The role of intracellular calcium signaling in premature protease activation and the onset of pancreatitis. (17/463)

The exocrine pancreas synthesizes and secretes large amounts of digestive proteases as inactive precursor zymogens. Under physiological conditions a variety of cellular defense mechanisms protect the pancreatic acinar cell against a premature and intracellular activation of these zymogens. When these defenses fail, pancreatic autodigestion is initiated and acute pancreatitis can develop. A number of experimental observations suggest that extra- as well as intracellular calcium concentrations play an important part in the initiation of pancreatic protease activation, but the intracellular signaling events that regulate this process are unknown. Using a model system in which we used pancreatic acini (freshly prepared functional units of living acinar cells), we were able to simulate the conditions found during experimental pancreatitis in rodents. By means of a cell permeant fluorescent trypsin substrate we could demonstrate in these acini that premature protease activation is initiated at the apical acinar cell pole and occurs only in the presence of secretagogue concentrations that exceed those required for a maximum secretory response. By combining this technique with fluorescence ratio imaging for the Ca(2+)-sensitive dye fura-2, we could further show that this protease activation is highly dependent on the spatial as well as the temporal distribution of the corresponding Ca(2+) release from stores within the same subcellular compartment and that it is not propagated to neighboring acinar cells.  (+info)

The effects of ammonia on pancreatic enzyme secretion in vivo and in vitro. (18/463)

BACKGROUND: Recent studies clearly demonstrate that Helicobacter pylori (H. pylori) infection of the stomach causes persistent elevation of ammonia (NH3) in gastric juice leading to hypergastrinemia and enhanced pancreatic enzyme secretion. METHODS: The aim of this study is to evaluate the influence of NH4OH on plasma gastrin level and exocrine pancreatic secretion in vivo in conscious dogs equipped with chronic pancreatic fistulas and on secretory activity of in vitro isolated acini obtained from the rat pancreas by collagenase digestion. The effects of NH4OH on amylase release from pancreatic acini were compared with those produced by simple alkalization of these acini with NaOH. RESULTS: NH4OH given intraduodenally (i.d.) in increasing concentrations (0.5, 1.0, 2.0, 4.0, or 8.0 mM/L) resulted in an increase of pancreatic protein output, reaching respectively 9%, 10%, 19%, 16% and 17% of caerulein maximum in these animals and in a marked increase in plasma gastrin level. NH4OH (8 x 0 mM/L, i.d.) given during intravenous (i.v.) infusion of secretin (50 pmol/kg-h) and cholecystokinin (50 pmol/kg-h) reduced the HCO3 and protein outputs by 35% and 37% respectively, as compared to control obtained with infusion of secretin plus cholecystokinin alone. When pancreatic secretion was stimulated by ordinary feeding the same amount of NH4OH administered i.d. decreased the HCO3- and protein responses by 78% and 47% respectively, and had no significant effect on postprandial plasma gastrin. In isolated pancreatic acini, increasing concentrations of NH4OH (10(-7)-10(-4) M) produced a concentration-dependent stimulation of amylase release, reaching about 43% of caerulein-induced maximum. When various concentrations of NH4OH were added to submaximal concentration of caerulein (10(-12) M) or urecholine (10(-5) M), the enzyme secretion was reduced at a dose 10(-5) M of NH4OH by 38% or 40%, respectively. Simple alkalization with NaOH of the incubation medium up to pH 8.5 markedly stimulated basal amylase secretion from isolated pancreatic acini, whereas the secretory response of these acini to pancreatic secretagogues was significantly diminished by about 30%. LDH release into the incubation medium was not significantly changed in all tests indicating that NH4OH did not produce any apparent damage of pancreatic acini and this was confirmed by histological examination of these acini. CONCLUSIONS: 1. NH4OH affects basal and stimulated pancreatic secretion. 2. The excessive release of gastrin may be responsible for the stimulation of basal pancreatic enzyme secretion in conscious animals, and 3. The inhibitory effects of NH4OH on stimulated secretion might be mediated, at least in part, by its direct action on the isolated pancreatic acini possibly due to the alkalization of these acini.  (+info)

Effects of M1 and CCK antagonists on latency of pancreatic amylase response to intestinal stimulants. (19/463)

