bluuebunny/crossref_metadata_2025 huggingface dataset:
TGF-beta and collagen-alpha 1 (I) gene expression are increased in hepatic acinar zone 1 of rats with iron overload
Authors: Houglum K. , Bedossa P. , Chojkier M.
Published: December 2017

We have shown that lipid peroxidation stimulates collagen-alpha 1 (I) gene transcription in cultured cells. Because iron is a transitional metal known to induce lipid peroxidation, we investigated whether hepatic lipid peroxidation modulates collagen gene expression in iron-overloaded rats. In this animal model of hemochromatosis, we show colocalization with iron in the hepatic acinar zone 1 of both lipid peroxidation and increased collagen-alpha 1 (I) transcripts, using immunohistochemistry for malondialdehyde-protein adducts and in situ hybridization, respectively. Iron overload stimulated the expression of the cytokine transforming growth factor-beta (TGF-beta) in acinar zone 1, in spite of the minor degree of hepatocellular necrosis and inflammation. The formation of reactive aldehydes and TGF-beta, both inducers of collagen gene expression, may play a role in the stimulation of hepatic collagen production in iron overload. These mechanisms could be a link between iron overload and fibrosis in genetic hemochromatosis.
Characterization and quantification of a pharyngo-UES contractile reflex in cats
Authors: Medda B. K. , Lang I. M. , Layman R. , Hogan W. J. , Dodds W. J. , Shaker R.
Published: December 2017

We characterized and quantified a reflex from the pharyngeal mucosa to the upper esophageal sphincter (UES). Seventeen cats were decerebrated, and the pharynx was exposed by opening the cricothyroid ligament. UES motor activity was assessed by recording electromyographic (EMG) activity from the pharyngeal constrictors, i.e., the thyropharyngeus (TP) and cricopharyngeus (CP). The pharyngeal mucosa was stimulated by touch or pressure. Both stimuli activated contraction of the CP primarily when applied to the naso-, laryngo-, or hypopharynx, but pressure was more effective. The anteromedial portion of the hypopharynx was the most sensitive zone, but there was no strong stimulus-response relationship. The reflex response to a 1-s stimulus occurred at a delay of 0.46 +/- 0.06 s and lasted 4.5 +/- 0.5 s. This pharyngo-UES reflex was blocked by anesthesia of the mucosa or transection of the glossopharyngeal or pharyngoesophageal nerves but not the vagus nerves. In contrast, the esophago-UES contractile reflex was not blocked by anesthesia of the pharyngeal mucosa or transection of the glossopharyngeal nerves but was blocked by transection of either the vagus or pharyngoesophageal nerves. We concluded that the pharyngo-UES contractile reflex was activated by pharyngeal mucosal mechanoreceptors whose afferent limb was the glossopharyngeal nerve and whose efferent limb was the pharyngoesophageal branch of the vagus nerve.
Enterocyte respiration rates in feline small intestine exposed to graded ischemia
Authors: Henninger D. D. , Granger D. N. , Aw T. Y.
Published: December 2017

The purpose of our study was to investigate the changes in enterocyte cellular and mitochondrial respiration rates subsequent to ischemia of graded duration. The small intestine of anesthetized adult cats was assigned to one of five treatment regimens: control or ischemia of 15-, 30-, 60-, or 90-min duration. Cellular and mitochondrial respiration was measured using a Clark-type O2 electrode at 0 and 4 h postharvest. Ischemia of increasing duration caused a progressive decrease in cellular and mitochondrial respiration in enterocytes at 0 h postharvest. By 4 h postharvest, cellular and mitochondrial respiration rates for the 15-, 30-, and 60-min ischemic groups had recovered to near control levels, whereas the 90-min group showed minimal recovery. These data suggest that ischemia suppresses cellular and mitochondrial respiration of intestinal epithelial cells, the magnitude of which is related to the ischemic duration. The ischemia-induced suppression in cellular respiration primarily reflects a reduction in mitochondrial respiration.
Changes in circulatory status and transport function of the liver induced by reactive oxygen species
Authors: Kawamoto S. , Tashiro S. , Miyauchi Y. , Inoue M.
Published: December 2017

To elucidate the pathogenesis of microcirculatory disturbance of the liver after ischemia and reperfusion, the effect of reactive oxygen species on hepatic circulatory status and transport function for a cholephilic compound was studied in an isolated perfused rat liver. Perfusion of the liver with a medium containing hypoxanthine and xanthine oxidase significantly increased the portal pressure, with concomitant decrease in intrahepatic vascular volume and hepatic uptake of bromosulfophthalein (BSP). Similar changes were also elicited by infusion of serotonin, which induces contraction of sinusoidal endothelial cells. Either superoxide dismutase or catalase added in the perfusion medium partially inhibited the oxidase-induced changes in portal pressure, vascular volume of hepatic sinusoid, and BSP transport. In the presence of superoxide dismutase, either catalase or erythrocytes inhibited the oxidase-induced changes completely. These results indicated that superoxide anion and hydrogen peroxide might induce contraction of hepatic resistance vessels, capacitance vessels, and/or sinusoidal endothelial cells and that this contraction decreased the vascular bed in the liver and the time for interaction of circulation substrates with hepatocytes, thereby decreasing hepatic transport for cholephilic ligands such as BSP.
Intralobular zonal heterogeneity and hepatic indicator dilution curves
Authors: Cai Z. S. , Luxon B. A. , Forker E. L.
Published: December 2017

