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Melatonin, a pineal hormone, is also produced in the gastrointestinal tract. Melatonin receptors have been detected in the stomach, intestine and pancreas. This indole inhibits insulin secretion but its role in the physiological modulation of exocrine pancreatic function is yet unknown. The aim of this study was to evaluate the pancreatic secretory effect of melatonin and its precursor; L-tryptophan given intraduodenally (i.d.) to the conscious rats with intact or capsaicin deactivated sensory nerves. CCK(1) receptor antagonist; tarazepide, was used in the part of the study to determine the involvement of CCK in the secretory effects of melatonin. The secretory studies were performed on awaken rats surgically equipped with silicone catheters, one of them was inserted into pancreato-biliary duct, the other one--into duodenum. Melatonin (1, 5 or 25 mg/kg) or L-tryptophan (10, 50 or 250 mg/kg) were administered i.d. Samples of pancreatic juice were collected in 15 minutes aliquots. Tarazepide (2,5 mg/kg i.p.) was given to the rats 15 min prior to the administration of melatonin or L-tryptophan. Neurotoxic dose of capsaicin (100 mg/kg s.c.) was used to deactivate afferent nerves and thus to assess the role of these nerves in the melatonin-induced pancreatic enzyme secretion. Administration of melatonin (1, 5 or 25 mg/kg i.d.) or L-tryptophan (10, 50 or 250 mg/kg i.d.) significantly increased pancreatic amylase outputs. Deactivation of sensory nerves by capsaicin or administration of CCK(1) - receptor antagonist; tarazepide, reversed the stimulatory effects of melatonin or L-tryptophan on pancreatic secretory function. Administration of melatonin or its amino-acid precursor to the rats resulted in the significant and dose-dependent rises of melatonin and CCK plasma levels. We conclude that melatonin or its precursor; L-tryptophan stimulates pancreatic enzyme secretion via stimulation of CCK release and activation of duodeno-pancreatic reflexes.

Leptin, 16- kDa protein produced and secreted from white adipocytes is known to regulate food intake and energy expenditure. Leptin receptors have been detected in the pancreas and it has been shown that systemic application of this protein diminished postprandial pancreatic secretion. Leptin is also produced in the stomach and released into the gastrointestinal lumen but the implication of luminal leptin in the regulation of pancreatic enzyme secretion has not been elucidated. The aim of our study was to evaluate the effects of intraduodenal (i.d.) leptin administration on pancreatic enzyme secretion and to assess the involvement of afferent nerves and CCK in above effects. The secretory studies were carried out on anaesthetized Wistar rats with acute pancreatic fistulae. Leptin was administered to the animals at doses of 0.1 1.0 or 10.0 microg/kg i.d. Tarazepide (2.5 mg/kg i.d.), a CCK(1) receptor antagonist, was given to the rats prior to the application of leptin. Rats with capsaicin deactivated sensory nerves were used in part of the study. Samples of pancreatic juice were taken at 15 min intervals to measure the volume flow and protein and amylase concentrations. CCK plasma level was measured by radioimmunoassay (RIA) following administration of leptin to the rats. Intraduodenal administration of leptin (1.0 or 10.0 microg/kg) to the fasted rats significantly and dose-dependently increased pancreatic protein and amylase outputs. Pancreatic secretory responses to leptin were totally abolished by prior capsaicin deactivation of sensory nerves or by pretreatment of the rats with tarazepide. Under basal conditions plasma CCK level averaged about 15.46 +/- 1,4 pg/ml. Exogenous leptin, given i.d. at doses of 0.1 1.0 or 10.0 microg/kg i.d. to the rats with intact or capsaicin-deactivated sensory nerves resulted in dose-dependent rise of plasma CCK level, reaching the highest value at the dose of 10.0 microg/kg i.d. We conclude that leptin given i.d. stimulates pancreatic enzyme secretion and this effect could be related to the stimulation of CCK release and activation of duodeno-pancreatic reflexes.

Melatonin, considered as a main pineal product, may be also synthetized in the gastrointestinal tract from L-tryptophan. Melatonin has been recently shown to affect insulin release and its receptors have been characterized in the pancreas however, the effects of melatonin on the pancreatic enzyme secretion have not been examined. The aim of this study was to investigate the effects of melatonin or L-tryptophan on amylase secretion in vivo in anaesthetized rats with pancreato-biliary fistulas, and in vitro using isolated pancreatic acini. Melatonin (1, 5 or 25 mg/kg) or L-tryptophan (10, 50 or 250 mg/kg) given to the rats as a intraperitoneal (i.p.) bolus injection produced significant and dose-dependent increases in pancreatic amylase secretion under basal conditions or following stimulation of enzyme secretion by diversion of bile-pancreatic juice. This was accompanied by a dose-dependent rise in melatonin plasma level. Stimulation of pancreatic enzyme secretion caused by melatonin or L-tryptophan was completely abolished by vagotomy, deactivation of sensory nerves with capsaicin or pretreatment with CCK1 receptor antagonists (tarazepide or L-364,718). Pretreatment with luzindole, an antagonist of melatonin MT(2) receptor failed to affect melatonin- or L-tryptophan-induced amylase secretion. Administration of melatonin (1, 5 or 25 mg/kg i.p.) or L-tryptophan (10, 50 or 250 mg/kg i.p.) to the rats resulted in the dose-dependent increase of cholecystokinin (CCK) plasma immunoreactivity. Enzyme secretion from isolated pancreatic acini was not significantly affected by melatonin or L-tryptophan used at doses of 10(-8) -10(-5) M. We conclude that exogenous melatonin, as well as that produced endogenously from L-tryptophan, stimulates pancreatic enzyme secretion in vivo while increasing CCK release. Stimulatory effect of melatonin or L-tryptophan on the exocrine pancreas involves vagal sensory nerves and the CCK release by these substances.

Melatonin, produced from L-tryptophan, protects the pancreas against acute damage by improving the antioxidative status of tissue. Melatonin receptors have been detected in the brain, but the contribution of these receptors to the pancreatic protection is unknown. The aim of our study was to compare the effects of melatonin precursor; L-tryptophan given intracerebroventricularly (i.c.v.) or intraperitoneally (i.p.) on the course of acute pancreatitis. Acute pancreatitis was induced by subcutaneous infusion of caerulein (5 microg/kg-h x 5 h). L-tryptophan was given i.p. (2.5, 25 or 250 mg/kg) or administered into right cerebral ventricle (0.02, 0.2 or 2.0 mg/rat) 30 min prior to the start of caerulein infusion. Plasma amylase, lipase and TNF alpha activities were measured to determine the severity of caerulein-induced pancreatitis (CIP). The lipid peroxidation products: malonylodialdehyde and 4-hydroksynonenal (MDA + 4-HNE) and activity of superoxide dismutase (SOD) were measured in the pancreas of intact or CIP rats with or without L-tryptophan pretreatment. Melatonin blood level was measured by RIA. CIP was confirmed by histological examination and manifested as an edema and rises of plasma levels of amylase, lipase and TNF alpha (by 550%, 1000% and 600%). MDA + 4-HNE was increased by 600%, whereas SOD activity was reduced by 75% in the pancreas of CIP rats. All manifestations of CIP were significantly reduced by pretreatment of the rats with L-tryptophan given i.c.v. at doses of 0.2 or 2.0 mg/rat, or by peripheral administration of this amino acid used at dose of 250 mg/kg i.p. In control rats plasma level of melatonin averaged about 40 +/- 2 pg/ml and was not significantly affected by CIP, by central application of L-tryptophan (0.02, 0.2 or 2.0 mg/rat) or by peripheral administration of this melatonin precursor used at doses of 2.5 or 25 mg/kg i.p. Plasma melatonin level was markedly increased by pretreatment of the rats with L-tryptophan given i.p. at dose of 250 mg/kg. We conclude that central administration of melatonin precursor; L-tryptophan, as well as peripheral application of high dose of this melatonin precursor prevented the pancreatic damage produced by CIP. The favorable effect of peripherally administered L-tryptophan could be related to the rise of melatonin plasma level and to pancreatoprotective action of this indoleamine. The beneficial effect of centrally administered L-tryptophan could be mediated through activation of central receptors for locally produced melatonin.

