bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrophysiological identification of vagally innervated enteric neurons in guinea pig stomach
Authors: Schemann M. , Grundy D.
Published: December 2017

Myenteric "command neurons" are thought to be the interface between extrinsic and intrinsic controls of gut functions and are thought to be responsible for transmission of vagal impulses to enteric microcircuits. To identify, electrophysiologically, myenteric neurons responding to electrical stimulation of the vagus, we developed an in vitro preparation of the gastric myenteric plexus in which the vagal innervation was preserved. The majority of myenteric neurons [102 of 155 (66%)] received fast excitatory postsynaptic potentials (fEPSPs) after stimulation of the vagus. The proportion of neurons receiving vagal input was highest at the lesser curve (98%) and decreased gradually when recordings were made from neurons located toward the greater curve. Only a small proportion of neurons (4 of 85 cells) showed a slow EPSP after a burst of vagal stimulation. No postsynaptic inhibitory potentials were observed. There was no preferential vagal input to either gastric I, gastric II, or gastric III neurons. The fEPSPs were due to the release of acetylcholine acting postsynaptically on nicotinic receptors. The behavior of the fEPSPs suggests multiple vagal inputs to a majority of myenteric neurons. Our observations call into question the concept of enteric command neurons in favor of a divergent vagal input with widespread modulatory influences over gastric enteric neurotransmission.
Human colon cancer cells express ICAM-1 in vivo and support LFA-1-dependent lymphocyte adhesion in vitro
Authors: Kelly C. P. , O'Keane J. C. , Orellana J. , Schroy P. C. , Yang S. , LaMont J. T. , Brady H. R.
Published: December 2017

Intercellular adhesion molecule-1 (ICAM-1) is a cell surface adhesion glycoprotein that mediates leukocyte adhesion through interaction with the leukocyte CD11/CD18 adhesion complex. The aim of this study was to determine whether ICAM-1 is expressed by normal or neoplastic colonic epithelial cells. Immunohistochemical studies on human colonic tissue demonstrated focal ICAM-1 expression by colonic carcinomas but not by normal colonic epithelium. ICAM-1 expression by colonic carcinomas showed a positive correlation with the presence of a peritumoral inflammatory infiltrate. Surface expression of ICAM-1 was also observed in HT-29 cultured human colon cancer cells by both immunohistochemistry and enzyme immunoassay. Interferon-gamma and interleukin-1 beta significantly increased ICAM-1 surface expression by HT-29 cells in a dose-dependent manner. Upregulation of ICAM-1 surface expression became evident some hours after cytokine stimulation and was inhibited by both actinomycin D and cycloheximide, indicating a requirement for de novo RNA and protein synthesis. HT-29 monolayers supported adhesion of human lymphocytes as determined by a quantitative 111In-labeled leukocyte adhesion assay. Adhesion was mediated in part via interaction of ICAM-1 on HT-29 cells with lymphocyte function-associated antigen-1 (CD11a/CD18) on lymphocytes, as defined by using blocking monoclonal antibodies. Expression of ICAM-1 and/or other leukocyte adhesion receptors by neoplastic epithelial cells may play a role in directing leukocyte trafficking and leukocyte-epithelial cell interactions in colonic carcinoma.
Na(+)-independent multispecific anion transporter mediates active transport of pravastatin into rat liver
Authors: Yamazaki M. , Suzuki H. , Hanano M. , Tokui T. , Komai T. , Sugiyama Y.
Published: December 2017

To examine whether the relatively selective inhibition of hepatic cholesterol synthesis by the hydrophilic 3-hydroxyl-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor pravastatin in vivo may be due to the existence of a specific uptake mechanism in the liver, the uptake by isolated rat hepatocytes was investigated. The uptake was composed of a saturable component [Michaelis constant (Km) 29 microM, maximal uptake rate 546 pmol.min-1.mg-1] and nonspecific diffusion (nonspecific uptake clearance 1.6 microliters.min-1.mg-1), inhibited by hypothermia, metabolic inhibitors, sulfhydryl-modifying reagents, and inhibitor of anion exchanger, whereas replacement of Na+ by choline+ or Cl- by gluconate- did not alter the uptake. Competitive inhibition was observed by a more highly lipophilic HMG-CoA reductase inhibitor simvastatin (open acid form), dibromosulfophthalein, cholate, and taurocholate. Pravastatin inhibited Na(+)-independent taurocholate uptake with an inhibition constant comparable with the Km value of pravastatin itself. Furthermore, the hepatic permeability clearance in vivo obtained with intact rats was comparable with that in vitro, indicating that the carrier-mediated active transport system we demonstrated in vitro is responsible for the hepatic uptake in vivo. These findings demonstrated that the hepatic uptake of pravastatin occurs via a carrier-mediated active transport mechanism utilizing the so-called multispecific anion transporter, which is common with the Na(+)-independent bile acid uptake system, and that this is one of the mechanisms for its selective inhibition of hepatic cholesterol synthesis in vivo.
Dual effects of cisapride on gastric emptying and antropyloroduodenal motility
Authors: Fraser R. , Horowitz M. , Maddox A. , Dent J.
Published: December 2017

