Bicarbonate Output Research Articles

Acid-induced duodenal mucosal nitric oxide output parallels bicarbonate secretion in the anaesthetized pig.

We recently showed the involvement of the L-arginine/nitric oxide (NO) pathway in acid-induced duodenal mucosal bicarbonate secretion in rats. The aim of the present study was to confirm this observation in pigs by direct measurements of NO production. Experiments were performed on 16 anaesthetized pigs of both sexes treated with guanethidine (6 mg kg-1, intravenously). A duodenal segment, devoid of pancreaticobiliary influxes, was perfused with saline and the duodenal mucosal bicarbonate secretion was calculated from continuous measurements of pH and PCO2. The perfusate contents of NO and its oxidative product nitrite were determined by chemiluminescence, after reduction of nitrite to NO. Luminal acidification with 30 mM hydrochloric acid increased the output of bicarbonate as well as NO to the perfusate, by 195 +/- 45% and 106 +/- 10%, respectively. These responses to acid were markedly inhibited by adding the NO synthase inhibitor NG-monomethyl-L-arginine (L-NMMA, 0.3 mM) to the perfusate. The inhibitory effect of L-NMMA could be reversed by administration of L-arginine (3 mM). The study presents simultaneous measurements of bicarbonate and NO outputs to a duodenal luminal perfusate. The results strongly support the view that the L-arginine/NO pathway is involved in the acid-induced duodenal mucosal bicarbonate secretory response.

Pancreatic bicarbonate response to intraduodenal tryptophan in dogs: role of muscarinic M1-receptors and cholecystokinin.

In dogs, 1. Activation of cholecystokinin-receptors is needed for an adequate pancreatic bicarbonate response to secretin; 2. Cholinergic nerve fibers ending on M1-receptors are probably of little or no importance for the bicarbonate response to secretin in the given dose; 3. The bicarbonate response to tryptophan, given with a secretin background, is controlled by cholinergic M1-fibers and by cholecystokinin; 4. M1-fibers mainly mediate the bicarbonate response to low loads of tryptophan, whereas cholecystokinin controls the response to low and high loads of tryptophan; and 5. Both mediators interact in a synergistic manner. In six conscious dogs with chronic gastric and duodenal fistulas, we compared the action of the M1-receptor antagonist telenzepine (20.25-81.0 nmol/kg/h), the cholecystokinin-receptor antagonist L-364,718 (0.025-0.1 mg/kg/h), and combinations of both on the pancreatic bicarbonate response to graded loads of intraduodenal tryptophan (0.37-10.0 mmol/h), given against a background of secretin (20.5 pmol/kg/h). Secretin significantly (p < 0.05) stimulated the pancreatic bicarbonate output above basal levels. All doses of L-374,718, but not telenzepine, significantly decreased the bicarbonate response to secretin by up to 64%. Additional administration of telenzepine together with L-364,718 had no further inhibitory effect on the secretin-stimulated bicarbonate output as compared to L-364,718 given alone. All loads of tryptophan significantly increased the bicarbonate output over that seen with secretin alone (= incremental bicarbonate response to tryptophan). Telenzepine significantly decreased the incremental bicarbonate response to the two lower loads (0.37-1.1 mmol/h) of tryptophan (by 82-124%); L-364,718 decreased the incremental bicarbonate response to all loads of tryptophan (by 50-118%). The incremental bicarbonate output, as well as the 180-min integrated bicarbonate response to all loads of tryptophan, were abolished by all combinations of both antagonists.

Gastrin inhibits secretin-induced ductal secretion by interaction with specific receptors on rat cholangiocytes.

