bluuebunny/crossref_metadata_2025 huggingface dataset:
Volitional augmentation of upper esophageal sphincter opening during swallowing
Authors: Kahrilas P. J. , Logemann J. A. , Krugler C. , Flanagan E.
Published: December 2017

Studies were done on eight normal subjects with synchronized videofluoroscopy and manometry to facilitate a biomechanical analysis of the extent and mechanism of voluntary augmentation of upper esophageal sphincter (UES) opening during swallowing. Movements of the hyoid and larynx, dimensions of sphincter opening, and intraluminal pressure events were determined at 1/30-s intervals during swallows of 1 and 10 ml of liquid barium. Swallows of each volume were obtained both before and after subjects were taught a maneuver designed to augment UES opening, the Mendelsohn maneuver (voluntary prolongation of laryngeal excursion at the midpoint of the swallow). At either volume, use of the maneuver increased the duration of the anterior-superior excursion of the larynx and hyoid and consequently delayed sphincter closure by maintaining traction on the anterior sphincter wall. The onset of the pharyngeal contraction (the event normally culminating in sphincter closure) was not affected by the maneuver. We conclude that swallow-related hyoid motion, laryngeal motion, and UES opening are subject to volitional augmentation, supporting the notion that biofeedback techniques can be used to modify impaired swallowing.
Role for iron in reactive oxygen species-mediated cytotoxicity to cultured rat gastric mucosal cells
Authors: Hiraishi H. , Terano A. , Ota S. , Mutoh H. , Razandi M. , Sugimoto T. , Ivey K. J.
Published: December 2017

The gastric epithelium is exposed to oxygen species that are generated within the lumen. Reactive oxygen species, enzymatically generated, cause injury to cultured rat gastric mucosal cells. Much interest has been focused on the role of iron in producing oxidant-mediated injury to the gastric mucosa, because iron is a catalyst that promotes the production of .OH possibly from O2-. and H2O2 (Haber-Weiss reaction) or from H2O2 alone (Fenton reaction). With the use of an iron chelator and an iron binding protein, we examined the role of iron in producing oxidant-mediated injury to cultured gastric mucosal cells. Reactive oxygen species and H2O2 were generated by hypoxanthine-xanthine oxidase and glucose-glucose oxidase, respectively, in buffer without iron. Pretreatment with deferoxamine diminished hypoxanthine-xanthine oxidase-induced 51Cr release from prelabeled cells, dose dependently. Furthermore, addition of deferoxamine to the reactive oxygen species-generating system also protected against the injury. However, apotransferrin (which binds extracellular iron) failed to protect cells. Pretreatment with .OH scavengers was partially protective. Depletion of glutathione with diethyl maleate enhanced reactive oxygen species-mediated cytolysis; such cytolysis was inhibited by deferoxamine. Deferoxamine also decreased 51Cr release induced by glucose-glucose oxidase. We conclude that intracellular iron plays a crucial role in mediating oxygen radical damage to gastric mucosal cells. The .OH, produced from H2O2 by the iron-catalyzed Fenton reaction, seems to be the main mediator of oxidant-induced cytotoxicity to gastric mucosal cells in vitro.
Mechanism of oleic acid-induced inhibition on gastric acid secretion in rats
Authors: Rhee J. C. , Chang T. M. , Lee K. Y. , Jo Y. H. , Chey W. Y.
Published: December 2017

We investigated the existence of an enterogastrone in rats induced by duodenal administration of oleic acid. Acid secretion by the luminally perfused stomach was stimulated in anesthetized rats by intravenous infusion of 0.3 micrograms.kg-1.h-1 pentagastrin. Intraduodenal administration of 3 mmol of oleic acid produced a profound inhibition (94%) of pentagastrin-stimulated acid output in 10 rats (P less than 0.01). Of several peptides in plasma including secretin, neurotensin, somatostatin, and peptide YY, only secretin was found to increase significantly (P less than 0.001). A similar degree of inhibition of acid output (93%) was caused by porcine secretin, 5.6 pmol.kg-1.h-1, given intravenously to mimic the plasma level of secretin produced by oleic acid infusion. The inhibitory effect of oleic acid on the acid secretion was completely reversed by intravenous injection of a rabbit antisecretin serum but not by a normal rabbit serum. These observations strongly suggest that the inhibition was mediated via circulating secretin. The inhibition produced by either oleic acid or secretin was completely blocked by indomethacin. The blocking action was completely reversed by intravenous administration of 48 micrograms.kg-1.h-1 prostaglandin E2. We conclude that endogenous secretin is a major enterogastrone released by oleic acid in anesthetized rats and that the inhibitory action of secretin requires endogenous prostaglandins.
Circadian rhythms of acid and bicarbonate efflux in fasting rat stomach
Authors: Larsen K. R. , Moore J. G. , Dayton M. T.
Published: December 2017

One model of gastric ulcerogenesis implicates a disruption of complementary circadian rhythms between protective and destructive factors. The purpose of this study was to compare circadian rhythms in gastric production of H+ and HCO3- in fasted rats. Sprague-Dawley rats were acclimatized in sound-attenuating, light-proof chambers for 3 wk on a 12:12-h light-dark schedule. Eighteen-hour fasted rats were studied at each of eight sampling times. After anesthesia, the stomachs were cannulated and filled with test solution. Thirty-minute gastric samples were titrated for H+ or assayed for HCO3-. Cosinor analysis of the data showed significant (P less than 0.05) circadian rhythms for both H+ and HCO3-. Peak times were 22:45 HALO (hours after lights on) (4:45 A.M.) for H+ and 05:41 HALO (11:41 A.M.) for HCO3-. These data demonstrate that H+ and HCO3- secretion in the fasting rat gastric lumen follow circadian rhythms with different peak times. Theoretically, this may result in circadian rhythmicity of relative mucosal vulnerability to injury.
Slow-wave activity in colon: role of network of submucosal interstitial cells of Cajal
Authors: Serio R. , Barajas-Lopez C. , Daniel E. E. , Berezin I. , Huizinga J. D.
Published: December 2017

