bluuebunny/crossref_metadata_2025 huggingface dataset:
Inhibitory effect of PYY on vagally stimulated acid secretion is mediated predominantly by Y1 receptors
Authors: Lloyd K. C. , Grandt D. , Aurang K. , Eysselein V. E. , Schimiczek M. , Reeve J. R.
Published: December 2017

Two molecular forms of peptide YY (PYY), PYY-(1--36) and PYY-(3--36), are abundant in rabbit intestine and blood. We have previously shown that PYY-(1--36) (PYYI) activates equipotently Y1 and Y2 receptors and PYY-(3--36) (PYY II) is a highly selective agonist for Y2 receptors. In the present study, we examined the effect of exogenous infusion of PYY on vagally stimulated gastric acid secretion in awake rabbits with chronic gastric fistula. To determine the specific PYY receptor(s) that mediates this effect, we used a highly selective Y1 agonist, Pro34-PYY, a synthetic PYY, and a Y2-selective agonist, PYY II. Vagal stimulation of acid secretion was elicited by an intravenous bolus injection of insulin (0.125 U/kg) 30 min after beginning a 180-min intravenous infusion of either PYY I, PYY II, or [Pro34]-PYY after a 50 micrograms/kg i.v. bolus of atropine followed immediately by a 500 micrograms/kg sc injection. During infusion of 200 pmol.kg 1.h-1 PYY I, acid output was significantly inhibited to 45 +/- 13% of maximum acid output 60 min after injection of insulin. Similarly, acid output during infusion of 200 pmol.kg-1.h-1 [Pro34]-PYY was significantly inhibited to 52 +/- 12% of maximum. In contrast, acid output during infusion of 200 pmol.kg-1.h-1 of PYY II was not significantly inhibited (101 +/- 18% of maximum). Infusion of double the dose (400 pmol.kg-1.h-1) of PYY II resulted in acid inhibition (51 = 15% of maximum), whereas infusion of the same dose did not significantly enhance acid inhibition by infusion of either PYY I or [Pro34]-PYY (28 +/- 11 and 42 +/- 15% of maximum). These results indicate that PYY, acting predominantly at Y1 receptors, is a potent inhibitor of vagally stimulated acid secretion in adult rabbits.
Early glycogenolysis and late glycogenesis in human liver after intravenous administration of galactose
Authors: Fried R. , Beckmann N. , Keller U. , Ninnis R. , Stalder G. , Seelig J.
Published: December 2017

Galactose is incorporated by a different metabolic pathway than glucose. Its contribution to glycogen synthesis has not been studied in humans. We administered galactose (0.5 g/kg iv) to overnight-fasted normal human volunteers and examined its effects on hepatic glycogen synthesis and hepatic glucose output (HGO). Hepatic glycogenesis was assessed noninvasively, determining glycogen concentration by 13C magnetic resonance spectroscopy (MRS) and liver volume by magnetic resonance imaging. HGO was determined by [6,6-2H2]glucose and gluconeogenesis calculated by adding the amount of hepatic glycogenesis to the HGO. After galactose administration, liver glycogen concentration (baseline 254 +/- 11 mmol/l) decreased in the first 45 min to 207 +/- 15 mmol/l (P < 0.05) and increased thereafter to 313 +/- 7 mmol/l (P < 0.01). Net hepatic glycogenesis was 101 +/- 12 mmol over 150 min. HGO (baseline 14.3 +/- 1.9 mumol.kg-1.min-1) increased threefold in the first 15 min and then returned to baseline. The average rate of gluconeogenesis was 12.3 mumol.kg-1.min-1. Intravenous galactose leads to an increase in hepatic glycogen and hepatic glucose output in normal humans. Competitive inhibition of UDP-glucose pyrophosphorylase by UDP-galactose could explain the apparent glycogenolysis observed early after galactose administration. 13C MRS in combination with a stable isotope tracer is a noninvasive and safe method to study hepatic carbohydrate metabolism in humans.
Salivary EGF regulates eosinophil-derived TGF-alpha expression in hamster oral wounds
Authors: Yang J. , Tyler L. W. , Donoff R. B. , Song B. , Torio A. J. , Gallagher G. T. , Tsuji T. , Elovic A. , McBride J. , Yung C. M. , Galli S. J. , Weller P. F. , Wong D. T.
Published: December 2017

Using hamster as an oral wound healing model, we examined eosinophils and their expression of transforming growth factor-alpha (TGF-alpha) and transforming growth factor-beta 1 (TGF-beta 1). Oral wounds healed approximately two times faster than their cutaneous counterparts. Eosinophils infiltrated prominently into oral wounds; however, unlike the dual expression of TGF-alpha and TGF-beta 1 in skin wounds, oral wound-associated eosinophils expressed TGF-beta 1, but not TGF-alpha. Because saliva is present in oral environments and contains epidermal growth factor (EGF) and TGF-alpha, sialoadenectomy was performed in this model to determine whether the lack of TGF-alpha expression by eosinophils in oral wounds is due to the presence of salivary EGF and/or TGF-alpha. We found that eosinophils in sialoadenectomized hamsters did express TGF-alpha during oral wound healing but that such expression was suppressed when EGF was added to their drinking water. Taken together, our findings suggest that eosinophil-derived TGF-alpha and salivary TGF-alpha/ EGF may have complementary roles in contributing to TGF-alpha in oral wound healing.
Glycine-extended gastrin potentiates gastrin-stimulated gastric acid secretion in rats
Authors: Higashide S. , Gomez G. , Greeley G. H. , Townsend C. M. , Thompson J. C.
Published: December 2017

