Bicarbonate Output Research Articles

Cholinergic mechanisms in the pancreas after extrinsic denervation in the rat.

Extrinsic denervations of the pancreas were carried out in rats using bilateral truncal abdominal vagotomy and/or celiac and superior mesenteric ganglionectomy. Chronic fistulas were produced and pancreatic secretion was then measured in conscious animals. In all three groups of extrinsically denervated animals the basal pancreatic secretion was significantly decreased by 15-44% (fluid), 32-59% (bicarbonate output), and 33-43% (protein output). Meal-stimulated secretion was decreased in denervated animals by 38-57% (fluid), 32-44% (bicarbonate output), and 36-64% (protein output). In extrinsically denervated rats, atropine inhibited basal pancreatic fluid by 26-38%, bicarbonate output by 46-71%, and protein output by 63-80%, whereas hexamethonium inhibited basal protein output by 36-58%. These data indicate that cholinergic mechanisms persist in the pancreas after extrinsic denervation. This may correspond either to the spontaneous activity of intrapancreatic excitatory cholinergic neurons or to the drive of these neurons by preganglionic fibers running through nonclassic (such as duodenopancreatic) pathways. No important difference was observed between the effects of vagotomy and those of celiac and superior mesenteric ganglionectomy, indicating that most of the excitatory vagal fibers for the exocrine pancreas run through the celiac pathway and that adrenergic fibers had little effect on the conditions tested.

Effects of proglumide on pancreatic endocrine and exocrine function in healthy humans

A comparative study was done on the pancreatic endocrine (insulin (IRI), human pancreatic polypeptide (hPP)) and exocrine secretion (fluid volume, amylase output, bicarbonate output), before and after administration of proglumide. At the time of the test meal loading, plasma hPP and cholecystokinin (CCK) were also measured. During continuous i.v. administration of proglumide 750 mg and 1650 mg/h 30 min before CCK-8 (20 ng/kg) stimulation, no significant difference in the rise of plasma hPP level was observed, as compared with a single stimulus of CCK-8, nor were there any significant differences in the exocrine secretion. The values of hPP and CCK-8 under a load of test meal significantly elevated after a food load. Although hPP showed a significant inhibition with the administration of proglumide 1650 mg/h, plasma CCK-8 and blood sugar levels were not significantly different from control groups. Therefore, while proglumide has a very weak effect on the action of pancreatic endocrine function, it does have an inhibitory effect on pancreatic function, during physiological stimulation.

Potential methodologic problems with in vivo immunoneutralization of pancreatic polypeptide.

Dogs with chronic pancreatic fistulae were given 0.5 ml of nonimmune rabbit serum or antibody S5, an antibody raised against the C-terminal pancreatic polypeptide (PP) hexapeptide. A 3-h infusion of secretin (125 ng/kg/h) and CCK8 (50 ng/kg/h) was started 30 min after injecting serum. Exogenous BPP (400 pmol/kg/h) was administered during the middle secretin/CCK hour. In a second protocol, 30 min after injecting nonimmune serum or PP-anti-serum, the animals were fed 15 g/kg cooked ground beef. Pretreatment with S5 enhanced secretin/CCK-induced bicarbonate outputs; protein outputs did not differ. Exogenous BPP inhibited pancreatic secretion, even in S5-treated animals. Meal-induced pancreatic secretion was not altered by S5 pretreatment. Significant increments in PP were measured by radioimmunoassay during administration of secretin/CCK and during BPP infusion. Anti-PP pretreatment abolished the former and significantly decreased, but did not abolish, the latter. The meal evoked significant postprandial increments in PP which were essentially abolished following S5 pretreatment. A physiological role for PP cannot be proved or refuted because antiserum pretreatment failed to block the effects of exogenous hormone. The latter must be established before excluding a peptide's physiological role based on negative in vivo immunoneutralization data.

