Normal Rat Pancreas Research Articles

Expression and function of leukaemia inhibitory factor and its receptor in normal and regenerating rat pancreas

It was recently reported that culturing adult exocrine cells in the presence of epidermal growth factor and leukaemia inhibitory factor (LIF) resulted in their transdifferentiation into endocrine beta cells. The aim of this study was to examine the expression and function of LIF in the pancreas. We studied the expression of LIF and its receptor components, LIF-receptor-beta and gp130, by immunohistochemistry, western blotting and RT-PCR in normal rat pancreas, pancreas with duct ligation-induced islet neogenesis, and in pancreatic cell cultures. Isolated duct fragments were cultured in the presence of LIF and a janus kinase 2 (JAK2) inhibitor. LIF was detected by immunohistochemistry, western blot and RT-PCR in the ducts of the normal pancreas. Both LIF-receptor-beta and gp130 were detected by RT-PCR in the pancreas. Immunostaining revealed gp130 exclusively in the ducts and centro-acinar cells. After duct ligation-induced tissue injury, upregulation of LIF and its receptor occurred in rat pancreas. Metaplastic exocrine cells also started to express LIF and this was increased after alloxan treatment. Signalling via LIF-receptor-beta/gp130 involves the JAK/signal transducer and activator of transcription (STAT) pathway. LIF induced increased activation of STAT3 in pancreatic cells. In isolated duct fragments, addition of LIF resulted in a significant increase in duct cell proliferation, while a specific inhibitor of the JAK/STAT signalling pathway inhibited proliferation. Our observations show that LIF and its receptor are expressed in cells from pancreatic ducts. The cytokine plays a role in pancreatic physiology, controls duct cell proliferation and is involved in repair processes following pancreatic injury.

Immunolocalization of orexin-1 receptor the pancreas of normal and diabetic rats

Orexins have been implicated in several biological functions, such as food and water intake. This study examined the pattern of distribution of orexin-1 receptor (OX1R) in the pancreas of normal and diabetic rats. Diabetes mellitus (DM) was induced by streptozotocin (STZ). Four weeks after the induction of DM, the pancreases of normal and diabetic rats were processed for immunohistochemistry. OX1R-positive cells were observed in the periphery of pancreatic islets of normal and in both the peripheral and central regions of the islet of diabetic rats. The number of OX1R-positive cells in the islets increased significantly (p < 0.0001) after the onset of diabetes. Moreover, ganglion cells and the periductal and interlobular nerve fibres of the exocrine pancreas also expressed OX1R. In conclusion, OX1R may play a role in the initiation of increased food intake via pancreatic hormones.

ACTIVATION OF RAT PANCREAS MECHANOSENSITIVE SPINAL AFFERENTS IN A NOVEL IN VITRO PREPARATION

Few studies have recorded afferent nerve discharge from the pancreas and the role of afferent nerves in pancreatic physiology and pathophysiology is very poorly understood. Aims: To map and characterise mechanosensitive afferents in the normal rat pancreas. Methods: A preparation consisting of the pancreas, attached spleen and duodenum, and including the pancreatic duct (PD), common bile duct (CBD) and the sympathetic chain was obtained from anaesthetised Sprague Dawley rats (n = 9). The CBD was cannulated. The preparation was placed in a 2 chamber organ bath. Extracellular nerve recordings were obtained from fibers teased from the sympathetic chain adjacent to the coeliac ganglia. Nerve discharge evoked by blunt probing, CBD/PD distension (44 mmHg), or electrical field stimulation (EFS; n = 3; 20 V, 0.5 ms duration) of pancreas was recorded. Results: Discharge from 137 fibers was recorded, of which 50% displayed spontaneous activity. Blunt probing evoked a discharge in 20% of fibers whereas EFS evoked discharge in 11/42 fibers, of which 3 receptive fields responded to blunt probing. Based on conduction velocity measurements (0.36 ± 0.06 m/s; n = 16 fibers), recordings were from C fibers. Mechanosensitive receptive fields were associated with arteries/blood vessels in the pancreas (16/32), pancreas near lymph nodes (2/32), pancreatic tissue (12/32), CBD (1/32) and duodenal mesentery (1/32). Non-mechanosensitive receptive fields were located in pancreatic tissue (5/11), arteries/blood vessels (5/11) or CBD/PD (1/11). CBD/PD distension did not evoke any discharge. Conclusion: Mechanosensitive and non-mechanosensitive afferent nerves are associated with several structures in the pancreas. Their role in physiological and pathophysiological signaling remains to be established. Supported by the FMC Foundation.

