bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of cholecystokinin in induction and maintenance of dietary protein-stimulated pancreatic growth
Authors: Green G. M. , Jurkowska G. , Berube F. L. , Rivard N. , Guan D. , Morisset J.
Published: December 2017

The role of cholecystokinin (CCK) in induction and maintenance of pancreatic growth stimulated by a high-protein diet was investigated. Rats adapted to 5% casein diet were switched to 70% casein for 21 days. MK-329, a CCK receptor antagonist, was administered at 2.5 mg.kg-1.day-1 ip, beginning on day zero (day zero treatment) or day 7 (midcourse treatment) of feeding 70% casein and thereafter. Another group was returned to 5% casein after 7 days of feeding 70% casein. Feeding 70% casein significantly stimulated increases of 32, 87, 74, 216, and 1,450% in pancreatic DNA, RNA, wet weight, protein content, and chymotrypsin content, respectively. Midcourse treatment with MK-329 was more effective than day zero treatment, and it completely reversed increases in pancreatic weight and RNA content, partially reversed increases in protein and chymotrypsin content, and had no effect on DNA content. Return to 5% casein rapidly reversed increases in pancreatic parameters, except for DNA. The results indicate that CCK is essential for induction and maintenance of dietary protein-stimulated pancreatic hypertrophy.
Crypt-villus site of glucose transporter induction by dietary carbohydrate in mouse intestine
Authors: Ferraris R. P. , Diamond J.
Published: December 2017

Intestinal brush-border glucose uptake rate is regulated by dietary carbohydrate level. However, this uptake response takes a day or more after a change in dietary carbohydrate level. Is this dietary signal perceived in the crypts, and is the glucose transporter activity of enterocytes irreversibly programmed there? If so, this time lag could reflect cell migration times along the crypt-villus axis, since glucose transport is not fully expressed until cells reach the midvillus. Alternatively, however, the time lag could arise from the induction process itself, if glucose transporter activity in mature villus enterocytes can be reversibly reprogrammed by dietary carbohydrate levels. Hence, we measured glucose-protectable phlorizin binding (as a measure of glucose transporter site density) in mouse enterocytes fractionated along the crypt-villus axis by the Weiser method, as a function of time after an abrupt switch in dietary carbohydrate level. For an increase or decrease in dietary carbohydrate, an increase or decrease in phlorizin binding site density first appeared in the crypts and marched over the course of several days to the villus tips. Hence, the signal for glucose transporter regulation is perceived in the crypts, and the observed lag in uptake is due largely to cell migration times.
Patch-clamp recording in myenteric neurons of guinea pig small intestine
Authors: Baidan L. V. , Zholos A. V. , Shuba M. F. , Wood J. D.
Published: December 2017

The results of our research established the feasibility of applying patch-clamp methods in the study of the cellular neurophysiology of myenteric neurons enzymatically dissociated from adult guinea pig small intestine. Recording in current-clamp mode revealed two populations of neurons. One population discharged repetitively during depolarizing current pulses and displayed anodal-break excitation reminiscent of S/type 1 myenteric neurons. In the second population, spike discharge was limited to one or two spikes at the onset of depolarizing pulses and was similar to the behavior of AH/type 2 neurons. Recording in voltage-clamp mode revealed a complex of overlapping inward and outward whole cell currents. Fast and slow components of inward current were interpreted as sodium and calcium currents, respectively. Outward currents were blocked by cesium and consisted of components with properties of delayed rectifier current and A-type potassium current.
Cholecystokinin at physiological levels evokes pancreatic enzyme secretion via a cholinergic pathway
Authors: Soudah H. C. , Lu Y. , Hasler W. L. , Owyang C.
Published: December 2017

The mechanism by which physiological concentrations of cholecystokinin (CCK) evoke pancreatic exocrine secretion in humans was investigated. CCK octapeptide (CCK-8) dose dependently increased trypsin and lipase output in healthy humans. Atropine inhibited CCK-8 (10 ng.kg-1.h-1)-stimulated trypsin output by 84.0 +/- 7.7% and lipase output by 78.6 +/- 9.2%. The inhibition with atropine was much less with a CCK-8 dose of 40 ng.kg-1.h-1 (41.8 +/- 6.6% for trypsin and 46.3 +/- 7.3% for lipase). CCK-8 at 10 ng.kg-1.h-1 produced plasma CCK levels similar to postprandial levels (6.0 +/- 1.3 vs. 6.9 +/- 0.8 pM), whereas the 40-ng.kg-1.h-1 dose produced supraphysiological levels (18.4 +/- 3.1 pM). To evaluate if CCK might act via stimulation of cholinergic nerves, in vitro studies were performed using rat pancreas. CCK-8 (10 nM-10 microM) stimulated [3H]acetylcholine release from pancreatic lobules that was blocked by tetrodotoxin, a calcium-free medium, and the CCK antagonist L364,718. In conclusion, CCK-stimulated pancreatic enzyme secretion is dependent on cholinergic neural and noncholinergic pathways. In humans, CCK infusions, which produce plasma CCK levels similar to those seen postprandially, stimulate the pancreas predominantly via a pathway dependent on cholinergic innervation. Correlative in vitro experiments suggest that CCK may act by stimulation of neural acetylcholine release. In contrast, supraphysiological CCK infusions act in part via noncholinergic pathways.
Innervation of pylorus in control of motility and gastric emptying
Authors: Holle G. E. , Hahn D. , Forth W.
Published: December 2017

