Pancreatic Secretory Response Research Articles

Efficiency of Bone Marrow-Derived Mesenchymal Stem Cells and Hesperetin in the Treatment of Streptozotocin-Induced Type 1 Diabetes in Wistar Rats.

Type 1 diabetes mellitus (T1DM) was established to be ameliorated by islet transplantation, but the shortage of the transplanted human islet tissue and the use of immunosuppressive drugs to inhibit the rejection of allogeneic grafts make this type of therapy is limited. Nowadays, therapy with stem cells is one of the most promising future treatments. This kind of therapy could have a profound impact on both replacement, as well as regenerative therapies, to improve or even cure various disorders, including diabetes mellitus. Flavonoids have also been shown to possess anti-diabetic effects. Thus, this study aims to evaluate the effectiveness of the bone marrow-derived mesenchymal stem cells (BM-MSCs) and hesperetin in the treatment of a T1DM rat model. T1DM was induced in male Wistar rats that had been starved for 16 h via intraperitoneal injection of STZ at a dose of 40 mg/kg body weight (b.wt.). After 10 days of STZ injection, the diabetic rats were allocated into four groups. The first diabetic animal group was considered a diabetic control, while the other three diabetic animal groups were treated for six weeks, respectively, with hesperetin (given orally at a dose of 20 mg/kg b.wt.), BM-MSCs (injected intravenously at a dose of 1 × 106 cells/rat/week), and their combination (hesperetin and BM-MSCs). The use of hesperetin and BM-MSCs in the treatment of STZ-induced diabetic animals significantly improved the glycemic state, serum fructosamine, insulin and C-peptide levels, liver glycogen content, glycogen phosphorylase, glucose-6-phosphatase activities, hepatic oxidative stress, and mRNA expressions of NF-κB, IL-1β, IL-10, P53, and Bcl-2 in pancreatic tissue. The study suggested the therapy with both hesperetin and BM-MSCs produced marked antihyperglycemic effects, which may be mediated via their potencies to ameliorate pancreatic islet architecture and insulin secretory response, as well as to decrease hepatic glucose output in diabetic animals. The improvement effects of hesperetin and BM-MSCs on the pancreatic islets of diabetic rats may be mediated via their antioxidant, anti-inflammatory, and antiapoptotic actions.

Heterogeneous expression of CFTR in insulin-secreting β-cells of the normal human islet.

Cystic fibrosis (CF) is due to mutations in the CF-transmembrane conductance regulator (CFTR) and CF-related diabetes (CFRD) is its most common co-morbidity, affecting ~50% of all CF patients, significantly influencing pulmonary function and longevity. Yet, the complex pathogenesis of CFRD remains unclear. Two non-mutually exclusive underlying mechanisms have been proposed in CFRD: i) damage of the endocrine cells secondary to the severe exocrine pancreatic pathology and ii) intrinsic β-cell impairment of the secretory response in combination with other factors. The later has proven difficult to determine due to low expression of CFTR in β-cells, which results in the general perception that this Cl−channel does not participate in the modulation of insulin secretion or the development of CFRD. The objective of the present work is to demonstrate CFTR expression at the molecular and functional levels in insulin-secreting β-cells in normal human islets, where it seems to play a role. Towards this end, we have used immunofluorescence confocal and immunofluorescence microscopy, immunohistochemistry, RT-qPCR, Western blotting, pharmacology, electrophysiology and insulin secretory studies in normal human, rat and mouse islets. Our results demonstrate heterogeneous CFTR expression in human, mouse and rat β-cells and provide evidence that pharmacological inhibition of CFTR influences basal and stimulated insulin secretion in normal mouse islets but not in islets lacking this channel, despite being detected by electrophysiological means in ~30% of β-cells. Therefore, our results demonstrate a potential role for CFTR in the pancreatic β-cell secretory response suggesting that intrinsic β-cell dysfunction may also participate in the pathogenesis of CFRD.

