bluuebunny/crossref_metadata_2025 huggingface dataset:
Gastric mucosal hyperemia due to acid backdiffusion depends on splanchnic nerve activity
Authors: Holzer P. , Lippe I. T.
Published: December 2017

Acid backdiffusion through a disrupted gastric mucosal barrier leads to an increase in gastric mucosal blood flow (MBF). This response involves afferent neurons that pass through the celiac ganglion. The present study examined the neural pathways that underlie the rise in MBF caused by gastric perfusion with 15% ethanol in 0.15 N HCl. MBF was measured by the hydrogen gas clearance technique in urethan-anesthetized rats. Mucosal hyperemia due to acid backdiffusion was not changed by acute bilateral subdiaphragmatic vagotomy but was blocked by acute removal of the celiac-superior mesenteric ganglion complex or acute bilateral transection of the greater splanchnic nerves. Hexamethonium (85 mumol/kg iv) also attenuated the rise in MBF due to acid backdiffusion, whereas guanethidine (0.225 mmol/kg sc) had no effect. None of the procedures and drug treatments altered basal MBF to a significant extent. Transection of the splanchnic nerves, hexamethonium, and guanethidine lowered mean arterial blood pressure, but hypotension as such did not significantly influence the hyperemic response under study. Taken together, the previous and present data indicate that the rise in MBF caused by acid backdiffusion depends on the integrity of afferent and efferent neural pathways that run in the splanchnic nerves and through the celiac ganglion. The efferent pathway involves ganglionic transmission through nicotinic acetylcholine receptors but is independent of noradrenergic neurons.
Evaluation of hepatic venous resistance responses using index of contractility
Authors: Lautt W. W. , Legare D. J.
Published: December 2017

Hepatic vascular responses to 1.25 micrograms.kg-1.min-1 norepinephrine, infused into the hepatic artery, and 8-Hz nerve stimulation were monitored in anesthetized cats using a recently introduced index of contractility (IC). IC was validated in that it did not change passively in response to passive changes in portal flow or distending blood pressure, whereas the distensible venous resistance sites showed dramatic changes in resistance. Resistance is altered by both active contractile responses and passive distensibility; IC is not altered passively but is affected by changes in vascular tone. Resistance was a less sensitive index of vasoconstriction because, although the constriction increased resistance, the subsequent elevation in portal and intrahepatic pressure counteracted the constriction; the extent of active neurogenic response using resistance as the index was grossly underestimated due to venous distensibility. IC showed that pre- and postsinusoidal constriction occurred to both norepinephrine and nerves; extensive vascular escape from neurogenic constriction occurred for the portal vein so that by 5 min almost all the rise in portal pressure was due to hepatic venous constriction.
Nicotine stimulates esophageal peristaltic contractions in cats by a central mechanism
Authors: Greenwood B. , Blank E. , Dodds W. J.
Published: December 2017

The aim of the present study was to 1) characterize nicotine-induced peristalsis in the feline esophagus and 2) determine the site of action of nicotine. Experiments were done on ketamine-sedated cats. Esophageal contractions were measured using a multilumen catheter assembly system. After recording 1 degree and 2 degrees peristaltic sequences nicotine (50-100 micrograms/kg iv) was administered. Nicotine induced a peristaltic contraction through the esophageal striated and smooth muscle part of the esophagus, which was not associated with any mylohyoid electromyogram activity or pharyngeal response, although the upper esophageal sphincter did relax. Addition of either atropine (20-50 micrograms/kg iv) or hexamethonium (10-20 mg/kg iv), a peripherally acting nicotinic antagonist, did not affect the striated muscle portion of the nicotine-induced esophageal contractile response but antagonized the smooth muscle response. However, mecamylamine (0.5-1 mg/kg iv), a ganglionic antagonist that crosses the blood-brain barrier, abolished the esophageal response to nicotine. Succinylcholine (0.5-1 mg/kg iv) abolished the striated muscle response without affecting the nicotine-induced smooth muscle contractility. Finally, the nicotine-induced peristaltic sequence was abolished after bilateral cervical vagotomy. In conclusion, nicotine, administered peripherally, activates central brain stem mechanisms that mediate a peristaltic sequence through the feline esophagus.
Ileal microvascular permeability: a comparison of PS and sigma d using lymphatic and isotopic protein clearances
Authors: Townsley M. I. , Smith S. M. , Reed R. K. , Pitts V. H. , Taylor A. E.
Published: December 2017

Lymphatic clearances of total protein, albumin, immunoglobulin (Ig) G, and IgM obtained in autoperfused cat ileum as venous pressure (Pv) was elevated were analyzed using traditional methods as well as the newer maximal diffusion (max,diff) method of Reed et al. [Am. J. Physiol. 261 (Heart Circ. Physiol. 30): H728-H740, 1991; Am. J. Physiol. 257 (Heart Circ. Physiol. 26): H1037-H1041, 1989] to determine capillary osmotic reflection coefficients (sigma d) and unique permeability surface area products (PS). In a control group (n = 6), sigma d max,diff and PSmax,diff for albumin, IgG, and IgM could not be determined due to their transiently high clearance patterns. These patterns were not altered by treatment with vasodilators (n = 6) to prevent redistribution of blood flow from the mucosal-submucosal to muscularis layer of the ileum, which accompanies elevation of ileal Pv. Furthermore, sigma d values for IgG in both groups were lower than those for both albumin and IgM, a finding inconsistent with predictions based on pore theory, together suggesting that lymphatic protein clearances were influenced by washout of interstitial proteins, a conclusion supported by the decrease in tissue content of albumin and IgG after elevation of Pv. Clearances of radiolabeled albumin (n = 10) and IgG (n = 6), measured after an initial 2-h steady-state period at a constant Pv, were markedly reduced at low lymph flow compared with those obtained in the shorter term experiments. In an additional group (n = 5), albumin clearance peaked at 10 times baseline within 15 min after a step increase in Pv to 30 mmHg but fell to only 3 times baseline within 1 h.(ABSTRACT TRUNCATED AT 250 WORDS)
Role of transglutaminase and protein cross-linking in the repair of mucosal stress erosions
Authors: Wang J. Y. , Johnson L. R.
Published: December 2017