The present study compares the electrophysiological properties of two preparations dissected from the canine colon circular muscle layer: first, containing the submucosal network of interstitial cells of Cajal (ICC) with two to four associated smooth muscle cell layers, and second, a circular muscle preparation devoid of the submucosal ICC network. In the ICC-rich preparations, consistent slow-wave activity was observed with prolonged plateau potentials of approximately 10-s duration. The plateau potentials were sensitive to D 600. In approximately 45% of circular muscle preparations devoid of the submucosal ICC network (confirmed using electron microscopy) slow waves, of different waveshape, were recorded at frequencies identical to those in whole circular muscle preparations. These slow waves did not show a plateau potential. Compared with ICC-rich preparations with a resting membrane potential of about -80 mV, circular muscle preparations had lower membrane potentials, about -70 mV when active, and about -60 mV when quiescent. Heptanol (1 mM) electrically uncoupled cells, since it abolished electrotonic current spread and allowed measurement of the input resistance by intracellular current injection. Heptanol also affected ionic conductances. Heptanol abolished slow waves; the underlying mechanism needs further investigation. In the presence of heptanol, cells in the isolated ICC network and in circular smooth muscle preparations showed spontaneous hyperpolarizing potential fluctuations at a frequency of four to six per second. These oscillations were abolished by current-induced hyperpolarization and TEA (30 mM) and are therefore likely due to spontaneously active K+ conductance.
Relationships between pressure and flow across the gastroduodenal junction in dogs
Authors: Malbert C. H. , Ruckebusch Y.
Published: December 2017

Antroduodenal pressure events were measured simultaneously with transpyloric flow, in conscious dogs, to evaluate the role of mechanical factors modulating this flow. The relationships between pressure and flow across the gastroduodenal junction were never linear. During the interdigestive state, terminal antral contraction occurred 0.9 +/- 0.29 s after the onset of the gush of gastric contents. Hence, the highest flow rate occurred during the period of lowest resistance. After a meal, terminal antral contraction began 3.3 +/- 0.87 s before the flow of chyme, and resistance rose simultaneously with flow rate. The antroduodenal resistance was 10 times higher than during the interdigestive state (8.33 +/- 1.56 vs. 0.73 +/- 0.34 mmHg.ml-1.s). The pyloroduodenal resistance was always lower than the antropyloric one. It is concluded that, because of the temporal relationship between motor events and flow, pure resistive behavior of the junction occurred only after a meal.
Cholinergic and noncholinergic submucosal neurons dilate arterioles in guinea pig colon
Authors: Vanner S. , Surprenant A.
Published: December 2017

Outside diameter of isolated submucosal arterioles in guinea pig colon were monitored to examine vasodilator innervation to these gastrointestinal microvessels. Electrical stimulation of intrinsic submucosal ganglia dilated submucosal arterioles that had been preconstricted with vasopressin or norepinephrine. In approximately 50% of arterioles examined, the muscarinic receptor antagonist 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP, 10 nM) abolished nerve-evoked vasodilations; 4-DAMP (500 nM) only partially inhibited the response in the other 50%. No significant differences in the nerve-evoked vasodilations were observed after extrinsic denervation of sympathetic and sensory fibers and removal of myenteric neurons by surgical myectomy. Immunohistochemistry demonstrated both substance P (SP) and vasoactive intestinal polypeptide (VIP) fiber projections to arterioles after sensory denervation and myectomy. Superfusion with muscarine and SP, but not with VIP or calcitonin gene-related peptide (CGRP), also dilated the arterioles; concentrations of muscarine and SP producing half-maximal responses were 35 and 6 nM, respectively. However, local pressure ejection of both CGRP and VIP dilated the arterioles. The SP receptor antagonist [D-Arg1,D-Phe5,D-Trp7,9,Leu11]SP reduced vasodilations in response to ganglionic stimulation as well as to pressure ejection of both SP and VIP. This study demonstrates that submucosal arterioles in the guinea pig distal colon receive a cholinergic as well as a noncholinergic vasodilator input from neurons in the submucosal plexus. SP and VIP are both likely candidates as the noncholinergic vasodilator transmitter to colonic gastrointestinal microvessels.
Impairment of hepatic insulin receptors during chronic ethanol administration
Authors: Patel B. C. , D'Arville C. , Iwahashi M. , Simon F. R.
Published: December 2017