The purpose of this study was to examine whether an intermediate form of amidated gastrin, glycine-extended gastrin (Gly-G), can stimulate gastric acid secretion in conscious rats prepared with gastric fistulas. Intravenous administration of Gly-G (20 nmol.kg-1.h-1) alone for 2 h did not stimulate gastric acid secretion; however, administration of Gly-G (20 nmol.kg-1.h-1) in combination with a bolus administration of gastrin (9.5 nmol/kg) potentiated acid secretion significantly. Gastric acid secretion in response to gastrin alone and gastrin plus Gly-G (2 nmol.kg-1.h-1) was 109.1 +/- 21.6 and 170.1 +/- 27.7 mueq.kg-1.h-1, respectively (P < 0.05). Gastric acid secretion in response to gastrin alone and gastrin plus Gly-G (20 nmol.kg-1.h-1) was 84.8 +/- 17.5 and 164.1 +/- 29.3 mueq.kg-1.h-1, respectively (P < 0.05). Intravenous administration of Gly-G (20 nmol.kg-1.h-1) failed to increase histamine (1 mg/kg)-stimulated acid output. These results demonstrate that Gly-G can selectively potentiate the stimulatory effect of gastrin on acid secretion in rats and that the unprocessed form of gastrin, Gly-G, can exert a biological effect in the stomach.
CFTR is required for cAMP inhibition of intestinal Na+ absorption in a cystic fibrosis mouse model
Authors: Clarke L. L. , Harline M. C.
Published: December 2017

Acute adenosine 3',5'-cyclic monophosphate (cAMP) stimulation of intestinal epithelium induces net transepithelial Cl- secretion and inhibits neutral coupled NaCl absorption. To investigate the role that the cystic fibrosis transmembrane conductance regulator (CFTR) plays in these events, we measured bioelectric changes and radioisotopic NaCl flux across jejunal tissues from gene-targeted cftr "knockout" mice [cftr(-/-) homozygotes] and their normal littermates [cftr(+/+) homozygotes and cftr(+/-) heterozygotes]. Before stimulation, the short-circuit current (Isc, an index of Cl- secretion) of the cftr(-/-) jejunum was essentially zero and significantly less than in the cftr(+/+) or cftr(+/-) intestine. Acute cAMP stimulation had little effect on the bioelectric parameters of the cftr(-/-) intestine but induced a marked increase of Isc and decrease of total tissue conductance in both the cftr(+/+) and cftr(+/-) intestine. Differences in the magnitude of the cAMP-induced Isc between the cftr(+/+) and cftr(+/-) intestine were only observed when the cell-to-lumen anion concentration gradient was maximized by removal of permeant anions from the luminal bath. Radioisotope flux measurements revealed that Na+ and Cl- were absorbed equally across the cftr(-/-) jejunum under basal conditions. In cftr(+/+) and cftr(+/-) intestine, Na+ was absorbed at a similar rate, but net Cl- absorption was reduced from that in cftr(-/-) intestine by an amount approximating the Isc. Acute cAMP stimulation of the cftr(+/+) and cftr(+/-) intestine abolished net NaCl absorption and induced electrogenic Cl- secretion. In contrast, net NaCl absorption was unchanged from the preceding flux period in the cftr(-/-) jejunum. The data suggest that CFTR not only mediates cAMP-induced transepithelial Cl- secretion but is also required for cAMP inhibition of neutral NaCl absorption in the intestine.
Electrophysiological effects of nitric oxide in mouse superior mesenteric ganglion
Authors: Mazet B. , Miller S. M. , Szurszewski J. H.
Published: December 2017

Effects of nitric oxide (NO) generated from sodium nitroprusside (SNP) on neurons of mouse superior mesenteric ganglion (SMG) were studied in vitro using intracellular recording techniques. SNP solutions caused a membrane hyperpolarization in the majority (64%) of the neurons tested or a hyperpolarization followed by a depolarization in 8% of the neurons tested. The SNP-induced hyperpolarization persisted in a low-Ca2+ high-Mg2+ solution, indicating a direct effect of NO on the postsynaptic membrane. The hyperpolarizing effect of SNP was reduced or abolished by oxyhemoglobin. Electrical stimulation of the colonic nerves evoked a late slow excitatory postsynaptic potential (late sEPSP) in a population of neurons in normal Krebs solution. The amplitude of the late sEPSP was significantly enhanced in the presence of NG-nitroL-arginine, a NO synthase inhibitor. The results, particularly those observed with the NO synthase inhibitor, suggest that endogenous NO was released in the mouse SMG by repetitive nerve stimulation and that it modulated slow synaptic transmission, presumably by a direct action on ganglionic neurons.
Glycine minimizes reperfusion injury in a low-flow, reflow liver perfusion model in the rat
Authors: Zhong Z. , Jones S. , Thurman R. G.
Published: December 2017

This study investigated the effects of glycine on reperfusion injury in a low-flow, reflow liver perfusion model. With this protocol, livers were perfused at low flow rates of approximately 1 ml.g-1. min-1 for 75 min, which caused cells in pericentral regions of the liver lobule to become anoxic because of insufficient delivery of oxygen. When normal flow rates (approximately 4 ml.g-1.min-1) were restored for 40 min, an oxygen-dependent reperfusion injury occurred. Upon reflow, lactate dehydrogenase (LDH), a cytosolic enzyme, and malondialdehyde (MDA), an end product of lipid peroxidation, were released into the effluent perfusate. LDH increased from basal levels of approximately 1-35 IU.g-1.h-1 in livers from control rats. Glycine (0.06-2.00 mM) minimized enzyme release in a dose-dependent manner (half-maximal decrease = 133 microM), with maximal values only reaching 5 IU.g-1.h-1 when glycine was increased to 2 mM. Reflow for 40 min after 75 min of low-flow hypoxia caused death in approximately 30% of previously anoxic parenchymal cells in pericentral regions; however, infusion of glycine (2 mM) decreased cell death to less than 10%. Strychnine (1 mM), which was found to mimic the cytoprotective effect of glycine in proximal renal tubules, also reduced LDH release to 11 IU.g-1.h-1 in this study. Bile was released at rates of approximately 42 microliters.g-1.h-1 in livers from control rats, but values were not altered significantly by glycine. Maximal MDA production during reperfusion decreased by 35% with 0.6 mM of glycine. Trypan blue distribution time, an indicator of hepatic microcirculation, was reduced significantly by glycine at 5 and 40 min after reflow, but changes were about twofold greater at later time points compared with earlier ones (half-maximal decrease = 225 microM). Time for oxygen to reach steady state upon reflow was reduced by glycine in a dose-dependent manner, and the rates of entry and exit of a dye confined to vascular space (fluorescein dextran) were increased two- to threefold by glycine, respectively. Taken together, these data indicate that a reperfusion injury that occurs in previously hypoxic pericentral regions of the liver upon reintroduction of oxygen is minimized by glycine, possibly by action on a glycine-sensitive anion channel to improve microcirculation during the reperfusion period.
Microvascular dysfunction induced by nonsteroidal anti-inflammatory drugs: role of leukocytes
Authors: Kurose I. , Wolf R. , Miyasaka M. , Anderson D. C. , Granger D. N.
Published: December 2017