There is little information about the effects of cisapride on human antropyloroduodenal motility, despite its documented efficacy for increasing the rate of gastric emptying in patients with gastroparesis. Cisapride has been reported to have little effect on gastric emptying in normal subjects. Antral, pyloric, and duodenal pressures were recorded simultaneously with gastric emptying in 20 healthy volunteers. Thirty minutes after the solid component of the meal had started to empty from the stomach, each subject received either 10 mg cisapride i.v. (11 subjects) or intravenous saline (9 subjects). Intravenous saline had no effect on either motility or gastric emptying. In contrast, cisapride administration was associated with a dual effect on motility, with initial suppression of antral pressure waves (P < 0.05) followed by stimulation of associated antropyloroduodenal pressure waves (P < 0.01). Gastric emptying slowed in the first 30 min after cisapride (P < 0.05), and this was followed by more rapid gastric emptying (P < 0.01). The amount of the meal emptied in the 60 min after cisapride correlated with the number of associated antroduodenal pressure waves (r = 0.75, P < 0.001) but not with the number of antral waves (r = 0.42, NS). These results indicate that cisapride in a dose of 10 mg i.v. has dual effects on gastric emptying and gastric motility. The stimulation of associated antral pressure waves is a plausible mechanism for the efficacy of cisapride in the treatment of gastroparesis.
Effects of autonomic antagonists and growth factors on activity-mediated hyperplasia of rat parotid
Authors: Schneyer C. A. , Humphreys-Beher M. G. , Jirakulsomchok D. , Hall H. D.
Published: December 2017

Administration of the autonomic antagonists atropine (1 mg/kg body wt), propranolol (2 mg/kg body wt), and phenoxybenzamine (2 mg/kg body wt) before the dietary change from all liquid to solid chow prevented an increase in uptake of [3H]thymidine into DNA of rat parotid gland associated with this dietary change. Administration of either the cholinergic antagonist alone or the adrenergic antagonists alone produced partial inhibition. The effects of complete autonomic blockade were not reversed when nerve growth factor (NGF) or epidermal growth factor (EGF) was given immediately after administration of antagonists. The effects of complete autonomic blockade were similar to those seen with surgical removal of the autonomic nerves to the parotid. The increased levels of beta 1-4-galactosyltransferase seen with the dietary change were not evident in rats given both muscarinic and adrenergic antagonists before the change to solid food nor did NGF or EGF reverse these inhibitory effects. Histological observation showed that the surgically denervated gland was morphologically less homogenous than the gland of rats given the antagonists and had infiltrating connective tissue. Nonetheless, with the reduced acinar cell pool, the [3H]thymidine uptake of the denervated parotid and that of antagonist-injected animals was similar.
K+ currents in rabbit esophageal muscularis mucosae
Authors: Akbarali H. I.
Published: December 2017

Single cells were obtained from esophageal muscularis mucosae of the rabbit using enzymatic dispersion. Their electrophysiological properties were studied with both conventional whole cell and nystatin-perforated patch techniques. The latter technique was used to prevent "washout" of intracellular constituents and to maintain endogenous buffering of Ca2+. The average resting potential of these cells was -54 +/- 3.2 mV in the conventional recording and -51 +/- 4.4 mV in perforated patch recordings. In the current-clamp mode, regenerative responses were consistently observed in perforated patch recordings, but not when conventional whole cell gigaseal methods were used. Conventional whole cell voltage-clamp methods revealed outward currents on depolarization from a holding potential of -70 mV. These currents were inhibited by extracellular tetraethylammonium (TEA, 5-10 mM) and CoCl2 (4 mM), indicating that the predominant outward current is a Ca(2+)-activated K+ current. In the presence of TEA, inward Ca2+ currents were unmasked. In contrast, when the nystatin-perforated patch technique was used, depolarizations resulted in a net inward current followed by an outward current. The outward current was inhibited by CoCl2 (2 mM) and TEA (5 mM) to the same extent as in conventional recordings. A second component of K+ current was observed in both types of recordings when extracellular Ca2+ influx was abolished and also in the presence of TEA. This slowly activating persistent K+ current resembled a delayed rectifier K+ current. These studies show that the rabbit tunica muscularis mucosal cells possess voltage-activated Ca2+ and K+ channels as well as the capability to elicit action potentials.
Posttranslational inhibition of Ito cell type I collagen production by triiodothyronine
Authors: Lissoos T. W. , Beno D. W. , Davis B. H.
Published: December 2017

Increased Ito cell collagen production occurs during in vivo liver fibrogenesis. Regulation of the overproduction of collagen was studied in cultured rat hepatic Ito cells, which resemble the myofibroblast associated with liver fibrosis. Previous studies suggest that the steroid hormones, retinoic acid, and glucocorticoids may have antifibrogenic properties in vitro and in vivo when used at pharmacological doses. Their potential roles at physiological levels are not well understood. The current study examined the potential regulation of the overproduction of type I collagen in cultured rat hepatic Ito cells by another steroid hormone, 3,5,3'-triiodo-L-thyronine (T3). T3 induced a 3.4-fold reduction in type I collagen production. The effect was dose dependent and was maximal with physiological levels of T3 (10(-9) M). The effect of T3 was independent of any suppression in total protein synthesis. The mechanism of the suppressive effect of T3 on collagen production was explored and was found to be at a posttranslational level. This study suggests that the inhibitory effects of T3 on type I collagen production are likely caused by enhanced intracellular turnover of type I collagen.
Transepithelial transport of cholyltaurine by Caco-2 cell monolayers is sodium dependent
Authors: Chandler C. E. , Zaccaro L. M. , Moberly J. B.
Published: December 2017