The motility index (MI) and contractile frequency were determined for the gastric antrum, pylorus, and duodenum during digestive and interdigestive states in eight dogs before and after resection of the ramus pyloricus nervi vagi (NR) and after selective proximal vagotomy (SPV) subsequent to NR. Neither NR nor subsequent SPV altered the migrating motor complex in the interdigestive state. In the digestive state, NR decreased the MI in the antrum, pylorus, and duodenum. The MI did not further change after SPV subsequent to NR. The cholecystokinin antagonist L364,718 decreased MI in the antrum, pylorus, and duodenum. After NR, L364,718 caused a further reduction in the MI during administration. Gastric emptying was accelerated after NR. SPV subsequent to NR increased gastric emptying further. L364,718, in the absence of NR, accelerated gastric emptying but only during the initial period of emptying. After NR, L364,718 also decreased the time required for emptying of 50 and 100% of the meal. After SPV subsequent to NR, no additional acceleration of emptying occurred.
Cholecystokinin inhibits gastric acid secretion through type "A" cholecystokinin receptors and somatostatin in rats
Authors: Lloyd K. C. , Raybould H. E. , Walsh J. H.
Published: December 2017

The purpose of this study was to determine whether selective antagonism of type "A" cholecystokinin (CCK) receptors blocks inhibition of gastric acid secretion produced by CCK and whether this inhibition is mediated through either a somatostatin-dependent pathway or a vago-vagal reflex. Intravenous infusion of CCK (0.04-10 nmol.kg-1.h-1) dose dependently inhibited pentagastrin-stimulated gastric acid secretion in urethan-anesthetized rats, with a 50% inhibitory dose of 0.9 nmol.kg-1.h-1 and a maximum inhibition of approximately 50%. Blockade of type A CCK receptors using the selective type A receptor antagonist MK-329 completely reversed the inhibitory effect produced by a maximal dose (4 nmol.kg-1.h-1) of CCK. Immunoneutralization of endogenous somatostatin by administration of somatostatin monoclonal antibody abolished the inhibition produced by CCK. Concentrations of somatostatin in portal venous plasma were significantly increased after CCK administration; the increase in somatostatin was blocked by pretreatment with MK-329. In contrast, CCK-induced inhibition of gastric acid secretion was unaltered after perivagal capsaicin treatment. These results indicate that CCK inhibits gastric acid secretion in rats by activation of type A CCK receptors and through release of endogenous somatostatin.
Role of prostaglandins in regulation of gastric mucosal blood flow and acid secretion
Authors: Holm L. , Jagare A.
Published: December 2017

The role of prostaglandins in the rat gastric mucosal vascular response to acid stimulation was studied. Blood flow was measured with laser-Doppler flowmetry (LDF) and with red blood cell velocity measurements in the superficial mucosa; acid secretion was determined by titration. Baseline acid output was calculated to be 0.026 +/- 0.011 mueq/min. Pentagastrin (20 and 40 micrograms.kg-1.h-1 iv) significantly increased acid output to 0.387 +/- 0.104 and 0.546 +/- 0.220 mueq/min and LDF to 119 +/- 10 and 132 +/- 13% of control, respectively. LDF was significantly reduced by 15% after indomethacin (3 mg/kg iv) and was not changed by pentagastrin, whereas acid secretion increased to similar levels as without indomethacin pretreatment. The H2-agonist impromidine (100 and 500 micrograms.kg-1.h-1 iv) induced a dose-dependent increase in acid secretion (0.178 +/- 0.068 and 0.330 +/- 0.072 mueq/min, respectively) while blood flow was unchanged. Despite a substantial blood flow reduction (-38%) by indomethacin, impromidine did not alter blood flow, and acid secretion was dose dependently increased to similar values as without indomethacin pretreatment. These results provide further evidence that there is not necessarily any correlation between blood flow and acid secretion and that the pentagastrin-induced blood flow increase depends on prostaglandin release.
Neurokinin3 receptor regulation of acetylcholine release from myenteric plexus
Authors: Yau W. M. , Mandel K. G. , Dorsett J. A. , Youther M. L.
Published: December 2017

This study sought to characterize the action of neurokinin B (NKB) and senktide, a selective synthetic agonist for NK3 receptors, on the myenteric plexus of the guinea pig small intestine. Both peptides stimulated a dose-dependent release of [3H]-acetylcholine (ACh). The mean effective dose values were 1 x 10(-9) for NKB and 3 x 10(-11) M for senktide. The action of these two neurokinins was blocked by the removal of Ca2+ and was sensitive to tetrodotoxin. The release of [3H]ACh was antagonized by omega-conotoxin GVIA, implying the involvement of N-type voltage-sensitive calcium channels. Senktide-evoked ACh release was also insensitive to nifedipine or flunarizine but was blocked by diltiazem. Treatment with protein kinase C (PKC) inhibitors (H-7 and polymyxin B) or activators (12-tetradecanoylphorbol 13-acetate and SC-9) failed to alter the NK3 receptor-mediated ACh output. Our data did not support an action mediated via PKC upon the activation of NK3 receptors on myenteric cholinergic neurons.
Pathway of insulin in pancreatic tissue on its release by the B-cell
Authors: Bendayan M.
Published: December 2017

