuals, but not in patients with T2D.

Diabetic Gastroparesis

This review covers the epidemiology, pathophysiology, clinical features, diagnosis, and management of diabetic gastroparesis, and more broadly diabetic gastroenteropathy, which encompasses all the gastrointestinal manifestations of diabetes mellitus. Up to 50% of patients with type 1 and type 2 DM and suboptimal glycemic control have delayed gastric emptying (GE), which can be documented with scintigraphy, 13C breath tests, or a wireless motility capsule; the remainder have normal or rapid GE. Many patients with delayed GE are asymptomatic; others have dyspepsia (i.e., mild to moderate indigestion, with or without a mild delay in GE) or gastroparesis, which is a syndrome characterized by moderate to severe upper gastrointestinal symptoms and delayed GE that suggest, but are not accompanied by, gastric outlet obstruction. Gastroparesis can markedly impair quality of life, and up to 50% of patients have significant anxiety and/or depression. Often the distinction between dyspepsia and gastroparesis is based on clinical judgement rather than established criteria. Hyperglycemia, autonomic neuropathy, and enteric neuromuscular inflammation and injury are implicated in the pathogenesis of delayed GE. Alternatively, there are limited data to suggest that delayed GE may affect glycemic control. The management of diabetic gastroparesis is guided by the severity of symptoms, the magnitude of delayed GE, and the nutritional status. Initial options include dietary modifications, supplemental oral nutrition, and antiemetic and prokinetic medications. Patients with more severe symptoms may require a venting gastrostomy or jejunostomy and/or gastric electrical stimulation. Promising newer therapeutic approaches include ghrelin receptor agonists and selective 5-hydroxytryptamine receptor agonists.

Cholinergic Control of Inflammation, Metabolic Dysfunction, and Cognitive Impairment in Obesity-Associated Disorders: Mechanisms and Novel Therapeutic Opportunities

Obesity and obesity-associated disorders have become world-wide epidemics, substantially increasing the risk of debilitating morbidity and mortality. A characteristic feature of these disorders, which include the metabolic syndrome (MetS) and type 2 diabetes, is chronic low-grade inflammation stemming from metabolic and immune dysregulation. Inflammation in the CNS (neuroinflammation) and cognitive impairment have also been associated with obesity-driven disorders. The nervous system has a documented role in the regulation of metabolic homeostasis and immune function, and recent studies have indicated the important role of vagus nerve and brain cholinergic signaling in this context. In this review, we outline relevant aspects of this regulation with a specific focus on obesity-associated conditions. We outline accumulating preclinical evidence for the therapeutic efficacy of cholinergic stimulation in alleviating obesity-associated inflammation, neuroinflammation, and metabolic derangements. Recently demonstrated beneficial effects of galantamine, a centrally acting cholinergic drug and cognitive enhancer, in patients with MetS are also summarized. These studies provide a rationale for further therapeutic developments using pharmacological and bioelectronic cholinergic modulation for clinical benefit in obesity-associated disorders.

Electroacupuncture via chronically implanted electrodes improves gastric dysmotility mediated by autonomic-cholinergic mechanisms in a rodent model of functional dyspepsia

BACKGROUND

Electroacupuncture (EA) has been shown to be effective in reducing symptoms in patients with functional dyspepsia (FD). However, its mechanisms remain largely unknown. The aim of this study was to investigate mechanisms of the prokinetic effects of EA in a rodent model of FD.

METHODS

A FD model was established by neonatal treatment of iodoacetamide (IA). Eight weeks later, the rats were implanted with electrodes in the stomach for the measurement of gastric slow waves (GSW) and electrodes into acupoints ST36 for EA. Autonomic functions were assessed by the spectral analysis of heart rate variability.

KEY RESULTS

(i) The IA-treated rats ("FD" rats) showed increased dysrhythmia in both fasting and fed states (P < .01) as well as during rectal distention (P < .02). EA reduced the percentage of dysrhythmia (P < .05 for both fasting and fed) and normalized RD-induced impairment in GSW in "FD" rats. Atropine blocked the effect of EA on GSW. (ii) "FD" rats showed delayed gastric emptying (P = .001 vs control) that was accelerated with EA (P = .01, vs sham-EA). (iii) "FD" rats showed increased plasma norepinephrine (P = .006, vs control) that was suppressed with EA (P = .003) and reduced vagal activity that was improved with EA.

CONCLUSIONS AND INFERENCES

Gastric motility (GSW and GE) is impaired in rats treated with IA, possibly attributed to impaired autonomic functions. EA improves GSW and accelerates GE mediated via the autonomic and cholinergic mechanisms.

The Cells of the Islets of Langerhans

Islets of Langerhans are islands of endocrine cells scattered throughout the pancreas. A number of new studies have pointed to the potential for conversion of non-β islet cells in to insulin-producing β-cells to replenish β-cell mass as a means to treat diabetes. Understanding normal islet cell mass and function is important to help advance such treatment modalities: what should be the target islet/β-cell mass, does islet architecture matter to energy homeostasis, and what may happen if we lose a particular population of islet cells in favour of β-cells? These are all questions to which we will need answers for islet replacement therapy by transdifferentiation of non-β islet cells to be a reality in humans. We know a fair amount about the biology of β-cells but not quite as much about the other islet cell types. Until recently, we have not had a good grasp of islet mass and distribution in the human pancreas. In this review, we will look at current data on islet cells, focussing more on non-β cells, and on human pancreatic islet mass and distribution.

Importance of the enteric nervous system in the control of the migrating motility complex

The migrating motility complex (MMC), a cyclical phenomenon, represents rudimentary motility pattern in the gastrointestinal tract. The MMC is observed mostly in the stomach and gut of man and numerous animal species. It contains three or four phases, while its phase III is the most characteristic. The mechanisms controlling the pattern are unclear in part, although the neural control of the MMC seems crucial. The main goal of this article was to discuss the importance of intrinsic innervation of the gastrointestinal tract in MMC initiation, migration, and cessation to emphasize that various MMC-controlling mechanisms act through the enteric nervous system. Two main neural regions, central and peripheral, are able to initiate the MMC. However, central regulation of the MMC may require cooperation with the enteric nervous system. When central mechanisms are not active, the MMC can be initiated peripherally in any region of the small bowel. The enteric nervous system affects the MMC in response to the luminal stimuli which can contribute to the initiation and cessation of the cycle, and it may evoke irregular phasic contractions within the pattern. The hormonal regulators released from the endocrine cells may exert a modulatory effect upon the MMC mostly through the enteric nervous system. Their central action could also be considered. It can be concluded that the enteric nervous system is involved in the great majority of the MMC-controlling mechanisms.