Bile acids are efficiently recovered from the intestinal lumen by a Na(+)-dependent transport process that is localized in the ileal enterocyte brush-border membrane. To establish a cell culture model for this process, we examined the Na+ dependence of cholyltaurine (C-tau; taurocholate) transport across monolayers of differentiated Caco-2 cells grown on permeable filter inserts. Transport of [3H]C-tau was Na+ dependent (> 20-fold stimulation), saturable, and time linear for at least 60 min. The apparent Michaelis constant of [3H]C-tau transport was approximately 65 microM, and the maximal transport rate was approximately 800 pmol.min-1.mg protein-1. Transport of [3H]C-tau in the apical-to-basolateral direction was 17-fold greater than transport in the reverse direction. Lowered incubation temperature, various metabolic inhibitors, and various unlabeled bile acids inhibited [3H]C-tau transport. Caco-2 cells thus transport bile acids in a manner similar to that described for ileal brush-border membrane vesicles and isolated ileal enterocytes and are therefore an appropriate model for studying the molecular basis of ileal bile acid transport.
Gastric vagal-evoked and greater splanchnic-evoked unitary responses in the hypothalamus
Authors: Barber W. D. , Yuan C. S.
Published: December 2017

Gastric vagal and greater splanchnic nerve fibers were electrically stimulated to localize and characterize neuronal interactions in the hypothalamus of anesthetized cats. Extracellular recordings from 635 hypothalamic units were identified that responded to electrical stimulation of the left greater splanchnic nerve or gastric vagal fibers serving the proximal stomach. A total of 504 hypothalamic units in this group received input from both gastric vagal and greater splanchnic nerves. The gastric vagal-evoked hypothalamic (GVeH) and greater splanchnic-evoked hypothalamic (SeH) responses were widely distributed in the medial, paraventricular, and dorsomedial nuclei and lateral hypothalamus. The conduction velocity of the SeH response was significantly greater than the GVeH response. The latency of the SeH response showed two peaks [58 +/- 15.7 (SD) ms and 136 +/- 18.3 (SD) ms] indicating that the splanchnic input terminated on two different groups or populations of hypothalamic neurons. It also suggested that different pathways or fiber diameters in the pathway may be involved in the transmission of splanchnic input to the hypothalamus. The majority of the GVeH and SeH unitary responses were multiple spikes or short trains of action potentials. Excitatory and inhibitory responses were observed in tonically active hypothalamic units that responded to gastric vagal or greater splanchnic input. The duration of decreased excitability to gastric vagal or greater splanchnic input was significantly greater than the period of increased excitability. The condition-test paradigm was used to determine the time course of convergent gastric vagal-greater splanchnic input on single hypothalamic neurons.(ABSTRACT TRUNCATED AT 250 WORDS)
Gastric damage caused by acidified ethanol: role of molecular HCl
Authors: Barreto J. C. , Smith G. S. , Russell D. H. , Miller T. A.
Published: December 2017

This study was undertaken to test the hypothesis that an increase in the concentration of molecular HCl in ethanolic solutions is at least partly responsible for the severity of damage seen with acidified ethanol. To accomplish this goal, we studied the synergistic relationship of HCl and ethanol by holding ethanol constant at 50% (vol/vol) and varying the acid concentration. In another experiment, acid concentration was held constant at 150 mM HCl, and the percentage of ethanol was varied. Our hypothesis was also tested by substituting sulfate for chloride to form H2SO4, a nonpermeant molecular acid. Results of our studies clearly showed that substitution of sulfate for chloride greatly reduced gastric damage, supporting the hypothesis that diffusion of molecular HCl is contributing to the damage by acidifying cells. In all cases, acidified ethanol solutions using HCl were more damaging than the individual components alone, and the severity of the damage caused by 50% ethanol was noted to be dependent on the concentration of HCl. We therefore conclude that the severity of acidified ethanol damage is dependent on cellular acidification caused by diffusion of molecular HCl.
Central and peripheral effects of CCK receptor antagonists on satiety in dogs
Authors: Cheng C. A. , Geoghegan J. G. , Lawson D. C. , Berlangieri S. U. , Akwari O. , Pappas T. N.
Published: December 2017

The role of cholecystokinin (CCK) as a central and peripheral satiety factor was studied using the CCK-B (L-365,260) and CCK-A (MK-329) receptor antagonists in esophageal-fistula dogs. Suppression of feeding was induced by either balloon gastric distension or small bowel nutrient infusion and was measured as the volume sham fed. Intracerebroventricular L-365,260 abolished satiety behavior from gastric distension (volume sham fed 2,667 +/- 211 ml vs. vehicle alone 1,217 +/- 446 ml, P < 0.05) but not small bowel infusion. Intravenous MK-329 abolished satiety behavior from small bowel infusion (volume sham fed 1,900 +/- 521 ml vs. vehicle alone 210 +/- 198 ml, P < 0.05) but not from gastric distension. The volume sham fed after intracerebroventricular MK-329 with balloon gastric distension or small bowel infusion did not differ from control. These results suggest that, in the brain, CCK is a physiological mediator of satiety behavior from gastric distension but not small bowel nutrients and, in the periphery, CCK is a physiological mediator of satiety behavior from small bowel nutrients but not gastric distension.
Omeprazole decreases H(+)-K(+)-ATPase protein and increases permeability of oxyntic secretory membranes in rabbits
Authors: Crothers J. M. , Chow D. C. , Forte J. G.
Published: December 2017