We assessed the effect of gastrin on ductal secretion in normal and bile duct-ligated (BDL) rats. The effect of gastrin on ductal secretion was examined in the presence of proglumide, a specific antagonist for gastrin receptor (GR). We isolated pure cholangiocytes from normal and BDL rats and assessed gastrin effects on secretin receptor (SR) gene expression and intracellular adenosine 3',5'-cyclic monophosphate (cAMP) levels. We examined the presence of GR mRNA in cholangiocytes by reverse transcription polymerase chain reaction (RT-PCR). In normal or BDL rats, gastrin produced no changes in spontaneous bile secretion. Simultaneous infusion of gastrin inhibited secretin-induced choleresis and bicarbonate output in BDL rats. In the presence of proglumide gastrin did not inhibit secretin-induced choleresis in BDL rats. Gastrin decreased in cholangiocytes from BDL rats 1) SR gene expression and 2) secretin-induced cAMP levels. With the use of RT-PCR, GR mRNA was detected in cholangiocytes. Similar to what is shown for secretin and somatostatin, we propose that the opposing effects of secretin and gastrin on cholangiocyte secretory activity regulate ductal secretion in rats.

The effect of selective sympathetic denervation on pancreatic exocrine secretion.

The purpose of this study was to investigate the influence of selective sympathetic denervation of the rat pancreas on exocrine secretion and to study whether the observed effects were due to pancreatic trophism. Sprague-Dawley rats were divided into two groups. One group underwent selective sympathetic denervation by skeletonizing the superior and inferior pancreaticoduodenal and splenic arteries. The other group underwent simple laparotomy and served as controls. One week after the operation a catheter was introduced into the bile-pancreatic duct and pancreatic juice was collected at 30-min intervals for 4 h. The output of bicarbonate, total protein, amylase, trypsin, chymotrypsin, lipase, colipase and carboxyesterlipase were determined. Following denervation secretion of pancreatic enzymes was significantly enhanced compared with sham-operated animals. We did not find any signs of pancreatic trophism 1 week after denervation.

Effect of acute hyperglycemia on basal and cholecystokinin stimulated exocrine pancreatic secretion in humans

This study was undertaken to investigate the effect of acute hyperglycemia on pancreatico-biliary secretion in healthy subjects. Duodenal outputs of bilirubin, amylase, trypsin and bicarbonate were measured by aspiration using a recovery marker under basal condition for 75 min and during continuous infusion of CCK (0.5 IDU kg.h for 60 min). Seven healthy subjects participated in two experiments performed in random order during normoglycemia and during acute hyperglycemie clamping at 15 mmol I . At regular intervals plasma PP levels were determined as an indirect measure of vagal-cholinergic tone. Basal pancreatico-biliary secretion was significantly (p <0.05) reduced during acute hyperglycemia. CCK significantly (p < 0.05) increased bilirubin, amylase and trypsin output both during normo- and hyperglycemia. During the initial 30 min of CCK infusion the bilirubin, amylase and trypsin outputs were significantly (p < 0.05) inhibited in the hyperglycemic experiment compared to normoglycemia. In the following 30 min of CCK infusion the bilirubin, amylase and trypsin output were not different between hyper- and normoglycemia. Basal and CCK-stimulated plasma PP concentrations were significantly (p <0.05) reduced during hyperglycemia. In summary: 1) basal pancreatico-biliary secretion is significantly reduced during acute hyperglycemia 2) during hyperglycemia CCK-stimulated pancreatico-biliary secretion is also significantly reduced with the pattern of a delayed response 3) hyperglycemia inhibits basal and CCK-stimulated PP secretion suggesting impaired vagal-cholinergic activity during hyperglycemia.

