Preparation and application of Procion Yellow starch for amylase assay

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

Background

Nicotine 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.

Methods

Isolated 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.

Results

Nicotine 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.

Conclusions

The 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.

Mitogenic and functional responses by nicotine and hydrogen peroxide in AR42J cells: a comparative study

The aim of the current study was to investigate the oxidative effects of nicotine by examining the mitogenic and functional responses in AR42J cells. As a control and for comparison, hydrogen peroxide (H2O2) was used as a source of known oxidative biomarker. Responses were examined by determining cell proliferation through the activation of ERK signaling, basal and CCK-stimulated cell function and measuring lipid peroxidation. AR42J cells have been exposed to either a non-cytotoxic dose of 20 muM H2O2 for 15 min or to 100 muM of nicotine for 3 min respectively. Nicotine and H2O2 at these dose and time intervals produced similar levels of malondialdyde (MDA) production and p-ERK1/2 activation. Immunofluorescence studies employing specific antibody to p-ERK1/2 confirmed the latter. Nicotine-induced increase in the proliferation of AR42J cells was significantly higher in comparison to H2O2 exposed cells. CCK-stimulated cell function induced by nicotine was significantly higher in AR42J cells as compared to the response by H2O2. These results suggest that nicotine- induced mitogenic and functional response in AR42J cells are associated with ERK signaling and increase in reactive oxygen species production. The data suggests that nicotine-induced mitogenic response in AR42J cells closely identifies the response induced by an oxidative biomarker.

Pharmacologic disruption of TRPV1-expressing primary sensory neurons but not genetic deletion of TRPV1 protects mice against pancreatitis

OBJECTIVES

Transient receptor potential subtype vanilloid 1 (TRPV1) is an ion channel that is primarily expressed by primary sensory neurons where it mediates pain and heat sensation and participates in neurogenic inflammation. In this study, we examined the role of TRPV1 during neurogenic activation of pancreatic inflammation using a secretagogue-induced model in mice.

METHODS

A supramaximal dose of caerulein (50 microg/kg) was injected hourly for 12 hours. Mice lacking TRPV1 were compared to wild-type animals.

RESULTS

All the parameters: serum amylase, pancreatic myeloperoxidase activity, histological scoring, pancreatic wet weight/body weight ratio, and quantification of neurokinin-1 receptor internalization indicated that null mice were not protected from acute pancreatitis. However, when primary sensory neurons were ablated by injection of the neurotoxin and TRPV1 agonist, resiniferatoxin, pancreatitis was ameliorated in wild-type mice but not in null mice, indicating that nerves bearing TRPV1 are part of the inflammatory pathway in acute pancreatitis because disappearance significantly reduced the inflammatory response.

CONCLUSIONS

Nerves expressing TRPV1 participate in the neurogenic inflammation during acute pancreatitis. The lack of protection in TRPV1 null mice suggests that an alternate pathway to TRPV1 coexists in the same neurons.

A cell-based approach to study changes in the pancreas following nicotine exposure in an animal model of injury

BACKGROUND

Cigarette smoking is a recognized risk factor for the induction of pancreatic diseases and is suspected to play a major role in the development of pancreatic cancer in smokers.

MATERIALS AND METHODS

This study was designed to characterize the mechanisms of nicotine-induced injury to the pancreas. AR42Jcells, a stable mutant pancreatic tumor cell line, was chosen for the study because of its stability in culture media and also because of its known secretory capacity, which is like that of a normal pancreatic acinar cell. It is hypothesized that nicotine-induced effects on the pancreas are triggered by oxidative stress induced in pancreatic acinar cell via oxidative stress signaling pathways.

RESULTS

The results from our study showed that, in vitro, nicotine induced generation of oxygen free radicals measured as malondialdehyde, an end product of lipid peroxidation. Treatment of AR42J cells with nicotine induced p-ERK 1/2 activation as confirmed by Western blot and immunofluorescence imaging of cytoplasmic localization of mitogen-activated protein kinase (MAPK) signals. Nicotine enhanced AR42J cell proliferation and cholecystokinin-stimulated amylase release in AR42J cells. These effects of nicotine were confirmed by simultaneous studies conducted on the same cells by hydrogen peroxide, a known oxidative biomarker. Allopurinol, a XOD inhibitor, suppressed these effects induced by nicotine and H(2)O(2) with the exception that cholecystokinin-stimulated amylase release by H(2)O(2) remained unaltered when AR42J cells were preincubated with allopurinol. These results suggest that nicotine-induced effects on pancreatic acinar cells were associated with generation of oxyradical mediated via the XOD pathway. The results have a direct impact on cell proliferation, MAPK signaling, and acinar cell function.

CONCLUSION

We conclude that nicotine induces oxidative stress in pancreatic acinar cells and that these events trigger pathophysiological changes in the pancreas, leading to increased cell proliferation and injury.

Nicotine-induced proliferation of isolated rat pancreatic acinar cells: effect on cell signalling and function

OBJECTIVES

The aim of the current study was to investigate whether nicotine treatment would induce the proliferation of isolated rat primary pancreatic acinar cells in culture by activating mitogen-activated protein kinase (MAPK) signalling and exocrine secretion.

MATERIALS AND METHODS

A nicotine dose- and time-response curve was initially developed to determine the optimal dose and time used for all subsequent studies. Proliferation studies were conducted by cell counting and confirmed further by bromodeoxyuridine (BrdU) incorporation and flow cytometry assays. MAPK signalling studies were conducted by Western blot analysis. Localization of ERK1/2 signals, with or without nicotine and the MAPK inhibitor, was visualized by immunofluorescence.

RESULTS

Nicotine treatment caused dose-dependent activation of extracellular signal-regulated kinases (ERK1/2), the maxima occurring at 100 micro m and at 3 min after treatment; the response was suppressed by the ERK1/2 inhibitor. Maximal nicotine-induced cell proliferation occurred at 24 h, and UO126-treatment significantly reduced this response. Exposure of cells to 100 microm nicotine for 6 min significantly enhanced both baseline and cholecystokinin-stimulated cell function, and these effects were not affected by treatment with the inhibitor of ERK1/2 but were suppressed by mecamylamine, a nicotinic receptor antagonist.

CONCLUSIONS

Our results suggest that nicotine treatment induced cell proliferation of isolated pancreatic acinar cells and that this is coupled with the activation of MAPK signalling with no effect on its function. Hence, in primary cells, the mechanism of induction and regulation of these two processes, cell proliferation and cell function, by nicotine treatment are independent of each other.

Local disruption of the celiac ganglion inhibits substance P release and ameliorates caerulein-induced pancreatitis in rats

Primary sensory neurons of the C and Adelta subtypes express the vanilloid capsaicin receptor TRPV1 and contain proinflammatory peptides such as substance P (SP) that mediate neurogenic inflammation. Pancreatic injury stimulates these neurons causing the release of SP in the pancreas resulting in pancreatic edema and neutrophil infiltration that contributes to pancreatitis. Axons of primary sensory neurons innervating the pancreas course through the celiac ganglion. We hypothesized that disruption of the celiac ganglion by surgical excision or inhibition of C and Adelta fibers through blockade of TRPV1 would reduce the severity of experimental pancreatitis by inhibiting neurogenic inflammation. Resiniferatoxin (RTX) is a specific TRPV1 agonist that, in high doses, selectively destroys C and Adelta fibers. Sprague-Dawley rats underwent surgical ganglionectomy or application of 10 microg RTX (vs. vehicle alone) to the celiac ganglion. One week later, pancreatitis was induced by six hourly intraperitoneal injections of caerulein (50 microg/kg). The severity of pancreatitis was assessed by serum amylase, pancreatic edema, and pancreatic myeloperoxidase (MPO) activity. SP receptor (neurokinin-1 receptor, NK-1R) internalization in acinar cells, used as an index of endogenous SP release, was assessed by immunocytochemical quantification of NK-1R endocytosis. Caerulein administration caused significant increases in pancreatic edema, serum amylase, MPO activity, and NK-1R internalization. RTX treatment and ganglionectomy significantly reduced pancreatic edema by 46% (P < 0.001) and NK-1R internalization by 80% and 51% (P < 0.001 and P < 0.05, respectively). RTX administration also significantly reduced MPO activity by 47% (P < 0.05). Neither treatment affected serum amylase, consistent with a direct effect of caerulein. These results demonstrate that disruption of or local application of RTX to the celiac ganglion inhibits SP release in the pancreas and reduces the severity of acute secretagogue-induced pancreatitis. It is possible that selectively disrupting TRPV1-bearing neurons could be used to reduce pancreatitis severity.

Sequence variation outside the "active" region of dog and rabbit cholecystokinin-58 results in bioactivity differences

OBJECTIVES

We propose that regions outside the bioactive 7-amino acid carboxyl terminus of cholecystokinin (CCK)-58 influence its biological activity. Here we evaluate if sequence variation of the N-terminal regions of rabbit and canine CCK-58 changes their biological activities.

METHODS

Cholecystokinin-like immunoreactivity was purified from rabbit intestinal extracts by reverse phase and ion-exchange high-performance liquid chromatography steps. The peptide was characterized by microsequence and mass spectral characterizations of the intact and tryptic peptides. Canine and rabbit CCK-58 were evaluated for their CCK1 and CCK2 receptor binding, receptor activation, and immunologic properties.