Insulin was revealed in the extracellular space and blood capillaries of the rat pancreas by applying protein A-gold immunocytochemistry. On the discharge by the B-cell, insulin diffuses in the extracellular space and interacts with the plasma membrane of all pancreatic cells. For the B-cell, the interstitial microvillar plasma membrane domain was preferentially labeled compared with the flat domain. In contrast, the digitations and flat domains of the basal plasma membrane of the acinar cells were equally labeled. In the endothelium, the labeling was superior in fenestrated areas than in the high cytoplasmic ones, the fenestrae, the luminal and abluminal plasma membranes being labeled. In the cytoplasmic areas the plasmalemmal vesicles were significantly labeled; the intercellular junctions were not. These results indicate that upon binding to the membrane, the transfer of insulin across the capillaries occurs through both the fenestrations and the vesicular system. The labeling of insulin in the subendothelial space and blood capillaries decreased significantly from the insular to the peri-insular and further to the teleinsular regions, demonstrating that insulin levels, high in insular tissue, decrease very rapidly as insulin circulates through and out of the pancreas. The pancreatic cells are thus exposed to very high levels of insulin that vary according to the regions, probably contributing to the topographical partition of the acinar parenchyma into peri-insular and teleinsular tissues.
Na(+)-dependent bile acid transport by hepatocytes is mediated by a protein similar to microsomal epoxide hydrolase
Authors: Von Dippe P. , Amoui M. , Alves C. , Levy D.
Published: December 2017

A protein mediating hepatocyte sodium-dependent bile acid transport across the sinusoidal plasma membrane has been purified by immunoprecipitation with monoclonal antibody (MAb) 25D-1, which specifically recognizes this protein on the surface of intact hepatocytes (Ananthanarayanan et al. J. Biol. Chem. 263: 8338-8343, 1988). The function of this protein was further established by proteoliposome reconstitution (von Dippe et al. J. Biol. Chem. 265: 14812-14816, 1990). NH2-terminal amino acid sequence analysis and amino acid composition revealed this protein to be closely related to the enzyme microsomal epoxide hydrolase (mEH). Both proteins exhibited the same elution times on a reverse-phase high-pressure liquid chromatography column, comigrated with an apparent molecular weight of 49,000 as measured by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and possessed identical isoelectric points of 8.2. The MAb was capable of immunoprecipitating chromatographically purified mEH, as well as a protein derived from the sinusoidal plasma membrane that exhibited mEH activity comparable to that of the protein isolated from the endoplasmic reticulum. The subtilisin fragmentation patterns derived from chromatographically purified mEH and the MAb-precipitated plasma membrane protein were also identical. Hydropathy profile analysis of the amino acid sequence of mEH suggested the presence of four transmembrane domains. The results of these studies indicate that a protein that is involved in mediating sodium-dependent bile acid transport is closely related to mEH.
Different relationships between cellular ATP and hepatic uptake among taurocholate, cholate, and organic anions
Authors: Yamazaki M. , Suzuki H. , Hanano M. , Sugiyama Y.
Published: December 2017

Effects of cellular ATP content on uptake of cholate (CA) and organic anions (OAs; dibromosulfophthalein and benzylpenicillin) by isolated rat hepatocytes were investigated and were compared with that on taurocholate (TCA). Within 5 min of exposure to metabolic inhibitors (MIs), cellular ATP content fell to less than one-fifth of the control value, and the initial velocity of the total uptake of CA, Na(+)-independent uptake of CA and TCA, and the uptake of the OAs dropped in parallel with the decrease in cellular ATP. Whereas for the total uptake of TCA, the initial uptake remained virtually unchanged for a 5-min incubation with the MIs; a significant decrease in uptake was observed only after longer incubation times. Under variously ATP-decreased conditions, the initial velocity of the total uptake of CA and OAs was demonstrated to have a saturable relation to cellular ATP content, irrespective of exposure time to MIs. A difference in the Na(+)-dependent uptake of TCA and CA was also observed in terms of the inhibitory effect of the organic anion pravastatin. That is, the inhibition by pravastatin was partial for TCA uptake but almost complete for CA uptake. These findings suggest the following. 1) The mechanism of Na(+)-dependent CA uptake is different from that of TCA. 2) The Na(+)-independent uptake of bile acids and organic anions may be driven either by ATP hydrolysis (primary active transport) or by an as yet unidentified ion gradient that dissipates more rapidly than the Na+ gradient.
Capsaicin treatment blocks development of hyperkinetic circulation in portal hypertensive and cirrhotic rats
Authors: Lee S. S. , Sharkey K. A.
Published: December 2017

To investigate a possible role of primary afferent innervation in the pathogenesis of hyperkinetic circulation in cirrhosis or portal hypertension, we used capsaicin to denervate the primary afferent nerves. Rat pups were injected with capsaicin (50 mg/kg) or a vehicle and were allowed to grow. When they reached young adulthood, operations to induce portal hypertension by portal vein stenosis or cirrhosis by bile duct ligation were performed. A control group had sham operation. Cardiac output and regional blood flows were measured in unrestrained conscious rats by radioactive microspheres. Capsaicin-treated portal hypertensive and cirrhotic rats had cardiac output and systemic vascular resistance similar to sham-operated rats, whereas the vehicle-treated portal hypertensive and cirrhotic rats showed the hyperkinetic circulation. No hemodynamic effect of capsaicin on sham-operated rats was detected. Capsaicin-treated rats did not demonstrate a splanchnic or renal hyperemia, but the percentage of cardiac output in these vascular beds was similar to controls. These results suggest that capsaicin treatment blocked the generalized vasodilatation in cirrhotic and portal hypertensive rats. Arterial pressure and heart rate were not modified in any group. These results show that denervation of capsaicin-sensitive primary afferent nerves in cirrhotic and portal hypertensive rats blocked the expected development of hyperkinetic circulation. We conclude that primary afferent innervation may be important in the genesis of hyperdynamic circulation in portal hypertension and cirrhosis.
Enteral nutrients promote postnatal maturation of intestinal motor activity in preterm infants
Authors: Berseth C. L. , Nordyke C.
Published: December 2017