Collection of pancreatic juice from growing pigs

The results of this study demonstrate that there are large differences in the amount of pancreatic juice secreted and in the chemical and enzymatic composition of pancreatic juice when the pouch and the catheter methods were used, and these differences must be taken into consideration in future studies with either method. A study was performed to compare the two most commonly used methods to collect pancreatic juice from growing pigs; namely, the pouch method (PM) and the catheter method (CM). In the first part of the study, three barrows (initial weight 37 kg) were fitted with a pancreatic pouch re-entrant cannula. An isolated pouch was prepared in which the pancreatic duct enters the duodenum. In the second part of the study, also with three barrows (initial weight 32 kg), a catheter was inserted into the pancreatic duct. At several points during the 24-h collection, the hourly rate of pancreatic juice secretion in CM pigs was larger (p < 0.05) than for PM pigs. CM pigs also had a higher (p < 0.05) daily volume of secretion, 4.09 vs 2.63 L/24 h for PM pigs. The pH of pancreatic juice collected from CM pigs was consistently higher (p < 0.01) throughout the 24-h collection. In contrast, the concentration and daily output of bicarbonate did not differ between CM and PM pigs. The concentration of protein in pancreatic juice from PM pigs (7.21 g/L) was higher (p < 0.001) than for CM pigs (4.08 g/L). Specific amylase and lipase and total amylase activities were greater (p < 0.01) in pancreatic juice collected from PM pigs. Specific and total carboxyl ester hydrolase and colipase activities were substantially (p < 0.01) larger in pancreatic juice collected from CM pigs. A major difference between the methods was that trypsin and chymotrypsin were fully active in pancreatic juice from PM pigs, whereas virtually no trypsin or chymotrypsin activity was detected in pancreatic juice from CM pigs. Specific and total chymotrypsin activities did not differ between PM and CM pigs. Both specific and total trypsin activities were substantially higher in pancreatic juice from CM pigs: 3682 U/L and 12,752 U/24 h, respectively, vs 1031 U/L and 2639 U/24 h, respectively, in pancreatic juice from PM pigs.

Role of endogenous nitric oxide in the control of exocrine and endocrine pancreatic secretion in humans.

Nitric oxide (NO) is an unstable vasodilator formed by NO synthetase (NOS) from L-arginine (L-Arg) in various cells but its role in the control of pancreatic secretion in humans has not been examined. This study was designed to determine the role of endogenous NO in the control of exocrine and endocrine pancreas using NOS inhibitor, NG-monomethyl-L-Arg (L-NMMA). Pancreatic secretion was stimulated by intravenous infusion of secretin (80 pmol/kg/h) plus caerulein (50 pmol/kg/h) and duodenal content was aspirated by gastroduodenal tube. Two series of tests with secretagogue infusion were performed, one, with addition of graded doses of L-NMMA and, another, with addition of a constant dose of L-Arg alone followed by L-NMMA alone and finally by a combination of L-Arg and L-NMMA. Addition of L-NMMA in graded doses (2-8 mumol/kg/h) reduced dose dependently the secretin-caerulein stimulated pancreatic enzyme secretion without alterations in the volume flow and bicarbonate outputs. The addition of L-Arg to L-NMMA reversed the inhibitory action of L-NMMA on protein enzyme response to secretin-caerulein in these subjects. Secretin-caerulein infusion caused significant increase in plasma insulin and pancreatic polypeptide levels but without changes in plasma glucagon or somatostatin levels. L-NMMA alone resulted in a significant fall in plasma insulin and pancreatic polypeptide levels, while L-Arg added to pancreatic secretagogue infusion caused a significant increase of plasma insulin and pancreatic polypeptide levels above those attained with secretagogues alone. After the addition of L-Arg to L-NMMA, both plasma insulin and pancreatic polypeptide levels rose significantly above the levels observed with L-NMMA plus secretin-CCK stimulation. This study provides evidence that the suppression of NOS reduces pancreatic enzyme secretion and the plasma insulin and pancreatic polypeptide levels suggesting that endogenous NO affects both exocrine and endocrine pancreatic secretion in humans.