RESULTS

The sequence of rabbit CCK-58 differs from that of canine CCK-58 in 9 of the amino terminal 40 residues. Canine CCK-58 was approximately 3-fold more potent than rabbit CCK-58 for CCK1 receptor binding and CCK2 receptor binding, but about the same potency for stimulation of amylase release from purified acinar cells. The canine peptide was 9-fold more immunoreactive than rabbit CCK-58.

CONCLUSIONS

Canine and rabbit CCK-58 have different biological and immunologic properties that can only result from differences in their N-terminal sequences which influence the properties of their identical carboxyl termini. These results are the first direct demonstration that amino acids outside the C-terminus of CCK-58 influence CCK biological activity.

Activation of p-ERK1/2 by nicotine in pancreatic tumor cell line AR42J: effects on proliferation and secretion

The objectives of the present study were to determine the effect of nicotine on MAPK signaling and on the proliferation of AR42J cells as well as to assess the relationship between MAPK activation and exocrine secretion in these cells. AR42J cells were incubated with nicotine and analyzed for the activation of MAPK by Western blot analysis using their respective antibodies and confirmed by immunohistochemistry. The effect of nicotine on cell proliferation was determined by the spectrophotometric method, and cell function was assessed by cholecystokinin (CCK)-stimulated amylase release into the culture medium. Nicotine at a dose of 100 microM induced phospho-ERK1/2 activation maximally in 3 min compared with untreated cells. Furthermore, immunofluorescence study confirmed the nicotine-induced increase in translocation of phospho-ERK1/2 to the nucleus. Activation of phospho-ERK1/2 was inhibited by an ERK1/2 pathway inhibitor but not by a nicotine receptor antagonist. At the same dose, there was significantly enhanced proliferation of AR42J cells until 72 h without toxic effect, as the percentage of lactate dehydrogenase release remained unchanged. Other MAPKs, c-Jun NH2-terminal kinase 1/2 and p38 MAPK, were not affected by nicotine treatment. At a nicotine dose of 100 microM, the CCK-stimulated release of amylase was maximal at 6 min, and, although a nicotinic receptor antagonist inhibited this response, it was not inhibited by the ERK1/2 pathway inhibitor. We conclude that nicotine treatment induced activation of ERK1/2 and increased the proliferation of AR42J cells. The data further indicate that MAPK signaling by nicotine is independent of the secretory response.

Induction of pancreatic trypsin by dietary amino acids in rats: four trypsinogen isozymes and cholecystokinin messenger RNA

We previously demonstrated that feeding a diet containing a high level of amino acid mixture simulating casein (AA) induced an increase in pancreatic protease activities in rats. In the present study, this effect of dietary AA was further characterized with three separate experiments. These experiments (1) examined periodic changes in pancreatic and small intestinal trypsin activities after switching from a 20% (a normal nitrogen level) AA diet to a 60% AA (a high nitrogen level) diet; (2) measured the abundance of mRNA for four trypsinogen isozymes and for intestinal cholecystokinin (CCK) and secretin in rats fed 20% and 60% AA diets for 10 days compared with rats fed 20% and 60% casein diets; and (3) measured the abundance of mRNA for four trypsinogen isozymes after chronic administration of CCK. Trypsin activities were gradually increased in both the pancreas and the small intestinal lumen and reached maximum at 5 days after the switch to the 60% AA diet (Exp. 1). This result is evidence that the increase in the protease activity in the pancreas is due to enhancement of pancreatic trypsin production. In experiment 2, pancreatic trypsinogen isozymes I, II, III, and IV mRNA abundance were evaluated by the Northern blotting method using cDNA probes specific for each isozyme mRNA. Abundance of trypsinogen mRNA without trypsinogen I tended to increase in the rats fed the 60% casein diet but tended to decrease in the rats fed the 60% AA diet compared with the respective normal nitrogen level diet groups without significant difference. CCK mRNA abundance in the jejunal mucosa increased as a result of feeding the 60% casein diet, but not the 60% AA diet. Subcutaneous CCK injections (3.5 nmole/kg body weight/day, twice daily, at 8:30 am and 7:30 pm) for 10 days resulted in increased pancreatic trypsin activity, whereas the changes in mRNA of the four trypsinogen isozymes was similar between the 20% and 60% casein groups but differed between the 20% and 60% AA groups (Exp. 3). These results suggest that CCK is not involved in the induction of pancreatic trypsin that occurs with feeding of a high AA diet and that the mechanism of protease induction by dietary AA is different from that in the case of dietary protein.

Chronic alcohol consumption accelerates fibrosis in response to cerulein-induced pancreatitis in rats

Alcohol consumption is a risk factor for chronic pancreatitis (CP), but the mechanism in humans remains obscure because prolonged alcohol consumption in most humans and animal models fails to produce alcoholic chronic pancreatitis (ACP). We hypothesize that the process leading to ACP is triggered by a sentinel acute pancreatitis (AP) event; this event causes recruitment of inflammatory cells, which initiates fibrosis driven by the anti-inflammatory response to recurrent AP and/or chronic oxidative stress. The aim was to determine whether chronic alcohol consumption accelerates fibrosis in response to cerulein-induced pancreatitis in the rat. Wistar male rats were pair-fed control (C) or 5% ethanol (E) Lieber-DeCarli liquid diets. Animals were studied without pancreatitis (P0), with cerulein pancreatitis induced once (P1), or with cerulein-induced pancreatitis weekly for 3 weeks (P3). AP markers, inflammation, and fibrosis were measured histologically, by gene expression profiling and protein expression. Macrophage infiltration was reduced in EP0 versus CP0 rats, but the pattern was reversed after AP. Microabscess, severe necrosis, and early calcification were only induced in the EP3 rats. Fibrosis was significantly induced in the EP3 rats versus EP1, CP1, and CP3 by histology, hydroxyproline content, and mRNA expression for collagen alpha1(1) and procollagen alpha2(1). Proinflammatory cytokine mRNAs were up-regulated shortly after induction of AP, while the anti-inflammatory cytokines (interleukin-10 and transforming growth factor-beta) were strongly up-regulated later and in parallel with fibrogenesis, especially in the EP3 rats. Pancreatic fibrosis develops after repeated episodes of AP and is potentiated by alcohol. Expression of fibrosis-associated genes was associated with expression of anti-inflammatory cytokines in alcohol-fed rats.

Transgenic expression of pancreatic secretory trypsin inhibitor-I ameliorates secretagogue-induced pancreatitis in mice

BACKGROUND & AIMS

Endogenous trypsin inhibitors are believed to inhibit protease activity if trypsin becomes inadvertently activated within the acinar cell. However, this action remains unproven, and the role of endogenous pancreatic trypsin inhibitors in acute pancreatitis is unknown. In this study, we tested whether increased levels of pancreatic secretory trypsin inhibitor-I (PSTI-I) in mice could prevent secretagogue-induced pancreatitis.

METHODS

Rat PSTI-I expression was targeted to pancreatic acinar cells in transgenic mice by creating a minigene driven by the rat elastase I enhancer/promoter. Secretagogue-induced pancreatitis was achieved by 12 hourly intraperitoneal injections of caerulein. The severity of pancreatitis was assessed by measurements of serum amylase, histologic grading, and pancreas wet weight-to-body weight ratio. Trypsinogen activation and trypsin activity were measured in pancreatic extracts.

RESULTS

Targeted expression of PSTI-I to the pancreas increased endogenous trypsin inhibitor capacity by 190% (P <.01) in transgenic vs. nontransgenic mice. Caerulein administration to nontransgenic mice produced histologic evidence of acute pancreatitis, and significantly elevated serum amylase and pancreas weight ratio. In caerulein-treated transgenic mice, the histologic severity of pancreatitis was significantly reduced. There was no difference in trypsinogen activation peptide levels between caerulein-treated transgenic and nontransgenic mice. However, trypsin activity was significantly lower in transgenic mice receiving caerulein compared with nontransgenic mice.

CONCLUSIONS

These data demonstrate that the severity of secretagogue-induced pancreatitis is significantly ameliorated in mice with higher pancreatic levels of trypsin inhibitor. We propose that PSTI-I prevents pancreatitis by inhibiting the activity of trypsin, rather than by reducing trypsinogen activation.