We have recently demonstrated that polyamines are absolutely required for gastric and duodenal mucosal repair after stress. Polyamines act as substrates for transglutaminase and facilitate protein cross-linking. The current study tests whether transglutaminase and protein cross-linking are involved in the mechanism of mucosal healing. Rats were fasted 22 h, placed in restraint cages, and immersed in water to the xiphoid process for 6 h. Animals were killed immediately or 4, 12, or 24 h after stress. Gastric and duodenal mucosa were examined histologically and grossly, and transglutaminase activity was measured. Transglutaminase activity in gastric and duodenal mucosa was increased significantly from 0 to 8 h, peaking 4 h after the 6-h stress period. By 12 h, enzyme activity in duodenal mucosa had returned to control values while gastric mucosal transglutaminase did not decrease to control values until 24 h. Mucosal recovery from lesions produced by stress was evident 12 h after stress and was almost complete by 24 h. Dansylcadaverine (100 mg/kg, orally), a specific inhibitor of protein cross-linking, not only prevented the increases in transglutaminase but significantly decreased healing in both tissues. Oral administration of the polyamine spermidine (100 mg/kg) immediately after stress totally prevented inhibition of repair caused by blocking ornithine decarboxylase with difluoromethylornithine (DFMO, 500 mg/kg). Administration of dansylcadaverine, together with spermidine, significantly prevented the beneficial effect of spermidine on mucosal healing in the DFMO-treated animals.(ABSTRACT TRUNCATED AT 250 WORDS)
Acceleration of gastric emptying with electrical stimulation in a canine model of gastroparesis
Authors: Bellahsene B. E. , Lind C. D. , Schirmer B. D. , Updike O. L. , McCallum R. W.
Published: December 2017

We investigated the effects of electrical stimulation of the stomach on gastric emptying and the electrical activity of the stomach in 10 dogs. A model of gastroparesis was developed in five dogs using truncal vagotomy combined with injections of glucagon. Glucagon also induced electrical dysrhythmias. Bipolar electrodes were implanted in the stomach and the duodenum for electrical stimulation and for recording electrogastrograms. Gastric emptying of an isotope-labeled solid meal was assessed for 2 h. External electrical stimulation was delivered to the corpus of the stomach at its own physiological frequency to investigate whether it could restore normal gastric emptying. Such stimulation had no significant effect on gastric emptying in intact animals (45 vs. 43%: retention of isotope after 2 h) or when only vagotomy was performed (78 vs. 66%), but it significantly accelerated gastric emptying in animals with vagotomy and glucagon (from 86 to 68%). From this model of delayed gastric emptying, we suggest that electrical stimulation of the stomach at its own intrinsic frequency may recoordinate uncoupled slow wave activity induced by glucagon after vagotomy thus improving the rate of gastric emptying.
Convective movement of Ca2+ across guinea pig gallbladder epithelium
Authors: Rege R. V. , Moore E. W.
Published: December 2017

Recently, much interest has developed in biliary calcium because of its importance in the pathogenesis and composition of gallstones. While much progress has been made in understanding the thermodynamic factors that control biliary calcium concentrations, little is known about the kinetic factors that control the movement of calcium across the gallbladder epithelium. These studies measure guinea pig gallbladder epithelial permeability to Ca2+ during in vivo convective water movement across the membrane. Water movement, ranging from -15.2 (absorption) to 6.3 microliters.min-1.cm-2 (water entry), was induced by placing hypotonic, isotonic, and hypertonic solutions into the gallbladder lumen. Calcium movement was found to be directly and linearly related to water flow, indicating that Ca2+ moved with the convective water flow, presumably across paracellular channels. The slope of this relationship (0.602), representing the concentration of calcium in the fluid translocated across the gallbladder epithelium, was only about half that of plasma or luminal contents, indicating that calcium movement across the membrane was restricted. The mean sieving coefficient (1 - r) of guinea pig gallbladder, calculated from this slope, was approximately 0.5, indicating that the epithelium is only moderately permeable to Ca2+. The results suggest that intraluminal chelation of Ca2+ for the possible prevention and/or treatment of calcium-containing gallstones is a potentially feasible therapeutic modality.
Uptake of biotin by isolated rat liver mitochondria
Authors: Said H. M. , McAlister-Henn L. , Mohammadkhani R. , Horne D. W.
Published: December 2017