Leptin released by adipocytes has been implicated in the control of food intake but recent detection of specific leptin receptors in the pancreas suggests that this peptide may also play some role in the modulation of pancreatic function. This study was undertaken to examine the effect of exogenous leptin on pancreatic enzyme secretion in vitro using isolated pancreatic acini, or in vivo in conscious rats with chronic pancreatic fistulae. Leptin plasma level was measured by radioimmunoassay following leptin administration to the animals. Intraperitoneal (i.p.) administration of leptin (0.1, 1, 5, 10, 20 or 50 microg/kg), failed to affect significantly basal secretion of pancreatic protein, but markedly reduced that stimulated by feeding. The strongest inhibition has been observed at dose of 10 microg/kg of leptin. Under basal conditions plasma leptin level averaged about 0.15 +/- 0.04 ng/ml and was increased by feeding up to 1.8 +/- 0.4 ng/ml. Administration of leptin dose-dependently augmented this plasma leptin level, reaching about 0.65 +/- 0.04 ng/ml at dose of 10 microg/kg of leptin. This dose of leptin completely abolished increase of pancreatic protein output produced by ordinary feeding, sham feeding or by diversion of pancreatic juice to the exterior. Leptin (10(-10)-10(-7) M) also dose-dependently attenuated caerulein-induced amylase release from isolated pancreatic acini, whereas basal enzyme secretion was unaffected. We conclude that leptin could take a part in the inhibition of postprandial pancreatic secretion and this effect could be related, at least in part, to the direct action of this peptide on pancreatic acini.

Background: Previous studies have shown that sensory nerves and calcitonin gene-related peptide (CGRP) affect caerulein-induced pancreatitis. The aim of this study was to examine the role of capsaicin-sensitive nerves and the impact of CGRP administration on necrotizing pancreatitis induced by ischemia/reperfusion., Material/methods: Ablation of sensory nerves was made by capsaicin 10 days before induction of pancreatitis. Acute pancreatitis was induced in rats by limitation of pancreatic blood flow (PBF) followed by reperfusion. Treatment with saline or CGRP (10 g/kg s.c.) or stimulation of sensory nerves by low doses of capsaicin (0.5 mg/kg s.c.) was performed 1 h before ischemia. After 1 h reperfusion we examined pancreatic blood flow (PBF), plasma amylase and lipase activity, plasma interleukin-1beta (IL-1beta) concentration, pancreatic DNA synthesis and morphological signs of pancreatitis., Results: Ischemia followed by 1 h reperfusion led to induction of necrotizing pancreatitis, manifested by morphological signs of pancreatic damage, decrease in pancreatic DNA synthesis and PBF, as well as an increase in plasma amylase and lipase activity and plasma IL-1beta concentration. Both, treatment with CGRP and stimulation of sensory nerves attenuated pancreatic damage. Ablation of sensory nerves enhanced I/R evoked pancreatic damage. The deleterious effect of deactivation of sensory nerves on I/R-induced pancreatitis was partly reversed by administration of CGRP prior to I/R., Conclusions: Stimulation of sensory nerves protects the pancreas against damage evoked by I/R, whereas ablation of these nerves aggravates tissue damage in the pancreas exposed to I/R. The beneficial effect of sensory nerves is partly dependent on CGRP release.

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

The present study investigated the involvement of endogenous melatonin in the prevention of pancreatic damage provoked by caerulein-induced pancreatitis (CIP) by using the luzindole, the antagonist of melatonin MT2 receptors. CIP was produced by subcutaneous infusion of caerulein to conscious rats (25 microg/kg). Luzindole (1, 2 or 4 mg/kg) was given as an intraperitoneal bolus injection 30 min prior to the start of CIP. Lipid peroxidation products, malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE) were measured in the pancreas by LPO-584 commercial kit. CIP was confirmed by histological examination and manifested by significant increases of plasma activities of amylase, lipase and tumor necrosis factor alpha (TNFalpha) (by 500%, 1000% and 600%, respectively) comparing to the control values. This was accompanied by a 40% limitation in pancreatic blood flow (PBF) and by 200% increase of MDA+4-HNE in the pancreas of CIP rats. Administration of luzindole to the CIP rats reduced PBF, aggravated the histological manifestations of pancreatitis, resulted in the significant augmentation of pancreatic MDA + 4-HNE content, and produced the marked increases of plasma levels of lipase, amylase and TNFalpha, comparing to the values observes in the rats with CIP alone. These results suggest that endogenous melatonin through its receptor MT2 plays an important role in the attenuation of pancreatic damage produced by overstimulation with caerulein.

Leptin is involved in the regulation of food intake and previous studies have shown that leptin affects the inflammatory response in various tissues. The objective of this study was to examine the influence of leptin administration on the development and the course of acute ischemic pancreatitis. Acute pancreatitis was induced by limitation of pancreatic blood flow by clamping of inferior splenic artery for 30 min, followed by reperfusion. Leptin was administered three times daily at the dose 10 or 50 microg/kg. Animals were sacrificed 1, 3, 5, 10 and 21 days after removal of vascular clips. Administration of leptin reduced development of pancreatic damage and accelerated pancreatic regeneration what was manifested by the improvement of pancreatic histology, the decrease in serum lipase and amylase activity, and the reduction in serum interleukin-1beta concentration. Also, treatment with leptin caused the increase in the pancreatic blood flow and pancreatic DNA synthesis. Leptin administration was without effect on serum interleukin-10 concentration. Leptin at the dose 50 microg/kg was more effective than 10 microg/kg. We conclude that leptin reduces the pancreatic damage in the course of ischemic pancreatitis and accelerates the pancreatic tissue repair. The beneficial effects of leptin appear to be dependent on the improvement of pancreatic blood flow, the increase in pancreatic cell growth, and the limitation of pro-inflammatory interleukin-1beta release.

