bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanisms of transit of lipid mediators of inflammation and bacterial peptides across intestinal epithelia
Authors: Riehl T. E. , Stenson W. F.
Published: December 2017

The transit of two lipid mediators of inflammation, leukotriene B4 (LTB4) and prostaglandin E2 (PGE2), and a formylated peptide produced by intestinal bacteria, N-formylmethionylleucylphenylalanine (FMLP), across Caco-2 cell monolayers was characterized and compared with the transit of mannitol, a hexose known to cross epithelial monolayers by paracellular pathways. The permeability of less mature low-resistance ( < 200 ohm.cm2) monolayers to all four test compounds was similar, but as monolayers matured and the transmonolayer resistance increased, the transit of LTB4, PGE2, FMLP, and mannitol decreased to different degrees, resulting in a selectivity of permeability to the four test compounds in the order LTB4 > PGE2 > mannitol > FMLP. The transit of all four test compounds across Caco-2 cell monolayers was bidirectional, nonsaturable, and energy independent. A small portion of the added LTB4 was incorporated into the cells, whereas the other three compounds were not. Thus the transit of PGE2, mannitol, and FMLP across Caco-2 monolayers appears to be solely by the paracellular pathway, whereas the transit of LTB4 also involves the paracellular pathway but may also involve diffusion through the cell membrane and around tight junctions.
Impact of leukocyte-endothelial cell interaction in hepatic ischemia-reperfusion injury
Authors: Vollmar B. , Menger M. D. , Glasz J. , Leiderer R. , Messmer K.
Published: December 2017

To clarify the in vivo relevance of leukocyte-endothelial cell interactions in the manifestation of hepatic ischemia-reperfusion (I/R) injury, we studied leukocyte flow behavior in sinusoids and postsinusoidal venules of postischemic hepatic tissue in rats using intravital microscopy. Reperfusion following either 20 min (n = 9) or 60 min (n = 9) of left hepatic lobar ischemia resulted in a significant increase of the number of stagnant leukocytes in sinusoids and adherent cells in postsinusoidal venules compared with sham-operated controls (n = 10). Transmission electron microscopy revealed the extravasation of leukocytes from both sinusoids (into the space of Disse) and postsinusoidal venules. In parallel, hepatic I/R was associated with increased serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities and reduced bile flow. Linear regression estimates revealed significant (P < 0.01) correlations between serum ALT (r = 0.76) and AST (r = 0.65) activities, bile flow (r = -0.62), and the number of adherent leukocytes in postsinusoidal venules. In contrast, parameters of hepatocellular integrity and function did not directly correlate with the number of stagnant leukocytes in liver sinusoids. We conclude that hepatic I/R induces accumulation, adherence, and extravasation of leukocytes in both hepatic sinusoids and postsinusoidal venules. However, the adherence of leukocytes to the endothelial lining of venules, rather than of sinusoids, may determine the manifestation of hepatocellular damage and liver dysfunction.
Acute stressors stimulate ion secretion and increase epithelial permeability in rat intestine
Authors: Saunders P. R. , Kosecka U. , McKay D. M. , Perdue M. H.
Published: December 2017

Wistar-Kyoto rats were subjected to 4 h restraint stress (RS) or cold restraint stress (CRS), and jejunal tissues were examined in Ussing chambers for alterations in transport functions compared with tissues from unstressed control rats. The baseline short-circuit current (Isc) was significantly elevated in tissues from RS (approximately 50%) and CRS (100%). Substitution of Cl- eliminated the abnormality, suggesting that stress stimulates Cl- secretion. Electrical transmural stimulation of enteric nerves caused a transient increase in Isc in all tissues. The magnitude of this response was significantly less in tissues from CRS than from control rats; however, the ability of the epithelium to secrete in response to exogenous stimulation with bethanechol or vasoactive intestinal polypeptide was unimpaired, implicating a neural change. Tissue conductance was higher in jejunum from RS and CRS rats than from controls. Increased intestinal epithelial permeability in stressed rats was confirmed by significantly greater fluxes of the inert radiolabeled probes, [3H]mannitol and 51Cr-labeled EDTA. No structural changes were observed. We conclude that acute stressors have profound effects on intestinal epithelial physiology, stimulating ion secretion and reducing barrier function.
Regulation of cholecystokinin secretion by bombesin in STC-1 cells
Authors: Snow N. D. , Prpic V. , Mangel A. W. , Sharara A. I. , McVey D. C. , Hurst L. J. , Vigna S. R. , Liddle R. A.
Published: December 2017

Bombesin stimulates cholecystokinin (CCK) secretion, presumably by a direct effect on the intestinal CCK cell. The present objectives were to characterize bombesin-stimulated CCK release and to investigate the role of calcium in CCK secretion in an intestinal CCK-producing cell line (STC-1). Bombesin caused a dose-dependent release of CCK, which was reduced either in the absence of extracellular calcium or by calcium channel blockade, suggesting that influx of calcium is necessary for CCK secretion. Bombesin caused an increase in intracellular calcium concentration ([Ca2+]i) and increased efflux of 45Ca2+ from 45Ca(2+)-loaded cells. Radioligand binding studies and Northern analysis were consistent with the expression of a bombesin receptor. Thus bombesin stimulation of CCK release occurs via binding to a receptor and is dependent on increased [Ca2+]i. We propose that the STC-1 cell line may provide a useful model for studying the regulation of intestinal CCK secretion.
Epidermal growth factor attenuates jejunal mucosal injury induced by oleic acid: role of mucus
Authors: Ishikawa S. , Cepinskas G. , Specian R. D. , Itoh M. , Kvietys P. R.
Published: December 2017

