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.

Role of endogenous nitric oxide in the control of gastric acid secretion, blood flow and gastrin release in conscious dogs.

Nitric oxide (NO) was shown to mediate gastric hyperemia following secretory stimulation but its role in the control of gastric secretion has not been clarified. Secretory studies were carried out on conscious dogs with chronic gastric fistula, Heidenhain pouch and esophageal fistula, while changes in gastric blood flow were measured in the mucosa of Heidenhain pouuch by laser Doppler flowmetry. Plasma gastrin was determined by radioimmunoassay. Infusion of NG-nitro-L-arginine (L-NNA) (bolus i.v. injection of 2.5 mg/kg followed by infusion of 0.5 mg/kg/h), a potent inhibitor of nitric oxide synthase, failed to affect basal gastric secretion or plasma gastrin level but suppressed an increase of this secretion induced by sham-feeding, ordinary meat feeding or i.v. infusion of bombesin (0.5 microgram/kg/h), pentagastrin (4 micrograms/kg/h) or histamine (40 micrograms/kg/h). In tests with feeding and bombesin infusion, L-NNA caused a significant and dose-dependent reduction in plasma gastrin levels. The inhibition by L-NNA of gastric acid secretory response to pentagastrin, histamine or feeding was accompanied by a decline in blood flow. Addition of L-arginine (bolus i.v. dose of 50 mg/kg followed by infusion of 5 mg/kg/h) significantly attenuated the L-NNA induced inhibition of gastric secretion and the reduction in plasma gastrin response as well as in the fall of gastric blood flow. We conclude that endogenous nitric oxide affects the gastric secretion and that this effect is mediated, at least in part, by the changes in the gastrin release and gastric blood flow.

Antagonism of receptors for gastrin, cholecystokinin and GRP/bombesin in postprandial stimulation of exocrine pancreas in dogs.

Postprandial pancreatic secretion results from the interaction of neural and hormonal factors such as cholecystokinin (CCK), gastrin and gastrin releasing peptide (GRP), but their contribution to the net secretion is not established. Recent description of highly specific and potent hormonal receptor antagonists allows the determination of the physiological role of CCK, gastrin and GRP. In six dogs with chronic pancreatic fistulas, the blockade of CCK receptors by L-364, 718, gastrin receptors by L-365, 260 or GRP/bombesin receptors by nonapeptide RC-3095 failed to affect basal or sham-feeding induced pancreatic secretion indicating that none of these hormonal peptides plays a major role in this secretion. In contrast, the pancreatic response to ordinary feeding (which includes cephalic, gastric and intestinal phases), that was accompanied by a significant increment in plasma CCK and gastrin levels, was strongly inhibited (by over 50%) by L-364, 718 and slightly (by 20-30%) by L-365, 260 but not by RC-3095. Each antagonist was given at a dose that eliminated the secretory response to CCK, gastrin or GRP, respectively. We conclude that specific receptor antagonists are useful tools in assessing the physiological role of gut hormones in the control of pancreatic secretion and that none of the peptides tested appears to be involved in the cephalic phase. However, CCK plays a major role in the postprandial stimulation of pancreatic secretion.

Role of endogenous nitric oxide in the control of canine pancreatic secretion and blood flow.

BACKGROUND: Endogenous nitric oxide has been implicated in the control of mesenteric circulation, but its role in the control of pancreatic blood flow and exocrine pancreatic secretion has not been studied. METHODS: Secretory studies were performed on conscious dogs with chronic pancreatic fistulas, and changes in pancreatic blood flow were measured by laser Doppler flowmetry in anesthetized animals. RESULTS: Infusion of NG-nitro-L-arginine did not affect basal pancreatic protein secretion but suppressed an increase of this secretion induced by L-arginine but not that induced by glyceryl trinitrate. Sham-feeding, meal feeding, and infusion of secretin plus cholecystokinin induced pancreatic protein outputs reaching, respectively, 30%, 74%, and 50% of cerulein maximum in these dogs. Infusion of NG-nitro-L-arginine caused a profound inhibition of these secretions, whereas the addition of L-arginine reversed this inhibition in part. NG-nitro-L-arginine or L-arginine added to the incubation medium of isolated canine pancreatic acini did not affect basal or cholecystokinin-induced amylase release. In anesthetized dogs, infusion of NG-nitro-L-arginine caused a significant reduction in the pancreatic blood flow both while resting and following stimulation with secretin plus cholecystokinin but did not affect this flow in animals treated with glyceryl trinitrate. Addition of L-arginine attenuated the decrease in pancreatic blood flow and the increase in systemic blood pressure caused by NG-L-nitro-arginine. CONCLUSIONS: Endogenous NO affects pancreatic secretion probably through the changes in the vascular bed.