In six conscious dogs with gastric and duodenal cannulas, secretin (164 pmol. kg(-1). h(-1) iv) was given to provide a flow of pancreatic juice of approximately 1 drop/s. Amylase activity was measured in each drop before and after rapid intravenous injection of caerulein (7.4 pmol/kg) or intraduodenal injection of L-tryptophan (1 mmol), sodium oleate (3 mmol), and HCl (3 mmol). All experiments were repeated in the presence of the M1 receptor antagonist telenzepine (81 nmol. kg(-1). h(-) iv) and the cholecystokinin (CCK) receptor antagonist L-364718 (0.1 mg/kg iv). Latency of amylase response (time between injection of stimulant and sustained increase in amylase activity greater than mean + 3 SD of prestimulatory activity) to tryptophan (17 +/- 7 s; n = 6) and oleate (16 +/- 5 s) was significantly (P < 0.05) shorter than to caerulein (28 +/- 4 s) and HCl (120 +/- 47 s). Telenzepine significantly increased the latency of amylase response to tryptophan and oleate by >10-fold but not the latency to caerulein or HCl. L-364718 abolished the amylase response to all stimulants. These findings indicate that the early amylase response to intraduodenal tryptophan and oleate is mediated by a neural enteropancreatic reflex ending on M1 receptors rather than by hormone release. However, the activation of (possibly vagal) CCK receptors is essential to run the reflex. The early amylase response to intraduodenal HCl is probably mediated by the release of CCK into the blood circulation.  (+info)

Role of cathepsin B in intracellular trypsinogen activation and the onset of acute pancreatitis. (20/463)

Autodigestion of the pancreas by its own prematurely activated digestive proteases is thought to be an important event in the onset of acute pancreatitis. The mechanism responsible for the intrapancreatic activation of digestive zymogens is unknown, but a recent hypothesis predicts that a redistribution of lysosomal cathepsin B (CTSB) into a zymogen-containing subcellular compartment triggers this event. To test this hypothesis, we used CTSB-deficient mice in which the ctsb gene had been deleted by targeted disruption. After induction of experimental secretagogue-induced pancreatitis, the trypsin activity in the pancreas of ctsb(-/-) animals was more than 80% lower than in ctsb(+/+) animals. Pancreatic damage as indicated by serum activities of amylase and lipase, or by the extent of acinar tissue necrosis, was 50% lower in ctsb(-/-) animals. These experiments provide the first conclusive evidence to our knowledge that cathepsin B plays a role in intrapancreatic trypsinogen activation and the onset of acute pancreatitis.  (+info)

Cerulein upregulates ICAM-1 in pancreatic acinar cells, which mediates neutrophil adhesion to these cells. (21/463)

Neutrophil infiltration into the pancreas is a key event in pancreatitis. Here we show that intercellular adhesion molecule-1 (ICAM-1), which regulates neutrophil adhesion, is present on rat pancreatic acinar cells, is upregulated by a hormone (cerulein) and mediates direct binding of neutrophils to acinar cells. ICAM-1 was upregulated in pancreas of rats with experimental pancreatitis induced by supramaximal doses of cerulein. Furthermore, cerulein time and dose dependently stimulated expression of ICAM-1 mRNA and protein in isolated pancreatic acinar cells. Inhibitory analysis showed that activation of transcription factor nuclear factor-kappaB (NF-kappaB) was involved in ICAM-1 upregulation by cerulein, but NF-kappaB did not mediate basal expression of ICAM-1 mRNA in acinar cells. With an adhesion assay, we found that neutrophils bind to isolated pancreatic acinar cells and that cerulein upregulates the extent of adhesion. Neutralizing ICAM-1 antibody blocked neutrophil binding to both control and cerulein-stimulated acinar cells, suggesting ICAM-1 involvement in this adhesion. Thus the acinar cell is capable of targeting neutrophils to its surface, a process that may be important for inflammatory and cell death responses in pancreatitis and other pancreatic disorders.  (+info)

The influence of sensory nerves and CGRP on the pancreatic regeneration after repeated episodes of acute pancreatitis in rats. (22/463)

