bluuebunny/crossref_metadata_2025 huggingface dataset:
Increase in oxygen uptake due to arachidonic acid is oxygen dependent in the perfused liver
Authors: Nakagawa Y. , Matsumura T. , Goto M. , Qu W. , Kauffman F. C. , Thurman R. G.
Published: December 2017

The purpose of this study was to determine whether the effect of arachidonic acid on hepatic O2 uptake is O2 dependent and which region of the liver lobule it affects. In livers perfused at normal flow rates, infusion of arachidonate increased O2 uptake significantly by about 20-25 mumol.g-1.h-1. When the flow rate was doubled to make the hepatic O2 gradient shallower, the increase in O2 uptake due to arachidonate was two to three times larger (i.e., approximately 50 mumol.g-1.h-1). In livers perfused in the retrograde direction, maximal rates of O2 uptake were about twofold higher in upstream pericentral than in downstream periportal regions, and arachidonic acid nearly doubled O2 uptake in downstream areas without affecting rates in upstream regions. Thus it is concluded that arachidonate stimulates O2 uptake in an O2-dependent manner. This effect was sensitive to an inhibitor of the lipoxygenase, nordihydroguaiaretic acid, in perfused liver but not in isolated hepatocytes. In addition, conditioned medium from Kupffer cells incubated at high O2 tension stimulated parenchymal cell O2 uptake. Furthermore, arachidonate increased intracellular Ca2+ in isolated Kupffer cells in a dose-dependent manner. These findings suggest that eicosanoids produced by nonparenchymal cells participate in a hepatic O2 sensor mechanism involving Ca2+ that regulates O2 uptake by parenchymal cells in the liver.
Microvascular permeability in isolated vascularly perfused small intestine of rats
Authors: Kraneveld A. D. , Koster A. S. , Nijkamp F. P.
Published: December 2017

Intestinal microvascular permeability was studied in the isolated vascularly perfused small intestine of the rat by arterial injection of tracer molecules and collection of venous samples. The injection mixture contained a rhodamine-labeled dextran and a fluorescein-labeled dextran or free fluorescein. Pharmacokinetic analysis, based on statistical moment theory, of the tracer outflow concentration-time curve and the application of either the well-stirred model (WSM) or parallel tube model (PTM) was used to assess vasopermeability. The results indicate that the experimental system cannot be considered a pure WSM or a PTM. No different intrinsic clearance (Clint,i) values were found by applying the two models: Clint,i (in ml/min) = 1.23 +/- 0.14 (radius 0.5 nm); 0.44 +/- 0.09 (radius 1.4 nm); 0.31 +/- 0.08 (radius 2.2 nm); 0.02 +/- 0.01 (radius 6.0 nm); and 0 (radius 20.8 nm). Infusion of histamine (10(-5)-10(-3) M) and destruction of the endothelium via perfusion with distilled water increased the permeability for the tracers. We have established a technique for measurement of microvascular permeability characteristics in the rat small intestine. Histamine-induced changes and destruction of the endothelium can be detected in a quantitatively reliable way.
Apical-to-basolateral transepithelial transport of human lactoferrin in the intestinal cell line HT-29cl.19A
Authors: Mikogami T. , Heyman M. , Spik G. , Desjeux J. F.
Published: December 2017

The role of human lactoferrin (hLf) in alimentary iron absorption across intestinal cells was explored using a human differentiated colon carcinoma cell line, HT-29cl.19A. The apical surface of HT-29cl.19A cell monolayers exhibited 1.5 x 10(6) specific binding sites for hLf per cell, with a dissociation constant of 8.3 x 10(-7) M. The apical-to-basolateral transport of 125I-labeled hLf (125I-hLf) or 125I-59Fe-labeled hLf (125I-[59Fe]hLf) was investigated using filter-grown HT-29cl.19A cell monolayers mounted in Ussing chambers. Transport of total (intact plus degraded) hLf, measured by the 125I flux, was not saturable up to an apical hLf concentration of 12.5 microM, whereas immunoreactive hLf transport measured by enzyme-linked immunoabsorbent assay was saturable at 3.75 microM. Lowering the temperature to 4 degrees C reduced the total and immunoreactive hLf fluxes by 77% and 90%, and colchicine (500 microM) reduced these fluxes by 30% and > 97%, respectively. These results indicate that both types of transport are transcellular. Electrophoretic analysis revealed that 125I-hLf transported to the basal compartment consisted of largely degraded fragments (< 2 and 10-20 kDa) and a small portion of intact hLf. At an apical concentration of 3.75 microM diferric 125I-[59Fe]hLf, the immunoreactive hLf flux (64.6 +/- 14.3 ng.h-1.cm-2) constituted approximately 12% of the total hLf flux (552.0 +/- 61.6 ng.h-1.cm-2) and was similar to the [59Fe]hLf-equivalent flux (77.0 +/- 12.3 ng.h-1.cm-2).(ABSTRACT TRUNCATED AT 250 WORDS)
Downregulation of taurocholate transport by ileal BBM and liver BLM in biliary-diverted rats
Authors: Higgins J. V. , Paul J. M. , Dumaswala R. , Heubi J. E.
Published: December 2017