Conventional interpretation of hepatic indicator dilution curves rests on the assumption, among others, that every hepatocyte operates with the same rate constants. When this assumption is false, owing to intralobular zonal variation in surface-to-volume ratios and/or to zonal differences in permeability, the apparent rate constants recoverable from outflow transients are wrong estimates of average liver performance. We develop the theoretical basis for this conclusion and illustrate by example how it can confuse the interpretation of experimental data. The analysis proceeds from vascular and extracellular reference curves recorded from perfused rat livers and from a simple model of intralobular architecture in which highly arborized periportal sinusoids have a larger surface-to-volume ratio than the less-branched vasculature around the central vein. The experimental data and the model, applied to a wide range of hypothetical solutes, are used to compare the true average rate constants for uptake, efflux, and intracellular removal with the apparent values recoverable from outflow curves. When zonal differences in surface-to-volume ratios are the sole source of heterogeneity, the wrong estimates prove of little practical importance. By contrast, assigning larger regional variations in permeability leads to substantial errors. The confusion arising from such errors may be qualitative as well as quantitative. The presence of heterogeneity and thus the risk of interpretive error appears unrecognizable from outflow curves.
Chronic iron overload causes activation of rat lipocytes in vivo
Authors: Ramm G. A. , Li S. C. , Li L. , Britton R. S. , O'Neill R. , Kobayashi Y. , Bacon B. R.
Published: December 2017

Chronic iron overload can result in hepatic fibrosis and cirrhosis. Activated lipocytes, through increased production of collagen and extracellular matrix, play an important role in hepatic fibrogenesis in several types of experimental liver injury, but their contribution to hepatic injury after iron overload is unknown. This study examines the effect of iron overload on lipocyte activation, in vivo. Male Sprague-Dawley rats were fed a chow diet supplemented with 1% carbonyl iron for up to 20 mo. Controls were fed the chow diet alone. Lipocytes were prepared by sequential pronase and collagenase perfusion of the livers, followed by density-gradient centrifugation. Lipocyte activation was assessed by immunohistochemistry of liver sections and by Western blot analysis of alpha-smooth muscle actin expression in freshly isolated lipocytes. In addition, to measure the biosynthetic capability of these lipocytes, collagen and noncollagen protein production was determined after 3 days in culture, using [3H]proline incorporation. The hepatic iron concentration was increased by eightfold in the iron-loaded rats, and lipocytes from these animals expressed alpha-smooth muscle actin. Collagen production was increased by 2.5-fold, and noncollagen protein production was elevated by twofold in lipocytes isolated from iron-loaded rats. In the iron-loaded livers, autofluorescent material with the characteristics of lipofusion was present in periportal zones. Chronic iron overload expression results in the activation of lipocytes, as determined by increased expression of alpha-smooth muscle actin and by increased production of both collagen and noncollagen protein. This activation may contribute to iron-induced hepatic fibrogenesis.
Quantifying oxidative injury in the liver
Authors: Poggetti R. S. , Moore E. E. , Moore F. A. , Koike K. , Tuder R. , Anderson B. O. , Banerjee A.
Published: December 2017

Oxidative injury is a mechanism common to both ischemia-reperfusion (IR) and leukocyte-mediated injury. Reperfused tissue beds and elaborated mediators can activate a cascade of intercellular and interorgan injuries that often precipitates multiple organ failure. Initiation of lung injury by gut IR is a case in point, but concomitant liver injury may have been overlooked because of the absence of comparably sensitive physiological markers. In this study, we explore the hypothesis that occurrence of portally derived oxidant-induced liver dysfunction may be detected with both sensitivity and specificity. We simulated pure oxidative injury to the liver and separated the contributions from secondary systemic oxidation. Both tissue and plasma indicators were evaluated, each reflecting aspects of oxidation, membrane integrity, and metabolic function. Tissue markers readily detect oxidative liver injury, but systemic 3-hydroxybutyrate (3-OHB) concentration and ketone body ratio (KBR) are the most sensitive. Comparison of 3-OHB concentrations against the corresponding KBR can be used to distinguish adjustments within a physiological range from the transition into injury.
Intestinal digestion, absorption, and transport of structured triglycerides and cholesterol in rats
Authors: Tso P. , Karlstad M. D. , Bistrian B. R. , DeMichele S. J.
Published: December 2017

We compared the intestinal absorption of trilinolein (1,2,3-tri-[1-14C]linoleyl-sn-glycerol) with two different structured triglycerides containing one linoleic acid (C18:2) and two octanoic acids (C8:0), 1,3-dioctanoyl-2-[1-14C]linoleyl-sn-glycerol (2-linoleate) and 1,2-di[1-14C]octanoyl-3-linoleyl-sn-glycerol (1,2-octanoate), respectively. Lymphatic radioactive lipid output of 2-linoleate resembled that of trilinolein rats but remained significantly lower during the lipid infusion. Radioactive lipid was recovered along the entire small intestinal lumen, with a significantly higher amount of [14C]lipid recovered in the lower small intestine and cecum in the 2-linoleate group. Delayed uptake of radioactive 2-linoleate was not due to poor digestion. In contrast, 1,2-octanoate was efficiently digested, and both the free fatty acid (FFA) and the monoacylglycerol (MG) containing octanoate were rapidly absorbed. Irrespective of its position on the triglyceride molecule, 14C-labeled octanoate was poorly transported into lymph. In addition, intestinal luminal and mucosal recovery of [14C]octanoate was significantly lower in the 1,2-octanoate group compared with [14C]linoleate recovery in the 2-linoleate or trilinolein groups. Total recovery of infused radioactive lipid was significantly less in the 1,2-octanoate group than in the 2-linoleate or trilinolein groups. Thus radioactive octanoate in the form of FFA or 2-MG was rapidly absorbed and transported via the portal vein. The infusion of either 2-linoleate or 1,2-octanoate did not affect the absorption and lymphatic transport of cholesterol compared with trilinolein. In summary, the type of the fatty acid on the structured triglyceride molecule affects its digestion, absorption, and lymphatic transport. Structured triglycerides containing octanoic acid in the 1- and 3-positions and linoleic acid in the 2-position may not be advantageous to use as a sole source of dietary lipid, but should be supplemented with long-chain triglycerides.
Production and metabolism of dopamine and norepinephrine in mesenteric organs and liver of swine
Authors: Eisenhofer G. , Aneman A. , Hooper D. , Holmes C. , Goldstein D. S. , Friberg P.
Published: December 2017