Stimulation of capsaicin sensitive nerves or administration of calcitonin gene-related peptide (CGRP) before induction of acute pancreatitis (AP) attenuates pancreatic damage, whereas CGRP administration after development of AP aggravates lesion of pancreatic tissue. The aim of this study was to determine the effect of prolonged activity of sensory nerves or CGRP administration on the pancreatic repair after repeated episodes of AP. Five episodes of acute caerulein-induced pancreatitis (10 microg/kg/h for 5 h s.c.) were performed at weekly intervals in rats receiving either vehicle or capsaicin at the sensory nerve stimulatory dose (0.5 mg/kg, 3 times daily), or CGRP (10 microg/kg, 3 times daily). Two weeks after the last induction of AP morphological signs of pancreatic damage, pancreatic blood flow (PBF), serum and pancreatic amylase activity, fecal chymotrypsin activity, pancreatic weight, pancreatic RNA and DNA content, as well as, serum interleukin-1beta (Il-1beta ) were assessed. Pancreata of animals receiving vehicle alone showed almost full recovery within two weeks after last episode of pancreatitis induction. In capsaicin-treated group of rats, we observed the increase in PBF by 44% and in serum Il-1beta concentration by 91%. The pancreatic amylase activity, fecal activity of chymotrypsin, pancreatic nucleic acids content and DNA synthesis were decreased. In rats treated with CGRP the alterations in PBF, serum Il-1beta concentration, as well as, in pancreatic and fecal activity of enzymes were similar to capsaicin treated group but less pronounced. We conclude that prolonged activity of capsaicin-sensitive sensory nerves and the presence of their main mediator-CGRP during pancreatic regeneration after AP leads to pancreatic functional insufficiency typical for chronic pancreatitis.  (+info)

The influence of secretin on the secretion of pepsin in response to acid stimulants in the anaesthetized cat. (23/463)

Peptic secretion was studied in fasting anaesthetized cats in which the pylorus and common bile duct had been occluded to prevent the release of duodenal hormones which might stimulate or inhibit gastric secretion. Dilute acid was instilled into the stomach at intervals to aid recovery of gastric secretion and to preserve peptic activity. 2. Caerulein, histamine and N-methyl histamine did not increase the output of pepsin when given on their own. Desulphated caerulein was a weak peptic stimulant. 3. Two C.H.R. u./kg per hour secretin initiated pancreatic secretion, the volume of which increased progressively as the dose was increased by stages to 32 C.H.R. u./kg per hour. 4. Four C.H.R. u./kg per hour secretin did not increase the output of pepsin. Peptic secretion was stimulated by 8 C.H.R. u./kg per hour. A maximal output of approximately 2000 u. pepsin/15 min was obtained when 16 C.H.R. u./kg per hour was infused. 5. When each acid stimulant was infused along with 4 C.H.R. u./kg per hour secretin the output of pepsin increased significantly. The peak output, which usually occurred between 15 and 30 min after stimulation, did not exceed 1000 u. pepsin/15 min. 6. The proposed explanation for the potentiation of the peptic response when an acid stimulant is infused along with a dose of secretin, in itself below the threshold of peptic stimulation, is that each acid stimulant increases gastric mucosal blood flow, approximately doubling the effective concentration of secretin delivered to the peptic cell.  (+info)

Water immersion stress prevents caerulein-induced pancreatic acinar cell nf-kappa b activation by attenuating caerulein-induced intracellular Ca2+ changes. (24/463)

Prior stress ameliorates caerulein-induced pancreatitis in rats. NF-kappaB is a proinflammatory transcription factor activated during caerulein pancreatitis. However, the effects of prior stress on pancreatic NF-kappaB activation are unknown. In the current study, the effect of prior water immersion stress on caerulein and tumor necrosis factor-alpha (TNF-alpha)-induced NF-kappaB activation in the pancreas was evaluated. Water immersion of rats for up to 6 h prevents supramaximal caerulein-induced pancreatic IkappaB-alpha degradation and NF-kappaB activation in vivo. NF-kappaB activity is also inhibited in vitro in pancreatic acini prepared from water-immersed animals. TNF-alpha-induced NF-kappaB activation in pancreas or in pancreatic acini is unaffected by prior water immersion. Chelation of intracellular Ca(2+) by 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetate/acetoxymethyl ester has similar effects to water immersion in preventing caerulein but not TNF-alpha-induced NF-kappaB activation in pancreas. Both the spike response and the sustained rise in [Ca(2+)](i) in response to supramaximal caerulein stimulation are reduced markedly in acini prepared from water-immersed animals as compared with normal animals. Our findings indicate that, in addition to Ca(2+)-dependent mechanisms, Ca(2+)-independent signaling events also may lead to NF-kappaB activation in pancreatic acinar cells. Water immersion stress prevents supramaximal caerulein-induced NF-kappaB activation in pancreas in vivo and in vitro by affecting intracellular Ca(2+) homeostasis.  (+info)