Differential increases in syntheses of newly identified trypsinogen 2 isoforms by dietary protein in rat pancreas

We have found that dietary protein markedly induced pancreatic serine protease activity via a mechanism independent of luminal trypsin activity in pancreaticobiliary-diverted (PBD) rats. The aim of this study was to examine the effects of dietary protein on the synthesis of trypsinogen isoforms by comparing in vivo incorporation of [35S] L-methionine into isoform proteins in PBD and sham-operated rats. A small duodenal segment including the ampulla of Vater was sectioned and transposed to the upper ileum with end-to-side anastomosis (PBD) or duodenal transection was followed by reanastomosis (sham) in male Sprague-Dawley rats. After recovery, PBD and sham rats were fed a 25% or 60% casein-sucrose-based diet (NC or HC) for 14 days. Rats were then intravenously injected with [35S] L-methionine (15 MBq/kg body weight) 30 mins before being sacrificed for analysis of pancreatic enzymes by two-dimensional SDS-polyacrylamide gel electrophoresis. By using electrophoresis with narrow range of isoelectric focusing (pI 4.5-5.5), five trypsinogen 2 (2-x) isoform spots were identified using both [35S] incorporation and Coomassie brilliant blue (CBB) staining in PBD rats, but not in sham rats. N-terminal sequences of these trypsinogen 2-x spots were identical to known rat trypsinogen 2 with the exception that the third valine was changed to isoleucine in one isoform. In PBD rats, feeding of HC specifically increased the [35S] and CBB intensities of these trypsinogen 2-x isoforms and trypsinogen 3. The degree of induction of the five trypsinogen 2-x molecules by HC varied greatly. Trypsinogen 1 and 4, which are the major trypsinogens in normal rats, showed no changes. We conclude that increases in synthesis of a few newly identified trypsinogen 2-x isoforms mainly contribute to the induction of trypsin activity in the pancreas by HC in PBD rats.

An exploratory study on the development of an animal model of acute pancreatitis following nicotine exposure

Cigarette smoking is known to be a major risk factor for pancreatic cancer and pancreatitis is believed to be a predisposed condition for pancreatic cancer. As of this date, there is no established experimental animal model to conduct detailed studies on these two deadly diseases. Our aim is to establish a rodent model by which we can systematically study the pathogenesis of pancreatitis and pancreatic cancer.

Adult Male Sprague Dawley rats were exposed to graded doses of nicotine by various routes for periods of three to 16 weeks. Blood samples were measured for hormonal and metabolic parameters. The pancreas was evaluated for histopathological changes and its function was assessed in isolated pancreatic acini upon stimulation with cholecystokinin (CCK) or carbachol (Cch). The pancreatic tissue was evaluated further for oncogene expression.

Body weight, food and fluid intakes, plasma glucose and insulin levels were significantly reduced in animals with nicotine exposure when compared to control. However, CCK and gastrin levels in the blood were significantly elevated. Pancreatic function was decreased significantly with no alteration in CCK receptor binding. Pancreatic histology revealed vacuolation, swelling, cellular pyknosis and karyorrhexis. Mutant oncogene, H-ras, was overexpressed in nicotine-treated pancreatic tissue.

The results suggest that alterations in metabolic, hormonal and pathologic parameters following nicotine-treatment appear consistent with diagnostic criteria of human pancreatitis. It is proposed that rats could be considered as a potential animal model to study the pathogenesis of pancreatitis.

Primary sensory neurons: a common final pathway for inflammation in experimental pancreatitis in rats

We hypothesized that neurogenic inflammation is a common final pathway for parenchymal inflammation in pancreatitis and evaluated the role of primary sensory neurons in secretagogue-induced and obstructive pancreatitis. Neonatal rats received either the primary sensory neuron-denervating agent capsaicin (50 mg/kg s.c.) or vehicle. At 8 wk of age, pancreatitis was produced by six hourly injections of caerulein (50 microg/kg i.p.) or by common pancreaticobiliary duct ligation (CPBDL). The severity of pancreatitis was assessed by serum amylase, pancreatic myeloperoxidase (MPO) activity, histological grading, pancreatic plasma extravasation, and wet-to-dry weight ratio. Caerulein significantly increased MPO activity and wet-to-dry weight ratio, produced histological evidence of edematous pancreatitis, induced plasma extravasation, and caused hyperamylasemia. CPBDL increased MPO activity and produced histological evidence of pancreatitis. Neonatal capsaicin administration significantly reduced tissue MPO levels, histological severity scores, and wet-to-dry weight ratio and abolished plasma extravasation. These results demonstrate that primary sensory neurons play a significant role in the inflammatory cascade in experimental pancreatitis and appear to constitute a common final pathway for pancreatic parenchymal inflammation.

Capsaicin vanilloid receptor-1 mediates substance P release in experimental pancreatitis

We examined whether the capsaicin vanilloid receptor-1 (VR1) mediates substance P (SP) release from primary sensory neurons in experimental pancreatitis. Pancreatitis was achieved by 12 hourly injections of caerulein (50 microg/kg ip) in mice. One group received capsazepine (100 micromol/kg sc), a competitive VR1 antagonist, at 4-h intervals. Neurokinin-1 receptor (NK1R) internalization in acinar cells, used as an index of endogenous SP release, was assessed by immunocytochemical quantification of NK1R endocytosis. The severity of pancreatitis was assessed by measurements of serum amylase, pancreatic myeloperoxidase (MPO) activity, and histological grading. Caerulein administration caused significant elevations in serum amylase and pancreatic MPO activity, produced histological evidence of pancreatitis, and caused a dramatic increase in NK1R endocytosis. Capsazepine treatment significantly reduced the level of NK1R endocytosis, and this was associated with similar reductions in pancreatic MPO activity and histological severity of pancreatitis. These results demonstrate that repeated caerulein stimulation causes experimental pancreatitis that is mediated in part by stimulation of VR1 on primary sensory neurons, resulting in endogenous SP release.

Changes in the exocrine pancreas secondary to altered small intestinal function in the CF mouse

The exocrine pancreas of the cystic fibrosis (CF) mouse (cftr(m1UNC)) is only mildly affected compared with the human disease, providing a useful model to study alterations in exocrine function. The CF mouse pancreas has approximately 50% of normal amylase levels and approximately 200% normal Muclin levels, the major sulfated glycoprotein of the pancreas. Protein biosynthetic rates and mRNA levels for amylase were not altered in CF compared with normal mice, and increases in Muclin biosynthesis and mRNA paralleled the increased protein content. Stimulated pancreatic amylase secretion in vitro and in vivo tended to be increased in CF mice but was not statistically significant compared with normal mice. We show for the first time that the CF mouse duodenum is abnormally acidic (normal intestinal pH = 6.47 +/- 0.05; CF intestinal pH = 6.15 +/- 0.07) and hypothesize that this may result in increased signaling to the exocrine pancreas. There were significant increases in CF intestinal mRNA levels for secretin (310% of normal, P < 0.001) and vasoactive intestinal peptide (148% of normal, P < 0.05). Furthermore, CF pancreatic cAMP levels were 147% of normal (P < 0.01). These data suggest that the CF pancreas may be chronically stimulated by cAMP-mediated signals, which in turn may exacerbate protein plugging in the acinar/ductal lumen, believed to be the primary cause of destruction of the pancreas in CF.

Non-essential amino acids play an important role in adaptation of the rat exocrine pancreas to high nitrogen feeding

We have previously demonstrated that feeding a diet with a high amino acid (60% AA diet) content, as a mixture simulating casein, induced pancreatic growth and pancreatic protease production in rats. In the present study, we examined the effects of an increasing dietary content of essential amino acids (EAA, x1 - x3 in exp. 1 and x1 - x3.3 in exp. 2) and non-essential amino acids (NEAA, x1 - x3 in exp. 1 and x1 - x5.2 in exp. 2) on pancreatic growth, amylase and protease adaptation using casein-type amino acid mixtures (exp. 1, basal diet; 20% AA diet) and egg white-type amino acid mixtures (exp. 2, basal diet; 12% AA diet). Pancreatic growth and trypsin activity were induced as the dietary content of NEAA was increased in experiments 1 and 2. Amylase activity in the pancreas was also induced as the dietary content of NEAA was increased, even with the decrease in dietary carbohydrate in experiment 2. The values of all pancreatic variables decreased with the increase in dietary EAA (x2 and x3) without an increase in NEAA. The changes in the pancreas were coincident with increases in plasma arginine and lysine concentrations and a decrease in the plasma alanine concentration. In rats fed a 60% AA diet (EAA and NEAA x3), in the case of which the EAA content was balanced with the NEAA content, pancreatic growth and protease production increased and reached maximum levels as the plasma amino acid concentrations decreased, except for alanine. These results show that NEAA, not EAA, are associated with induction of pancreatic growth and protease production upon feeding a diet with a high AA content, and that some metabolites may be involved in the induction process. The suppression of pancreatic growth and protease production in rats fed the high EAA diets without balanced NEAA may be associated with impairment of amino acid metabolism rather than the increments in the concentration of one or more essential amino acids. Our results also suggest that there is an unknown mechanism or unknown factors involved in regulating pancreatic amylase.

Effect of somatostatin on cholecystokinin-induced amylase release in rat pancreatic acini

The effect of somatostatin on cholecystokinin-induced amylase release was investigated in isolated rat pancreatic acini. Acini were isolated by enzymatic digestion and incubated in a HEPES buffered Ringer's solution with testing reagents for 30 minutes at 37 degrees C. The activity of released amylase, cAMP, and inositol phosphate formation were measured. Intracellular calcium concentration ([Ca2+]i) was also checked. Somatostatin 14 and octreotide, a somatostatin analog, inhibited CCK-stimulated amylase release in a concentration-dependent manner. The inhibitory effect of octreotide on CCK-induced amylase release was not shown when the acini were treated with 8-Br-cAMP, irrespective of the presence of IBMX. Forskolin potentiated CCK-induced amylase release and this effect was blocked by octreotide treatment; although CCK-8 (3 x 10(-11) M) failed to stimulate cAMP formation, octreotide significantly inhibited basal cAMP formation in the acini. The increase of [Ca2+]i in response to CCK was inhibited by octreotide. However, CCK-induced inositol phosphate formation was not changed by 10(-9) M octreotide. Octreotide had no effect on CCK-stimulated tyrosine phosphorylation, and tyrosine phosphatase inhibitors (NaF and Na2WO4) did not influence the effect of octreotide on CCK-induced amylase release. From these results, we conclude that octreotide inhibits CCK-induced amylase release by inhibiting basal cAMP formation and decreasing the [Ca2+]i stimulated by CCK.