Effect of 15(R), 15-methyl prostaglandin E2 and indomethacin on pancreatic secretion in man

In addition to gastric mucosal cytoprotective and antisecretory effects, prostaglandin E2 has a beneficial effect on experimental pancreatitis in some animal models, while prostaglandin synthesis inhibitors such as indomethacin and salicylates may induce pancreatitis at maximal doses. However, their effect on human pancreas is unclear. For this reason we considered it necessary to delineate their actions on human pancreatic secretion. Six healthy volunteers were studied on six separate days. On day 1, against a background of 1 pmol/kg/hr secretin, increasing doses of CCK were infused intravenously. On day 2, increasing doses of an amino acid mixture were infused intraduodenally and both studies were repeated on two occasions, following 100 micrograms 15(R), 15-methyl prostaglandin E2 per os on one and following indomethacin 50 mg orally 12 and 1 hr prior to the study on the other. Both indomethacin and PGE2 had no significant effect on pancreatic secretion in response to graded doses of CCK. 15(R),15-Methyl prostaglandin E2 and indomethacin caused a reduction of amylase output in response to the higher doses of intraduodenal amino acids. The prostaglandin E2 derivative also elicited a significant increase in basal bicarbonate output. the acute effects of 15(R),15-methyl prostaglandin E2 and indomethacin on human pancreatic secretion do not seem to offer an explanation for the mechanisms of protection against experimental acute pancreatitis or an association with pancreatitis, respectively.

Comparison of gastrointestinal pH in cystic fibrosis and healthy subjects

The primary objective of this study was to define the pH conditions under which supplemental pancreatic enzyme preparations must function in the upper gastrointestinal tract. The hypothesis was that normal or greater acid output in patients with cystic fibrosis (CF), combined with low pancreatic bicarbonate output, results in an acidic duodenal pH, compromising both dosage-form performance and enzyme activity. Gastrointestinal pH profiles were obtained in 10 CF and 10 healthy volunteers under fasting and postprandial conditions. A radiotelemetric monitoring method, the Heidelberg capsule, was used to continuously monitor pH. Postprandial duodenal pH was lower in CF than in healthy subjects, especially in the first postprandial hour (mean time greater than pH 6 was 5 min in CF, 11 min in healthy subjects, P less than 0.05). Based on the dissolution pH profiles of current enteric-coated pancreatic enzyme products, the duodenal postprandial pH in CF subjects may be too acidic to permit rapid dissolution of current enteric-coated dosage forms. However, the pH was above 4 more than 90% of the time on the average, suggesting that irreversible lipase inactivation in the duodenum is not likely to be a significant limitation to enzyme efficacy. Overall results suggest that slow dissolution of pH-sensitive coatings, rather than enzyme inactivation, may contribute to the failure of enteric-coated enzyme supplements to normalize fat absorption.

Impaired proximal duodenal mucosal bicarbonate secretion in patients with duodenal ulcer.

The defensive factors that prevent the human duodenal mucosa from acidic and peptic damage have not been fully evaluated. To determine whether duodenal mucosal bicarbonate production was altered in patients with inactive duodenal ulcer, we measured basal and acid-stimulated bicarbonate output from the duodenal bulb and the distal duodenum in healthy subjects and patients with inactive duodenal ulcer. As compared with 16 normal subjects, the 12 patients had significantly less mean (+/- SE) basal proximal duodenal mucosal bicarbonate secretion (185 +/- 13 vs. 107 +/- 18 mumol per centimeter per hour; P less than 0.001). Moreover, in response to a physiologic amount of hydrochloric acid (2 mmol per five minutes) instilled directly into the duodenal bulb, peak proximal duodenal bicarbonate output in the patients was 41 percent of the normal response (263 +/- 65 vs. 642 +/- 77 mumol per centimeter per hour; P less than 0.01). There was little overlap between groups. In contrast, bicarbonate outputs in the distal duodenum were similar in the two groups. We conclude that most patients with duodenal ulcer disease have decreased proximal duodenal mucosal bicarbonate production at rest, in response to hydrochloric acid, and in relation to peak gastric acid secretion. Impaired proximal duodenal mucosal bicarbonate secretion may be an important factor in the development and natural history of duodenal ulcer.

Effects of antral distension on pancreatic exocrine secretion in dogs: evidence for a short reflex.