Amounts and fractional distributions of gastric H(+)-K(+)-adenosinetriphosphatase (ATPase) activity and H(+)-K(+)-ATPase protein as well as properties of H(+)-K(+)-ATPase-containing membranes were studied in rabbits injected with omeprazole (OM; 1 mg/kg sc twice daily for 5 days). Total H(+)-K(+)-ATPase activity decreased to 22 +/- 2% of control (n = 4). Densitometry of sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blots showed H(+)-K(+)-ATPase protein was decreased to 60-70% of control. In vitro reduction of the enzyme-OM disulfide bond with 0.1 M 2-mercaptoethanol increased microsomal H(+)-K(+)-ATPase activity to 56 +/- 7% of control (n = 3), consistent with a substantial decrease in enzyme protein. Incorporation of 35S-labeled methionine for 30 min before death resulted in 2.2-fold more label per unit of microsomal alpha-subunit protein (5 days OM vs. control). Thus the decrease in enzyme protein resulted from increased breakdown rather than decreased synthesis. A striking shift in distribution of H(+)-K(+)-ATPase-containing microsomes (tubulovesicles) on sucrose gradients reflected slow equilibration of most control vesicles with the gradient medium and faster equilibration after 5 days OM, indicating increased permeability. After 5 days OM, microsomal vesicle acidification (by acridine orange uptake assay) was negligible, even with 2-mercaptoethanol treatment, and H+ leakage on sudden delta pH was faster than control. We conclude that extended OM treatment not only inhibits H(+)-K(+)-ATPase but accelerates its breakdown and renders H(+)-K(+)-ATPase-containing membranes more permeable. It is thus possible that increased backward H+ flux contributes to profound inhibition of acid secretion during extended omeprazole treatment. In parallel experiments, H(+)-K(+)-ATPase activity and density gradient sedimentation of tubulovesicles returned to near normal 3 days after OM withdrawal.
Epidermal growth factor and the maturation of intestinal sucrase in suckling rats
Authors: Foltzer-Jourdainne C. , Garaud J. C. , Nsi-Emvo E. , Raul F.
Published: December 2017

The regulatory effect of epidermal growth factor (EGF) on the postnatal maturation of sucrase was investigated in the small intestine of suckling and weanling rats. Administration of EGF (0.5 micrograms.g body wt-1.day-1) to suckling rats caused a slight precocious induction of sucrase expression. In weanling rats EGF markedly stimulated sucrase activity; however, at both ages, the effect of hydrocortisone was more potent. When the glucocorticoid antagonist RU-38486 was administered to sucklings, the precocious induction of sucrase activity by hydrocortisone was inhibited by 80%. However, RU-38486 or adrenalectomy did not prevent the inductive effect of EGF, indicating that EGF acts in a glucocorticoid-independent manner. EGF also potentiated the effect of hydrocortisone and dietary sucrose on the precocious induction of sucrase activity in the sucklings. At weaning, administration of an antiserum specific to rat EGF significantly decreased sucrase activity. This study shows the involvement of EGF in the postnatal maturation of intestinal sucrase in the rat.
Distribution of adenylate cyclase and GTP-binding proteins in hepatic plasma membranes
Authors: Dixon B. S. , Sutherland E. , Alexander A. , Nibel D. , Simon F. R.
Published: December 2017

Hepatic membrane subfractions prepared from control rats demonstrated forskolin (FSK)-stimulated adenylate cyclase activity in the basolateral (sinusoidal) but not apical (canalicular) plasma membrane. After bile duct ligation (BDL) for 12 or 24 h, there was an increase in FSK-stimulated adenylate cyclase activity in the apical membrane (54.2 +/- 3.9 pmol.mg-1 x min-1). The mechanism for this increase was explored further. ATP hydrolysis was found to be much higher in the apical than the basolateral membrane. Increasing the ATP levels in the assay enhanced apical membrane adenylate cyclase activity (10.5 +/- 0.2 pmol.mg-l.min-1); however, total adenosinetriphosphatase (ATPase) activity was not altered after BDL. Extraction of the apical membrane with bile acids or other detergents resulted in a two- to threefold increase in adenylate cyclase activity (30.6 +/- 3.6 pmol.mg-1 x min-1; detergent C12E8) This suggested that bile duct ligation was acting via the detergent-like action of bile acids to uncover latent adenylate cyclase activity on apical membranes. Further studies demonstrated that both BDL and detergent extraction also enhanced toxin-directed ADP-ribosylation of Gs alpha (cholera toxin) and Gi alpha (pertussis toxin) in the apical but not the basolateral membrane. After BDL, Gi alpha was found to be twofold greater in the apical membrane than the basolateral membrane. Immunoblotting using specific G protein antibodies further confirmed that apical membranes from control rats had a higher concentration of Gi1, 2 alpha and beta and slightly elevated levels of Gi3 alpha and Gs alpha compared with the basolateral membrane. The results demonstrate that adenylate cyclase and heterotrimeric GTP-binding proteins are present on the apical membrane, but measurement of their functional activity requires detergent permeabilization of apical membrane vesicles and is limited by the presence of high ATPase activity.
Effects of gastric pacing on canine gastric motility and emptying
Authors: Eagon J. C. , Kelly K. A.
Published: December 2017

Gastric pacing has been achieved in dogs and humans, but its effects on gastric motility and emptying have not been thoroughly explored. Seven dogs had bipolar electrodes placed 1 and 10 cm proximal to the pylorus for reverse and forward pacing and monopolar recording electrodes and strain gauges placed 3, 5, and 7 cm proximal to the pylorus. After recovery, myoelectrical and contractile activity and gastric emptying of a mixed meal (50 g 99mTc-labeled liver and 250 ml 111In-labeled 5% dextrose broth solution) were measured in each of three conditions: no pacing, reverse pacing, and forward pacing (frequency 0.5 cycles/min above intrinsic pacesetter potential frequency). Reverse pacing reversed the direction of > 90% of antral pacesetter potentials and peristaltic waves in six of seven dogs, prolonged the lag phase of solid emptying, prolonged the half emptying time of solids and liquids, and increased the antral motility index. Forward pacing entrained pacesetter potentials but had no consistent effect on emptying or antral contractions. In conclusion, reverse gastric pacing slows gastric emptying of digestible solids and liquids by reversing the direction of antral peristalsis and increasing the antral motility index, whereas forward pacing has no such effects.
Effect of ursodeoxycholic acid on intracellular pH regulation in isolated rat bile duct epithelial cells
Authors: Alvaro D. , Mennone A. , Boyer J. L.
Published: December 2017

