Role of tachykinins in the control of pancreatic secretion and circulation.

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.     

A secretin releasing peptide exists in dog pancreatic juice

Canine pancreatic juice has been shown to stimulate exocrine pancreatic secretion in the dog. In the present study we investigated whether there is a secretin-releasing peptide in canine pancreatic juice. Pancreatic juice was collected from the dogs with Thomas gastric and duodenal cannulas while pancreatic secretion was stimulated by intravenous administration of secretin at 0.5 microg/kg/h and CCK-8 at 0.2 microg/kg/h, respectively. The pancreatic juice was separated into three different molecular weight (MW) fractions (Fr) by ultrafiltration (Fr 1; MW > 10,000, Fr 2; MW=10,000-4,000 and Fr 3; MW < 4,000), respectively. All the fractions were bioassayed in anesthetized rats. Fraction 3 dose-dependently and significantly stimulated pancreatic juice flow volume from 78.0% to 99.4% (p<0.05) and bicarbonate output from 128.9% to 202.1% (p<0.01), respectively. Plasma secretin concentration also increased from 1.2 +/- 0.5 pM to 5.0 +/- 0.8 pM and 6.0 +/- 1.0 pM (p<0.05). None of these fractions increased pancreatic protein secretion or plasma CCK level. The stimulatory effect of Fraction 3 on pancreatic secretion and the release of secretin was completely abolished by treatment with trypsin (1 mg/ml for 60 min at 37 degrees C) but not by heating (100 degrees C, 10 min). Intravenous injection of a rabbit anti-secretin serum, which rendered plasma secretin almost undetectable in rat plasma, also abolished Fr 3-stimulated pancreatic secretion of fluid and bicarbonate secretion. These observations suggest that a secretin-releasing peptide exists in the canine pancreatic juice. It is trypsin-sensitive and heat-resistant. This peptide may play a significant physiological role on the release of secretin and regulation of exocrine pancreatic secretion.     

吗啡和纳洛酮对酸化十二指肠引起狗胰液分泌的影响

本工作用制备 Thomas 胰瘘和胃痿的5条狗进行慢性实验。实验时用0.1N 盐酸灌入十二指肠以刺激胰液分泌,并分別注射吗啡或/和纳洛酮,观察它们对胰液分泌和对胰液中碳酸氢盐和蛋白质浓度的影响。另外我们还观察了吗啡和纳洛酮对6条狗离体胰主导管紧张性的影响。结果表明:(1)吗啡抑制了胰液分泌量,对胰液中碳酸氢盐和蛋白质浓度无影响,由于分泌量减少故两者的排出量显著减少(P<0.05),(2)纳洛酮本身对胰液分泌量和碳酸氢盐及蛋白质浓度均无影响;(3)纳洛酮可以加强吗啡抑制胰液分泌的作用(P<0.01);(4)吗啡能增加狗的离体胰主导管肌条的紧张性,纳洛酮不能阻断或翻转吗啡的这一效应,相反能加强其效应。本工作表明,吗啡抑制酸化十二指肠所引起的胰碳酸氢盐和蛋白质排出量,其机制可能是吗啡刺激胰导管收缩,而纳洛酮则加强吗啡的这种抑制效应。     

The effect of oleate on pancreatic and bile secretion in the conscious rat

The effects of sodium oleate infused into either the duodenum or the terminal ileum on bile and pancreatic secretion were examined in the conscious rat. Rats were prepared with cannulae draining pure bile and pancreatic juice separately, and with an ileal and two duodenal cannulae. A 40 mM taurocholate solution containing 7 mg/ml bovine trypsin was infused into the duodenum throughout the experiment to replace diverted bile-pancreatic juice to maintain the normal regulation of pancreatic secretion. The intraduodenal infusion of sodium oleate significantly increased pancreatic juice flow, protein, and bicarbonate outputs, whereas it did not affect bile secretion. Intravenous infusion of proglumide (300 mg/kg/hr) did not inhibit pancreatic secretion stimulated by intraduodenal infusion of sodium oleate. An intravenous infusion of atropine (100 micrograms/kg/hr) attenuated protein and fluid secretions but not that of bicarbonate in response to intraduodenal oleate. In contrast, the intraileal infusion of oleate had no effect on pancreatic secretion, whereas it decreased bile flow, bicarbonate, and bile salt outputs. In conclusion, sodium oleate introduced in the duodenum stimulates pancreatic secretion but oleate in the terminal ileum inhibits bile secretion.     

Comparison of helodermin, VIP and PHI in pancreatic secretion and blood flow in dogs

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.     