Epidermal growth factor (EGF) is present in biliary, pancreatic, and Brunner's gland secretions. The aim of the present study was to assess the effects of EGF on lipid-induced mucosal injury. The proximal jejunum of anesthetized rats was cannulated for perfusion of the lumen with emulsified oleic acid (40 mM oleic acid in 20 mM sodium taurocholate; pH 6.0). Mucosal epithelial integrity was monitored by measuring the blood-to-lumen clearance of 51Cr-labeled EDTA. Perfusion of the lumen with emulsified lipid increased EDTA clearance. Addition of EGF (0.5 ng/ml) to the lipid emulsion ameliorated the lipid-induced increase in EDTA clearance. Perfusion of the lumen with EGF alone stimulated mucus secretion from goblet cells. This effect of EGF was abolished by atropine. In addition, in atropinized animals there was 1) an exaggeration of the lipid-induced injury and 2) a loss of the protective effect of EGF. Our findings provide evidence supporting the hypothesis that EGF provides protection against lipid-induced mucosal injury, in part, by stimulating mucus production.
Regional differences in glycoconjugates of intestinal M cells in mice: potential targets for mucosal vaccines
Authors: Giannasca P. J. , Giannasca K. T. , Falk P. , Gordon J. I. , Neutra M. R.
Published: December 2017

We have used a panel of lectins and antibodies to describe the composition of complex carbohydrates associated with M cells in various regions of the intestinal tract of adult BALB/c mice. The fucose-specific lectin Ulex europaeus agglutinin type I (UEA I) is a marker of M cells in the small intestine and recognized M cells at an early stage of differentiation. Subpopulations of M cells in a single follicle-associated epithelium (FAE) could be distinguished by different fucose-specific probes. Certain lectins revealed that M cells have basal processes that extend into the underlying lymphoid tissue. Colonic and rectal M cells display glycosylation patterns distinct from M cells of Peyer's patches and are characterized by terminal galactose. UEA I selectively adhered to Peyer's patch M cells in mucosal explants and in ligated intestinal loops in vivo. The lectin was taken up into endocytic vesicles and transported to the intra-epithelial pocket and other domains of the basolateral membrane. Thus M cell-specific glycoconjugates could serve as "receptors" for targeting of lectin-antigen conjugates to the mucosal immune system.
Induction of postprandial intestinal motility and release of cholecystokinin by polyamines in rats
Authors: Fioramonti J. , Fargeas M. J. , Bertrand V. , Pradayrol L. , Bueno L.
Published: December 2017

Polyamines are known to play a major role in postprandial adaptation of the digestive tract. Experiments were designed to determine whether ingested polyamines induce change in intestinal motility associated with a cholecystokinin (CCK) release and whether endogenous polyamines are involved in the intestinal and colonic motor response to a meal. Intestinal and colonic motility was assessed in rats equipped with intestinal electrodes, and plasma CCK was determined using a bioassay. Orogastric administration of putrescine, spermidine, or spermine (20 mumol) disrupted intestinal migrating myoelectric complexes (MMCs) and increased the frequency of colonic spike bursts. After a 6-day treatment with the ornithine decarboxylase inhibitor alpha-difluoromethylornithine, the duration of postprandial disruption of MMCs, but not the stimulation of colonic motility, induced by a 3-g meal was significantly reduced. The duration of MMC disruption and the increase in colonic spike burst frequency after spermidine administration (20 mumol) were significantly reduced by CCK-A and CCK-B antagonists. Eight minutes after saline administration plasma CCK concentration was 0.9 +/- 0.4 pM; it rose to 4.7 +/- 2.8 pM, 8 min after spermidine (20 mumol). These results indicate that exogenous polyamines disrupt intestinal MMCs and stimulate colonic motility through a release of CCK acting at CCK-A and CCK-B receptors and suggest that endogenous polyamines are involved in the postprandial control of intestinal motility.
Distinguishing normal and glucocorticoid-induced maturation of intestine using bromodeoxyuridine
Authors: Nanthakumar N. N. , Henning S. J.
Published: December 2017

Exogenous glucocorticoids administered during the first two postnatal weeks are capable of eliciting precocious maturation of the rat intestine. However, it is not known whether this represents an alternative developmental pathway or is essentially an advancement of normal ontogeny. The goal of the present study was to address this question using the thymidine analogue 5-bromo-2'-deoxyuridine (BrdU), which is known to selectively inhibit differentiation in a number of tissues. Intestinal development was assessed by following changes in sucrase, trehalase, glucoamylase, and lactase activities. The first experiment assessed whether BrdU has any influence on the cellular differentiation that occurs continuously along the crypt-villus axis. After administration of BrdU to suckling and mature animals, there was no effect on lactase and sucrase activities, respectively. Thus BrdU does not inhibit crypt-villus differentiation in either the suckling or mature jejunum. In the second experiment, dexamethasone was used to induce precocious maturation in the rat jejunum on day 10. BrdU treatment significantly inhibited glucocorticoid-induced elevation of sucrase, trehalase, and glucoamylase but had no effect on the lactase activity. In contrast, treatment with BrdU during normal development significantly accelerated the ontogenic rise of sucrase and trehalase as well as the ontogenic decline of lactase. The acceleration of development was also seen in adrenalectomized rats, indicating that it is the glucocorticoid-independent component of normal intestinal ontogeny that is activated by BrdU. The opposite effect of BrdU on glucocorticoid-induced precocious maturation suggests that such maturation involves different molecular mediators than normal ontogeny.
Presynaptic inhibition by serotonin of nerve-mediated secretion of pancreatic amylase
Authors: Kirchgessner A. L. , Gershon M. D.
Published: December 2017