Chronic alcoholism is frequently associated with impaired intermediary metabolism and insulin resistance. The cellular defects leading to insulin resistance have not been clearly defined but could result from reduced insulin binding or abnormalities in any one of several postreceptor steps. The purpose of the present studies was to measure 125I-insulin binding and internalization kinetics and postreceptor response of the enzyme activity of tyrosine aminotransferase in isolated cultured rat hepatocytes. Four weeks of alcohol ingestion significantly reduced to 47% of control the 125I-insulin binding sites measured either as surface or total (after digitonin permeabilization). In contrast, 125I-epidermal growth factor binding was not significantly changed. Internalization of surface-bound 125I-insulin was decreased, but degradation was not increased, indicating that altered kinetics did not account for the change. Ethanol ingestion markedly reduced in liver cytosol some enzymes regulated by insulin and involved in glucose homeostasis. Basal activities of tyrosine aminotransferase and glucokinase were reduced 51% (P less than 0.01) and 32% (P less than 0.01), respectively. In contrast, phosphoenolpyruvate carboxykinase was unchanged. In short-term cultured hepatocytes from ethanol-fed rats, the maximum response of tyrosine amino-transferase to insulin was reduced 40% (P less than 0.01) without a change in the concentration causing 50% of the maximum response (EC50) compared with controls. In contrast, dexamethasone increased tyrosine aminotransferase to similar maximal levels and with similar EC50, indicating that ethanol did not alter the intracellular response. In conclusion, chronic ethanol ingestion caused significant time-dependent and selective changes in cell surface binding of insulin that was associated with subsequent postreceptor events.
Gastric acid and pepsin hypersecretion in conscious rabbits
Authors: Redfern J. S. , Lin H. J. , McArthur K. E. , Prince M. D. , Feldman M.
Published: December 2017

In conscious, gastric fistula rabbits, gastric acid and pepsin secretion averaged 4.5 +/- 0.1 mmol/h (1.3 mmol.kg-1.h-1) and 4.9 +/- 0.3 IU/h (1.6 IU.kg-1.h-1), respectively; these values represent approximately 40-50% of maximal output. Basal serum gastrin concentrations averaged 24 +/- 4 pg/ml and did not correlate with basal acid secretion. Atropine and vagotomy incompletely inhibited basal acid secretion (by 84 and 50%, respectively) and completely inhibited 2-deoxy-D-glucose-stimulated gastric acid secretion. Atropine and vagotomy similarly inhibited basal pepsin secretion by 50 and 40%, respectively. Ranitidine decreased acid and pepsin secretion, but as with atropine, inhibition was not complete (73 and 37%, respectively). Although omeprazole did not affect pepsin secretion, omeprazole completely inhibited basal acid secretion and elevated postprandial intragastric pH above 5.0. Conscious, gastric fistula rabbits have the highest basal acid and pepsin output among species commonly studied. Both vagal-cholinergic pathways and histamine drive basal acid and pepsin secretion in the rabbit.
Effect of increased intra-abdominal pressure on peristalsis in feline esophagus
Authors: Ren J. L. , Dodds W. J. , Martin C. J. , Dantas R. O. , Mittal R. K. , Harrington S. S. , Kern M. K. , Brasseur J. G.
Published: December 2017

Our aim in this study was to determine the effect of variations in intrabolus pressure on esophageal peristalsis. In five cats, intrabolus pressure was altered by increasing intragastric pressure to 20-45 mmHg by use of a pressure cuff to compress the abdomen. In each cat, increases in intragastric pressure were associated with comparable increases in pressure of the esophageal bolus while the bolus was in the distal esophagus during esophageal peristalsis. Secondary peristalsis induced by a 5-ml injection of barium into the proximal esophagus was recorded by synchronized videofluoroscopy and esophageal manometry. Graded increases in intrabolus pressure caused an increased prevalence of ineffective, incomplete peristaltic sequences that did not completely clear barium from the esophagus. At intragastric pressures greater than 45 mmHg, 63% of the peristaltic sequences were incomplete. Increases in intrabolus pressure elicited by increased intragastric pressure also caused 1) slowing of the peristaltic wave in the distal esophagus, 2) increased pressure wave duration in the distal esophagus, 3) increased esophageal diameter, and 4) increased duration of lower esophageal sphincter opening. The incidence of retrograde bolus escape was inversely related to the difference between peristaltic wave amplitude and intrabolus pressure. A pressure difference of greater than 20 mmHg prevented retrograde barium escape at all esophageal levels, whereas a difference of less than 20 mmHg was generally associated with retrograde escape of barium in the distal esophagus. We conclude that an increase in intrabolus pressure causes an increase in esophageal distension that is transduced into alterations of esophageal peristalsis by either a myogenic or neural mechanism.
Alpha 2-adrenergic model of gastroparesis: validation with renzapride, a stimulator of motility
Authors: Gullikson G. W. , Virina M. A. , Loeffler R. , Erwin W. D.
Published: December 2017

Motility-stimulating drugs can increase gastric antral and intestinal contractions but do not usually enhance emptying unless gastroparesis is present. An alpha 2-adrenergic agonist (SC-39585A) was used to inhibit antroduodenal motility and simulate gastroparesis in dogs. SC-39585A caused dose-related inhibition of emptying of solid and liquid meals as well as the antral and duodenal motility responses to the solid meal. The motility-enhancing agent renzapride (100 micrograms/kg iv) did not enhance emptying of the solid meal under nondelayed conditions. However, at the same dose it partially reversed the delay in solid emptying but only when antroduodenal motility was incompletely (30 micrograms/kg sc) and not totally (100 micrograms/kg sc) inhibited by SC-39585A. This was done in part by antagonizing antral but not duodenal inhibition of motility. Renzapride was also effective orally in reversing the delay in solid emptying. Similarly, renzapride reversed the delay in liquid emptying caused by SC-39585A (30 micrograms/kg sc). An alpha 2-adrenergic agonist can be used to model gastroparesis in dogs by inhibiting antroduodenal motility and can also be used to examine the actions of motor stimulants, such as renzapride, which promote gastric emptying.
Fatty acids stereospecifically stimulate neurotensin release and increase [Ca2+]i in enteric endocrine cells
Authors: Barber D. L. , Cacace A. M. , Raucci D. T. , Ganz M. B.
Published: December 2017