To determine if ursodeoxycholic acid (UDCA) induces a HCO3(-)-rich hypercholeresis by stimulating HCO3- secretion from bile duct epithelial (BDE) cells, we studied the effect of UDCA, sodium tauroursodeoxycholate (TUDCA), and cholic acid on intracellular pH (pHi) regulation and HCO3- excretion in BDE cells isolated from normal rat liver. Exposure of BDE cells to UDCA (0.5-1.5 mM) produced a dose-dependent initial acidification [from -0.05 to -0.16 pH units (pHu)], which was lower in Krebs-Ringer bicarbonate than in N-2-hydroxyethylpiperazine-N'-2- ethanesulfonic acid (HEPES), because of the higher cell-buffering power in the presence of HCO3-. In contrast, TUDCA (1 mM) had no effect on pHi in either media. BDE acidification induced by UDCA (1.5 mM) in KRB was not inhibited by Cl- depletion excluding activation of Cl(-)-HCO3- exchange. Most BDE cells spontaneously recovered their basal pHi during the UDCA infusion (0.5-1 mM) by a secondary activation of the Na(+)-H+ exchanger (amiloride inhibition of pHi recovery; n = 4), and pHi overshot basal levels by 0.1-0.2 pHu after UDCA withdrawal. The activity of Cl(-)-HCO3- exchange (Cl- removal/readmission maneuver) as well as the activities of Na(+)-H+ exchange and Na(+)-HCO3- symport (NH4Cl acid load in HEPES and KRB, respectively) were unaffected by UDCA (0.5 mM) compared with controls. Cholic acid (1.5 mM), which does not produce a hypercholeresis, also acidified BDE cells in KRB media. These studies indicate that UDCA does not stimulate HCO3- excretion from isolated rat BDE cells but modifies pHi in BDE cells as a weak acid.
Structural characterization of PACAP receptors on rat liver plasma membranes
Authors: Nguyen T. D. , Heintz G. G. , Wolfe M. S.
Published: December 2017

Pituitary adenylate cyclase-activating polypeptide-38 (PACAP-38) and PACAP-27 are recently characterized hypothalamic peptides with marked homology with vasoactive intestinal peptide (VIP), which are concentrated in the innervation of the digestive tract. We now report that, on rat liver plasma membranes, PACAP interacts with at least two types of receptors: receptors demonstrating equally high affinity for PACAP and VIP and receptors with high affinity for PACAP but low affinity for VIP. In contrast, on rat intestinal epithelial cell laterobasal membranes, only receptors with high affinities for PACAP and VIP were observed. After 125I-labeled VIP or 125I-labeled PACAP-27 was cross-linked to the liver plasma membrane receptors with the use of either disuccinimidosuberate or disuccinimido dithiobis(propionate), analysis of the resulting ligand-receptor complexes on sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that the structures of the VIP and PACAP receptors were similar: both ligand-receptor complexes displayed two radioactive bands with relative molecular weights of 80,000 and 56,000 under reducing conditions and of 75,000 and 53,000 under nonreducing conditions. These findings suggest that the receptors for the PACAP peptides and VIP are closely related, reflecting the marked homology between these peptides. The presence of receptors specific for PACAP on rat liver plasma membranes should stimulate further studies of the interaction between PACAP and the liver.
Effect of cyclooxygenase inhibition on macromolecular transport in rat gastric mucosa
Authors: Curtis G. H. , MacNaughton W. K. , Gall D. G.
Published: December 2017

We have shown that the rat gastric mucosa takes up antigenically intact protein in vitro. The present study investigated the effect of two cyclooxygenase inhibitors, indomethacin and piroxicam, on gastric transport of BSA. Fasted rats were given indomethacin, piroxicam, or vehicle. After 30 min, the stomach was removed, stripped, and mounted in a Ussing chamber. Each side was bathed with Krebs buffer. Bovine serum albumin (BSA), 125I-labeled BSA (125I-BSA), and 51Cr-labeled EDTA (51Cr-EDTA) were added to the mucosal fluid and equilibrated for 30 min. Serosal fluids were sampled for two subsequent 30-min periods, and mean fluxes for immunologically intact BSA (enzyme-linked immunoabsorbent assay), total BSA (125I-BSA), and 51Cr-EDTA were calculated. Cyclooxygenase inhibition significantly (P < 0.01) reduced tissue prostaglandin E2 synthetic capacity (indomethacin, 97%; piroxicam, 92%) but did not cause either macroscopic or microscopic mucosal injury. Both inhibitors significantly (P < 0.05) decreased uptake of immunologically intact BSA (indomethacin, 91%; piroxicam, 81%) and 51Cr-EDTA. In contrast, the movement of degraded BSA was not altered by indomethacin. These findings suggest that a selective pathway exists for the uptake of intact proteins in gastric mucosa and that the pathway is modulated by cyclooxygenase metabolites.
Autonomic pathways in development of neural stimulation-induced gastric mucosal damage
Authors: Hierlihy L. E. , Wallace J. L. , Ferguson A. V.
Published: December 2017