Alterações histológicas e imunoistoquímicas em pâncreas de ratos normais e diabéticos tratados com Syzygium cumini

Avaliou-se o efeito da administração oral do extrato da casca de Syzygium cumini sobre o pâncreas de ratos normais e diabéticos. Os animais foram divididos em grupo controle (C), controle tratado (CT), diabético controle (DC) e diabético tratado (DT). Os tratados receberam dose diária de 1g kg-1 de peso vivo, durante 30 dias. Os animais foram submetidos à eutanásia e o pâncreas retirado para análise histológica e imunoistoquímica para insulina. Neste estudo observou-se uma diminuição (P&lt;0,001) no número e tamanho das ilhotas pancreáticas, alteração na sua citoarquitetura e diminuição (P&lt;0,0001) do número de células com marcação positiva para insulina nos animais diabéticos em relação aos não diabéticos. Não foi observada diferença entre os animais dos grupos DC e DT e entre os dos grupos C e CT. Estes resultados indicam que o extrato da casca de Syzygium cumini não afeta o número, o tamanho e a citoarquitetura das ilhotas pancreáticas e não promove um aumento no número de células beta em animais tratados com a planta.

Gliclazide at a lower concentration than therapeutic dose increases the sensitivity of insulin secretion to glucose in perfused rat pancreas

We studied the difference between effects of therapeutic dose and sub-therapeutic dose of gliclazide on the glucose-induced insulin secretion. The normal rat pancreas was isolated and perfused with Krebs-Ringer buffer containing 1-14 mmol/l glucose. Influcences of 0.25 and 2.5 microg/ml gliclazide on the glucose concentration-insulin secretion curve was examined. Gliclazide at 0.25 microg/ml significantly potentiated 5-8 mmol/l glucose-induced insulin secretion (2.5 +/- 0.5 vs 1.0 +/- 0.3 mU for 15 min at 6.5 mmol/l glucose, P<0.01), but did not give influence on either 1-3 or 10-14 mmol/l glucose-induced insulin secretion. The glucose concentration, at which half-maximal insulin secretion was observed, was lower with gliclazide (5.9 mmol/l) than in the control (7.5 mmol/l). Gliclazide at 2.5 microg/ml markedly increased the maximally glucose-stimulated insulin secretion from 3.9 +/- 0.5 mU for 15 min in the control to 6.6 +/- 0.7 mU for 15 min (P<0.01). The half-maximal insulin secretion was observed at a lower glucose concentration (5.0 mmol/l) than in the absence of gliclazide. Gliclazide in sub-therapeutically low dose has different effects on insulin secretion from in therapeutic dose, namely sharpens the insulin secretion sensitivity to glucose with no influence on the maximal insulin secretion. It is possible that low doses of gliclazide might be of interest in some type 2 diabetics whose main pathophysiology is the blunting of insulin secretion response to hyperglycemia.

Lisofylline, a novel anti-inflammatory agent, enhances glucose-stimulated insulin secretion in vivo and in vitro: studies in prediabetic and normal rats