In primary cultures of canine enteric endocrine cells, fatty acids directly stimulated the release of neurotensin-like immunoreactivity (NTLI). This stimulatory effect was cell specific, selective for long-chain unsaturated fatty acids, and stereospecific. Saturated fatty acids of comparable chain length and trans isomers of long-chain unsaturated fatty acids had no effect on basal NTLI secretion. NTLI release in response to oleic acid (cis-11) was dose dependent with an apparent EC50 of 37 +/- 0.18 microM. Cyclooxygenase inhibitors had no effect on fatty acid-stimulated NTLI release, indicating the response was not mediated by the production of active arachidonic acid metabolites. Somatostatin (100 nM) inhibited maximal oleic acid-stimulated NTLI release by 92%. Long-chain unsaturated fatty acids also selectively and stereospecifically stimulated an increase in the mobilization of [Ca2+]i to 313.5 +/- 28.6% of resting [Ca2+]i. Staurosporine, an inhibitor of protein kinase C, dose dependently inhibited oleic acid-stimulated NTLI release with an IC50 value of 22 +/- 0.4 nM. Long-chain unsaturated fatty acids had no effect on basal NTLI secretion from rat pheochromocytoma cells and medullary thyroid carcinoma cells, two clonal lines that express NTLI. The cell-specific, selective stereospecific, and inhibitable action of fatty acids on NTLI secretion suggests that the effect of fatty acids on enteric endocrine cells is indicative of a receptor-mediated mechanism.
Portal transport of absorbed lipids in rats
Authors: Mansbach CM I. I. , Dowell R. F. , Pritchett D.
Published: December 2017

Previous studies [C. M. Mansbach II and A. Arnold. Am. J. Physiol. 251 (Gastrointest. Liver Physiol. 14): G263-G269, 1986] have shown that only 41% of the mass and 54% of the disintegrations per minute (dpm) are recovered in lymph on duodenal infusion of 3H-labeled glyceryl trioleate (TO). The present studies evaluate the potential that the unaccounted for lipids were transported via the protal vein. Rats received portal vein, carotid artery (surrogate for the mesenteric artery), and duodenal cannulas and an ultrasonic flow probe around the portal vein. [3H]TO (135 mumol/h) was infused into the duodenum, and blood samples were collected from the other cannulas. Portal flow was recorded. Portal fatty acid (FA) increased from 220 to 705 nmol/ml during the 6-h infusion and was 201 mumol/h in excess in the portal vein vs. the carotid artery. All common FAs were increased in the portal vein vs. the carotid artery except C18:3 and C20:4. Thirty-nine percent of the dpm infused was calculated to be transported via the portal vein. We conclude that considerable endogenous FA and infused lipid, mostly as triacylglycerol, are transported in the portal vein in response to TO infusion. We speculate that TO infusion induces endogenous FA mobilization from the mesenteric bed.
Secretagogue-specific effects of interleukin-1 on gastric acid secretion
Authors: Wallace J. L. , Cucala M. , Mugridge K. , Parente L.
Published: December 2017

Interleukin-1 beta (IL-1 beta) has recently been shown to reduce the severity of experimental gastroduodenal damage and to inhibit acid secretion in the pylorus-ligated rat. In the present study, the effects of IL-1 beta on pentagastrin-stimulated acid secretion were compared with those of two other cytokines, namely IL-1 alpha and tumor necrosis factor (TNF) alpha. Also, the effects of IL-1 beta on gastric acid secretion stimulated by bethanechol or histamine were assessed. Anesthetized rats were pretreated intravenously with one of the cytokines, at doses in the 0.1-5 micrograms/kg range, 30 min before starting an intravenous infusion of pentagastrin. TNF alpha failed to significantly affect acid secretion, whereas IL-1 alpha and IL-1 beta exhibited significant inhibitory effects. For example, at a dose of 5 micrograms/kg, IL-1 alpha and IL-1 beta reduced acid secretion by 33 and 80%, respectively. The inhibitory effects of IL-1 beta on acid secretion could be completely inhibited by preincubation with an antibody directed against IL-1 beta but not by pretreatment with indomethacin (5 mg/kg sc) or by bilateral vagotomy. If acid secretion was stimulated by intravenous infusions of histamine or bethanechol, neither IL-1 beta nor TNF alpha produced significant inhibitory effects. Inhibition of acid secretion by IL-1 was also observed when the IL-1 was administered subsequent to stimulation by pentagastrin administration. These results demonstrate that IL-1 beta is an extremely potent inhibitor of acid secretion stimulated by pentagastrin but not that stimulated by histamine or bethanechol, through a mechanism that is at least in part independent of the vagus nerve and of prostaglandin synthesis. IL-1 alpha is less potent as an inhibitor of gastric acid secretion, whereas TNF appears to be inactive. Because pentagastrin-stimulated acid secretion could be completely inhibited by a histamine H2-receptor antagonist (cimetidine) and because IL-1 had no effect on histamine-stimulated acid secretion, it is possible that IL-1 exerts its antisecretory actions by inhibiting pentagastrin-stimulated histamine release.
Erythromycin contracts rabbit colon myocytes via occupation of motilin receptors
Authors: Hasler W. L. , Heldsinger A. , Chung O. Y.
Published: December 2017