Role of cholecystokinin in the intestinal fat- and acid-induced inhibition of gastric secretion.

This study was designed to determine the role of cholecystokinin (CCK) in the inhibition of gastric HCl secretion by duodenal peptone, fat and acid in dogs with chronic gastric and pancreatic fistulas. Intraduodenal instillation of 5% peptone stimulated both gastric HCl secretion and pancreatic protein secretion and caused significant increments in plasma gastrin and CCK levels. L-364,718, a selective antagonist of CCK-A receptors, caused further increase in gastric HCl and plasma gastrin responses to duodenal peptone but reduced the pancreatic protein outputs in these tests by about 75%. L-365,260, an antagonist of type B receptors, reduced gastric acid by about 25% but failed to influence pancreatic response to duodenal peptone. Addition of 10% oleate or acidification of peptone to pH 3.0 profoundly inhibited acid secretion while significantly increasing the pancreatic protein secretion and plasma CCK levels. Administration of L-364,718 reversed the fall in gastric HCl secretion and significantly attenuated pancreatic protein secretion in tests with both peptone plus oleate and peptone plus acid. Exogenous CCK infused i.v. in a dose (25 pmol/kg per h) that raised plasma CCK to the level similar to that achieved by peptone meal plus fat resulted in similar inhibition of gastric acid response to that attained with fat and this effect was completely abolished by the pretreatment with L-364,718. We conclude that CCK released by intestinal peptone meal, containing fat or acid, exerts a tonic inhibitory influence on gastric acid secretion and gastrin release through the CCK-A receptors.

Role of cholecystokinin in the inhibition of gastric acid secretion in dogs.

1. This study was designed to determine the involvement of cholecystokinin (CCK) in the gastric secretory responses to exogenous and endogenous secretagogues in conscious dogs with chronic gastric fistulae (GF), pancreatic fistulae (PF) and Heidenhain pouches (HP). 2. A meal of meat or intragastric application of peptone (300 mosM) increased secretion of HCl from the HP and pancreatic secretion of protein and plasma levels of gastrin, CCK and somatostatin. 3. The CCK receptor antagonist L-364,718 caused a further increase in the postprandial HCl secretion from the HP and in the plasma levels of gastrin and CCK but pancreatic output of protein and plasma concentration of somatostatin were significantly reduced. 4. Addition to intragastric peptone of 10% oleate or its acidification to pH 3.0 profoundly inhibited the HP secretion and gastrin release but significantly increased pancreatic secretion of protein and plasma levels of CCK and somatostatin. Administration of L-364,718 reversed the fall in the HP secretion and plasma gastrin while significantly attenuating pancreatic protein secretion and plasma somatostatin levels. 5. Intragastric administration of hyperosmolar (1200 mosM) peptone also inhibited HCl secretion from the HP but this was not affected by L-364,718. 6. Exogenous CCK and bombesin (but not gastrin) caused a small increase in HCl secretion from the HP and marked stimulation of pancreatic protein secretion accompanied by a significant rise in plasma levels of gastrin, CCK and somatostatin. Administration of L-364,718 resulted in a further increase in the HCl response of HP to bombesin and in plasma levels of gastrin and CCK but caused a reduction in plasma levels of somatostatin. 7. We conclude that CCK released by a meal of meat, intragastric peptone, oleate or acidified peptone and intravenous bombesin exerts tonic inhibitory influences on gastric acid secretion and that this effect is mediated, at least in part, by somatostatin.