Previous studies from this laboratory have shown that the novel anti-inflammatory agent, lisofylline (LSF), improves oral glucose tolerance in streptozotocin (STZ) diabetic rats. Subsequent studies suggested that the improved glucose tolerance could be the result of enhanced β-cell functioning. The possibility that LSF enhancement of insulin release in these animals is the result of direct effects of this agent on a residual population of functionally normal β cells was further evaluated in these studies. In vivo studies: 6- to 8-week-old male rats were administered STZ (35 mg/kg body weight) intravenously. After 10 days, LSF administration (25 mg/kg body weight, twice daily) was initiated in the treated group (n = 11) for comparison with the vehicle-injected controls (n = 10). Body weight, food intake, and serum glucose and insulin levels were monitored weekly. Glucose and insulin responses to an oral glucose bolus were measured at 4 to 5 weeks as an index of LSF effects on impaired glucose tolerance. Glucose areas under curve (AUC) during the 2-hour tolerance tests in the LSF-treated rats (n = 11) were 23,390 ± 253 versus 29,390 ± 1,006 mg/dL × min ( P < .0001) in the vehicle-injected rats (n = 10). Improved glucose tolerance was associated with increases in blood insulin levels in the LSF-treated rats, AUC (+LSF) = 6,564 ± 66 versus 5,127 ± 633 μU/mL × min in the vehicle-injected STZ-rats (not significant [NS]). These observations suggested that the improved glucose tolerance is the result of direct effects of LSF on glucose-induced release of insulin. In vitro studies: the validity of this hypothesis was subsequently tested using isolated perfused pancreas preparations from normal rats. In this series of experiments, 12-week-old animals were used, and pancreases were perfused in situ using single-pass technique. Three levels of LSF were directly infused into individual pancreas preparations and included 20 (n = 5), 40 (n = 4), and 60 (n = 4) μmol/L. First (minutes 3 to 10) and second (minutes 13 to 35) phase glucose-stimulated (300 mg/dL) insulin response areas (AUC) for the 2 phases measured in the LSF-infused pancreases were compared with AUC in vehicle-infused pancreases (n = 4). At LSF concentrations of 20 and 40 μmol/L, total insulin released during the first phase of glucose stimulation was more than twice that of the controls (3,919 ± 739 and 3,643 ± 630 μU, respectively v 1,481 ± 269 μU, P < .03). A total of 60 μmol/L LSF did not significantly enhance first phase glucose-induced insulin secretion. Second phase comparisons of total insulin released in the LSF-infused versus the controls showed differences of comparable magnitude (about 2-fold) with statistical significance ( P < .03) observed at all 3 levels of LSF. These findings demonstrate that LSF enhances glucose-stimulated insulin release in vitro. Enhanced β-cell functioning by LSF likely represents an important factor underlying improved glucose tolerance in vivo. In addition, the in vitro observations in normal rat pancreas indicate that the LSF effect is not limited to β-cell dysfunction per se. These results support the conclusion that agents, such as LSF, may have therapeutic benefits in type 2 diabetes.

The expression of pancreatic endocrine markers in centroacinar cells of the normal and regenerating rat pancreas: their possible transformation to endocrine cells.

To determine the progenitor nature of centroacinar cells (CACs), we attempted to compare the expression pattern of endocrine cell markers and PDX-1 (pancreatic duodenal homeobox gene 1) in CACs of both the quiescent and the regenerating rat pancreas. In the normal pancreas, most CACs were relatively small cells with sparse cytoplasm and oval or elongated nuclei. In addition, we noticed a distinct population of a small number of large cells with round nuclei in the centroacinar region. By immunohistochemistry, 0.21% and 0.3% of CACs in normal rat pancreas were respectively found positive for glucagon and insulin, being large CACs and designated as GL-CAC and IL-CAC. They also exhibited the mRNA of each hormone by in situ hybridization (ISH). The ISH signal for glucagon but not insulin was also detected in a subset of small CACs (designated GS-CAC). The expression of PDX-1 was also observed in subsets of small and large CACs (PS-CAC and PL-CAC, respectively). After a 90% pancreatectomy, the relative frequency for GS-CACs, but not those for other CACs, was significantly reduced in two days after surgery. On day 7 after surgery, the number of GS-CACs recovered to preoperative levels, whereas GL-CACs, IL-CACs, PS-CAC, and PL-CAC gradually increased to about double in number. From these results, a portion of CACs was suggested to differentiated into endocrine cells. A possible cell lineage is discussed for endocrine neogenesis during pancreatic regeneration.

Protective effect of melatonin and its precursor L-tryptophan on acute pancreatitis induced by caerulein overstimulation or ischemia/reperfusion.