Enteric cholinergic and serotonergic neurons innervate pancreatic ganglia. Enteropancreatic cholinergic neurons are secretomotor, bu the function of the serotonergic cells is unknown and was investigated. Postganglionic cholinergic nerve-mediated amylase secretion was evoked by veratridine in isolated pancreatic lobules. This concentration-dependent response was inhibited by tetrodotoxin (1.0 microM), atropine (5.0 microM), 5-hydroxytryptamine (5-HT; 5.0 microM), 5-hydroxyindalpine (5-OHIP; 10.0 microM; a 5-HT1P agonist), and 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT; 0.1 microM), but not by hexamethonium (100.0 microM), 2-methyl-5-HT (10 microM), or 5-carboxyamidotryptamine (10 microM). The effects of 5-HT and 5-OHIP were blocked by the 5-HT1P antagonist N-acetyl-5-hydroxytryptophyl-5-hydroxytryptophan amide (5-HTP-DP; 100.0 microM). Carbachol (5.0 microM)-evoked secretion was not affected by 5-HT or 5-OHIP. Veratridine induced c-fos expression in pancreatic neurons and acinar cells. This expression was inhibited by tetrodotoxin, 5-HT, and 5-OHIP. These observations suggest that the serotonergic enteropancreatic innervation inhibits pancreatic secretion via presynaptic receptors on cholinergic nerves. Although the data are consistent with the hypothesis that the inhibitory receptor is a 5-HT1P site, positive identification awaits further study.
Nuclear serine protease activity contributes to bile acid-induced apoptosis in hepatocytes
Authors: Kwo P. , Patel T. , Bronk S. F. , Gores G. J.
Published: December 2017

Glycodeoxycholate (GDC) induces apoptosis in hepatocytes by a mechanism associated with DNA cleavage by endonucleases. In many models of apoptosis, proteolysis is required prior to DNA cleavage. Our aims were to determine if enhanced proteolysis is a mechanism causing GDC-mediated apoptosis. In cultured rat hepatocytes exposed to 50 microM GDC for 4 h, nonlysosomal proteolysis increased by 65% compared with controls. The serine protease inhibitor N alpha-p-tosyl-L-lysine chloromethyl ketone (TLCK; 100 microM) reduced cell death from apoptosis by 75% after 4 h of treatment with GDC. TLCK also inhibited DNA fragmentation. There was a twofold increase in nuclear serinelike protease activity during GDC-induced apoptosis accompanied by a 2.5-fold reduction in nonnuclear serine protease activity, suggesting translocation of the protease from the cytosol to the nucleus. Zn2+, an inhibitor of apoptosis, also inhibited nonlysosomal proteolysis and nuclear serinelike protease activity. These novel data suggest that nonlysosomal serinelike protease activity contributes to hepatocyte apoptosis. These data may be important in understanding apoptosis in other cell types and in providing insight into the mechanisms of liver injury during cholestasis.
The selective beneficial effects of nitric oxide inhibition in experimental colitis
Authors: Hogaboam C. M. , Jacobson K. , Collins S. M. , Blennerhassett M. G.
Published: December 2017

We investigated the involvement of nitric oxide in trinitrobenzene-sulfonic acid (TNB) colitis. Every 24 h after TNB, rats were orally dosed with NG-nitro-L-arginine methyl ester (L-NAME; 30 mg/kg), NG-nitro-D-arginine methyl ester (D-NAME), or water, and food intake, body weight, and plasma nitrite levels were measured. On day 6, colonic nitric oxide synthase and myeloperoxidase (MPO) activity, histology, intestinal muscle growth, NADPH-diaphorase, and myenteric nerve function were assessed. Food intake and body weight were reduced during the first 72 h of colitis. On day 6 post-TNB, a fourfold increase in mucosal nitric oxide synthase, a 30-fold increase in MPO, and a fivefold elevation in plasma nitrite were measured. Smooth muscle hyperplasia and hypertrophy in both colonic muscle layers, numerous diaphorase-positive macrophages in the myenteric plexus, and a suppression of myenteric nerve function were also observed. Unlike D-NAME, oral L-NAME reduced MPO and intestinal muscle hyperplasia by > 90%. Likewise, plasma nitrite and colonic nitric oxide synthase were reduced by > 70%. L-NAME completely prevented macrophage infiltration into the muscle. Conversely, it had no effect on anorexia or intestinal smooth muscle hypertrophy, nor did it affect suppressed myenteric nerve neurotransmitter release. These results demonstrate the selective transmural protective effects of L-NAME in the inflamed colon, implicating nitric oxide as a mediator.
Increased expression of sulfated gp300 and acinar tissue pathology in pancreas of CFTR(-/-) mice
Authors: De Lisle R. C.
Published: December 2017

The CFTR (-/-) mouse model of cystic fibrosis (CF) has revealed that the mouse pancreatic duct has a Ca(2+)-regulated chloride conductance that allows ductal electrolyte transport to remain unaffected by loss of the cystic fibrosis transmembrane conductance regulator (CFTR). Therefore, this model provides a unique opportunity to investigate effects of CF on the acinar tissue. It has been reported that exocrine secretions contain higher levels of sulfate in CF. We discovered in CFTR(-/-) acini that gp300, the major sulfated glycoprotein of the mouse acinar cell, has increased steady-state and biosynthetic levels. However, there are no apparent changes in sulfate or carbohydrate composition of gp300, indicating that posttranslational processing of this sulfated glycoprotein is not altered in CF. In addition to the increase in gp300, the morphology of CF acinar tissue is dramatically altered: acinar lumina of CFTR(-/-) mice are greatly dilated and filled with aggregated protein. gp300, which in the normal tissue is mainly localized to the zymogen granule membrane, was found to line the distended luminal membranes in the CF tissue. These results demonstrate that the acinar tissue is affected in the CF mouse and that expression of the major sulfated glycoprotein is also increased. It is suggested that increased expression of gp300 in CFTR(-/-) mice may cause poorly soluble exocrine protein secretion, contributing to the development of CF in the pancreas.
Effect of aging on the secondary esophageal peristalsis: presbyesophagus revisited
Authors: Ren J. , Shaker R. , Kusano M. , Podvrsan B. , Metwally N. , Dua K. S. , Sui Z.
Published: December 2017