The objectives of this study were to determine whether 1) the leukocyte-endothelial cell adhesion observed in venules exposed to nonsteroidal anti-inflammatory drugs (NSAIDs) is accompanied by enhanced albumin extravasation, and 2) leukocytes mediate this endothelial cell barrier dysfunction. Intravital video microscopy was used to monitor leukocyte-endothelial cell adhesion and the leakage of fluorescein isothiocyanate-labeled albumin in rat mesenteric venules exposed to either indomethacin or aspirin. Both NSAIDs induced the recruitment of adherent and emigrated leukocytes with temporally related increases in albumin leakage. Agents that effectively decreased or prevented the NSAID-induced leukocyte adherence/emigration (leukotriene B4 receptor antagonist or adhesion molecule-specific monoclonal antibodies) also blocked the corresponding albumin leakage response. These findings indicate that adherent and/or emigrating leukocytes mediate the early endothelial cell barrier dysfunction elicited by NSAIDs.
cGMP stimulates bile acid-independent bile formation and biliary bicarbonate excretion
Authors: Myers N. C. , Grune S. , Jameson H. L. , Sawkat-Anwer M.
Published: December 2017

The effect of guanosine 3',5'-cyclic monophosphate (cGMP) on hepatic bile formation was studied in isolated perfused rat livers and rat hepatocytes. Studies in isolated perfused rat livers showed that infusion of 8-bromoguanosine 3',5'-cyclic monophosphate (8-BrcGMP, 3 micromol/min or 100 microM) 1) increased bile flow without affecting biliary excretion of simultaneously infused taurocholate, 2) increased biliary concentration and excretion of HCO3(-) but did not affect biliary excretion of glutathione, and 3) increased net perfusate H+ efflux without affecting hepatic O2 uptake. Studies in isolated rat hepatocytes showed that 1) 8-BrcGMP increased intracellular pH in the presence (but not in the absence) of extracellular HCO-3, and effect inhibited by 4,4' -diisothiocyanostilbene-2,2'-disulfonic acid and Na+ replacement, 2) 8-BrcGMP did not affect taurocholate uptake and intracellular [Ca2+], and 3) bile acids, like ursodeoxycholate and cholate, did not increase cellular cGMP. Taken together, these results indicate that cGMP stimulates bile acid-independent bile formation, in part by stimulating biliary HCO3- excretion. cGMP may increase HCO3- excretion by stimulating sinusoidal Na+ - HCO3- cotransport, but not Na+/H+ exchange. cGMP, unlike adenosine 3',5'-cyclic monophosphate, may not regulate hepatic taurocholate transport, and bile acid-induced HCO3- rich choleresis may not be mediated via cGMP.
Toxic dilatation of colon in a rat model of colitis is linked to an inducible form of nitric oxide synthase
Authors: Mourelle M. , Vilaseca J. , Guarner F. , Salas A. , Malagelada J. R.
Published: December 2017

The contribution of nitric oxide (NO) to the altered colonic contractility of acute colitis was investigated in the 2,4,6-trinitroben-zenesulfonic acid model. NO synthase was measured in colonic tissue; the effects of NO synthase inhibition on colonic contractility were studied in vitro and in vivo. Inducible NO synthase was not detected in normal colons, whereas inflamed colons showed high activity. Acute inflammation was associated with enlarged colonic perimeter. NO synthase inhibitors or selective inhibitors of the inducible enzyme prevented colonic dilatation. In vitro, contractile responses to KCl were lower in muscle from colitic than control rats. After NO synthase inhibition, however, no difference was observed between colitic and control muscle contractility. In vivo, intracolonic pressure was lower in colitic than in control rats. Selective inhibition of inducible NO synthase increased intracolonic pressure in colitic but not in control rats. In conclusion, NO generation by inducible enzymes impairs smooth muscle contractility in colitis and may be involved in the pathogenesis of toxic dilatation of the colon.
Frequency of gastric pacesetter potential depends on volume and site of distension
Authors: Lin H. C. , Zhao X. T. , Chung B. , GU Y. G. , Elashoff J. D.
Published: December 2017

Little is known about the response of the frequency of gastric pacesetter potential (PP) to luminal distension. When volume distension occurs as a result of a meal, gastric emptying may play an important role, since the site of distension shifts as the meal is displaced from the stomach to the small bowel. In this study, using does equipped with duodenal fistulas and serosal electrodes on the antrum, we compared the frequency of gastric PP during the course of gastric emptying while isolating the volume distension to either the stomach or the small bowel. We found that 1) the frequency of gastric PP decreased linearly with greater initial meal volume when volume distension was isolated to either the stomach -P<0.05, analysis of variance (ANOVA)- or small bowel (P<0.01, ANOVA), and 2) the frequency of gastric PP decreased linearly with increased volume remaining in the stomach or increased volume entering the small intestine. We conclude that the frequency of gastric PP depends on the volume and site of distension.
Chronic hypoxia and glutathione-dependent detoxication in rat small intestine
Authors: LeGrand T. S. , Aw T. Y.
Published: December 2017