Concentrations of catecholamines and their metabolites in plasma entering and exiting mesenteric organs, liver, and kidneys were examined to assess the regional production and metabolism of catecholamines in anesthetized swine. Higher portal venous than arterial plasma concentrations of norepinephrine and its metabolites, 3,4-dihydroxyphenylglycol (DHPG) and 3-methoxy-4-hydroxyphenylglycol (MHPG), and of dopamine and its metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), indicated substantial production of both catecholamines by mesenteric organs, representing 45-50% of total body production. Most dopamine was not metabolized to norepinephrine, suggesting a large nonnoradrenergic contribution to total body dopamine production. Concentrations of norepinephrine, DHPG, normetanephrine, and MHPG were lower in plasma exiting than entering the liver, whereas concentrations of the end-product of norepinephrine metabolism, vanillylmandelic acid (VMA), were higher in outflowing than inflowing plasma. Over 94% of the VMA removed by the kidneys was produced in the liver, consistent with the hepatic source of this metabolite. Removal of DOPAC and HVA by the liver exceeded removal by the kidneys or production by mesenteric organs, indicating greater hepatic than renal elimination of these metabolites from the body and underestimation of mesenteric organ dopamine production based on summed spillovers of dopamine metabolites from the liver into the systemic circulation.
Downregulation of hepatic beta-adrenergic receptors after trauma and hemorrhagic shock
Authors: Tait S. M. , Wang P. , Ba Z. F. , Chaudry I. H.
Published: December 2017

Although it is well known that sympathoadrenal activity increases under various adverse circulatory conditions, it is not known whether there are any alterations in hepatic plasma membrane beta-adrenergic receptors after trauma-hemorrhage and crystalloid resuscitation. To study this, rats underwent a 5-cm midline laparotomy (i.e., trauma induced) and were bled to and maintained at a mean arterial pressure of 40 mmHg until 40% of the maximal bleedout (MB) volume was returned in the form of Ringer lactate. The animals were then resuscitated with four times the volume of MB in the form of Ringer lactate over 60 min. Hepatic plasma membranes were isolated using discontinuous Percoll gradient centrifugation. The maximal binding capacity and dissociation constant (i.e., 1/affinity) of [125I]iodopindolol binding to beta-adrenergic receptors were determined using a membrane filtration assay and Scatchard analysis. The results indicate that there was a significant decrease in the maximal binding capacity at the time of MB, which persisted despite crystalloid resuscitation after hemorrhage. However, there were no significant changes in the dissociation constant at any time point during this study. The downregulation of beta-adrenergic receptor binding capacity may be responsible for metabolic abnormalities observed after hemorrhagic shock.
Chronic renal failure increases cytosolic Ca2+ of hepatocytes
Authors: Klin M. , Smogorzewski M. , Massry S. G.
Published: December 2017

Chronic renal failure (CRF) is associated with increased Ca2+ content of liver and reduced hepatic lipase activity. This has been attributed to a rise in cytosolic Ca2+ ([Ca2+]i) of the hepatocytes, but data on this issue are lacking. We examined the [Ca2+]i and ATP content of hepatocytes as well as the activity of Na(+)-K(+)-adenosinetriphosphatase (Na(+)-K(+)-ATPase), Ca(2+)-ATPase, and Na+/Ca2+ exchanger of hepatic membrane vesicles from normal rats, animals with 6 wk of CRF, CRF normocalcemic parathyroidectomized (CRF-PTX) rats, and CRF and normal animals treated with verapamil (CRF-V, normal-V). [Ca2+]i in hepatocytes of CRF rats was higher (281 +/- 7.4 nM) and ATP lower (6.4 +/- 1.8 nmol/mg protein) than in normal (209 +/- 5.3 nM; 12.5 +/- 0.89 nmol/mg protein), CRF-PTX (212 +/- 1.0 nM; 13.7 +/- 0.79 nmol/mg protein), normal-V (215 +/- 2.3 nM; 14.2 +/- 0.77 nmol/mg protein), and CRF-V rats (209 +/- 7.4 nM; 14.8 +/- 0.72 nmol/10(6) cells). The Na(+)-K(+)-ATPase, the maximal velocity of Ca(2+)-ATPase, and the activity of the Na+/Ca2+ exchanger were reduced, whereas the Michaelis constant of Ca(2+)-ATPase was increase in CRF rats compared with the other four groups of rats. The values in the latter groups were not different.(ABSTRACT TRUNCATED AT 250 WORDS)
Equine pelvic flexure myoelectric activity during fed and fasted states
Authors: Merritt A. M. , Panzer R. B. , Lester G. D. , Burrow J. A.
Published: December 2017

The pelvic flexure is the midpoint of the equine large colon that marks the junction of dorsal and ventral components. Previous studies of intraluminal pressure in this region indicate that it could be an important motility control center. The present study was undertaken to expand our knowledge of normal myoelectric activity around the pelvic flexure region. Eight bipolar silver wire electrodes were surgically fixed at 5-cm intervals to the colonic serosa of five adult horses, starting 30 cm oral to the pelvic flexure on the left ventral colon and ending 15 cm aboral to the pelvic flexure on the left dorsal colon (LDC). Recordings of myoelectric activity were done after feed had been withheld for 20 h or when the horses had been allowed to eat hay up to the time of the recording session. The activity was recorded on a polygraph, digitized, processed through a commercial graphics software package, and stored on magnetic tape for later analysis. Action potential activity was basically separated into long spike bursts (LSB) that were > or = 4 s duration and short spike bursts (SSB) that were < 4 s duration and quantified by a software program developed exclusively for the equine large intestine.(ABSTRACT TRUNCATED AT 250 WORDS)
Nerve growth factor synthesis by intestinal epithelial cells
Authors: Varilek G. W. , Neil G. A. , Bishop W. P. , Lin J. , Pantazis N. J.
Published: December 2017