Background: Lipopolysaccharides (LPS) are responsible for septic shock but low doses of LPS reduce pancreatic damage produced by caerulein-induced pancreatitis (CIP) in rats. Leptin, produced by adipocytes attenuates the severity of CIP. The aim of this study was to evaluate the effect of intracerebroventricular (i.c.v.) administration of LPS on CIP and plasma leptin level and to investigate the involvement of sensory nerves (SN) in the effects of LPS on CIP., Material/methods: CIP was produced by subcutaneous (s.c.) infusion of caerulein (25 Kg/kg) to conscious rats. SN were deactivated with capsaicin (100 mg/kg s.c.). LPS (0.2, 2, or 20 Kg/rat) were applied to the right cerebral ventricle 30 min prior to CIP., Results: CIP was manifested by an increase in plasma levels of amylase, lipase, leptin and an anti-inflammatory interleukin 10 (IL-10), (by 400%, 1000%, 700% and 50%, respectively), confirmed by histological examination and accompanied by 40% reduction in pancreatic blood flow. Pretreatment of CIP rats with i.c.v. LPS resulted in significant reduction of CIP accompanied by dose-dependent increase in plasma levels of leptin and IL-10. Deactivation of SN, which by itself failed to affect CIP, completely reversed the beneficial effects of i.c.v. administration of LPS on CIP and reduced plasma leptin and IL-10 concentrations., Conclusions: Pretreatment with LPS given i.c.v. prevents the development of caerulein-induced pancreatitis through the activation of SN and though the release of leptin.

Central nervous system affects pancreatic secretion of enzymes however, the neural modulation of acute pancreatitis has not been investigated. Leptin and melatonin have been recently reported to affect the inflammatory response of various tissues. The identification of specific receptors for both peptides in the pancreas suggests that leptin and melatonin could contribute to the pancreatic protection against inflammation. The aim of this study was: 1/ to compare the effect of intracerebroventricular (i.c.v.) or intraperitoneal (i.p.) administration of leptin or melatonin on the course of caerulein-induced pancreatitis (CIP) in the rat, 2/ to examine the involvement of sensory nerves (SN) and calcitonin gene-related peptide (CGRP) in pancreatic protection afforded by leptin or melatonin, 3/ to assess the effect of tested peptides on lipid peroxidation products (MDA + 4-HNE) in the pancreas of CIP rats, 4/ to investigate the influence of leptin or melatonin on nitric oxide (NO) release from isolated pancreatic acini and 5/ to determine the effects of caerulein and leptin on leptin receptor gene expression in these acini by RT-PCR. CIP was induced by subcutaneous (s.c.) infusion of caerulein (25 microg/kg) to the conscious rats, confirmed by the significant increases of pancreatic weight and plasma amylase and by histological examination. This was accompanied in marked reduction of pancreatic blood flow and significant rise of MDA + 4-HNE in the pancreas. Leptin or melatonin were administered i.p. or i.c.v. 30 min prior to the start of CIP. Deactivation of SN was produced by s.c. capsaicin (100 mg/kg). An antagonist of CGRP, CGRP 8-37 (100 microg/kg i.p.), was given together with leptin or melatonin to the CIP rats. MDA + 4-HNE was measured using LPO commercial kit. NO was determined using the Griess reaction. Pretreatment of CIP rats with i.p. leptin (2 or 10 microg/kg) or melatonin (10 or 50 mg/kg) significantly attenuated the severity of CIP. Similar protective effects were observed following i.c.v. application of leptin (0.4 or 2 microg/rat) but not melatonin (10 or 40 microg/rat) to the CIP rats. Capsaicin deactivation of SN oradministration of CGRP 8-37 abolished above beneficial effects of leptin on CIP, whereas melatonin-induced protection of pancreas was unaffected. Pretreatment with i.p. melatonin (10 or 50 mg/kg), but not leptin, significantly reduced MDA + 4-HNE in the pancreas of CIP rats. Leptin (10(-10) - 10(-6) M) but not melatonin (10(-8) - 10(-5) M) significantly stimulated NO release from isolated pancreatic acini. Leptin receptor gene expression in these acini was significantly increased by caerulein and leptin. We conclude that 1/ central or peripheral pretreatment with leptin protects the pancreas against its damage induced by CIP, whereas melatonin exerts its protective effect only when given i.p., but not following its i.c.v. adminstration, 2/ activation of leptin receptor in the pancreatic acini appears to be involved in the beneficial effects of leptin on acute pancreatitis, 3/ the protective effects of leptin involve sensory nerves, CGRP and increased generation of NO whereas melatonin-induced protection of the pancreas depends mainly on the antioxidant local effect of this indole, and scavenging of the radical oxygen species in the pancreatic tissue.

Background: Recent identification of specific leptin receptors in the pancreas suggests that this peptide may also play some role in this gland., Aim: To examine the effect of intraperitoneal (i.p.) or intracerebroventricular (i.c.v.) administration of leptin in rats on caerulein-induced pancreatitis (CIP), pancreatic gene expression of leptin and inflammatory cytokine production., Methods: Caerulein (25 micrograms/kg) was infused subcutaneously into conscious rats over 5 h to produce CIP. Leptin (1, 5, or 10 micrograms/kg) was injected i.p. or i.c.v. 30 min prior to the CIP induction. The plasma level of TNF alpha and IL-4 was determined by ELISA, while plasma leptin was measured by RIA and leptin gene expression in pancreas by RT-PCR., Results: CIP was characterized by the usual pancreatic edema, reduction in pancreatic blood flow (PBF) and an increase in serum levels of amylase, TNF alpha and IL-4. Pretreatment with i.p. or i.c.v. leptin of the CIP rats partially reversed the harmful effects of CIP on the pancreas, and reduced pancreatic inflammation and the fall in PBF. This was accompanied by a dose-dependent reduction in serum levels of amylase and TNF alpha, while serum IL-4 in the CIP rats pretreated with leptin rose dose-dependently as compared to control rats with CIP alone. Pretreatment with leptin resulted in the dose-dependent rise in plasma leptin level over that observed in vehicle-treated controls. Leptin mRNA expression in the pancreas was dose-dependently increased after infusion of caerulein. Leptin content in isolated pancreatic acini was also increased dose-dependently by caerulein added to the incubation medium bathing these acini., Conclusions: (1) Exogenous leptin protects the pancreas against damage by CIP; (2) endogenous leptin seems to limit the extend of pancreatic damage, and (3) these protective effects of leptin could be attributed to the reduction in TNF alpha and to the increase in IL-4 production.