It has previously been found that chronic O2 deficiency decreases activity of the enzymes of the glutathione (GSH) redox system in the liver. To study the effects of O2 deficiency on intestinal detoxication capacity, pair-fed (16 g food/day) Sprague-Dawley rats were exposed to air (20.9% O2; n = 4) or 10% O2 (n = 4) for 10 days. Animals were killed, and intestinal mucosal homogenate (20% wt/vol) was obtained and assayed for activities of glucose-6-phosphate dehydrogenase (G6PD), GSH peroxidase (GSHPx), GSH disulfide reductase (GSSGRd), and gamma-glutamyl cysteine synthetase (gamma-GCS). Hypoxia decreases activities of GSHPx, GSSGRd, and gamma-GCS by approximately 50%, which suggests compromised detoxication. A proximal-to-distal reduction in enzymatic capacity indicates impairment of detoxication may be more pronounced in the distal intestine. G6PD, a key enzyme in NADPH production, remains unchanged. Urinary malondialdehyde was also monitored. Hypoxic rats exhibited a threefold increase in thiobarbituric acid-reactive substance, consistent with a generalized oxidative stress in these animals. Taken together, the results indicate that chronic hypoxia promotes tissue oxidative stress and impairs the ability of the enterocyte to metabolize ingested oxidants.
Potassium and chloride currents in rat gastric enterochromaffin-like cells
Authors: Loo Donald D. F. , Sachs George , Prinz Christian
Published: December 2017

The gastric enterochromaffin-like (ECL) cell se cretes histamine in response to secretagogues (gastrin, acetylcholine) by calcium signaling-dependent exocytosis of intracellular vacuoles containing the hormone. ECL cells were isolated from rat fundic gastric mucosa by elutriation and density-gradient centrifugation. Currents across the plasma membrane were measured using whole cell patch-clamp methods. These cells had a low conductance of 0.5 nS and resting potential of -50 mV Depolarization activated a K+ current that was blocked by Ba2+. Steady-state current in absence of K+ was due to Cl- because of the magnitude of the reversal potential and the effects of Cl- removal. Stimulation of secretion by gastrin, cholecystokinin octapeptide (CCK-8), and the phorbol ester 12-O-tetradecanoylphorbol 13-acetate activated the Cl- conductance with a time course similar to that of histamine release. Therefore the ECL cell maintains a high resting potential, largely due to K+ currents, and stimulation of secretion activates a Cl- current, perhaps deriving from the membrane of the secretory granule that fuses with the plasma membrane. The depolarization that ensues may activate the K+ current to maintain the membrane potential during exocytosis.

exocytosis; acid secretion

Submitted on July 31, 1995

Accepted on October 2, 1995
Leukocyte stasis in hepatic sinusoids
Authors: Vollmar B. , Richter S. , Menger M. D.
Published: December 2017

There is ongoing debate on the significance of capillary leukostasis for the manifestation of ischemia-reperfusion (I/R)-induced capillary “no-reflow”. Using intravital fluorescence microscopy, we studied leukocyte trafficking through the hepatic microvasculature and the relevance of sinusoidal leukostasis for nutritive perfusion failure in rats after hepatic I/R (n = 8). Sham-operated animals (n = 8) served as controls. Hepatic reperfusion was characterized by perfusion failure of individual sinusoids and a significant increase of sinusoidal leukostasis. However, in both nonischemic and postischemic livers, the major fraction of sinusoids presenting with stagnant leukocytes were found perfused (97 +/- 1 and 73 +/- 5%, respectively), whereas only 3 +/- 1 and 27 +/- 5% failed to conduct flow. Analysis of leukocyte trafficking in sinusoids with leukostasis revealed a marked reduction of leukocyte velocity and leukocyte flux in nonischemic and postischemic livers compared with sinusoids without leukostasis. Thus stagnant leukocytes retard cellular passage through hepatic sinusoids, probably due to an increase of flow resistance. However, the fact that during postischemic reperfusion > 70% of the sinusoids accommodating stagnant leukocytes are still perfused indicates that sinusoidal leukostasis per se does not necessarily determine perfusion failure ("no-reflow") after I/R of the liver.
Bile secretion in rats with indomethacin-induced intestinal inflammation
Authors: Yamada T. , Hoshino M. , Hayakawa T. , Kamiya Y. , Ohhara H. , Mizuno K. , Yamada H. , Nakazawa T. , Inagaki T. , Uchida A. , Miyaji M. , Takeuchi T.
Published: December 2017

The objective of this study was to characterize the bile secretion, including the composition of biliary bile acids, bile salt pool size, and transcytotic vesicle transport, in a rat model of subacute intestinal inflammation induced by indomethacin. Indomethacin treatment significantly decreased bile acid-independent bile flow and biliary secretion of bile acid and cholesterol, while increasing biliary phospholipid output in vivo. Although indomethacin treatment did not change the bile salt pool size in vivo, alpha- and beta-muricholic acids were significantly deceased and hyodeoxycholic and deoxycholic acids were increased in bile. Bile flow and the transport maximum of taurocholate did not decrease, and biliary horseradish peroxidase output was significantly enhanced in isolated perfused livers from indomethacin-treated rats. Endotoxin in the portal blood was significantly increased in rats treated with indomethacin. Clindamycin slightly reduced intestinal inflammation but significantly prevented decreases in bile flow, bile acid output, and transport maximum of taurocholate. We conclude that, although biliary secretory function was apparently decreased in vivo, that of hepatocyte function was maintained in this model.
Evidence that CCK-58 has structure that influences its biological activity
Authors: Reeve J. R. , Eysselein V. E. , Rosenquist G. , Zeeh J. , Regner U. , Ho F. J. , Chew P. , Davis M. T. , Lee T. D. , Shively J. E. , Brazer S. R. , Liddle R. A.
Published: December 2017