Effect of intraduodenal sodium bicarbonate in rat and rabbit exocrine pancreatic secretion.

The effect of intraduodenal sodium bicarbonate, 0.1 M, on exocrine pancreatic secretion and the release of two peptides, secretin and VIP, was studied in anesthetized rats and rabbits, two species largely used in the gastroenterology laboratories. In the rabbit, intraduodenal sodium bicarbonate perfusion had no effect either on exocrine pancreatic secretion or on portal plasma levels of secretin and VIP. By contrast, in the rat, intraduodenal sodium bicarbonate perfusion significantly increased hydroelectrolyte exocrine pancreatic secretion and portal plasma secretin levels. A clear interspecific difference reflecting the different gastrointestinal physiology of both species is observed.     

Neurotensin stimulates pancreatic exocrine secretion in rats

Neurotensin (NT) stimulates pancreatic exocrine secretion in dogs and humans. The purpose of this study was to examine the effect of exogenous neurotensin on pancreatic exocrine secretion in rats. Five Sprague-Dawley male rats were prepared with pancreatic, gastric and duodenal fistulas. Bile was shunted into the duodenum in order to collect pure pancreatic juice. 24 h later, neurotensin (0.05, 0.1, 0.2, 0.3, 1.0 nmol/kg) was infused intravenously in a random fashion. Pancreatic juice was collected every 10 min, and the volume was recorded and protein and bicarbonate were measured. Neurotensin stimulated, in a dose-related manner, the pancreatic secretion of water, protein and bicarbonate. Neurotensin may be involved in the physiologic control of pancreatic secretion in rats.     

The effects of ammonia on pancreatic enzyme secretion in vivo and in vitro.

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.     

Vasoactive intestinal polypeptide (VIP) in the pig pancreas: role of VIPergic nerves in control of fluid and bicarbonate secretion

Vasoactive intestinal polypeptide (VIP) in the pig pancreas is localized to nerves, many of which travel along the pancreatic ducts. VIP stimulates pancreatic fluid and bicarbonate secretion like secretin. Electrical vagal stimulation in the pig causes an atropine-resistant profuse secretion of bicarbonate-rich pancreatic juice. In an isolated perfused preparation of the pig pancreas with intact vagal nerve supply, electrical vagal stimulation caused an atropine-resistant release of VIP, which accurately parallelled the exocrine secretion of juice and bicarbonate. Perfusion of the pancreas with a potent VIP-antiserum inhibited the effect of vagal stimulation on the exocrine secretion. It is concluded, that VIP is responsible for (at least part of) the neurally controlled fluid and bicarbonate secretion from the pig pancreas.     

Effects of growth hormone releasing factor on pancreatic secretion in vivo and in vitro

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.     

Effects of cyclic hexapeptide analog of somatostatin on pancreatic secretion in dogs

The effects of a cyclic hexapeptide analog of somatostatin, [cyclo(Pro-Phe-D-Trp-Lys-Thr-Phe)] (cyclo-SS), administered intravenously (iv) or instilled into the duodenum (id) on the pancreatic response to endogenous (meal and duodenal acidification) and exogenous (secretin, CCK) stimulants were compared in five dogs with esophageal, gastric, and pancreatic fistulae. Cyclo-SS given iv in graded doses against a constant background stimulation with secretin caused a similar and dose-dependent inhibition of pancreatic HCO3 and protein secretion being about twice as potent as somatostatin-14 (SS-14). Cyclo-SS, whether applied topically to the duodenal mucosa in a dose of 1 microgram/kg or given iv at a dose of 0.5 microgram/kg-hr, resulted in a similar inhibition of pancreatic secretion induced by feeding a meat meal, sham-feeding, duodenal acidification, or infusion of secretin or CCK. The inhibition of pancreatic secretion by cyclo-SS was due in part to direct inhibitory action on the exocrine pancreas as well as to the suppression of the release of secretin, insulin, and pancreatic polypeptide. It is concluded that cyclo-SS is a more potent inhibitor of pancreatic secretion than SS-14 and that it is active when administered both parenterally and intraduodenally.     

Effect of somatostatin on exocrine pancreatic secretion stimulated by pancreozymin-secretin or by a test meal in the dog

In 4 dogs with chronic duodenal and gastric fistulae, exocrine pancreatic function was assessed by cannulating the pancreatic duct and collecting the duodenal contents. Both methods were applied in each animal. Pancreatic secretion was stimulated by infusion of 2 CHR units of pancreozymin and secretin or by administration of a liquid test meal, injected into the stomach through the gastric fistula. During both experiments 3.5 microgram/kg somatostatin was given as bolus injection followed by an infusion of 3.5 microgram/kg/h. Somatostatin caused a significant reduction in protein and amylase output and in the bicarbonate concentration during stimulation with pancreozymin-secretin. Volume and bicarbonate slightly decreased but not to a significant extent. Duodenal volume and the duodenal activities of trypsin and amylase were significantly reduced during test meal stimulation and somatostatin infusion. Somatostatin is a potent inhibitor of exocrine pancreatic function mainly influencing enzyme secretion.     