The enterohepatic circulation of bile salts may be substrate dependent. We hypothesize that decreased intestinal delivery of bile salts results in downregulation of ileal and hepatocyte bile salt transport in the biliary-diverted rat. Maximal velocity (Vmax) of taurocholate transport by ileal brush-border membrane (BBM) vesicles was downregulated in the bile-diverted animals by 45.5% (559.9 +/- 57.8 pmol.mg protein-1.min-1 in bile-diverted rats vs. 1,026.6 +/- 170.9 pmol.mg protein-1.min-1 in shams). Similarly, taurocholate transport Vmax by hepatocyte basolateral membrane (BLM) was downregulated by 37.8% (2.62 +/- 0.18 pmol.mg protein-1.min-1 in bile-diverted rats vs. 6.93 +/- 0.41 pmol.mg protein-1.min-1 in shams). Cholesterol content (mumol/mg protein) of the membranes was increased in both BBM (0.478 +/- 0.055 vs. 0.272 +/- 0.029) and BLM (0.410 +/- 0.052 vs. 0.294 +/- 0.044) in diverted rats compared with shams. Fluorescence anisotropy was significantly higher in diverted animals compared with shams for both BBM (0.2333 +/- 0.001 vs. 0.2120 +/- 0.004) and BLM (0.1524 +/- 0.002 vs. 0.1426 +/- 0.005). We conclude that biliary diversion in the rat leads to downregulation of both ileal BBM and hepatocyte BLM taurocholate transport. Alterations in transporter expression caused by diversion may, in part, be mediated by changes in membrane lipid composition or fluidity.
Carrier-mediated electrogenic transport of estradiol-17 beta-glucuronide in rat liver BMV
Authors: Vore M. , Hoffman T.
Published: December 2017

Estradiol-17 beta-glucuronide (E(2)17G) is one of a series of naturally occurring glucuronide conjugates of the steroid D-ring that induce cholestasis in the rat and nonhuman primate. The present studies characterized the transport of [3H]E(2)17G in basolateral membrane vesicles (BMVs) from male rat liver. The uptake of E(2)17G was temperature dependent, occurred into an osmotically sensitive space, and was saturable, with an apparent Michaelis constant and maximal velocity of 13 microM and 29 pmol.mg protein-1.5 s-1, respectively. Uptake was not coupled to the uptake of Na+ nor to Cl-or OH- exchange but was markedly stimulated by an inside-positive membrane potential. Bromosulfophthalein inhibited the uptake of E217G noncompetitively; estriol-16 alpha-glucuronide, but not estradiol-3-glucuronide or estradiol-3-SO4-17 beta-glucuronide, inhibited the uptake of E(2)17G. Thus E(2)17G is transported as an anion by facilitated diffusion by a system that differs from the multispecific Na(+)-taurocholate cotransport system and the bromosulfophthalein transport system.
Regulation of pancreatic amylase and lipase gene expression by diet and insulin in diabetic rats
Authors: Tsai A. , Cowan M. R. , Johnson D. G. , Brannon P. M.
Published: December 2017

Although insulin has been proposed to mediate the dietary regulation of pancreatic amylase, its interaction with diet in the regulation of amylase and lipase is not well understood and was examined in diabetic rats fed diets high in carbohydrate (HC), protein (HP), or fat (HF) and treated with insulin. Diabetes, independent of diet, decreased amylase content (97%; P < 0.0001) and mRNA (90%; P < 0.0001), but insulin only restored amylase content and mRNA to respective dietary control values. Diabetes, independent of diet, also increased lipase mRNA 1.6-fold (P < 0.004) but interacted (P < 0.0003) with diet on lipase content, resulting in opposite effects in HC- (increased 202%) and HF-diabetic rats (decreased 40%). Insulin partially restored lipase content and mRNA to respective dietary control values. Diet, independent of diabetes, regulated amylase content (P < 0.0001) and mRNA (P < 0.0003), which were three- to fourfold greater in HC- than in HF-fed rats, and lipase content (P < 0.001) and mRNA [rat pancreatic lipase 1 (rPL-1), P < 0.04; rPL-3, P < 0.0001], which were 1.8-fold greater in HF- than in HC- or HP-fed rats. Insulin failed to stimulate maximal amylase gene expression in HP- or HF-fed diabetic rats, suggesting that it is necessary, but not sufficient, for this dietary regulation. Differential regulation of lipase activity and mRNA by diet and insulin raises the possibility that lipase gene expression is regulated by a complex interaction of diet and insulin.
Microfluorometric studies of intracellular Ca2+ and Na+ concentrations in normal human labial gland acini
Authors: Valdez I. H. , Paulais M. , Fox P. C. , Turner R. J.
Published: December 2017

The responses of human labial salivary acini to muscarinic, adrenergic, and substance P peptidergic stimulation were studied using the fluorescent indicators fura 2 for intracellular Ca2+ concentration ([Ca2+]i) and sodium-binding benzofuran isophthalate for intracellular Na+ concentration ([Na+]i). Of the agents tested (carbachol, epinephrine, isoproterenol, and substance P) only the muscarinic agonist carbachol increased [Ca2+]i substantially above basal levels (three to fourfold; half-maximal effect approximatley 1 microM). Experiments with the Ca(2+)-adenosinetriphosphatase inhibitor thapsigargin indicated the presence of both thapsigargin-sensitive and thapsigargin-insensitive intracellular Ca2+ stores, both of which were mobilized by carbachol. [Na+]i in resting labial acini was approximately 20 mM. On stimulation with carbachol, [Na+]i rose transiently to more than three times this value and then partially recovered. This carbachol-induced rise in [Na+]i was largely blocked by bumetanide, a specific inhibitor of the Na(+)-K(+)-2Cl- cotransporter. These results are consistent with an intact muscarinic fluid secretory response in human labial acini with transepithelial Cl- secretion driven via Na(+)-K(+)-2Cl- cotransport and the secretion of fluid presumably following Cl- loss via an apical Ca(2+)-dependent anion channel, as observed in salivary acini from other species.
Developmentally regulated Gb3 galactosyltransferase and alpha-galactosidase determine Shiga toxin receptors in intestine
Authors: Mobassaleh M. , Koul O. , Mishra K. , McCluer R. H. , Keusch G. T.
Published: December 2017