Adrenergic innervation plays an important role in the control of electric activity and circulatory parameters of the gut. Importance of adrenergic system as a modulator of motor, neural and metabolic activity of the intestine is studied extensively but still not well understood. We use 6-OHDA a neurotoxin and a blocking agent of adrenergic fibers, to evaluate their exact role in the control of vital parameters of the intestine and vagal nerves. 50 Wistar rats were used. Animals were fasted 24 h prior to experiment with free access to water allowed. Acute experiments were performed on 30 rats, divided in the three groups. Four experimental groups were established. I--sham operated. II and III--pretreated with 6-ODHA (25 mg//kg/24 h s.c.) 3 days before experiment. IV group were used for chronic procedure. Thiopental anesthesia (Vetbutal Biovet) was applied. Animals were artificially ventilated with positive pressure rodent ventilator (Ugo Basile), and heated with continuous temperature control by rectal thermistor (FST). Left carotid artery was cannulated and connected with electro manometer--arterial pressure (AP) was expressed in mm Hg. Right jugular vein was cannulated for continuous saline administration 0.2 ml/h. Mesenteric blood flow (MBF) was recorded with use of ultrasonic probe (Transonic systems T206). Microcirculatory blood Flow (LDBF) was estimated by laser Doppler flowmetry (Periflux 2001 Master). Arterio-venous difference (AVO2) was estimated from whole blood (AVOXimeter 1000 E). Oxygen uptake was calculated from MBF and AVO2 and expressed in ml/min/100 g tissue. Chronic experiments were performed on conscious animals with electrodes implanted to the serosal surface of the intestinal wall. Measurements of intestinal myoelectric parameters were performed one, two and three weeks after 6-OHDA administration. Vagal activity was recorded in left vagus nerve in the neck with suction electrodes (one month after 6-OHDA). 6-OHDA pretreatment evoked increase of dominant slow wave frequency by 0.1 Hz from 0.62 +/- 0.10 to 0.74 (+/- 0.03) Hz in the first week after treatment (p < 0.05). Slow wave frequency was no markedly influenced in acute experiments. In the chronic experiments after initial increase gradual decrease of slow wave frequency was observed reaching control values of 0.62 +/- 0.17 Hz after 28 days. After 6-OHDA administration in chronic experiments no substantial changes in slow waves amplitude was observed. Frequency and amplitude of spikes activity in vagus nerve after sympatectomy increased from 7.96 +/- 1.3 to 10.3 +/- 2/min and 0.18 +/- 0.09 to 1.13 +/- 0.8/mV. Chemical denervation evoked increase of MBF and LDBF by 18 +/- 3.6% and 22 +/- 6.4% respectively. Intestinal oxygen uptake (VO2) was increased by 10.2 +/- 1.2% in comparison to control. Heart rate and arterial pressure was decreased by 18 +/- 4% and 12 +/- 2.4% respectively in comparison to control. Adrenergic system plays profound role in the modulation of both myoelectric and motor activity of the intestine in the rat. Continuous activity of adrenergic neurons affects vascular conductance, capillary density and oxygen diffusion parameters.

Prostaglandins (PG), the products of arachidonate metabolism through cyclooxygenase (COX) pathway, protect the pancreas from the acute damage. The existence of two isoforms of COX was documented including: COX-1, present in normal tissues and COX-2, expressed at the site of inflammation, such as induced by bacterial lipopolysaccharide (LPS). Pretreatment with low dose of LPS and activation of nitric oxide (NO) synthase (NOS) has been shown to prevent the injury caused by caerulein-induced pancreatitis (CIP) in the rat. The aim of this study was to investigate the role of COX-1 and COX-2 in the LPS-induced protection of the pancreas against CIP and the involvement of NOS in the activation of COX-PG system in the rats with CIP. CIP was produced by subcutaneous (s.c.) infusion of caerulein (5 microg/kg-h for 5 h) to the conscious rats. Protective dose of LPS, from Escherichia coli, (1 mg/kg) was given intraperitoneally (i.p.) 15 min prior to the start of CIP. Nonselective inhibitor of COX; indomethacin (5 or 10 mg/kg), selective inhibitor of COX-1: resveratrol, or a highly selective inhibitors of COX-2: rofecoxib or NS-398 (2 or 10 mg/kg) were injected i.p. 15 min prior to the administration of LPS. COX-1 or COX-2 mRNA was determined by reverse transcription-polimerase chain reaction (RT-PCR) in the pancreatic tissue. Pancreatic blood flow (PBF) was measured by a laser Doppler flowmetry. PGE2 content in the pancreas was measured by radioimmunoassay. CIP was manifested by an increase of pancreatic weight and plasma amylase activity (by 500% and 700%, respectively) and it was confirmed by histological examination. CIP slightly increased pancreatic PGE2 generation (by 12%) and diminished PBF (by about 40%). LPS (1 mg/kg i.p.), given prior to the start of CIP, increased PGE2 generation in the pancreas (by 45%), reversed the histological manifestations of pancreatitis, reduced the rise in amylase blood level and improved PBF. Administration of nonselective inhibitor of COX; indomethacin (5 or 10 mg/kg i.p.) prior to the injection of LPS abolished its protective effects on CIP and reduced pancreatic PGE2 generation. Selective inhibitor of COX-1; resveratrol (10 mg/kg i.p.) given prior to the injection of LPS reversed its protective effects against CIP. Pretreatment with a selective inhibitors of COX-2: rofecoxib or NS-398 (10 mg/kg) attenuated LPS-induced pancreatic protection in the CIP rats. COX-1 expression was detected in the intact pancreas and was not significantly changed by CIP, LPS, indomethacin, NS-389 and their combination, while COX-2 mRNA expression appeared in the pancreas of ratssubjected to CIP and was significantly increased after LPS injection to these rats. Addition of selective COX-2 inhibitor; NS-389, or nonselective inhibitor of COX; indomethacin, enhanced COX-2 mRNA expression in the rats with CIP pretreated with LPS. Pretreatment of the rats with inhibitor of NOS; L-NNA (20 mg/kg i.p.), given together with LPS, 15 min prior to the start of caerulein overstimulation, resulted in complete reversion of LPS-induced pancreatic protection and decreased PGE2 generation stimulated by LPS. Addition to L-NNA of the substrate for NOS; L-arginine (100 mg/kg i.p.), restored pancreatic protection afforded by low dose of LPS and increased pancreatic PGE2 level in the rats with CIP. We conclude that: 1. increased pancreatic PGE2 generation, induced by low dose LPS pretreatment, contributes to the pancreatic resistance to acute damage produced by caerulein overstimulation and 2. the NO-system is involved in above stimulation of PGE2 generation and pancreatic protection against acute damage.

Calcitonin gene related peptide (CGRP) is widely distributed in the myenteric neurons along GI tract. Biological effects of CGRP on gastrointestinal tract include increase in the intestinal blood flow, relaxation of the smoth muscle and slight increase in the slow wave amplitude (SWA) with no effect on frequency (SWF) of intestinal myoelectric activity (IMA). The aim of this study was to evaluate the possible protective effects of endo- and exogenous CGRP against ischemia/reperfusion (I/R) induced bowel injury in rats. Experiments were performed on 30 fasted anesthetized Wistar rats. Systemic arterial blood pressure (AP), mesenteric blood flow (MBF) and microcirculatory intestinal blood flow (LDBF) were measured. Oxygen consumption (VO2) was estimated from MBF and mesenteric AVO2 difference. IMA was recorded by 4 monopolar electrodes in proximal jejunum and analyzed using computer program with Fourrier analysis of SWF. Control ischemia induced by 30 min total occlusion of anterior mesenteric artery (AMA) reduced SWA by 25+/-5% and SWF by 24+/-4%. At the end of 60 minute reperfusion period SWA and SWF values were restored to control values but SWF showed instability. At the 15th minute of reperfusion period MBF, LDBF and VO2 increased to 109+/-6, 119+/-11 and 120+/-7% of control values respectively. Infusion of exogenous CGRP (0,16 microg/kg/min i.a.) increased MBF, LDBF and VO2 by 26+/-6, 31+/-9 and 20+/-4% respectively in comparison to control values. In the same experimental group SWA increase of 14% was observed with not significant changes in SWF. In the group where CGRP was administrated before and during 30 min period of intestinal ischemia MBF, LDBF and VO2 values at 15th minute of reperfusion were significantly higher by 24+/-6, 32+/-7 and 17+/-5% respectively in comparison to the values observed in the control reperfusion. In that group SWA values were restored to preocclusion values at 15th minute of reperfusion yet and SWF showed much more stability. Infusion of CGRP receptor antagonist (CGRP 8-37) reduced MBF, LDBF and VO2 by 12+/-7, 14+/-8 and 11+/-6% respectively (differences not significant versus control). In I/R group when CGRP 8-37 was given hemodynamic parameters (during reperfusion) were significantly lower and IMA parameters were not restored to preocclusion values. We conclude, that endogenous and exogenous CGRP attenuate circulatory parameters of the small intestine during ischemia and reperfusion. A direct correlation exists between hemodynamic, metabolic and myoelectric effects of CGRP.

