bluuebunny/crossref_metadata_2025 huggingface dataset:
Biliary obstruction dissipates bioelectric sinusoidal-canalicular barrier without altering taurocholate uptake
Authors: Cotting J. , Zysset T. , Reichen J.
Published: December 2017

To study immediate events during extrahepatic cholestasis, we investigated the effect of short-term biliary obstruction on the bioelectrical sinusoidal-canalicular barrier in the rat using molecular weight-matched uncharged and negatively charged inert solute pairs. The bioelectrical barrier averaged -22 +/- 5 and -18 +/- 4 mV (NS) using the pair carboxy-/methoxyinulin and ferrocyanide/sucrose, respectively. After a 20-min biliary obstruction both decreased by 61 and 11%, respectively, but only the large molecular weight pair (the inulins) returned to base line after release of the obstruction. Inert solute clearances were increased after short biliary obstruction depending on molecular size and negative charge (ferrocyanide greater than sucrose greater than carboxyinulin greater than inulin), suggesting that both permeability and bioelectrical barriers were affected by obstruction. The hepatic extraction in vivo of a passively transported drug not excreted into bile (D-propranolol) was not affected by obstruction, whereas that of an actively transported drug (glycocholate) decreased from 66 +/- 8 to 41 +/- 20% during biliary obstruction (P less than 0.01). Unidirectional transfer of glycocholate was not affected by short-term biliary obstruction in the situ perfused rat liver; however, 2 min after [14C]glycocholate administration, increased return was observed in hepatic venous effluent in obstructed animals. Our findings demonstrate a loss of the bioelectrical barrier immediately after short-term biliary obstruction. Decreased hepatic extraction in the view of unaltered sinusoidal uptake demonstrates regurgitation of bile into blood during short-term biliary obstruction.
Effects of ethanol on amino acid transport in basolateral liver plasma membrane vesicles
Authors: Moseley R. H. , Murphy S. M.
Published: December 2017

Ethanol has been reported to inhibit hepatocellular processes such as gluconeogenesis and protein synthesis that depend, in part, on amino acid uptake. Since previous studies in cultured hepatocytes indicate that ethanol may have a direct and selective inhibitory effect on amino acid transport, the effects of ethanol on amino acid uptake into basolateral (sinusoidal) rat liver plasma membrane (blLPM) vesicles were examined. Uptake of [3H]alanine, [3H]leucine, and [35S]cysteine was measured by a rapid Millipore filtration technique in the presence of inwardly directed Na+ and K+ gradients and under tetramethylammonium (TMA+)- and Na+-equilibrated conditions. Ethanol preincubation produced a concentration-dependent inhibition of Na+-dependent alanine and cysteine uptake; no effect was observed on either Na+-independent alanine and cysteine uptake or Na+-independent leucine transport. Ethanol had no effect on L-alanine transport under Na+-equilibrated conditions; however, initial rates of 22Na flux were enhanced in the presence of ethanol. On the basis of differences in 2-(methylamino)isobutyrate and L-cysteine sensitivity, ethanol inhibition of Na+-dependent alanine transport in blLPM vesicles largely but not exclusively corresponded to the hormone-responsive system A for amino acid transport described in isolated hepatocytes. Kinetic analysis showed that ethanol treatment resulted in an alteration in the apparent maximum velocity of reaction (Vmax) of Na+-dependent alanine transport without affecting the apparent Km for alanine. The inhibitory effects of ethanol on the time course of Na+-dependent alanine uptake were reversible.(ABSTRACT TRUNCATED AT 250 WORDS)
Basolateral inositol transport by intestines of carnivorous and herbivorous teleosts
Authors: Reshkin S. J. , Vilella S. , Ahearn G. A. , Storelli C.
Published: December 2017

Myoinositol transport by isolated basolateral membrane vesicles was characterized from intestines of the herbivorous tilapia (Oreochromis mossambicus) and the carnivorous eel (Anguilla anguilla). [3H]myoinositol transport occurred by nonelectrogenic, facilitated diffusion independent of cation gradients and was inhibited by phloretin (Ki = 0.6 and 0.9 mM for tilapia and eel, respectively) but not by phloridzin. Kinetic analysis of myoinositol influx disclosed no differences in concentration yielding half-maximal influx or maximum influx between these species. D-Glucose inhibition of myoinositol influx was shown to be noncompetitive. Additional inhibition studies with a range of sugars demonstrated that aldohexoses in the C-1 chair conformation were preferred substrates. Myoinositol had no inhibitory effect on D-glucose transport. Preloading vesicles with myoinositol transstimulated [3H]myoinositol uptake, while the use of internal D-glucose was without effect. These basolateral data support the contention that epithelial myoinositol carriers are separate from D-hexose transport systems present on the same membrane but are modulated by hexose binding to a regulator site on the myoinositol transporter. Furthermore, the comparison of two fish species suggests that genetic dietary transport adaptation occurs on the brush-border membrane, while no such adaptation is present at the epithelial basolateral pole.
Ascending enteric reflex: multiple neurotransmitter systems and interactions
Authors: Holzer P.
Published: December 2017