Erythromycin stimulates gastroduodenal motility via action on motilin receptors. We evaluated erythromycin as a colonic muscle motilin agonist using in vitro rabbit colon studies. Isolated myocytes contracted to erythromycin with a half-maximal effective concentration of 2 pM and peak shortening of 22.4 +/- 2.5% at 1 nM, which was superimposable with the response to motilin. 125I-labeled motilin binding to colon muscle homogenates was saturable and specific with a dissociation constant (Kd) of 0.39 nM and maximal binding (Bmax) of 41 +/- 3 fmol/mg protein. Motilin displaced specifically bound 125I-motilin, with a Kd of 0.31 nM. Erythromycin displaced 125I-motilin but was less potent, with an inhibitory constant of 84.0 nM. Bmax values from displacement studies were similar to the Scatchard data. Motilin receptor protection from alkylation by N-ethylmaleimide preserved contraction to motilin and erythromycin but not acetylcholine or cholecystokinin, whereas protection with erythromycin preserved contraction to motilin but not other agonists. In conclusion, erythromycin binds to colon muscle motilin receptors present in densities similar to reported values for the upper gut. Furthermore, erythromycin contracts colonic myocytes via specific action on motilin receptors. Thus erythromycin may have colonic motor-stimulating properties by action on motilin receptors.
[15N]- and [14C]glutamine fluxes across rabbit ileum in experimental bacterial diarrhea
Authors: Nath S. K. , Dechelotte P. , Darmaun D. , Gotteland M. , Rongier M. , Desjeux J. F.
Published: December 2017

L-Glutamine (Gln) fluxes and the effects of Gln on Na and Cl transport were studied across the ileum of healthy and rabbit diarrheagenic Escherichia coli (RDEC-1)-infected weanling rabbits. Stable ([alpha-15N]Gln) and radioisotopic ([U-14C]Gln) tracers provided identical estimates of Gln transport both in healthy (H) and infected (I) rabbits. RDEC-1 infection, however, decreased net Gln flux [Jnet[14C]Gln = 682 +/- 147 (H) vs. 278 +/- 63 (I); Jnet[15N]Gln = 739 +/- 160 vs. 225 +/- 110 nmol.h-1.cm-2] due to a reduction in mucosal-to-serosal flux. After addition of Gln, increases in net Na absorption [delta Jnet[15N]Gln = 1.87 +/- 0.45 (H) vs. 0.70 +/- 0.27 (I) microeq.h-1.cm-2] and short-circuit current (delta Isc) [1.80 +/- 0.40 (H) vs. 0.74 +/- 0.14 (I) microeq.h-1.cm-2] were also reduced in infected rabbits. Addition of glucose after Gln, however, stimulated Na absorption further. These results indicate that 1) Gln is actively absorbed as intact Gln molecule across rabbit ileum; 2) Gln stimulates an electrogenic Na absorption in a 1:2 ratio that may be further stimulated by glucose; and 3) in RDEC-1 infection electroneutral NaCl absorption, intact Gln absorption, and electrogenic stimulation of Na absorption by glutamine are reduced.
Taurine transport in skate hepatocytes. I. Uptake and efflux
Authors: Ballatori N. , Boyer J. L.
Published: December 2017

Taurine is an amino sulfonic acid maintained at relatively high concentrations in skate (Raja erinacea) hepatocytes (65 mmol/l intracellular water). To identify the transport mechanisms involved in intracellular taurine accumulation, uptake and efflux of [14C]taurine was measured in freshly isolated skate hepatocytes. Uptake of 50 microM taurine at 15 degrees C was essentially linear over 3 h when measured in normal elasmobranch Ringer, was diminished by replacement of extracellular Cl- with NO3-, and was almost completely abolished by replacement of Na+ with choline+ or K+. Kinetic studies suggested the presence of two saturable Na(+)-dependent taurine uptake systems [apparent taurine Michaelis constant = 0.089 +/- 0.028 and 4.47 +/- 0.49 mM and maximal velocity (Vmax) = 0.19 +/- 0.07 and 1.65 +/- 0.42 (SE) nmol.microliter-1.15 min-1 for high- and low-affinity components, respectively; n = 4], as well as a small contribution from an Na(+)-independent uptake system. Uptake was inhibited by other beta-amino acids but not by alpha-amino acids, taurocholate, or 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (0.5 mM). In contrast to uptake, efflux of [14C]taurine was relatively slow (approximately 10% in 2 h) and was unaffected by isosmotic replacement of extracellular Na+ with choline+ or K+ or by replacing Cl- with NO3-. These findings suggest distinct mechanisms for taurine uptake and efflux in skate hepatocytes; uptake is largely Na+ dependent and requires Cl- for maximal activity, whereas the efflux pathway is independent of transmembrane Na+, K+, or Cl- gradients. Maintenance of high intracellular taurine levels in skate hepatocytes is achieved by active Na(+)-dependent uptake processes and a relatively slow efflux.
Vagal and splanchnic sensory pathways mediate inhibition of gastric motility induced by duodenal distension
Authors: Holzer H. H. , Raybould H. E.
Published: December 2017

Afferent pathways mediating gastric corpus relaxation after duodenal distension were studied in urethan-anesthetized rats in which the sensory neurotoxin capsaicin (1%) or its vehicle was applied directly to the cervical vagus nerve trunks or the celiac-superior mesenteric ganglia 10-20 days before experiments. Distension (0.05-0.5 ml) of a closed loop of proximal duodenum decreased gastric intraluminal pressure. Perineural capsaicin treatment to the vagus nerves decreased by 73 and 80% the response to low volumes of distension (0.05 and 0.1 ml). Perineural capsaicin treatment of the celiac-superior mesenteric ganglia significantly attenuated by 46-88% the response to all volumes of distension. Bilateral cervical vagotomy or ganglionectomy reduced the response to all volumes of duodenal distension and, in combination, abolished the response. It is concluded that the decrease in gastric corpus motility after duodenal distension is dependent on the extrinsic innervation to the upper gastrointestinal tract and is mediated by both vagal and spinal capsaicin-sensitive afferents. Capsaicin-sensitive vagal afferents mediate responses to low volumes of distension that may be physiological. Capsaicin-sensitive spinal afferents mediate the gastric response to higher volumes of distension and may be involved in mediating visceral and somatic responses to pathophysiological intestinal obstruction.
Enteric GABA: mode of action and role in the regulation of the peristaltic reflex
Authors: Grider J. R. , Makhlouf G. M.
Published: December 2017