The receptor for Shiga toxin on rabbit intestinal microvillus membranes (MVMs) has been identified as a developmentally regulated glycolipid, globotriaosylceramide [galactose alpha 1-4 galactose beta 1-4 glucose beta 1-1 ceramide (Gb3)]. MVM Gb3 levels increase markedly in the third week of life, concomitant with fluid secretory responses to the toxin. To study mechanisms controlling developmental regulation of MVM Gb3, we measured the specific synthetic Gb3 galactosyltransferase and degradative alpha-galactosidase activities and subcellular distribution of Gb3 at various ages. Quantitative high-performance liquid chromatography demonstrated a similar developmental pattern in both microsomal and MVM Gb3, indicating that late expression of MVM Gb3 is not due to delayed migration of Gb3 from the microsomal to the MVM. The specific Gb3 galactosyltransferase activity increased with age, with a sharp increase seen at 18 days of age, whereas alpha-galactosidase activity followed an inverse pattern. Thus, regulation of both synthetic and degradative pathways for Gb3 appears to explain the observed changes in Gb3 levels with age. The nature of the signals for developmental regulation of Gb3 levels is unknown, as are the physiological consequences of altered MVM glycolipid composition other than mediating response to Shiga toxin.
Dual pathways regulate neurite outgrowth in enteric ganglia
Authors: Simeone D. M. , Romanchuk G. , Mulholland M. W.
Published: December 2017

Primary cultures of guinea pig myenteric plexus ganglia were used to examine the ability of agents that activate adenylate cyclase or mimic intracellular adenosine 3',5'-cyclic monophosphate (cAMP) to stimulate morphological growth. Dose-dependent increases in neurite length and density were produced in enteric neuronal cultures by forskolin (212% of control), cholera toxin (356% of control), or the permeant cAMP analogues 8-bromoadenosine 3',5'-cyclic monophosphate and dibutyryl cAMP. (R)-p-adenosine 3',5'-cyclic monophosphorothioate, an inhibitor of cAMP-dependent kinases, blocked the growth-promoting effects of cAMP analogues but not of nerve growth factor (NGF). Activation of cAMP-dependent signaling pathways also increased production of mRNA for alpha-tubulin and microtubule-associated protein 2. Dual pathways, regulated by NGF and cAMP-dependent protein kinases, influence growth signaling in enteric ganglia.
Mechanisms coordinating gastric and small intestinal MMC: role of extrinsic innervation rather than motilin
Authors: Chung S. A. , Rotstein O. , Greenberg G. R. , Diamant N. E.
Published: December 2017

We have investigated the role of vagal and efferent adrenergic innervation coordinating the gastric and small intestinal migrating motor complexes (MMCs) after removal of the pylorus, duodenum, and upper jejunum in three dogs. The cervical vagus nerves were previously isolated in bilateral skin loops to permit reversible cooling blockade of the vagi. Pharmacological alpha- and beta-receptor blockade was accomplished by bolus intravenous injection of phentolamine and propranolol followed by intravenous infusion of the combined drugs. Gastric and upper jejunal MMC-like activity was initially absent after bowel resection but reappeared after 1-4 mo with the gastric and jejunal MMC-like activities coordinated as if the jejunum were the duodenum. Motilin peaks were absent. All gastric contractions were abolished by vagal blockade. Pharmacological adrenergic blockade immediately induced an intense burst of contractile and electrical activity in the stomach, which propagated to the distal ileum. This phase III-like burst was followed by ongoing intermittent bursts of contractile and electrical activity in the stomach and small intestine, lasting throughout the blockade, without further MMC-like activity. Vagal cooling blockade in combination with adrenergic blockade did not restore gastric MMC-like activity but abolished or decreased the number of gastric contractions, with the reappearance of the small intestinal MMC. Atropine boluses abolished all control and adrenergic blockade-induced stomach and small intestinal contractile and electrical activity. In conclusion, after duodenectomy, the gastric MMC-like activity that is reestablished and is coordinated with the small intestinal MMC is vagally dependent and cholinergic, but its cyclical nature requires adrenergic efferent pathways. Under these circumstances, coordination of the gastric and jejunal MMCs appears to require extrinsic innervation.
In vivo measurement of feline esophageal tone
Authors: Mayrand S. , Tremblay L. , Diamant N.
Published: December 2017

Using an isotonic recording device (barostat), we assessed feline esophageal smooth and striated muscle tone in vivo and determined the effects of a cholinergic agonist (bethanechol) and antagonist (atropine) and the effect of body position on this tone. Studies were performed on six cats under light intravenous ketamine anesthesia. Two parameters were analyzed: compliance and resistance to initial stretch (resting tone). Smooth muscle compliance (0.51 +/- 0.03 ml/mmHg) was significantly greater than that of the striated muscle section (0.26 +/- 0.02 ml/mmHg; P = 0.0260). Resting tone was low in both esophageal sections. Neither atropine nor bethanechol had any significant effect on the two tone parameters measured in smooth muscle. Change in body position had no influence on the intraesophageal balloon volume. We conclude that esophageal wall compliance varies according to location (smooth vs. striated muscle) and that esophageal smooth muscle tone is not under cholinergic excitatory control. Isotonic recording in vivo should allow further investigations of the nature of the neural and myogenic control of esophageal tone and of the relationships between phasic and tonic activity.
Small intestinal capsaicin-sensitive afferents mediate feedback inhibition of gastric emptying in rats
Authors: Zittel T. T. , Rothenhofer I. , Meyer J. H. , Raybould H. E.
Published: December 2017