Isolated segments of the guinea pig small intestine were used to examine the transmitter circuitry of the neural pathways subserving the ascending enteric reflex (AER) contraction of the circular muscle. Inflation of an intraluminal balloon provided the distension stimulus for the AER. The ascending contraction was reduced to 5% of its original amplitude by atropine and to 10% by hexamethonium, which indicates that cholinergic interneurons and cholinergic motor neurons constitute the main AER pathway. However, in the continued presence of atropine or hexamethonium for 60 min, the AER recovered to approximately 30% of its original amplitude. The atropine-resistant AER was blocked by hexamethonium and the tachykinin antagonist spantide [( D-Arg1,D-Trp7,9, Leu11]-substance P) suggesting that it involved cholinergic interneurons and tachykinin-utilizing motor neurons. The hexamethonium-resistant AER was abolished by atropine but left unaffected by spantide, suggesting the participation of as yet unidentified interneurons and cholinergic motor neurons. These findings demonstrate that the AER is mediated by multiple neural pathways with different transmitters and that adaptive interactions between these pathways take place after blockade of one of its neurotransmitters systems.
D-glucose and L-leucine transport by human intestinal brush-border membrane vesicles
Authors: Harig J. M. , Barry J. A. , Rajendran V. M. , Soergel K. H. , Ramaswamy K.
Published: December 2017

This study utilized intestinal brush-border membrane vesicles obtained from organ donor intestine to characterize the absorption of D-glucose and L-leucine in the human intestine. Both D-glucose and L-leucine were taken up by sodium gradient-dependent active transport along the entire length of the small intestine. The relative magnitude of transport for both substrates under sodium gradient conditions followed the order distal jejunum greater than proximal jejunum greater than distal ileum. The number of carrier systems in these brush-border membrane vesicles was estimated by Eadie-Hofstee plot analysis. This analysis revealed that L-leucine was actively transported via a single high-affinity transport system for the length of the human small intestine. In contrast, the transport of D-glucose occurred via a high-affinity system along the length of the intestine and via a low-affinity, high-flux transport system that was limited to the proximal intestine. Both glucose transport systems were sodium dependent and phlorizin sensitive. The locations and apparent kinetic parameters of these transport systems indicated that these systems function efficiently in vivo as important mechanisms for carbohydrate and protein assimilation in humans. The presence of these active transport systems along the entire small intestine explains the formidable capacity for carbohydrate and protein assimilation in humans.
Carbonic anhydrase II gene expression in isolated canine gastric parietal cells
Authors: Campbell V. W. , Del Valle J. , Hawn M. , Park J. , Yamada T.
Published: December 2017

The participation of carbonic anhydrase (CA II) in the gastric acid secretory process has been the subject of considerable controversy. We utilized a cDNA probe for CA II to measure CA II gene expression in canine gastric parietal cells that had been stimulated with the three principal acid secretagogues, carbachol, gastrin, and histamine. Hybridization to dot blots of total parietal cell RNA showed a significant increase in specific CA II mRNA content within minutes of secretagogue addition: carbachol stimulation led to an increase of 52 +/- 8.9%, reaching a maximum within 20 min; gastrin stimulation led to an increase within 60 min of 104 +/- 10.6%; stimulation with histamine was followed within 20 min by an increase of 30 +/- 7.2%. We also measured transcription rates for the CA II gene in cells stimulated by each agent and found an increase within 15 min. Our results show that CA II gene expression is regulated by agents that stimulate the parietal cell to secrete acid and that the accumulation of CA II mRNA subsequent to the initial interaction of stimulant appears to result from new transcription of the CA II gene. These data suggest the participation of CA II in the acid secretory response of the parietal cell to secretagogues.
Permeability of the rat biliary tree to ursodeoxycholic acid
Authors: Farges O. , Corbic M. , Dumont M. , Maurice M. , Erlinger S.
Published: December 2017