In this study we determined the effect of aging on the capability of the human esophagus to generate secondary peristalsis. We studied nine healthy young (35 +/- 2 yr, 25-45 yr) and nine healthy elderly (74 +/- 3 yr, 70-83 yr) volunteers. We stimulated secondary peristalsis by intraesophageal air injection and balloon distension. All young volunteers exhibited secondary esophageal peristalsis. In four elderly volunteers, secondary peristalsis could not be elicited with injection of any of the tested air volumes. Frequency of stimulation of secondary peristalsis and lower esophageal sphincter (LES) relaxation in response to intraesophageal air distension in the elderly was significantly lower than that in the young (P < 0.01). Stimulation of secondary peristalsis by balloon distension was less consistent compared with the air injection. In conclusion, 1) in the elderly, compared with the young, secondary esophageal peristalsis is either absent or is evoked less frequently after esophageal distension, and complete LES relaxation in response to esophageal air distension is less frequent, and 2) in both young and elderly, secondary esophageal peristalsis is induced more frequently after generalized esophageal distension by air than its segmental distension by a balloon.
Identification and characterization of a basolateral dicarboxylate/cholate antiport system in rat hepatocytes
Authors: Boelsterli U. A. , Zimmerli B. , Meier P. J.
Published: December 2017

The mechanisms and driving forces for the uptake of the unconjugated bile acid cholate were investigated both in cultured rat hepatocytes and in rat liver basolateral (sinusoidal) plasma membrane (BLPM) vesicles. Determination of initial uptake rates of [3H]cholate (0.1 microM) into cultured hepatocytes confirmed that the majority (75%) of the transmembrane transport was mediated by Na(+)-independent mechanisms. This portion of cholate uptake consisted of a pH-sensitive moiety representing nonionic diffusion, which may become quantitatively important at low pH and high cholate concentrations, as well as of a saturable (Michaelis constant 7.4 microM), 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS)-sensitive transport moiety, suggesting the involvement of a carrier. This latter transport system was functionally characterized by 1) inhibition of cellular cholate uptake in the absence of extracellular sodium by the dicarboxylic acid alpha-ketoglutarate (alpha-KG; 1 mM) and by the organic anion p-aminohippurate (PAH; 1 mM); 2) stimulation of cellular cholate uptake by alpha-KG (10 microM) or PAH (1 mM) in the presence of an inwardly directed sodium gradient; 3) lack of sensitivity toward lithium in BLPM vesicles; 4) trans-stimulation of vesicular cholate uptake by alpha-KG or PAH, but not by benzoate; and 5) cis-inhibition of alpha-KG/alpha-KG self-exchange by extravesicular cholate (400 microM), PAH (5 mM), probenecid, or DIDS. Collectively, these data indicate the presence of a Na(+)-dicarboxylate cotransport-coupled organic anion exchanger in the hepatocyte basolateral plasma membrane that may be involved in cholate uptake in the liver.(ABSTRACT TRUNCATED AT 250 WORDS)
Mechanism and timing of nasopharyngeal closure during swallowing and belching
Authors: Dua K. , Shaker R. , Ren J. , Arndorfer R. , Hofmann C.
Published: December 2017

The mechanism(s) of nasopharyngeal closure (NPC) and its temporal relationship with other biomechanical events during swallowing and belching were studied in seven healthy volunteers, aged 26-39 yr, by concurrent videoendoscopic, videofluoroscopic, and manometric technique. Analysis of the videoendoscopic recordings showed that deglutitive NPC consisted of elevation of the soft palate and adduction of the superior pharyngeal constrictor muscle. Videofluoroscopy identified only the palatal elevation clearly. During belching, however, only palatal elevation occurred. Deglutitive NPC ranged between 0.73 and 0.94 s (0.8 +/- 0.04 SE), with a tendency to be longer with larger swallowed volumes. Onset of NPC was identified earlier endoscopically than as seen fluoroscopically. Complete NPC preceded the arrival of barium bolus into the pharynx, and this pattern was seen for all volumes tested. Manometric onset of upper esophageal sphincter (UES) relaxation was seen before the onset of NPC, but the physical opening of the UES as seen fluoroscopically occurred after complete closure of the nasopharynx. We conclude the following: 1) The mechanism of NPC during swallowing and belching is different. During swallowing, NPC has two tiers of closure, palatal elevation and superior pharyngeal muscle adduction; during belching only palatal elevation occurs. 2) NPC is tightly coordinated with other biomechanical events during swallowing and belching.
Transient outward current in opossum esophageal circular muscle
Authors: Akbarali H. I. , Hatakeyama N. , Wang Q. , Goyal R. K.
Published: December 2017