Low-compliance perfusion manometry and clinical outcome were used to assess the chronic effects of feeding on functional maturation of the preterm intestine in 32 infants. During the first postnatal week, 16 infants received a small volume of formula to supplement their routine parenteral nutrition (24 ml.kg-1.day-1), and 16 received an equal volume of water. After 10 days of enteral "feedings," the manometric tracings of those infants who had received nutrient feedings had more migrating activity (P < 0.01) and less clustered phasic activity (P < 0.05) during fasting than did the tracings of those infants who had received nonnutrient feedings containing sterile water. Infants who received nutrient feedings demonstrated a change in motor activity in response to feeding; infants who had received water feedings failed to show a change in motor activity in response to feeding. After water-fed infants were given formula feedings for 2 wk, their motor activity patterns were similar to those who had initially been fed formula, and their motor responses to feeding were restored. Despite normalization of their motor activity patterns by 1 mo of age, these water-fed infants established full enteral nutrition and full nipple feedings later than did infants who had been fed formula (P < 0.01), suggesting that the delay of enteral feedings in preterm infants does not permit optimal intestinal maturation of nonmucosal functions.
Relations among intragastric pressure, postcibal perception, and gastric emptying
Authors: Moragas G. , Azpiroz F. , Pavia J. , Malagelada J. R.
Published: December 2017

Our aims were to investigate, first, the relationship between gastric tone (measured with a barostat) and gastric emptying (measured by radioscintigraphy with and without barostat) and, second, to determine the effect of a symptomatic intragastric pressure increment on gastric emptying. In 16 healthy subjects we quantified simultaneously gastric tone, emptying, and perception at two different intragastric pressure levels: 2 mmHg (low pressure) or 8 mmHg above intra-abdominal pressure (high pressure). At the low intragastric pressure level, ingestion of the meal induced an additional expansion in intragastric volume of 285 +/- 50 ml (P < 0.001), which reflected a gastric accommodative relaxation. At the high pressure level, intragastric volume expanded further, but neither low nor high pressure levels had significant effects on solid emptying. Interestingly, low and high pressure levels produced a similar, modest but significant, acceleration of liquid emptying (17 +/- 5 and 17 +/- 4%, respectively). However, although the low pressure was largely unperceived (score 1.0 +/- 0.5; NS), the high pressure level produced significant symptomatic perception (score 2.5 +/- 0.9; P < 0.05 vs. low pressure). We conclude that 1) gastric accommodation to a meal prevents volume-dependent wall tension increments and 2) the stomach adapts to increments in postcibal intragastric pressure by a limited acceleration of liquid emptying, but wall stress triggers a symptomatic alert mechanism.
Regulation of hepatic Na(+)-HCO3- cotransport and pH by membrane potential difference
Authors: Fitz J. G. , Lidofsky S. D. , Scharschmidt B. F.
Published: December 2017

Hepatocytes possess several mechanisms for membrane acid-base transport, which work in concert to maintain intracellular pH (pHi) in a narrow physiological range, despite metabolic processes that produce and consume substantial quantities of H+ and HCO3-.Na(+)-H+ and Cl(-)-HCO3- exchangers contribute to recovery from intracellular acidosis and alkalosis, respectively, but are largely inoperative at physiological values of pHi. Recent studies indicate that hepatocytes also possess a mechanism for coupled transport of Na+ and HCO3- across the basolateral membrane. This appears to be the dominant pathway for membrane acid-base transport operative under basal conditions, mediates influx of Na+ and HCO3-, and is an important contributor to recovery from intracellular acidosis. In this review, the properties of hepatic Na(+)-HCO3- cotransport are described with emphasis on its effects on pHi and Na+ homeostasis and on the possible role of membrane potential difference as a signal modulating the rate of HCO3- influx and pHi of hepatocytes through effects on this transporter.
Cholinergic regulation of guinea pig duodenal bicarbonate secretion
Authors: Odes H. S. , Muallem R. , Reimer R. , Beil W. , Schwenk M. , Sewing K. F.
Published: December 2017