Melatonin, a pineal secretory product, synthesized from l-tryptophan, has received increased attention because of its antioxidative and immunomodulatory properties. It has been detected in the gut and shown to protect the gastric mucosa, and liver from acute damage, but the role of melatonin in the protection of the pancreas against acute inflammation is not clear. The aim of this study was to investigate the effects of melatonin and its precursor, l-tryptophan, on caerulein-induced pancreatitis (CIP) and on ischemia/reperfusion (I/R)-provoked pancreatitis in rats. CIP was induced by subcutaneous infusion of caerulein to the rats (25 microg/kg). I/R was induced by clamping of the inferior splenic artery for 30 min followed by 2 hr of reperfusion. Melatonin (10, 25 or 50 mg/hr) or l-tryptophan (50, 100 or 250 mg/kg) was given as a bolus intraperitoneal (i.p.) injection 30 min prior to the onset of pancreatitis. CIP and I/R were confirmed by histologic examination and manifested by typical pancreatic edema, by an increase of plasma levels of amylase (by 500% in CIP and by 40% in I/R) and the pro-inflammatory tumor necrosis factor alpha (TNFalpha) (by 500%). Lipid peroxidation products such as malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE), were increased several fold in the pancreas CIP and I/R, whereas pancreatic blood flow (PBF) was significantly reduced in these animals. Pretreatment of rats subjected to CIP or to I/R with melatonin (25 or 50 mg/kg i.p.) or l-tryptophan (100 or 250 mg/kg i.p.) significantly reduced pancreatic edema, plasma levels of amylase and TNFalpha and diminished pancreatic MDA + 4-HNE contents, while enhancing PBF, pancreatic integrity and plasma levels of the anti-inflammatory interleukin 10 (IL-10). This was accompanied by a marked and dose-dependent rise of plasma melatonin immunoreactivity. Gene expression of N-acetyl transferase, an enzyme involved in melatonin biosynthesis, was detected in the pancreas of normal rats and was significantly enhanced in the rats with CIP. We conclude that exogenous melatonin, and that produced from l-tryptophan, attenuates pancreatic damage induced by CIP or by I/R and this effect may be attributable to the reduction in lipid peroxidation and TNFalpha release combined with an increase of plasma anti-inflammatory IL-10 in rats with acute pancreatitis.

The time course of gap-junctional protein connexin 32 expression in the pancreas after the induction of acute pancreatitis by caerulein in rats.

We previously demonstrated that the immunostaining of the gap-junction protein, connexin 32 (Cx 32), in the pancreas was markedly reduced in caerulein (Cn)-induced acute pancreatitis. The expression of Cx 32 in the pancreas during the course of acute pancreatitis is unclear. To address this, we examined Cx 32 mRNA and protein expression in the pancreas. Cx 32 mRNA and protein expression in the pancreas was examined by Northern blot analysis and Western blot analysis, respectively, 1, 4, 7, and 14 days after the induction of acute pancreatitis. Cx 32 mRNA was identified in normal rat pancreas, and the value for the relative intensity against 18S rRNA was 0.57 +/- 0.15 (mean +/- SD). After the induction of acute pancreatitis by caerulein, the Cx 32 mRNA expression levels were increased on day 1, day 4, day 7, and day 14 compared with levels in the normal pancreas (1.63-fold, 1.61-fold, 1.49-fold, and 1.35-fold, respectively). A significant increase in Cx 32 protein expression was detected on day 1 and day 4 (1.67 +/- 0.15-fold and 1.72 +/- 0.2-fold, respectively), while Cx 32-positive spots, determined by immunohistochemical analysis, were markedly decreased on day 1 and had returned to normal by day 14. These results show that the expression of Cx 32 increases early on after the induction of pancreatitis by Cn, and that the normalization of Cx 32-immunostained spots in Cn-induced acute pancreatitis occurs after the increase in Cx 32 mRNA and protein expression.

Ghrelin stimulates insulin secretion from the pancreas of normal and diabetic rats.