Auricular vagal nerve stimulation ameliorates burn-induced gastric dysmotility via sympathetic-COX-2 pathways in rats

BACKGROUND

Severe burn injury has been demonstrated to delay gastric emptying. The aim of this study was to investigate effects and cellular mechanisms of auricular electroacupuncture (AEA) at the acupoints innervated by the auricular branch of vagus nerve on burn-induced gastric dysmotility in rats.

METHODS

Propranolol (β-adrenoceptor antagonist) was injected intraperitoneally after the rats underwent burn injury. All experiments were performed 6 h following burn/sham burn injury. AEA was performed at bilateral auricular acupoints for 45 min. Electrocardiogram was recorded for 30 min. Plasma hormones were measured; cyclooxygenase (COX)-2 expressions in gastric tissue were measured using western blotting and real-time RT-PCR.

KEY RESULTS

(i) Burn injury delayed gastric emptying (p = 0.006) and AEA increased gastric emptying by 49% (p = 0.045). (ii) Burn injury evoked a significant elevation in plasma noradrenaline, which was suppressed by AEA. (iii) Burn injury significantly increased protein and mRNA expressions of COX-2 in gastric fundus and antrum. AEA suppressed burn-induced increase in protein expressions, but not mRNA expressions of COX-2.

CONCLUSIONS & INFERENCES

Burn injury delays gastric emptying by up-regulating COX-2 attributed to sympathetic overactivity. AEA improves burn-induced delay in gastric emptying, possibly mediated via the sympathetic-COX-2 pathway.

The role of pancreatic polypeptide in the regulation of energy homeostasis

Imbalances in normal regulation of food intake can cause obesity and related disorders. Inadequate therapies for such disorders necessitate better understanding of mechanisms that regulate energy homeostasis. Pancreatic polypeptide (PP), a robust anorexigenic hormone, effectively modulates food intake and energy homeostasis, thus potentially aiding anti-obesity therapeutics. Intra-gastric and intra-intestinal infusion of nutrients stimulate PP secretion from the gastrointestinal tract, leading to vagal stimulation that mediates complex actions via the neuropeptide Y4 receptor in arcuate nucleus of the hypothalamus, subsequently activating key hypothalamic nuclei and dorsal vagal complex of the brainstem to influence energy homeostasis and body composition. Novel studies indicate affinity of PP for the relatively underexplored neuropeptide y6 receptor, mediating actions via the suprachiasmatic nucleus and pathways involving vasoactive intestinal polypeptide and insulin like growth factor 1. This review highlights detailed mechanisms by which PP mediates its actions on energy balance through various areas in the brain.

The role of efferent cholinergic transmission for the insulinotropic and glucagonostatic effects of GLP-1

The importance of vagal efferent signaling for the insulinotropic and glucagonostatic effects of glucagon-like peptide-1 (GLP-1) was investigated in a randomized single-blinded study. Healthy male participants ( n = 10) received atropine to block vagal cholinergic transmission or saline infusions on separate occasions. At t = 15 min, plasma glucose was clamped at 6 mmol/l. GLP-1 was infused at a low dose (0.3 pmol·kg−1·min−1) from t = 45–95 min and at a higher dose (1 pmol·kg−1·min−1) from t = 95–145 min. Atropine blocked muscarinic, cholinergic transmission, as evidenced by an increase in heart rate [peak: 70 ± 2 (saline) vs. 90 ± 2 (atropine) beats/min, P < 0.002] and suppression of pancreatic polypeptide levels [area under the curve during the GLP-1 infusions (AUC45–145): 492 ± 85 (saline) vs. 247 ± 59 (atropine) pmol/l × min, P < 0.0001]. More glucose was needed to maintain the clamp during the high-dose GLP-1 infusion steady-state period on the atropine day [6.4 ± 0.9 (saline) vs. 8.7 ± 0.8 (atropine) mg·kg−1·min−1, P < 0.0023]. GLP-1 dose-dependently increased insulin secretion on both days. The insulinotropic effect of GLP-1 was not impaired by atropine [C-peptide AUCs45–145: 99 ± 8 (saline) vs. 113 ± 13 (atropine) nmol/l × min, P = 0.19]. Atropine suppressed glucagon levels additively with GLP-1 [AUC45–145: 469 ± 70 (saline) vs. 265 ± 50 (atropine) pmol/l × min, P = 0.018], resulting in hypoglycemia when infusions were suspended [3.6 ± 0.2 (saline) vs. 2.7 ± 0.2 (atropine) mmol/l, P < 0.0001]. To ascertain whether atropine could independently suppress glucagon levels, control experiments ( n = 5) were carried out without GLP-1 infusions [AUC45–145: 558 ± 103 (saline) vs. 382 ± 76 (atropine) pmol/l × min, P = 0.06]. Our results suggest that efferent muscarinic activity is not required for the insulinotropic effect of exogenous GLP-1 but that blocking efferent muscarinic activity independently suppresses glucagon secretion. In combination, GLP-1 and muscarinic blockade strongly affect glucose turnover.

Changes in gut hormones and leptin in military personnel during operational deployment in Afghanistan

OBJECTIVE

Understanding the mechanisms that drive weight loss in a lean population may elucidate systems that regulate normal energy homeostasis. This prospective study of British military volunteers investigated the effects of a 6-month deployment to Afghanistan on energy balance and circulating concentrations of specific appetite-regulating hormones.

METHODS

Measurements were obtained twice in the UK (during the Pre-deployment period) and once in Afghanistan, at Mid-deployment. Body mass, body composition, food intake, and appetite-regulatory hormones (leptin, active and total ghrelin, PYY, PP, GLP-1) were measured.

RESULTS

Repeated measures analysis of 105 volunteers showed body mass decreased by 4.9% ± 3.7% (P < 0.0001) during the first half of the deployment. Leptin concentrations were significantly correlated with percentage body fat at each time point. The reduction in percentage body fat between Pre-deployment and Mid-deployment was 8.6%, with a corresponding 48% decrease in mean circulating leptin. Pre-deployment leptin and total and active ghrelin levels correlated with subsequent change in body mass; however. no changes were observed in the anorectic gut hormones GLP-1, PP, or PYY.

CONCLUSIONS

These data suggest that changes in appetite-regulating hormones in front line military personnel occur in response to, but do not drive, reductions in body mass.

Gut hormones and obesity: physiology and therapies

Over the past 30 years, it has been established that hormones produced by the gut, pancreas, and adipose tissue are key players in the control of body weight. These hormones act through a complex neuroendocrine system, including the hypothalamus, to regulate metabolism and energy homeostasis. In obesity, this homeostatic balance is disrupted, either through alterations in the levels of these hormones or through resistance to their actions. Alterations in gut hormone secretion following gastric bypass surgery are likely to underlie the dramatic and persistent loss of weight following this procedure, as well as the observed amelioration in type 2 diabetes mellitus. Medications based on the gut hormone GLP-1 are currently in clinical use to treat type 2 diabetes mellitus and have been shown to produce weight loss. Further therapies for obesity based on other gut hormones are currently in development.