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.

Lipopolysaccharide (LPS) derived from the bacterial cell wall activates the inflammatory response in the tissue but the role of LPS in the pathogenesis of pancreatic damage and in the activation of NO system in the pancreas has not been fully explained. The aim of this study was to investigate the effect of repeated administration of LPS to the rats on the integrity of the pancreas, on the ability of isolated pancreatic acini to secrete the amylase and on the plasma level of tumor necrosis factor alpha (TNFalpha). The role of NO in the pancreatic resistance to the damage was assessed in animals subjected to repeated administration of LPS. To induce pancreatic damage one group of rats received intraperitoneal (i.p.) injection of LPS (from E. coli) every day during 5 consecutive days (10 mg/kg--day). Another groups of animals were given N(G)-nitro-L-arginine (L-NNA), an inhibitor of NO synthase (NOS) (20 mg/kg i.p.) alone or in combination with L-arginine (100 mg/kg i.p.), 30 min prior to each LPS injection. Plasma level of TNFalpha was determined by ELISA kit. Repeated administration of LPS produced mild pancreatic inflammation that was most pronounced at day 5 of LPS treatment and manifested as edema, neutrophil infiltration and hemorrhage of the pancreas. The survival rate after 5 days treatment with LPS was 87.5%. Pancreatic weight, plasma levels of TNFalpha and amylase, pancreatic blood flow (PBF) and NO generation by pancreatic acini were markedly increased in rats subjected to repeated administration of LPS whereas the amylase response of isolated pancreatic acini to pancreatic secretagogues was significantly attenuated. Suppression of NOS by L-NNA resulted in a dramatic increase in the mortality of the animals reaching 50% and significantly increased inflammatory changes in the pancreatic tissue, decreased PBF, abolished the ability of pancreatic acini to release NO and to secrete amylase. Pancreatic weight and plasma levels of amylase and TNFalpha significantly increased in the group of rats treated with combination of LPS+L-NNA as compared to the animals received LPS alone. Addition of L-arginine to L-NNA+LPS administration reversed all harmful effects produced by L-NNA in the pancreas. We conclude that repeated administration of high doses of bacterial LPS to the rats could induce pancreatic tissue damage by itself, however, it is not able to produce severe pancreatitis. Suppression of NO generation significantly aggravates the pancreatic lesion produced by LPS leading to the dramatic mortality in treated rats. The rise of plasma level of TNFalpha corresponds to the severity of pancreatic inflammation.

Conclusion: Stimulation of pancreatic sensory nerves by capsaicin produced secretory effects probably caused, at least in part, by the release of CGRP., Background: In the pancreas calcitonin gene-related peptide (CGRP) has been localized in the sensory nerves, but its physiological role is unknown. This study was undertaken to compare the changes of pancreatic enzyme secretion produced by CGRP and by stimulation or destruction of sensory nerves., Methods: To stimulate sensory nerves, low doses of capsaicin (0.25-0.5 mg/kg) were given intraduodenally to the conscious rats with chronic pancreatic fistula. To inactivate sensory nerves high doses of capsaicin (100 mg/kg) were given subcutaneously 10 d before tests. For the in vitro experiments pancreatic slices and isolated pancreatic acini were prepared from intact and capsaicin-denervated rats., Results: In conscious rats, CGRP given subcutaneously (5-10 micrograms/kg) and low doses of capsaicin given intraduodenally reduced basal pancreatic secretion. In isolated pancreatic acini, CGRP (10(-10)-10(-6) M), but not capsaicin, increased basal or secretagog-stimulated amylase release. In pancreatic slices (containing nerve fibers) capsaicin (10(-10)-10(-6) M) increased enzyme secretion, and this secretion was abolished by previous inactivation of sensory nerves by this neurotoxin. Capsaicin deactivation did not affect the secretory response of pancreatic acini to CGRP, cerulein, or urecholine. Sensory denervation by capsaicin did not change basal protein secretion, but reduced that produced by feeding or diversion of pancreatic juice to the exterior during first 2 h of the tests.

Sensory nerves are implicated in gastroprotection and regulation of visceral circulation but their role in exocrine secretion and pancreatic circulation in intact pancreas and in acute pancreatitis has not been established. We investigated the role of sensory fibers in pancreatic secretion in vivo and amylase release from pancreatic slices (containing nerve fibers) or isolated pancreatic acini, and in caerulein-induced pancreatitis. In conscious rats, the stimulation of sensory nerves by low dose of capsaicin given intraduodenally (0.25-0.5 mg/kg) reduced basal pancreatic secretion, whereas dose of 1 mg/kg increased this secretion. Deactivation of sensory nerves by neurotoxic dose of capsaicin (100 mg/kg over 3 days s.c.) 10 days before tests failed to affect basal secretion but diminished the secretion induced by feeding or the diversion of pancreatic juice. In pancreatic slices, capsaicin (10(-10)-10(-6) M) increased enzyme secretion and this response was abolished by atropine (10(-6) M) or previous deactivation of sensory nerves. In pancreatic acini, capsaicin failed to affect basal and stimulated amylase secretion in response to caerulein or urecholine. In intact rats, stimulatory dose of capsaicin (0.5 mg/kg i.g.) caused about 32% increase of pancreatic blood flow and it was without any effect on the pancreatic DNA synthesis, weight, RNA, DNA and protein content. In contrast, neurotoxic dose of capsaicin caused a reduction (by 27%) in pancreatic blood flow followed by a significant decrease in RNA content and DNA synthesis in pancreatic tissue. Infusion of caerulein (10 g/kg-h) for 5 h produced acute edematous pancreatitis accompanied by over 60% decrease in DNA synthesis, nearly 50% inhibition of pancreatic blood flow, and a significant increase in pancreatic weight, protein content and plasma amylase concentration. Stimulatory dose of capsaicin attenuated the pancreatic tissue damage in caerulein induced pancreatitis, as manifested by a significant reversal of pancreatic blood flow and DNA synthesis decrease. Capsaicin induced inactivation of sensory nerves prior to pancreatitis caused an increase of all parameters of pancreatic damage; pancreatic blood flow dropped by 68%, DNA synthesis decreased by 70%; pancreatic weight, protein content and plasma amylase were also significantly enhanced. We conclude that sensory neurons are involved in the regulation of pancreatic secretion by an indirect mechanism and exhibit a beneficial effect on the pancreatic integrity, mainly due to improving the pancreatic blood flow.