Role of liver and intestines in the degradation of epidermal growth factor.

Epidermal growth factor (EGF) is widely distributed in the gastrointestinal tissues and released into the gut lumen but its physiological role is questionable because of the postulated high uptake and degradation of this peptide in the liver. This study was designed to examine the action of EGF administered intraduodenally (i.d.), intravenously (i.v.) or intraportally (i.p.) on pentagastrin-stimulated gastric and pancreatic secretion and to determine the role of liver in the EGF uptake. In conscious dogs with gastric and pancreatic fistulas, EGF infused i.v. or i.p. in graded doses (0.12-1.0 microgram/kg.h) caused a dose-dependent inhibition of pentagastrin-induced gastric H+ secretion without alteration in pancreatic protein secretion. EGF infused i.v. and i.p. raised significantly plasma levels of the peptide but these increments were significantly lower with i.p. than with i.v. infusion. EGF given i.d. did not affect gastric or pancreatic secretion and failed to raise significantly plasma EGF level. In anesthetized dogs, no difference was found in the basal plasma EGF levels between arterial and portal or hepatic blood. during i.v. infusion of EGF, plasma EGF level in hepatic venous blood was about 40% lower and that in the portal blood was about 30% lower than that in arterial blood indicating a marked uptake of peptide during the passage through the liver and the intestines, respectively. EGF was present in negligible amounts in gastric secretion but appeared in nanogram concentrations in the pancreatic secretion and increased after pentagastrin stimulation. We conclude that (1) the liver and the intestines are almost equally involved in partial degradation of EGF and that the kidneys may also contribute to the elimination of circulating EGF; (2) the uptake of EGF by these organs is limited and can be overcome by increasing doses of infused EGF, and (3) absorption of EGF from the intestinal lumen does not contribute to its circulating concentrations.

Comparison of telenzepine, pirenzepine and atropine on gastric acid and pepsin secretion in response to histamine, pentagastrin, bethanechol, sham-feeding and feeding.

This study was designed to compare gastric antisecretory effects of telenzepine, a new antimuscarinic agent, with those of pirenzepine and atropine in dogs. None of these antimuscarinics affected gastric acid secretion induced by histamine but all of them caused a dose-dependent inhibition of acid secretion from the gastric fistula (GF) and Heidenhain pouches (HP) stimulated by pentagastrin and bethanechol, telenzepine being 5-9 times more potent than pirenzepine and equipotent with atropine. All antimuscarinics were also effective inhibitors of acid responses to sham feeding and ordinary feeding. The inhibitory effect of telenzepine and pirenzepine were not accompanied by any major alterations in plasma gastrin or somatostatin but those of atropine were related to significant increase in plasma gastrin and to significant decrease in plasma somatostatin levels, suggesting the involvement of M2 receptors in the cholinergic control of these hormones. All three antimuscarinics were effective inhibitors of pepsin secretion induced both from the GF and HP by all secretagogues used. Neither telenzepine nor pirenzepine administered in various doses affected the heart rate while atropine caused a significant increase in heart rate confirming that the former agents are selective M1 receptor antagonists. This study provides evidence that telenzepine is more potent than pirenzepine in the inhibition of gastric secretion induced by pentagastrin, bethanechol, sham-feeding and ordinary feeding and that, unlike atropine, it does not increase plasma gastrin responses to meat feeding. In fact, telenzepine and pirenzepine alike reduced plasma gastrin concentrations under these conditions. No influence of these antimuscarinics on plasma somatostatin levels was observed.

Effects of non-peptidal CCK receptor antagonist (L-364,718) on pancreatic responses to cholecystokinin, gastrin, bombesin, and meat feeding in dogs.