Roles of 5-HT receptors in the release and action of secretin on pancreatic secretion in rats

5-Hydroxytryptamine (serotonin, 5-HT) is a hormone and neurotransmitter regulating gastrointestinal functions. 5-HT receptors are widely distributed in gastrointestinal mucosa and the enteric nervous system. Duodenal acidification stimulates not only the release of both 5-HT and secretin but also pancreatic exocrine secretion. We investigated the effect of 5-HT receptor antagonists on the release of secretin and pancreatic secretion of water and bicarbonate induced by duodenal acidification in anesthetized rats. Both the 5-HT(2) receptor antagonist ketanserin and the 5-HT(3) receptor antagonist ondansetron at 1-100 microg/kg dose-dependently inhibited acid-induced increases in plasma secretin concentration and pancreatic exocrine secretion. Neither the 5-HT(1) receptor antagonists pindolol and 5-HTP-DP nor the 5-HT(4) receptor antagonist SDZ-205,557 affected acid-evoked release of secretin or pancreatic secretion. None of the 5-HT receptor antagonists affected basal pancreatic secretion or plasma secretin concentration. Ketanserin or ondansetron at 10 microg/kg or a combination of both suppressed the pancreatic secretion in response to intravenous secretin at 2.5 and 5 pmol x kg(-1) x h(-1) by 55-75%, but not at 10 pmol x kg(-1) x h(-1). Atropine (50 microg/kg) significantly attenuated the inhibitory effect of ketanserin on pancreatic secretion but not on the release of secretin. These observations suggest that 5-HT(2) and 5-HT(3) receptors mediate duodenal acidification-induced release of secretin and pancreatic secretion of fluid and bicarbonate. Also, regulation of pancreatic exocrine secretion through 5-HT(2) receptors may involve a cholinergic pathway in the rat.     

Absorption of amino acids from the small bowel and their activity in releasing of cholecystokinin

The ability of essential and nonessential amino acids to stimulate the release of CCK was investigated in dogs using a bioassay procedure based on the perfusion of intestinal Thiry-Vella loops and determing the increase of pancreatic protein response as well as the potentiation of pancreatin bicarbonate secretion by a background doses of secretin (0.2 units/kg/h). All essential amino acids, except threonine, and all nonessential amino acids except cysteine were effective in CCK release when perfused in equimolar concentration (50-mM) through the intestinal loop. The peak pancreatic protein in response to tryptophan was about 89% of the maximal response to exogenous CCK in a dose of 25 units/kg/h. These data have also indicated that tryptophan and phenyloalanine are able to release small amounts of secretin.     

Three-day continuous drainage of pancreatic juice in the cortisone-treated conscious rat: Analysis of enzyme activities and ultrastructural changes

Summary We have investigated the short-term effects of hydrocortisone (60 mg/kg per day) and placebo on basal and stimulated pancreatic secretion in the conscious rat. Volume and enzyme secretion were determined; fine structural changes were examined simultaneously.The pancreatic and bile ducts were cannulated separately; pancreatic juice was drained via an isolated fistula, and bile was recirculated into the duodenum. The application of hydrocortisone led to an almost complete inhibition of the secretory response of the exocrine pancreas when stimulated with 0.25 U secretin in combination with 5 × 10^-8 g caerulein per h. It strongly affected the secretion rates of volume, protein, lipase, chymotrypsin, trypsin and carboxypeptidase, whereas the secretion rate of alpha-amylase continued to show a slight increase after stimulation.After stimulation with secretin and caerulein, the hydrocortisone-treated animals showed a higher density of zymogen granules in the acinar cell and an increase in the number of autophagic vacuoles in comparison to the equally stimulated placebo-treated rats.It is concluded that the short-term inhibition of pancreatic secretion by hydrocortisone occurs largely as a result of an inhibition of cellular enzyme discharge.Supported by the Deutsche Forschungsgemeinschaft, Ga 279     

Effect of glucagon on canine exocrine pancreatic secretion stimulated by a test meal

The effect of glucagon on exocrine pancreatic secretion stimulated by a test meal was studied in three dogs with a chronic gastric fistula and a modified Thomas duodenal fistula which allows easier collection of pure pancreatic juice after a meal. Glucagon was given by continuous intravenous infusion in doses of 5, 10, 15, or 30 microgram/kg per hour, before and during a test meal. At each dose level glucagon significantly reduced the water and electrolyte secretion of the pancreas. At 15 and 30 microgram/kg per hour glucagon inhibited protein output; this effect was absent at lower doses. These findings demonstrate a dose-dependent inhibition by glucagon of the pancreatic bicarbonate and protein response to a meal. Inhibition of bicarbonate output was more sensitive to glucagon than that of protein output.     