In chloralose anesthetized dogs and decerebrated dogs whose pyloric sphincter was submucosally ligated, the pancreatic exocrine secretory response to antral distension was studied. Distensions of the antral pouch with Tyrode's solution and 0.1 N HCl caused graded rises in pancreatic flow and protein and bicarbonate outputs. The serum gastrin concentration gradually rose after the distention with Tyrode's solution, while no rise in serum gastrin was elicited by acid distension. After cervical vagotomy, a reduced pancreatic response persisted but no rise in the serum gastrin was seen. After splanchnicectomy following vagotomy, the pancreatic response became greater than before splanchnicectomy. This pancreatic response was observed even after caeliac and superior mesenteric ganglionectomies, but was completely abolished by an external tight ligature around the pyloric sphincter, or by administration of hexamethonium or atropine sulfate. The results suggest the existence of an antropancreatic short reflex in addition to a long route vago-vagal reflex.

Beta-Adrenergic Inhibition of Pancreatic Secretion in Dogs

Terbutaline, a beta-adrenergic agonist, administered subcutaneously inhibits pancreatic exocrine secretion. We studied the effects of intravenous terbutaline and propranolol on cholecystokinin-stimulated pancreatic secretion in conscious dogs. Terbutaline inhibited pancreatic juice volume, bicarbonate concentration, bicarbonate output and protein output, but had no effect on protein concentration. Propranolol blocked this inhibition and had no effect on the response to cholecystokinin. These observations suggest that (1) terbutaline inhibits pancreatic secretion by a beta-adrenergic mechanism and (2) the primary effect of terbutaline on canine exocrine pancreas is inhibition of water and bicarbonate secretion.

Basal and stimulated human gastric bicarbonate secretion.

The mucus-bicarbonate barrier on the gastric mucosa is regarded as a first-line of defence against acid. Both mucus and bicarbonate originate from the mucus cells in the gastric mucosa. Bicarbonate is secreted actively by Cl-/HCO3- exchange at the luminal cell membrane. A computer based system with continuous measurement of pH and PCO2 in a gastric perfusion system was used to determine human gastric bicarbonate secretion. The rate of basal gastric bicarbonate secretion in 24 healthy subjects was 386 +/- 31 mumol/h (mean +/- SEM). The 95% confidence interval for basal bicarbonate output was 103-669 mumol/h. Vagal stimulation by sham feeding increased the bicarbonate output by 63% and instillation of 16,16 dimethyl prostaglandin E2 increased the bicarbonate output by 214%. The response to vagal stimulation was independent of intragastric pH. The sham feeding response was abolished by premedication with anticholinergics. Basal and vagally stimulated bicarbonate secretion was unaffected by prostaglandin biosynthesis blockade.

Gastrin is not a physiological regulator of pancreatic exocrine secretion in the dog.

The role of gastrin as a regulator of exocrine pancreatic secretion has not been proven adequately. In the present study we therefore compared the relative molar potencies of sulfated and unsulfated gastrin 17 with structurally related CCK peptides (synthetic CCK-8 and natural porcine CCK-33) in stimulating exocrine pancreatic secretion in conscious dogs. Dose response curves were constructed for pancreatic and gastric acid secretion. Plasma gastrin levels after exogenous gastrin 17-I and -II were compared with postprandial gastrin concentrations (meal: ground beef 20 g/kg body wt). The molar potency estimates calculated with synthetic CCK8 as standard (potency = 1.00) for pancreatic protein secretion were natural porcine 50% pure CCK-33 1.60, gastrin 17-I 0.12, and gastrin 17-II 0.16. All four peptides induced a dose-dependent increase in pancreatic bicarbonate output. However, the blood concentrations needed to stimulate pancreatic secretion were above the postprandial gastrin levels. Our data indicate that both gastrin 17 peptides are not physiological regulators of pancreatic enzyme secretion in dogs.

The effect of neurotensin on pure pancreatic secretion in man.