Endogenous cholecystokinin plays a role in down-regulation of pancreatic amylase independent of dietary carbohydrate in rats

The role of cholecystokinin (CCK) in the regulation of pancreatic amylase has not been fully clarified. We examined the effects of hyperCCKemia with chronic pancreatico-biliary diversion (PBD) and blockade of CCK(A)-receptor on rat pancreatic amylase activity and mRNA abundance. Also, we examined the relationship between diet and CCK in terms of regulation of pancreatic amylase. PBD was produced by transposition of the duodenal segment containing the ampulla of Vater to the upper ileum. A potent CCK(A)-receptor antagonist, devazepide, was injected (6 mg/kg body weight per day for 5 days) in the PBD rats fed with diets containing normal or low level of carbohydrate (695 or 345 g sucrose/kg diet). The specific activity and mRNA abundance of the pancreatic amylase were constantly lower 4, 10 and 28 days after PBD than those after the sham operation. Devazepide treatment completely restored the amylase activity lowered by PBD without any increases in amylase mRNA. Feeding a high-protein low-carbohydrate diet suppressed the pancreatic amylase activity and mRNA abundance in PBD rats to a similar degree in those treated, and those untreated, with devazepide. We conclude that endogenous CCK suppresses pancreatic amylase production, and we speculate that CCK reduced translational efficiency of amylase mRNA. The effect of CCK on amylase production is independent of regulation by dietary carbohydrate.

A possible role for Ca(2+)/calmodulin-dependent protein kinase IV during pancreatic acinar stimulus-secretion coupling

Ca(2+)/calmodulin-dependent protein kinases (CaMKs) are important intracellular mediators in the mediation of stimulus-secretion coupling and excitation-contraction coupling in a wide variety of cell types. We attempted to identify and characterize the functional roles of CaMK in mediating pancreatic enzyme secretion. Immunoprecipitation and immunoblotting studies using a CaMKII or CaMKIV antibody showed that rat pancreatic acini expressed both CaMKII and CaMKIV. Phosphotransferase activities of CaMKs were measured by a radioenzyme assay (REA) using autocamtide II, peptide gamma and myosin P-light chain as substrates. Although CaMKII and CaMKIV use autocamtide II as a substrate, peptide gamma is more efficiently phosphorylated by CaMKIV than by CaMKII. Intact acini were stimulated with cholecystokinin (CCK)-8, carbachol (CCh) and the high-affinity CCK-A receptor agonist, CCK-OPE, and the cell lysates were used for REA. CCK-8, CCh and CCK-OPE caused a concentration-dependent increase in CaMKs activities. When autocamtide II was used, maximal increases were 1.5-1.8-fold over basal (20.2+/-2.0 pmol/min/mg protein), with peaks occurring at 20 min after cell stimulation. In separate studies that used peptide gamma, CCK-8, CCh and CCK-OPE dose-dependently increased CaMKIV activities. Maximal increases were 1.5-2.4-fold over basal (30.7+/-3. 2 pmol/min/mg protein) with peaks occurring at 20 min after cell stimulation. Peak increases after cell stimulation induced by peptide gamma were 1.8-2.8-fold higher than those induced by autocamtide II. CCK-8, CCh and CCK-OPE also significantly increased phosphotransferase activities of myosin light chain kinase (MLCK) substrate (basal: 4.4+/-0.7 pmol/min/mg protein). However, maximal increases induced by MLCK substrate were less than 10% of those occurring in peptide gamma. Characteristics of the phosphotransferase activity were also different between autocamtide II and peptide gamma. When autocamtide II was used, elimination of medium Ca(2+) in either cell lysates or intact cells resulted in a significant decrease in the activity, whereas it had no or little effect when peptide gamma was used. This suggests that Ca(2+) influx from the extracellular space is not fully required for CaMKIV activity and Ca(2+) is not a prerequisite for phosphotransferase activity once CaMKIV is activated by either intracellular Ca(2+) release or intracellular Ca(2+) oscillations. The specific CaMKII inhibitor KN-62 (50 microM) had no effect on the CaMKIV activity and pancreatic enzyme secretion elicited by CCK-8, CCh and CCK-OPE. The specific MLCK inhibitor, ML-9 (10 microM), also did not inhibit CCK-8-stimulated pancreatic amylase secretion. In contrast, wide spectrum CaMK inhibitors, K-252a (1 microM) and KT5926 (3 microM), significantly inhibited CaMKIV activities and enzyme secretion evoked by secretagogues. Thus, CaMKIV appears to be an important intracellular mediator during stimulus-secretion coupling of rat pancreatic acinar cells.

Response of rat exocrine pancreas to high-fat and high-carbohydrate diets

Intake of diets with high fat content is a risk factor for acute pancreatitis and pancreatic cancer. The underlying mechanisms leading to the development of these diseases due to high fat intake are currently unknown. The current study was designed in rats to determine the physiologic and pathological consequences of a highfat diet that contained excess amounts of cottonseed oil or a high-carbohydrate diet that contained high amounts of sucrose on the exocrine pancreas. Rats were maintained on the diets for 4 weeks, and a cannula was inserted into the right jugular vein and one into the pancreatic duct for collection of pancreatic juice. Volume of the pancreatic juice and concentrations of amylase, lipase, and trypsinogen in the pancreatic juice were measured before and after infusions of CCK-8. Results showed that basal and CCK-stimulated pancreatic outputs of volume, amylase and lipase but not trypsinogen, were significantly elevated in intact rats given a high-fat diet when compared with rats given a high-carbohydrate diet. Forty-eight hours later, rats were sacrificed, and parts of the pancreas were removed for isolation of pancreatic acinar cells and for histopathologic studies. Pancreatic acini isolated from rats on a high-fat diet showed significantly lower basal and CCK-stimulated amylase release when compared with those on a high-carbohydrate diet. Histology of the pancreas of rats on a high-carbohydrate diet appeared normal; however, the pancreas of rats on high-fat diet showed significant alterations in exocrine pancreas. These results showed abnormalities in the exocrine pancreas of rats on a high-fat diet, that were not found in rats on a high-carbohydrate diet; further, they support the contention that a high-fat diet has a deleterious effect on the pancreas.

Role of adrenergic receptors in veratridine-stimulated amylase secretion from rabbit pancreatic lobules

Sympathetic inhibition of pancreatic enzyme secretion has been attributed to vasoconstriction and direct inhibition of acinar cells. We observed both adrenergic inhibition and facilitation of cholinergic transmission in rabbit pancreatic ganglia, which innervate acini. Here we used pancreatic lobules to determine whether adrenergic receptors also regulate synaptic transmission between pancreatic nerves and acini. Stimulation of pancreatic nerve terminals with veratridine (Ver), an activator of voltage-dependent Na+ channels, resulted in a 102% increase in amylase secretion, which was unaffected by alpha and beta receptor antagonists but inhibited 65% by atropine. At a concentration of 10 microM, norepinephrine inhibited (38%) and epinephrine potentiated (40%) Ver-stimulated secretion. At the same concentration, the alpha2 agonist clonidine (Clon) inhibited (39%), whereas the nonselective beta agonist isoproterenol (Iso) and the selective beta3 agonist BRL 37344 potentiated (71 and 67%, respectively) nerve-stimulated secretion. The effects of Clon and Iso and BRL 37344 were antagonized by yohimbine and propranolol, respectively. Phenylephrine, dobutamine, and terbutaline had no effect. Neither basal, bethanechol-stimulated, nor noncholinergic nerve-stimulated secretion was significantly altered by Clon or Iso. Thus, cholinergic nerve terminals innervating pancreatic acini exhibit both inhibitory alpha2 and atypical facilitatory beta adrenergic receptors. The apparent lack of adrenergic innervation suggests that adrenergic receptors on the nerve terminals of cholinergic pancreatic neurons are under hormonal control by circulating catecholamines. These results provide further evidence that intrinsic pancreatic neurons, which supply most, if not all, of the cholinergic innervation of acini, are important sites of sympathetic regulation of pancreatic exocrine secretion.