Feedback Regulation of Pancreatic Exocrine Secretion in Minipigs

Background: The mechanism behind the possible feedback regulation of pancreatic exocrine secretion is not well understood. Methods: Thirteen minipigs were prepared with fistulas to the pancreatic duct and the duodenum. Peripheral venous blood was obtained for determination of secretin and cholecystokinin (CCK) levels. Four different experiments were performed: 1) diversion and reinfusion of pancreatic juice; 2) intraduodenal infusion of NaHCO3 solution, with the same volume, bicarbonate concentration, and osmolality as the collected pancreatic secretion, and reinfusion of pancreatic juice; 3) reinfusion of pancreatic secretion for 1 h before and 2 h after a meal; and 4) diversion of pancreatic secretion and intraduodenal infusion of NaHCO3 solutions before and after a meal. Results: Reinfusing pancreatic juice significantly decreased pancreatic juice volume and bicarbonate output and slightly decreased the level of secretin in plasma. Alternating infusions of substitute NaHCO3 and pancreatic juice did not change pancreatic output of bicarbonate and protein, nor did it change the CCK and secretin levels in plasma. Replacing pancreatic juice with intraduodenal NaHCO3 infusions during a meal did not significantly modify the pancreatic secretion of bicarbonate and protein or the hormonal levels in blood. Conclusions: A negative feedback regulation of pancreatic exocrine secretion is present in starved minipigs. Duodenal acidity and plasma levels of secretin seem to be of importance, whereas duodenal enzymatic activity and the level of CCK in plasma probably are not. A postprandial negative feedback regulation through duodenal enzymatic activity and release of CCK into blood could not be shown.

Effects of the Amount and Type of Dietary Fat on Exocrine Pancreatic Secretion in Dogs after Different Periods of Adaptation

Mongrel dogs were fed, from weaning to 6 months of age, on one of two 9% lipid diets that differed only in the type of fat content (sunflower oil or virgin olive oil) to study their effects on exocrine pancreatic secretion, in the basal period and in response to food. In addition, the results were compared with those obtained in a previous work performed by us on dogs adapted for 8 months to diets containing a higher (15%) amount of the same dietary fats to further evaluate the influence of the amount of dietary fat and the length of the adaptation period. The results from the present study show that both the volume and bicarbonate secreted in the absence of stimuli are unaffected by the quality of dietary fat. In contrast, in response to food, the pancreatic juice flow and the bicarbonate output were significantly higher in the group of animals given the sunflower oil diet. The differences seem to be related with the oleic acid content in the diets and the effectiveness of this fatty acid in triggering the release of inhibitory peptides such as pancreatic polypeptide and peptide YY. The comparison between the results from our present and previous studies supports the afore-mentioned hypothesis and confirms the existence of a clear influence of the amount and type of dietary fat, especially the oleic acid content, upon the pancreatic response to food, without ruling out a role for the duration of the adaptation period.

Pancreatic exocrine function during acute exacerbation in WBN/Kob rats with spontaneous chronic pancreatitis.

Pancreatic exocrine hypofunction is markedly deteriorated during acute exacerbation in a rat model with chronic pancreatitis. Little is known about pancreatic exocrine function during acute exacerbation in patients with chronic pancreatitis. We investigated changes in pancreatic exocrine function after inducing acute pancreatitis in an animal model of spontaneous chronic pancreatitis. WBN/Kob rats with chronic pancreatitis sequentially underwent pancreatic exocrine function test 1-6 d after surgical preparation with external pancreatic fistula. We induced acute pancreatitis in another WBN/Kob rats by i.v. administration of cerulein at a rate of 10 micrograms/kg/h for 4 h 4 d after surgical preparation. Pancreatic exocrine function test was undertaken in a conscious state 1 d before and after cerulein administration. In WBN/Kob rats not given cerulein, pancreatic exocrine function remained almost constant at 3-6 d after surgery. Marked hyperamylasemia developed immediately after cerulein administration. After its administration, the pancreas microscopically showed prominent interstitial edema and intracellular vacuolization of acinar cells in addition to the finding of pre-existing chronic pancreatitis. Basal and cholecystokinin-stimulated flow rate, bicarbonate output, and protein output, which were substantially impaired 1 d before cerulein administration, were further reduced 1 d after its administration.