The permeability of the biliary epithelium to [14C]ursodeoxycholic acid (UDCA), a hypercholeretic bile acid, was compared to that of the 14C-labeled nonhypercholeretic bile acids cholic acid (CA), taurocholic acid (TCA), and tauroursodeoxycholic acid (TUDCA) by means of anterograde intrabiliary infusions and retrograde intrabiliary injections in the anesthetized rat. Anterograde intrabiliary infusions were performed by perfusing an isolated segment of common bile duct in vivo. After anterograde intrabiliary infusions, the fraction of unrecovered UDCA (that had presumably been absorbed from the biliary lumen) was 11.03 +/- 1.03 (SE)% (n = 6) of the administered dose. It was significantly higher than that of TUDCA (1.25 +/- 0.27%; n = 5; P less than 0.01), CA (2.62 +/- 0.43%; n = 4; P less than 0.01), and TCA (2.57 +/- 0.79%; n = 6; P less than 0.01). In separate experiments, bile was collected from the common bile duct and from the left hepatic duct. UDCA recovered from the left hepatic duct was found in the conjugated form, indicating that, after absorption in the common bile duct, it had been conjugated by the hepatocyte and secreted into bile. After retrograde intrabiliary injections of UDCA and CA, the cumulative percentages of recovered radioactivity were not significantly different (84.50 +/- 2.65 and 87.33 +/- 1.80%, respectively); however, peak recovery of UDCA was significantly delayed compared with that of CA. Moreover, UDCA was recovered mostly in the conjugated form, while CA was recovered mostly in the unconjugated form. These results suggest that, in the rat, UDCA is significantly more absorbed by the biliary tree than CA, TUDCA, and TCA. They support the hypothesis that UDCA undergoes a cholehepatic circulation.
Electrolyte transport in rabbit cecum. I. Effect of RDEC-1 infection
Authors: Tai Y. H. , Gage T. P. , McQueen C. , Formal S. B. , Boedeker E. C.
Published: December 2017

To investigate the characteristics of intestinal ion and fluid secretion induced by the adherent, effacing enteropathogenic Escherichia coli strain RDEC-1, we infected weanling rabbits with 10(7)-10(8) RDEC-1 organisms and then studied cecal ion transport under short-circuit conditions in Ussing chambers. Results in tissues with confluent adherent organisms were compared with those in uninfected ceca and in ceca stimulated with dibutyryl adenosine 3',5'-cyclic monophosphate (DBcAMP). The short-circuited cecum normally absorbed Na and Cl, secreted bicarbonate (as represented by the residual ion flux), and displayed a high rate of nondiffusional Na and Cl transport. RDEC-1 infection did not alter the short-circuit current (Isc), but it increased the conductance (Gt), decreased the potential difference (PD), abolished net Na absorption, and reversed Cl absorption to secretion. The changes in Na and Cl net fluxes may be explained by inhibition of a Na-Cl linked absorptive process. In contrast, DBcAMP significantly increased the Isc, PD, and Gt, decreased net Na flux, and abolished net Cl absorption by stimulating electrogenic Cl secretion. These results suggest that RDEC-1-induced changes in cecal ion transport are not mediated by cAMP. The reduction in Na-Cl linked absorption is consistent with anatomic changes in the apical surfaces of absorptive epithelial characteristic of effacing enteroadherence, whereas the increased conductance is consistent with tight junction disruption seen with RDEC-1 infection.
Beta-adrenergic and prostanoid inhibition of canine fundic mucosal mast cells
Authors: Soll A. H. , Toomey M.
Published: December 2017

We examined regulation of histamine release from canine hepatic and fundic mucosal mast cells in short-term culture. We found that beta- but not alpha-adrenergic agonists markedly inhibited concanavalin A (ConA)-stimulated histamine release. Inhibition by epinephrine was reversed by the beta-antagonist propranolol, but not by the alpha-adrenergic antagonists phentolamine or yohimbine. The beta 2-selective antagonist ICI 115881 reversed the effects of epinephrine, whereas the beta 1-antagonists practolol and betaxolol had little effect. Prostaglandin E2 (PGE2), but not its analogue enprostil, inhibited ConA-stimulated histamine release. This difference may relate to the ability of PGE2, but not enprostil, to stimulate adenosine 3',5'-cyclic monophosphate (cAMP) production. Forskolin, cAMP analogues, and the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine also effectively inhibited ConA-stimulated histamine release. Neither adrenergic agonists nor PGE2 inhibited histamine release stimulated by the combination of phorbol 12-myristate-13-acetate plus the calcium ionophore A23187. These data suggest that inhibition was mediated via cAMP-dependent mechanisms and was exerted on primary cell activation, rather than on postreceptor activating events.
Pancreatic digestive enzyme gene expression: effects of CCK and soybean trypsin inhibitor
Authors: Rosewicz S. , Lewis L. D. , Wang X. Y. , Liddle R. A. , Logsdon C. D.
Published: December 2017