Ghrelin is a novel 28-amino acid gut-brain peptide, which was first isolated in the rat stomach. This study examined the effect of ghrelin on insulin secretion from the isolated pancreas of normal and diabetic rats. Diabetes was induced by a single dose of streptozotocin. Four weeks after the induction of diabetes, pancreatic tissue fragments of normal and diabetic rats were treated with different concentrations (10(-12), 10(-9) and 10(-6) M) of ghrelin. Ghrelin evoked large and significant increases in insulin secretion from the pancreas of both normal and diabetic rats. In the pancreas of normal rats, diltiazem (calcium channel antagonist) or a combination of atropine (muscarinic cholinergic receptor antagonist), propranolol (beta-adrenergic receptor antagonist) and yohimbine (alpha2-adrenergic receptor antagonist) significantly reduced the stimulatory effect of ghrelin on insulin secretion. Diltiazem and yohimbine failed to inhibit ghrelin-evoked insulin release in diabetic rat pancreas. Ghrelin-immunoreactivity cells was observed in 2.6% and 3.8% of the total cell population in the islet of Langerhans of normal and diabetic rats, respectively.

Effect of adrenergic and cholinergic neurotransmitters on insulin secretion from the pancreas of normal and diabetic rats

The effect of noradrenaline (NA), adrenaline (ADR), and acetylcholine (ACh) on insulin secretion from the isolated pancreas of normal and diabetic rats was examined using radioimmunoassay technique. Diabetes mellitus was induced by streptozotocin. Pancreatic tissue fragments of normal and diabetic rats were removed and incubated with different concentrations (10 -8 , 10 -6 , 10 -4 M) of NA, ADR and ACh. Insulin secretion into the supernatant was later determined by radioimmunoassay. NA at a concentration of 10 -8 M evoked a six-fold increase in insulin secretion from normal pancreatic tissue fragments compared to basal. NA induced a three-fold increase in insulin output from the pancreas of diabetic rats when compared to basal. ADR (10 -8 M) induced a three-fold increase in insulin secretion from isolated normal rat pancreas. In contrast, inhibition of insulin secretion was observed when ADR (10 -8 , 10 -6 , 10 -4 M) was incubated with pancreatic tissue fragments of diabetic rats. ACh evoked a six-fold increase in insulin secretion when incubated with normal rat pancreas tissue fragments at a concentration of 10 -8 M. Similarly, ACh (10 -4 M) evoked a two-fold increase in insulin secretion from the in vitro diabetic rat pancreas. In conclusion NA, ADR and ACh have potent secretagogue effect on insulin secretion from the pancreas of normal rat.

The gastrin receptor promotes pancreatic growth in transgenic mice.

We demonstrated previously, in two different rodent models of pancreatic cancer, that the gastrin receptor is present on malignant pancreatic tumors in spite of the fact that the normal adult rat and mouse pancreas does not express gastrin receptors. To determine whether gastrin receptors mediate pancreatic growth or promote carcinogenesis or both, we created a transgenic mouse that constitutively expresses gastrin receptors in the exocrine pancreas. The transgene construct contained the full-length rat gastrin receptor cDNA sequence under the control of the rat elastase promoter. Receptor presence and function on exocrine pancreatic tissue of transgenic but not control mice were confirmed by (125)I-gastrin-I binding studies and by gastrin stimulation of intracellular calcium release. Eighteen-month-old transgenic animals had larger pancreas-to-body weight ratios than their nontransgenic littermate controls (p < 0.001 for females; p < 0.01 for males); however, histopathologic examination revealed no neoplasms or other abnormalities. In both female and male transgenic mice, the expression of the gastrin receptor in the exocrine pancreas is associated with a significant increase in pancreas weight, but it does not appear to promote the development of spontaneous pancreatic tumors.