This study examined the mechanism of biotin uptake by liver mitochondria. Mitochondria were isolated from rat liver by an established procedure and demonstrated normal respiratory control ratios. Uptake of biotin with time at incubation buffer pH 6.1 was rapid and linear and occurred with a distinct "overshoot" phenomenon that peaked at approximately 1 min of incubation. At incubation buffer pH 7.4, however, uptake of biotin with time was significantly slower and no overshoot was observed. Gradual lowering of incubation buffer pH from 7.9 to 6.1 caused a similar pattern of increase in uptake of low (0.024 microM) and high (8 and 30 microM) concentrations of biotin. At incubation buffer pH 6.1 and 7.4, uptake of biotin as a function of concentration (0.012-30 microM) was linear and occurred at rates of 3.62 and 1.90 pmol.mg protein-1.5 s-1, respectively. Addition to the incubation medium of high concentrations of unlabeled biotin, its related compounds (biocytin, desthiobiotin, biotin methyl ester, thioctic acid, and thioctic amide), or substrates of known mitochondrial transporters (succinate, pyruvate, glutamate, malate, and phosphate) failed to cause any significant inhibition in uptake of [3H]biotin by mitochondria incubated in buffer pH 6.1 and 7.4. Furthermore, preloading mitochondria with unlabeled biotin, biocytin, malate, or aspartate failed to cause any significant stimulation in biotin uptake. At incubation buffer pH 6.1, treatment of mitochondria with the protonophore FCCP caused significant inhibition in pH-dependent overshoot of biotin uptake. However, treatment of mitochondria with the potassium ionophore valinomycin caused significant stimulation in the pH-dependent overshoot of biotin uptake.(ABSTRACT TRUNCATED AT 250 WORDS)
The liver as a stem cell and lineage system
Authors: Sigal S. H. , Brill S. , Fiorino A. S. , Reid L. M.
Published: December 2017

We propose that the liver is a stem cell and lineage system with many parallels to lineages in the bone marrow, gut, and epidermis, varying from them only in kinetics. All are organized with three compartments: a slow cycling stem cell compartment with cells expressing a fetal phenotype and responding slowly to injury; an amplification compartment with cells of intermediate phenotype rapidly proliferating in response to regenerative stimuli or acute injuries; and a terminal differentiation compartment in which cells increasingly differentiate and gradually lose their ability to divide. In all systems, both those with slow or rapid kinetics, the various compartments are positioned in a polarized organization, are associated with a gradient in the chemistry of the extracellular matrix, and show lineage-position-dependent growth responses, gene expression, pharmacological and toxicological responses, and reaction to viruses and radiation. In general, known oncogens selectively kill cells in the differentiation compartment inducing chronic regenerative responses of the cells in stem cell and/or amplification compartment. Tumors arise by subsequent transformation of the activated stem cells or early precursor cells. The evidence for a lineage model consists of the data implicating gradients in cell size, ploidy, growth potential, and antigenic and gene expression in the liver parenchyma along the sinusoidal plates. The traditional explanation for this heterogeneity is that it represents adaption of cells to a changing sinusoidal microenvironment dictated by the direction of blood flow. However, we review the extant data and suggest that it more readily supports a lineage model involving a maturation process beginning with stem cells and precursors in the periportal zone and ending with sensescing parenchyma near the central vein. Support for this theory is provided by the studies on phenotypic heterogeneity in liver, investigations into the embryology of the liver, and analyses of the responses of liver to chemical and viral oncogens that induce rapid proliferation of small cells with oval-shaped nuclei, "oval cells," now thought to be closely related to liver stem cells. The lineage model provides clarity and insights into many aspects of liver biology and disease including the limited proliferative ability of in vitro parenchymal cultures, liver regeneration, gene expression, viral infection, hepatocellular carcinogenesis, liver cell transplantation, and aging.
NADPH diaphorase and nitric oxide synthase colocalization in enteric neurons of canine proximal colon
Authors: Ward S. M. , Xue C. , Shuttleworth C. W. , Bredt D. S. , Snyder S. H. , Sanders K. M.
Published: December 2017

Considerable evidence has recently been presented that suggests that nitric oxide (NO) is a nonadrenergic noncholinergic (NANC) neurotransmitter in gastrointestinal tissues. One of the criteria that must be satisfied before this hypothesis can be accepted is that enteric neurons must be shown to contain the enzymatic apparatus necessary to synthesize NO. Specific antibodies have been developed for NO synthase (NOS) isolated from rat cerebellum, and studies have shown that NOS copurifies and colocalizes with NADPH diaphorase activity, a commonly used neural marker. We used antibodies raised against the cerebellar NOS to determine the distribution of NOS-like immunoreactivity (NOS-LI) in enteric neurons of the canine proximal colon. We also tested whether NADPH diaphorase staining would label the population of neurons containing NOS-LI in this species. A subpopulation of neurons in myenteric and submucosal ganglia displayed NOS-LI and were colabeled with NADPH diaphorase. Labeled neurons had morphological characteristics similar to the Dogiel type I morphology. Cryostat sections showed NOS-positive nerve trunks throughout the circular and longitudinal muscle layers, but a high density of NOS-LI was observed within the submucosal pacemaker region, as predicted from physiological studies. These studies provide the first morphological support for the hypothesis that NO serves as a NANC neurotransmitter in the canine colon. The study also shows that the NADPH diaphorase reaction provides a useful method to label cells with NOS-LI.
CCK, bombesin, and carbachol stimulate c-fos, c-jun, and c-myc oncogene expression in rat pancreatic acini
Authors: Lu L. , Logsdon C. D.
Published: December 2017