Although it is well known that vagal stimulation induces duodenal HCO3- secretion, there is presently no information about the nature of the cholinoceptor and the intracellular signals involved. In a series of experiments performed in a guinea pig duodenal loop model in situ, intravenous carbachol, atropine, pirenzepine, and hexamethonium were used to determine the extent of cholinergic stimulation and the types of cholinoceptors. Carbachol (2 micrograms.kg-1.5 min-1) stimulated HCO3- secretion threefold, and atropine (0.1 mg.kg-1.5 min-1) and pirenzepine (1 mg.kg-1.5 min-1) both abolished this effect. In addition, hexamethonium (0.3 mg.kg-1.5 min-1) inhibited carbachol-stimulated duodenal HCO3- secretion. Vasoactive intestinal peptide (VIP, 5 micrograms.kg-1.5 min-1) stimulated duodenal HCO3- secretion, and this action was partly inhibited by atropine (0.1 mg.kg-1.5 min-1) but not by pirenzepine (1 mg.kg-1.5 min-1). [4Cl-D-Phe6,Leu17]VIP (3.3 mg/kg), an antagonist to VIP, reduced basal, VIP-stimulated, and carbachol-stimulated HCO3- secretion. To examine the role of Ca2+ in this process, Ca2+ ionophore A23187, verapamil, and nifedipine were employed. A23187 (5, 50, 500 micrograms.kg-1.5 min-1) stimulated duodenal HCO3- secretion, an effect blocked by the VIP antagonist, and modestly augmented the effect of carbachol. Verapamil (0.2 mg.kg-1.5 min-1) and nifedipine (1.7 mg.kg-1.5 min-1) stopped the effect of carbachol on duodenal HCO3- secretion. These results suggest, that in cholinergic regulation of duodenal HCO3- secretion, the M-cholinoceptor pathway, Ca2+, and VIP are involved.
PACAP is a stimulator of neurogenic contraction in guinea pig ileum
Authors: Katsoulis S. , Clemens A. , Schworer H. , Creutzfeldt W. , Schmidt W. E.
Published: December 2017

The myotropic effect of pituitary adenylate cyclase-activating polypeptide (PACAP), a novel brain-gut peptide with high sequence homology to vasoactive intestinal polypeptide (VIP), was studied in the isolated guinea pig ileum in vitro. PACAP contracts the guinea pig ileum significantly more potently and efficiently compared with VIP. PACAP-induced contraction was abolished by tetrodotoxin, dynorphin, and somatostatin, partially reduced by atropine, and not affected by ganglionic and adrenergic blockade. The atropine-resistant component was sensitive to spantide, to the induction of tachyphylaxis with substance P, and to omega-conotoxin. Ileal strips desensitized to PACAP did not respond to VIP, although they maintained their sensitivity to PACAP after desensitization to VIP. COOH-terminal-truncated derivatives of PACAP exhibited full biological activity, although some of them showed substantially reduced potency. Deletion of NH2-terminal amino acids abolished biological activity. PACAP produced a concentration-dependent increase in the release of [3H]acetylcholine from longitudinal muscle-myenteric plexus preparations preloaded with [3H]choline. This effect was Ca2+ dependent, tetrodotoxin sensitive, and resistant to hexamethonium and scopolamine. In contrast, PACAP inhibited release of acetylcholine evoked by field stimulation. In summary, PACAP-induced contraction of the guinea pig ileum is mediated via release of acetylcholine and substance P through interaction with PACAP-1 and VIP/PACAP-2 receptors. PACAP has to be added to the list of myotropic neuropeptides of the gastrointestinal tract.
Na(+)-K(+)-2Cl- cotransport and Cl- secretion evoked by heat-stable enterotoxin is microfilament dependent in T84 cells
Authors: Matthews J. B. , Awtrey C. S. , Thompson R. , Hung T. , Tally K. J. , Madara J. L.
Published: December 2017

We previously reported that adenosine 3',5'-cyclic monophosphate-mediated stimulation of Cl- secretion in the human intestinal epithelial cell line T84 is accompanied by significant remodeling of F-actin and that both the secretory and cytoskeletal responses may be inhibited by phalloidin derivatives, agents that polymerize actin and prevent dynamic reorganization of microfilaments. In contrast, the carbachol-elicited Cl- secretory response (Ca2+ mediated) was not attenuated by phalloidin (J. Clin. Invest. 87: 1903-1909, 1991). In the present study, we examine the effect of phalloidin on the Cl- secretory response elicited by the heat-stable enterotoxin of Escherichia coli (STa), which induces elevations in intracellular guanosine 3',5'-cyclic monophosphate. We find that apical administration of 1 microM STa results in a regionally restricted redistribution of F-actin confined to the basal pole of the cells. In monolayers pretreated with phalloidin, the Cl- secretory response to STa was inhibited by > 60%. Sequential treatment of phalloidin-loaded monolayers with STa followed by carbachol resulted in a synergistic secretory response that was not different from control (unloaded) monolayers. Examination of efflux/uptake through specific membrane transport pathways involved in STa-stimulated Cl- secretion indicated normal activation of apical Cl- and basolateral K+ channels under phalloidin-loaded conditions. The ability of STa-treated monolayers to pump Na+ in an absorptive direction was also unaffected by phalloidin. der phalloidin-loaded conditions, STa-stimulated Na(+)-K(+)-2Cl- cotransporter activity was reduced by approximately 60%, sufficient to account for the observed inhibition of net Cl- secretory response.(ABSTRACT TRUNCATED AT 250 WORDS)
Endogenous somatostatin inhibits histamine release from canine gastric mucosal cells in primary culture
Authors: Chuang C. N. , Tanner M. , Lloyd K. C. , Wong H. , Soll A. H.
Published: December 2017