The effect of neurotensin on human pancreatic secretion and its role in the control of pancreatic function are not well defined. In the present investigation I have studied the effect of low doses of neurotensin on pure pancreatic secretion in six subjects with external transduodenal drainage of the main pancreatic duct performed after biliary tract surgery. Intravenous infusion of neurotensin at doses of 0.5 and 2.5 pmol X kg-1 X min-1, administered during submaximal pancreatic stimulation with secretin and cerulein, caused a significant and dose-dependent stimulation of pancreatic secretion (volume, bicarbonate, and protein). The effect of neurotensin was rapid, persisted for the duration of neurotensin infusions, and ceased immediately when the administration of the peptide was discontinued. Compared with control values, the increase in bicarbonate output averaged 24.8% and 44.8% and the increase in protein output 29.2% and 54% for the two different doses of neurotensin used, respectively. The clear effectiveness of the small doses of neurotensin used in the present study strongly suggests that the stimulatory effect of the peptide on pancreatic secretion may be of physiologic significance.

Changes in biliary secretion and lactate metabolism induced by diethyl maleate in rabbits

Diethyl maleate is a compound which binds with glutathione by means of a glutathione S-transferase and is excreted into bile leading to a rapid depletion of hepatic glutathione. In the rabbit, the activity of the enzyme is fairly low and we were thus prompted to study the possible effects of diethyl maleate on biliary secretion and metabolic status in this species. The administration of diethyl maleate induced a transient choleresis followed by cholestasis. The choleresis coursed with increases in the biliary output of sodium and unacounted anions, whereas those of chloride, bicarbonate and bile acids were unaffected. Our data seem to confirm that choleresis is due to the osmotic activity of diethyl maleate compounds excreted into bile, as has been reported in rats and dogs. The cholestasis observed coursed with falls in the outputs of sodium, chloride and bicarbonate though that of bile acids remained constant. Following diethyl maleate administration, a metabolic acidosis appeared with progressive increases of blood lactate concentration. In bile the concentration of this anion closely followed that of plasma. The cholestasis is attributed to a lowered biliary secretion of bicarbonate probably secondary to the metabolic alteration. The hepatic values of cytoplasmic and mitochondrial NADH/NAD ratios and of adenine nucleotide concentrations suggest that the increase in blood lactate results rather from a fall in its hepatic utilization that from an increase in its production.

Cholecystokinetic and Pancreozymic Effect of O-Sulfated Gastrin Compared With Nonsulfated Gastrin and Cholecystokinin

To assess whether sulfated gastrin contributes to the cholecystokinetic and pancreozymic activity of plasma in humans, 8 healthy subjects on separate days received a mixed meal, graded i.v. infusions of synthetic human tyrosine-O-sulfated gastrin 17 (10.9, 32.7, and 98.1 pmol/kg X h), which was compared with nonsulfated gastrin 17 (12.2, 36.6, and 109.8 pmol/kg X h) and O-sulfated cholecystokinin-octapeptide (5.5, 16.5, and 49.5 pmol/kg X h). Gallbladder volumes were measured by ultrasonography, and the concentrations of gastrin and cholecystokinin in the circulation were determined by specific radioimmunoassays. Neither of the gastrins induced changes in gallbladder volume at serum concentrations occurring postprandially, whereas cholecystokinin-octapeptide produced a significant reduction in gallbladder volume even at a plasma cholecystokinin concentration lower than observed postprandially. Another 8 subjects received the same infusions in combination with a background infusion of synthetic secretin (0.3 CU/kg X h). Gastric and duodenal juice was continuously aspirated using a double-marker perfusion technique. Neither of the gastrins caused an increase in the output of amylase, lipase, trypsin, chymotrypsin, or bilirubin, but both induced a modest increase in the output of bicarbonate and duodenal juice, the former only significantly during infusion of sulfated gastrin 17. The output of all parameters was significantly elevated during all doses of cholecystokinin-octapeptide. The results indicate that neither of the gastrins stimulates gallbladder contraction and pancreatic enzyme secretion in humans under physiologic conditions. However, gastrin may, like cholecystokinin, potentiate the effect of secretin on pancreatic secretion of juice and bicarbonate.

Effect of licorice extract (Fm100) on release of secretin and exocrine pancreatic secretion in humans.