To identify possible nuclear signals mediating long-term regulation of the pancreas by gastrointestinal hormones, the expression of c-fos, c-jun, and c-myc was investigated in rat pancreatic acini. Stimulation of the acini with cholecystokinin octapeptide (CCK-8, 100 pM), bombesin (10 nM), or carbachol (10 microM), but not gastrin (100 nM), secretin (100 nM), or vasoactive intestinal peptide (10 nM) induced an increase in oncogene mRNA expression. The percent increases of c-fos, c-jun, and c-myc mRNA were 207 +/- 40, 171 +/- 26, and 46 +/- 19 (n = 5) for CCK-8; 223 +/- 71, 159 +/- 31, and 43 +/- 21 (n = 5) for bombesin; and 125 +/- 51, 123 +/- 58, and 67 +/- 19 (n = 5) for carbachol, respectively. CCK-induced increases in oncogene mRNA were rapid and transient. c-fos and c-jun mRNA levels were increased after 30 min stimulation, peaked at 1 h, and returned to basal level in 2 h. Activation of c-myc was more prolonged with levels remaining elevated for at least 3 h. The effects of CCK-8 were concentration dependent. Detectable stimulation was seen at 10 pM; maximal stimulation occurred at 10 nM and was not affected by further increase in the concentration of CCK-8. JMV-180, a high-affinity site CCK receptor agonist and low-affinity site antagonist, alone did not stimulate c-fos mRNA expression but inhibited c-fos mRNA expression induced by CCK-8. These results suggest that the interaction between CCK and the low-affinity state of the CCK receptor is responsible for oncogene activation.
Hypothalamic neuropeptide Y inhibits gastric acid output in rat: role of the autonomic nervous system
Authors: Humphreys G. A. , Davison J. S. , Veale W. L.
Published: December 2017

Injection of neuropeptide Y (NPY) into the hypothalamic paraventricular nucleus (PVN) inhibits gastric acid secretion in anesthetized rats. The role of the autonomic nervous system in mediation of this response was investigated. Unilateral microinjection of 200 pmol NPY into the PVN of anesthetized rats inhibited spontaneous and pentagastrin-stimulated gastric acid output. Inhibition was abolished by subdiaphragmatic vagotomy, atropine, and bethanechol but was restored by electrical stimulation of the distal cut end of the vagus in cervically vagotomized rats. Although sympathectomy, phenoxybenzamine, and yohimbine abolished the inhibition, it was not affected by prazosin treatment. Gastric blood flow was not altered by injection of NPY. These results suggest that the antisecretory effect of NPY in the PVN was sympathetically mediated via suppression of gastric vagal cholinergic tone through activation of alpha 2-adrenoceptors.
Cation channels in basolateral membranes of sheep parotid secretory cells
Authors: Wegman E. A. , Ishikawa T. , Young J. A. , Cook D. I.
Published: December 2017

We observed 240-pS K+ channels in 63% of cell-attached patches, and 30-pS K+ channels were observed in 95% of cell-attached patches. The 240-pS K+ channel had the relative permeability sequence of K+ (1) = Rb+ (1) > Cs+ (0.3) >> Na+ (0.03) and the relative conductance sequence of K+ (1) > Rb+ (0.22) > Cs+ (0.05) > Na+ (0). It was activated by intracellular free Ca2+ and by depolarization. It was blocked by 10 mmol/l tetraethylammonium (TEA) applied extracellularly. The 30-pS K+ channel had the relative permeability sequence of K+ (1) = Rb+ (1) > Cs+ (> Na+ (< 0.09) and the relative conductance sequence of K+ (1) > Rb+ (0.45) > Cs+ (0) = Na+ (0). Its activity was not sensitive to cytosolic free Ca2+ or membrane potential, and it was not blocked by 10 mmol/l TEA extracellularly. Acetylcholine (10 mumol/l) activated the 240-pS voltage-activated and Ca(2+)-activated K+ channels but did not activate the 30-pS K+ channels. We conclude that the 30-pS K+ channel probably determines the properties of the basolateral membrane in unstimulated sheep parotid secretory cells, whereas the 240-pS voltage-activated and Ca(2+)-activated K+ channel may be important during parasympathomimetic stimulation.
Regulation of electrolyte and fluid secretion in salivary acinar cells
Authors: Nauntofte B.
Published: December 2017

The primary secretion from exocrine gland cells is a fluid rich in Na+ and Cl- with a plasmalike ionic composition. Activation of specific receptors on the plasma membrane by hormones and neurotransmitters, which leads to activation of the phosphoinositol metabolism, results in release of Ca2+ from internal Ca2+ stores. Intracellular free Ca2+ concentration ([Ca2+]i) then rises simultaneously at both the basolateral and luminal parts of the acinar cell, reaching maximum values within 1 s after stimulation. In parotid acinar cells, increased [Ca2+]i activates the opening of maxi K+ channels located on the basolateral membrane and Cl- channels presumably located on the luminal membrane, resulting in rapid loss of K+ and Cl- and water and cell shrinkage. Extracellular electroneutrality is maintained by a paracellular Na+ flux into the lumen. Because of the simultaneous activation of K+ and Cl- channels, secretion occurs at a virtually constant membrane potential of about -60 mV. After maximal muscarinic cholinergic stimulation, loss of K+, Cl-, and water results in an approximate 25% reduction in cell volume within 10-15 s after receptor activation. Concomitant with loss of Cl-, there is a loss of HCO3- from the cell, causing a decrease in intracellular pH of 0.1 pH units because of the carbonic anhydrase-mediated conversion of CO2 into H+ and HCO3-. H+ generated from the metabolism and HCO3- production is compensated for by extrusion of H+ by a Na(+)-H+ exchange mechanism, which is responsible for approximately 75% of net Na+ gain that occurs after stimulation. Increased [Na+]i activates the Na(+)-K+ pump, which in turn extrudes Na+ from the cells. In both the unstimulated and stimulated states, cellular production of HCO3- can drive a net uptake of Cl- via the Cl(-)-HCO3- exchange mechanism operating in parallel with the Na(+)-H+ exchanger. The operation of the Cl(-)-HCO3- exchanger is, together with a Na(+)-K(+)-2Cl- cotransport system, essential for maintainance of a high [Cl-]i both in the unstimulated state and during Cl- reuptake.
Hepatic Na(+)-dicarboxylate cotransport: identification, characterization, and acinar localization
Authors: Moseley R. H. , Jarose S. , Permoad P.
Published: December 2017