Liquid meal composition, postprandial satiety hormones, and perceived appetite and satiety in obese women during acute caloric restriction

OBJECTIVE

The purpose of this study was to compare postprandial satiety regulating hormone responses (pancreatic polypeptide (PP) and peptide tyrosine tyrosine (PYY)) and visual analog scale- (VAS) assessed perceived appetite and satiety between liquid high-protein (HP) and high-carbohydrate (HC) meals in obese women during acute (24-h) caloric restriction.

DESIGN

Eleven obese premenopausal women completed two conditions in random order in which they consumed 1500 calories as six 250-calorie HP meals or six 250-calorie HC meals over a 12-h period. Blood samples were taken at baseline and every 20 min thereafter and analyzed for PP and PYY concentrations. At these same points, perceived hunger and fullness were assessed with a VAS. The incremental area under the curve (iAUC) was used to compare postprandial responses.

RESULTS

The 12-h PP and PYY iAUC were greater (P≤0.05) during the HP condition (PP: 4727±1306 pg/ml×12 h, PYY: 1373±357 pg/ml×12 h) compared with the HC condition (PP: 2300±528 pg/ml×12 h, PYY: 754±246 pg/ml×12 h). Perceived hunger and fullness were not different between conditions (P>0.05). The greatest changes in PYY and perceived fullness occurred after the morning meals during both conditions.

CONCLUSIONS

These data suggest that in obese women during acute caloric restriction before weight loss, i) liquid HP meals, compared with HC meals, result in greater postprandial PP and PYY concentrations, an effect not associated with differential appetite or satiety responses, and ii) meal-induced changes in PYY and satiety are greatest during the morning period, regardless of dietary macronutrient composition.

Neuropeptide Y, peptide YY and pancreatic polypeptide in the gut-brain axis

The gut-brain axis refers to the bidirectional communication between the gut and the brain. Four information carriers (vagal and spinal afferent neurons, immune mediators such as cytokines, gut hormones and gut microbiota-derived signalling molecules) transmit information from the gut to the brain, while autonomic neurons and neuroendocrine factors carry outputs from the brain to the gut. The members of the neuropeptide Y (NPY) family of biologically active peptides, NPY, peptide YY (PYY) and pancreatic polypeptide (PP), are expressed by cell systems at distinct levels of the gut-brain axis. PYY and PP are exclusively expressed by endocrine cells of the digestive system, whereas NPY is found at all levels of the gut-brain and brain-gut axis. The major systems expressing NPY comprise enteric neurons, primary afferent neurons, several neuronal pathways throughout the brain and sympathetic neurons. In the digestive tract, NPY and PYY inhibit gastrointestinal motility and electrolyte secretion and in this way modify the input to the brain. PYY is also influenced by the intestinal microbiota, and NPY exerts, via stimulation of Y1 receptors, a proinflammatory action. Furthermore, the NPY system protects against distinct behavioural disturbances caused by peripheral immune challenge, ameliorating the acute sickness response and preventing long-term depression. At the level of the afferent system, NPY inhibits nociceptive input from the periphery to the spinal cord and brainstem. In the brain, NPY and its receptors (Y1, Y2, Y4, Y5) play important roles in regulating food intake, energy homeostasis, anxiety, mood and stress resilience. In addition, PP and PYY signal to the brain to attenuate food intake, anxiety and depression-related behaviour. These findings underscore the important role of the NPY-Y receptor system at several levels of the gut-brain axis in which NPY, PYY and PP operate both as neural and endocrine messengers.

Improvement in β-cell function after diet-induced weight loss is associated with decrease in pancreatic polypeptide in subjects with type 2 diabetes

OBJECTIVE

The aim of our study was to evaluate the effect of a lifestyle intervention program on β-cell function and to explore the role of gastrointestinal peptides in subjects with T2D.

METHODS

Subjects with T2D (n=74) received 24 weeks of intervention: 12 weeks of slimming diet (-500 kcal/day) and the subsequent 12 weeks of diet were combined with aerobic exercise. All subjects were examined at weeks 0, 12 and 24. β-cell function was assessed during standard meal tests. Insulin secretory rate (ISR) was calculated by C-peptide deconvolution, and β-cell function was quantified with a mathematical model. Plasma concentrations of gastrointestinal peptides were measured in a fasting state and during hyperinsulinemia induced by hyperinsulinemic isoglycemic clamp.

RESULTS

Mean weight loss was 5.03±4.38 kg (p<0.001) in weeks 0-12. Weight did not change significantly in weeks 12-24. Both insulin secretion at the reference level and glucose sensitivity increased in weeks 0-12 (by 33%±54% and by 26%±53%, respectively, p<0.001) and remained unchanged in weeks 12-24. Both fasting and hyperinsulinemic plasma concentrations of pancreatic polypeptide (PP) decreased in weeks 0-12 (p<0.05 for both) and did not change significantly in weeks 12-24. Changes in insulin secretion at the reference level correlated negatively with plasma concentrations of PP during hyperinsulinemia (r=-0.36; p<0.001). Changes in glucose sensitivity correlated negatively with changes in plasma concentrations of PP, both in fasting and during hyperinsulinemia (r=-0.2; p=0.01 for both). The correlations remained significant after adjustment for changes in body-mass-index.

CONCLUSIONS

After diet-induced weight loss, β-cell function improved in T2D subjects and remained unchanged after the addition of exercise. We demonstrate for the first time that these changes are associated with a decrease in PP secretion.

Hepatic steatosis in type 1 diabetes

Islet autoimmunity in type 1 diabetes results in the loss of the pancreatic β-cells. The consequences of insulin deficiency in the portal vein for liver fat are poorly understood. Under normal conditions, the portal vein provides 75% of the liver blood supply. Recent studies suggest that non-alcoholic fatty liver disease (NAFLD) may be more common in type 1 diabetes than previously thought, and may serve as an independent risk marker for some chronic diabetic complications. The pathogenesis of NAFLD remains obscure, but it has been hypothesized that hepatic fat accumulation in type 1 diabetes may be due to lipoprotein abnormalities, hyperglycemia-induced activation of the transcription factors carbohydrate response element-binding protein (ChREBP) and sterol regulatory element-binding protein 1c (SREBP-1c), upregulation of glucose transporter 2 (GLUT2) with subsequent intrahepatic fat synthesis, or a combination of these mechanisms. Novel approaches to non-invasive determinations of liver fat may clarify the consequences for liver metabolism when the pancreas has ceased producing insulin. This article aims to review the factors potentially contributing to hepatic steatosis in type 1 diabetes, and to assess the feasibility of using liver fat as a prognostic and/or diagnostic marker for the disease. It provides a background and a case for possible future studies in the field.