Many biologically active peptides exist in multiple molecular forms, but the functional significance of regions outside the region of bioactivity is unknown. The biological and immunological data presented in this study indicate that cholecystokinin-58 (CCK-58), unlike other forms of cholecystokinin, has structure that influences its bioactivity. CCK-58 was purified from acid extracts of canine intestinal mucosa until a single absorbance peak was obtained during reverse-phase chromatography. Amino acid analysis precisely determined the peptide concentrations of purified CCK-58 and synthetic CCK-8. Our hypothesis was that if the amino terminus of CCK-58 influences its bioactivity then its activity would be modified when this region was removed from the peptide. To evaluate the importance of the amino terminus of CCK-58 to influence its biological activity, the abilities of CCK-58 and CCK-8 to release amylase from pancreatic acini were compared before and after tryptic digestion. Tryptic digestion of CCK-58 decreased the half-maximal stimulation (EC50) for amylase release from 96 to 28 pM. The EC50 for digested CCK-58 was similar to that for CCK-8 (17 pM). These results suggest that CCK-58 has a structure that shields its bioactive carboxyl terminus. This is further supported by the finding that carboxyl fragments generated from CCK-58 by trypsin or by partial acid hydrolysis were greater than twofold more immunoreactive than the intact CCK-58. The diminished activity of CCK-58 SK shields the carboxyl terminus, which is important to its biological and immunological activities.
Neural reflexes controlling intestinal microcirculation
Authors: Vanner S. , Surprenant A.
Published: December 2017

It has long been established that neural reflexes are involved in the regulation of gastrointestinal vascular function, in particular the mucosal hyperemia that follows food ingestion. However, more precise identification of reflex pathways involved in the control of mucosal blood flow had not previously been forthcoming because of a lack of adequate methods to examine resistance arterioles within the intestinal wall. Recent advances have employed novel in vitro preparations and videomicroscopic techniques to investigate the neural control of the gastrointestinal microvasculature and involvement of intrinsic and extrinsic vasodilatory neurons in mucosal reflexes. Vasoconstrictor innervation to submucosal arterioles is mediated solely by extrinsic sympathetic nerves that release ATP onto arteriolar P2n-purinoceptors. Neurogenic vasodilation of submucosal arterioles occurs by release of acetylcholine and/or neuropeptides from intrinsic submucosal neurons as well as by release of substance P and calcitonin gene-related peptide from extrinsic sensory nerves. Both vasodilator pathways can be activated independently by mucosal stimulation, and both have afferent and efferent components confined to the mucosa and submucosal neuronal plexus. We speculate that the intrinsic enteric cholinergic reflex pathways are involved in local physiological control of mucosal blood flow, whereas extrinsic sensory reflex pathways are preferentially activated during inflammatory states.
Regulation of cell volume in a human biliary cell line: activation of K+ and Cl- currents
Authors: Roman R. M. , Wang Y. , Fitz J. G.
Published: December 2017

The mechanisms responsible for recovery from cell swelling were evaluated in Mz-ChA-1 cells from human cholangiocarcinoma, a model biliary cell line. Exposure to hypotonic buffer (40% less NaCl) rapidly increased relative cell volume to 1.35 +/- 0.10 as measured by a Coulter Multisizer, followed by regulatory volume decrease to 1.08 +/- 0.03 by 30 min. The same maneuver increased 86Rb (69 +/- 17%) and 125I (422 +/- 58%) efflux in cell monolayers. 86Rb efflux was selectively inhibited by Ba2+ [half-maximal inhibitory concentration (IC50) approximately 1.5 mM], and 125I by 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB) (IC60 approximately 50 microM). Inhibition of these conductive pathways partially inhibited recovery from swelling. Membrane conductance measured by whole cell patch-clamp analysis increased in 57 of 57 cells during swelling due to activation of both K+ and Cl- conductances in most cells. K+ currents (75% of cells, 881 +/- 150 pA at 0 mV) were nearly linear and Ba2+ sensitive; Cl- currents (70% of cells, 2,696 +/- 244 pA at +60 mV) were outwardly rectified, showed time-dependent inactivation at depolarizing potentials, and were inhibited by NPPB. Chelation of cytosolic Ca2+ decreased swelling-induced isotope efflux, prevented activation of macroscopic K+ and Cl- currents, and blocked volume recovery. These studies indicate that biliary cells are able to regulate cell volume during osmotic stress by activation of separate K+ and Cl- conductances through a mechanism that depends in part on Ca(2+)-sensitive signaling pathways.
Transport of n-butyrate into human colonic luminal membrane vesicles
Authors: Harig J. M. , Ng E. K. , Dudeja P. K. , Brasitus T. A. , Ramaswamy K.
Published: December 2017

Human colonic short-chain fatty acid (SCFA) absorption is associated with increased luminal pH and HCO3- and enhanced Na+ absorption. Therefore, the mechanism of colonic SCFA transport, its dependence on Na+ and HCO3- and interactions with Cl-/HCO3- and Na+/H+ exchangers were characterized. Luminal membrane vesicles (LMV) isolated by divalent cation precipitation from organ donor colons were used for n-butyrate transport. Uptake of n-butyrate into the human colonic LMV was minimal even in the presence of an inward pH gradient, but an outward HCO3- gradient significantly increased uptake rates. HCO3(-)-stimulated butyrate uptake was saturable with an apparent Michaelis constant of 1.5 +/- 0.2 mM and maximal velocity of 105 +/- 3 nmol.mg protein-1.3 s-1. Intravesicular butyrate resulted in trans-stimulation of n-[1-14C]butyrate uptake. Butyrate uptake was inhibited approximately 25-40% by C2-C5 SCFAs and approximately 40% by niflumic acid. Butyrate uptake was not affected by extravesicular Na+, and 22Na uptake was unaltered by extravesicular butyrate. Butyrate uptake was independent of extra- or intravesicular CI-, and butyrate loading produced no changes in 36Cl uptake. We conclude that the predominant mechanism of n-butyrate transport across the human colonic luminal membrane appears to be via a HCO3-/SCFA antiport system independent of Cl-/HCO3- exchange and Na+ transport.
Role of cholecystokinin as a regulator of solid and liquid gastric emptying in humans
Authors: Borovicka J. , Kreiss C. , Asal K. , Remy B. , Mettraux C. , Wells A. , Read N. W. , Jansen J. B. , D'Amato M. , Delaloye A. B. , Fried M. , Schwizer W.
Published: December 2017