Postprandial pancreatic secretion results from the interaction of neural and hormonal factors but their contribution to the net postprandial secretion is unknown. Recent description of highly specific and potent cholecystokinin (CCK) receptor antagonists allows the determination of the physiological role of CCK in the postprandial pancreatic secretion. In six dogs with chronic pancreatic fistulae, the blockade of CCK receptors by non-peptidal agent (L-364,718) caused little change in basal pancreatic secretion, but decreased significantly (p less than 0.05) by about 60% the pancreatic protein response to meat feeding and virtually abolished the pancreatic responses to CCK-8 and bombesin. The pancreatic protein responses to pentagastrin, reaching about 37% of CCK maximum, was also significantly reduced but this effect was less pronounced than that observed in tests with CCK-8 or bombesin stimulation. In contrast, cholinergically stimulated pancreatic secretion, reaching about 40% of CCK maximum, was unaffected by L-364,718. Cholecystokinin antagonism also failed to affect the postprandial and bombesin induced increments in plasma CCK and gastrin concentrations, but significantly reduced the PP responses to CCK-8 bombesin and meat feeding possibly as a result of the removal of the CCK mediated release of PP. We conclude that CCK plays a crucial role in the mediation of the postprandial and bombesin induced pancreatic secretion and in the PP release.

Effect of cholecystokinin receptor antagonist on pancreatic responses to exogenous gastrin and cholecystokinin and to meal stimuli.

Exocrine pancreatic response to food is believed to result from the interaction of neural and hormonal factors, but their contribution in the net postprandial secretion is unknown. Recent description of a highly specific and potent cholecystokinin (CCK)-receptor antagonist permitted the evaluation of the physiologic role of CCK in postprandial pancreatic secretion. In dogs with chronic pancreatic fistula, CCK antagonism caused little alteration in sham feeding- or urecholine-induced pancreatic protein secretion, but reduced by approximately 60% the pancreatic protein response to a gastrointestinal meal and virtually abolished the pancreatic responses to duodenal perfusion with amino acids or oleate and to exogenous CCK, but not to secretin or neurotensin. The pancreatic protein responses, particularly to lower doses of gastrin, were also reduced by CCK-receptor antagonist, but no changes in the responses to secretin or neurotensin were detected. Cholecystokinin antagonism also significantly reduced the pancreatic polypeptide responses to CCK, gastrin, and the gastrointestinal meal, possibly due to removal of the CCK-mediated release of pancreatic polypeptide. We conclude that CCK plays a crucial role in the mediation of the gastrointestinal phase, but not the cephalic phase, of pancreatic secretion.

Cephalic phase of gastroduodenal alkaline secretion.

Alkaline secretion measured under basal conditions in the intact stomach of conscious dogs averaged 47 mumol/30 min and was about twice lower than that recorded in the proximal (approximately 7 cm long) portion of the duodenum. Vagal excitation elicited by sham feeding and insulin resulted in a marked stimulation of alkaline secretion both from the stomach and the duodenum. Atropine significantly reduced gastric and duodenal alkaline secretion under basal state. It abolished gastric and diminished duodenal alkaline response to sham feeding and insulin hypoglycemia, while propranolol was without significant influence. Indomethacin reduced by approximately 75% basal duodenal alkaline secretion but did not prevent the increment in alkaline response to vagal stimulation. We postulate the existence of the cephalic phase of gastroduodenal alkaline secretion, which seems to be cholinergically dependent in the stomach and partly of noncholinergic and nonadrenergic character but prostaglandin dependent in the duodenum.

Subtypes of muscarinic receptors in canine pancreatic secretion in vivo and in vitro.

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.

Cephalic phase of gastroduodenal alkaline secretion.