The aim of the present study was to determine the role of endogenous nitric oxide (NO) in pancreatic secretion in vivo and amylase release from pancreatic acini in vitro and in caerulein-induced acute pancreatitis in rats. Blockade of NO synthase by NG-nitro-L-arginine (L-NNA) (2.5 mg/kg i.v.) significantly reduced basal pancreatic protein secretion and that induced by the infusion of CCK (0.5 micrograms/kg-h), feeding, and the diversion of pancreatic juice in rats with pancreatic fistula. This inhibitory effect was partially reversed when L-arginine (50 mg/kg-h i.v.) was added to L-NNA. L-Arginine alone (50 mg/kg i.v.) did not affect basal or caerulein-induced pancreatic secretion. L-NNA, L-arginine, or their combination added in various concentrations to the incubation medium of dispersed acini failed to affect basal or secretagogue (caerulein or urecholine) stimulated amylase release. Infusion of caerulein (5 micrograms/kg-h) for 5 h produced histological changes of acute edematous pancreatitis accompanied by a marked increase in pancreatic protein content and about 50% reduction in tissue blood flow. L-NNA alone also reduced the pancreatic blood flow and caused a significant increase in pancreatic weight and protein content. L-NNA significantly potentiated the inflammatory changes in the pancreas caused by caerulein. Addition of L-arginine enhanced the pancreatic blood flow and ameliorated the pancreatitis induced by caerulein alone or that combined with L-NNA. We conclude that NO is involved in the stimulation of pancreatic secretion in vivo and exhibits a beneficial effect on pancreatitis, probably by improving the pancreatic blood flow.

Exogenous eicosanoids were reported to affect pancreatic secretion, but it is unknown whether this effects is mediated by the changes in pancreatic circulation or by direct action on pancreatic secretory cells. In this study the effects of prostaglandins (PG), leukotriene C4 (LTC4) and platelet activating factor (PAF) and the blockers of their biosynthesis or receptor antagonists on amylase release from the isolated rat pancreatic acini were examined. The acini were incubated with pancreatic secretagogues, such as caerulein or urecholine in the presence or absence of various concentrations (10(-9)-10(-5) M) of PGE2, Nocloprost (stable analog of PGE2), PGI2, PGF1 alpha, LTC4, PAF, indomethacin (inhibitor of endogenous PG formation) and A-63162 (blocker of endogenous LT biosynthesis). PGE2, PGI2 and PGF1 alpha inhibited secretagogues-stimulated enzyme secretion from isolated pancreatic acini but their inhibitory potency was about 1000 times lower, on molar basis, than that of Nocloprost. PAF and LTC4 produced concentration-dependent stimulation of amylase release from the unstimulated acini reaching about 50% of caerulein-induced maximal response and enhanced amylase release induced by caerulein or urecholine. The effects of PAF and LTC4 were reversed by the addition of respective receptor antagonist for PAF (TCV-309) and for LTC4 (FPL-55712). These results indicate that PG inhibit, while PAF and LTC4 stimulate pancreatic enzyme secretion and thus could be implicated in the control of this secretion.

Recently synthesized highly specific and potent bombesin receptor antagonists permit study of the role of endogenous bombesin-like peptides in the physiological regulation of pancreatic secretion. We now tested the action of three novel pseudononapeptide bombesin/gastrin releasing peptide (GRP) antagonists (RC-3095, RC-3100 and RC-3120) on amylase release in vitro from isolated rat pancreatic acini and on protein secretion in vivo in chronic pancreatic fistula rats. In isolated pancreatic acini, all three bombesin receptor antagonists inhibited the amylase secretion induced by bombesin by shifting to the right the amylase response to bombesin without altering the maximal response. These antagonists alos reduced concentration dependently the near-maximal amylase response to bombesin, the concentration required for 50% reduction (IC50) being about 10(-7) M for RC-3095 and RC-3100 and 10(-6) M for RC-3120. None of the bombesin/GRP antagonists used affected the amylase response to CCK, pentagastrin or urecholine. In conscious rats with a chronic pancreatic fistula, all three bombesin antagonists shifted to the right the pancreatic protein response to graded doses of bombesin without changing the maximal response. These antagonists inhibited the protein response to constant background stimulation with bombesin in a dose-dependent manner, the ID50 being about 20 nmol/kg per h for RC-3095 and RC-3100 and about 160 nmol/kg per h for RC-3120. None of the antagonists significantly affected basal pancreatic secretion or secretion induced by sham-feeding, ordinary feeding or the diversion of pancreatic juice from the duodenum. These results indicate that exogenous bombesin is a potent direct stimulant of pancreatic enzyme secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Tachykinins (TK) are family of peptides including substance P (SP), substance K (SK) and neuromedin K (NK) that have been found in the nerves of the gastrointestinal tract and proposed to act as neurotransmitters to affect the motor, secretory and circulatory functions of the gut, but little is known about their action on the pancreas. In this study three series of tests were carried out to determine the action of SP, SK and NK on pancreatic secretion in conscious dogs and amylase release from the dispersed rat pancreatic acini and to correlate the alterations in pancreatic secretory and circulatory effects of TK in anesthetized dogs. SP, SK and NK infused i.v. in graded doses (0.12-1.0 microgram/kg per h) in conscious dogs stimulated pancreatic protein outputs reaching, respectively, 38% and 23% of the maximal response to CCK (40 pmol/kg per h). HCO3- outputs were also significantly increased but the highest response did not exceed about 5% of secretin (328 pmol/kg per h) maximum. Cholinergic blockade by atropine abolished the pancreatic responses to tachykinins. When added at various concentrations (10(-11)-10(-7) M) to the incubation medium of rat dispersed pancreatic acini, SK, SP and NK increased in concentration-dependent manner the release of amylase from the resting pancreatic acini and augmented the enzyme release induced by CCK-8 and by urecholine. In anesthetized dogs infused with a background dose of secretin (82 pmol/kg per h), addition of SP, SK and NK caused an immediate and dose-dependent increase in the pancreatic blood flow, oxygen consumption and pancreatic secretion accompanied by a dose-dependent decrease in arterial blood pressure. This study shows that TK are potent pancreatic circulatory stimulants and moderate secretagogues both in vivo and in vitro, acting, at least in part, via cholinergic pathway.

Previous studies showed that EGF is produced by salivary and duodenal glands and released in saliva and duodenal secretion. Using specific radioimmunoassay of EGF, this study showed that the salivary glands and duodenal mucosa contain high levels of EGF, reaching, respectively, about 38 and 4 micrograms/g of tissue weight. EGF immunoreactivity was also found in high amounts in the pancreatic tissue (20 micrograms/g) and the pancreatic juice (32 ng/mL), where the content of EGF was found to increase in response to feeding, cholecystokinin, or bombesin and to decrease after the administration of atropine and somatostatin. Studies on the binding of EGF revealed that pancreatic acinar membranes possess the specific and saturable EGF receptors with a high affinity sites with Kd of about 4.3 nM and binding capacity of about 62 fmol/mg of protein, and with low affinity sites with Kd of 21 nM and binding capacity of about 180 fmol/mg of protein. The observed high content of immunoreactive EGF in the pancreatic tissue and the presence of high and low affinity binding sites for EGF in the pancreatic acinar membranes, as well as the high EGF output in the pancreatic juice and its alterations in response to hormonal and postprandial stimulation, suggest an important role of EGF in pancreatic physiology.