GABA in the endocrine pancreas: cellular localization and function in normal and diabetic rats

Gamma amino butyric acid (GABA) and its related enzymes have been demonstrated in pancreatic beta cells of normal rat. Antibodies against GABA-synthesizing enzymes have been implicated in the pathogenesis of Type I diabetes. In spite of the importance of GABA in the aetiology ofdiabetes mellitus, detailed morphological data on the pattern of distribution of GABA in the pancreas of normal and diabetic rats are lacking. Diabetes mellitus (DM) was induced by a single dose of streptozotocin (STZ) given intraperitoneally (60mg kg body weight−1). Four weeks after the induction of DM, normal (n = 6) and diabetic (n = 6) rats were anesthetized with chloral hydrate and their pancreata were removed and processed for the localization and effect of GABA on insulin secretion using immunohistochemistry and radioimmunoassay techniques. The number of GABA-like immunoreactive (GABA-LIR) cells in the pancreatic islets of STZ-diabetic rats decreased significantly (P<0.0001) when compared to non-diabetic control rats. The pattern and percentage distribution of GABA in the islet of Langerhans of normal and diabetic rat was similar to that of insulin. GABA induced a significant (P<0.0007) increase in insulin secretion from the pancreas of normal rats. In diabetic pancreas, GABA evoked a higher but not significant (P<0.1) increase in insulin secretion. These findings showed that the number of GABA-LIR cells is reduced significantly in diabetes. Moreover, GABA is a strong secretagogue of insulin from the pancreas of normal rat.

The ultrastructure of primary cilia in the endocrine and excretory duct cells of the pancreas of mice and rats.

A primary cilium was frequently observed in the endocrine alpha, beta and delta cells, as well as in the excretory duct cells of the pancreas of normal mice and rats. The characteristic components of the cilium including the basal body, axoneme (shaft), and terminal part were clearly recognizable. The basal body or distal centriole surrounded by Golgi vesicles was perpendicularly oriented to the proximal centriole, and a dense striated band was seen filling the gap between them. The microtubules of the basal body consisted of nine peripheral triplets exhibiting a 9 + 0 pattern, an appearance similar to that of the proximal centriole. Rootlets, basal feet and alar sheets associated with the basal body were occasionally seen. The axoneme usually consisted of a 9 + 0 pattern of microtubule doublets, but other irregular patterns of 7 + 2, 7 + 3, and 8 + 1 were also seen. The microtubules in the terminal part of the cilium became fewer in number and had no peculiar arrangement. The cilium of the endocrine cells always projected into the intercellular canaliculus and was covered by the ciliary sheath, and occasionally, double cilia were visualized in the vicinity of beta cells. In the excretory duct cells, the cilium showed similar features, but it was slightly longer and always projected into the dense secretory content of duct lumen. On the other hand, no primary cilium was ever observed in the acinar cells of mouse and rat pancreas. In conclusion, the present study describes the morphology of primary cilia and its associated components in the endocrine and excretory duct cells of the pancreas of mice and rats. The findings suggest that the primary cilium should be considered as a constant intracellular organelle though its function and significance remain speculative.

L-arginine stimulates insulin secretion from the pancreas of normal and diabetic rats.

Several reports have shown that nitric oxide (NO) stimulates glucose-induced insulin secretion in the pancreas of normal rat but the effect of L-arginine (a NO donor) on insulin secretion from the pancreas of diabetic pancreas is unknown. Fragments of pancreatic tissue from normal and diabetic rats were incubated for 45 min in Krebs solution containing 100mM L-arginine. The supernatant was subsequently analyzed for the insulin content using radioimmunoassay technique. L-arginine evoked large increases in insulin secretion from the pancreas of diabetic rat. The insulin secreted from the pancreas of diabetic rat was numerically but not significantly lower compared to that of normal rat pancreas. In conclusion, L-arginine, a nitric oxide donor stimulates insulin secretion from the pancreas of diabetic rats.

Identification of mediators stimulating proliferation and matrix synthesis of rat pancreatic stellate cells.