Effect of pituitary adenylate cyclase-activating polypeptide on exocrine and endocrine secretion in the ovine pancreas

The role of pituitary adenylate cyclase-activating polypeptide (PACAP) in the regulation of exocrine and endocrine pancreas was investigated in conscious sheep. Intravenous infusions of PACAP-27 and PACAP-38 (1, 3, and 10 pmol/kg/min) for 10 min during phase II of the duodenal migrating myoelectric complex accelerated pancreatic protein and amylase outputs dose-dependently. The responses in enzyme secretion to both PACAPs at the highest doses were inhibited significantly by atropine infusion (14.4 nmol/kg/min). Vasoactive intestinal polypeptide (VIP) at 3 pmol/kg/min significantly accelerated protein but not amylase outputs, although the response to the highest dose was not significantly influenced by atropine. PACAP-27 and VIP increased pancreatic juice flow and bicarbonate output dose-dependently; however, the responses to the highest dose were not altered significantly by atropine. On the other hand, intravenous injection of PACAP-38 (100 pmol/kg) did not influence basal plasma concentration of insulin, glucagon, and glucose. Moreover, PACAP-38 (1–100 pmol/kg) altered neither pancreatic endocrine response to intravenous infusion of glucose (20 μmol/kg/min) nor that to n-butyric acid (33 μmol/kg/min). These results suggest that PACAP contributes to the regulation of exocrine secretion of the ovine pancreas but not to endocrine secretion. PACAP appears to accelerate pancreatic enzyme secretion mostly via the cholinergic nerves.

Age-related changes in gastric mucosal bicarbonate secretion in rats

The present study was designed to examine the effects of aging on gastric bicarbonate secretion, a major mucosal defensive factor, basally and after treatment with 16,16-dimethyl-prostaglandin (PG) E2, a known stimulant of gastric bicarbonate secretion. Our data have demonstrated that aging was associated with significant decline in basal gastric bicarbonate secretion (as reflected by luminal pH and bicarbonate output). While 16,16-dimethyl-PGE2 significantly stimulated both luminal pH and bicarbonate output in 3-month-old and 1-year-old rats; no significant changes in either luminal pH or bicarbonate output were noted in the 2-year-old rats after treatment with 16,16-dimethyl-PGE2. In summary, aging was associated with significantly lower gastric luminal pH and bicarbonate output in the rat stomach, and aging also blunted the PG-mediated increases in gastric bicarbonate secretion in the rat.

Effects of MCI-727 on pancreatic exocrine secretion and acute pancreatitis in two experimental rat models.

The effects of a newly developed compound having antiulcer action, (Z)-2-(4-methylpiperazin-1-yl)-1-[4-(2-phenyl-ethyl)phenyl]-eth anone oxime hydrochloride monohydrate (MCI-727), on pancreatic exocrine secretion were studied in anesthetized rats and evaluated its preventive and therapeutic effects on acute pancreatitis in two experimental rat models. Intraduodenal administration of MCI-727 [25, 50, or 100 mg/kg body weight (wt)] stimulated a dose-dependent increase in pancreatic juice and bicarbonate output without increasing the protein output or plasma cholecystokinin concentration. MCI-727-stimulated pancreatic exocrine secretion was completely abolished by antisecretin serum but not by the cholecystokinin receptor antagonist loxiglumide (50 mg/kg body wt/h) or cholinergic receptor antagonist atropine (100 mu g/kg body wt/h). In rats with acute pancreatitis induced by four subcutaneous injections of 20 mu g/kg body wt cerulein at hourly intervals over 3 h, MCI-727 administered orally at a dose of 100 mg/kg body wt 30 min before the first cerulein injection significantly reduced the increases in serum amylase and lipase activity and pancreatic wet weight and induced improvements in the results of histologic examination. Moreover, when given 30 min before and 90 min after the first cerulein injection, MCI-727 had even more dramatic protective effects on all these parameters. In addition, even when administered immediately after the last cerulein injection, MCI-727 effectively ameliorated all these alterations of acute pancreatitis. However, MCI-727 had no apparent beneficial effects on the biochemical and histologic alterations of acute pancreatitis in the severe form induced by retrograde intraductal injection of 1.0 ml/kg body wt of 4% sodium taurocholate. These findings suggest that oral administration of MCI-727 stimulates pancreatic exocrine secretion by endogenous secretin release and that it has therapeutic as well as preventive effects on mild forms of acute pancreatitis in rats.