The role of endogenous cholecystokinin (CCK) in the regulation of gastric emptying remains controversial. We therefore studied the effect of the CCK-A receptor antagonist loxiglumide on gastric emptying of a high-caloric solid-liquid meal in humans. Gastric emptying was assessed in eight volunteers using intravenous loxiglumide or placebo in a randomized double-blind order. Subjects were studied by a dual-headed gamma camera after ingestion of a pancake (570 kcal) labeled with 99mTc-sulfur colloid and 500 ml 10% glucose containing 111In-diethylenetriamine pentaacetic acid. Plasma CCK was measured by a specific radioimmunoassay. Loxiglumide markedly accelerated gastric emptying of both phases of the meal. The lag period was shortened by 26% (P < 0.03); the area under the emptying curve and half-emptying time of solid emptying were lowered by 19 and 24% (P < 0.02) and of liquid emptying by 18 and 24% (P < 0.04), respectively. Plasma CCK levels were higher during infusion of loxiglumide compared with placebo (P < 0.02). These data demonstrate that post-prandially released CCK is a major regulator of gastric emptying of physiological meals containing both solid and liquid components.
Parietal cell MAP kinases: multiple activation pathways
Authors: Nakamura K. , Zhou C. J. , Parente J. , Chew C. S.
Published: December 2017

Epidermal growth factor (EGF) is a potent mitogen for many cell types; however, the best known effect of EGF on gastric parietal cell HCl secretion is inhibition of this response. Using rabbit parietal cells in primary culture, we recently showed that the effect of EGF is biphasic with acute inhibition followed by sustained enhancement of acid secretory-related responses. We hypothesized that EGF might activate a mitogen-activated protein (MAP) kinase signaling pathway in parietal cells, and this pathway might play a role in mediating sustained and/or acute effects of EGF on parietal cell acid secretory-related functions [C. S. Chew, K. Nakamura, and A. C. Petropolous. Am. J. Physiol. 267 (Gastrointest. Liver Physiol. 30): G818-G826, 1994]. We used several methodological approaches to demonstrate the presence of MAP kinase (MAPK) isoforms, extracellular signal-regulated kinases (ERKs) 1 and 2, in parietal cells and to begin to characterize their mechanisms of activation in this highly differentiated cell type. In acutely isolated, 90-98% enriched parietal cells, EGF biphasically activated ERK-1 and ERK-2, with peak response occurring at approximately 5 min followed by a sustained lower level of activation for at least 2 h. The EC50 for EGF (1.2 +/- 0.4 nM) was similar to the previously determined EC50 for the stimulatory effect of EGF on acid secretory responses. In contrast to EGF, the phorbol ester protein kinase C activator 12-O-tetradecanoylphorbol 13-acetate (TPA) induced a sustained activation of ERK-1 and ERK-2 for at least 2 h. Carbachol also activated ERK-1 and ERK-2; however, this response was weaker and monophasic. Neither the Ca2+ ionophore ionomycin nor the adenylyl cyclase activator forskolin altered basal or stimulated ERK activity. Carbachol, but not EGF or TPA, also activated an unidentified 70-kDa protein kinase as detected with in-gel myelin basic protein (MBP) kinase renaturation assays. Parietal cell MAPK activation was not correlated to a shift in apparent relative molecular mass on sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels, suggesting that basal phosphorylation of ERK isoforms may be higher in parietal cells compared with actively proliferating cell lines. Also, in contrast to observations in neutrophils, the phosphatidylinositol 3-kinase (PtdIns 3-kinase) inhibitor, wortmannin (0.3-3 microM), failed to inhibit ERK activation in response to EGF, carbachol, or TPA. The combined data indicate that 1) EGF, TPA, and carbachol activate overlapping as well as distinct intracellular signaling pathways in gastric parietal cells, 2) EGF activates ERKs and enhances parietal cell acid secretory related functions via receptors with similar affinities, and 3) in contrast to some cell types, the parietal cell ERK-signaling cascade does not appear to be directly modulated by the PtdIns 3-kinase pathway or by elevated intracellular free Ca2+ or adenosine 3',5'-cyclic monophosphate concentrations.
GSH transport and GSH-dependent detoxication in small intestine of rats exposed in vivo to hypoxia
Authors: Bai C. , Jones D. P.
Published: December 2017

The effects of hypoxia on glutathione (GSH) concentration and GSH-related enzyme and transport systems were studied in the small intestine of rats exposed to 8-10 days of 10.5% O2. Exposure to hypoxia resulted in a 40% lower GSH concentration in enterocytes and a 50% lower concentration in blood plasma. Activities of GSH-related detoxication enzymes in the intestinal epithelium were largely unaffected by hypoxic exposure. GSH degradation and synthesis rates in enterocytes isolated from hypoxic rats were comparable with rates in normoxic controls, but GSH uptake rate was decreased by 30%. Stimulation of absorption of GSH by phenylephrine, such as occurs in control rats, was not detectable in isolated, vascularly perfused intestines of hypoxic rats. Decreased GSH uptake was associated with enhanced transepithelial appearance of thiobarbituric acid-reactive substances in everted intestinal sacs incubated with peroxidized methyl linoleate. These results suggest that chronic hypoxia results in impaired uptake of GSH in the small intestine, and this may result in impaired GSH-related defense mechanisms in the small intestine.
Gut adaptation and the insulin-like growth factor system: regulation by glutamine and IGF-I administration
Authors: Ziegler T. R. , Mantell M. P. , Chow J. C. , Rombeau J. L. , Smith R. J.
Published: December 2017