Circulating markers for endocrine tumours of the gastroenteropancreatic tract

The diffuse endocrine system (DES) includes a wide range of secretory cells that may be the source of tumours. Gastroenteropancreatic endocrine (GEP) tumours arising within the DES secrete a variety of peptides and amines that are found in the circulation and are responsible for the syndromes associated with these tumours. In this review, the most common tumours of the GEP tract are outlined and the circulating products of these tumours identified. Where differential diagnosis is difficult these points are addressed. The peptides most commonly secreted by GEP neuroendocrine tumours are identified and described and their biological activities are discussed. Current methods available for measurement of these peptides are described. Attention is drawn towards molecular specificity where appropriate, as many pancreatic and gut peptides fall within families which show considerable homology, such as the tachykinin family or the glucagon family. Other peptides such as gastrin circulate in multiple molecular forms. This homology and diversity may cause difficulty in the interpretation of peptide measurements in the clinical situation if assays are not specific.

Longitudinal changes in pancreatic and adipocyte hormones following Roux-en-Y gastric bypass surgery

AIMS/HYPOTHESIS

Bariatric surgery is an effective treatment for severe obesity, as in addition to dramatic weight loss, co-morbidities such as type 2 diabetes are frequently resolved. Although altered gastrointestinal peptide hormone secretion and its relationship with post-surgical improvements in insulin sensitivity has been studied, much less is known about long-term changes in pancreatic and adipose tissue-derived hormones. Our objective was to conduct a comprehensive longitudinal investigation of the endocrine changes following Roux-en-Y gastric bypass surgery (RYGBP), focusing on pancreatic and adipocyte hormones and systemic markers of inflammation.

METHODS

Nineteen severely obese women (BMI 45.6 +/- 1.6 kg/m(2)) were studied prior to RYGBP, and at 1, 3, 6, and 12 months after RYGBP. Body composition was assessed before surgery and at 1 and 12 months.

RESULTS

Pre-surgical adiposity was correlated with circulating adipocyte hormones (leptin, visfatin) and inflammatory molecules (IL-6, high sensitivity C-reactive protein [hsCRP], monocyte chemoattractant protein-1). As expected, RYGBP reduced fat mass and fasting insulin and glucose concentrations. In addition, reductions of fasting pancreatic polypeptide (PP) and glucagon concentrations were observed at 1 and 3 months, respectively. In the 12 months following RYGBP, concentrations of most adipocyte hormones (leptin, acylation-stimulating hormone and visfatin, but not retinol-binding hormone-4) and inflammatory molecules (IL-6, hsCRP and soluble intracellular adhesion molecule-1) were significantly reduced. Reductions of insulin resistance (measured by homeostasis model assessment of insulin resistance) were independently associated with changes of glucagon, visfatin and PP. Pre-surgical HMW adiponectin concentrations independently predicted losses of body weight and fat mass.

CONCLUSIONS/INTERPRETATION

These results suggest that pancreatic and adipocyte hormones may contribute to the long-term resolution of insulin resistance after RYGBP.

Insulin, glucose, and pancreatic polypeptide responses to a test meal in restricting type anorexia nervosa before and after weight restoration

Prolonged malnutrition in individuals with anorexia nervosa (AN) has been associated with alterations in endocrine function that may play a sustaining role in the disorder. We hypothesized that abnormalities in endocrine responses to ingestion of a meal in AN are reversible and depend on weight restoration. We measured meal-induced endocrine responses in AN subjects at three time points during hospitalization: before refeeding (n = 13, mean BMI 16.7 kg/m(2)), after 2 wk of refeeding (mean BMI 18.0 kg/m(2)), and in the weight-restored state (mean BMI 20.3 kg/m(2)). Control subjects (n = 13, BMI 19-24.9 kg/m(2)) were tested once. Tests were 2.5-h sessions in which blood was drawn every 15 min before, during, and after a approximately 650-kcal test breakfast. Relative to controls, peak levels of glucose were depressed and peak levels of insulin in response to ingestion of the test meal were delayed, with response patterns in the third trial most similar to controls. Pancreatic polypeptide (PP) levels were increased in AN relative to controls regardless of weight status. The delay in insulin release and elevated PP levels did not correct with short-term refeeding and may contribute to the high relapse rates and maintenance of AN.

Y2, Y4 receptors and obesity

The neuropeptide Y system - comprising neuropeptide Y, peptide YY, pancreatic polypeptide and the Y receptors through which they act (Y1, Y2, Y4, Y5 and y6) - has been at the center of attention with regards to regulation of feeding behavior and its possible involvement in obesity. In the past, research has focused mainly on the orexigenic and obesogenic action of this system, with Y1 and Y5 receptors being prime candidates as mediators of neuropeptide Y-induced hyperphagia and obesity. However, in recent years, the role of other members of the neuropeptide Y family, peptide YY, pancreatic polypeptide and the Y2 and Y4 receptors through which they predominantly act, have commanded increasing attention on account of their effects to mediate satiety and promote weight loss via actions in key brain structures, such as the arcuate nucleus of the hypothalamus and the brain stem. This review focuses on the role of peptide YY- and pancreatic polypeptide-like compounds as possible antiobesity drugs, taking into account their effects, not only on energy balance, but also in the regulation of bone formation, and highlights potential benefits of using Y2 and/or Y4 antagonists (as opposed to agonists such as peptide YY or pancreatic polypeptide) in the treatment of obesity.

Plasma pancreatic polypeptide levels are associated with differences in body fat distribution in human subjects

AIMS/HYPOTHESIS

Pancreatic polypeptide (PP) is produced by the F-cells of the pancreas, and its plasma concentration has been used as a marker of parasympathetic activity. Recent work in rodents suggests that there is both sympathetic and parasympathetic innervation of white adipose tissue and that parasympathetic activity is anabolic resulting in lipid accumulation. We have examined whether in humans increased PP levels are associated with increased intra-abdominal fat (IAF), and thereby insulin resistance.

MATERIALS AND METHODS

We measured PP levels in 177 non-diabetic subjects (75 male/102 female; age 32-75 years) 3 min after an i.v. glucose bolus during a frequently sampled intravenous glucose tolerance test. IAF and s.c. fat (SCF) areas were measured by CT scan. The insulin sensitivity index (S (I)) was quantified using Bergman's minimal model.