The aim of this study was to identify fibrogenic mediators stimulating activation, proliferation, and/or matrix synthesis of rat pancreatic stellate cells (PSC). PSC were isolated from the pancreas of normal Wistar rats and from rats with cerulein pancreatitis. Cell activation was demonstrated by immunofluorescence microscopy of smooth muscle alpha-actin (SMA) and real-time quantitative RT-PCR of SMA, fibronectin, and transforming growth factor (TGF)-beta(1). Proliferation was measured by bromodeoxyuridine incorporation. Matrix synthesis was demonstrated on the protein and mRNA level. Within a few days in primary culture, PSC changed their phenotype from fat-storing to SMA-positive myofibroblast-like cells expressing platelet-derived growth factor (PDGF) alpha- and PDGF beta-receptors. TGF-beta(1) and tumor necrosis factor (TNF)-alpha accelerated the change in the cells' phenotype. Addition of 50 ng/ml PDGF and 5 ng/ml basic fibroblast growth factor (bFGF) to cultured PSC significantly stimulated cell proliferation (4.37 +/- 0.49- and 2.96 +/- 0.39-fold of control). Fibronectin synthesis calculated on the basis of DNA was stimulated by 5 ng/ml bFGF (3.44 +/- 1.13-fold), 5 ng/ml TGF-beta(1) (2.46 +/- 0.89-fold), 20 ng/ml PDGF (2.27 +/- 0.68-fold), and 50 ng/ml TGF-alpha (1.87 +/- 0.19-fold). As shown by RT-PCR, PSC express predominantly the splice variant EIII-A of fibronectin. Immunofluorescence microscopy and Northern blot confirmed that in particular bFGF and TGF-beta(1) stimulated the synthesis of fibronectin and collagens type I and III. In conclusion, our data demonstrate that 1) TGF-beta(1) and TNF-alpha accelerate the change in the cell phenotype, 2) PDGF represents the most effective mitogen, and 3) bFGF, TGF-beta(1), PDGF, and, to a lesser extent, TGF-alpha stimulate extracellular matrix synthesis of cultured rat PSC.

Large reduction in the number of galanin-immunoreactive cells in pancreatic islets of diabetic rats.

Although galanin has been shown to be present in pancreatic islet cells, there is no literature available on the pattern of distribution and the effect of galanin in the pancreas of diabetic animals or human models. The aim of this study was to examine whether galanin immunoreactivity changes after the onset of diabetes mellitus in the rat model. The present study used immunohistochemical techniques to examine the pattern of distribution of galanin-like immunoreactive cells in the pancreas of rats with streptozotocin-induced diabetes. The effect of galanin on insulin secretion from intact rat pancreatic tissue fragments was also investigated using a radioimmunoassay technique. Numerous galanin-like immunoreactive cells were observed in both the peripheral and central regions of the islet of Langerhans of normal rat pancreas. By contrast, the islets of diabetic rat pancreas contained significantly (P < 0.0001) fewer galanin-like immunoreactive cells than nondiabetic rats. Galanin was colocalized with insulin in the islets of normal and diabetic rats. Galanin had an inhibitory effect on insulin secretion from the isolated pancreatic tissue fragments of normal and diabetic rats at all concentrations (10(-12) to 10(-6) M) employed. Galanin at 10(-9) M caused a significant (P < 0.02) decrease in insulin secretion from normal rat pancreatic tissue fragments compared to basal. These observations indicate that galanin may play a significant role in the regulation of insulin secretion.

Effect of electrical field stimulation on insulin and glucagon secretion from the pancreas of normal and diabetic rats.

The effect of electrical field stimulation (EFS) on insulin (INS) and glucagon (GLU) secretion from normal and diabetic rat pancreas is poorly understood. In our study, EFS (5-20Hz, 50 V amplitude and 1.0 ms pulse width), when applied alone, resulted in a significant (p<0.05) increase in INS secretion from the pancreas of both normal and diabetic rats. Atropine (10(-5) M) did not inhibit the EFS (5 Hz)-evoked INS secretion in normal pancreas and failed to alter the effect of EFS (10-20 Hz) on INS secretion from the pancreas of both normal and diabetic rats. Propranolol (Prop) inhibited INS secretion to below basal level in the presence of EFS (5 Hz) but not at EFS (10- 20 Hz). Tetrodotoxin (TTX) also significantly (p = 0.002) inhibited INS secretion from normal pancreas in the presence of EFS (5-20 Hz). The decrease in insulin secretion observed when pancreatic tissue fragments were incubated in Prop and TTX in the presence of EFS was reversed by yohimbine (10(-5) M). In contrast, TTX did not significantly modify INS secretion from diabetic pancreas in the presence of EFS. EFS (5-20 Hz) significantly (p<0.05) increased GLU release from normal and diabetic rat pancreas when applied alone. Neither atropine, Prop nor TTX significantly modified GLU release from the pancreas of either normal or diabetic rats. This suggests that GLU secretion may be controlled through a different pathway. The EFS-evoked INS and GLU secretion is probably executed via different mechanisms. These mechanisms include 1) activation of cholinergic nerves by EFS; 2) EFS of alpha- and beta-adrenergic nerves; 3) activation of non-adrenergic non-cholinergic pathway by EFS; 4) EFS-induced depolarization and subsequent action potential in pancreatic endocrine cells and 5) electroporosity caused by EFS-induced membrane permeability. All of these effects may be summative. In conclusion, EFS (5-20 Hz), when applied alone, can evoke significant increases in INS and GLU secretion from the pancreas of both normal and diabetic rats. Insulin secretion is controlled via alpha-2 adrenergic (inhibition) and beta-adrenergic (stimulation) receptors. Glucagon secretion is enhanced by alpha2 adrenergic stimulation.