Glutamine deprivation induces metabolic adaptations associated with beta cell dysfunction and exacerbate lipotoxicity

Studies have reported that plasma glutamine is reduced in type 2 diabetes (T2D) patients. Glutamine supplementation improves glycaemic control, however the mechanisms are unclear. Here, we evaluated in vitro the pancreatic beta cell bioenergetic and insulin secretory responses to various levels of glutamine availability, or treatment in the presence of an inhibitor of intracellular glutamine metabolism. The impact of glutamine deprivation to the pathological events induced by the saturated fatty acid palmitate was also investigated. Glutamine deprivation induced a reduction in mitochondrial respiration and increase in glucose uptake and utilization. This phenotype was accompanied by impairment in beta cell function, as demonstrated by diminished insulin production and secretion, and activation of the unfolded protein response pathway. Palmitate led to insulin secretory dysfunction, loss of viability and apoptosis. Importantly, glutamine deprivation significantly exacerbated these phenotypes, suggesting that low glutamine levels could participate in the process of beta cell dysfunction in T2D.

Pancreatic Exocrine Function in Chickens

The pancreatic secretory response to the Garlic allicin dietary supplement under the conditions of an experiment with chickens implanted with pancreatic duct chronic fistulas has been studied. The results prove that the amylolytic and proteolytic activities increase the secretion at 1 mL in chickens in the test period (8 days). However, there is no significant change in the total volume of juice for 180 minutes. The analysis of the adaptation mechanism in the postprandial phase indicates an enzyme activity increase in the complex reflective cycle caused by both the receptors responding to the food tastes and the conditioned reflex factors. The adaptation developed within 8 days is associated with a sharp (twofold) increase in the proteolytic activity on the third day and the following proteinase activity decrease up to the initial rate of the enzyme activity.

Prospective Assessment of Normal Pancreatic Secretory Function Measured by MRI in a Cohort of Healthy Children.

Magnetic resonance imaging (MRI) with secretin stimulation promises to allow non-invasive testing for exocrine pancreatic insufficiency but normal data do not exist for children. The purpose of this study was to define, in healthy children, normal pancreatic secreted fluid volume and secretion rate, measured by MRI, in response to secretin. In this Institutional Review Board-approved, prospective, cross-sectional study, 50 healthy children ages 6 to <16 years underwent MRI with secretin stimulation. Images were obtained before and at 1, 5, 10 and 15 min after secretin administration to calculate total secreted fluid volume and secretion rate based on image segmentation. Regression was used to define the relationship between secretory function and participant size measures, and linear quantile regression was used to define normal secretory values based on size measures. Median total secreted fluid volume post secretin was 79 mL (range: 32-162 mL; 5th and 95th percentiles: 43 and 123 mL) and median secretion rate was 5.1 mL/min (range: 2-9.4 mL/min; 5th and 95th percentiles: 2.3 and 7.7 mL/min). Secreted volume and secretion rate had the strongest correlation with body surface area (BSA) (r = 0.54 and 0.59, respectively) and multiple regression defined BSA as the only significant predictor of secretory function. Each 1 m2 increase in BSA was associated with a 38 mL increase in secreted fluid volume. In children, pancreatic secretory response to secretin, measured by MRI, depends on participant size, particularly BSA. Secreted volume <43 mL or a secretion rate <2.3 mL/min (5th percentile values) can be considered abnormal for children.

Tu1377 - Pancreatic Stellate Cells Increase Insulin Secretory Response from Min6 Cells: Is Interleukin 6 the Mediator?

Tu1377 - Pancreatic Stellate Cells Increase Insulin Secretory Response from Min6 Cells: Is Interleukin 6 the Mediator?

Effect of Endotoxemia in Suckling Rats on Pancreatic Integrity and Exocrine Function in Adults: A Review Report.