Gastric mucosal erosions can be induced by electrical stimulation of either vagus nerves (5 Hz, 5 V, 1 ms) or the paraventricular nucleus (PVN) of the hypothalamus (200 microA, 60 Hz, 100-microseconds pulse width). We have utilized various pharmacological and surgical interventions to determine the contributions of different components of the autonomic nervous system to the development of this neurally induced gastric damage in urethan-anesthetized Sprague-Dawley rats. In all experiments damage was assessed macroscopically and scored blindly on a 0 (normal) to 3 (severe) scale with samples sectioned for subsequent histological assessment of damage at the light microscopic level. Animals pretreated with either hexamethonium (30 mg/kg iv) or atropine (2 mg/kg iv) demonstrated reduced gastric damage scores after vagal stimulation compared with untreated control animals (P < 0.05). In contrast animals that underwent cervical cord transection exhibited gastric damage after both vagal and PVN stimulation that was not significantly different compared with animals with an intact cord undergoing similar stimulation (P > 0.05). Such cord transection itself did not cause any significant change to the gastric mucosa in the time period studied. These data emphasize the importance of the autonomic nervous system, in particular the parasympathetic component in the development of vagal stimulation-induced gastric damage. In addition, the present studies suggest that neither vagal nor PVN stimulation-induced gastric damage is dependent on neural projections to sympathetic preganglionic neurons of the intermediolateral cell column of the spinal cord.
Role of leukocytes in indomethacin-induced small bowel injury in the rat
Authors: Chmaisse H. M. , Antoon J. S. , Kvietys P. R. , Grisham M. B. , Perry M. A.
Published: December 2017

This study assesses the role of neutrophils in indomethacin-induced small bowel injury and determines the influence of intestinal pH on the magnitude of this injury. Rat jejunum was perfused via the lumen with buffer, and mucosal injury was assessed by blood-to-lumen clearance of 51Cr-EDTA and quantitative histology. Reduction in luminal pH from 7.4 to 6.0 in the presence of indomethacin (1.0 mg/ml) increased 51Cr-EDTA clearance from 2.0 +/- 0.1 to 6.5 +/- 0.3 microliter.min-1.g-1. Indomethacin caused a reduction in villus length, an increase in villus width, and an increase in lesion score. Depletion of neutrophils with antiserum largely prevented the increase in 51Cr-EDTA clearance and morphological changes. Intravenous indomethacin given at a dose to mimic therapeutic plasma levels (1 mg/kg iv) had no significant effect on 51Cr-EDTA clearance but caused similar morphological changes to those observed following intraluminal administration. The data suggest that neutrophils play a role in acute indomethacin injury and that the drug given intravenously can cause morphological changes without necessarily altering mucosal permeability to 51Cr-EDTA.
Dexamethasone inhibits mucosal adaptation after small bowel resection
Authors: Park J. H. , McCusker R. H. , Mohammadpour H. , Blackwood D. J. , Hrbek M. , Vanderhoof J. A.
Published: December 2017

The present study examined the effects of dexamethasone on mucosal adaptation after massive small bowel resection. Rats underwent 80% jejunoileal resection or a sham operation and received either vehicle or 128 micrograms.kg-1.day-1 sc dexamethasone for 7 days. Dexamethasone infusion resulted in decreased weight, DNA content, and protein content in the duodenojejunal and ileal mucosa in both sham and resected rats. Sucrase, lactase, and maltase activities (all in mumol.g protein-1.min-1) in the duodenojejunal mucosa were elevated by dexamethasone infusion. By contrast, enzyme activities were elevated only in the ileal mucosa of dexamethasone-infused sham-operated rats compared with sham-operated control rats, and dexamethasone did not elevate enzyme activities in resected rats. We further examined whether the inhibitory effects of dexamethasone on mucosal adaptation may be related to changes in either insulin-like growth factor (IGF) or IGF binding protein (BP) serum levels. Serum IGF-I and IGF-II levels were markedly decreased in dexamethasone-infused resected and sham-operated rats. IGF BP-1 serum levels were elevated by dexamethasone treatment with a concomitant depression in serum IGF BP-2 levels. IGF BP-3 levels were lowered by dexamethasone treatment in sham-operated rats and by gut resection, and serum IGF BP-4 levels did not change. These results suggest that the growth-inhibiting effects of dexamethasone in small intestinal mucosa may be partially mediated by decreased serum IGF levels or by alterations in IGF activity associated with changes in serum levels of IGF BPs.
Precocious and reversible expression of sucrase-isomaltase unrelated to intestinal cell turnover
Authors: Nsi-Emvo E. , Foltzer-Jourdainne C. , Raul F. , Gosse F. , Duluc I. , Koch B. , Freund J. N.
Published: December 2017

The effect of starvation and refeeding on the developmental pattern of intestinal sucrase-isomaltase (SI) was analyzed in preweaned rats. Starvation at postnatal day 12 caused a precocious expression of SI activity and mRNA. Alkaline phosphatase activity was slightly reduced, and no significant change was observed for aminopeptidase and lactase activities. Immunostaining showed that SI molecules appear in cells at the base of the villus. Sucrase expression was further increased by prolonged food deprivation, whereas enzyme activity as well as the amount of SI mRNA dropped to reach the low level found in control sucklings when 48 h-starved pups were refed by returning them to their dams. During the refeeding period, the enterocytes that were committed to produce SI by starvation continued to express the enzyme while migrating up the villi. However, the new epithelial cells arising from the crypts no longer synthesized the disaccharidase. The starvation-evoked appearance of SI was preceded by a transient burst of expression of the protooncogene c-fos, an event that may be correlated to the ontogenic rise of c-fos mRNA observed before weaning. However, in contrast to the normal weaning condition, SI induction by starvation occurred without obvious increase of epithelial cell proliferation and turnover. During the starvation and refeeding period, patterns of sucrase activity and SI mRNA paralleled the serum level of glucocorticoids.(ABSTRACT TRUNCATED AT 250 WORDS)
Thapsigargin defines roles of Ca2+ in initial, sustained, and potentiated stimulation of pepsinogen secretion
Authors: Kitsukawa Y. , Felley C. , Metz D. C. , Jensen R. T.
Published: December 2017