Intestinal fat suppresses protein-induced exocrine pancreatic secretion in chronically bile-pancreatic juice-diverted rats

Previously, we showed that the increase in pancreatic enzyme secretion was lower after feeding a casein diet containing fat than that after feeding a fat-free casein diet in chronically bile-pancreatic juice (BPJ)-diverted rats. In the present study, we determined whether the suppressive effects of fats on flow volume of BPJ and pancreatic enzyme secretion depend on delaying gastric emptying and examined the characteristics of the suppression with intraduodenal instillation of soybean oil or lecithin in BPJ-diverted rats. The study was conducted as three separate experiments using conscious rats with chronic BPJ diversion by means of a common bile-pancreatic duct catheter. The flow volume of BPJ and the secretion of pancreatic amylase and trypsin were determined after intraduodenal instillation of the test solution. Exocrine pancreatic secretion was strongly stimulated by administration of guanidinated casein hydrolysate (HGC, 150 mg/ml) in chronic BPJ-diverted rats. However, pancreatic secretion after administration of an emulsion containing HGC with either soybean oil (100 mg/ml) or mixed fat (50 mg/ml soybean oil + 50 mg/ml lecithin) was much lower than that after administration of HGC alone. In contrast, administration of the soybean oil emulsion without HGC resulted in a small, but significant increase in the volume of BPJ. The suppressive effects of soybean oil (100 mg/ml) on the increases in the BPJ flow and enzyme secretion were similar to those of sodium taurocholate (10 mg/ml), and there was no additive effect of soybean oil on taurocholate suppression. In conclusion, duodenally instilled soybean oil suppressed increases in flow volume of BPJ and pancreatic enzyme secretion induced by HGC in chronic BPJ-diverted rats, showing that the suppressive effect of the fat does not depend on delaying gastric emptying.

High-affinity cholecystokinin type A receptor/cytosolic phospholipase A2 pathways mediate Ca2+ oscillations via a positive feedback regulation by calmodulin kinase in pancreatic acini

In rat pancreatic acini, we previously demonstrated that depending on the agonist used, activation of cholecystokinin type A (CCKA) receptor (CCK-AR) results in the differential involvement of the cytosolic phospholipase A2 (cPLA2), phospholipase Cbeta1 (PLCbeta1) and Src/protein tyrosine kinase (PTK) pathways. The high-affinity CCK-AR appears to be coupled to the Gbeta/cPLA2/arachidonic acid (AA) cascade in mediating Ca2+ oscillations. The low-affinity CCK-AR is coupled to both the Galphaq/11/PLCbeta1/inositol 1,4,5-trisphosphate (IP3) to evoke intracellular Ca2+ release and the Src/PTK pathway to mediate extracellular Ca2+ influx. The objectives of this study were to provide evidence that cPLA2 is present in pancreatic acini and to evaluate the possibility that its activation results in Ca2+ oscillations and amylase secretion. Furthermore, we investigated the mechanism of Ca2+ oscillations mediated by the high-affinity CCK-AR. In rat pancreatic acini, immunoprecipitation studies using an anti-cPLA2 monoclonal antibody, demonstrated a cPLA2 band at the location of 110 kDa. A selective inhibitor of cPLA2, AACOCF3 (100 microM), inhibited production of AA metabolites, Ca2+ oscillations and amylase secretion elicited by the high-affinity CCK-AR agonist, CCK-OPE (10-1000 nM). In addition, through the repetitive release of intracellular Ca2+, CCK-OPE enhanced phosphotransferase activities of Ca2+/calmodulin-dependent protein kinase type IV (CaMK IV), which were inhibited by AACOCF3. The CaMK inhibitor, K252-a (1-3 microM), also abolished basal and CCK-OPE-stimulated CaMK IV activities. The CaM inhibitor, W-7 (100 microM), and K252-a inhibited Ca2+ oscillations and amylase secretion evoked by CCK-OPE without affecting the AA formation. Therefore, it appears that Ca2+ oscillations elicited by the high-affinity CCK-AR/Gbeta/cPLA2/AA pathway activate CaMK IV. Activated CaMK, in turn, regulates Ca2+ oscillations through a positive feedback mechanism to mediate pancreatic exocytosis.

Estradiol alters cholecystokinin stimulus-response coupling in rat pancreatic acini

We have previously demonstrated that altered exocrine pancreatic stimulus-secretion coupling is associated with ovariectomy and chronic estradiol administration. To elucidate possible mechanisms underlying those effects we examined the ability of chronic administration of different doses of estradiol to regulate the CCK signal transduction pathway in isolated rat pancreatic acini. Doses of estradiol ranging from 0.5 to 119 micrograms/day were administered to ovariectomized rats for 18 days. Ovariectomy was associated with enhanced CCK-stimulated pancreatic amylase release, whereas estradiol dose dependently decreased the magnitude of CCK-stimulated amylase release. Ovariectomy was also associated with enhanced CCK receptor numbers on acinar cell membranes. Estradiol administration was associated with dose-dependent decreases in CCK receptor numbers. Neither ovariectomy nor estradiol administration affected CCK receptor affinity. Moreover, estradiol administration was associated with increased expression of the alpha-subunit of the heterotrimeric G protein Gq/11 (Galphaq/11). Recent findings (H. Ohnishi, S. A. Ernst, D. I. Yule, C. W. Baker, and J. A. Williams. J. Biol. Chem. 272: 16056-16061, 1997) demonstrate that Galphaq/11 may exert a tonic inhibitory effect on pancreatic enzyme release. In view of these findings, the increased expression of Galphaq/11 induced by estradiol likely contributes to the inhibition of pancreatic enzyme release. We conclude that the effect of estradiol to decrease pancreatic secretion is mediated through regulation of CCK receptor density and Galphaq/11 expression.

Metabolism of ethanol by rat pancreatic acinar cells

It has been postulated that ethanol-induced pancreatic injury may be mediated by the oxidation of ethanol within the pancreas with secondary toxic metabolic changes, but there is little evidence of pancreatic ethanol oxidation. The aims of this study were to determine whether pancreatic acinar cells metabolize significant amounts of ethanol and, if so, to compare their rate of ethanol oxidation to that of hepatocytes. Cultured rat pancreatic acinar cells and hepatocytes were incubated with 5 to 50 mmol/L carbon 14-labeled ethanol (25 dpm/nmol). Ethanol oxidation was calculated from the production of 14C-labeled acetate that was isolated by Dowex ion-exchange chromatography. Ethanol oxidation by pancreatic acinar cells was demonstrable at all ethanol concentrations tested. At an intoxicating ethanol concentration (50 mmol/L), 14C-labeled acetate production (227+/-20 nmol/10(6) cells/h) approached that of hepatocytes (337+/-61 nmol/10(6) cells/h). Phenanthroline (an inhibitor of classes I through III isoenzymes of alcohol dehydrogenase (ADH)) inhibited pancreatic ethanol oxidation by 90%, but 4-methylpyrazole (a class I and II ADH inhibitor), carbon monoxide (a cytochrome P450 inhibitor), and sodium azide (a catalase inhibitor) had no effect. This study has shown that pancreatic acinar cells oxidize significant amounts of ethanol. At intoxicating concentrations of ethanol, pancreatic acinar cell ethanol oxidation may have the potential to contribute to pancreatic cellular injury. The mechanism appears to involve the class III isoenzyme of ADH.

Metallothionein is a component of exocrine pancreas secretion: implications for zinc homeostasis

Using transgenic mice that overexpress metallothionein-I (MT-I) and zinc-induced normal and transgenic animals, we have explored the localization of MT in the pancreas. Light-level immunocytochemistry demonstrated MT in acinar cells but not islet cells. Immunolabeling also revealed the presence of MT in pancreatic ducts, suggesting that it is released from acinar cells. Ultrastructural immunolocalization showed that MT was cytoplasmic, and no MT immunoreactivity was detected in lumens of the vesicular secretory pathway. Secreted pancreatic juice was collected from pilocarpine-stimulated mice and assayed for MT by a 109Cd-labeled hemoglobin-exchange assay and by radioimmunoassay. Both methods revealed high (> 1,000 ng/ml) levels of MT in the stimulated secretion. The level of MT in pancreatic juice from transgenic mice was only slightly (2-fold) increased despite dramatic overexpression of MT-I in the pancreas (> 20-fold). In contrast, zinc induction of MT significantly increased MT by 5- to 10-fold in the pancreatic juice, in normal and transgenic mice. These data indicate that MT is released from pancreatic acinar cells but not by the classical vesicular secretory pathway. In addition, MT levels in pancreatic juice are regulated by zinc, suggesting a physiological role of the pancreas in metal homeostasis.

Structural and functional changes of rat exocrine pancreas exposed to nicotine

Nicotine, an addictive agent in cigarette smoking, has been implicated in the etiology of pancreatitis and pancreatic carcinoma. Very little experimental data are, however, available regarding the effects of nicotine on the structural and functional changes in the exocrine pancreas. Two groups of rats divided into control and nicotine exposed were used. The animals in the nicotine group were maintained for 28 d with ad libitum water containing 0.77 mM of nicotine. At term, the animals were sacrificed, and pancreas was examined for pathological and functional changes. Nicotine induced cytoplasmic vacuolation and cellular edema in the exocrine pancreas. Plasma levels of glucose and insulin and CCK-8-stimulated amylase release in isolated acini were significantly decreased by nicotine, whereas the total cellular amylase content was significantly increased. Analysis of competitive ligand binding data on membranes from isolated acini showed that the Bmax and Kd values for CCK receptors were not significantly changed by nicotine, p > 0.05. These data indicate that a postreceptor mechanism is involved in the inhibition in stimulus-secretion coupling of enzyme secretion by nicotine. The increase in total cellular amylase content and decreased enzyme secretion by nicotine may be implicated in the induction of pancreatic pathology.