The effects of somatostatin on histamine release were studied using primary cultures of canine oxyntic mucosal cells in which mast cell content was reduced by density gradient. The S6 monoclonal antibody to somatostatin, but not control antibodies, enhanced gastrin-stimulated histamine release. In the presence of S6, the somatostatin analogue SMS-201-995 (10(-7) M) inhibited gastrin-stimulated histamine release by 95%. The dose producing 50% inhibition for this inhibition was approximately 3 x 10(-10) M and was completely reversed by pertussis toxin treatment. In contrast to somatostatin, epinephrine failed to inhibit this gastrin stimulation. However, the lectin concanavalin A (ConA) also stimulated histamine release from these cultures, and this response was inhibited by epinephrine but not by somatostatin. Thus somatostatin selectively inhibited the gastrin-responsive histamine pool, which presumably is stored in oxyntic mucosal endocrine cells. In contrast, epinephrine selectively inhibits histamine release from the ConA-sensitive pool, which is presumably stored in mast cells. Furthermore, enhancement of gastrin-stimulated histamine release by immunoneutralization of somatostatin indicates an important role for endogenous somatostatin as a paracrine inhibitor of non-mast cell histamine release.
Evaluation and validation of microsphere technique for determination of pancreatic blood flow
Authors: Harringer W. , Fernandez-del Castillo C. , Rattner D. W. , Guerrero J. L. , Warshaw A. L. , Vlahakes G. J.
Published: December 2017

The purpose of this study was to evaluate the radiolabeled microsphere technique for pancreatic blood flow measurements. Using a canine model with an isolated pancreatic circulation, we assessed the shunting of 11- and 15-microns-diam microspheres in the pancreas, correlated pancreatic blood flow measurements obtained with the microsphere technique with those made with an ultrasonic flow probe, and determined the effects of high doses of microspheres on pancreatic blood flow and its measurement. Microspheres of 11 microns demonstrate significant shunting through the pancreatic microcirculation with underestimation of pancreatic blood flow of approximately 10% compared with results obtained with 15-microns microspheres. There is a close linear relationship between flow results obtained with 15-microns microspheres and with an ultrasonic flow probe for both the resting (r = 0.85) and the secretin-stimulated pancreas (r = 0.97). Left atrial injections of very large doses of 15-microns microspheres (50 x 10(6)) caused an acute transient reduction of pancreatic blood flow (to 39% of baseline flow) with a return to baseline values within 2 min. The accuracy of flow results and absence of physiological changes after repeated injections support the use of 15-microns microspheres for pancreatic blood flow measurements.
Identification of cholinergic neurons in enteric nervous system by antibodies against choline acetyltransferase
Authors: Schemann M. , Sann H. , Schaaf C. , Mader M.
Published: December 2017

Several different monoclonal and polyclonal antibodies to choline acetyltransferase (ChAT) were screened to identify effective antibodies for immunocytochemical marking of cholinergic neurons in the enteric nervous system. Excellent immunohistochemical results were obtained with two of the antibodies in the myenteric plexus of the guinea pig stomach and small intestine. One was a mouse monoclonal antibody designated B3.9B3, and the second was a rabbit polyclonal antibody referred to as Peptide 3. Both antibodies clearly stained neuronal cell bodies as well as nerve fibers to the muscle layers and fibers encircling stained and unstained cell bodies. Cell counts indicated that approximately 64% (21.0 +/- 8.6 cells/ganglion) of gastric myenteric neurons are ChAT positive. Pelvic ganglia and the inferior mesenteric ganglia were examined as controls. Strong labeling of the majority of neurons was found in the pelvic ganglia, whereas few immunoreactive cells were apparent in the predominantly noradrenergic inferior mesenteric ganglion. Lack of effective antibodies to enteric neuronal ChAT has hampered progress in the study of the neurophysiology of cholinergic neurons in the digestive tract. Application of the B3.9B3 and Peptide 3 antibodies now promises to facilitate investigation of this important subset of enteric neurons.
Nonparallel secretion of pepsinogen and acid by gastric oxyntopeptic cells of the toad (Bufo marinus)
Authors: Ruiz M. C. , Acosta A. , Abad M. J. , Michelangeli F.
Published: December 2017

Pepsinogen and HCl secretion in the amphibian stomach are performed by a single cell type, the oxyntopeptic cell. These functions were studied in gastric mucosae of toads (Bufo marinus) mounted in Ussing-type chambers. HCl and peptic activity of luminal fluid were measured by titration and proteolysis of albumin, respectively. Distribution of pepsinogen in the gastric mucosa was heterogeneous, activity being highest in the proximal part of the stomach. Zymogen granules in the oxyntopeptic cell were more abundant in the deeper cells of the glands and in the fundus. On stimulation, the granules were released into the lumen of the glands by exocytosis. Histamine, forskolin, or carbachol alone each induced an increase in HCl and pepsinogen secretion. Carbachol after maximal histamine or forskolin stimulation produced an extra increase in both secretions that was greater for pepsinogen response. Similarly, joint addition of carbachol and histamine was more potent than histamine alone for both parameters; however, the effect was greater on pepsinogen release. Pretreatment with cimetidine blocked HCl and pepsinogen responses to carbachol but did not affect responses to forskolin. Addition of omeprazole to forskolin-stimulated mucosae uncoupled the two secretions, inducing a total inhibition of HCl secretion with a slight reduction in pepsinogen secretion. Thus pepsinogen release, similar to HCl secretion, is sensitive to cAMP and Ca(2+)-dependent secretagogues. However, the action of Ca2+ would require the previous elevation of cAMP induced by the different secretagogues. In such a case, the increase in intracellular Ca2+ would result in a nonparallel activation of the two secretions.
Duodenal mucosal alkaline secretion, permeability, and blood flow
Authors: Nylander O. , Hallgren A. , Holm L.
Published: December 2017