Nerve growth factor (NGF) exists in the gut of adult rats. The cells responsible for NGF synthesis in the gut remain unknown. IEC-6 and Caco-2 cells, established cell culture models of intestinal epithelial cells, were studied to determine whether intestinal epithelial cells, were studied to determine whether they synthesize and release NGF. Conditioned media from both IEC-6 and Caco-2 cells stimulated neurite outgrowth in both rat pheochromocytoma (PC-12) cells and sensory neurons derived from embryonic chick dorsal root ganglia (DRG). The addition of anti-NGF antibody blocked neurite outgrowth in PC-12 cells and partially blocked outgrowth in DRG cells. An NGF-enzyme-linked immunosorbant assay readily detected immunoreactive NGF in conditioned media from both cell lines, whereas cellular extracts from IEC-6, Caco-2, and isolated rat intestinal epithelial cells had low levels of immunoreactivity. Caco-2 monolayers primarily secreted NGF from the basolateral compartment, and interleukin-1 enhanced its secretion. IEC-6, Caco-2, and isolated rat intestinal epithelial cells expressed NGF mRNA as determined by reverse transcription polymerase chain reaction. These observations suggest that intestinal epithelial cells are capable of NGF synthesis.
Signal-transduction pathways causing slow synaptic excitation in guinea pig myenteric AH neurons
Authors: Bertrand P. P. , Galligan J. J.
Published: December 2017

Intracellular recordings were obtained from myenteric AH neurons of guinea pig ileum in vitro. Slow excitatory synaptic responses associated with decreased potassium conductance (gK), inhibition of the spike afterhyperpolarization current (AHC), and increased chloride conductance (gCl) were mimicked by senktide, a neurokinin3 receptor agonist. Intracellular guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) decreased gK and increased gCl irreversibly after nerve stimulation or senktide application. Myenteric neurons in pertussis toxin (PTX)-treated tissues responded normally to senktide and nerve stimulation. Forskolin and phorbol 12,13-dibutyrate (PDBu) inhibited gK and the AHC but did not activate gCl. The AHC was not reduced by subthreshold concentrations of forskolin (10 nM) or PDBu (3 nM) alone but was inhibited by forskolin and PDBu applied together. Inhibitors of phospholipase C (D-609) or protein kinases (staurosporine) reduced slow synaptic and senktide responses. The protein phosphatase inhibitor, calyculin A, caused an inward current, a decrease in gK, and AHC inhibition but did not activate gCl. We conclude that slow excitatory synaptic responses are mediated by PTX-insensitive G proteins and activation of phospholipase C and protein kinases. Forskolin and PDBu activate pathways that inhibit gK. The mechanisms for activation of gCl are unknown.
Expression of somatostatin receptor genes and their role in inhibiting Cl- secretion in HT-29cl.19A colonocytes
Authors: Warhurst G. , Barbezat G. O. , Higgs N. B. , Reyl-Desmars F. , Lewin M. J. , Coy D. H. , Ross I. , Grigor M. R.
Published: December 2017

Recent studies in a cultured model of the intestinal epithelium (HT-29cl.19A) have shown that somatostatin-14 (SS-14) inhibits the Cl- secretory process by acting at multiple G protein-dependent sites. These actions may underlie the antidiarrheal properties of SS peptides. This study has investigated the expression of specific SS receptor subtypes (SSTR) in HT-29cl.19A and examined their role in mediating SS antisecretory actions. Two predominant SSTR, SSTR1 and SSTR2, were identified by reverse transcriptase-polymerase chain reaction (RT-PCR) of mRNA from polarized HT-29cl.19A monolayers. Receptor binding studies showed evidence of two distinct populations of binding sites consistent with the known properties of SSTR1 and SSTR2. The role of SSTR in inhibition of secretion was investigated by comparing the effectiveness of native and synthetic SS peptides on adenosine 3',5'-cyclic monophosphate (cAMP)-dependent Cl- secretion. Secretion stimulated by the receptor-mediated agonist prostaglandin E2 (PGE2) was inhibited > 70% by SS-14 with a 50% effective concentration (EC50) of 32 nM. In contrast, SMS-201-995 (SMS) and RC-160 exhibited little or no antisecretory activity (maximum inhibition of 15 +/- 1.9 and 2.8 +/- 1.9%, respectively, at 100 microM; EC50 > 1.5 microM). Similar effects on PGE2-stimulated cAMP accumulation were also observed. SS-14, but not SMS, also inhibited secretion stimulated by dibutyryl cAMP, which acts independently of changes in cellular cAMP. Pretreatment with pertussis toxin reversed the antisecretory effects of SS peptides.(ABSTRACT TRUNCATED AT 250 WORDS)
La3+ and pH sensitivity of Ca2+ entry and intracellular store filling in gastric parietal cells
Authors: Negulescu P. A. , Machen T. E.
Published: December 2017