We investigated the effect of a fraction of licorice extract (Fm100) on release of endogenous secretin in seven human volunteers using radioimmunoassay and exocrine pancreatic secretion using a dye dilution technique with polyethylene glycol 4000 as a non-absorbable marker. Intrajejunal administration of Fm100 (pH 6.5) in three different doses (200, 400, and 800 mg/30 min) resulted in significant increases in both plasma secretin concentration and pancreatic bicarbonate output in a dose-dependent manner (r = 0.737, p less than 0.001, and r = 0.483, p less than 0.01, respectively). However, it did not influence pancreatic secretion of protein or amylase. The correlation between plasma secretin concentrations and bicarbonate outputs was also significant (r = 0.483; p less than 0.01). These results indicate that endogenous secretin is released by Fm100 in humans and suggest strongly that the increased pancreatic bicarbonate secretion is attributable to the increased plasma concentration of secretin.

Release of cholecystokinin and exocrine pancreatic secretion in response to an elemental diet in human subjects.

We investigated in human volunteers the effects of an elemental diet (ED) containing amino acids on release of endogenous cholecystokinin (CCK) using a highly sensitive and specific radioimmunoassay of CCK and exocrine pancreatic secretion using a dye dilution technique with polyethylene glycol 4000 as a nonabsorbable marker. Intrajejunal administration of ED at three different infusion rates (12.5, 25, and 50 ml/30 min) resulted in a significant increase in plasma CCK concentration in a dose-related manner. Plasma concentrations of gastrin or secretin, however, did not change. Pancreatic secretion of protein, amylase, and bicarbonate also increased significantly. The change in pancreatic secretion of protein, amylase, and bicarbonate output paralleled that of the circulating CCK level but not that of plasma secretin. Thus, the dose of amino acid contained in ED recommended for clinical use can significantly stimulate the release of CCK from the upper small intestine, raising the plasma concentration of CCK. This level can evoke a significant increase in exocrine pancreatic secretion.

Release of secretin by licorice extract in dogs.

To determine the effect of a fraction of licorice extract, FM100, on the endogenous release of secretin and exocrine pancreatic secretion, five dogs were prepared with chronic pancreatic fistulas and gastric cannulas. Intraduodenal administration of licorice extract (pH 7.4) in three different doses (0.5, 1.0, and 2.0 g) resulted in significant increases of both plasma secretin concentrations and pancreatic bicarbonate secretion in a dose-related manner. The plasma secretin concentration and pancreatic bicarbonate output produced by licorice extract correlated well. Intragastric administration of licorice extract (2 g) in 5% liver extract meal (in which pH was maintained at 5.5 by the intragastric titration method) resulted in significant increases of both plasma secretin concentration and pancreatic bicarbonate output. The increase in pancreatic bicarbonate secretion was completely abolished by intravenous infusion of a rabbit antisecretin serum in the two dogs so studied. Thus, the present study indicates that the endogenous release of secretion is involved in a mechanism of an increase in exocrine pancreatic secretin induced by FM100.

A difference in stimulatory effects on pancreatic exocrine secretion between ursodeoxycholate and trypsin inhibitor in the rat

We previously reported that intraduodenally infused ursodeoxycholate produced hypersecretion of pancreas in bicarbonate and fluid secretion in the rabbit (Digestive Diseases and Sciences, 28:942, 1983). Since trypsin inhibitor stimulates pancreatic secretion in the rat whose pancreatic exocrine secretion is regulated by a luminal feedback mechanism, in the present study we examined the stimulatory effect of ursodeoxycholate in comparison to Trasylol in unanesthetized rats with both the presence and the absence of returning bile-pancreatic juice. Under the condition in which bile-pancreatic juice were continuously returned to the intestine, the intraduodenally infused ursodeoxycholate produced significant increases in juice flow and bicarbonate and protein outputs, while Trasylol significantly increased protein output only. After an 8- to 10-hr period of bile-pancreatic juice diversion, Trasylol no longer affected pancreatic secretion, whereas ursodeoxycholate still stimulated the bicarbonate output significantly. Trypsin activities in the proximal half of the small intestine were not decreased by the infusion of UDCA. The mechanism of stimulatory effect of ursodeoxycholate on pancreatic secretion is independent of luminal feedback regulation and appears to differ from that of trypsin inhibitor.