The whole cell patch-clamp technique was used to record a transient outward K+ current (ITO) from single smooth muscle cells isolated from opossum esophageal circular muscle. The threshold for its activation was -50 mV from holding potentials negative to -70 mV. The current peaked within 10 ms and decayed completely in 200 ms between test depolarization of -40 and -10 mV. ITO was recorded at room temperature in the presence of 5 mM internal ethylene glycol-bis(beta-amino-ethyl ether)-N,N,N',N'-tetraacetic acid. Both activation and inactivation kinetics of ITO were markedly changed when recordings were made at higher temperatures (32 degrees C). 4-Amino-pyridine (4-AP, 3 mM) abolished the fast component of the outward current. Tetraethylammonium ion (TEA, 1-30 mM) reduced the sustained component but did not affect ITO. In the presence of TEA and nifedipine, the voltage dependence of the steady-state inactivation data was well fitted by a Boltzmann distribution with a half-inactivation potential of -57 mV. The half-inactivation potential was shifted to a more positive potential in the presence of Cd2+ (-35 mV). The steady-state inactivation and activation data overlap between -50 and -30 mV, suggesting the presence of a "window" current in this potential range. In current-clamp mode, 4-AP depolarized single esophageal cells by approximately 8 mV and shifted the upstroke of the action potential to the left. These results indicate that, in the esophageal circular muscle, ITO is involved in the resting membrane potential and modulation of the onset of action potential.
Substance P induces ion secretion in mouse small intestine through effects on enteric nerves and mast cells
Authors: Wang L. , Stanisz A. M. , Wershil B. K. , Galli S. J. , Perdue M. H.
Published: December 2017

We used genetically mast cell-deficient WBB6F1 W/Wv (W/Wv) mice and congenic WBB6F1 +/+ normal (+/+) mice to examine the role of mast cells in substance P-induced intestinal ion secretion. Isolated sheets prepared from segments of the midportion of the small intestine were studied in Ussing chambers. Substance P caused a dose-dependent increase in short-circuit current (Isc) that was approximately 50% less in intestine from W/Wv than from +/+ mice. Similar results were obtained for substance P-(4-11) (the COOH terminus) and substance P methyl ester [a selective neurokinin (NK)-1 agonist]. Histamine H1 or H2 antagonists reduced the Isc responses to substance P in intestine from +/+ mice but had no effect in intestine from W/Wv mice. In addition, reconstitution of intestinal mast cells in W/Wv mice by intravenous injection of +/+ bone marrow cells normalized the tissues' secretory responses to substance P or substance P methyl ester. However, in W/Wv and +/+ mice, the selective NK1 antagonist CP-96345 virtually abolished intestinal responses to substance P, and the responses were also markedly inhibited by neural blockade with tetrodotoxin. In contrast, in tetrodotoxin-pretreated intestine, histamine antagonism caused a further reduction in the responses to substance P only in +/+ mouse tissues. Taken together, our results suggest that the effects of substance P on intestinal Isc KN1 receptors but that the neuropeptide acts via effects on enteric nerves and mast cells. The data thus support the concept that mast cells and enteric nerves participate in the regulation of substance P-induced intestinal ion secretion.
Role for 5-HT and ACh in submucosal reflexes mediating colonic secretion
Authors: Sidhu M. , Cooke H. J.
Published: December 2017

Neural reflex pathways activated in response to mucosal stroking were investigated in segments of distal colon from guinea pigs. Stroking the mucosal surface of whole thickness or muscle-stripped segments with a brush at 1/s evoked an increase in short-circuit current (Isc) whose duration and amplitude were dependent on the number of strokes. The increase in Isc induced by mucosal stroking was virtually abolished by inhibitors of chloride secretion and by tetrodotoxin. The response was reduced by atropine, renzapride, and N-acetyl-5-hydroxytryptophyl-5-hydroxytryptophan amide but not by mecamylamine, ketanserin, tropisetron, or SDZ-205-557. Mucosal application of 5-hydroxytryptamine and 5-hydroxyindalpine increased Isc, which was attenuated by tetrodotoxin and renzapride. The results suggest that mucosal stroking evokes chloride secretion by activating neural reflex pathways utilizing serotoninergic receptors, of the 5-HT1P class, as well as muscarinic receptors within the submucosal plexus.
cAMP regulates gastrin gene expression
Authors: Shiotani A. , Merchant J. L.
Published: December 2017

Gastrin is one of the most potent regulators of acid secretion and gastrointestinal cell growth. A variety of signals regulate gastrin release from the antral G cell. However, whether these secretagogues also stimulate gastrin gene expression has not been established. Dramatic increases in gastrin gene expression occur in the stomach after birth and in response to chronic achlorhydria. Moreover, gastrin gene expression in malignant islet cell tumors (gastrinomas) appears to represent reactivation of the fetal pattern of expression in the pancreas. Thus differential expression of the gastrin gene is a reflection of differences in transcriptional control. Since various luminal and humoral factors stimulate the production of cAMP and gastrin secretion in both gastrinoma and antral G cells, we studied the effect of cAMP on gastrin gene expression. Using stable and transient transformants of a pituitary cell line containing the human gastrin gene, we found that cAMP stimulates a three-fold increase in gastrin mRNA levels and that the response maps to elements located between -148 and -40 base pairs upstream from the cap site. Collectively, these studies link an important regulator of gastrin secretion to regulation of gastrin gene expression.
Ontogenic regulation of spatial differentiation in the crypt-villus axis of normal and isografted small intestine
Authors: Gutierrez E. D. , Grapperhaus K. J. , Rubin D. C.
Published: December 2017