RESULTS

PP levels were higher in men than in women (96.2 +/- 72.2 vs 76.1 +/- 55.0 pg/ml, mean +/- SD, p = 0.037), as was IAF area (124.7 +/- 67.4 vs 83.0 +/- 57.7 cm(2), p < 0.001). While PP levels were significantly associated with IAF (r = 0.16, p = 0.031), WHR (r = 0.30, p < 0.001) and age (r = 0.37, p < 0.01), they were not associated with SCF (r = 0.02, p = 0.829). The association between PP and IAF was not independent of age and/or sex. S(I) was negatively associated with PP levels (r = -0.17, p = 0.026) and IAF area (r = -0.65, p < 0.001). The association between S(I) and PP disappeared after adjusting for IAF area, indicating that S(I) was not a major determinant of PP levels.

CONCLUSIONS/INTERPRETATION

In humans, age and sex may modulate the association between plasma PP level and IAF area, suggesting that they may be determinants of parasympathetic activity and thus IAF accumulation.

Glucagon secretion and autonomic signaling during hypoglycemia in late pregnancy

We examined net pancreatic norepinephrine (NE) spillover, pancreatic polypeptide (PP) release, and the decrement in C-peptide to identify factors involved in the blunted counterregulatory glucagon response in pregnancy. Conscious pregnant [pregnant hypoglycemic (Ph); 3rd trimester; n = 8] and nonpregnant [nonpregnant hypoglycemic (NPh); n = 6] dogs were studied during insulin-induced (approximately 12-fold basal insulin concentrations) hypoglycemia (plasma glucose 3.1 mM). Additional dogs were studied during hyperinsulinemic euglycemia [nonpregnant euglycemic (NPe), n = 4; pregnant euglycemic (Pe), n = 5; plasma glucose 6 mM]. Arterial glucagon concentrations declined similarly in NPe and Pe. Areas under the curve (AUCs) of the changes in glucagon and epinephrine were seven- and threefold greater in NPh than Ph (P < 0.05 between groups for both). Glucagon secretion fell below basal in NPe, Pe, and Ph but rose significantly in NPh. C-peptide declined 0.25 +/- 0.06, 0.12 +/- 0.11, 0.28 +/- 0.05, and 0.13 +/- 0.02 ng/ml in NPe, Pe, NPh, and Ph, respectively (P < 0.05, NPh vs. Ph). AUCs of NE spillover were 516 +/- 274, 265 +/- 303, 506 +/- 94, and -63 +/- 79 ng, respectively (P < 0.05, NPh vs. Ph). The AUC of PP release was approximately threefold greater in NPh than Ph (P < 0.05) but not different between euglycemic groups. The current evidence strongly suggests that the blunting of glucagon secretion during insulin-induced hypoglycemia in pregnancy is related to generalized impairment of a number of different signals, including parasympathetic and sympathoadrenal stimuli and altered sensing of circulating and/or intraislet insulin.

Gastric electrical stimulation significantly increases canine lower esophageal sphincter pressure

This study determined the effect of low-frequency and high-frequency gastric electrical stimulation (GES) on canine lower esophageal sphincter (LES) pressure and also evaluated the effect of such stimulation on neurohumoral factors that modulate LES pressure. Eight dogs were fitted with stimulation wires along the greater curvature of the stomach. A sleeve device measured LES pressure before, during, and after GES, and regulatory peptides were measured during fasting and after a meal. A consistent and significant rise in LES pressure was observed during GES, and it was sustained after GES was discontinued. Plasma concentration and area under the curve of pancreatic polypeptide, motilin, gastrin and neurotensin were not affected by GES. We conclude that acute low- and high-frequency GES significantly increases LES pressure. This effect may not be modulated by efferent vagal activity or release of regulatory peptides.

Achalasia presenting after operative and nonoperative trauma

Achalasia has been described following fundoplication and is attributed to vagal nerve damage during surgery. Similarly, other traumatic events to the distal esophagus may be linked to the development of achalasia. Operative and nonoperative trauma as a possible factor in the development of achalasia was studied. A retrospective analysis of patients with achalasia (n = 64) at our institution was performed. Collected data included age, gender, symptoms, and history of operative and nonoperative traumatic events. Comparisons were made to a group of patients with similar symptoms but normal esophageal manometry (n = 73). Achalasia was diagnosed by manometry in 125 patients over a 6-year period. All patients with complete medical records (n = 64) were studied. A history of operative or nonoperative trauma to the upper gastrointestinal tract prior to the development of symptomatic achalasia was present in 16 of 64 (25%). Significantly fewer patients (9.5%) with symptoms of dysphagia, but normal manometry and upper endoscopy, had precedent trauma to the upper gastrointestinal tract (P < 0.05). All cases of nonoperative trauma occurred in motor vehicle accidents. Cases of operative trauma included coronary artery bypass surgery (n = 4), bariatric surgery (n = 2), fundoplication (n = 3), heart/lung transplantation (n = 1), and others (n = 5). Patients with proven achalasia and a history of trauma were more likely to have chest pain (RR, 4.5; P = 0.012) but less likely to have regurgitation (RR, 0.51; P = 0.01) or nausea/vomiting (RR, 0.0; P = 0.27) than those without a history of antecedent trauma. In this series, significantly more patients with achalasia had a history of preceding trauma than did patients with similar symptoms and normal esophageal manometry. Following trauma, patients may be at increased risk for developing achalasia, possibly from neuropathic dysfunction due to vagal nerve damage. Patients with posttraumatic achalasia may have symptoms which differ from those of other achalasia patients.

Gastric electrical stimulation is associated with improvement in pancreatic exocrine function in humans

OBJECTIVE

To define the possible effects of gastric electrical stimulation (GES) for gastroparesis on pancreatic function, we performed 2 related human studies.

METHODS

Fecal elastase values were compared in 2 patient groups: (1) GES devices ON and (2) GES devices OFF and (2) in 3 control groups: (1) no response (NR) to prokinetic medications, (2) positive response (RES) to medications, and (3) normal controls. Polypeptide levels in 7 of 9 GES patients with device ON and OFF, elastase results, GI symptoms (TSS), and heart rate variability (HRV) were compared by paired t tests and/or ANOVA and reported as mean +/- SE.

RESULTS

Elastase was different for GES-ON and OFF (508.0 +/- 92.2 vs. GES-OFF 378.6 +/- 87.4, P < 0.05). Elastase was lower in medication NR and RES than in normal controls. Postprandial pancreatic polypeptide was greater with GES ON than OFF (P = 0.07). HRV revealed a lower percentage of change with device ON versus OFF (44.2 +/- 5.5 vs. 48.5 +/- 5.2, P = 0.08) and lower TSS with ON versus OFF (15.9 +/- 4.5 vs. 25.7 +/- 5.3, P < 0.05).