The effects of bombesin, gastrin and cholecystokinin (CCK) on amylase secretion from the isolated rat pancreatic acini and on DNA synthesis (as biochemical indicator of trophic action) in the pancreas have been examined in 48-hour fasted and 16-hour refed rats with and without administration of specific receptor antagonists for bombesin, gastrin and CCK. Studies on the isolated rat acini revealed that bombesin, gastrin and CCK-8 all showed the same efficacy in their ability to stimulate amylase release. RC-3095, bombesin pseudo-peptide antagonizing bombesin receptors, was effective only in suppressing the amylase response to bombesin but not to gastrin or CCK. Benzodiazepine receptor antagonists for gastrin (L-365,260) and for CCK (L-364,718) showed higher efficacy in the inhibition of amylase release induced by pentagastrin and CCK, respectively, but failed to affect that induced by bombesin. These peptides administered 3 times daily for 48 h in fasted rats increased the rate of DNA synthesis as measured by the incorporation of [3H]thymidine into DNA. The blockade of bombesin receptors abolished the DNA synthesis induced only by bombesin but not by gastrin or CCK. The blockade of gastrin receptors by L-365,260 suppressed the DNA synthesis induced by gastrin while the antagonism of CCK receptors by L-364,718 was effective only against CCK. Refeeding of 48-hour fasting rats strongly enhanced DNA synthesis which was significantly reduced by blocking only the CCK receptors (with L-364,718), but not the bombesin (with RC-3095) or gastrin receptors (with L-365,260).(ABSTRACT TRUNCATED AT 250 WORDS)

This study was designed to determine the distribution of immunoreactive epidermal growth factor (EGF) in the gastrointestinal tract and the action of this peptide on pancreatic secretion in vivo and in vitro. Immunoreactive EGF was found in large amounts in the salivary glands and the pancreas and in the pancreatic juice. EGF infused subcutaneously (50 micrograms/kg-h) in conscious rats with intact or removed salivary glands stimulated pancreatic protein secretion after 4 h of peptide infusion; this effect was completely prevented by the pretreatment with DL-difluoromethyl-ornithine (DFMO) (200 mg/kg), an irreversible inhibitor of activity of ornithine decarboxylase (ODC), a key enzyme in polyamine synthesis. EGF added to the incubation medium in concentrations ranging from 10(-10)-10(-6) M increased, in a concentration-dependent manner both unstimulated and stimulated by caeruelin or urecholine, amylase release from dispersed pancreatic acini obtained from rats pretreated in 3 h with EGF in a dose of 50 micrograms/kg-h. Spermine given at concentrations ranging from 10(-12)-10(-6) M to the freshly prepared rat pancreatic acini also increased amylase release in a concentration-related manner. DFMO injected in a single dose (200 mg/kg), before the infusion of EGF to the rats, completely abolished the stimulatory effect of EGF on amylase release, but failed to affect that of spermine. This study shows that 1. EGF is present in large amounts in pancreatic tissue and pancreatic juice. 2. EGF stimulates pancreatic secretion in vivo and amylase release in vitro from isolated rat pancreatic acini. 3. The activation of ODC and polyamine biosynthesis in acinar cells plays an important role in EGF-induced stimulation of pancreatic secretion.

CCK-8, bombesin, secretin and urecholine added in various concentrations to the incubation medium of the dispersed pancreatic acini, obtained from rats, resulted in a dose-dependent stimulation of amylase secretion, the half-maximal response being achieved at 3 X 10(-12), 10(-10), 10(-7) and 10(-5) M, respectively. Pirenzepine (selective muscarinic M1 receptor blocker) or atropine failed to affect the amylase responses to all these secretagogues except that to urecholine, which was reduced by both antimuscarinic agents. The inhibition of urecholine-induced half-maximal amylase secretion by both anticholinergics was concentration-dependent, and the inhibitory potency of pirenzepine was about 1,000 times lower than that of atropine.

The effects on pancreatic responses of highly potent cyclic hexapeptide (cyclo (N-Me-Ala-Phe-D-Trp-Lys-Thr-Phe)) (Veber analog) and octapeptide analogs of somatostatin such as D-Phe-Cys-Phe-D-Trp-Lys-Thr-Cys-Thr-ol (SMS 201-995), D-Phe-Cys-Tyr-D-Trp-Lys-Val-Cys-Thr-NH2 (RC-121), and D-Phe-Cys-Tyr-D-Trp-Lys-Val-Cys-Trp-NH2 (RC-160) have been compared with somatostatin tetradecapeptide (SS-14) and atropine. The parameters evaluated were pancreatic responses to secretin and meat feeding in conscious dogs with chronic pancreatic fistula and amylase release from the dispersed pancreatic acini. The analogs were administered intravenously or intraduodenally. The cyclic hexapeptide and octapeptide analogs, given iv in graded doses against a constant background stimulation with secretin, produced similar and dose-dependent inhibition of pancreatic HCO3- and protein secretion. Analogs RC-121, RC-160, and the Veber analog were about two to four times more active than SS-14 in suppressing HCO3- secretion and equipotent in reducing protein secretion, but SMS 201-995 was only about half as potent as somatostatin in inhibiting HCO3-. RC-160 was effective in inhibiting secretin-induced protein secretion at lower doses than other analogs. In tests with feeding, SMS 201-995, the Veber analog, RC-121, and RC-160 were more potent inhibitors of exocrine pancreatic secretion of HCO3- and protein and exhibited more prolonged inhibitory effects than SS-14. The Veber analog, RC-121, and RC-160 were also more effective after intraduodenal administration. Atropine also caused significant inhibition of both HCO3- and protein responses to secretin and meal feeding. All four analogs decreased the postprandial insulin and pancreatic polypeptide release to a similar degree as SS-14. Neither SS-14 nor the analogs tested significantly affected basal or caerulein-, gastrin-, secretin-, or bethanechol-stimulated amylase release from the dispersed canine pancreatic acini. Atropine reduced amylase release induced by bethanechol, but not that stimulated by caerulein, gastrin, or secretin. This indicated that the analogs, as somatostatin, are ineffective as secretory inhibitors in vitro. We conclude that cyclic hexapeptide and octapeptide analogs are more potent and longer acting inhibitors of pancreatic secretion than somatostatin-14 in vivo.

The nature and extent of enkephalin- and morphine-induced inhibition of pancreatic bicarbonate and protein secretion were studied in dogs with chronic pancreatic fistulae after administering exogenous secretin or octapeptide of cholecystokinin and stimulants for the endogenous release of these hormones. Enkephalin and morphine competitively inhibited the pancreatic bicarbonate secretion induced either by exogenous secretin or duodenal acidification. This inhibition was partially reversed by naloxone, an opiate antagonist. Opiate substance also profoundly inhibited pancreatic protein response to octapeptide of cholecystokinin and to various stimulants of endogenous cholecystokinin release. We conclude that enkephalin and morphine strongly inhibit the pancreatic responses to exogenous and endogenous stimulants by a mechanism involving separate opiate receptors.