This study was designed to determine gastric alkaline secretion (GAS) and duodenal alkaline secretion (DAS) and their relation to the duodenal motility pattern in conscious dogs under basal conditions and after vagal stimulation by sham-feeding and insulin hypoglycaemia. GAS was measured in the gastric perfusate and DAS was determined in the perfusate of the upper duodenum (7 cm in length between occluding balloons). Resting GAS and DAS showed typical periodicity in phase with myoelectric and motor activity, reaching peaks during phases II and III, respectively, and nadir during phase I of the migrating motor cycle (MMC). Vagal excitation by sham-feeding or insulin hypoglycaemia resulted in an immediate rise in GAS and DAS, accompanied by a suppression of MMC. Atropine (25 micrograms/kg) reduced basal GAS and DAS by about 50% and abolished GAS but not DAS in response to vagal stimulation, being accompanied by complete suppression of MMC for several hours. Following injection of indomethacin (2.5 mg/kg) to suppress the generation of endogenous prostaglandins, a prolonged reduction in basal GAS and DAS and an increase in the myoelectric activity and the disruption of the MMC occurred. Neither GAS nor DAS responses to vagal stimulation were affected by indomethacin. We conclude that resting GAS and DAS fluctuate cyclically in phase with gastroduodenal motor activity, and that vagal excitation results in a potent stimulation of alkaline secretion and myoelectric activity which are, in part, cholinergic and do not depend upon the generation of endogenous prostaglandins.

Comparison of gastric inhibitory polypeptide and intraduodenal or intravenous fat on gastric acid secretion from vagally innervated and denervated canine stomach.

Gastric inhibitory polypeptide (GIP), given to dogs in graded doses (range 0.25-2 micrograms/kg/hr) against a constant background stimulation with pentagastrin (4 micrograms/kg/hr), failed to affect the acid secretion at all doses used except the largest one (2 micrograms/kg/hr) which significantly reduced the acid secretion only from the vagally denervated portion of the stomach (Heidenhain pouch, HP) while raising plasma GIP two to three times above the levels reached with duodenal fat. GIP infused in a constant dose (1 microgram/kg/hr) significantly reduced the HP responses to lower (0.5-2 micrograms/kg/hr) but not to higher (4-16 micrograms/kg/hr) doses of pentagastrin, the kinetics of this inhibition being of competitive type. GIP was ineffective against a constant near maximal stimulation with pentagastrin (4 micrograms/kg/hr), histamine (40 micrograms/kg/hr), or liver extract meal, whereas fat (10 g), given intraduodenally or intravenously, was a powerful inhibitor of acid responses to these stimulants both from the innervated and denervated stomach. Plasma GIP reached similar levels with exogenous GIP and duodenal fat but remained unchanged with intravenous infusion of fat.

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.

Effects of epidermal growth factor on gastrointestinal secretions.

Epidermal growth factor (EGF) has been reported to stimulate epithelial cell proliferation and to inhibit gastric H+ secretion, but no details of the latter effect have been studied. This paper reports the effects of EGF on gastric and pancreatic secretions induced by various stimulants in vivo on conscious dogs and in vitro on isolated rabbit gastric glands. EGF was found to be an effective inhibitor of H+ secretion induced from the fully innervated and vagally denervated portions of the stomach stimulated by secretagogues activating receptors of the parietal cells (pentagastrin, histamine, and urecholine) and by natural stimulants such as sham or ordinary feeding. It appears to act directly on the parietal cells, as the inhibitory effect in vivo was not accompanied by any change in postprandial serum gastrin level. In addition, EGF was found to suppress H+ formation in the isolated gastric glands, both under resting conditions and after stimulation with histamine, carbachol, or dibutyryl cAMP. EGF failed to affect pancreatic response to exogenous hormones (secretin and cholecystokinin) but reduced postprandial secretion probably because of inhibition of H+ secretion from the subsequent reduction in duodenal acid loads. We conclude that EGF is a potent, specific, and direct inhibitor of H+ secretion from the parietal cells and that it does not affect alkaline gastroduodenal or pancreatic secretion.

Effects of omeprazole, a substituted benzimidazole, on gastrointestinal secretions, serum gastrin, and gastric mucosal blood flow in dogs.