Background. Endotoxin (LPS), the component of Gram-negative bacteria, is responsible for sepsis and neonatal mortality, but low concentrations of LPS produced tissue protection in experimental studies. The effects of LPS applied to the suckling rats on the pancreas of adult animals have not been previously explored. We present the impact of neonatal endotoxemia on the pancreatic exocrine function and on the acute pancreatitis which has been investigated in the adult animals. Endotoxemia was induced in suckling rats by intraperitoneal application of LPS from Escherichia coli or Salmonella typhi. In the adult rats, pretreated in the early period of life with LPS, histological manifestations of acute pancreatitis have been reduced. Pancreatic weight and plasma lipase activity were decreased, and SOD concentration was reversed and accompanied by a significant reduction of lipid peroxidation products (MDA + 4 HNE) in the pancreatic tissue. In the pancreatic acini, the significant increases in protein signals for toll-like receptor 4 and for heat shock protein 60 were found. Signal for the CCK1 receptor was reduced and pancreatic secretory responses to caerulein were diminished, whereas basal enzyme secretion was unaffected. These pioneer studies have shown that exposition of suckling rats to endotoxin has an impact on the pancreas in the adult organism.

Intergenerational impact of maternal overnutrition and obesity throughout pregnancy in sheep on metabolic syndrome in grandsons and granddaughters

We previously reported that maternal overnutrition and obesity (MO) throughout pregnancy and lactation in sheep (MOF0) decreases term fetal pancreatic β-cell numbers and increases perirenal adiposity producing hyperphagia, increased adiposity and insulin resistance in adult female offspring (MOF1) fed ad libitum. Pregnant female MOF1 exhibited increased blood glucose from mid to late gestation vs control F1 (CTRF1) though both groups ate only to NRC recommendations. MOF1 ewes delivered female offspring (F2) who like their MOF1 mothers exhibited increased abdominal adiposity and absent neonatal leptin surge. In the current work, we determined if adult MOF2 exhibited metabolic syndrome components when fed ad libitum. After weaning, MOF2 males (n = 5), MOF2 females (n = 6), CTRF2 males (n = 5), and CTRF2 females (n = 6) were fed to NRC requirements until 19 mo followed by 12-wk ad libitum feeding. Body weight and % fat increased (P < 0.01) in all F2 during this feeding trial. MOF2 males were heavier (P < 0.01) than CTRF2 males and females, and MOF2 females throughout the trial. By wk 8, baseline blood glucose concentrations increased (P < 0.001) in MOF2 females, but not other groups, remaining elevated throughout the trial. Baseline insulin was similar through wk 6, increasing (P < 0.05) at wk 8 in MOF2 females only. MOF2 female insulin returned to CTRF2 female levels during wk 10 and 12. The progressive increase of plasma glucose on wk 8 in association with increased insulin in MOF2 females but not other groups demonstrated a diet-induced increase (P < 0.001) in MOF2 female insulin resistance. The subsequent decline in insulin during wk 10 and 12 despite elevated glucose in MOF2 females is consistent with a decrease in glucose-stimulated pancreatic β-cell function. These data indicate that ad libitum feeding exceeds the pancreatic secretory response predisposing MOF2 females to hyperglycemia. Furthermore, there was a sex difference where MOF2 males increased body mass and MOF2 females displayed insulin/glucose dysregulation.

I10W]tigerinin-1R enhances both insulin sensitivity and pancreatic beta cell function and decreases adiposity and plasma triglycerides in high-fat mice.

We have previously described the insulinotropic activities of [I10W]tigerinin-1R (RVCSAIPLPWCH.NH2) in vitro. In this study, we investigated the effects of the peptide on nutrient homoeostasis in mice with diet-induced obesity and insulin resistance. Male NIH Swiss mice were maintained on a high-fat diet for 12 weeks prior to the study. Twice-daily intraperitoneal injections of [I10W]tigerinin-1R (75nmol/kg body weight) were administered for 28days. Body weight, energy intake, body fat content, and plasma concentrations of triglyceride, cholesterol, non-fasting glucose and insulin were monitored. Effects of the peptide on glycaemic control were measured by glucose tolerance and insulin sensitivity tests. Pancreatic hormone content and insulin secretory responses of islets isolated from treated and untreated mice were examined. Immunohistochemical analysis was performed to study possible changes in islet morphology. Administration of [I10W]tigerinin-1R to high-fat-fed mice produced significant (P<0.05) decreases in plasma glucose, glucagon and triglyceride concentrations and an increase in plasma insulin compared to high-fat-fed controls. No changes in body weight or energy intake were observed with peptide treatment, but glycaemic control was significantly improved in response to oral or intraperitoneal glucose. Insulin sensitivity and secretory responses of islets to established insulin secretagogues were also significantly improved in peptide-treated mice. Total body fat, pancreatic insulin and glucagon contents, islet, beta and alpha cell areas were all significantly decreased in treated mice. This study shows that [I10W]tigerinin-1R improves insulin sensitivity, islet function and glycaemic control in high-fat-fed mice and has potential as a template for development of novel anti-diabetic agents.