Despite rapid proliferation, the mammalian intestinal epithelium maintains precise spatial differentiation from crypt to villus tip and from duodenum to colon. During perinatal life, the rodent gut undergoes a dramatic morphogenesis, resulting in formation of the crypt-villus and duodenal-colonic axes. The ontogeny of regional differences in gene expression in the emerging vertical axis has not been well described. We used the liver fatty acid binding protein (L-FABP) and apolipoprotein (apo) AIV genes as markers of neonatal enterocytic differentiation. In situ hybridization analyses revealed that both genes exhibit unique spatial patterns of expression along the jejunal crypt-villus axis during ontogeny, characterized by increased cellular mRNA levels in villus base enterocytes. To examine the requirement for a normal luminal environment to generate these precise patterns of cellular gene expression, we employed intestinal isograft techniques. Fetal intestines were implanted as early as embryonic day 12. Appropriate expression of the apo AIV and L-FABP genes was recapitulated during villus morphogenesis in fetal life. However, spatial patterns of gene expression in the isografted postnatal cryptvillus axis were altered. The preferential accumulation of L-FABP and apo AIV mRNA in villus base enterocytes was never observed in isografts. These results suggest that a “basal” differentiation program is encoded in fetal endoderm and mesenchyme, yet extracellular substances contained in the lumen or extrinsic to the intestine play an important modulatory role in generating spatial differentiation during ontogeny.
Effect of short-term starvation on gastric emptying in humans: relationship to oral glucose tolerance
Authors: Corvilain B. , Abramowicz M. , Fery F. , Schoutens A. , Verlinden M. , Balasse E. , Horowitz M.
Published: December 2017

To evaluate the effects of short-term starvation on gastric emptying in normal and obese subjects, the relationship between gastric emptying and oral glucose tolerance, and the mechanisms responsible for the delay in the systemic appearance of oral glucose observed after short-term fasting, we determined the effects of a 4-day fast on 1) gastric emptying and oral glucose tolerance in normal subjects and 2) gastric emptying in obese patients. Gastric emptying of 75 g glucose (320 ml) labeled with 99mTc colloid was measured in 12 healthy volunteers and 11 obese subjects after 12-h and 4-day fasts. In seven other obese subjects, the effect of a 4-day fast on gastric emptying of 320 ml normal saline was quantified. Gastric emptying of glucose was slower after the 4-day than after the overnight fast in both normal (P > 0.02) and obese (P < 0.001) subjects, with no difference between the two groups. In normal subjects, the rate of gastric emptying was related directly to the rise in plasma glucose at 30 min (r = 0.60; P < 0.05) but inversely to the plasma glucose at 180 min (r = -0.64; P < 0.02). In the obese subjects, gastric emptying of saline was not affected by fasting. These observations indicate that 1) gastric emptying of glucose is retarded by a 4-day fast, 2) the changes in gastric emptying reported in obesity may reflect different patterns of prior nutrient intake, and 3) delay in gastric emptying accounts for the slower systemic appearance of glucose after fasting.
Differential expression and regulation of SSTR2 messenger RNA in rat gastric antrum and corpus
Authors: Sandvik A. K. , Dimaline R. , Brenna E. , Waldum H. L.
Published: December 2017

Somatostatin modulates both endocrine and exocrine functions in the gastric mucosa, where three of the five cloned somatostatin receptors are present. This study examines changes in somatostatin receptor (SSTR) mRNA abundance during fasting, feeding, and profound acid inhibition with omeprazole. Serum gastrin as well as somatostatin and SSTR mRNA abundances were measured in antrum and corpus. In Northern blots of corpus RNA, the SSTR2 probe hybridized with two previously reported species of mRNA (2.4 and 2.8 kb); in addition, a weak previously unreported 1.6-kb band was detected. In antrum, the 1.6-kb band dominated. Fasting increased antral somatostatin mRNA from 100 +/- 8 to 161 +/- 24% and SSTR mRNA from 100 +/- 10 to 179 +/- 14% (P < 0.05). Omeprazole reduced antral somatostatin mRNA to 34 +/- 4% of control (P < 0.05) and elevated SSTR mRNA to 135 +/- 5% of control (P < 0.01). Omeprazole treatment reduced corpus somatostatin mRNA to 59 +/- 5% (P < 0.05), and elevated SSTR mRNA to 140 +/- 3% of control (P < 0.01). The results therefore indicate that a novel SSTR mRNA subtype exists in the stomach and predominates in the antrum. The abundance of this SSTR mRNA is upregulated by both fasting and achlorhydria; conditions that increase or decrease endogenous antral somatostatin, respectively.
Adenosine nucleotides in bile
Authors: Chari R. S. , Schutz S. M. , Haebig J. E. , Shimokura G. H. , Cotton P. B. , Fitz J. G. , Meyers W. C.
Published: December 2017

Activation of purinergic receptors by ATP stimulates Cl- efflux in biliary epithelial cells. To determine whether purinergic agonists are present under physiological conditions, we have assayed mammalian bile for nucleotides and assessed whether hepatoma and cholangiocarcinoma cell lines are capable of nucleotide release. Bile samples were collected from human, rat, and pig donors and assayed for nucleotide concentrations by luminometry. ATP, ADP, and AMP were present in bile from each species, and the average total nucleotide concentration in human bile was 5.21 +/- 0.91 microM (n = 16). In an in vitro model of HTC rat hepatoma cells or Mz-ChA-1 cholangiocarcinoma cells on a superfused column, nucleotides were present in the effluent from each cell type. Addition of alpha, beta-methyleneadenosine 5'-diphosphate (50 microM) to inhibit 5'-nucleotidase activity increased AMP concentrations two- to threefold. Exposure to forskolin (100 microM) or ionomycin (2 microM) stimulated nucleotide release from cholangiocarcinoma but not hepatoma cells. These studies indicate that adenosine nucleotides are present in bile in concentrations sufficient to activate purinergic receptors. Purinergic receptor activation by local nucleotide release might constitute an autocrine and/or paracrine mechanism for modulation of biliary secretion.
Rat liver ferritin selectively inhibits expression of alpha-smooth muscle actin in cultured rat lipocytes
Authors: Ramm G. A. , Britton R. S. , O'Neill R. , Kohn H. D. , Bacon B. R.
Published: December 2017