The fluorescent Ca2+ indicator fura 2 was used to measure cytosolic free [Ca2+] ([Ca2+]i) in order to obtain information about relative rates of Ca2+ influx into parietal cells during treatment with carbachol (a cholinergic agonist) or thapsigargin (TG, a Ca(2+)-mobilizing agent) or during reloading of the internal Ca2+ stores. In Ca(2+)-containing solutions, carbachol-, TG-, and reloading-stimulated Ca2+ entry exhibited nearly identical sensitivity to La3+ [inhibition constant (Ki) approximately 10 microM] or low pH (pKi approximately 7.0). In experiments in which carbachol and TG were used, there was no additional increase in [Ca2+]i when TG was added to carbachol-treated cells or when carbachol was added to cells previously treated with TG. Thus it is likely that a single Ca2+ entry pathway serves a signaling function as well as a role in refilling the Ca2+ store during reloading. Because the Ca2+ pathway is exquisitely sensitive to pH and serosal pH increases during stimulant-induced H+ secretion (which is activated by increases in [Ca2+]i), this mechanism will exert positive feedback on parietal cells in the intact stomach. When parietal cells were pretreated with carbachol in Ca(2+)-free solutions, reloading was independent of pH and La3+, suggesting that Ca(2+)-containing solutions should be used to determine the properties of the influx pathway.
Vagal and sympathetic components of the heart rate reflex in chronic portal vein stenosis
Authors: Battarbee H. D. , Zavecz J. H. , Betzing K. W.
Published: December 2017

The effects of portal hypertension and portosystemic shunting on autonomic components of the heart rate (HR) baroreflex and on skeletal muscle blood flow changes were investigated using the chronic portal vein-stenosed rat. Phenylephrine- and sodium nitroprusside-induced changes in mean arterial pressure (MAP), HR, and skeletal muscle conductance (SMC) were assessed before and after muscarinic or beta-adrenoceptor blockade. Stenosed rats had lower MAP than sham-operated rats (90 +/- 3 vs. 81 +/- 2 mmHg, P < 0.05), and their portal pressure was higher (7.4 +/- 0.5 vs. 13.9 +/- 1.0 mmHg, P < 0.005). Phenylephrine pressor responses were reduced in stenosed animals, their associated bradycardic responses were enhanced [-1.912 +/- 0.109 vs. -1.427 +/- 0.148 beats per minute (bpm)/mmHg, P < 0.01], and their SMC responses were diminished. Methylatropine abolished bradycardic responses and enhanced pressor responses without affecting SMC. After propranolol, reflex bradycardic responses in stenosed rats were less than in shams (-0.492 +/- 0.085 vs. -0.738 +/- 0.058 bpm/mmHg, P < 0.01), and their pressor and SMC responses became indistinguishable from shams. In contrast, tachycardic responses to nitroprusside-induced hypotension before propranolol were impaired in stenosed rats (-1.492 +/- 0.114 vs. -2.225 +/- 0.347 bpm/mmHg, P < 0.05), and their SMC responses were reduced. Muscarinic blockade did not affect HR or SMC responses to hypotension in either stenosed or sham rats. beta-Adrenoceptor blockade, however, prevented hypotension-induced tachycardia, enhanced nitroprusside depressor responses, and eliminated the between-group differences in SMC responses. These studies indicate that increased gain of the parasympathetic limb of the cardiac baroreflex was responsible for attenuated pressor responses to phenylephrine in portal vein-stenosed animals and that beta-adrenoceptors contributed to skeletal muscle vascular hyporesponsiveness to phenylephrine in portal-vein stenosed animals. Altered beta-adrenoceptor function also appears to contribute to impaired chronotropic and skeletal muscle conductance responses to hypotension.
Effect on muscarinic acetylcholine receptors after experimental neuronal ablation in rat colon
Authors: Inoue T. , Okasora T. , Okamoto E.
Published: December 2017

The etiology of denervation hypersensitivity was studied using a rat model. Degeneration of the myenteric plexus was produced by direct application of 0.1% benzalkonium chloride to the serosal surface of the distal colon. Thirty days later, the treated group was compared with a control group undergoing a sham operation. The treated group showed that the decreased number of ganglion cells of the myenteric plexus on routine stain and acetylcholinesterase staining demonstrated the myenteric plexus in the treated group diminished acetylcholinesterase activity. Methacholine (1%), a muscarinic agonist, increased intraluminal pressure in treated but not control rats. The dose-response curve of colonic muscle strips to oxotremorine showed a shift to the left, indicating greater sensitivity, in the treated bowel, with a 50% effective dose (ED50) of 2.5 x 10(-8) in treated muscle and 2.2 x 10(-7) in controls. Binding studies using [3H]quinuclidinyl benzilate ([3H]QNB) showed that the specific maximal binding (Bmax) for [3H]QNB was greater in treated than in untreated animals (228 +/- 26.1 and 135 +/- 42.9 fmol/mg protein, respectively; P < 0.01), even though the dissociation constants (Kd) were the same (0.398 +/- 0.083 and 0.406 +/- 0.065). These findings show that acquired denervation hypersensitivity in this model is due to an increase in the number of muscarinic acetylcholine receptors.
Barrier function of the gastric mucus gel
Authors: Engel E. , Guth P. H. , Nishizaki Y. , Kaunitz J. D.
Published: December 2017

The gastric epithelium is covered by a continuous layer of secreted mucus and bicarbonate. The function of this mucobicarbonate layer in terms of protecting the epithelial cells from luminal acid is controversial. Several studies conducted in vitro have shown that gastric mucus can slow proton diffusion and can enable the formation of a pH gradient across the mucobicarbonate layer. In our laboratory, simultaneous measurements of intracellular pH and the thickness of the mucus gel overlying gastric surface cells in vivo indicated that surface cell acidification rates and mucus gel thickness were inversely related. This suggests that the gastric mucobicarbonate layer delays proton permeation into gastric surface cells, enabling secreted bicarbonate to neutralize luminal acid. Several theoretical models, including the effects of mucus and bicarbonate secretion, convection, stirring, and lipids are offered as a possible explanation for the experimental observations. Lipid content and additional unstirred layers outside of the mucus gel are offered as possible explanations for the experimental observations. On the basis of the available data and theoretical considerations, we can conclude that all of these factors probably interact in an integrated manner to protect the gastric epithelial cells from damage due to luminal acid.
Chylomicron remnant uptake by enterocytes is receptor dependent
Authors: Soued M. , Mansbach C. M.
Published: December 2017