CONCLUSIONS

GES improves exocrine pancreatic release, effects autonomic control, and improves GI symptoms, suggesting a possible role for GES in the treatment of pancreatic insufficiency associated with gastroparesis.

Synergistic effects of Y2 and Y4 receptors on adiposity and bone mass revealed in double knockout mice

Neuropeptide Y regulates numerous physiological processes via at least five different Y receptors, but the specific roles of each receptor are still unclear. We previously demonstrated that Y2 receptor knockout results in a lean phenotype, increased cancellous bone volume, and an increase in plasma pancreatic polypeptide (PP), a ligand for Y4 receptors. PP-overexpressing mice are also known to have a lean phenotype. Deletion of the Y4 receptor also produced a lean phenotype and increased plasma PP levels. We therefore hypothesized that part of the Y2 phenotype results from increased PP action on Y4 receptors and tested this in PP transgenic Y4(-/-) and Y2(-/-) Y4(-/-) double knockout mice. Bone mass was not altered in Y4 knockout mice. Surprisingly, despite significant hyperphagia, Y2(-/-) Y4(-/-) mice retained a markedly lean phenotype, with reduced body weight, white adipose tissue mass, leptinemia, and insulinemia. Furthermore, bone volume was also increased threefold in Y2(-/-) Y4(-/-) mice, and this was associated with enhanced osteoblastic activity. These changes were more pronounced than those observed in Y2(-/-) mice, suggesting synergy between Y2 and Y4 receptor pathways. The lack of bone changes in PP transgenic mice suggests that PP alone is not responsible for the bone mass increases but might play a major role in the lean phenotype. However, a synergistic interaction between Y2 and Y4 pathways seems to regulate bone volume and adiposity and could have important implications for possible interventions in obesity and for anabolic treatment of osteoporotic bone loss.

Cardiac function in neuropeptide Y Y4 receptor-knockout mice

Autonomic control of cardiovascular function in neuropeptide Y (NPY) Y4 receptor-knockout mice was investigated using pancreatic polypeptide (PP), NPY and specific agonists and antagonists for other NPY receptors well characterised in cardiovascular function. Y4 receptor-knockout mice, anaesthetised with sodium pentobarbitone, displayed slower heart rate, indicated by a higher pulse interval and lower blood pressure compared to control mice. After vagus nerves were cut heart rate increased but was still significantly slower than in control mice. PP had no effect on blood pressure or cardiac vagal activity in either group of mice, which was consistent with earlier studies in other species. Injection of NPY evoked an increase in blood pressure but the response was significantly reduced in Y4 receptor-knockout mice compared to the controls. The reduction in pressor activity was not Y1 mediated as the selective Y1 antagonist, BIBP 3226, was effective in blocking NPY pressor activity in knockout mice. In addition, cardiac vagal inhibitory activity evoked by low doses of NPY was also reduced when compared to control responses. As N-acetyl [Leu(28, 31)] NPY 24-36 inhibited vagal activity dose dependently in both groups of mice with no difference in response at any dose, it is unlikely that this effect also is receptor mediated. We propose that the reduced vasoconstrictor and vagal inhibitory activity evoked by NPY in Y4 receptor-knockout mice is due to a lack of adrenergic tone bought about by a proposed reduction in sympathetic activity, possibly resulting from altered NPY activity secondarily affecting adrenergic transmission. We conclude that Y4 receptor deletion disrupts autonomic balance within the cardiovascular system.

Important role of hypothalamic Y2 receptors in body weight regulation revealed in conditional knockout mice

Neuropeptide Y is implicated in energy homeostasis, and contributes to obesity when hypothalamic levels remain chronically elevated. To investigate the specific role of hypothalamic Y2 receptors in this process, we used a conditional Y2 knockout model, using the Cre-lox system and adenoviral delivery of Cre-recombinase. Hypothalamus-specific Y2-deleted mice showed a significant decrease in body weight and a significant increase in food intake that was associated with increased mRNA levels for the orexigenic NPY and AgRP, as well as the anorexic proopiomelanocortin (POMC) and cocaine- and amphetamine-regulated transcript (CART) in the arcuate nucleus. These hypothalamic changes persisted until at least 34 days after Y2 deletion, yet the effect on body weight and food intake subsided within this time. Plasma concentrations of pancreatic polypeptide and corticosterone were 3- to 5-fold increased in hypothalamus-specific Y2 knockout mice. Germ-line Y2 receptor knockout also produced a significant increase in plasma levels of pancreatic polypeptide. However, these mice differed from conditional knockout mice in that they showed a sustained reduction in body weight and adiposity associated with increased NPY and AgRP but decreased POMC and CART mRNA levels in the arcuate nucleus. The transience of the observed effects on food intake and body weight in the hypothalamus-specific Y2 knockout mice, and the difference of this model from germ-line Y2 knockout mice, underline the importance of conditional models of gene deletion, because developmental, secondary, or extrahypothalamic mechanisms may mask such effects in germ-line knockouts.

Y4 receptor knockout rescues fertility in ob/ob mice

Hypothalamic neuropeptide Y (NPY) has been implicated in the regulation of energy balance and reproduction, and chronically elevated NPY levels in the hypothalamus are associated with obesity and reduced reproductive function. However, it is not known which one of the five cloned Y receptors mediates these effects. Here we show that crossing the Y4 receptor knockout mouse (Y4(-/-)) onto the ob/ob background restores the reduced plasma testosterone levels of ob/ob mice as well as the reduced testis and seminal vesicle size and morphology to control values. Fertility in the sterile ob/ob mice was greatly improved by Y4 receptor deletion, with 100% of male and 50% of female Y4(-/-),ob/ob double knockout mice producing live offspring. Development of the mammary ducts and lobuloalveoli was significantly enhanced in pregnant Y4(-/-) and Y4(-/-),ob/ob females. Consistent with the improved fertility and enhanced mammary gland development, gonadotropin releasing hormone (GnRH) expression was significantly increased in Y4(-/-) and Y4(-/-),ob/ob animals. Y4(-/-) mice displayed lower body weight and reduced white adipose tissue mass accompanied by increased plasma levels of pancreatic polypeptide (PP). However, Y4 deficiency had no beneficial effects to reduce body weight or excessive adiposity of ob/ob mice. These data suggest that central Y4 receptor signaling specifically inhibits reproductive function under conditions of elevated central NPY-ergic tonus.