Intracerebroventricular secretin enhances pancreatic volume and bicarbonate response in rats

Although secretin has been found within the brain, its central role in pancreatic exocrine function has not been previously addressed. The hypothesis that intracerebroventricular secretin enhances pancreatic volume and bicarbonate output at doses that have no effect when given intravenously was tested. Sprague-Dawley rats had a cannula stereotactically placed into the left lateral cerebral ventricle 24 hours before study. At laparotomy the bile and pancreatic ducts were separately cannulated and excluded for tared collections and bicarbonate assay. Increasing doses of intracerebroventricular secretin (0.005, 0.05, and 0.5 microgram/1.0 microliter) induced a significant dose-related increase in bicarbonate output (2.95, 3.32, and 4.02 microEq/30 min, respectively) above basal (2.62 microEq/30 min) compared with control or intracerebroventricular saline treated animals. Pancreatic volume increased to 59.7 microliters at the lowest intracerebroventricular dose and increased (p < 0.025) to 65.8 microliters at the 0.05 intracerebroventricular secretin dose when compared with basal (59.4 microliters). To show that this was not a systemic effect of secretin, intravenous infusion of secretin at 0.005 and 0.05 microgram/kg/hr failed to stimulate either volume or bicarbonate output compared with that observed with intracerebroventricular secretin over the same dose range. These observations indicate that intracerebroventricular secretin stimulates pancreatic volume and bicarbonate output and suggest that central secretin may play a role in the regulation of exocrine pancreatic secretion.

The effect of pancreatic denervation and atropine on the cholecystokinin-induced pancreatic exocrine response.

To study the influence of extrapancreatic neural and cholinergic activity on the pancreatic response to cholecystokinin (CCK), six dogs underwent creation of Herrera pancreatic fistulas, placement of Thomas gastric cannulas, and distal pancreatectomies (innervated; INN). Six additional dogs were prepared similarly, with the addition of total extrinsic pancreatic denervation (denervated; DEN). The pancreatic protein and bicarbonate response to graded 12.5 to 200 ng/kg/h CCK doses was determined for INN and DEN animals both alone and with 10 micrograms/kg/h atropine infusion. The influence of extra-pancreatic neural and cholinergic activity on secretin's potentiation of the CCK-induced pancreatic response was then determined by repeating the studies with a 125 ng/kg/h secretin infusion. The latter results were compared to those predicted by summating the responses seen during separate 12.5-200 ng/kg/h CCK dose-response and 125 ng/kg/h secretin studies. Unstimulated protein output was diminished by atropine in INN animals (78 +/- 21 vs. 39 +/- 9 mg/15 min; p < 0.05) but not in DEN animals. Unstimulated bicarbonate outputs, integrated bicarbonate and protein outputs, and bicarbonate and protein dose-response curves were unaffected by denervation or atropine. Potentiation of CCK-induced bicarbonate output by secretin was also unaffected by atropine and denervation. We conclude that cholinergic elements are involved in unstimulated, but not CCK-induced, enzyme secretion. Further, potentiation of CCK-induced bicarbonate output by secretin does not depend on extrinsic neural or cholinergic elements.

Insulin inhibits secretin-stimulated pancreatic bicarbonate output by a dose-dependent neurally mediated mechanism