Genetics of acute and chronic pancreatitis: An update.

Progress made in identifying the genetic susceptibility underlying acute and chronic pancreatitis has benefitted the clinicians in understanding the pathogenesis of the disease in a better way. The identification of mutations in cationic trypsinogen gene (PRSS1 gene; functional gain mutations) and serine protease inhibitor kazal type 1 (SPINK1 gene; functional loss mutations) and other potential susceptibility factors in genes that play an important role in the pancreatic secretory functions or response to inflammation during pancreatic injury has changed the current concepts and understanding of a complex multifactorial disease like pancreatitis. An individual's susceptibility to the disease is governed by genetic factors in combination with environmental factors. Candidate gene and genetic linkage studies have identified polymorphisms in cationic trypsinogen (PRSS1), SPINK1, cystic fibrosis trans-membrane conductance regulator (CFTR), Chymotrypsinogen C (CTRC), Cathepsin B (CTSB) and calcium sensing receptor (CASR). Individuals with polymorphisms in the mentioned genes and other as yet identified genes are at an enhanced risk for the disease. Recently, polymorphisms in genes other than those involved in "intra-pancreatic trypsin regulatory mechanism" namely Claudin-2 (CLDN2) and Carboxypeptidase A1 (CPA1) gene have also been identified for their association with pancreatitis. With ever growing number of studies trying to identify the genetic susceptibility in the form of single nucleotide polymorphisms, this review is an attempt to compile the available information on the topic.

Efficacy and safety of sitagliptin in Japanese patients with type2 diabetes switched from glinides.

The efficacy and safety of sitagliptin, a dipeptidyl peptidase (DPP)-4 inhibitor, were compared with those of glinides in Japanese patients with type2 diabetes. The participants were 82 patients with type2 diabetes (glycated hemoglobin [HbA1c] ≥6.0% and <10%) under treatment with glinides for glucose control. The participants were randomly assigned to a group (n=44) receiving continuous treatment with glinides and a group (n=38) switched to sitagliptin. Patients were followed for 12weeks to evaluate glucose control. A meal tolerance test was carried out in weeks 0 and 12 to examine the pancreatic secretory response to postprandial hyperglycemia. The changes in HbA1c from week 0 to week 12 were -0.25 and -0.05% in the sitagliptin and glinide groups, respectively, with a significant improvement with sitagliptin. The differences in fasting plasma glucose (FPG), glycoalbumin and 1,5-anhydroglucitol between the two groups were 14.2mg/dL, 0.7% and 1.7μg/mL, respectively, showing significant improvements with sitagliptin. In the meal tolerance test, glucose at 0min was lower in the sitagliptin group; however, there were no differences in glucose elevation at 30 and 60min compared with 0min. Plasma insulin and glucagon secretion at week12 were significantly lower than at baseline in the sitagliptin group. Adverse events including hypoglycemia did not differ between the groups. FPG decreased and glucose control improved in patients who switched from glinides to sitagliptin. Sitagliptin decreased secretion of insulin and glucagon in a meal tolerance test compared with glinides, whereas the agents showed similar inhibition of postprandial hyperglycemia. This trial was registered with UMIN (UMIN-CTR no. 000003479).