Pancreatic polypeptide in pancreatitis

Pancreatitis is a disease with increasing incidence which can be divided into an acute and a chronic form. In both acute and chronic pancreatitis, changes in plasma concentration of pancreatic polypeptide (PP) and its regulation have been reported. In daily clinical work a serologic test for the precise diagnosis and staging of acute and chronic pancreatitis is still desirable. Therefore, many studies have investigated plasma concentrations of PP in acute and chronic pancreatitis as a diagnostic marker and as a therapeutic option to treat pancreatogenic diabetes mellitus. Although the study results are presently inconclusive and potentially contradictory, the findings are nevertheless encouraging, and indicate that PP might have a role in diagnosis, grading and estimation of the prognosis of pancreatitis. Further data and prospective controlled studies are needed to judge whether PP is of clinical value for diagnosing, staging and predicting long-term outcome in acute and chronic pancreatitis.

Central but not peripheral glucocorticoid infusion in adrenalectomized male rats increases basal and substrate-induced insulinemia through a parasympathetic pathway

OBJECTIVE

Glucocorticoids acting through the central nervous system are postulated to play a role in the hyperinsulinemia and increased adiposity of obesity. We investigated the role of parasympathetic activation in glucocorticoid-induced hyperinsulinemia.

RESEARCH METHODS AND PROCEDURES

Plasma pancreatic polypeptide (PP) levels were used as an index of parasympathetic output. Insulinemia and plasma PP levels were measured basally and after intravenous glucose injection (300 mg/kg) in adrenalectomized male rats infused with dexamethasone (7.5 microg/kg per day) intracerebroventricularly (ICV) or subcutaneously (SC) for 3 to 6 days in the presence or absence of acute atropine blockade (1.0 mg/kg). Food intake was controlled between groups.

RESULTS

Compared with normal rats, adrenalectomy decreased white adipose tissue depot weights and leptinemia, and these were restored to normal values by ICV but not SC dexamethasone infusion. Adrenalectomy significantly reduced insulinemia below normal levels, which was restored by SC dexamethasone replacement. However, ICV dexamethasone replacement increased insulinemia of adrenalectomized rats to levels higher than normal control values (basal, 500 +/- 40 pM vs. 280 +/- 40 pM; 1-minute postglucose, 2500 +/- 180 pM vs. 1240 +/- 260 pM; p < 0.0001) and increased plasma PP levels, which were correlated with insulinemia. Atropine significantly reduced plasma insulin and PP to levels similar to normal controls but had no effect in any other group.

DISCUSSION

These data show that glucocorticoids act within the brain to increase insulinemia, most likely through activation of parasympathetic efferent fibers. Such an affect would contribute to the adipogenic effects of central glucocorticoids.

Direct quantification of norepinephrine spillover and hormone output from the pancreas of the conscious dog

To estimate pancreatic neural activity and to assess the potential role of the pancreatic nerves in the regulation of hormone secretion, the methodology necessary to quantify neurotransmitter spillover and hormone output in the conscious dog was developed. A femoral artery and the superior pancreaticoduodenal vein (SPDV) were chronically cannulated, and a flow probe was placed on the SPDV. Hormone output was calculated using the pancreatic arteriovenous concentration difference and the SPDV plasma flow. Basal glucose levels were 103 +/- 1 mg/dl; the pancreatic outputs of insulin, glucagon, and pancreatic polypeptide (PP, an index of parasympathetic neural activity) were 2,900 +/- 700 microU/min, 1,900 +/- 400 pg/min, and 9.3 +/- 4.6 ng/min, respectively. Pancreatic norepinephrine (NE) spillover was calculated similarly; however, pancreatic extraction of epinephrine was used as an index of NE extraction. Basal NE spillover was 3,600 +/- 700 pg/min, greatly exceeding that reported using anesthetized, laparotomized dogs. Intravenous glucose infusion increased plasma glucose to 146 +/- 13 mg/dl, increased insulin output approximately twofold, and suppressed glucagon output by approximately 50%. Hyperglycemia markedly reduced PP output. Hyperglycemia failed to influence pancreatic NE spillover. Insulin-induced hypoglycemia (36 +/- 2 mg/dl) completely suppressed insulin output and stimulated glucagon output (> 10-fold). Hypoglycemia increased NE spillover and PP output to 19,900 +/- 4,600 pg/min and 117 +/- 22 ng/min, respectively. We conclude that pancreatic neurotransmitter spillover in the basal state is much higher than previously appreciated and that neural signaling to the pancreas is responsive to physiological and pathophysiological changes in the metabolic state.

Autonomic function in systemic lupus erythematosus

A controlled study with paired analysis of data was performed in 34 patients with systemic lupus erythematosus (SLE) and 34 age and sex-matched healthy controls. Autonomic function was not affected significantly in SLE patients as judged by standardised cardiovascular tests. Pancreatic polypeptide (PP) response to meal stimulation, which is impaired in parasympathetic failure, was for unknown reasons found to be significantly increased in SLE patients both in unstimulated and stimulated states. Neither cardiovascular nor serological tests could thus reveal significant autonomic dysfunction in SLE. Drugs with cardiovascular effects highly influenced autonomic function and could thus be misinterpreted as autonomic dysfunction caused by SLE itself.

Abnormal alpha cell hypoglycemic recognition in children with insulin dependent diabetes mellitus (IDDM)

Children with IDDM have diminished glucagon responses to hypoglycemia. We evaluated possible mechanisms in 60 children and adolescents with IDDM (age 15.4 +/- 2.6 years, duration 7.8 +/- 3.5 years [mean +/- SD]) and without diabetic complications. These were: 1) suppression by hyperinsulinism, 2) autonomic neuropathy, 3) a pan-islet cell defect, and 4) a glucotoxic effect. Glucagon and pancreatic polypeptide responses to hypoglycemia (insulin bolus 0.15-0.75 U/kg) were studied after insulin withdrawal and 3 days of intensive insulin therapy. Responses to arginine and mixed meal were also studied. The control group consisted of children with non-growth hormone deficient short stature. IDDM children had lower glucagon responses to hypoglycemia than controls (p < 0.001), the response to arginine did not differ from controls, and was greater than the response to hypoglycemia (p < 0.001). Responses to hypoglycemia after insulin withdrawal and intensive therapy did not differ. Basal pancreatic polypeptide levels were lower in IDDM than in controls (p < 0.05) but responses to hypoglycemia did not differ between groups. Thus the diminished glucagon response to hypoglycemia reflects a defect in hypoglycemic recognition or response by the alpha cells.