Chronic oral administration of synthetic trypsin inhibitor camostate reduces amylase release from isolated rat pancreatic acini

In the present study, we examined stimulus-secretion coupling in pancreatic acini prepared from rats given synthetic protease inhibitor camostate at a dose of 200 mg/kg body wt by an orogastric tube once a day for 10 d. Camostate treatment significantly increased pancreatic weight, protein, DNA, and enzyme contents. In acini prepared from the camostate-treated rats, responsiveness to both CCK-8 and carbamylcholine was greatly decreased with no shift in the dose-response curves compared to control acini prepared from saline-treated rats. There were no major changes in the affinity for both high- and low-affinity sites of CCK receptors, but there was a significant reduction in the capacity of low-affinity site based on acinar protein. Responsiveness to secretin in the camostate-treated rat acini was also significantly reduced compared with that in the controls. However, amylase release from the camostate-treated rat acini in response to an increase in intracellular calcium levels induced by the calcium ionophores A23187 or to an increase in intracellular cyclic 3',5'-monophosphate (cyclic AMP) levels caused by 8 bromo cyclic AMP was not significantly different from the control rat acini, suggesting that both Ca(2+)-dependent tyrosine kinase and nucleotide-activated kinases are not impaired. On the other hand, the responsiveness to phorbol ester TPA, which stimulates amylase secretion via a calcium-independent cascade by activating protein kinase C directly, was reduced in the camostate-treated rat acini compared with the controls. These results suggest the possibilities that the reduced amylase secretion in the camostate-treated rats is owing to alterations in both the transmembrane signal transduction and the phosphorylation of regulatory proteins by the Ca(2+)-independent, protein kinase C-dependent mechanisms.

The effect of chronic alcohol administration on cerulein-induced pancreatitis

Alcohol consumption i associated with pancreatitis, but the mechanism underlying this injury remains unclear. Alcohol consumption has recently been shown to increase the fragility of both rat pancreatic lysosomes and zymogen granules in vitro, which may predispose to autodigestion via the intracellular activation of digestive enzymes by lysosomal enzymes. Cerulein-induced pancreatitis is also associated with lysosomal fragility. To determine the effect of alcohol consumption on this form of pancreatic injury, the severity of pancreatitis was compared in three groups of rats following i.v. cerulein infusion: rats fed alcohol in a liquid diet, pair-fed dextrose controls, and chow-fed controls. The histological severity of pancreatitis induced by supramaximal cerulein infusion was not found to be increased by prior alcohol consumption. Since alcohol did not appear to increase the severity of pancreatic injury induced by cerulein, we sought to define biochemical parameters that might precede obvious injury. The subcellular distribution of cathepsin B activity and markers of lysosomal fragility were compared in the same groups of experimental animals. Cerulein infusion led to a marked redistribution of cathepsin B activity from the lysosomal to the zymogen-granule-enriched fractions.For animals killed in the fed state, a redistribution of cathepsin B activity toward the zymogen-granule-enriched fraction was also demonstrated in alcohol-fed animals compared to their pair-fed controls. However, chronic alcohol administration did not influence the effect of cerulein on subcellular cathepsin B distribution or lysosomal fragility. In this rat study, administration of alcohol did not increase the effects of supramaximal doses of cerulein on the pancreas.

Evidence for autoregulation of cholecystokinin secretion during diversion of bile pancreatic juice in rats

BACKGROUND & AIMS

The mechanism regulating cholecystokinin (CCK) secretion during prolonged diversion of bile pancreatic juice (BPJ) is unknown. We examined the hypothesis that the decrease of plasma CCK levels after prolonged diversion of BPJ is mediated by an increase in plasma somatostatin levels evoked by hypercholecystokinemia and somatostatin in turn inhibits CCK-releasing peptide (CCK-RP) bioactivity and decreases plasma CCK levels.

METHODS

Pancreatic secretion, plasma CCK levels, and somatostatin levels were monitored for 7 hours after diversion of BPJ in anesthetized rats. Secretion of CCK-RP bioactivity during diversion of BPJ was examined in the presence or absence of somatostatin.

RESULTS

Diversion of BPJ for 2 hours caused a 13- and 2.5-fold increase in plasma CCK and somatostatin levels. The increase in somatostatin levels was blocked by the CCK antagonist L364,718. At 5 hours after diversion of BPJ, plasma CCK and somatostatin levels and luminal CCK-RP bioactivity decreased to basal levels. The decrease in plasma CCK levels was prevented by the administration of a specific somatostatin antagonist. We also showed that the stimulatory effect of the CCK-RP bioactivity was eliminated when the donor rat was pretreated with somatostatin.

CONCLUSIONS

Autoregulation of CCK secretion occurs during the diversion of BPJ and this is mediated by somatostatin, which inhibits the secretion of CCK-RP bioactivity and decreases plasma CCK levels.

Peptide cholesystokinin receptor antagonist increases food intake in rats

An analogue of the C-terminal heptapeptide of cholecystokinin (CCK) t-Boc-Tyr(SO3-)-Nle-Gly-D-Trp-Nle-Asp-a-2-phenylethylester is a potent, specific CCK receptor antagonist. Intraperitoneal injection of the antagonist abolished suppression of real feeding and sham feeding by exogenous CCK-8 (1.8 nmol/kg), and significantly increased real feeding. Assuming an antagonist distribution like that of exogenous CCK-8, our results suggest that exogenous CCK-8 and endogenous CCK reduce food intake by acting at a site(s) accessible to peripherally administered peptides.

Effects of ethanol and protein deficiency on pancreatic digestive and lysosomal enzymes

The pathogenesis of alcoholic pancreatitis is not fully understood. An increase in pancreatic digestive and lysosomal enzyme synthesis because of ethanol consumption could contribute to the development of pancreatic injury in alcoholics. This study aimed, firstly, to determine the effect of ethanol on the content and messenger RNA levels of pancreatic digestive enzymes and on the messenger RNA level of the lysosomal enzyme cathepsin B, and secondly, to examine the influence of concomitant protein deficiency (a known association of alcoholism and pancreatic injury) on these effects. A rat model of chronic ethanol administration was used in which rats were fed in groups of four, and for four weeks, protein sufficient and protein deficient diets with or without ethanol. Ethanol increased the pancreatic content of lipase but did not influence chymotrypsinogen or trypsinogen values. mRNA levels for lipase, trypsinogen, and chymotrypsinogen were raised in rats fed ethanol. Protein deficiency resulted in reduced tissue levels of lipase, chymotrypsinogen, and amylase but did not influence trypsinogen values. mRNA levels for proteases were increased in protein deficient rats, while those for lipase remained unaltered. Both ethanol and protein deficiency increased mRNA levels for cathepsin B. It is concluded that chronic ethanol consumption, in both protein sufficient and protein deficient states, increases the capacity of the pancreatic acinar cell to synthesise digestive and lysosomal enzymes.

Characterization of the major sulfated protein of mouse pancreatic acinar cells: a high molecular weight peripheral membrane glycoprotein of zymogen granules

The major sulfated protein of the mouse pancreatic acinar cell, gp300, has been identified and characterized with monoclonal and polyclonal antibodies. gp300 is a glycoprotein of M(r) = 300,000 which contains approximately 40% of metabolically incorporated [35S]sulfate in the acinar cell. Sulfate on gp300 is resistant to hot 1N HCl, but sensitive to alkaline hydrolysis, demonstrating that the sulfate is carbohydrate-linked rather than tyrosine-linked. gp300 metabolically labeled with [3H]glucosamine and [35S]sulfate was chemically and enzymatically treated followed by Bio-Gel P-10 gel filtration. Both labels were resistant to treatments which degrade glycosaminoglycans. Treatment of dual-labeled gp300 with PNGase F to cleave N-linked oligosaccharides released approximately 17% of [3H] and little [35S]. Mild alkaline borohydride treatment after removal of N-linked sugar released the remainder of both labels, indicating the presence of sulfated O-linked oligosaccharides. Biosynthesis studies and PNGase F digestion indicate that the core protein is approximately 210 kDa, with apparent contributions of approximately 35 kDa N-linked sugar, and approximately 55 kDa O-linked sugar. Lectin blotting and glycosidase digestion demonstrated the presence of Gal beta(1-3)GalNAc and sialic acid alpha(2-3)Gal in O-linked oligosaccharide, and Gal beta(1-4)GlcNAc in N-linked oligosaccharide. Immunolocalization and subcellular fractionation showed that gp300 is a peripheral membrane protein localized to the lumenal face of the zymogen granule membrane. gp300 was not secreted in response to hormone stimulation of acini, so it is not a secretory product. Immunoblot analysis showed that gp300 is present in other gastrointestinal tissues and parotid glands. Localization of this nonsecreted sulfated glycoprotein to exocrine secretory granule membranes suggests that gp300 may have a role in granule biogenesis.