Effect of nicotine on exocytotic pancreatic secretory response: role of calcium signaling

BackgroundNicotine is a risk factor for pancreatitis resulting in loss of pancreatic enzyme secretion. The aim of this study was to evaluate the mechanisms of nicotine-induced secretory response measured in primary pancreatic acinar cells isolated from Male Sprague Dawley rats. The study examines the role of calcium signaling in the mechanism of the enhanced secretory response observed with nicotine exposure.MethodsIsolated and purified pancreatic acinar cells were subjected to a nicotine exposure at a dose of 100 μM for 6 minutes and then stimulated with cholecystokinin (CCK) for 30 min. The cell’s secretory response was measured by the percent of amylase released from the cells in the incubation medium Calcium receptor antagonists, inositol trisphosphate (IP3) receptor blockers, mitogen activated protein kinase inhibitors and specific nicotinic receptor antagonists were used to confirm the involvement of calcium in this process.ResultsNicotine exposure induced enhanced secretory response in primary cells. These responses remained unaffected by mitogen activated protein kinases (MAPK’s) inhibitors. The effects, however, have been completely abolished by nicotinic receptor antagonist, calcium channel receptor antagonists and inositol trisphosphate (IP3) receptor blockers.ConclusionsThe data suggest that calcium activated events regulating the exocytotic secretion are affected by nicotine as shown by enhanced functional response which is inhibited by specific antagonists… The results implicate the role of nicotine in the mobilization of both intra- and extracellular calcium in the regulation of stimulus-secretory response of enzyme secretion in this cell system. We conclude that nicotine plays an important role in promoting enhanced calcium levels inside the acinar cell.

Emergence of ageing-related changes in insulin secretion by pancreatic islets of male rat offspring of mothers fed a low-protein diet

Maternal low-protein (LP) diets programme β-cell secretion, potentially altering the emergence of ageing of offspring pancreatic function. We hypothesised that isolated pancreatic islet β-cell secretory responses are blunted in offspring exposed to LP during development and age-related reduction is influenced by the developmental stage of exposure to decreased nutrition. We studied male offspring of rats fed control (C) or LP protein (R) diets in pregnancy, first letter and/or lactation second letter of CC, RR, CR or RC groups. Serum glucose, insulin and homeostatic model assessment (HOMA) were measured. Pancreatic islets were isolated and in vitro insulin secretion quantified in low (LG - 5 mM) or high glucose (HG - 11 mM). Body weight and serum values between groups were similar at all ages. Insulin and HOMA rose with age and were highest at postnatal day (PND) 450 in all groups. At PND 36, insulin secretion was greatest in RR and RC. Only CC increased insulin secretion to HG. By PND 110, restricted groups responded less to LG but increased secretion to HG. By PND 450, CC offspring alone increased secretion to HG. Despite minimal differences in circulating insulin and glucose, reduced maternal protein intake affected insulin secretion at all ages. In addition, ageing reduced function in all R groups compared with CC by PND 110 and further by PND 450 most markedly in RC. We conclude that maternal LP diet during pregnancy and/or lactation impairs offspring insulin secretory response to a glucose challenge and alters the trajectory of ageing of pancreatic insulin secretion.

Recent Developments in Acute Pancreatitis

The incidence of acute pancreatitis (AP) has been increasing worldwide, but the major etiologies remain gallstones and alcohol. Several studies have reported that smoking is an independent risk factor for developing AP. Classification of AP has traditionally used the categories of mild and severe disease. However, a new intermediate category of moderately severe AP has been described with intermediate characteristics including a high incidence of local complications but a low mortality. Assessment criteria that can serve as early predictors of AP severity are often complex and not sufficiently accurate. However, several recently described criteria that rely on criteria such as the body mass index, physical findings, and simple laboratory measurements could prove useful if validated in large prospective studies. Many issues related to the therapy of AP are still unresolved. Although preliminary studies support the importance of early volume expansion for the treatment of acute pancreatitis, optimization of the amount and type of fluids will require further studies. Similarly, preliminary studies suggest that enteral nutrition might benefit patients with AP and could even be useful early in the course of disease. However, the timing and type of fluids as well as the intestinal infusion site require further study. Finally, issues related to the prophylactic use of antibiotics in patients with severe AP have not been resolved. While the process of clinical investigation moves slowly, progress has been made in clinical studies of AP.