The relationship between duodenal mucosal alkaline secretion, permeability, and blood flow was examined in anesthetized rats. Duodenum was perfused with saline, and rate of luminal alkalinization (LA), mucosal permeability (clearance of 51Cr-EDTA from blood to lumen), effluent volume, mean arterial blood pressure (MABP), and blood flow (laser-Doppler flowmetry) were determined. Infusion of vasoactive intestinal polypeptide (VIP, 13.5 micrograms.kg-1 x h-1 i.v.) increased LA and fluid secretion but decreased MABP and mucosal permeability. The concentration of base in the secreted fluid was 45 mM. Systemic infusion of VIP (2.5 micrograms.kg-1 x h-1) increased LA and fluid secretion; the HCO3- concentration in secreted fluid was 86 mM. The lower VIP dose affected neither blood flow nor mucosal permeability. Both intravenous (10 mg/kg + 3 mg.kg-1 x h-1) and intraluminal (3 x 10(-3) M) N omega-nitro-L-arginine (L-NNA) increased LA and effluent volume; the HCO3- concentration in the secreted fluid was 38 and 44 mM, respectively. Intravenous, but not intraluminal, L-NNA increased mucosal permeability and decreased blood flow. Reduction of arterial blood pressure by blood withdrawal or by injection of prazosin (50 micrograms/kg i.v.) or hexamethonium (20 mg/kg i.v.) decreased LA and mucosal permeability. Prazosin decreased blood flow, whereas hexamethonium slightly increased blood flow. We conclude that NO may be an inhibitory regulator of LA and that both L-NNA and VIP increase LA via stimulation of active HCO3- transport. VIP probably increases HCO3- and fluid secretion by two separate ion transport mechanisms. No causal relationship exists between LA and blood flow, between LA and mucosal permeability, or between mucosal permeability and blood flow. A positive linear correlation exists between MABP and mucosal permeability, suggesting that marked changes of MABP may influence permeation of small water-soluble solutes across duodenal mucosa.
Interaction between signal transduction pathways contributing to gallbladder tonic contraction
Authors: Yu P. , Harnett K. M. , Biancani P. , De Petris G. , Behar J.
Published: December 2017

Muscle strips were used to study the mechanisms that generate cat gallbladder tone. Strontium substitution for calcium and the protein kinase C (PKC) inhibitor H-7 abolished the tone, whereas the calmodulin antagonist W-7 had no effect, suggesting that tone depends on intracellular calcium release and the PKC pathway. Basal levels of diacylglycerol (DAG) and inositol-1,4,5-trisphosphate (IP3) were higher in gallbladder muscle than in esophageal muscle, which does not maintain tone. These data suggest that IP3 might interact with DAG to activate PKC during tonic contraction. This interaction was demonstrated in single cells in which a low dose of IP3 potentiated DAG and the potentiation was blocked by H-7. Furthermore, low doses of IP3 induced contraction, which was blocked by H-7 and unaffected by the calmodulin antagonist CGS-9343B; high doses of IP3 were unaffected by H-7 but were blocked by CGS-9343B; DAG-induced contraction was blocked by activated calmodulin. We conclude that 1) the synergistic action of DAG and IP3-calcium release, which further activates PKC, might be responsible for gallbladder tone and 2) activated calmodulin appears to inhibit the effect of PKC.
Murine intestinal disaccharidases: identification of structural variants of sucrase-isomaltase complex
Authors: Quezada-Calvillo R. , Markowitz A. J. , Traber P. G. , Underdown B. J.
Published: December 2017

This study was directed to determine the extent of variability in structure or expression of intestinal disaccharidase [gamma-glucoamylase (gamma-GA), sucrase-isomaltase (SI), and lactase] between different strains of mice. Reduced levels of sucrase activity (approximately 20 U/g of protein) were observed in three strains of mice belonging to the CBA/Ca lineage. Four other strains of mice analyzed exhibited higher levels of sucrase activity (approximately 50 U/g of protein). Decreased levels of sucrase in CBA/Ca mice were not associated with decreased levels of activity associated with the isomaltase subunit or with decreased levels of SI mRNA expression. High-performance liquid chromatographic gel filtration, heat inactivation, and kinetic analysis indicated that the differences between strains in sucrase activity might be attributed to structural differences in the sucrase subunit of the SI complex, thus rendering it more susceptible to cleavage and inactivation. However, no differences in kinetic properties of the sucrase subunit were observed between strains. Murine gamma-GA was found to account for a greater proportion of maltase activity (approximately 70%) than that observed in other species (i.e., approximately 20%). In addition, CBA/Ca mice were found to be deficient in intestinal maltase activity (approximately 60 U/g) compared with the other strains studied (approximately 300 U/g).
Neuroimmune signaling in regulation of intestinal ion transport
Authors: Cooke H. J.
Published: December 2017

Complex interactions between the enteric nervous system, the immune system, and the epithelium govern the transport rates of salt and water across the intestinal lining. Luminal antigens or bacterial products are detected by the immune system, which triggers a cascade of events associated with the release of inflammatory mediators. These mediators, by lowering the response threshold for transmission in some neural circuits, augment ongoing neural reflexes that promote secretion. Associated with these effects is a dampening of responses in other neural circuits innervating the mucosal effectors. Selective excitation and inhibition of the neural reflex circuitry coupled with direct actions of inflammatory mediators on epithelial cells result in stereotypical motility and secretory patterns that are characterized by strong muscular contractions, copious secretion, and diarrhea.
Adrenal secretion of BAM-22P, a potent opioid peptide, is enhanced in rats with acute cholestasis
Authors: Swain M. G. , MacArthur L. , Vergalla J. , Jones E. A.
Published: December 2017