Rat liver perfusion studies suggest that the transport of alpha-ketoglutarate (KG) and related dicarboxylates exhibits acinar heterogeneity, in that the uptake and subsequent metabolism of these organic anions appears to occur predominantly in the perivenous region. However, the isolated perfused liver as an experimental model cannot distinguish intra-acinar differences in either the rate of solute uptake and/or efflux or intracellular binding and/or metabolism. Therefore, the driving forces and acinar localization of KG transport were examined using rat basolateral liver plasma membrane vesicles (blLPMV) isolated from control animals and animals treated 24 h before with selective perivenous and periportal toxins [carbon tetrachloride (CCl4) and allyl alcohol (AA), respectively]. In control blLPMV, [14C]KG uptake into an osmotically sensitive space was markedly stimulated by an inwardly directed Na+ gradient but not by inwardly directed gradients of other monovalent cations. The Na+ ionophore, gramicidin, had a small but significant inhibitory effect on Na(+)-dependent KG uptake, demonstrating that KG uptake was not the result of an intravesicular positive Na+ diffusion potential. The protonophore, carbonyl cyanide-p-trifluoromethoxyphenylhydrazone, had no effect on Na+ gradient-driven KG uptake, indicating that KG uptake was not the indirect result of coordinated activities of Na-H and KG-OH exchange. Na+ gradient-driven KG uptake was electrogenic (occurring with the net transfer of positive charge), and cis-inhibited by other tricarboxylic acid cycle intermediates, including succinate, fumarate, and malate and by citrate, but not by the dicarboxylates oxalate and malonate nor by glutamate and taurocholate (TC).(ABSTRACT TRUNCATED AT 250 WORDS)
L-glutamine with D-glucose stimulates oxidative metabolism and NaCl absorption in piglet jejunum
Authors: Rhoads J. M. , Keku E. O. , Woodard J. P. , Bangdiwala S. I. , Lecce J. G. , Gatzy J. T.
Published: December 2017

To explore the relationship between intestinal fluid absorption and oxidative metabolism, we measured the effects of amino acids and glucose on piglet jejunal ion transport and oxygen consumption (QO2) in vitro. Jejunal QO2 was stimulated by L-glutamine and D-glucose but not by the nonmetabolizable organic solutes methyl beta-D-glucoside or L-phenylalanine. QO2 was maximally enhanced by the combination of D-glucose and L-glutamine (5 mM). Even though 5 mM L-glutamine was previously found to be insufficient to stimulate NaCl absorption, 5 mM L-glutamine enhanced jejunal NaCl flux when combined with equimolar mucosal D-glucose. Either D-glucose or methyl beta-D-glucoside caused an increase in short-circuit current (Isc), an increase in Na+ absorption in excess of Isc, and a decrease in Cl- secretion, when L-glutamine was substituted for D-glucose (10 mM) on the serosal side. This relationship suggests that mucosal sugars, if combined with L-glutamine, enhance neutral NaCl absorption as well as electrogenic Na+ flow. (Aminooxy)acetate, an inhibitor of alanine aminotransferase, abolished the stimulation of QO2 and the NaCl-absorptive response to L-glutamine. We conclude that the oxidative metabolism fueled by L-glutamine is linked to a NaCl-absorptive mechanism in the intestine. We propose that the CO2 produced by glutamine metabolism yields carbonic acid, which dissociates to H+ and HCO3-, which may stimulate parallel antiports in the apical membrane.
Lactoferrin interferes with uptake of iron from transferrin and asialotransferrin by the rat liver
Authors: Hu W. L. , Regoeczi E. , Chindemi P. A. , Bolyos M.
Published: December 2017

Intravenous injection of bovine or human lactoferrin (6.25 x 10(-2) mumol/100 g body wt) in rats resulted in marked reduction of hepatic iron uptake from transferrin and asialotransferrin. The effect was dose dependent, saturable at approximately 5 mg/100 g body wt, and independent of lactoferrin's iron content. At this dose level, iron uptake from transferrin was reduced by 28% and from asialotransferrin by 43% in experiments lasting 90 min. Bovine lactoperoxidase, another basic protein, was similarly effective. The clearance of asialofetuin and pinocytosis of polyvinylpyrrolidone remained unaffected. Perfusion of isolated rat livers at 4 degrees C showed a strong reduction in asialotransferrin binding in the presence of lactoferrin. Chromatography of hepatic heparan sulfate proteoglycan on immobilized lactoferrin, lactoperoxidase, asialotransferrin, and transferrin showed that it possessed affinity for each of these proteins, more for the first two than the latter two. Heparan sulfate proteoglycan binding and efficacy in reducing hepatic iron uptake were also studied after selective modifications of positively charged amino acids in these proteins. The data obtained are compatible with the hypothesis that lactoferrin and other proteins with similarly high affinity for hepatic heparan sulfate exert their negative effect on iron uptake by preventing transferrin binding to the proteoglycan. The possibility is thus raised that the large number of low-affinity transferrin binding sites reported by earlier investigators for the liver may be heparan sulfate molecules.
HCO3- reduces paracellular permeability of guinea pig duodenal mucosa by a Ca2+ (prostaglandin)-dependent action
Authors: Macherey H. J. , Sprakties G. , Petersen K. U.
Published: December 2017