Intestinal adaptation after extensive small bowel resection in rats is augmented by the provision of diets supplemented with the amino acid glutamine (Gln) or by administration of insulin-like growth factor-I (IGF-I). The goal of this study was to investigate potential synergistic effects of Gln and IGF-I on postresection ileal hyperplasia. Rats underwent 80% small bowel resection (SBR) and then were fed low-Gln or L-Gln-enriched diets and subcutaneously given recombinant human IGF-I or vehicle for 7 days. Gln and IGF-I each significantly enhanced adaptive ileal hyperplasia (DNA content) compared with rats receiving vehicle and low-Gln diet. Ileal DNA content was highest when IGF-I was administered together with Gln supplementation. Combined IGF-I plus Gln synergistically increased ileal weight and protein content. This was associated with higher plasma concentrations of IGF-I and Gln than observed when IGF-I or Gln was given individually. Ileal IGF-I mRNA expression rose nearly twofold during gut adaptation after SBR; this response was augmented with IGF-I administration but was unaltered by Gln feeding. In contrast, dietary Gln, but not IGF-I therapy, prevented a decrease in hepatic IGF-I mRNA induced by SBR. We conclude that parenteral IGF-I and enteral Gln have both individual and synergistic effects on ileal adaptation after massive small intestinal resection. These findings support the concept that specific gut-trophic nutrients and growth factors may be combined to enhance intestinal adaptation and possibly reduce the severity of short bowel syndrome after intestinal resection.
Actions of calcitonin gene-related peptide in guinea pig gallbladder ganglia
Authors: Gokin A. P. , Jennings L. J. , Mawe G. M.
Published: December 2017

The actions of calcitonin gene-related peptide (CGRP) have been determined from intracellular recordings obtained from gallbladder neurons in intact whole mount preparations. In most cells, pressure microejection of CGRP elicited a slow, monophasic depolarization, 4 mV in amplitude, that was associated with a decrease in input resistance and increased excitability. The CGRP-induced depolarization was attenuated in a low-Na+ solution and had a reversal potential of -8 mV. In 10% of the cells, microejection of CGRP elicited a biphasic response that was composed of a rapid transient depolarization followed by a slow depolarization that was similar to the monophasic response. Addition of CGRP (1–10 nM) to the bathing solution elicited a monophasic depolarization and desensitized the cells to applications of CGRP by microejection. Forskolin, applied either by microejection or bath application, also depolarized gallbladder neurons and produced cross-desensitization to CGRP. Responses to substance P were not enhanced by CGRP, and CGRP did not affect fast synaptic responses. It is concluded that CGRP may contribute to a local axon reflex response in gallbladder ganglia.
Continuous measurement of gastric nitric oxide production
Authors: Aneman A. , Snygg J. , Fandriks L. , Pettersson A.
Published: December 2017

With the use of a double-lumen catheter, nitric oxide (NO) was dialyzed across a Gore-Tex membrane into a gas phase and subsequently analyzed on-line by chemiluminescence. This new technique for the continuous measurement of NO was evaluated bench-side and applied in the human stomach in vivo to measure the nonenzymatic formation of NO generated from nitrite in an acidic milieu. A linear relation (r2 = 0.991, P < 0.0001) between concentrations of NO in aqueous solutions (2.5-52.5 mM) and NO in the corresponding gas phases obtained by the dialysis technique (50-1,000 parts per billion) validated the present method for quantitative analyses of NO. Interassay and intra-assay coefficients of variation at all concentrations of NO for six experiments were < 5%. High intragastric concentrations of NO (in the micromolar range) were found during basal conditions. The requirement of both nitrite from the saliva and an acidic environment for NO formation is indicated, since depletion of saliva as well as acid neutralization greatly reduced gastric NO concentrations. Furthermore, large amounts of gastric NO were formed after intake of sodium nitrate. With the use of this technique, NO can be continuously measured with accuracy experimentally and clinically in any organ accessible to intubation.
Ethinyl estradiol cholestasis involves alterations in expression of liver sinusoidal transporters
Authors: Simon F. R. , Fortune J. , Iwahashi M. , Gartung C. , Wolkoff A. , Sutherland E.
Published: December 2017

The mechanisms involved in ethinyl estradiol-induced cholestasis are controversial. Basal bile flow was reduced by ethinyl estradiol administration, with a half time (t1/2) of 12.5 +/- 0.6 h. In contrast, initial taurocholate uptake was not significantly reduced until 3 days to 59% of control and to 13 and 10% of control at 5 and 7 days, respectively. The t1/2 was 4.3 +/- 0.1 days. These physiological changes were correlated with measurement of protein mass and steady-state mRNA for Na(+)-K(+)-adenosinetriphosphatase (Na(+)-K(+)-ATPase), Na(+)-dependent taurocholate transporter, organic anion transporters, and membrane lipid fluidity. Ethinyl estradiol significantly decreased Na(+)-K(+)-ATPase activity and membrane fluidity. However, neither Na(+)-K(+)-ATPase alpha-subunit nor beta-subunit mass was altered by ethinyl estradiol administration. In contrast, protein content of the Na(+)-dependent taurocholate transporter was significantly reduced to 21% of control (P < 0.001) at 5 days. The Na(+)-dependent taurocholate transporter was identified in sinusoidal membrane fractions as a doublet with a molecular size estimated to be 51 and 56 kDa. Although both bands were reduced with ethinyl estradiol treatment, the 56-kDa band was decreased more rapidly and to a greater extent than the 51-kDa band. The estimated t1/2 of 4.8 +/- 0.6 days for the doublet was similar to that for Na(+)-dependent taurocholate uptake. The organic anion transporter protein mass was similarly reduced with time of ethinyl estradiol administration to 21% of control (P < 0.01) at 5 days. Ethinyl estradiol also rapidly decreased the steady-state mRNA levels of Na(+)-dependent and organic anion transporters to approximately 50% and 15% of control at 5 days, respectively. These studies indicate early generalized abnormalities of the sinusoidal membrane lipid fluidity, Na(+)-K(+)-ATPase activity, and bile acid transport protein content.
Evidence for Cl(-)-independent HCO3- transport in basolateral membranes of Necturus oxyntopeptic cells
Authors: Klingensmith M. E. , Cima R. R. , Gadacz A. E. , Soybel D. I.
Published: December 2017