In dogs with gastric fistulas and vagally denervated Heidenhain pouches, omeprazole, a benzimidazole derivative infused intravenously or given intraduodenally, dose-dependently inhibited gastric acid secretion, which had been induced by histamine, pentagastrin, or urecholine. It also suppressed gastric acid response to physiologic stimulants such as sham-feeding and gastric peptone meal without affecting serum gastrin level. The inhibition of histamine-induced acid secretion was accompanied by a parallel reduction in the mucosal blood flow, but no significant alteration in the ratio (R) value, indicating that omeprazole primarily affected gastric acid secretion but did not limit gastric mucosal microcirculation. Omeprazole, infused into the Heidenhain pouch, caused a dose-dependent inhibition of the Heidenhain pouch response to intravenous histamine without any significant change in the acid response of the main stomach and plasma concentrations of the drug. This indicates that omeprazole may exhibit local inhibitory action on the oxyntic glands. Omeprazole did not affect gastric mucosal integrity or the rate of alkaline secretion from the gastroduodenal mucosa or the pancreas stimulated by duodenal acidification or secretin.

Comparison of effects of neurotensin and fat on pancreatic stimulation in dogs.

In six conscious dogs with esophageal, gastric, and pancreatic fistulas, the effects of intravenous infusion of neurotensin and intraduodenal instillation of sodium oleate on gastric and pancreatic secretion were determined under basal conditions and after exogenous (secretin and cholecystokinin octapeptides) or endogenous stimulants (feeding and duodenal acidification). Neurotensin given intravenously in graded doses (1.5-200 pmol . kg-1 . min-1) to fasted dogs produced a dose-dependent stimulation of pancreatic bicarbonate and protein secretion reaching, respectively, about 18 and 100% of maximal responses to secretin and cholecystokinin octapeptide (CCK). Duodenal oleate in graded doses (0.5-16 mmol/h) resulted in a similar pattern of bicarbonate and protein secretion but increased plasma neurotensin only to about 10% of that achieved with infusion of exogenous neurotensin producing an equal rate of pancreatic secretion. Neurotensin, like oleate, potentiated the action of secretin and CCK on pancreatic bicarbonate and had additive effects on protein response to these secretagogues. Both neurotensin and oleate increased pancreatic response to liver extract meal kept in the stomach at constant pH (5.5) and the response to sham feeding but decreased the response to ordinary feeding, probably due to the inhibition of gastric acid secretion and reduction of duodenal acidification. Neurotensin given intra-arterially directly to the pancreas or to isolated intestinal segment increased dose dependently the blood flow and oxygen consumption without affecting general circulation. We conclude that 1) neurotensin mimics the pancreatic secretory effects of intestinal fat, 2) neurotensin may contribute in part to fat-induced stimulation of the pancreatic secretion, and 3) the secretory effects of neurotensin are accompanied by a marked stimulation of intestinal and pancreatic circulation and metabolism.

Comparison of enkephalin and atropine in the inhibition of vagally stimulated gastric and pancreatic secretion and gastrin and pancreatic polypeptide release in dogs.

Enkephalins have been detected in vagal nerves and myenteric plexus neurons but no study has been performed to determine their action on vagally stimulated gastric and pancreatic secretion. In this study we infused IV methionine-enkephalin (Met-enk) alone, naloxone (a pure opiate antagonist) alone, or their combination before, during and after vagal stimulation in 4 dogs with esophageal, gastric and pancreatic fistulas. For the comparison, atropine was given before, during and after vagal stimulation in the same animals. Vagal stimulation was obtained by 15 min sham-feeding, which produced an increase in gastric H+ output to a peak of about 75% of the maximal response to pentagastrin and pancreatic protein secretion amounting to about 71% of the maximal response to caerulein. It was accompanied by a significant rise in serum gastrin and pancreatic polypeptide (PP) levels. Met-enk inhibited significantly both gastric H+ and pancreatic protein secretion and reduced plasma PP but not gastrin levels. Similar effects were obtained after the administration of atropine. The effects of Met-enk were partly reversed by the addition of naloxone. We conclude that (1) enkephalin suppresses vagally stimulated gastric and pancreatic secretion and plasma PP release; (2) these secretory effects of enkephalin seem to be mediated by opiate receptors and could be explained by its inhibitory action on acetylcholine release ("anticholinergic" action) in the stomach and the pancreas.