During glyceryl trioleate absorption in the rat, mucosal triacylglycerol (TG) fatty acids have been shown to consist of only 71% exogenous oleate. Chylomicron remnants are enriched with endogenous TG fatty acids, compared with their parent chylomicrons, which consist primarily of exogenous TG fatty acids. Because enterocytes have the apolipoprotein B-100/E receptor, this study was directed at determining whether the cells can take up and metabolize chylomicron remnants and, if so, whether this was receptor mediated. Isolated enterocytes were incubated with purified 3H-labeled chylomicron remnants. The remnants were shown to be taken up by the basolateral membrane, not the apical membrane. Remnant uptake was proportional to time and number of enterocytes, and saturation kinetics were observed. Nonradiolabeled remnants, human low-density lipoprotein (LDL), anti-LDL receptor antibody, and receptor-associated protein, an LDL-related receptor inhibitor, were all shown to compete for or reduce 3H-remnant uptake. Remnants taken up by the enterocytes could not be removed on incubation with excess human LDL. Uptake was shown to be greatest in the villus tips of the proximal intestine. These studies suggest that enterocytes take up chylomicron remnants by a receptor-mediated process from their basolateral membranes and that the remnants could provide a source of endogenous TG fatty acids for the enterocytes.
In vivo amino acid metabolism of gut and liver during short and prolonged starvation
Authors: de Blaauw I. , Deutz N. E. , Von Meyenfeldt M. F.
Published: December 2017

During starvation, splanchnic organs are proportionally more affected by protein loss than other organs. Amino acid membrane transport is one of the regulating mechanisms of protein turnover, but until now in vivo data were lacking. To study in vivo phenylalanine and tyrosine membrane transport and protein turnover in splanchnic organs, a primed continuous infusion of L-[2,6-3H]phenylalanine was given to control rats (postabsorptive) and after short (40 h) and prolonged (112 h) starvation. Data were analyzed using a three-compartment model previously used in muscle membrane transport studies. Inward and outward amino acid plasma-tissue membrane transport rates in both the liver and gut were upregulated after prolonged starvation. Metabolic shunting of phenylalanine and tyrosine increased in the gut but decreased to zero in the liver after prolonged starvation. In conjunction with this, gut and liver protein turnover increased after prolonged starvation. In the liver the net uptake of gluconeogenic precursors also increased, indicative for increased gluconeogenesis. The observed changes in amino acid metabolism in both splanchnic organs after prolonged starvation may reflect an adaptation of the gut and liver to nutritional deprivation and could be of benefit during refeeding.
Progesterone and estrogen are potential mediators of gastric slow-wave dysrhythmias in nausea of pregnancy
Authors: Walsh J. W. , Hasler W. L. , Nugent C. E. , Owyang C.
Published: December 2017

Women in pregnancy experience nausea, which correlates with gastric slow-wave rhythm disruption. Mediators of these dysrhythmias were explored. To quantitate slow-wave disruption, eight pregnant women with first-trimester nausea underwent electrogastrography after a 250-kcal meal. Results were compared with nonpregnant women with nausea during a prior pregnancy who received estradiol and/or progesterone to levels of the first trimester of pregnancy. Five pregnant women exhibited dysrhythmias, with increases in combined recording time in tachygastria plus bradygastria, as well as decreases in the percentage of electrogastrography signal power in the normal 3 cycle/min range (cpm), compared with nonpregnant women (P<0.05). Estradiol did not evoke dysrhythmias in nonpregnant women; however, progesterone induced increases in recording time in bradygastria plus tachygastria and increases in bradygastric signal power with corresponding decreases in signal power in the 3-cpm range (P<0.05). With estradiol and progesterone coadministration, an additive effect was observed at 3.3 +/- 0.8 h, with increased recording time in bradygastria alone and in bradygastria plus tachygastria with corresponding increases in bradygastric signal power and decreases in power in the 3-cpm range (P<0.05). In conclusion, women with nausea of pregnancy exhibit slow-wave rhythm disruption. Similar dysrhythmias are evoked in nonpregnant women by progesterone alone or in combination with estradiol in doses that reproduce levels in pregnancy. Thus gastric dysrhythmias in pregnancy may be due to a combination of elevated progesterone and estrogen levels.
Effects of bradykinin on lymphatic pumping in rat mesentery
Authors: Yokoyama S. , Benoit J. N.
Published: December 2017

The effects of bradykinin on lymphatic pump activity of rat mesenteric collecting duct were studied, and the receptor subtype responsible for the bradykinin response was evaluated. Rats were anesthetized with intraperitoneal alpha-chloralose and urethan, and exteriorized mesenteries were studied using intravital microscopic techniques. The diameter of the collecting lymph vessels (approximately 100 microns) was continuously monitored and lymphatic pump parameters (end diastolic diameter, end systolic diameter, stroke volume index, ejection fraction, contraction frequency, and pump flow index) were calculated. Bradykinin (0.1-1.0 nM) did not affect end diastolic diameter, end systolic diameter, stroke volume index, and ejection fraction. Bradykinin increased lymphatic contraction frequency and pump flow index in a dose-dependent manner. Des-Arg9-[Leu8]bradykinin (B1 antagonist, 0.1 microM) had no effect on baseline lymphatic pumping but completely inhibited the bradykinin-induced increase in contraction frequency. N-acetyl-D-Arg-[Hyp3,Thi5,8,D-Phe7] bradykinin (B2 antagonist, 0.1 microM) significantly depressed lymphatic contraction frequency in baseline conditions but had no effect on bradykinin-induced increases in contraction frequency. These results indicate that bradykinin induces positive chronotropic but not inotropic effects on lymphatic pump activity through the stimulation of B1 receptors.
Mononuclear cells and cytokines stimulate gastrin release from canine antral cells in primary culture
Authors: Lehmann F. S. , Golodner E. H. , Wang J. , Chen M. C. , Avedian D. , Calam J. , Walsh J. H. , Dubinett S. , Soll A. H.
Published: December 2017