Functional studies have implied the existence of small intestinal receptive mechanisms for components of chyme to mediate feedback inhibition of gastric function. However, it is not known if the sensors are in the wall of the small intestine or located at another site. The present studies evaluated the localization of receptive mechanisms mediating intestinal feedback inhibition of gastric emptying by functional ablation of intestinal capsaicin-sensitive afferents. Perfusion of the small intestine of conscious rats with hydrochloric acid (0.1 N; total amount 50 meq), glucose (1 M; total amount 90 mg), or a lipid emulsion (Intralipid 10%; total amount 50 mg) inhibited gastric emptying. One to 7 days after perfusion of the intestine with capsaicin (3.6 mumol), feedback inhibition of gastric emptying produced by acid, glucose, or lipid was inhibited 100, 59, and 42%, respectively. We conclude that acid-induced inhibition of gastric emptying is mediated entirely by small intestinal capsaicin-sensitive afferent neurons and that a major portion of the glucose-induced inhibition of gastric emptying is mediated by small intestinal afferents. However, only a minor part of the response to lipid is mediated by this pathway.
Criteria for objective definition of transient lower esophageal sphincter relaxation
Authors: Holloway R. H. , Penagini R. , Ireland A. C.
Published: December 2017

We developed and evaluated objective manometric criteria that define transient lower esophageal sphincter (LES) relaxation. In 23 normal subjects and 9 patients with gastroesophageal reflux disease, systematic analysis of swallow-induced LES relaxation showed that dry swallows preceded LES relaxation by a median of 1.4 s. The relaxation rate was always > 1 mmHg/s, the relaxation nadir always occurred within 7 s, and the duration of relaxation was < 9 s. During concurrent esophageal manometry and pH monitoring, 104 reflux episodes associated with a LES pressure fall that was not related to swallowing were identified and the pressure falls classified as transient LES relaxations or not by visual recognition. LES pressure was always < or = 2 mmHg at time of reflux, and relaxation was significantly longer than for swallow-induced LES relaxation. Of 88 pressure falls classified visually as transient LES relaxations, 90% reached nadir pressure within 7 s at a rate of > 1 mmHg/s. Sixteen pressure falls were classified as a gradual downward drift in LES pressure, which in 15 cases was < 1 mmHg/s. Based on the analysis, transient LES relaxation can be defined by 1) absence of swallowing for 4 s before to 2 s after the onset of LES relaxation, 2) relaxation rate of > or = 1 mmHg/s, 3) time from onset to complete relaxation of < or = 10 s, and 4) nadir pressure of < or = 2 mmHg.(ABSTRACT TRUNCATED AT 250 WORDS)
Adaptation of rat gastric mucosa to aspirin requires mucosal contact
Authors: Wallace J. L. , McKnight G. W. , Bell C. J.
Published: December 2017

Adaptation of the gastric mucosa to repeated administration of aspirin is a well-documented phenomenon, but the underlying mechanism is not fully understood. In this study, we tested the hypothesis that adaptation of the rat stomach to chronic aspirin administration required contact between the aspirin and the gastric mucosa. Rats were orally treated twice daily with either aspirin (100 mg/kg) or the vehicle. After various periods of treatment (< or = 20 days), the rats were given a higher dose of aspirin (250 mg/kg po), and the extent of gastric damage was assessed 3 h later. Rats receiving chronic aspirin demonstrated the development, in a time-dependent manner, of resistance to the damaging effects of aspirin. Chronic aspirin administration also significantly decreased the susceptibility of the rat stomach to damage induced by indomethacin or naproxen. The adaptation phenomenon was associated with a parallel increase in inflammatory infiltration of the mucosa, as measured by tissue myeloperoxidase activity and histology. Prostaglandin synthesis was markedly suppressed (> 80%) in all rats treated with aspirin. Gastric mucosal ornithine decarboxylase activity was not affected by chronic aspirin administration. If aspirin was administered subcutaneously or intrajejunally for 20 days, neither adaptation nor inflammation of the gastric mucosa was observed. These studies demonstrate that the rat stomach adapts to chronic oral administration of aspirin, but not to aspirin administration via other routes. Adaptation of the gastric mucosa occurred in parallel to infiltration of granulocytes. Whether these two phenomena are mechanistically or causally linked is not yet clear.
Tobacco cigarette smoke aggravates gastric ulcer in rats by attenuation of ulcer margin hyperemia
Authors: Iwata F. , Leung F. W.
Published: December 2017

We tested the hypothesis that attenuation of the hyperemia at the margin of acetic acid-induced gastric ulcer in rats by tobacco cigarette smoke will increase the size of the ulcer in the acute and the healing stages. Compared with the adjacent mucosa, blood flow measured by hydrogen gas clearance at the ulcer margin was significantly higher (ulcer margin hyperemia). Tobacco cigarette smoke and subcutaneous nicotine but not nicotine-free smoke from non-tobacco cigarettes significantly attenuated the ulcer margin hyperemia in a dose-related fashion. Repeated exposure of the rats to tobacco cigarette smoke increases ulcer size in the acute and the healing stages. Subcutaneous nicotine but not nicotine-free smoke also increased the size of ulcers in the acute stage. These results indicate that the nicotine in tobacco cigarette smoke may be responsible in part for its adverse effects. We conclude that attenuation of the hyperemia at the ulcer margin is a plausible explanation for the mechanism of the adverse effect of the tobacco cigarette smoke on experimental gastric ulcers in rats.
Nitric oxide causes hyporeactivity to phenylephrine in isolated perfused livers from endotoxin-treated rats
Authors: Pastor C. M. , Billiar T. R.
Published: December 2017