The mechanism of HCO3(-)-induced decrease in electrical conductance (Gt) of guinea pig duodenal mucosa was investigated in vitro. Gt and unidirectional fluxes of mannitol (M), Na+, and Cl- were straightly correlated. In the presence of HCO3- (20 mM), elevating the bath concentration of Ca2+ from 0 to 1.2 mM caused decreases in Gt and Na+ fluxes by approximately 30%. Smaller reductions were found in the absence of HCO-3. With the addition of Ca2+, Gt and unidirectional fluxes were lower with than without HCO3-. In the latter condition, PM/PNa, PM/PCl, and PNa/PCl (P is permeability) were close or equal to ratios predictable from free solution diffusion coefficients; with HCO3-, ratios became different or more different and PM/PNa was reduced. Straightly correlated were conductivities of six differently composed HCO3(-)-free salines and Gt of tissues bathed therein. This correlation did not embrace HCO3- Ringer. The Gt effect of Ca2+ (HCO3- present) was mimicked by prostaglandin E2 and reduced (by approximately 40%) by Ca2+ channel blockers (diltiazem, gallopamil), cyclooxygenase inhibitors (meclofenamate, diclofenac), cytochalasin D, and trifluoperazine. We conclude that without HCO3-, paracellular solute flow occurs mainly via structures resembling a free-solution shunt; HCO3-, through an action made more efficient by Ca(2+)-mediated prostaglandin synthesis and possibly involving microfilaments, strengthens a discriminatory barrier.
Characterization of an apical sodium conductance in rabbit cecum
Authors: Sellin J. H. , Hall A. , Cragoe E. J. , Dubinsky W. P.
Published: December 2017

Rabbit cecum in vitro exhibits electrogenic Na+ absorption not blocked by amiloride but inhibited by the amiloride analogue phenamil, suggesting transport mediated by modified Na+ channels in the apical membrane. To further characterize the mechanism(s) of Na+ absorption, microelectrode impalements of single epithelial cells were performed to measure intracellular potential difference (psi mc) and fractional resistance of the apical membrane, to characterize ionic conductances of the apical and basolateral membranes, and to determine the response to phenamil. The electrical potential profile of cecum (psi mc = -31 +/- 2 mV, fractional resistance = 0.71 +/- 0.03) was qualitatively similar to distal colon. The apical membrane exhibited responses suggesting both Na+ and K+ conductances, whereas the basolateral membrane appeared to have a predominant K+ conductance. Phenamil elicited a depolarization of psi mc and a decrease in fractional resistance; neither response is consistent with inhibition of an apical Na+ conductance. Studies were performed in apical membrane vesicles to characterize ionic conductances by a second independent methodology. These additional studies confirmed the presence of an apical Na+ conductance not inhibited by either amiloride or phenamil. Thus both microelectrode impalement and vesicle studies demonstrated an apical membrane Na+ conductance in rabbit cecum; this is the likely mechanism of electrogenic Na+ absorption in this epithelium. However, the anomalous response to phenamil suggests that the inhibitory effect of this agent is not directly on the conductance. The cecal transporter may be one of a family of cation channels related to, but significantly different from, the classic Na+ channel found in distal colon and other tight epithelia.
Characterization of a distinct Na(+)-H+ exchanger in basolateral membranes of human jejunum
Authors: Acra S. , Dykes W. , Nylander W. , Ghishan F. K.
Published: December 2017

Kinetically distinct Na(+)-H+ exchangers exist on the apical and basolateral membranes of rabbit ileal enterocytes. The apical Na(+)-H+ exchanger appears to function in electroneutral NaCl transport, whereas the basolateral Na(+)-H+ exchanger may function in homeostatic intravesicular pH (pHi) regulation and volume regulation. This study is designed to determine the presence and characteristics of the Na(+)-H+ exchanger in basolateral membrane vesicles (BLMV) prepared from jejunal tissues of human organ donors. A well-validated Percoll-gradient technique was used to prepare BLMV. An outwardly directed H+ gradient [pHi/extravesicular pH (pHo) = 5.2/7.5] resulted in a Na+ uptake overshoot (1.45 +/- 0.21 nmol/mg protein) 2.5-fold above equilibrium values (0.59 +/- 0.13 nmol/mg protein). Na+ uptake at equilibrium represented transport into an osmotically sensitive intravesicular space as validated by an osmolality study. Na+ uptake represented an electroneutral process, as shown by studies in which negative membrane potentials were induced by K+ and the ionophore valinomycin. Na+ uptake was linear for the first 15 s of transport as depicted by y = 0.042x + 0.002, r2 = 0.98. Dixon plot analysis of amiloride sensitivity revealed an ID50 value for amiloride of 29 microM (fourfold lower than ID50 for brush-border Na(+)-H+ exchanger). Kinetic studies of amiloride-sensitive Na+ uptake revealed a maximal velocity = 1.53 +/- 0.19 nmol.mg protein-1.5 s-1 and Michaelis constant = 9.83 +/- 3.5 mM. By varying pHi a sigmoidal effect of internal H+ on Na+ uptake was noted consistent with an internal modifier site for protons. To confirm this finding, the effect of pHi on Na+ efflux and Na(+)-Na+ exchange was studied.(ABSTRACT TRUNCATED AT 250 WORDS)
Calcium mediates gastrin-induced gastric histamine release in the rat
Authors: Sandvik A. K. , Brenna E. , Waldum H. L.
Published: December 2017