A numerical deconvolution method to estimate C-peptide secretion in humans after an intravenous glucose tolerance test

Quantitative assessment of pancreatic insulin secretion rate in individuals may help advance our understanding and treatment of diabetes. We describe for the first time the application of a long-established numerical deconvolution procedure in which a prescribed input function is used to represent first-phase pancreatic secretion response to an intravenous glucose challenge (intravenous glucose tolerance test [IVGTT]) in individual subjects. We identify that C-peptide secretory response to an IVGTT can be described by a basal secretion rate ( S b) (picomoles per liter per minute) and a first-phase secretory response characterized by a Gaussian function. The Gaussian function contains 3 parameters: P 1 (picomoles per liter per minute), which represents the peak rate secretion; P 2 (per square minute), which is related to the inverse of peak width at half-peak height; and P 3 (minutes), which is the time of the peak secretion rate. When applied to data from 8 healthy Chinese subjects, the estimated parameter values (mean ± SD) were 19.2 ± 12.9 pmol L −1 min −1, 1548 ± 1143 pmol L −1 min −1, 1.09 ± 1.21 min −2, and 2.94 ± 1.13 minutes for S b, P 1, P 2, and P 3, respectively. The Gaussian input functions are shown to have similar shapes and to be highly concordant in magnitude with secretory responses estimated by means of the method of Eaton et al (1980) and by the ISEC computer program. In conclusion, we have presented a simple, integrated, validated, and easily implemented method suitable for quantifying pancreatic C-peptide and insulin secretion in individual human subjects. The superiority of our method in comparison with other methods is that it uses as an input function the Gaussian, which has been experimentally verified as describing in vivo the profile of pulsatile insulin secretion. The particular strength of our method is that the Gaussian parameters and simple indices derived from them provide a standardized and interpretable means for carrying out comparative investigations aimed at quantifying how pancreatic secretory responses to an IVGTT differ in various demographic groups or in response to therapeutic treatments.

Secretion from acinar cells of the exocrine pancreas: Role of enteropancreatic reflexes and cholecystokinin

Although the molecular machinery and mechanism of cell secretion in acinar cells of the exocrine pancreas is well documented and clear, only recently has the pharmacophysiology of pancreatic exocrine secretion come to light. Therefore, we focus in this article on the current understanding of the pharmacophysiology of pancreatic exocrine secretion. The pancreatic secretory response to ingestion of a meal is mediated via a complex interplay of neural, humoral and paracrine mediators. A major role in the control of the intestinal phase of pancreatic secretion is attributed to vago-vagal enteropancreatic reflexes. In the scheme of this control mechanism, afferents originating in the duodenal mucosa, and efferents mediating central input on the pancreatic ganglia, activate intrapancreatic postganglionic neurons. Experiments utilizing specific receptor antagonists demonstrate the involvement of both muscarinic M1 and M3 receptors expressed in pancreatic acinar cells. Cholecystokinin (CCK), originally implicated in the humoral secretion of pancreatic enzymes, through a direct action on acinar CCK receptors, is also essential to the enteropancreatic reflex mechanism. CCK stimulation of the exocrine pancreatic secretion through excitation of sensory afferents of the enteropancreatic reflexes, is a paracrine mode of CCK action, and is probably the only one in humans and the predominant one in rats. In dogs, however, CCK acts on the pancreas via both the humoral and a paracrine route. More recent experiments suggest further possible sites of CCK action. Additionally, at the brain stem, vago-vagal enteropancreatic reflexes may be modulated by input from higher brain centres, particularly the hypothalamic-cholinergic system in the tonic stimulation of preganglionic neurons of the dorsal motor nucleus of the vagus projecting into the pancreas.