The role of ferritin in lipocyte activation is unknown. This study examined the effect of rat liver ferritin (RLF), human recombinant H-ferritin (HrHF), human recombinant L-ferritin (HrLF), apo-ferritin (apo-RLF), and hemin on lipocyte activation. Lipocytes were cultured on uncoated plastic and were incubated with these agents for 7 days, at concentrations ranging from 10(-14) to 10(-7) M (0.5 to 50 microM for hemin). Collagen/noncollagen protein production and lipocyte proliferation were determined by [3H]proline and [3H]thymidine incorporation, respectively, and the expression of alpha-smooth muscle actin (alpha-SMA) and desmin was determined by Western blot. RLF, at concentrations ranging from 10(-10) to 10(-7) M, decreased alpha-SMA expression by 65-88%. Apo-RLF, HrHF, and HrLF decreased alpha-SMA by 17-45% at 10(-7) and 10(-8) M. Hemin (10 or 50 microM) inhibited alpha-SMA by 37 and 54%, respectively. Desmin expression was not altered by ferritin or hemin. Collagen and noncollagen protein production were not altered by either RLF or apo-RLF. Lipocyte proliferation was decreased by 54, 32, and 40%, by 10(-7) M RLF, HrHF, and HrLF, respectively, whereas apo-RLF had no effect. Thus RLF inhibited lipocyte alpha-SMA expression, which may be due to an effect of sequestered iron, since neither apo-RLF, HrHF, nor HrLF had a potent effect on alpha-SMA expression and all are essentially iron-free. The inhibitory effect of iron-loaded RLF on alpha-SMA expression suggests that tissue ferritin does not initiate lipocyte activation in iron overload, but rather may have a suppressive action on this process.
Rab11 is an apically located small GTP-binding protein in epithelial tissues
Authors: Goldenring J. R. , Smith J. , Vaughan H. D. , Cameron P. , Hawkins W. , Navarre J.
Published: December 2017

Rab proteins are involved in many aspects of dynamic vesicle processing within eukaryotic cells. We have previously identified Rab11 in gastric parietal cell tubulovesicle membranes. We have produced a monoclonal antibody that is specific for Rab11. In all rabbit tissues examined, Rab11 immunoreactivity was highly enriched in epithelial cells. In the gastric fundus, parietal cells were stained in a pattern consistent with localization on tubulovesicles. Surface mucous cells of both the fundus and antrum demonstrated punctate subapical staining. Ileal and proximal colonic enterocyte labeling was observed deep to the brush borders. In the distal colon, staining was observed in the apical regions of mid-crypt cells. In skin and esophagus, punctate immunoreactivity was present in the medial layers of the squamous epithelia. Prominent Rab11 immunoreactivity was present in hepatocytes deep to the bile canaliculi. Punctate subapical staining was observed in pancreatic acinar cells. Apical staining was also observed in collecting duct cells and in the glandular cells of the prostate. These results indicate the Rab11 is expressed in apical vesicular populations in discrete epithelial cell populations.
Facilitating effect of CCK on nicotinic neurotransmission in cat pancreatic ganglion
Authors: Ma R. C. , Szurszewski J. H.
Published: December 2017

Previous studies have demonstrated the presence of cholecystokinin (CCK)-like peptides in nerve terminals surrounding ganglion neurons of the cat pancreas. The present study was undertaken to determine the effect of cholecystokinin octapeptide (CCK-8) on ganglionic transmission. Recordings were made intracellularly in vitro from ganglion neurons in isolated pieces of the pancreas. Sulfated CCK-8 (S-CCK-8) and nonsulfated CCK-8 initiated or increased ongoing fast excitatory postsynaptic potential (fEPSP) activity, an effect antagonized by hexamethonium. Superfusion of S-CCK-8 in concentrations ranging from 10(-11) to 10(-8) M significantly augmented the amplitude of nerve-evoked subthreshold fEPSPs without a significant change in either membrane potential or membrane input resistance. S-CCK-8 (10(-8)M) also increased the quantal content and quantal size of nerve-evoked fEPSPs and increased the response to exogenously applied acetylcholine (ACh). Concentrations of S-CCK-8 higher than 10(-8)M caused depolarization and an increase in membrane input resistance, an effect unaltered by a low-Ca+, high-Mg2+ solution. It was concluded that S-CCK-8 potentiated nicotinic transmission by facilitating release of ACh from preganglionic nerve terminals and by increasing the postsynaptic membrane sensitivity to ACh.
Opossum colonic mucosa contains uroguanylin and guanylin peptides
Authors: Hamra F. K. , Krause W. J. , Eber S. L. , Freeman R. H. , Smith C. E. , Currie M. G. , Forte L. R.
Published: December 2017

Uroguanylin and guanylin are structurally related peptides that activate an intestinal form of membrane guanylate cyclase (GC-C). Guanylin was isolated from the intestine, but uroguanylin was isolated from urine, thus a tissue source for uroguanylin was sought. In these experiments, uroguanylin and guanylin were separated and purified independently from colonic mucosa and urine of opossums. Colonic, urinary, and synthetic forms of uroguanylin had an isoelectric point of approximately 3.0, eluted from C18 reverse-phase high-performance liquid chromatography (RP-HPLC) columns at 8-9% acetonitrile, elicited greater guanosine 3', 5'-cyclic monophosphate (cGMP) responses in T84 cells at pH 5.5 than pH 8, and were not cleaved and inactivated by pretreatment with chymotrypsin. In contrast, colonic, urinary, and synthetic guanylin had an isoelectric point of approximately 6.0, eluted at 15-16% acetonitrile on C18 RP-HPLC columns, stimulated greater cGMP responses in T84 cells at pH 8 than pH 5.5, and were inactivated by chymotrypsin, which hydrolyzed the Phe-Ala or Try-Ala bonds within guanylin. Uroguanylin joins guanylin as an intestinal peptide that may participate in an intrinsic pathway for cGMP-mediated regulation of intestinal salt and water transport. Moreover, uroguanylin and guanylin in urine may be derived from the intestinal mucosa, thus implicating these peptides in an endocrine mechanism linking the intestine with the kidney.
Characterization of cytosolic Ca2+ signaling in rat bile duct epithelia
Authors: Nathanson M. H. , Burgstahler A. D. , Mennone A. , Boyer J. L.
Published: December 2017