This study examined the second messenger system responsible for gastrin-induced histamine release from the rat stomach. We examined the effect of different concentrations of ionized calcium, the calcium-channel blockers verapamil and nicardipine, and the intracellular calcium-chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid/acetoxymethyl ester (BAPTA/AM) on gastrin-stimulated histamine release in the totally isolated vascularly perfused rat stomach. Moreover, the effect on baseline histamine release of caffeine as well as of forskolin and 3-isobutyl-1-methylxanthine (IBMX) was tested. Gastrin induced an immediate 10- to 15-fold increase in venous histamine. Perfusate ionized calcium in the 0.25-1.25 mM range did not affect histamine release; histamine release was attenuated by the 0.00 and 1.75 mM calcium concentrations. Verapamil, nicardipine, and BAPTA/AM inhibited gastrin-stimulated histamine release. Caffeine stimulated the release, whereas forskolin and IBMX had no effect. We conclude that gastrin-induced histamine release from the rat stomach is mediated by calcium, probably both from the intracellular pool and by transmembrane flux from the extracellular space.
Swallowing and upper esophageal sphincter contraction with transcranial magnetic-induced electrical stimulation
Authors: Valdez D. T. , Salapatek A. , Niznik G. , Linden R. D. , Diamant N. E.
Published: December 2017

This study in three dogs explores the effect of magnetically induced electrical stimulation of the brain to induce swallowing and produce contraction of the upper esophageal sphincter (UES). Single stimuli were delivered at intervals from 15 s to 3 min. Studies were performed with and without perfusion of fluid into the pharynx and upper esophagus. Results showed that magnetic stimulation produced a twitch contraction of the UES when stimulus intensity was above a threshold that varied between 14 and 20% of the stimulator output. Increasing stimulus intensity progressively increased twitch amplitude. Magnetic stimulation also induced swallowing, above a stimulus threshold similar to that for induction of the UES twitch contraction. Fluid perfusion augmented the ability of the magnetic stimulus to induce swallowing. We concluded that a magnetically induced single electrical stimulus of the cerebral cortex produces UES contraction and induces swallowing. The effect on swallowing is facilitated by sensory stimulation of the pharynx. This technique holds the potential for further study of 1) motor and sensory neural mechanisms involved in the control of swallowing and 2) the assessment and management of oropharyngeal dysphagia in humans.
Effect of epidermal growth factor on enterocyte brush-border surface area
Authors: Hardin J. , Buret A. , Meddings J. B. , Gall D. G.
Published: December 2017

The effect of acute in vivo epidermal growth factor (EGF) exposure on intestinal absorptive surface area was examined in blind jejunal loops in New Zealand White rabbits (500-900 g). Brush-border surface area was assessed by electron microscopy at 30 and 120 min, and total surface area was assessed by the fluorophore 1-[4-(trimethylamino)phenyl)]-6-phenylhexatriene (TMA-DPH) at 10 and 60 min after EGF exposure. Mucosa obtained at 120 min was also used for morphometrics and analysis of membrane composition and fluidity. Brush-border surface area was significantly increased in EGF-treated tissue after 30 (42%) and 120 min (60%). Total absorptive surface area measured by TMA-DPH was increased more than twofold after 10 and 60 min EGF exposure. The increase in absorptive surface area was abolished by pretreatment with intravenous verapamil. Mucosal morphometrics and membrane sucrase activity, total phospholipids, cholesterol content, cholesterol-to-phospholipid ratio, phospholipid species (wt%), phospholipid fatty acid composition, and fluidity did not differ between control and EGF-treated tissue. These findings indicate that EGF can rapidly increase brush-border surface area by a mechanism that appears to be due to a redistribution of existing performed microvillus plasma membrane.
Receptor antagonists for gastrointestinal peptides
Authors: Presti M. E. , Gardner J. D.
Published: December 2017

Receptors for gastrointestinal peptides are all G protein-coupled receptors. Since the discovery that dibutyryl guanosine 3',5'-cyclic monophosphate was a cholecystokinin-receptor antagonist, a variety of receptor antagonists have been developed for a number of different gastrointestinal peptides. These antagonists have been useful in classifying receptors for gastrointestinal peptides and in elucidating complex regulation of gastrointestinal function. Some antagonists also have therapeutic potential. Based on the receptors with which they interact, gastrointestinal peptides can be grouped into families, and, in general, a given receptor antagonist is specific for a given family. This review covers the different families of gastrointestinal peptides and the major antagonists that exist for each family.
Duodenal lipid inhibits gastric acid secretion by vagal, capsaicin-sensitive afferent pathways in rats
Authors: Lloyd K. C. , Holzer H. H. , Zittel T. T. , Raybould H. E.
Published: December 2017

Neural and endocrine pathways mediate the inhibitory effects of intestinal fat on gastric acid secretion. To study whether vagal and/or spinal afferent nerves contribute to the neural component of the enterogastric reflex, the sensory neurotoxin capsaicin was applied topically either to the vagus nerves bilaterally or to the celiac-superior mesenteric ganglia in rats with chronic gastric and duodenal fistulas. In lightly restrained, awake rats acid secretion was stimulated for 2 h by continuous intragastric perfusion with 8% peptone and was measured by extragastric titration to pH 5.5. Duodenal lipid perfusion (0-20%) during the 2nd h caused inhibition of peptone-stimulated acid output. Acid output was inhibited by 81% during 5% lipid perfusion of the duodenum and was restored after capsaicin treatment of the vagus nerves. In contrast, capsaicin treatment of the celiac ganglion did not alter the acid inhibitory response to any dose of intestinal lipid. Basal and maximum acid outputs were not significantly different among rats treated by either method with capsaicin. The neural component of the enterogastric reflex in awake rats is mediated in part by a capsaicin-sensitive, vagal-afferent neural reflex.
Vitamin D-sensitive and quinacrine-sensitive zinc transport in human intestinal cell line Caco-2
Authors: Fleet J. C. , Turnbull A. J. , Bourcier M. , Wood R. J.
Published: December 2017