Association between islets of Langerhans and pancreatic ductal system in adult rat. Where endocrine and exocrine meet together?

Studies on the functional and morphological relations between exocrine and endocrine pancreas have been conducted mainly to disclose the influence of islets of Langerhans on acinar parenchyma. Less attention has been paid to the relations occurring between islets and pancreatic ducts. A series of consecutive sections of normal adult rat pancreas were double stained with islet (hormones) and duct (cytokeratin 20) markers. Electron microscopy was conducted to investigate the ultra-structural features of duct-islet relations and anti-insulin immunogold labelling was carried out to reveal the presence of insulin in the pancreatic duct system. Consecutive double-stained sections demonstrated that 73.60 +/- 2.97% of the islets were attached to the ducts. For each series, 93.48 +/- 5.43 % of the islets contacting the duct tree were associated with small-sized ducts or centroacinar cells. Electron microscopy revealed that some insulin and somatostatin cells do face the duct lumen. Insulin was detected within the duct lumen and in the endosomal compartment of the duct cells. The finding that most islets are connected with the duct system in the adult pancreas is discussed in terms of hormone secretion into the ducts, islet histogenesis and the relation among the three tissue components of the pancreas, the endocrine, the exocrine and the duct system.

Distribution of vasoactive intestinal polypeptide, neuropeptide-Y and substance P and their effects on insulin secretion from the in vitro pancreas of normal and diabetic rats☆

This study examined the pattern of distribution of vasoactive intestinal polypeptide (VIP), neuropeptide-Y (NPY) and substance P (SP) in the pancreas of diabetic rat to determine whether there are changes in the number and pattern of distribution of these neuropeptides after the onset of diabetes. Moreover, the effect of VIP, NPY and SP on insulin secretion from the pancreas of normal and diabetic rats was also examined. Diabetes mellitus (DM) was induced by a single dose of streptozotocin (STZ) given intraperitoneally (i.p.) (60 mg kg body weight −1). Four weeks after the induction of DM, diabetic ( n = 6) and normal ( n = 6) rats were anesthetized with chloral hydrate and their pancreases removed and processed for immunohistochemistry and insulin secretion. The number of insulin-positive cells in the islets of Langerhans was reduced while that of VIP and NPY increased significantly after the onset of diabetes. The pattern of distribution of VIP, NPY and SP in the nerves innervating the pancreas was similar in both normal and diabetic rats. VIP-evoked large and significant ( P < 0.02) increases in insulin secretion from the pancreas of normal and diabetic rats. NPY also induced a marked ( P < 0.005) increase in insulin release from pancreatic tissue fragments of normal rat. Stimulation of pancreatic tissue fragments of diabetic rat with NPY resulted in a slight but not significant increase in insulin release. SP induced a large and significant ( P < 0.005) increase in insulin secretion from the pancreas of normal rat but inhibited insulin secretion significantly ( P < 0.03) from isolated pancreas of diabetic rat. In summary, VIP and NPY can stimulate insulin secretion from the pancreas after the onset of diabetes. The stimulatory effect of SP on insulin secretion is reversed to inhibitory in diabetic rats.