Chronic ethanol consumption increases the fragility of rat pancreatic zymogen granules

Intracellular activation of pancreatic digestive enzymes by lysosomal hydrolases is thought to be an early event in the pathogenesis of pancreatic injury. As ethanol excess is an important association of pancreatitis, experimental work has been directed towards exploring possible mechanisms whereby ethanol may facilitate contact between inactive digestive enzyme precursors and lysosomal enzymes. The aim of this study was to find out if chronic ethanol administration increases the fragility of rat pancreatic zymogen granules. Sixteen male Sprague-Dawley rats were pair fed ethanol and control liquid diets for four weeks. Zymogen granule fragility was then assessed in pancreatic homogenate by determination of (a) latency and (b) per cent supernatant enzyme after sedimentation of zymogen granules. Amylase was used as a zymogen granule marker enzyme. Latency was significantly reduced in pancreatic homogenates of ethanol fed animals suggesting increased zymogen granule fragility. In support of this finding, there was a trend towards increased supernatant enzyme after ethanol feeding. In conclusion, administration of ethanol increases the fragility of pancreatic zymogen granules in the absence of morphological evidence of pancreatic injury. It is proposed that zymogen granule fragility may play an early part in the pathogenesis of alcoholic pancreatitis by permitting contact between digestive and lysosomal enzymes.

Mouse pancreatic acinar/ductular tissue gives rise to epithelial cultures that are morphologically, biochemically, and functionally indistinguishable from interlobular duct cell cultures

Most of the pancreatic exocrine epithelium consists of acinar and intralobular duct (ductular) cells, with the balance consisting of interlobular and main duct cells. Fragments of mouse acinar/ductular epithelium can be isolated by partial digestion with collagenase and purified by Ficoll density gradient centrifugation. We investigated whether previously developed culture conditions used for duct epithelium would result in the selective survival and proliferation of ductular cells from the acinar/ductular fragments. The fragments were cultured on nitrocellulose filters coated with extracellular matrix. After 2 to 4 wk the filters were covered with proliferating cells resembling parallel cultures of duct epithelium by the following criteria: protein/DNA ratio, light and electron microscopic appearance, the presence of duct markers (carbonic anhydrase [CA] activity, CA II mRNA, the cystic fibrosis transmembrane conductance regulator), the near absence of acinar cell markers (amylase and chymotrypsin), a similar polypeptide profile after sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and the presence of spontaneous and secretin-stimulated electrogenic ion transport. Both duct and ductular epithelia formed fluid-filled cysts in collagen gels and both could be subcultured. We conclude that acinar/ductular tissue gives rise to ductular cells in culture by some combination of acinar cell death and/or transdifferentiation to a ductular phenotype, accompanied by proliferation of these cells and preexisting ductular cells. These cultures may be used to investigate the properties of this part of the pancreatic duct system, from which most of the pancreatic juice water and electrolytes probably originates.

Endogenous cholecystokinin stimulates pancreatic enzyme secretion via vagal afferent pathway in rats

BACKGROUND/AIMS

Recently we showed that doses of cholecystokinin octapeptide (CCK-8) that produce physiological plasma CCK levels act via stimulation of afferent vagal pathway to mediate pancreatic enzyme secretion. In this study we investigated if endogenous CCK also acts via similar pathway.

METHODS

In anesthetized rats, plasma CCK levels were elevated by diversion of bile pancreatic juice and duodenal casein feeding. The effects of acute vagotomy as well as that of chemical ablation of the afferent vagal pathway on pancreatic enzyme secretion evoked by increased endogenous plasma CCK levels were investigated.

RESULTS

Diversion of bile pancreatic juice elevated plasma CCK levels from a basal level of 0.6 +/- 0.1 pmol/L to 8.9 +/- 2.1 pmol/L and caused a more than twofold increase in pancreatic protein secretion. Similar increases in plasma CCK levels and pancreatic secretion were observed with duodenal administration of casein. Vagotomy or perivagal application of capsaicin, a sensory neurotoxin, abolished increases in pancreatic secretion but not plasma CCK levels in response to diversion of bile pancreatic secretion or duodenal administration of casein. In contrast, pancreatic protein responses to 2-deoxy-D-glucose, a central vagal stimulant, remained intact in rats with perivagal capsaicin treatment indicating capsaicin did not affect efferent vagal function.

CONCLUSIONS

Endogenous CCK under physiological conditions act via stimulation of vagal afferent pathway to mediate pancreatic enzyme secretion.

L-phenylalanine releases cholecystokinin (CCK) and is associated with reduced food intake in humans: evidence for a physiological role of CCK in control of eating

Exogenous administration of cholecystokinin (CCK) reduces food intake in humans; however, it is not clear if endogenous CCK is a true satiety hormone. The aim of this experiment was to manipulate endogenous release of CCK using L-phenylalanine (L-PA), a potent releaser of CCK, and to measure subsequent food intake. On separate occasions, six normal-weight fasted subjects (four men, two women) were administered 10 g of L-PA, D-PA, or placebo 20 minutes before being presented with a standard meal of known calorie content. Preliminary experiments had shown that peak plasma concentrations of CCK were obtained 20 minutes after administering L-PA. The test meal was given to coincide with this peak. One hundred-millimeter visual analog scales (VAS) to assess hunger, desire to eat, and fullness were completed premeal, postmeal, and at intervals thereafter. Blood was taken before administering PA/placebo immediately premeal and postmeal and stored for measurement of CCK levels by bioassay. Subjects consumed 1,089 +/- 86 kcal after L-PA (P = .03) compared with 1,587 +/- 174 kcal after placebo and 1,492 +/- 126 kcal after D-PA. The reduction in calorie intake after L-PA was associated with a significantly greater sensation of fullness. Basal levels of CCK were 1.10 +/- 0.12 pmol/L; 20 minutes after L-PA, CCK levels increased to 5.49 +/- 0.83 pmol/L. There was no increase in CCK following D-PA or placebo. Release of CCK by L-PA is associated with a reduction in subsequent food intake, and this suggests that CCK is an important satiety hormone in humans.

A new CCK-B/gastrin receptor antagonist acts as an agonist on the rat pancreas

The new CCK-B/gastrin receptor antagonist PD 136450 is of potential value in treating neurologic and psychiatric disorders. We investigated possible side effects on the rat pancreas using acute and chronic administration schedules. In chronic experiments, four groups of rats were given either PD 136450, the proton pump inhibitor BY 308 (in order to induce hypergastrinemia), a combination of both, or control solutions over 14 d. Pancreatic growth, DNA, and protein content were significantly increased in rats given PD 136450 irrespective of circulating gastrin levels. Furthermore, an anticoordinate shift in pancreatic enzyme content in favor of trypsin and chymotrypsin at the expense of amylase and lipase was observed. Plasma CCK levels remained unchanged in this group making a role of circulating hormone unlikely. In order to investigate a possible direct agonist effect of the CCK-B/gastrin receptor antagonist, we studied amylase release from isolated rat pancreatic acini in response to PD 136450 and sulfated CCK8 alone and in combination with the specific CCK-A receptor antagonist MK 329. Increasing concentrations of PD 136450 caused a monophasic dose-response curve in contrast to the well-known biphasic amylase release in response to CCK8. Addition of increasing doses of PD 136450 to a concentration of CCK causing maximal stimulation of amylase release (0.1 nM) further enhanced amylase release from pancreatic acini. The specific CCK-A receptor antagonist MK 329 dose-dependently inhibited CCK8- and PD 136450-induced amylase release. In conclusion, the new CCK-B/gastrin receptor antagonist PD 136450 exhibited profound agonist actions on the rat pancreas mediated via CCK-A receptors.

CCK antagonists reveal that CCK-8 and JMV-180 interact with different sites on the rat pancreatic acinar cell CCKA receptor

The ability of CCKA antagonists to inhibit full and partial CCK agonists of the rat pancreatic acinar cell CCKA receptor has been studied. When isolated rat pancreatic acini were superfused with CCK-8 (10 pM-1 nM) or CCK-4 (1 microM), an increase in [Ca2+]i signal was initiated. Concurrent superfusion of either L-364,718 (0.1 microM) or lorglumide (10 microM), chemically distinct, specific, potent antagonists of the CCKA receptor, resulted in a rapid inhibition of the [Ca2+]i signal initiated by all concentrations of CCK-8. In contrast, Ca2+ oscillations, initiated by JMV-180 (25 nM-1 microM), a partial agonist analogue of CCK-8, were essentially unaffected by concurrent superfusion of either L-364,718 or lorglumide. When JMV-179, an analogue of JMV-180 that exhibits characteristics of a pure antagonist, was superfused concurrently with either CCK-8 or JMV-180, Ca2+ oscillations were inhibited, even in the presence of 0.1 microM L-364,718. In a similar fashion, amylase secretion stimulated by CCK-8 was markedly attenuated by L-364,718, lorglumide, and JMV-179, whereas secretion stimulated by JMV-180 was only inhibited by JMV-179. A model is proposed to reconcile this data, based on the assumption that JMV-180 and CCK-8 interact with discrete sites on the CCKA receptor, which are differentially affected by the binding of antagonists. This model may also explain how a single receptor may transduce multiple signals in response to different agonists.

Nitric oxide participates in the regulation of pancreatic acinar cell secretion

The role of nitric oxide (NO) in the regulation of exocrine secretion was investigated in isolated rat pancreatic acini. NO synthase activity was detected in the extract of acini and purified by ion-exchange and 2',5'-ADP agarose chromatographies. Enzyme activity was determined by conversion of 3H-arginine to 3H-citrulline, by measurement of nitrite (a breakdown product of NO) and by generation of cyclic GMP. Treatment of acini with L-arginine increased nitrite as well as cyclic GMP and amylase release, which were prevented by the nitric oxide synthase inhibitors N-monomethyl-arginine [NMMA] and NG-nitro-L-arginine [NNA]. These nitric oxide inhibitors also blocked carbachol-induced amylase release as well as elevation of acinar cell cyclic GMP. NNA was a potent inhibitor of carbamylcholine-induced amylase release (est. Ki = 2.2 uM). Nitric oxide apparently participates significantly in the overall control of pancreatic acinar cell secretory function.