Human duodenal mucosal bicarbonate secretion: Evidence for basal secretion and stimulation by hydrochloric acid and a synthetic prostaglandin E1 analogue

The factors responsible for prevention of duodenal mucosal injury are not known. This series of experiments was performed to determine whether the human duodenum secretes bicarbonate that could prevent mucosal damage. To isolate a 4-cm segment of proximal (i.e., the duodenal bulb) or distal duodenum free of contamination from either gastric or pancreaticobiliary secretion, or both, methods were developed using occlusive balloons. The test segment was perfused with NaCl (2 ml/min, 37 °C) containing [14C]PEG as a nonabsorbable marker, and bicarbonate output was quantitated. Mean (±SE) basal proximal duodenal bicarbonate output was 143 ± 17 μmol/cm · h. A 5-min infusion of 25, 50, and 100 mM HCl directly into the isolated proximal duodenal test segment increased bicarbonate output to 167 ± 29, 199 ± 19, and 278 ± 49 μmol/cm · h, respectively, during the hour after acidification. Distal duodenal acidification (25, 50, and 100 mM) also increased bicarbonate output from the isolated proximal duodenal test segment. A synthetic prostaglandin E1 analogue, misoprostol (1.67–13.3 μg/min), infused directly into proximal or distal test segments significantly stimulated bicarbonate outbreak; peak responses were 644 ± 35 μmol/cm · h and 171 ± 20 μmol/cm · h (p < 0.001), repectively. Thus, in humans, (a) the proximal and distal duodenal mucosa secretes bicarbonate at rest; (b) direct acidification of the proximal duodenum stimulates bicarbonate output; (c) acidification of the distal duodenum beyond the isolated test segment also increased proximal duodenal bicarbonate output; and (d) a synthetic prostaglandin E1 analogue stimulated both proximal and distal bicarbonate output; however, distal duodenal bicarbonate output was significantly less, indicating a proximalto-distal gradient in bicarbonate secretion.

Effects of sex and age on pancreatic secretion

The secretory response of the exocrine pancreas to an intravenous bolus of secretin (1.0 U/kg) was studied in healthy men and women below and above 45 years of age. We studied the secretory pattern, i.e., electrolyte and enzyme secretion in 8 sequential, 10-min collections and cumulative values for each parameter. Within the male group, no significant changes were observed, except for higher amylase and lipase secretions in the older subjects. On the other hand, females over 45 yr old had secretory patterns that showed a decline of flow and of bicarbonate concentration and output. No significant secretory differences were observed in the groups of younger males and females. When the over-45 groups of men and women were compared, the women exhibited a significant decrease in bicarbonate concentration and output. Moreover, this group of women had a cumulative 80-min output of bicarbonate and lipase significantly below these parameters in the men. Possible mechanisms are discussed.

Effect of rabbit anti-pancreatic polypeptide serum on postprandial pancreatic exocrine secretion in dogs

To determine whether pancreatic polypeptide (PP) is a physiologic inhibitor of pancreatic secretion, we have studied the effects of normal rabbit serum and anti-PP serum on pancreatic secretion during infusion of a physiologic dose of PP or intragastric food instillation in dogs. Infusion of 180 pmol/kg · h of PP, previously incubated with normal rabbit serum, induced increases in plasma PP (220 ± 21 pmol/L) similar to those after the meal (213 ± 51 pmol/L) and was accompanied by significant inhibition of pancreatic flow rate, bicarbonate output, and protein output (p < 0.05) stimulated by secretin and cholecystokinin (n = 6). However, when the effect of exogenous PP was studied after in vivo administration of anti-PP serum or after previous in vitro incubation with anti-PP serum, no inhibition of pancreatic secretion was found, indicating that immunoneutralization of PP blocks the biologic activity of the hormone. Intragastric instillation of 400 ml of liver extract resulted in significant increases in pancreatic flow rate and outputs of protein and bicarbonate (p < 0.01; n = 8), both during administration of normal rabbit serum and anti-PP serum. The postprandial increase in pancreatic secretion during administration of anti-PP serum was not significantly different from that during administration of normal rabbit serum. We, therefore, conclude that PP is not a physiologic inhibitor of postprandial pancreatic secretion.