Biliary and pancreatic exocrine secretions via endogenous secretin by intestinal infusion of propionate and propionate analogues in piglets

1. The secretory responses of hepatic bile and exocrine pancreas by intraduodenal infusion of propionate (PA), 3Cl-PA, 2Cl-PA, 3Br-PA and 2Br-PA solutions were examined in anesthetized piglets. 2. Pancreatic juice and protein secretions were enhanced by infusion of PA and PA analogue solutions of pH 2.0 following increase of plasma secretin level but not pH 7.0. The order of response time was as follows: 3Br-PA greater than 2Cl-PA greater than 2Br-PA greater than 3Cl-PA greater than PA. 3. The response of bile flow depended on endogenous secretin and showed almost the same pattern as that of pancreatic juice secretion. 4. The results suggested that pancreatic exocrine secretion via endogenous secretin was not always dependent on the dissociation constant of weak acids.     

The importance of gastric secretion in the feedback control of interdigestive and postprandial pancreatic secretion in rats.

Previous studies demonstrated that pancreatic enzyme secretion in rats is stimulated by the diversion of pancreatic juice from the duodenum or by the inhibition of pancreatic proteinases in the intestinal lumen but little attention has been paid to the role of gastric secretion in this stimulation. This study, carried out on conscious rats with large gastric (GF) and pancreatic fistulas, confirms that diversion of pancreatic juice in rats with the GF closed results in the progressive stimulation of pancreatic secretion reaching the maximum similar to that induced by exogenous CCK. When the GF was kept open, the diversion resulted in only small increment in pancreatic secretion and this was accompanied by progressive increase in gastric acid outputs. Similar amounts of HCl (25-400 mumol/h) instilled intraduodenally (i.d.) in rats with the GF open fully reproduced the increase in pancreatic secretion observed after the diversion of pancreatic juice and this effect was completely abolished by the pretreatment with L-364,718, a specific CCK receptor antagonist. Pretreatment with omeprazole to suppress completely gastric acid secretion in the diverted state resulted in a decline in pancreatic secretion similar to that observed after opening the GF. Camostate given in graded doses (6-200 mg/kg) either i.d. or s.c. in rats with pancreatic juice returned to the duodenum caused a dose-dependent increase in pancreatic secretion, but after opening the GF or after omeprazole this increase was reduced by about 50% while after L-364,718 it was abolished. This study provides evidence that gastric secretion plays an important role in the pancreatic response to diversion of pancreatic juice or inhibition of luminal proteinases (but not to feeding) and the elimination of gastric acid reduces this response.     

Cyclic nucleotides, calcium, bicarbonate, and protein secretion in canine pancreatic juice in response to cholecystokinin-pancreozymin.

The secretion of cyclic AMP, cyclic GMP, protein, calcium, and bicarbonate in the pancreatic juice of three nonanesthetized dogs with chronic gastric and duodenal Thomas cannulae has been studied. Intravenous infusions of increasing doses of cholecystokinin-pancreozymin (CCK) (1.5, 3, 6, 12, 24 Crick Harper-Raper (CHR) U kg-1 h-1) were administered together with a continuous submaximal dose of secretin (1 clinical unit (CU) kg-1 h-1). Doubling CCK doses every 45 min induced a parallel increase in the output of both cyclic nucleotides. Cyclic AMP output peaked at between 15 and 30 min for 3 and 6 U kg-1 h-1 of CCK and later for 12 and 24 U kg-1 h-1 of CCK whereas cyclic GMP output increased more constantly. Calcium output followed a pattern similar to that of cyclic GMP secretion. Flow rate and protein output attained their peaks at between 30 and 45 min. A strong linear correlation was found between the quantities of cyclic AMP, cyclic GMP, and the quantities of protein secreted in response to each CCK dose. This study demonstrates the presence of cyclic GMP in the canine pancreatic juice and the dose-dependent stimulation of the secretion of cyclic GMP and cyclic AMP by CCK in the presence of secretin.