Cathepsin B inhibition in two models of acute pancreatitis

The possible role of cathepsin B in the pathogenesis of two forms of acute pancreatitis was studied using the cathepsin B inhibitor known as E-64. In an edematous, nonfatal pancreatitis induced by supramaximal doses of cerulein, increases in the serum amylase and lipase levels were less pronounced in rats pretreated with E-64. Other parameters of pancreatic injury were unaffected by inhibition of cathepsin B. In a necrohemorrhagic type of pancreatic injury induced by retrograde infusion of bile salts into the pancreatic duct, E-64 partially attenuated increases in serum levels of amylase and lipase, and in addition, reduced the activation of trypsinogen. However, the high mortality in this model of pancreatitis was not modified.

Exogenous administration of estradiol and cholecystokinin alters exocrine pancreatic function in rats

This study was conducted in rats to investigate the influence of exogenously administered estradiol (ESD) and/or cholecystokinin (CCK) on components and secretions of the pancreatic acini. Intact male rats were treated for 14 d with exogenous administration of ESD, CCK, or ESD+CCK. After 14 d CCK treatment induced significant increases in DNA and RNA contents, and DNA/RNA ratio in the pancreas, indicating hyperplasia and hypertrophy of the pancreas, however, ESD treatment did not have these effects. Both ESD treatment and CCK treatment induced significant increases in amylase and trypsinogen contents in pancreatic acini and each decreased secretion from acini in response to CCK. Combined treatment with ESD plus CCK augmented these effects on enzyme contents and secretion. The results indicate that exogenous administration of CCK has trophic effects on the exocrine pancreas, increasing effects on enzyme contents and inhibitory effects on amylase secretion. In contrast, exogenous administration of ESD had no trophic effects on pancreas, but had increasing effects on enzyme contents and inhibitory effects on amylase secretion. The results suggest that the effects of exogenous ESD and CCK on pancreas are not similar to each other, but both ESD and CCK may be involved in regulating pancreatic exocrine functions.

Structural and functional changes of exocrine pancreas induced by FK506 in rats

BACKGROUND

The pancreas has been reported as a possible target for FK506 toxicity. This study was conducted to examine the effects of FK506 on the structure and function of pancreatic acinar cells.

METHODS

Male Sprague-Dawley rats received an intramuscular injection of saline or FK506, and pancreatic acini were isolated on the day of sacrifice.

RESULTS

FK506 caused a time-dependent suppression in amylase secretory response to cholecystokinin or carbachol at days 3-14, and increases in amylase and trypsinogen content at days 7-14. The properties of cholecystokinin and scopolamine binding sites in acini were not altered by FK506. Amylase release by A23187 and secretin were decreased by FK506, but those by phorbol ester 12-O-tetradecanoylphorbol-13-acetate, forskolin, 5'-cyclic adenosine monophosphate and vasoactive intestinal peptide were not changed. Increases in cytosolic free calcium concentration induced by cholecystokinin were not changed by FK506. Histologically, a significant increase in cytoplasmic zymogen granules was observed in pancreas from FK506-treated rats.

CONCLUSION

These data suggest that FK506 induced changes in function and metabolism in pancreatic acinar cells, and these changes might be caused by altering postreceptor loci in stimulus-secretion coupling.

Effects of calyculin A on amylase release in streptolysin-O permeabilized acinar cells

The effects of the phosphatase inhibitors calyculin A and okadaic acid on amylase release from streptolysin-O permeabilized rat pancreatic acini were investigated. Both agents induced similar biphasic effects with moderate potentiation of calcium-stimulated amylase release at medium and strong inhibition at higher concentrations. Calyculin A was thirty times more potent than okadaic acid and at 100 nM totally inhibited calcium-induced amylase release while 3 microM okadaic acid reduced amylase release by 78%. 100nM calyculin A also completely inhibited GTP gamma S-potentiated amylase release and partially inhibited phorbol ester potentiated secretion. The data indicate that inhibition of a serine/threonine phosphatase, probably a type 1 phosphatase, leads to inhibition of calcium-induced amylase release in permeabilized pancreatic acini.

Effects of okadaic acid indicate a role for dephosphorylation in pancreatic stimulus-secretion coupling

Okadaic acid completely inhibits phosphatase 2A at nanomolar concentrations, while complete inhibition of type 1 phosphatases occurs at 1 microM. Phosphatase 2B is significantly inhibited only at concentrations > 1 microM. In rat pancreatic acini, 1 microM okadaic acid shifted the cholecystokinin (CCK) dose-response curve for stimulating amylase release to the right without reducing maximal secretion. At 3 microM, okadaic acid inhibited maximal CCK-induced amylase release to 78 +/- 7% of control, whereas the inactive analogue 1-Nor-okadaone had no effect. Three lines of evidence indicate that this inhibition by okadaic acid occurs at a late step in stimulus-secretion coupling: 1) intracellular Ca2+ signaling in response to agonist stimulation was not appreciably altered by okadaic acid; 2) stimulation with phorbol ester plus thapsigargin (thus by-passing receptor activation), which gave 85 +/- 4% of maximal CCK-induced amylase release, was inhibited 66 +/- 4% by 3 microM okadaic acid; and 3) Ca(2+)-induced amylase secretion in streptolysin O-permeabilized cells was also reduced by 85 +/- 7%. Two-dimensional polyacrylamide gel electrophoresis of 32P-labeled acini and autoradiography demonstrated that okadaic acid dose dependently increased overall protein phosphorylation. Correspondingly, okadaic acid also led to an inhibition of CCK-induced dephosphorylation. These results show that okadaic acid inhibits pancreatic acinar secretion at a step after generation of intracellular messengers and indicate a role for protein dephosphorylation in stimulus-secretion coupling.

Characterization of interactions between CCK-33 and CCK receptors in isolated dispersed pancreatic acini

In isolated dispersed pancreatic acini, we have characterized the interactions between cholecystokinin (CCK) and CCK receptors by simultaneously measuring CCK-33 immunoreactivity and CCK bioactivity. Incubation of acinar cells with CCK-33 at cell density of 0.2-0.3 mg acinar protein per ml resulted in stimulation of amylase release concomitant with significant and time-dependent decrease of the immunoreactive CCK. With L-364,718 (0.1 microM), a specific CCK receptor antagonist, immunoreactive CCK levels in the media were not significantly altered during incubation; however, CCK-stimulated amylase release was almost completely abolished (94% inhibition). Vasoactive intestinal peptide (1 nM) significantly potentiated CCK stimulated amylase release without affecting immunoreactive CCK in the media. Insulin (167 nM) did not affect the CCK stimulated amylase release or immunoreactive CCK in the media. Incubation of acinar cells with CCK-33 at 4 degrees C did not affect the levels of immunoreactive CCK; however, a significant change in levels of immunoreactive CCK were found at 37 degrees C at 90 min. Incubation of cell free medium with CCK-33 in the presence or absence of secreted enzymes revealed no changes in CCK immunoreactivity in the medium at 90 min. Addition of bacitracin in the incubation media did not affect the CCK immunoreactivity or bioactivity. These findings indicate that in isolated rat pancreatic acini, CCK-33 stimulates amylase release through a receptor that is specifically blocked by L-364,718. Specificity of the interactions of CCK-33 with acinar cells in the media appears to be receptor-mediated and time- and temperature-dependent.

Exocrine pancreatic function in obstructive jaundice rats: studies with isolated dispersed pancreatic acini

This study was conducted to investigate pancreatic exocrine function and pancreatic growth in rats with obstructive jaundice (OJ). OJ was produced in adult male Sprague-Dawley rats by bile duct ligation; control rats underwent laparotomy only. Induction of OJ was associated with significant hyperplasia and hypertrophy of the pancreas in rats as shown by increased DNA and RNA contents of pancreatic tissue. Factors associated with pancreatic growth in OJ rats were further examined in isolated dispersed pancreatic acini from OJ rats and the data were compared with those for control rats. Studies with isolated dispersed acini from OJ rats showed that pancreatic growth was accompanied by significant increases in total cellular amylase content; however, amylase release (percentage of initial) in response to cholecystokinin octapeptide was significantly decreased in OJ rats compared to control rats. Total amylase output in response to 100 pM cholecystokinin (CCK) was higher in the OJ group when compared to the control group (8.6 U/mg protein versus 6.4 U/mg protein), as calculated from the total amylase content and percentage of amylase released. Receptor binding data showed that the capacity of CCK receptors in OJ rats was significantly lower when it was compared with control. In addition, plasma levels of CCK were significantly elevated in OJ rats when compared to controls. These results suggest that obstructive jaundice induces pancreatic growth that is associated with alteration of exocrine pancreatic function. Abnormally high levels of stored amylase in pancreatic acini may be implicated in the development of pancreatitis as often seen in obstructive jaundice patients.