The adrenal gland is known to produce and release endogenous opioids into the circulation. Bovine adrenal medulla docosapeptide (BAM-22P) is a potent opioid agonist, derived from the proenkephalin A gene, which is present in the adrenal medulla. This study was undertaken to determine whether BAM-22P is released into plasma during acute cholestatic liver injury, which increases plasma total opioid activity. Acute cholestasis was induced by bile duct ligation or administration of the hepatotoxin alpha-naphthylisothiocyanate. Plasma levels of BAM-22P were determined by a sensitive radioimmunoassay, and the specificity of the assay was confirmed using high-performance liquid chromatography. Plasma BAM-22P levels was cholestatic rats were significantly higher than those in control rats. This increase in plasma BAM-22P levels was completely prevented by adrenalectomy. Adrenal steady-state levels of proenkephalin mRNA, as determined by Northern blot hybridization analyses, were also increased significantly in cholestatic rats. These increases in proenkephalin mRNA levels were not paralleled by changes in adrenal BAM-22P peptide levels, which were similar in cholestatic rats and their respective controls. Similar levels of proenkephalin mRNA expression were observed in innervated and denervated adrenal glands from cholestatic rats, suggesting that the increase in adrenal proenkephalin mRNA levels in acute cholestasis is not due to splanchnic nerve activation. Thus acute cholestasis in the rat is associated with adrenal secretion and accumulation in plasma of the highly potent opioid peptide BAM-22P and an augmentation of adrenal proenkephalin mRNA expression. The increase in plasma BAM-22P levels may contribute substantially to the increase in total circulating opioid activity documented in cholestatic rats.
Relaxation oscillator and core conductor models are needed for understanding of GI electrical activities
Authors: Daniel E. E. , Bardakjian B. L. , Huizinga J. D. , Diamant N. E.
Published: December 2017

This review examines the applicability of modeling of intestinal electrical activities (slow waves or pacesetter potentials) by coupled relaxation oscillator models, in comparison to a “multidimensional model” based on core conductor theory. We briefly review the relaxation oscillator model and correct some misunderstandings. We point out that new insights about the role of networks of interstitial cells of Cajal in intestinal pacemaking require reconsideration of the mechanisms producing oscillations, the coupling between oscillators, and how the oscillator network is coupled to the driven cells. Recent advances in relaxation oscillator models allow the production of pacemaking pacemaking activity, which can be selectively varied as to waveform, frequency, and occurrence of silent periods. Core conductor models do not produce pacemaking activity or permit this flexibility. We point out that many of the criticisms leveled against relaxation oscillator models relate to studies made in simplified in vitro systems constrained by extensive dissection. Such systems do not adequately reflect the in vivo systems. We conclude that a full understanding of control of electrical (and mechanical) events in the gastrointestinal tract requires that better understanding of relaxation oscillator models growing out of recent research be combined with improved applications of core conductor theory to multidimensional models.
Analyses of normal and abnormal esophageal transport using computer simulations
Authors: Li M. , Brasseur J. G. , Dodds W. J.
Published: December 2017

Mathematical modeling and computer simulations are combined with concurrent manometric and videofluoroscopic data to analyze the contractile behavior of the esophageal wall during normal and abnormal esophageal bolus transport. The study focuses on axial variations in intraluminal pressure in relationship to deformations of the esophageal wall during the transport process. Four case studies of esophageal bolus transport described by Kahrilas et al. (Gastroenterology 94: 73-80, 1988), one normal and three abnormal, are analyzed in detail by capturing the major elements of both the videofluoroscopic and concurrent manometric data in the mathematical model. In all cases a strong correlation between the deformations of the luminal wall and the axial variations of intraluminal pressure is observed. Simulation of normal bolus transport shows that, whereas only gentle variations in intrabolus pressure occur in the main body of the bolus due to weak frictional forces there, large frictional forces force a rapid rise in pressure near the bolus tail induced by circular muscle squeeze. Of particular interest is the analysis of incomplete clearance of bolus fluid in the aortic arch region. The only physically correct model consistent both with the videofluoroscopic and the manometric data implies the existence of two separate contraction waves, one above and one below the transition zone.(ABSTRACT TRUNCATED AT 250 WORDS)
Neural control of small intestinal giant migrating contractions
Authors: Otterson M. F. , Sarna S. K.
Published: December 2017

We investigated the neural mechanisms of control of giant migrating contractions (GMCs) in five conscious dogs. After control recordings, a Thiry-Vella loop was prepared from the middle segment, and the remaining two segments were reanastomosed. GMCs were stimulated by intravenous administration of fentanyl and erythromycin lactobionate, oral administration of loperamide and erythromycin stearate, and gastric or intraluminal administration of cider vinegar in the loop. In the intact state, the agents stimulated GMCs in all three segments, and they propagated uninterruptedly from the point of their origin to the terminal ileum. The propagation velocity of GMCs increased, whereas that of migrating motor complexes (MMCs) decreased distally. After Thiry-Vella loop formation, the agents stimulated GMCs independently in the three segments, and they propagated only to the end of the segment in which they started. In the intact small intestine, the GMCs produced ascending and descending inhibition of spontaneous phase II contractions but did not interrupt the caudad propagation of the ongoing MMC. After Thiry-Vella loop formation, the ascending inhibition was unaltered, but the descending inhibition occurred only in the segment containing the GMC. We conclude that the propagation of GMCs in the small intestine is controlled by the enteric nerves. The extrinsic nerves control the ascending inhibition produced by GMCs, whereas the enteric nerves control the descending inhibition.