Luminal H+ secretion by gastric mucosa is accompanied by basolateral HCO3- release. A basolateral Cl-/HCO3- exchanger is known to mediate HCO3- extrusion from oxyntopeptic cells during resting and secretagogue-induced apical HCl secretion. From recent work, we hypothesized that there might be a Cl(-)-independent pathway for basolateral HCO3- exit in Necturus oxyntopeptic cells. In this study, we used a fluorescent pH indicator [2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein] to evaluate Cl(-)-independent HCO3- transport across the basolateral membranes of intact oxyntopeptic cells. Removal of serosal Cl- increased intracellular pH (pHi) (7.05 to 7.25), consistent with Cl(-)-dependent HCO3- extrusion. Removal of serosal Na+ in the absence of Cl- resulted in significant acidification of pHi (7.10 to 6.89), but studies involving amiloride, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), and 0 HCO3(-)-N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid-buffered solutions suggest that Na(+)-dependent changes in pHi are due to Na+/H+ exchange. Our studies demonstrate a marked concentration-dependent alkalinization when tissues are exposed to increases in serosal K+. A substantial part of this alkalinization in response to increases in serosal K+ (pHi 7.00 to 7.46) appears to be a HCO3- exit pathway that is independent of both Na+ and Cl-, unaffected by bumetanide or amiloride, but sensitive to DIDS. We propose the presence of a Cl(-)- and Na(+)-independent K(+)-dependent HCO3- cotransporter in Necturus oxyntopeptic cell basolateral membranes.
Fos is required for EGF stimulation of the gastrin promoter
Authors: Marks P. , Iyer G. , Cui Y. , Merchant J. L.
Published: December 2017

Gastrin gene expression is regulated by developmental cues, pH, and inflammation. These processes are mediated by various extracellular ligands, e.g., growth factors, cytokines, and neuropeptides that also stimulate c-fos gene expression. Therefore, to determine whether Fos is required for stimulation of the gastrin promoter, a c-fos sense expression vector was coexpressed with a gastrin reporter construct in a GH4 rat pituitary cell line. We found that epidermal growth factor (EGF) and tumor necrosis factor-alpha (TNF-alpha) transiently stimulate an increase in Fos protein that precedes stimulation of the gastrin promoter. However, the induction mediated by TNF-alpha was weaker than that mediated by EGF, indicating minimal overlap of the signaling pathways activated by EGF and TNF-alpha. Accordingly, overexpression of c-fos mRNA facilitated primarily EGF rather than TNF-alpha induction of the gastrin promoter. Expression of the c-fos gene in the absence of ligand did not stimulate the gastrin promoter. Thus c-fos gene expression is required but is not sufficient for induction of the gastrin promoter by EGF.
Tumor necrosis factor unresponsiveness after surgery in bile duct-ligated rats
Authors: Houdijk A. P. , Boermeester M. A. , Wesdorp R. I. , Hack C. E. , Van Leeuwen P. A.
Published: December 2017

In obstructive jaundice, postoperative complications are related to gut-derived endotoxemia and possibly mediated by cytokines such as tumor necrosis factor (TNF) and interleukin-6 (IL-6). This study investigated the course of IL-6 and TNF after surgery in bile duct-ligated rats (BDL) treated with and without an enteral endotoxin binder (cholestyramine). Endotoxin in rat plasma was determined by blocking cytokine production in whole blood cell cultures stimulated by rat plasma using antibodies directed against the endotoxin (CD14) receptor. Surgery elicited a significant IL-6 response in saline-treated BDL rats (BDL-SAL). TNF, however, remained at its low preoperative levels. Cholestyramine treatment resulted in undetectable preoperative TNF and IL-6 levels, but levels of both cytokines were significantly raised after surgery. Endotoxin, as determined by the CD14 blockade test, was identified in the BDL-SAL group, before (time 0) and after surgery (2 and 4 h), whereas in the cholestyramine group endotoxin was only present at 2 h after surgery. The lack of a postoperative plasma TNF response in the BDL-SAL group in the continuous presence of endotoxin suggests endotoxin tolerance for TNF production in obstructive jaundice.
Progressive defect in biliary GSH secretion in streptozotocin-induced diabetic rats
Authors: Lu S. C. , Kuhlenkamp J. , Wu H. , Sun W. M. , Stone L. , Kaplowitz N.
Published: December 2017

This study examined the effect of streptozotocin-induced diabetes on biliary reduced glutathione (GSH) efflux. Biliary GSH efflux was measured before and after acivicin, an irreversible inhibitor of gamma-glutamyl transpeptidase (GGT). One week after streptozotocin treatment, liver GGT activity doubled in diabetic rats but was inhibited by approximately 90% after acivicin to levels comparable to controls. Despite maximal GGT inhibition, biliary GSH efflux in untreated diabetic rats decreased progressively to approximately 10% of control levels by week 4 and was partially restored by insulin. The mechanism for the decrease in biliary GSH efflux was not increased paracellular permeability. GSH transport kinetics, ATP-stimulated taurocholate, and oxidized glutathione (GSSG) transport in canalicular liver plasma membrane prepared from diabetic and control rats were similar. Inhibition of protein kinase C (PKC) with high-dose H-7 increased biliary GSH efflux in diabetic animals to near control basal levels. In conclusion, streptozotocin-induced diabetic rats exhibit a progressive impairment in biliary GSH transport. One of the responsible mechanisms is heightened PKC tone in diabetic animals.