The roles of Ca2+ in agonist-induced pepsinogen secretion from guinea pig chief cells remain unclear. We used cholecystokinin octapeptide (CCK-8) or secretin alone or with thapsigargin (TG) to clarify these roles. TG releases Ca2+ from intracellular stores by inhibiting microsomal Ca(2+)-adenosinetriphosphatase (ATPase), thereby depleting intracellular Ca2+ (Cai2+) stores. In most cells TG also causes Ca2+ influx. In the present study, with an extracellular Ca2+ concentration ([Ca2+]o) of 1.5 mM, CCK-8 (0.1 microM) caused a rapid increase in pepsinogen secretion; however, the rate decreased with time. With [Ca2+]o = 0, the initial increase was similar but later secretion was abolished, suggesting that Ca2+ influx was important for sustained secretion. With [Ca2+]o = 1.5 mM, TG (0.1 microM) caused a 2.7-fold sustained increase in in Cai2+ concentration ([Ca2+]i) and a ninefold sustained increase in pepsinogen secretion. With [Ca2+]o = 0, TG caused a transient 66% increase in [Ca2+]i and a 50% increase in pepsinogen secretion. The time course of TG-induced pepsinogen secretion correlated with the time course of TG-induced increases in [Ca2+]i. These data demonstrated that Ca2+ influx itself was a potent stimulant of pepsinogen secretion. We further focused on the roles of increasing [Ca2+]i from Cai2+ stores. With or without extracellular Ca2+ (Cao2+) present, addition of CCK-8 (0.1 microM) 10 min after TG caused no further increase in [Ca2+]i, demonstrating depletion of the inositol 1,4,5-trisphosphate-sensitive pool. The Ca(2+)-mobilizing agent CCK-8 caused no pepsinogen secretion 10 min after TG preincubation, demonstrating that mobilization of Ca2+ from intracellular stores was important in the rapid initial phase stimulation of pepsinogen secretion caused by CCK-8. In contrast, preincubation with TG had no effect on pepsinogen secretion by secretin, an agent that increases adenosine 3',5'-cyclic monophosphate. A 6-min preincubation with TG potentiated the subsequent stimulation of pepsinogen secretion caused by secretin in the presence of Cao2+ where [Ca2+]i remained elevated. However, TG-induced potentiations of secretin-stimulated pepsinogen secretion was abolished once [Ca2+]i had returned to the basal level in the absence of Cao2+.(ABSTRACT TRUNCATED AT 400 WORDS)
Visualization of gene expression of short and long forms of prolactin receptor in rat digestive tissues
Authors: Ouhtit A. , Kelly P. A. , Morel G.
Published: December 2017

Several effects of prolactin have been characterized in various tissues of the gastrointestinal tract. In the present study, the expression of short and long forms of prolactin receptor was explored and quantified in the digestive tract and correlated to the prolactin specific functions. Sections of all digestive tissues were analyzed by in situ hybridization, using 35S-labeled oligoprobes unique to each form of receptor. Macroautoradiogram signals were quantified and expressed in arbitrary units. In rat liver, prolactin receptor mRNAs are expressed to a much greater degree in females than in males. The short-form transcript is significantly expressed to a greater degree in liver, whereas the long form predominates in the pancreas and esophagus. In the remainder of the gastrointestinal tract, there is an equivalent distribution of short- and long-form transcripts. Relatively high signal intensities are seen in the stomach, duodenum, jejunum, ileum, and colon, whereas the rectum is essentially negative. The identification of prolactin receptor gene expression to limited regions should help establish specific functions associated with this hormone in the digestive tissues.
Modulation of secretagogue-induced chloride secretion by intracellular bicarbonate
Authors: Dagher P. C. , Morton T. Z. , Joo C. S. , Taglietta-Kohlbrecher A. , Egnor R. W. , Charney A. N.
Published: December 2017

We have previously demonstrated inhibition of basal Cl- secretion by intracellular bicarbonate concentration ([HCO3-]i) in rat distal colon. We now examined whether secretagogue-induced Cl- secretion is inhibited by [HCO3-]i as well. Stripped segments of distal colon from male Sprague-Dawley rats and the colon tumor cell line T84 were studied. Flux measurements were performed in the Ussing chamber under short-circuit conditions. [HCO3-]i was calculated from intracellular pH (pHi) values that were estimated with the pH-sensitive dye 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. Dibutyryl adenosine 3',5'-cyclic monophosphate (cAMP) and carbachol were used as secretagogues. In both distal colon and T84 cells, [HCO3-]i did not affect cAMP-induced Cl- secretion. However, carbachol-induced secretion was inhibited by [HCO3-]i; in rat colon, Cl- secretion decreased from 2.3 to 1.5 mueq.cm-2.h-1 when [HCO3-]i was increased from 15.0 to 28.4 mM (P < 0.05). In T84 cells, the change in short-circuit current decreased from 8.1 to 1.1 microA/cm2 over a range of [HCO3-]i from 0 to 15.6 mM (P < 0.001). We conclude that [HCO3-]i is an important modulator of carbachol-stimulated Cl- secretion in both rat distal colon and the T84 cell line. cAMP-mediated secretion is not affected by [HCO3-]i.
Relationship of blood flow to antral lesion incidence in rat gastric mucosa after hemorrhage and retransfusion
Authors: Hachiya A. , Bessho M.
Published: December 2017