We studied the mechanism of transepithelial zinc (Zn) transport using monolayers of Caco-2 cells grown on permeable filter supports. 65Zn transport could be fitted to a modified Michaelis-Menten equation, which includes a nonsaturable [linear diffusion constant of nonsaturable component (Kd) = 0.08%.cm-2.90 min-1] and a saturable component [upper well Zn concentration at half Jmax (Kt) = 226 microM and maximal rate of saturable Zn transport (Jmax) = 1.06 nmol.cm-2.90 min-1]. Caco-2 cells contained metal-inducible metallothionein (MT) protein and mRNA as well as mRNA for cysteine-rich intestinal protein (CRIP). Cells pretreated with 10 nM 1 alpha,25-dihydroxyvitamin D3 [1 alpha,25(OH)2D3] for 3 days transported more Zn (159%) than controls (0.48 +/- 0.02 nmol.cm-2.90 min-1) when each was incubated with 100 microM Zn for 90 min. This effect was significant after 24 h of 1 alpha,25-(OH)2D3 pretreatment and continued to increase up to 72 h, with concomitant increases in MT mRNA levels being observed (4-fold by 24 h, 10-fold by 72 h). MT protein levels were only modestly elevated by 72 h 1 alpha,25(OH)2D3 treatment (from 0.32 +/- 0.04 to 0.45 +/- 0.03 nmol MT/mg protein). CRIP mRNA levels were reduced by 1 alpha,25(OH)2D3 treatment. The lysosome-disrupting agent quinacrine (0.5 mM) inhibited basal Zn transport by 68%, suggesting the possible presence of a lysosome-mediated component for transepithelial Zn transport in Caco-2 cells. 1 alpha,25(OH)2D3-stimulated Zn transport was not affected by quinacrine, suggesting that 1 alpha,25(OH)2D3-induced Zn transport is distinct from the putative lysosome-mediated Zn transport pathway.
Dietary regulation of rat intestinal angiotensin-converting enzyme and dipeptidyl peptidase IV
Authors: Suzuki Y. , Erickson R. H. , Sedlmayer A. , Chang S. K. , Ikehara Y. , Kim Y. S.
Published: December 2017

The small intestinal brush-border membrane contains several peptidases that are involved in the hydrolysis of dietary peptides containing proline. A high-proline (gelatin) diet was administered to one of several groups of rats to study its possible regulatory effect on levels of two prolyl peptidases, namely angiotensin-converting enzyme (ACE) and dipeptidyl peptidase IV (DPP IV). Groups of rats were maintained on isocaloric diets containing either low (4%), normal (17%), or high (50%) protein (casein) or high (50%) gelatin. After 7 days, brush-border membranes and total RNA were prepared from the small intestine. ACE activity was 3- to 10-fold higher in brush-border membranes from the gelatin group compared with the low-protein group. DPP IV exhibited a three- to sixfold increase. Immunoblot analysis of brush-border membrane-associated ACE protein indicated a six- to eightfold increase in the high-gelatin group. There was also a 1.5- to 3-fold increase in steady-state levels of ACE and DPP IV mRNA. These results suggest that a diet high in proline (gelatin) is particularly effective in increasing intestinal levels of these two enzymes.
Stimulation of Cl permeability in colonic crypts of Lieberkuhn measured with a fluorescent indicator
Authors: Halm D. R. , Kirk K. L. , Sathiakumar K. C.
Published: December 2017

Crypts of Lieberkuhn were isolated from rabbit distal colon and the halide-sensitive dye 6-methoxy-N-[3-sulfopropyl]quinolinium was used to monitor changes in cell Cl by fluorescence microscopy. Distal colon from rabbits actively secretes Cl and K when stimulated with prostaglandin (PG) E2 but secretes only K in response to epinephrine. The secretagogues PGE2 and epinephrine each produced transient decreases of the apparent cell Cl concentration in about one-half of the crypt cells. Permeability to Cl was assessed by brief substitutions with gluconate or Br in the bath. After stimulation of secretion by PGE2 or epinephrine, Cl efflux and Br influx were increased but only in the cells that exhibited the decrease in cell Cl at the onset of stimulation. Although Cl efflux during gluconate substitution was stimulated similarly with either PGE2 or epinephrine, epinephrine stimulation led to a lower apparent Cl concentration after 2 min of gluconate substitution. Together these results support the concept that a particular epithelial cell type in the crypts responds to secretagogues and that the Cl permeability pathways differ between the secretory states induced by PGE2 and epinephrine.
Plasticity in the gastric inhibitory innervation after immunization against VIP and vagotomy in the ferret
Authors: Grundy D. , Gharib-Naseri M. K. , Hutson D.
Published: December 2017

Changes in gastric corpus tone have been characterized during two procedures that compromise the major inhibitory innervation of the stomach: immunoneutralization of endogenous vasoactive intestinal polypeptide (VIP) and chronic vagotomy. After both procedures, there was a small but significant increase in intracorpus pressure generated during ramp increases in volume compared with sham immunized controls but not when the procedures were combined in vagotomized immunized animals. Adaptation in the mechanisms controlling corpus tone was most apparent after atropine (100 micrograms/kg) and acute vagal section when tone was low in sham immunized vagotomized and vagotomized immunized animals (4.4 +/- 0.3 and 3.7 +/- 0.8 cmH2O, respectively) and high in immunized and sham immunized animals (6.5 +/- 0.4 and 6.2 +/- 0.5 cmH2O) despite a similar sensitivity to atropine. Corpus responses to low-frequency vagal stimulation were maintained in immunized animals despite the absence of a response to exogenous VIP. We conclude that gastric reservoir function adapts to the loss of the vagal inhibitory innervation by an upregulation of intrinsic reflex pathways controlling myenteric inhibitory neurons, which are non-VIPergic.