Although previous reports suggest interactions between endocrine and exocrine pancreas, insulin's effect on pancreatic exocrine function remains unclear. Chronic pancreatic fistulas were created in six dogs with innervated INN and five dogs with denervated (DEN) pancreata; these animals were studied using the euglycemic, hyperinsulinemic clamp technique. After a 30-min unstimulated period, both groups received a 60-min 1.5 mU.kg-1.min-1 insulin (clamp) or vehicle (control) infusion. Intravenous secretin was then initiated at 16 ng.kg-1.h-1; the secretin dose was doubled every 30 min until 125 ng.kg-1.h-1 was achieved. These studies were then repeated in INN animals during infusion of a 10 micrograms.kg-1.h-1 atropine background. Finally, INN animals underwent a similar unstimulated period followed by a 1.25 mU.kg-1.min-1 insulin (clamp) or vehicle (control) infusion. after 60 min, a 64 ng.kg-1.h-1 secretin infusion was initiated. Insulin infusion was then increased by 0.25 mU.kg-1.min-1 at 30-min intervals until 2.0 mU.kg-1.min-1 was reached. Unstimulated (0-30 min) serum glucose and insulin levels and pancreatic bicarbonate and protein outputs did not differ between groups. Clamp (30-90 min) and stimulated (90-210 min) insulin were each significantly elevate in clamp groups (81.9 +/- 2.4 vs. 7.0 +/- 0.3 microU/ml, P < 0.001); glucose and bicarbonate were unchanged. Protein outputs during clamp (64 +/- 9 vs. 24 +/- 6 mg/10 min; P < 0.05) and secretin-stimulated (52 +/- 9 vs. 29 +/- 3 mg/10 min; P < 0.05) periods were diminished by atropine but were unaffected by insulin. Secretin-stimulated (90-210 min) bicarbonate output was diminished by insulin (0.03 +/- 0.01 vs. 0.31 +/- 0.05 meq/10 min; P < 0.003) in INN but not DEN animals; this effect was partially reversed by atropine. Dose-response studies demonstrated a threshold for insulin's inhibitory actions between 1.5 and 1.75 mU.kg-1.min-1. These data provide further evidence for exocrine-endocrine regulatory interactions and suggest that insulin may influence secretin's stimulation of ductal cell secretion by a mechanism that is at least partially cholinergic in character.

Mechanisms behind changes in gastric acid and bicarbonate outputs during the human interdigestive motility cycle.

Human gastric interdigestive acid and bicarbonate outputs vary cyclically in association with the migrating motor complex (MMC). These phenomena were studied in 26 healthy volunteers by constant-flow gastric perfusion, with continuous recording of pH and Pco2 in mixed gastric effluent and concomitant open-tip manometry of gastroduodenal motility. Stable acid and bicarbonate outputs were registered during less than 50% of the MMC cycle. Acid secretion started to increase 71 +/- 3% into the cycle, with maximum output during antral phase III. Bicarbonate output increased biphasically 1) 40 +/- 5% into the cycle, coinciding with reflux of bile, and 2) at the end of duodenal phase III when the aspirate was devoid of bile. The bicarbonate peak associated with phase III was abolished by atropine (0.01 mg/kg iv, n = 8) and by pyloric occlusion (n = 9) but remained unchanged after omeprazole (n = 10). The acid peak was abolished by both atropine and omeprazole. It is concluded that the MMC-related changes in acid and alkaline outputs represent two different and independent phenomena. Acid secretion cyclicity is due to periodical variations in cholinergic stimulation of the parietal cells. In contrast, the phase III-associated increase in bicarbonate output is due to duodenogastric reflux.

Effects of KSG-504, a New Cholecystokinin-A-Receptor Antagonist, on Pancreatic Exocrine and Endocrine Secretions in Rats

The effects of KSG-504 ((S)-arginium (R)-4-[N-(3-methoxypropyl)-N-pentylcarbamoyl]-5-(2-naphthylsulf onyl) pentanoate monohydrate), a new cholecystokinin (CCK)-A-receptor antagonist, on pancreatic exocrine secretion in anesthetized rats and endocrine secretion in conscious rats were studied. Intravenous injection of KSG-504 inhibited the pancreatic amylase output stimulated by intravenous infusion of CCK-8 in a dose-dependent manner (ED50: 18 micrograms/kg/min). Moreover, KSG-504 significantly reduced the CCK-8-stimulated increases in pancreatic juice volume and outputs of protein, trypsin and lipase. Intraduodenal infusion of casein increased the plasma CCK concentration and the pancreatic amylase output. KSG-504 significantly inhibited the pancreatic amylase output stimulated by casein. Pancreatic juice volume and bicarbonate output were significantly stimulated by intravenous infusion of secretin, but were not changed by KSG-504. When pancreatic exocrine secretion was stimulated by secretin plus CCK-8, KSG-504 suppressed the increases in juice volume and bicarbonate output to the level stimulated by secretin alone. Basal pancreatic amylase output was decreased by KSG-504. KSG-504 decreased the level of plasma immunoreactive insulin (IRI) stimulated by glucose plus CCK-8, but had no effect on IRI stimulated by glucose alone and the basal IRI. These in vivo studies suggest that KSG-504 has significant inhibitory effects both on the pancreatic exocrine and endocrine secretion stimulated by CCK, but has no effect on the exocrine secretion stimulated by secretin.