The mode of action of gamma-aminobutyric acid (GABA) and the role of myenteric GABA neurons in the regulation of peristalsis were examined in various preparations of rat colonic muscle. GABA had no contractile, relaxant, or modulatory effect on smooth muscle cells isolated from the circular muscle layer. In innervated circular muscle strips, GABA elicited concentration-dependent relaxation accompanied by release of vasoactive intestinal peptide (VIP). Relaxation and VIP release were inhibited by tetrodotoxin and by the GABAA receptor antagonist bicuculline but not by the GABAB receptor antagonist phaclofen. Relaxation was inhibited by the VIP receptor antagonist VIP-(10-28) implying that VIP release was coupled to muscle relaxation. Relaxation was augmented by atropine implying that GABA also activated cholinergic neurons causing release of acetylcholine that attenuated the relaxant response. This pharmacological profile was evident when GABA was released from intrinsic GABA neurons during peristalsis induced by radial stretch. Blockade of GABAA receptors with bicuculline inhibited the descending relaxation mediated by VIP motor neurons and the ascending contraction mediated by cholinergic motor neurons. Stimulation of these receptors with exogenous GABA had the opposite effect. We conclude that on release from myenteric neurons, GABA acts via GABAA receptors on cholinergic and VIP motor neurons responsible for the two components of the peristaltic reflex.
Regulatory volume decrease stimulates bile flow, bile acid excretion, and exocytosis in isolated perfused rat liver
Authors: Bruck R. , Haddad P. , Graf J. , Boyer J. L.
Published: December 2017

To study the effect of volume regulation on bile secretory function, isolated perfused rat livers (IPRL) were exposed to hypotonic stress (45 mM NaCl) while bile flow and the biliary excretion of bile acids and horseradish peroxidase (HRP) were assessed. Hypotonic stress induced a biphasic increase in bile flow, which rose in the first minute from 1.1 +/- 0.2 to 1.7 +/- 0.1 microliter.min-1.g liver-1 (P less than 0.01), an effect attributed to rapid osmotic equilibration of water, then increased further between 3 and 5 min to 1.6 +/- 0.1 microliter.min-1.g liver-1 (P less than 0.01, followed by a subsequent return to baseline. HRP excretion in bile increased during the second peak of bile flow from 0.9 +/- 0.2 to 1.1 +/- 0.2 ng.min-1.g liver-1, P less than 0.01. Pretreatment with colchicine but not lumicolchicine completely abolished the latter increase in bile flow and HRP excretion as did BaCl2 (1 mM), an inhibitor of both K+ channels and regulatory volume decrease (RVD) in hepatocytes. When sodium taurocholate was infused (1 mumol/min), hypotonic stress induced an even larger increase in the second peak of bile flow (5.1 +/- 0.7 microliters/g liver, P less than 0.01) and higher rates of bile acid excretion than in control perfusions with bile acid (126.2 +/- 21.0 vs. 99.0 +/- 17.1 nmol.min-1.g liver-1, P less than 0.05). These data suggest that both bile flow and bile acid excretion are stimulated during RVD by mechanisms that involve both K+ channels and microtubule-dependent exocytosis at the canalicular (apical) membrane domain.
Effect of short-chain fatty acids on contractile activity and fluid flow in rat colon in vitro
Authors: Squires P. E. , Rumsey R. D. , Edwards C. A. , Read N. W.
Published: December 2017

The effect of short-chain fatty acids (SCFAs) on the contractile activity and fluid output of the large bowel of the rat was studied using an isolated segment of cecum and colon, mounted in vitro. The rate of contractile activity per minute in the proximal, mid, and distal regions of the colon was depressed by luminal infusion of associated SCFAs either as a mixture (acetic, propionic, and butyric) or individually (100 mM/pH = 4.1, in each case). Dose responses were observed for the individual fatty acids, with the 100 mM solutions eliciting a more prominent reduction in colonic motor activity than that induced by 10 mM. Neither the Na salt of the fatty acids nor an acidified Krebs solution (pH = 4.1) inhibited contractile activity or fluid output. No reduction in the rate of contractile activity was observed in the cecum with any test solutions, except 100 mM butyric acid. The data suggest that SCFAs inhibit smooth muscle contractility and resultant fluid transit.
Indomethacin-induced leukocyte adhesion in mesenteric venules: role of lipoxygenase products
Authors: Asako H. , Kubes P. , Wallace J. , Gaginella T. , Wolf R. E. , Granger D. N.
Published: December 2017