The relationship of gastric mucosal hemodynamics, energy metabolism, and acid to antral histological lesion incidence following hemorrhage and retransfusion was investigated in rats. Decrease of mucosal blood flow and of the index of mucosal oxygen saturation (ISO2) during hemorrhage were slightly greater in the corpus than in the antrum. ATP content and redox ratio in the corpus were decreased by shock; however, these hardly changed in the antrum. The index of tissue hemoglobin concentration (IHb) recovered to above the prehemorrhage value only in the antrum after retransfusion. Histological lesion incidence in the antral mucosa was more markedly increased by acid instillation and/or retransfusion than in the corpus. From these results, it was concluded that the decrease of blood flow is related as an underlying factor to induction of ischemic damage in the antral mucosa and that intraluminal acid and/or postischemic hyperemia play a causative role in the development of histologic lesions in the antral mucosa during shock and retransfusion in the rat stomach.
Effect of sodium nitroprusside on Ca2+ currents in opossum esophageal circular muscle cells
Authors: Akbarali H. I. , Goyal R. K.
Published: December 2017

The effects of sodium nitroprusside (SNP) on ionic currents in single opossum esophageal circular muscle cells were examined. In voltage clamp, Ca2+ currents were studied after K+ currents were blocked with Cs+ in the patch pipette. The threshold for inward Ca2+ currents was -30 mV with peak current between 0 and +10 mV from holding potentials of -90 mV. The Ca2+ currents had both transient and sustained phases. The transient phase was partially resistant to nifedipine (1 microM). SNP (100 microM) reversibly decreased both the transient and sustained phases of the Ca2+ currents by approximately 20%. In cells dialyzed with high-K+ solutions, voltage-clamp recordings demonstrated the presence of an inward current followed by an outward current at potentials positive to -30 mV. SNP under these conditions resulted in a decrease in the Ca2+ current and decreased the outward current during test depolarizations. Action potentials were evoked during current-clamp recordings that consisted of multiple spikes, depending on the stimulus strength. The threshold for spike generation was close to -30 mV and was blocked by Cd2+, suggesting that the upstroke of the action potential was dependent on Ca2+ influx. SNP significantly attenuated action potentials and produced a small hyperpolarization (5-7 mV). These results suggest that SNP has a direct inhibitory effect on Ca2+ currents and thereby decreases evoked action potentials, and that SNP hyperpolarization is not due to Ca(2+)-activated K+ channels.
Modulation of beta-lactoglobulin transport in rabbit ileum
Authors: Caillard I. , Tome D.
Published: December 2017

This study was undertaken to investigate the mechanisms of beta-lactoglobulin transport and its regulation in rabbit intestinal mucosa. beta-Lactoglobulin, the major bovine milk whey protein, was slightly degraded by ileal brush-border membranes, indicating the presence of phosphoramidon-insensitive neutral endoproteases. Modulation of 14C-radiolabeled beta-lactoglobulin transport across rabbit ileum mounted in Grass diffusion cells was studied in Ringer solution in the presence and absence of (in mM) 25 glucose, 10 galactose, and 0.5 colchicine. The transport was also measured in Dulbecco's modified Eagle's medium as a more "balanced" medium. The transport of the degraded products and of [3H]polyethylene glycol-4000, which was used as an extracellular marker, was enhanced by addition of glucose, presumably indicating passage through the tight junctions. The transepithelial passage of intact protein was estimated to be 10-20% by trichloroacetic acid precipitation and high-performance liquid chromatography, thus indicating the effective transport of the intact protein. The passage of the intact protein was inhibited by both colchicine, a microtubule-depolymerizing agent, and galactose by 50 and 30%, respectively. Galactose-like glycoconjugates, known to be present on the membrane, might be involved in the interaction between the protein and the brush border.
Ion transport in rabbit proximal colon: effects of sodium, amiloride, cAMP, and epinephrine
Authors: Hyun C. S. , Ahn J. , Minhas B. S. , Cragoe E. J. , Field M.
Published: December 2017

Effects on ion transport of extracellular Na+ and Cl- ([Na+]o and [Cl-]o, respectively), HCO3(-)-CO2, 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP), epinephrine, and transport inhibitors were examined in short-circuited rabbit proximal colonic mucosa. Net Na+ flux was independent of Cl- but partially (60%) dependent on HCO3(-)-CO2. Net Cl- flux was partially (70%) dependent on Na+ and totally dependent on HCO3(-)-CO2. Both fluxes peaked between 25 and 60 mM and decreased at higher concentrations. Apical Na+ influx but not Cl- influx obeyed the same pattern. The inhibition resulted from increases in mucosal but not serosal [Na+]o and not from increases in [Cl-]o. Amiloride and benzamil (0.2-0.3 mM) partially inhibited net Na+ absorption, as did 8-BrcAMP, but these effects were independent of the inhibition seen at high [Na+]o. Net Cl- absorption was inhibited by 8-BrcAMP but not by 0.2 mM amiloride. At high [Na+]o and [Cl-]o, there were a residual ion flux suggesting HCO3- secretion and, in the presence of 8-BrcAMP and amiloride or benzamil, net secretions of Na+ and Cl-, the former larger than the latter. Epinephrine, via alpha 2-receptors, reversed the ion-transport effects of high [Na+]o but did not stimulate a mucosal-to-serosal unidirectional HCO3- flux (as shown in rabbit ileum). 4-Acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (0.5 mM) and bumetanide (10 microM) had no effect on ion transport. The results suggest 1) Na+ entry via two Na(+)-H+ exchangers, one inhibited by amiloride and cAMP and the other inhibited by high [Na+]o and stimulated by epinephrine; 2) Cl- entry via Cl(-)-HCO3- exchange; 3) HCO3- secretion at high [Na+]o and [Cl-]o; and 4) cAMP-induced secretion of Na+ and Cl- at high [Na+]o and [Cl-]o.