Free Fatty Acids Have More Potent Effects on Gastric Emptying, Gut Hormones, and Appetite Than Triacylglycerides

The effects of fat on gastric emptying (GE), gut hormones, and energy intake are dependent on digestion to free fatty acids (FFAs). In animals, small intestinal oleic acid inhibits energy intake more potently than the triacylglyceride (TG) triolein, but there is limited information about the comparative effects of FFA and TG in human beings. We compared the effects of FFA and TG on GE, gut hormone secretion, appetite, and energy intake in healthy males. Nine men (age, 23 +/- 2 y; body mass index, 22 +/- 1 kg/m(2)) were studied on 3 occasions to evaluate the effects of (1) 40 g oleic acid (FFA, 1830 kJ), (2) 40 g macadamia oil (TG, 1856 kJ; both 600-mL oil-in-water emulsions stabilized with 4% milk protein and labeled with 15 MBq (123)I), or (3) 600 mL 4% milk protein (control, 352 kJ), administered intragastrically, on GE, plasma cholecystokinin (CCK) and peptide-YY (PYY) levels, appetite perceptions, and subsequent energy intake. GE of FFA was much slower than that of TG (P < .05), with greater retention of FFA, than TG, in the proximal stomach (P < .001). Hunger was less (P < .05), and fullness was greater (P < .05), after FFA when compared with control and TG. Increases in plasma CCK and PYY levels were greater after FFA than TG or control (P < .05). Energy intake tended to be less after FFA compared with TG (control, 4754 +/- 610 kJ; TG, 5463 +/- 662 kJ; FFA, 4199 +/- 410 kJ). FFAs empty from the stomach more slowly, but stimulate CCK and PYY and suppress appetite more potently than TG in healthy human beings.

Pioglitazone reverses insulin resistance and impaired CCK-stimulated pancreatic secretion in eNOS(−/−) mice: therapy for exocrine pancreatic disorders?

In mice, eNOS (endothelial nitric oxide synthase) maintains in vivo pancreatic secretory responses to carbachol or cholecystokinin octapeptide (CCK-8), maintains insulin sensitivity, and modulates pancreatic microvascular blood flow (PMBF). eNOS(-/-) mice are insulin resistant, and their exocrine pancreatic secretion is impaired. We hypothesized that the reduced exocrine pancreatic secretion in eNOS(-/-) mice is due to insulin resistance or impaired PMBF. To test this hypothesis, we gave eNOS(-/-) and wild-type (WT) mice pioglitazone (20 or 50 mg.kg(-1).day(-1)), an insulin-sensitizing peroxisome proliferator-activated receptor-gamma (PPAR-gamma) activator, and measured pancreatic protein secretion evoked by CCK-8 (160 pmol.kg(-1).h(-1), a maximal stimulus). We also measured insulin resistance, serum glucose, C-peptide, insulin, pancreatic RNA digestive enzyme expression, and PMBF (microsphere technique). In WT mice, pioglitazone did not increase CCK-8-stimulated protein output over baseline. In eNOS(-/-) mice, however, pioglitazone substantially increased the low CCK-8-stimulated protein output that is characteristic of these mutant mice (P < 0.005). Pioglitazone abolished the CCK-8-evoked hyperinsulinemia (P < 0.005) and increased insulin sensitivity of eNOS(-/-) mice (P < 0.05), the latter based on hyperinsulinemic-euglycemic clamp studies. Pioglitazone had no effect on PMBF or pancreas mRNA expression of insulin or digestive enzymes. We conclude that in hyperinsulinemic eNOS(-/-) mice, a nonobese model of insulin resistance relevant to diabetes mellitus and possibly chronic pancreatitis, reduced pancreatic secretion is caused, at least in part, by insulin resistance. Insulin-sensitizing PPAR-gamma agonists such as pioglitazone may thus simultaneously correct endocrine and exocrine pancreatic disorders.

NORMALIZATION OF INSULIN RESISTANCE & IMPAIRED CCK STIMULATED PANCREATIC SECRETION IN eNOS (???/???) MICE BY PIOGLITAZONE. POTENTIAL FOR CORRECTING HUMAN ENDOCRINE & EXOCRINE DISORDERS?