Although the pathogenetic mechanisms underlying indomethacin-induced mucosal injury remain undefined, the results from recent studies suggest that leukocyte adherence in gastric microvessels may be an important component of this injury process. The objective of this study was to determine whether clinically relevant plasma concentrations of indomethacin promote leukocyte-endothelial cell adhesive interactions in postcapillary venules. Erythrocyte velocity, vessel diameter, leukocyte rolling velocity, and the number of adherent (stationary for greater than or equal to 30 s) and emigrated leukocytes were measured in rat mesenteric venules. Repeat measurements of all parameters were obtained within 20 min after addition of either 2.5 or 25 micrograms/ml indomethacin to the mesenteric superfusate. In some experiments, rats were pretreated with either a leukotriene (LT) synthesis inhibitor (L 663,536), an LTD4 (MK-571) or LTB4 (SC 41930) receptor antagonist, misoprostol, or prostacyclin (PGI2). Indomethacin alone increased the number of adherent leukocytes, reduced both leukocyte rolling velocity and venular shear rate, but did not promote leukocyte emigration. L 663,536 and SC 41930 prevented all of the adhesive and hemodynamic alterations induced by indomethacin; misoprostol and PGI2, but not MK-571, exerted similar beneficial effects. These results indicate that indomethacin promotes leukocyte adherence in postcapillary venules through an LTB4-dependent mechanism.
Release of reactive oxygen by hepatocytes on reoxygenation: three phases and role of mitochondria
Authors: Littauer A. , de Groot H.
Published: December 2017

Reoxygenation of isolated hepatocytes in primary culture resulted in a three-phase response in the release of reactive oxygen species (ROS) as determined by peroxidase-dependent luminol chemiluminescence. Release of ROS within the first and second phase correlated well with the extent of reoxygenation injury, both being most significant after approximately 4 h of hypoxic incubation. During the third phase, some of the ROS were released by already nonviable cells. Both antimycin A and rotenone significantly increased release of ROS, indicating severe alterations of the mitochondrial respiratory chain caused by hypoxia and suggesting that the altered mitochondrial respiratory chain represents an important source for the release of ROS on reoxygenation. Generation of ROS rose sharply when the O2 content was increased from 0 to 2%, whereas a further increase in the O2 content, of up to 95%, resulted in only small but steady increases in the formation of ROS. The latter suggests that, in addition to enzymatic sources such as the mitochondrial respiratory chain, nonenzymatic reactions may also contribute to the formation of ROS on reoxygenation.
Nitric oxide modulates epithelial permeability in the feline small intestine
Authors: Kubes P.
Published: December 2017

The objective of this study was to assess whether inhibition of nitric oxide production leads to increased epithelial permeability in feline small intestine. Local intra-arterial infusion of the nitric oxide synthesis inhibitor NG-nitro-L-arginine-methyl ester (L-NAME; 0.025 mumol.ml-1.min-1) was performed in autoperfused segments of cat ileum for 90 min. An exogenous source of nitric oxide, sodium nitroprusside (SNP) was infused (0.025 mumol.ml-1.min-1) for the last 30 min of the 90-min L-NAME infusion. Epithelial permeability was quantitated by measuring blood-to-lumen clearance of 51Cr-labeled EDTA throughout the experiment. An increase of approximately sixfold in mucosal permeability was observed within 30 min of L-NAME infusion and this effect was completely reversed by infusion of either SNP or L-arginine (0.125 mumol.ml-1.min-1). NG-nitro-D-arginine-methyl ester (D-NAME) had no effect on mucosal permeability. The increase in epithelial permeability was sufficiently large that rhodamine-dextran (mol wt = 17,200) clearance from interstitium to lumen was increased. Pretreatment with IB4, a monoclonal antibody directed against the leukocyte adhesive glycoprotein complex (CD11/CD18) did not prevent the L-NAME-induced increase in epithelial permeability. These data suggest that inhibition of nitric oxide production leads to a reversible circulating leukocyte-independent increase in epithelial permeability.
Effect of vitamin D status on the rapid actions of 1,25-dihydroxycholecalciferol in rat colonic membranes
Authors: Wali R. K. , Baum C. L. , Sitrin M. D. , Bolt M. J. , Dudeja P. K. , Brasitus T. A.
Published: December 2017

Recent studies from our laboratory have demonstrated that the in vitro addition of 1,25-dihydroxycholecalciferol [1,25(OH)2D3] rapidly (seconds to minutes) stimulated membrane phosphoinositide turnover, translocated protein kinase C from the cytosolic to particulate fraction, increased cytosolic calcium ([Ca2+]i), and decreased cytoplasmic pH (pHi) via inhibition of Na(+)-H+ exchange in rat colonic epithelium of dietary vitamin D-sufficient rats and in Caco-2 cells. In contrast to these prior findings, in the present experiments, 1,25(OH)2D3 failed to elicit any of these colonic biochemical responses in vitamin D-deficient animals. Bethanechol chloride also failed to alter this signal transduction pathway, [Ca2+]i, or pHi. In vivo administration of this hormone for 5-7 days, moreover, to vitamin D-deficient animals restored the rapid biochemical effects of in vitro 1,25(OH)2D3 and bethanechol chloride. These studies, therefore, indicate that alterations in the vitamin D status of rats modulate the action of 1,25(OH)2D3 and other agents on the colonic phosphoinositide signal transduction system and on [Ca2+]i, which, in turn, may influence important cellular processes in this organ such as Na(+)-H+ exchange.
Differential alterations in microvascular perfusion in various organs during early and late sepsis
Authors: Wang P. , Zhou M. , Rana M. W. , Ba Z. F. , Chaudry I. H.
Published: December 2017