Systemic vascular hyporeactivity to vasoconstrictors has been described in rats following endotoxin administration. Inducible nitric oxide synthase (iNOS) expression is known to occur in the liver in endotoxemia, but consequences of iNOS induction on hepatic hemodynamics are unknown. The reactivity of the hepatic circulation to phenylephrine was tested in perfused livers from normal rats and rats previously injected with endotoxin (20 mg/kg ip). In control rats (n = 5), phenylephrine-induced portal pressure increases were similar in livers perfused with Krebs-Henseleit-bicarbonate (KHB) buffer, KHB plus the NOS inhibitor NG-monomethyl-L-arginine (L-NMMA, 1 mM), or KHB plus the substrate for NO synthesis, L-arginine (1 mM). In contrast, livers from endotoxin-treated rats (n = 5) exhibited a marked reduction in the vasoconstrictive response to phenylephrine (14.6 vs. 55.1% in livers from control rats, P < 0.05). Perfusion with L-NMMA restored the phenylephrine response, and the L-NMMA effect was reversible with L-arginine. Perfusate NO2-/NO3- and guanosine 3',5'-cyclic monophosphate (cGMP) levels were increased in endotoxin-treated rats and significantly reduced by L-NMMA perfusion. In control livers, the NO donor S-nitroso-N-acetyl-DL-penicillamine blocked the portal pressure increase after phenylephrine administration. These results suggest that rat hepatic circulation takes part in the systemic vascular hyporeactivity to vasoconstrictors observed in endotoxemia and that NO is involved in this hyporeactivity to phenylephrine.
Expression of sodium-independent organic anion uptake systems of skate liver in Xenopus laevis oocytes
Authors: Jacquemin E. , Hagenbuch B. , Wolkoff A. W. , Meier P. J. , Boyer J. L.
Published: December 2017

The expression of the basolateral sodium-independent organic anion uptake system of the little skate (Raja erinacea) has been studied in Xenopus laevis oocytes. Injection of oocytes with skate liver poly(A)+ RNA resulted in the functional expression of chloride-dependent sulfobromophthalein (BSP) uptake and sodium-independent taurocholate uptake within 3-5 days. The expressed chloride-dependent BSP uptake activity exhibited saturation kinetics [apparent Michaelis constant (Km) 1.8 microM] and efficiently extracted BSP from its binding sites on bovine serum albumin. The chloride-sensitive portion of BSP uptake was inhibited by bilirubin (10 microM; 27%), 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (100 microM; 57%), bumetanide (100 microM; 48%), taurocholate (200 microM; 51%), and cholate (200 microM; 45%). Size fractionation of total skate liver mRNA revealed that a 1.8- to 2.9-kb size class mRNA was sufficient to express chloride-dependent BSP uptake and sodium-independent taurocholate uptake. In addition, a 1- to 1.7-kb size class mRNA expressed sodium-independent taurocholate uptake but had no effects on BSP uptake. This study confirms that an organic anion transport system for chloride-dependent BSP uptake, with characteristics similar to rat liver, is already expressed in the liver of lower vertebrates and thus represents a phylogenetically old system. Sodium-independent taurocholate uptake in skate liver may be mediated by two different transport systems.
Inhibition of bombesin-stimulated acid secretion by immunoneutralization of gastrin in dogs
Authors: Kovacs T. O. , Lloyd K. C. , Wong H. , Walsh J. H.
Published: December 2017

Bombesin-like peptides stimulate gastrin release and gastric acid secretion. The increase in gastric acid output is thought to be secondary to gastrin release. A monoclonal antibody (MAb) directed specifically to gastrin (MAb 28.2) was used to study the role of circulating gastrin in the regulation of bombesin-stimulated acid secretion in dogs. Seven conscious, fasted dogs with gastric fistulas received intravenous bombesin infusions in fourfold increasing doses from 200 to 3,200 pmol.kg-1.h-1. Each dose was given for 45 min. On separate days, dogs were pretreated with an intravenous infusion of 7 mg of MAb 28.2 or vehicle (0.1% canine serum albumin). Samples of gastric effluent were collected by gravity drainage through the gastric fistula, and acid output was measured by titration of gastric effluent to pH 7.0, using 0.2 N NaOH. Plasma gastrin concentrations were determined by radioimmunoassay. Bombesin infusion produced dose-dependent increases in plasma gastrin concentrations and gastric acid output. Administration of gastrin MAb 28.2 abolished bombesin-stimulated gastric acid output. Immunoneutralization of circulating gastrin in vivo using a gastrin monoclonal antibody in dogs indicates that the acid stimulatory response to bombesin is mediated by gastrin.
Intestinal peptide YY: ontogeny of gene expression in rat bowel and trophic actions on rat and mouse bowel
Authors: Gomez G. , Zhang T. , Rajaraman S. , Thakore K. N. , Yanaihara N. , Townsend C. M. , Thompson J. C. , Greeley G. H.
Published: December 2017

The purpose of this study was twofold: 1) to characterize the profile of colonic peptide YY (PYY) gene expression in rats and 2) to examine for potential trophic effects of PYY on the intestine in rats and mice. Expression of PYY mRNA (analyzed by Northern blotting and in situ hybridization) and PYY (analyzed by high-performance liquid chromatography and radioimmunoassay) was detected initially at day 17 of gestation in colonic extracts of Sprague-Dawley and Fischer rats. Expression of colonic PYY mRNA increased until 7 days of age and remained at its highest level (approximately twofold greater than the adult level) through the end of the nursing period. After weaning (21 days of age), PYY mRNA levels declined quickly to adult levels. Colonic PYY concentrations followed, in a coordinated manner, with some temporal delay after birth, the increase and decrease of its mRNA. Administration of PYY increased the weight and DNA content of the duodenum significantly in nursing rats and adult mice. In mice, PYY treatment also increased weight and DNA content of the ileum and colon. The trophic effects of PYY were dose related, peptide specific, and independent of species and sex. From these findings, we hypothesize that PYY plays an important role in intestinal development and dietary adaptation.
Lovastatin induces synthesis of cholesterol, which acts as a secretagogue of biliary phospholipids in rats
Authors: Linscheer W. G. , Atreyee B. , Uma K. M. , John W. , Sandor N. , Jyotirmoy N.
Published: December 2017