Background: Recently we showed that eNOS (endothelial NO synthase) maintains in vivo murine pancreatic secretion response to carbachol and CCK-8. Because eNOS also maintains insulin sensitivity and modulates pancreatic blood flow (PBF), our aims were to detemine if pioglitazone (insulin sensitizer) reduces insulin resistence, improves exocrine pancreatic secretion and if changes in pancreatic secretion are coupled to PBF. Methods: WT & eNOS (−/−) mice were gavaged with pioglitazone (20 or 50 mg/kg/d) or vehicle × 5 days. Then mice were anesthetized and the bile-pancreatic duct was cannulated to collect in vivo pancreatic secretion in response to maximal stimulatory CCK-8 (160 pmol/kg/h). We measured serum glucose, parameters of insulin secretion and insulin resistance, pancreatic digestive enzyme mRNA expression, and PBF by microsphere technique. Results: In comparison to vehicle, 20 & 50 mg/kg pioglitazone increased CCK-8 stimulated output (over basal) in eNOS (−/−) mice by 195+/−29%, 266+/−39% and 357+/−47%, respectively (p < 0.005), but not in WT mice (328+/−35%, 336+/−46% and 284+/−48%, respectively, p = ns). During maximal stimulatory CCK, pioglitazone (50 mg/kg) normalized serum hyperinsulinemia in eNOS (−/−) mice receiving vehicle (p < 0.005), had no effect on pancreas insulin mRNA expression or serum c-peptide levels, but increased mRNA expression of a central hepatic insulin signaling intermediate IRS-2 by 1.6-2.0 fold vs. WT and eNOS (−/−) controls, respectively (p < 0.005). Pancreatic mRNA expression of multiple digestive enzymes was unaffected by eNOS genotype. Pioglitazone had no effect on PBF in CCK treated eNOS (−/−) mice, consistent with findings that baseline PBF in WT mice was unaffected by submaximal & maximal stimulatory CCK-8 (40-160 pmol/kg/h). Conclusion: Reduced pancreatic secretion is partially coupled to insulin resistance in eNOS (−/−) mice, and possibly in diabetes mellitus & chronic pancreatitis. Although the mechanism remains unclear, PPAR-gamma agonists may simultaneously correct endocrine & exocrine pancreas disorders.

Pancreatic secretion after selective and truncal vagotomy in the dog.

Abstract External pancreatic secretion was studied in 4 dogs: 2 with a Thomas cannula and 2 with a new cannula in which a duodenal pouch acts as an extension of the pancreatic duct. Peak bicarbonate outputs after a meal were about a third of the maximal secretory capacity of the pancreas in response to single intravenous injections of pure secretin, whereas peak protein concentrations and outputs after a meal were of the order of the maximum response to injections of secretin and pancreozymin. There were no consistent changes in hormonestimulated pancreatic secretion after selective vagotomy. Meal-stimulated pancreatic secretion was markedly reduced after truncal vagotomy (81 per cent reduction in peak bicarbonate output, 65 per cent in peak protein output). Secretin-stimulated bicarbonate output was markedly decreased 3 weeks after truncal vagotomy, but then gradually increased to control values, and in 1 dog to twice the control. Pancreozymin-stimulated protein output was increased after truncal vagotomy, reaching values two to three times the control. Local anaesthetics applied topically to the periampullary duodenal mucosa markedly inhibited secretin-stimulated bicarbonate output even after truncal vagotomy, but there was only slight reduction after subcutaneous lignocaine. The reduction in food-stimulated pancreatic secretion after truncal vagotomy is unlikely to be caused by pancreatic denervation, since the postvagotomy pancreatic response to direct stimulation with exogenous hormones is normal or supranormal, and is probably due to decreased release of gastrointestinal hormones after a meal. Local reflex arcs may influence the pancreas and may explain (by denervation supersensitivity) the post-vagotomy increase in pancreatic secretion as well as the effects of topical local anaesthetics. The role of neural factors in the regulation of external pancreatic secretion has long been disputed. This subject is now of particular clinical interest in relation to the causes of post-vagotomy diarrhoea and steatorrhoea (for a review of the literature, see Cox, 1969). With the development of a new cannula for studying external pancreatic secretion in the unanaesthetized dog (Thambugala, 1971) the opportunity was taken to study the effects of selective and truncal vagotomy on the pancreatic secretory responses to food and pure secretin and pancreozymin.