Although cellular dysfunction occurs very early in sepsis, it remains controversial whether this is solely due to a decrease in tissue perfusion. Recent studies have indicated that while active hepatocellular function was depressed, hepatic surface microvascular blood flow (MBF) increased in early sepsis but decreased in late sepsis as produced by cecal ligation and puncture (CLP). However, it is not known whether microvascular hyperperfusion in early sepsis and microvascular hypoperfusion in late sepsis are common events in other organs under such conditions. To study this, rats were subjected to sepsis by CLP, after which these and the corresponding shams received 3 ml/100 g body wt normal saline. Microvascular perfusion and MBF in various tissues were assessed by colloidal carbon infusion and laser-Doppler flowmetry, respectively, at 5 h (i.e., early sepsis) or 20 h (late sepsis) after CLP or sham operation. Carbon-perfused areas were quantitated by an Optomax image analyzer. The results indicate that the carbon-perfused areas and MBF in the liver, renal cortex, spleen, and small intestinal serosa (only MBF) increased significantly 5 h after CLP. In late sepsis, however, the carbon-perfused areas and MBF were found to be significantly decreased. A highly linear relationship was observed between the changes of carbon-perfused areas and MBF during sepsis in the tested organs. Thus the microvascular responses in the fluid-resuscitated sepsis model are characterized by hyperperfusion in the early stage and hypoperfusion in the late stage of sepsis in the tested tissues. The cellular dysfunctions observed during the early stage of sepsis are, therefore, not due to any reduction in tissue perfusion.
Guanylate cyclase inhibitors: effect on tone, relaxation, and cGMP content of lower esophageal sphincter
Authors: Murray J. A. , Du C. , Ledlow A. , Manternach P. L. , Conklin J. L.
Published: December 2017

Relaxation of the lower esophageal sphincter (LES) results from activation of its intrinsic innervation. This relaxation is associated temporally with an increase in the guanosine 3',5'-cyclic monophosphate (cGMP) content of the muscle. This study tests the hypothesis that variations in the production of cGMP mediate resting LES tone and nerve-induced relaxation. We examined the effects of guanylate cyclase inhibitors, such as cystamine and methylene blue (MB), on the resting tone, resting membrane potential, electrical field stimulation (EFS)-induced relaxation, and cGMP content of circular smooth muscle from the LES of the opossum. Strips of sphincter muscle were placed in a tissue bath and stretched to 125% resting length. Both cystamine and MB increased the resting tone of LES muscle in a concentration-dependent manner (EC50 = 1.1 +/- 0.2, n = 12, and 1.6 +/- 0.4 mM, n = 10, respectively). The increase in tone by cystamine was not blocked by tetrodotoxin, atropine, or propranolol. Cystamine (1 mM) did not alter the resting membrane potential of circular muscle cells of the LES. The removal of extracellular Ca2+ by the addition of ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA, 4 mM) and nifedipine (1 microM) shortened the duration but not the amplitude of the response to cystamine. Pretreatment with caffeine (5 mM) in the presence of EGTA and nifedipine to deplete intracellular Ca2+ stores blocked the increase in tone by cystamine. Cystamine (1 mM) failed to inhibit LES relaxation induced by EFS. Carbachol, at a concentration that induced a similar increase in base-line tone, attenuated the nerve-mediated relaxation. Cystamine did not alter basal cGMP levels, but inhibited the rise in cGMP induced by EFS. The data indicate that cystamine increases LES tone but does not inhibit EFS-induced relaxation, even though it inhibits EFS-induced increases in cGMP content. The increase in tone is dependent on the presence of intracellular Ca2+ stores.
Cardiac performance in the portal vein-stenosed rat
Authors: Battarbee H. D. , Zavecz J. H.
Published: December 2017

Patient studies and experimental models suggest that impaired cardiac function might contribute to the altered pressor responses and compromised reflex responses to hypotension observed in liver disease. To elucidate the role that portosystemic shunting plays in cardiac impairment, right atrial chronotropic and right ventricular inotropic responses to a beta-adrenoceptor agonist were compared using isolated cardiac tissues from sham-operated and chronic portal vein-stenosed rats. Maximal chronotropic responses of sinoatrial tissue from portal vein-stenosed rats to isoproterenol were reduced 18% (P less than 0.05) with no change in sensitivity [mean effective dose (ED50)]. Basal indexes of contraction were diminished 48% (P less than 0.0025) and 60% (P less than 0.0005) for developed tension and change in force over change in time (dF/dt), respectively, in ventricular tissue from portal vein-stenosed animals. In addition, the maximal response for isoproterenol-induced ventricular contraction was smaller in portal hypertensive animals (-44%, P less than 0.0005, and -52%, P less than 0.01 for developed tension and dF/dt, respectively), but no changes in isoproterenol ED50 values were found. These results indicate that portal venous hypertension with extensive portosystemic shunting leads to impairment of basal myocardial contraction and decreased chronotropic and inotropic responsiveness to beta-adrenoceptor agonists.
Changes in antroduodenal resistance induced by Cisapride in conscious dogs
Authors: Malbert C. H. , Serthelon J. P. , Dent J.
Published: December 2017

The effects of Cisapride on gastric outflow/pressure relationships have been examined in conscious dogs. In the digestive state, after inhibition of emptying in the first 10 min, Cisapride accelerated gastric emptying for 110 min by increasing the volume (7.3 +/- 1.2 vs. 2.3 +/- 0.3 ml) rather than by decreasing the interval between flow pulses (4.9 +/- 0.2 vs. 4.5 +/- 0.1s). After non-nutrient gastric loading, Cisapride also first inhibited and then accelerated gastric emptying as the consequence of both a larger stroke volume (8.0 +/- 1.7 vs. 3.2 +/- 0.5 ml) and more frequent pulses (3.9 +/- 0.1 vs. 4.9 +/- 0.1 s). In both situations, Cisapride increased the amplitude of the antral/pyloric pressure waves. Antropyloroduodenal resistance increased substantially in the first 10 min after Cisapride then recovered to its control value. We conclude that stimulation of antropyloroduodenal motility by Cisapride can both impede and increase gastric emptying by changes in antroduodenal resistance.