The effects of treatment with lovastatin (LS), a hypocholesterolemic drug, on hepatic metabolism of cholesterol (CH) and phosphatidylcholine (PC) were studied in rats. Hepatic synthesis of CH was increased, as previously reported by our laboratory. Total plasma CH was increased, and biliary secretion of CH was raised fourfold, but biliary secretion of bile salts was not affected. Because CH is practically insoluble in an aqueous milieu, we tested the hypothesis that excessive CH is solubilized and secreted into bile as cholesterol-phospholipid (CH-PL) vesicles. The effects of LS-induced increase in CH synthesis on hepatic metabolism of PC after 7 days of oral LS treatment (17.5 mg/day) were studied. Our results showed accelerated synthesis of PC and increased biliary secretion of newly formed PC into bile, as evidenced by the following. 1) Phosphocholine cytidylyltransferase (EC 2.7.7.15) activity, the rate limiting enzyme in the synthesis of PC, increased 2.5-fold in the hepatic microsomes of the hepatocytes. 2) After intravenous administration of [14C]choline, a precursor of PC, [14C]PC increased significantly in bile. 3) Biliary output of PC increased twofold. 4) Quasi-elastic light scattering measurements of bile showed a 3.5-fold increase in intensity of the CH-PL vesicles, indicating higher concentrations of CH-PL vesicles, but there was no change in the intensity of the micelles. These observations support the hypothesis that PC synthesis was enhanced as a transport mechanism for secretion of the excessive amounts of cholesterol from the hepatocytes into bile as CH-PC vesicles.
Hemileaflet susceptibility to oxidative damage in the intestinal brush-border membrane
Authors: Jourd'heuil D. , Mehta S. , Meddings J. B.
Published: December 2017

Oxidation of biological membranes is characteristic of many types of tissue injury, including those observed with inflammatory bowel disease. The lipid compositions of the inner and outer leaflets of biological membranes differ significantly, making one leaflet theoretically more susceptible to oxidative stress than the other. In this study, we evaluated the susceptibility of each membrane hemileaflet for peroxyl radical-mediated oxidation. In vitro peroxidation of intestinal brush-border membrane was initiated with the peroxyl radical-generator 2,2'-azobis-(2-amidinopropane)hydrochloric acid (AAPH). Oxidation events were monitored by following the oxidation-sensitive degradation of the lipid-soluble fluorescent probe cis-parinaric acid (PnA). The degradation patterns were clearly distinct in the inner and outer hemileaflet. PnA degradation in the inner hemileaflet was consistent with a slow first-order reaction, whereas degradation in the outer leaflet appeared as two first-order processes delayed in time. The results suggest that the sum of available antioxidants and endogenous substrates for oxidation are consumed more rapidly in the outer membrane hemileaflet, making this leaflet more susceptible to peroxidation compared with the cytofacial leaflet.
Effects of 5-HT alone and its interaction with TRH on neurons in rat dorsal motor nucleus of the vagus
Authors: Travagli R. A. , Gillis R. A.
Published: December 2017

The purpose of this study was to determine whether exposure to thyrotropin-releasing hormone (TRH) enhances the excitatory effect of 5-hydroxytryptamine (5-HT) on motoneurons of the dorsal motor nucleus of the vagus (DMV) as described in whole animal studies. For this purpose we used the patch-clamp technique applied to rat brain stem slices. Exposure of DMV motoneurons to concentrations of 5-HT (0.1-3 microM) resulted in a concentration-related increase in spontaneous firing rate. As previously described by Travagli et al. [Am. J. Physiol. 263 (Gastrointest. Liver Physiol. 26): G508-G517, 1992], TRH (1-30 microM) increased action potential firing rate. Indeed, when TRH perfusion increased the firing rate, addition of 5-HT to the perfusing solution exerted no further excitation of the DMV motoneuron, indicating that there was no summation of response. Studies using whole cell current recordings showed a common action of 5-HT and TRH in antagonizing the Ca(2+)-dependent afterhyperpolarizing current (IAHP). Again, interaction studies between TRH and 5-HT indicated no enhancing effect of TRH on 5-HT-induced antagonism of IAHP. In conclusion, our data indicated that the enhancement of 5-HT-induced excitation of DMV motoneurons by TRH described by in vivo rat experiments is not due to an interaction of TRH and 5-HT directly on the DMV motoneuron.
Defective interleukin-1-induced ACTH release in cholestatic rats: impaired hypothalamic PGE2 release
Authors: Swain M. G. , Maric M. , Carter L.
Published: December 2017