Bile duct epithelia play an important role in the formation and conditioning of bile. However, hormonal responses in this epithelial tissue are incompletely understood. Secretin increases ductular secretion through the intracellular messenger adenosine 3',5'-cyclic monophosphate (cAMP), but whether hormones increase cytosolic Ca2+ (Ca2+(i)) in these cells and whether Ca2+(i) regulates duct secretion is unknown. To address these questions, we examined Ca2+(i) signaling in isolated rat bile duct units using ratio microspectrofluorometry and confocal microscopy. We also used videomicroscopy to examine secretion and cell volume in isolated bile duct cells and duct units. Acetylcholine (ACh) and ATP both increased Ca2+(i) in bile duct units and elicited patterns of Ca2+(i) increases and oscillations that were distinct and dose dependent. In contrast, Ca2+(i) was not increased by the hepatocyte Ca2+(i) agonists vasopressin, angiotensin, and phenylephrine or by the exocrine pancreas agonists cholecystokinin (CCK) and bombesin. In addition, secretin did not increase Ca2+(i) in the isolated bile duct units, whereas ACh did not increase Ca2+(i) in isolated hepatocytes. Mobilization of internal, thapsigargin-sensitive Ca2+ stores contributed more than influx of extracellular Ca2+ to the Ca2+(i) increases induced in the duct units, and ATP-induced increases in Ca2+(i) could be blocked by microinjection of heparin but not de-N-sulfated heparin. ACh transiently decreased bile flow in the isolated perfused rat liver, although neither ACh nor ATP altered secretion in isolated ducts or changed the volume of single isolated bile duct cells. These findings demonstrate that bile duct epithelial cells possess both muscarinic and purinergic receptors that activate Ca2+(i) signaling pathways similar to those seen in other types of epithelia, but that the two types of receptors elicit distinct patterns of Ca2+(i) signals. Increases in Ca2+(i) have minimal direct effects on bile duct secretion, although it remains to be determined whether such signals selectively modulate other aspects of bile duct epithelial cell function.
Lipoprotein and apolipoprotein secretion by a newborn piglet intestinal cell line (IPEC-1)
Authors: Gonzalez-Vallina R. , Wang H. , Zhan R. , Berschneider H. M. , Lee R. M. , Davidson N. O. , Black D. D.
Published: December 2017

The aim of these studies was to characterize the synthesis and secretion of lipoproteins and apolipoprotein B (apo B) and apo A-I by a newborn swine intestinal epithelial cell line (IPEC-1). Differentiated cells exhibited enterocytic features, including microvilli. [3H] oleic acid was taken up and incorporated into cellular lipids and secreted into the basolateral medium in lipoproteins. Total apo B and apo A-I secreted increased with oleic acid incubation. However, cellular apo B and apo A-I content did not change. Whereas undifferentiated cells synthesized and secreted only apo B-100, both apo B-100 and apo B-48 were produced by differentiated cells. The ratio of radiolabeled apo B-48 to apo B-100 in both basolateral medium and cell homogenate increased with oleic acid treatment after 24-h steady-state labeling. However, apo B mRNA editing was unchanged, indicating posttranslational regulation of this ratio. Pulse-chase radiolabeling demonstrated no major changes in cellular or basolateral medium apolipoprotein labeling kinetics with oleic acid or dexamethasone incubation. The dissociation of apo B and apo A-I mass secretion from the secretion of radiolabeled apo B and apo A-I in response to oleic acid absorption suggests the presence of an intracellular pool of apolipoprotein with a slow turnover that is mobilized for secretion in response to fatty acid uptake.
Effects of increasing solid component size of a mixed solid/liquid meal on solid and liquid gastric emptying
Authors: Collins P. J. , Horowitz M. , Maddox A. , Myers J. C. , Chatterton B. E.
Published: December 2017

This study evaluated the hypothesis that an increase in the volume of the solid component of a mixed solid/nutrient liquid meal will result in more rapid emptying of the solid but slower liquid emptying. Eight normal volunteers were studied on two occasions after ingesting a meal containing 150 ml of 10% dextrose with either 100 g(small) or 400 g (large) of ground beef. Subjects ingested the solid component before the liquid. For the solid component, the lag phase was longer for the larger meal (56 vs. 31 min, P < 0.001). However, the absolute emptying rate for the proximal stomach and the postlag emptying rate of solid from the total stomach, when expressed as kilocalories per minute, were greater with the larger meal (P < 0.002). The lag phase was prolonged (P < 0.03) and the rate of emptying of liquid from the total and proximal stomach was slower (P < 0.001) in the large compared with the small meal. The total amount of energy delivered to the duodenum (from solid and liquid components) after the solid lag phase was greater for the larger meal (4.8 vs. 2.5 kcal/min, P < 0.002). These results indicate that an increase in the volume of the solid component of a mixed solid/liquid meal 1) prolongs the lag phase but accelerates the postlag emptying rate of solid and 2) retards intragastric distribution and emptying of liquid.