Effect of loxiglumide, a cholecystokinin antagonist, on pancreatic polypeptide release in humans

The purpose of this study was to determine the role of cholecystokinin in the regulation of postprandial pancreatic polypeptide secretion in humans. The pancreatic polypeptide responses to modified sham feeding and gastric instillation of a test meal were first compared with the response to oral ingestion of the same meal. The experiments were repeated under cholinergic (atropine) and cholecystokinin (loxiglumide) blockade. Atropine completely abolished the pancreatic polypeptide response to sham feeding and caused significant reductions after gastric and oral food intake. Loxiglumide, on the other hand, significantly reduced pancreatic polypeptide release to oral food (51% inhibition) without affecting the response to sham feeding. In separate experiments using a duodenal perfusion system, the effects of atropine and loxiglumide on intestinal phase-stimulated pancreatic polypeptide release were examined, and both cholinergic and cholecystokinin blockade induced complete suppression. It was concluded (a) that cholecystokinin is involved in postprandial pancreatic polypeptide response, especially during the intestinal phase stimulation, and (b) that the cholinergic system is crucial and superimposed on cholecystokinin in stimulating pancreatic polypeptide release.

Cholecystokinin is a regulator of intestinal phase-stimulated PP release

The purpose of this study was to determine the role of CCK during the intestinal phase of pancreatic polypeptide (PP) release in man. We first compared the PP response to exogenous caerulein infusion in the presence or absence of either loxiglumide (a specific CCK antagonist) or atropine in six healthy subjects. In the second part of the study, a meal was perfused to the duodenum with and without either loxiglumide or atropine. Both loxiglumide and atropine completely abolished the PP response to exogenous or endogenous stimulation (P less than 0.05). We conclude that CCK participates in the intestinal phase of PP secretion.

Stress-induced changes in gastric emptying, postprandial motility, and plasma gut hormone levels in dogs

The influence of acoustic stress on postprandial gastrointestinal motility, gastric emptying, and plasma gastrin, pancreatic polypeptide, motilin, and somatostatin was evaluated in conscious dogs. Six dogs were equipped with strain-gauge transducers and were exposed from 1-3 h after the meal to prerecorded music (80-90 dB broad frequency noise), which produced a significant (p less than or equal to 0.05) lengthening of the gastric (31.2%) and jejunal (37.0%) postprandial pattern. In 4 other dogs with gastric cannula, a 2-h session of acoustic stress beginning just after eating a radiolabeled standard meal induced a slowing of gastric emptying of both liquid (45.7%) and solid (47.1%) phases of the test meal when measured 0.5 h after feeding. In contrast, when measured 2 h after feeding, similar values of gastric emptying of liquids and solids were observed in stressed and control animals. Compared with controls, the postprandial increases of plasma gastrin and pancreatic polypeptide levels were significantly enhanced in stressed animals and occurred early (15 min after the meal). Although postprandial decrease in plasma motilin was unchanged by acoustic stress, the rise in plasma somatostatin level was significantly (p less than or equal to 0.05) prolonged in stressed dogs. These results indicate that acoustic stress affects gastric and intestinal postprandial motility in dogs, delaying the recovery of the migrating motor complex pattern, inducing a transient slowing of gastric emptying, and enhancing the feeding-induced release of gastrin, pancreatic polypeptide, and somatostatin. Such hormonal changes might be due to a direct effect of stress rather than being the consequence of acoustic stress-induced slowing of gastric emptying.

CCK receptors in release of pancreatic polypeptide (PP) in dogs

Pancreatic polypeptide (PP) is released after ingestion of protein-fat meals and following administration of some gut hormones (CCK and bombesin), but the hormonal contribution to the physiological release of PP has not been elucidated. We used specific and potent CCK-receptor antagonist, L-364,718, administered intravenously in a dose of 0.5 mumol/kg or intraduodenally in a dose of 2 mumol/kg to assess the role of CCK in the release of PP. Exogenous CCK-8 infused intravenously in gradually increasing doses (12.5-400 pmol/kg/hr) caused a dose-dependent increase in plasma PP from basal 28 +/- 4 pM to 136 +/- 18 pM, and this PP increase was completely suppressed by both intravenous and intraduodenal administration of L-364,718. Meat feeding caused a dramatic increase in plasma PP from a basal level of 26 +/- 4 pM to a peak of about 190 +/- 32 pM, and the pretreatment with intravenous or intraduodenal L-364,718 reduced this PP increase by about 60%. Duodenal perfusion with oleate (0.12-4.0 mmol/hr) or L-Trp (0.12-4.0 mmol/hr) also increased plasma PP, reaching, respectively, 180 +/- 28 pM and 76 +/- 6 pM. Pretreatment with intravenous or intraduodenal L-364,718 completely abolished the plasma PP responses to oleate and L-Trp. Bombesin (100 pmol/kg/hr) raised plasma PP to the level similar to that achieved by meat feeding and L-364,718 given intravenously or intraduodenally blocked completely these plasma PP increments.(ABSTRACT TRUNCATED AT 250 WORDS)

Asthma and diabetes mellitus: a biochemical basis for antithetical features

Diabetes mellitus and asthma have many antipodal features. Although both are common disorders, concurrence occurs less often than would be predicted. When co-existence does occur, the cases are generally mild, and effective treatment of one disease frequently exacerbates the other. The hypothesis is advanced that basilar membrane concentrations of heparan sulfate differ in these two diseases and that this difference may account for the antithetical features. An experimental basis for postulating increased concentrations of extracellular heparan sulfate in asthma and diminished concentrations in diabetes is cited. A rationale for tying these differences to the polar activities of cholinergic transmission and atherogenesis in the two diseases is advanced. Diminished heparan sulfate concentrations in diabetes may down-regulate the transmission of vagal impulses to insulin-producing pancreatic cells, and thereby impair both the continued vitality of these cells, and the acetylcholine modulated potentiation of glucose-induced insulin release.

Elevated levels of fasting and glucose-stimulated pancreatic polypeptide in patients with duodenal ulcer

Mean fasting preoperative pancreatic polypeptide levels in a group of 18 patients with duodenal ulcer disease were 462 +/- 88 pg/ml, with 13 patients having markedly elevated levels (mean 600 +/- 106 pg/ml) and 5 patients having normal or minimally elevated levels (mean 112 +/- 32 pg/ml). Mean fasting postoperative pancreatic polypeptide levels significantly decreased to 136 +/- 36 pg/ml, with decreases occurring in 12 of 13 patients who had had markedly elevated preoperative values. Parietal cell vagotomy and truncal vagotomy produced significant reductions in both fasting pancreatic polypeptide levels and in the glucose-stimulated pancreatic polypeptide response during the first 60 minutes. There was no correlation between pancreatic polypeptide levels (fasting and stimulated) and duration of ulcer disease, indications for ulcer operation, type of operation, or age of patient. These results suggest that elevated fasting pancreatic polypeptide levels may indicate vagal hyperactivity in some patients with duodenal ulcer.