A complete regulatory loop exists between the immune and neuroendocrine systems. Proinflammatory mediators such as endotoxin (lipopolysaccharide) and interleukin-1 (IL-1) are capable of activating the hypothalamic-pituitary-adrenal (HPA) axis at the hypothalamic level, presumably by inducing the synthesis of prostaglandins. We have recently identified abnormalities in the stress-induced activation of the HPA axis in cholestatic rats. Therefore, in rats with cholestasis due to bile duct resection and sham-resected controls, we studied alterations in proinflammatory mediator-induced activation of the HPA axis and documented the role of alterations in hypothalamic prostaglandin synthesis in these abnormalities. Systemic administration of endotoxin and IL-1 resulted in a significant attenuation of adrenocorticotropic hormone (ACTH) release into plasma in bile duct-resected compared with sham-resected animals. This suppression of endotoxin- or IL-1-induced ACTH release in bile duct-resected rats was associated with a complete absence of IL-1-induced hypothalamic release of prostaglandin E2 (PGE2) in vitro in these animals. In contrast, sham-resected rats exhibited a 70% increase in hypothalamic PGE2 secretion in vitro in response to IL-1. However, bile duct-resected rats exhibited HPA axis activation similar to that of sham-resected animals in response to intracerebroventricularly infused PGE2. Therefore, cholestasis in the rat is associated with an attenuation of central activation of the HPA axis by proinflammatory mediators that appears to be mediated, at least in part, by defective IL-1-induced hypothalamic prostaglandin production.
Cardiac beta-adrenoceptor-effector coupling in portal vein-stenosed rats
Authors: Zavecz J. H. , Battarbee H. D. , O'Donnell J. M.
Published: December 2017

Cardiac beta-adrenergic signal transduction was examined in chronic portal vein-stenosed rats. Basal tension and maximum rate of tension development were significantly depressed in left ventricular papillary muscles (0.21 +/- 0.03 N/cm2 and 8.2 +/- 1.7 N.s-1.cm-2, respectively) compared with sham-operated controls (0.51 +/- 0.05 N/cm2 and 19.9 +/- 4.4 N.s-1.cm-2, respectively). The positive inotropic response to isoproterenol was also attenuated. Adenosine 3',5'-cyclic monophosphate formation was decreased significantly when GTP (-41.9%), isoproterenol with GTP (-45.3%), or guanosine 5'-O-(3-thiotriphosphate) (-52.4%) was used to stimulate adenylyl cyclase, but not when Mn2+ or forskolin was used. Beta-Adrenoceptor density (sham operated 24.6 +/- 2.0 fmol/mg; portal vein stenosed 26.4 +/- 2.1 fmol/mg) and the apparent dissociation constant (sham operated 0.26 +/- 0.04 nM; portal vein stenosed 0.29 +/- 0.04 nM) were unaffected. Portal venous hypertension did not alter beta-adrenergic receptor affinity for isoproterenol. However, it was necessary for isoproterenol to occupy three times the number of receptors in papillary muscles from stenosed animals to produce an equal increase in force generation. These data suggest that although portal vein stenosis does not alter cardiac beta-adrenoceptor density or affinity for ligands, transduction of the signal between the receptor and adenylyl cyclase is adversely influenced and may be responsible for the diminished responsiveness of beta-adrenoceptors in the myocardium.
In vivo and in vitro influence of human recombinant hemoglobin on esophageal function
Authors: Chakder S. , Rosenthal G. J. , Rattan S.
Published: December 2017

The purpose of the present investigation was to examine the influence of a nitric oxide scavenger, hemoglobin (Hb), on esophageal function. Intraluminal pressures of anesthetized opossums were recorded from lower esophageal sphincter (LES) and 1, 5, and 9 cm above the LES. The influence of a representative Hb-based oxygen carrier was examined on swallowing-induced esophageal peristalsis and LES relaxation. In in vitro studies, LES relaxation and esophageal peristaltic contractions were induced by the activation of nonadrenergic noncholinergic (NANC) neurons by electrical field stimulation (EFS). Hb caused significant impairment in swallowing- and EFS-induced LES relaxation and a significant increase in the speed of esophageal peristalsis. In some experiments, swallowing caused simultaneous contractions in the esophagus following Hb administration. Although Hb completely blocked LES relaxation by NO and significantly attenuated that by NANC nerve stimulation, it had no significant effect on isoproterenol-induced LES relaxations. The data support the role of NO in LES relaxation and esophageal peristalsis. This esophageal model may be important in understanding the influence of NO inhibitors and scavengers in gastrointestinal motility.
Clostridium difficile toxin B activates calcium influx required for actin disassembly during cytotoxicity
Authors: Gilbert R. J. , Pothoulakis C. , LaMont J. T. , Yakubovich M.
Published: December 2017

The principal cellular response to Clostridium difficile toxin B, a protein toxin associated with antibiotic-associated colitis, is the disassembly of actin microfilaments. Although receptor-activated signal transduction mechanisms have been proposed to mediate these effects, the intracellular events that precede actin breakdown are unknown. In NIH-3T3 fibroblasts, toxin B induced an elevation of intracellular calcium possessing either a slow (minutes) or fast (seconds) rise time, followed by a sustained elevation of calcium concentration. Subcellular analysis of steady-state calcium distribution after toxin B demonstrated that the increase of calcium was homogeneous throughout the cytosol and did not vary based on the kinetics of the initial calcium rise. All calcium responses were blocked by substitution with calcium-free buffer or buffer containing lanthanum chloride, indicating that the rise in calcium was attributable to calcium influx from the extracellular space. Quantitatively similar responses were observed in primary cultured gastric smooth muscle and AR42J pancreatic tumor cells, suggesting that toxin-induced calcium signal transduction was conserved between cell types. The morphological response to toxin B consisted of sequential dissociation of the actin cytoskeleton from membrane attachments, retraction of actin stress fibers from the periphery to the perinuclear region, loss of fibre alignment, and cell rounding. The actin reorganization associated with toxin B was blocked by incubation of cells in calcium-free media or the clamping of intracellular calcium with cell-permeant calcium chelating agents. These results demonstrate that the calcium influx activated by C. difficile toxin B is a necessary condition for the breakdown of filamentous actin associated with cytotoxicity.
Interstitial buffer capacity influences Na+/H+ exchange kinetics and oxyntic cell pHi in intact frog gastric mucosa
Authors: Seidler U. , Stumpf P. , Classen M.
Published: December 2017