Neuronal regulation of the release and action of secretin-releasing peptide and secretin

The acid-stimulated release of secretin is mediated by a secretin-releasing peptide (SRP) in rats. In the present study we investigated to determine whether a neural mechanism(s) is involved in the regulation of release and action of SRP in anesthetized rats. A concentrated acid perfusate (CAP) containing SRP was obtained from donor rats. CAP administered to recipient rats significantly increased pancreatic flow volume (81.6 +/- 18.3%), bicarbonate output (188.7 +/- 15.6%), and plasma secretin level (from 0.9 +/- 0.2 to 4.4 +/- 0.5 pM). However, this effect was attenuated by CAP from donor rats pretreated with tetrodotoxin (TTX), propranolol, bilateral subdiaphragmatic vagotomy (BSV), or systemic and topical administration of capsaicin. In contrast, CAP from donor rats pretreated with phentolamine, atropine, or hexamethonium did not alter the increase in plasma secretin concentration and pancreatic secretion. Moreover, the action of CAP on secretin release was significantly inhibited in the recipient rats pretreated with TTX, BSV, and topical applications of capsaicin but was not suppressed in the recipient rats pretreated with atropine, hexamethonium, or propranolol. Furthermore, perivagal and duodenojejunal mucosal application of capsaicin abolished the pancreatic secretory response to secretin at 5 pmol.kg-1.h-1. In conclusion, the release and action of both SRP and secretin are mediated by a vagal afferent pathway. beta-Adrenergic receptors also play a significant role in the release of SRP.

Bile formation and hepatic plasma membrane composition in guinea-pigs and rats

We compared bile formation, and biliary and liver plasma membrane composition in guinea-pigs and rats in an attempt to explain the observation that the bile flow rate and the bile acid independent fraction of bile flow (BAIF) in guinea-pigs is about five to seven times higher than in rats. Analysis of electrolytes in bile showed that bicarbonate was significantly [acid] higher in guinea-pigs while Cl −, phosphate and Ca 2+ were markedly lower than in rats. High bile independent secretion in guinea-pigs was associated with a significantly lower concentration of total bile acid, phospholipid and cholesterol than in rats. Bile acid distribution studies showed that glycine conjugated chenodeoxycholate and ketolithocholate were the main bile acids in guinea-pigs, while taurine conjugated cholate and muricholate were the predominant bile acids in rats. Total fatty acid analysis of bile indicated that in rats the major fatty acids were palmitic acid (C16:0) and linoleic acid (C18:2, n-6). In guinea-pigs, the contribution of these fatty acids was lower than in rats and compensated with a significantly higher percentage of oleic acid (C18:1, n-9). Concentrations of anionic polypeptide fraction (APF), an acidic calcium binding apoprotein closely associated with biliary phospholipid and cholesterol secretion was also significantly lower in guinea-pigs. Canalicular plasma membrane analysis showed that as compared with rats, specific activities of Na +,K + ATPase, and cholesterol and phospholipid content were markedly lower in guinea-pigs. Total fatty acid analysis of the membrane revealed that palmitic acid (C16:0), stearic acid (C18:0) and linoleic acid (C18:2, n-6) were the predominant fatty acids in guinea-pigs, while palmitic acid (C16:0), stearic acid (C18:0) and arachidonic acid (C20:4, n-6) were the most important in rats. Thus, high bile flow rate and BAIF in the guinea-pig may be attributed to the low bile acid concentration (below the critical micellar concentration), secretion of hypercholeretic bile acids (e.g. ketolithocholate) and high bicarbonate output.