Patients with Helicobacter pylori-associated gastritis have an increased release of gastrin. The mechanisms by which H. pylori affects the endocrine cells are unclear. We have used primary cultures containing canine antral G cells to examine the effects of human blood mononuclear cells, purified monocytes and lymphocytes, recombinant cytokines, and NH4Cl on gastrin release. Mononuclear cells and purified monocytes in direct contact with G cells stimulated gastrin release dose dependently. Separating mononuclear cells from G cells by Transwell filters with 0.4-micron pore size still produced a significant increase of gastrin release. Three human recombinant cytokines, interferon-gamma, tumor necrosis factor-alpha, and interleukin-2, but not interleukin-6 and interleukin-1 beta, each produced dose-dependent increases of gastrin stimulation. NH4Cl did not stimulate gastrin release. We conclude that mononuclear cells and purified monocytes prepared from human blood, as well as several cytokines, stimulate gastrin release from antral G cells. These factors may play an important role in the pathogenesis of H. pylori-associated hypergastrinemia.
Endogenous glucocorticoids inhibit neutrophil recruitment to inflammatory sites in cholestatic rats
Authors: Tjandra K. , Kubes P. , Rioux K. , Swain M. G.
Published: December 2017

Since glucocorticoids have been shown to inhibit leukocyte accumulation to inflammatory sites (6,9) and endogenous glucocorticoid levels are elevated in our cholestatic rat model, we investigated their role during acute inflammation. Sprague-Dawley rats (150-200 g) were either bile duct resected (BDR) or sham resected (sham). Five days later, a 2% carrageenan solution in saline was injected subcutaneously into preformed air pouches on their backs. Animals were killed 5 h later, and inflammatory response was quantitated by measuring the exudate volume, cell count, and myeloperoxidase (mainly in neutrophils) activity. We also pretreated BDR/sham rats with RU-486 (2 mg/kg ip), a glucocorticoid receptor antagonist, 1 h before carrageenan injection. BDR rats exhibited an impaired inflammatory response reflected by 20, 52, and 42% decreases in exudate volume, cell count, and myeloperoxidase activity, respectively (all P ⊂ 0.05). RU-486 treatment significantly increased the inflammatory response in BDR rats (to sham levels), but not in sham rats. These results suggest that endogenous glucocorticoid suppresses the inflammatory response in BDR rats.
Kinetic and specificity differences between rat, human, and rabbit Na+-glucose cotransporters (SGLT-1)
Authors: Hirayama B. A. , Lostao M. P. , Panayotova-Heiermann M. , Loo D. D. , Turk E. , Wright E. M.
Published: December 2017

The Na+ activation and substrate specificity of human, rabbit, and rat Na+-glucose cotransporter (SGLT-1) isoforms were characterized using the Xenopus oocyte expression system and the two-electrode voltageclamp method. We find that there are differences, major and minor, in both the kinetics and substrate specificities between these isoforms; the substrate concentration at half-maximal current (K0.5) for hexoses varies from 0.2 to > 40 mM, depending on the species and sugar; the affinity constant (Ki) for phlorizin, the classic competitive inhibitor of SGLT-1, varies lover two orders of magnitude (rat Ki = 0.03 microM vs. rabbit Ki = 1.4 microM); and some glucoside inhibitors of the rabbit isoform, p-nitrophenyl glucose and beta-naphthyl glucose, are transported by the human and rat transporters. Na+ activation is more sensitive to membrane potential in the human and rat isoforms compared with rabbit. The rabbit isoform has a higher apparent affinity for alpha-methylglucose and 3-O-methylglucose by a factor of two than either human or rat. These results can be quantitatively fitted by our six-state kinetic model of SGLT-1, providing insight into the processes involved in these changes. For example, the model predicts that Na+ binding (rate constant, k12) in human and rat SGLT-1 is similar but is fourfold larger than in rabbit, whereas sugar binding (k23) in rabbit and rat is similar but double the value in human SGLT-1. The differences in the primary amino acid sequences between these three homologous proteins must account for the kinetic and substrate specificity differences, and comparisons of the functional properties and amino acid sequences of SGLT-1 isoforms provide useful information about structure/function relationships.
Neural circuitry of capsaicin-sensitive afferents innervating submucosal arterioles in guinea pig ileum
Authors: Vanner S. , Bolton M.
Published: December 2017

The circuitry of capsaicin-sensitive nerves innervating submucosal arterioles in the guinea pig ileum was examined. The orientation of in vitro submucosal preparations in a double-chamber bath was varied so that nerves on differing segments of arterioles could be stimulated with capsaicin. Capsaicin-evoked dilation of preconstricted arterioles was recorded using videomicroscopy. Superfusion of capsaicin onto either proximal or distal segments of a parent arteriole divided between the chambers evoked a dilation in the opposite chamber (63 and 58%, respectively) but had no effect on extrinsically denervated preparations. When the divider separated the vascular arcades joining the two parent arterioles on the opposite or same side of the intestine, capsaicin evoked little or no response (8 and 11%, respectively). Capsaicin stimulation confined to one branch of a single vessel dilated the opposite branch (42%). In preparations with adjacently attached mucosa, application of capsaicin to the mucosa dilated arterioles in the opposite chamber. These findings suggest that capsaicin stimulation of the mucosa evokes dilation of arterioles through a submucosal reflex and that both afferent and efferent elements are confined to the submucosa and mucosa.
Physiological mechanisms of cholecystokinin action on pancreatic secretion
Authors: Owyang C.
Published: December 2017