In conscious dogs with esophageal, gastric and pancreatic fistulae, sham-feeding and meat feeding increased the pancreatic protein secretion to a peak, reaching about 39% and 69% of CCK8 maximum, and raised plasma pancreatic polypeptide (PP) levels. Pirenzepine given intravenously (i.v.) (30 nmol.kg-1 or 3 mumol.kg-1) reduced dose-dependently the pancreatic protein and plasma PP responses to sham-feeding and meat feeding, being about 100 times less potent as an inhibitor than atropine. Neither pirenzepine nor atropine affected near-maximal pancreatic bicarbonate and protein responses to secretin (164 pmol.kg-1.h-1) and CCK8 (170 pmol.kg-1.h-1), but both antimuscarinic agents significantly inhibited pancreatic responses to lower doses of these secretagogues. When added to the incubation medium of dispersed canine pancreatic acini, pirenzepine reduced dose-dependently the amylase responses only to urecholine, and not to CCK or gastrin, being about 1000 times less potent as an inhibitor than atropine. This report provides an evidence that pirenzepine inhibits pancreatic secretion in a similar manner to atropine, but that pirenzepine, in both in vivo and in vitro studies, is 2-3 orders of magnitude less potent as an inhibitor than atropine, indicating that the muscarinic pathway of the exocrine pancreas has a low affinity for pirenzepine and may thus involve M2-receptors.

The action of peptide YY (PYY) on exocrine pancreatic secretion in dogs and rats was compared in in vivo and in vitro studies. PYY infused i.v. in the physiological dose range (125-1000 pmol/kg.h) reduced in a dose-dependent manner the pancreatic protein response to caerulein and suppressed basal and meat feeding or duodenal oleate-induced pancreatic secretion in conscious dogs. Both meat feeding and duodenal oleate caused significant elevation of plasma PYY levels and these showed several-fold increase during infusion of exogenous PYY (500 pmol/kg.h) inducing significant inhibition of the postprandial or oleate-stimulated pancreatic secretion. PYY in a dose range of 2.5-40 nmol/kg.h also inhibited the response to caerulein in conscious rats but failed to prevent the increment in the postprandial protein secretion in this species. PYY added in various concentrations (10(-11)-10(-6) M) to the incubation medium of the isolated dog and rat pancreatic acini failed to affect basal or caerulein- and urecholine-stimulated amylase release. This study shows that PYY is an effective inhibitor of the pancreatic secretion in vivo but not in vitro suggesting that the inhibition is mediated by an indirect mechanism.

This study was undertaken to compare the potency of L- and D-isomers of natural amino acids (AA's) infused intravenously for stimulation of gastric acid secretion in 3 dogs with Heidenhain pouches (HP) and gastric fistulae. L-Isomers of all natural AA's were found to stimulate acid secretion from the HP, whereas D-isomers were significantly less effective. The most potent L-isomers of AA's were histidine, phenylalanine, glycine, tryptophan, and alanine, which caused an increase in acid output reaching, respectively, 63, 45, 42, 39, and 33% of the maximal response to histamine. The stimulation of acid secretion was not accompanied by any significant change in serum gastrin level. Distention of the HP during intravenous infusion of L-histidine or L-phenylalanie solution caused a pressure-related increase in acid output reaching a peak at 30 cm distention pressure. Decreasing the luminal pH of the HP in sequential order from 7.0 to 2.5 resulted in a stepwise reduction of the HP response to intravenous histidine or phenylalanine, falling at pH 2.5 to about 20% of the peak response achieved at pH 7.0. Metiamide caused a profound reduction of histidine but had only a slight effect on acid secretion induced by intravenous infusion of other AA's suggesting that histidine excites the oxyntic cells mainly through the transformation to histamine and activation of H2-receptors. Atropine also suppressed gastric acid secretion stimulated by intravenous AA infusion, suggesting a role of a cholinergic mechanism in this stimulation. We conclude that L- and, to a lesser degree, D-isomers of natural AA's infused intravenously cause stimulation of gastric acid secretion by a gastrin-independent mechanism sensitive to distention pressure and pH of gastric content.

Helodermin, VIP and PHI, which share a high degree of homology with secretin, have been identified in the gut but their physiological role is unknown. In this study 3 series of tests were carried out to determine the actions of helodermin, VIP and PHI on pancreatic secretion in 6 conscious dogs and amylase release from the dispersed canine pancreatic acini and to correlate the alterations in pancreatic secretory and circulatory effects in 24 anesthetized dogs. Helodermin, VIP and PHI infused i.v. in graded doses (12.5-200 pmol/kg.h) resulted in a dose-dependent increase in pancreatic HCO3 secretion reaching, respectively, 100%, 7% and 2% of secretin maximum. When combined with constant dose infusion of CCK-8 (100 pmol/kg.h), helodermin but not VIP or PHI augmented dose-dependently the HCO3 secretion. When added in various concentrations (10(-10)-10(-5)M) to the incubation medium of dispersed pancreatic acini only helodermin but not VIP or PHI increased dose-dependently amylase release reaching about 50% of CCK-8 maximum. In anesthetized dogs, the pancreatic blood flow (PBF) measured by electromagnetic blood flowmetry showed an immediate and dose-dependent increase following the injections of various doses of helodermin, VIP, PHI and secretin, the peak blood flow preceding by about 1 min the peak secretory stimulation. This study shows that helodermin resembles secretin in its potent pancreatic HCO3 stimulation but differs from VIP or PHI which are poor secretagogues but potent vasodilators. We conclude that if tested peptides are released in the gut, helodermin, like secretin, may be involved in the hormonal stimulation of exocrine pancreas, whereas VIP and PHI may serve mainly as vasodilators in the pancreatic circulation.

In four dogs provided with pancreatic, gastric, and esophageal fistulae, the effects of bovine pancreatic polypeptide (BPP) infused at a physiological dose level (240 pmol per kg/hr) on gastric and pancreatic responses to sham-feeding were studied. The maximal gastric and pancreatic secretion was produced by pentagastrin and secretin, and OP-CCK infusion, respectively, with or without additions of BBP. Exogenous BPP did not change gastric acid and pepsin outputs stimulated by pentagastrin or sham-feeding, but significantly inhibited basal and maximally stimulated pancreatic protein secretion. The peak pancreatic protein, but not bicarbonate response to sham-feeding was reduced by about 31% by BPP. This reduction by BPP amounted to about 57% when the pancreas was stimulated maximally by OP-CCK. It is concluded the PP released by cephalic-vagal excitation does not affect gastric secretion, but inhibits pancreatic protein secretion, and thus might contribute to the lower pancreatic response to sham-feeding as compared with that produced by exogenous stimulants such as secretin and OP-CCK.

Growth hormone releasing factor (GRF), a 44-residue peptide originally isolated from human pancreatic tumors, shows structural similarities to the members of the secretin-vasoactive intestinal peptide (VIP) peptides. This study was designed to determine the effects of human GRF (hGRF-(1-44] on pancreatic secretion in vivo in conscious dogs and in vitro in dispersed rat pancreatic acini. GRF given i.v. in graded doses in dogs caused a small but significant stimulation of pancreatic HCO3- and protein outputs and potentiated secretin- and cholecystokinin (CCK)-induced pancreatic HCO3- but not protein secretion. When given together with somatostatin, GRF failed to reverse the inhibitory action of this peptide on HCO3- and protein responses to secretin plus CCK in dogs. Studies in vitro dispersed rat pancreatic acini showed that GRF added to the incubation medium of these acini caused an increase in basal amylase release and shifted to the left the amylase dose-response curve to caerulein and urecholine but failed to affect the amylase response to VIP. This study indicates that GRF in vivo stimulates basal and augments secretin- or CCK-induced pancreatic HCO3- secretion and that this is probably due to direct stimulatory action of the peptide on pancreatic secretory cells.