We studied the influence of interstitial buffer capacity and CO2-HCO3- on oxyntic cell intracellular pH (pHi) in intact frog gastric mucosa. Oxyntic cells in stripped gastric mucosa of Rana esculenta were loaded with the pH-sensitive dye 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein, and pHi was assessed fluorometrically. In the presence of a constant serosal and luminal pH, oxyntic cell pHi was dependent on the serosal but not the luminal concentration of cell-impermeable buffer ions such as N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES), tris(hydroxymethyl)aminomethane, N-tris(hydroxymethyl)methyl-2-aminoethanesulfonic acid, and 3-(N-morpholino)propanesulfonic acid. The stepwise increase in oxyntic cell pHi from 6.74 +/- 0.05 with 1 mM HEPES to 7.23 +/- 0.08 was almost completely inhibited by removal of serosal Na+ and by amiloride and dimethyl amiloride, suggesting that it was largely due to Na+/H+ exchange. Increasing the serosal concentration of a CO2-HCO3- buffer from 1% CO2-4 mM HCO3- to 10% CO2-40 mM HCO3- increased oxyntic cell pHi from 7.03 +/- 0.06 to 7.39 +/- 0.07. This CO2-HCO(3-)-dependent pHi increase was also Na+ and amiloride sensitive, but high HCO3- concentrations increased pHi even in the absence of Na+, K+, or Cl-, and in the presence of omeprazole, bafilomycin A1, or acetazolamide. We suggest that in intact frog gastric mucosa, cellular proton extrusion acidifies the interstitial pH immediately adjacent to the basolateral membrane of the oxyntic cells in the absence of a high interstitial buffer capacity.(ABSTRACT TRUNCATED AT 250 WORDS)
Activation of the hypothalamic dorsomedial nucleus stimulates intestinal motility in rats
Authors: Greenwood B. , DiMicco J. A.
Published: December 2017

Blockade of gamma-aminobutyric acidA (GABAA) receptors in the dorsomedial nucleus of the hypothalamus (DMH) in rats induced cardiovascular and behavioral changes resembling those associated with emotional stress. The purpose of this study was to test the hypothesis that microinjection of the GABA antagonist bicuculline methiodide (BMI) into the DMH of anesthetized rats would produce increases in intestinal motility measured manometrically with saline-filled cannulas. Arterial pressure and heart rate were also recorded. Microinjection of BMI (15-30 pmol/15 nl) into the region of the DMH elicited reproducible and dose-related increases in jejunal motility, colonic motility, heart rate, and arterial pressure. Similar microinjection at sites anterior to the DMH into or nearer to the hypothalamic paraventricular nucleus elicited significantly attenuated cardiovascular effects accompanied by either no change in intestinal function or changes that were significantly reduced. Either vagotomy or treatment with atropine methyl bromide (1 mg/kg i.v.) blocked the increase in jejunal motility and reduced but did not abolish the colonic stimulation. Increases in heart rate and arterial pressure were essentially unaffected by either intervention. The observations suggest that disinhibition of neurons in the DMH increases jejunal motility through vagal cholinergic pathways and enhances colonic motility through vagal and nonvagal cholinergic and noncholinergic pathways.
Contractile mechanisms of canine colonic propulsion
Authors: Sethi A. K. , Sarna S. K.
Published: December 2017

We investigated the contractile mechanisms of propulsion in the dog colon. "Propagation index" indicating caudad or orad propagation of contractile states exhibited the strongest correlation with transit during both the fasting and the postprandial states. Other parameters, such as total duration of contractile states and area under contractions, also contributed to transit, but to a lesser degree. All parameters exhibited a stronger correlation with transit during the fasting than during the postprandial state. During the fasting state, the transit rate was faster in the proximal than in the middle colon. The transit rate was linear through the proximal and the middle colon during the postprandial state. In contrast to the phasic contractions and the contractile states, the giant migrating contractions were ultrapropulsive. We conclude that the propagation of contractile states in the colon is a major factor in the slow net distal propulsion of colonic contents. The individual phasic contractions may mainly produce mixing and agitation of colonic contents. Giant migrating contractions rapidly propel colonic contents over long distances.
Regulation of system y+ arginine transport capacity in differentiating human intestinal Caco-2 cells
Authors: Pan M. , Malandro M. , Stevens B. R.
Published: December 2017

This study describes the ability of passaged human intestinal Caco-2 cells to regulate transport of L-arginine via system y+. Subconfluent and confluent cells possessed system y+ activity, as determined by the sodium independence of uptake and the pattern of inhibition by amino acid analogues or N-ethylmaleimide. Initial rates of arginine uptake via system y+ decreased as the cells advanced from the undifferentiated to the differentiated state following culture passaging. Furthermore, kinetic analysis of the leucine-insensitive portion of uptake indicated that the Caco-2 system y+ transport capacity decreased with cell age, dropping from a maximal velocity (Vmax) = 1,094 pmol.mg-1.min-1 [Michaelis constant (Km) = 41 microM] in undifferentiated cells 2 days postseeding to Vmax = 320 pmol.mg-1.min-1 (Km = 37 microM) in confluent cells 9 days postseeding (from cells of the same passage). Northern analysis indicated that the levels of a single 7.9-kb mCAT-1 mRNA species were relatively constant over the course of Caco-2 differentiation and therefore were unsynchronized with the system y+ relative transport activities. It is concluded that the Caco-2 capacity to transport arginine via system y+ may be downregulated by posttransitional modifications in confluent cells compared with newly passaged undifferentiated cells. These data serve as a well-defined in vitro model for further studies regarding regulation of arginine transport in epithelial cells.