Recent experimental studies in animals and humans provide strong evidence that cholecystokinin (CCK) acts via cholinergic pathways to mediate pancreatic enzyme secretion. These studies indicate that the sites of CCK's action to stimulate pancreatic secretion are dose dependent. Doses of CCK that produce physiological plasma CCK levels act via stimulation of the vagal afferent pathway originating from the gastroduodenal mucosa, whereas doses that produce supraphysiological CCK levels act to stimulate intrapancreatic neurons and pancreatic acini. These CCK-sensitive fibers are also responsive to a wide range of chemical and osmotic stimuli. In this manner, gastrointestinal afferents responding to hormones such as CCK and the ever-changing chemical and physical luminal environment provide sensory information to the central nervous system, which in turn stimulates pancreatic secretion via a vagal cholinergic pathway.
Physicochemical characteristics of emulsions during fat digestion in human stomach and duodenum
Authors: Armand M. , Borel P. , Pasquier B. , Dubois C. , Senft M. , Andre M. , Peyrot J. , Salducci J. , Lairon D.
Published: December 2017

Seven fasting subjects were fitted with nasogastric and nasoduodenal tubes and received intragastrically a coarsely emulsified test meal. Gastric and duodenal aspirates were collected after 1, 2, 3, and 4 h. In the duodenum, most lipids (> 90%) were present as emulsified droplets 1-100 microns in size. Large droplets and unemulsified material present in the test meal (> 100 micron) disappeared, whereas smaller droplets (1-50 microns) were generated after 1 h of digestion. Thus the median lipid droplet diameter significantly decreased (19.6 vs. 56.5 microns in the test meal) and the droplet surface area significantly increased (1.58 vs. 0.70 micron2/g fat). Intermediate droplet diameters were 34.3, 46.3, and 27.6 microns after 2, 3, and 4 h, respectively. In the stomach, a comparable emulsion particle size pattern was observed, with median droplet diameters of 17.2, 37.9, 52.4, and 41.6 microns after 1, 2, 3, and 4 h, respectively. However, the extent of triglyceride hydrolysis was much lower in the stomach (6-16%) than in the duodenum (42-45%), where small droplets were enriched in lipolytic products, cholesterol, and phospholipids. The present findings show for the first time that most dietary lipids are present in the human duodenum as emulsified droplets 1-50 microns in size and that no further marked emulsification of dietary fat occurs in the duodenum compared with the stomach.
Role of transforming growth factor-beta in the restitution of injured guinea pig gastric mucosa in vitro
Authors: Yanaka A. , Muto H. , Fukutomi H. , Ito S. , Silen W.
Published: December 2017

The role of transforming growth factor-beta (TGF-beta) in restitution was examined in intact sheets of injured guinea pig gastric mucosa in which the epithelial cell-collagen interaction can be quantitatively evaluated. The luminal surface of intact sheets of in vitro guinea pig gastric mucosa was injured by exposure to 1.25 mol/l NaCl for 10 min. Restitution was evaluated by measurement of transmucosal electrical resistance and [3H]mannitol flux before and after injury. Recovery of electrical resistance and [3H]mannitol flux was retarded by inhibition of endogenous TGF-beta with either aprotinin or anti-TGF-beta antibody; effects were restored by human recombinant TGF-beta1. During inhibition of endogenous TGF-beta, type IV collagen accelerated the recovery. Inhibition of reconstruction of the basement membrane by simultaneous addition of cis-4-OH-L-proline and anti-type IV collagen completely abolished the enhancement of the recovery by TGF-beta 1. These results suggest that endogenous TGF-beta is required for restitution to occur in guinea pig gastric mucosa and that type IV collagen plays an important role in TGF-beta-abetted restitution.
Regulation of inducible nitric oxide synthase in hepatic sinusoidal endothelial cells
Authors: Rockey D. C. , Chung J. J.
Published: December 2017

Nitric oxide (NO) has many important physiological effects that depend in part on its cellular source(s). In liver, NO is produced by all major cell types, including hepatocytes, Kupffer, stellate, and sinusoidal endothelial cells (SECs). Although endothelial cells have been commonly associated with constitutive NO production, recent evidence suggests that NO is inducible in this cell type. Here, we investigated the regulation of inducible NO synthase (iNOS) in SECs. Interferon-gamma (IFN-gamma) and lipopolysaccharide (LPS) as individual compounds induced iNOS mRNA in SECs. Interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha) had no effect when used alone but enhanced iNOS mRNA upregulation by IFN-gamma. iNOS transcription after LPS was present only for 4 h after exposure yet was more sustained after IFN-gamma/TNF-alpha, LPS was unique in that it transiently induced iNOS mRNA, whereas IFN-gamma/TNF-alpha resulted in prolonged increases in iNOS mRNA. Both LPS and IFN-gamma/TNF-alpha caused prolonged elevation of immunoreactive protein. However, when stimulated by LPS, iNOS remained enzymatically active for only 24-48 h. After IFN-gamma or IFN-gamma/TNF-alpha, iNOS activity declined only moderately. LPS added to IFN-gamma alone or IFN-gamma/TNF-alpha did not result in more rapid decay of iNOS enzymatic activity. These data indicate that induction of iNOS by sinusoidal endothelial cells is prominent and that it is regulated both transcriptionally and by its inactivation. Such complex regulation of iNOS has important implications for NO biology in liver disease.