Regulation of pancreatic gene expression by cholecystokinin (CCK) was examined in the rat using cloned cDNA probes to quantify changes in specific mRNAs (amylase, trypsinogen I, chymotrypsinogen B, and ribonuclease). Rats were administered intraduodenally an elemental liquid diet. Plasma CCK levels were raised to levels comparable to physiological postprandial levels either by intraduodenal perfusion with soybean trypsin inhibitor (SBTI) (6.9 +/- 1.0 pM, n = 8) or by continuous intravenous infusion with cholecystokinin octapeptide (CCK-8, 6.0 +/- 0.9 pM, n = 6). SBTI infusion resulted in fivefold increases in trypsinogen I and chymotrypsinogen B mRNA levels after 48 h. In contrast SBTI infusion had no effect on amylase mRNA levels and led to a decrease in ribonuclease mRNA levels to approximately 50% of control after 48 h. Intravenous infusion with CCK-8 for 24 h resulted in plasma levels of CCK comparable to those obtained with SBTI and had similar effects on digestive enzyme mRNA levels. These data suggested that SBTI acted via its ability to raise plasma CCK levels. To further test the specificity of these effects, animals were infused intraduodenally with the specific CCK receptor antagonist L364,718. Although the antagonist itself had no effect on digestive enzyme mRNA levels, antagonist treatment totally abolished the effects of both CCK infusion and SBTI treatment. These data therefore indicate that CCK regulates digestive enzyme gene expression at plasma concentrations comparable to physiological postprandial levels. Furthermore, the ability of SBTI infusion to increase plasma CCK accounts for its effects on pancreatic digestive enzyme mRNA levels.
Ca2+-dependent and -independent secretagogue action on gastric mucus secretion in rabbit mucosal explants
Authors: Seidler U. , Sewing K. F.
Published: December 2017

The secretion of high-molecular weight glycoprotein was studied in rabbit antral and fundic explants in response to acetylcholine (ACh), the calcium ionophore A23187, the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA), forskolin, histamine, pentagastrin, and prostaglandin E2 (PGE2). Glycoprotein secretion was measured in pulse-chase experiments by incorporation of [14C]N-acetyl-D-glucosamine into explants and quantification of the secreted high-molecular weight-labeled glycoprotein. All tested agents except histamine and pentagastrin stimulated glycoprotein secretion in a concentration-dependent manner. The response to A23187 was abolished by removal of extracellular Ca2+ and greatly reduced by the calmodulin antagonist N-(6-amino-hexyl)-l-naphthalenesulfonamide (W7). The response to ACh was abolished by equimolar concentrations of atropine and by depletion of intracellular Ca2+ stores, an effect which was reversible on addition of Ca2+, and reduced by W7. The response to forskolin and PGE2 was not significantly affected by either extracellular or intracellular Ca2+ depletion. The combination of ACh with forskolin and A23187 with TPA had a synergistic effect on secretion. The absolute dependence of cholinergic stimulation on the presence of intracellular Ca2+ and the Ca2+-independent stimulatory effect of forskolin and PGE2 suggest that gastric mucus secretion can be elicited by at least two distinct pathways.
Calcium sources utilized by cholecystokinin and acetylcholine in the cat gallbladder muscle
Authors: Lee K. Y. , Biancani P. , Behar J.
Published: December 2017

The calcium sources responsible for gallbladder contraction in response to cholecystokinin (CCK) and acetylcholine were studied in vitro in the cat. Sudden replacement of normal physiological salt solution (PSS) with calcium-free PSS blocked the contraction induced by KCl (60 mM) but did not affect the response to CCK (10(-7) M) or acetylcholine (3 x 10(-3) M). Thirty-minute incubation in PSS in which strontium (2.5 mM) was substituted for calcium blocked completely CCK (10(-10) - 10(-6) M)-induced contraction without impairing the response to acetylcholine (10(-7) - 10(-3) M) or KCl (20-80 mM). The contraction induced by acetylcholine (10(-7) - 10(-3) M) was partially blocked by hydroxyverapamil (D-600) (10(-5) M) in normal PSS (Ca 2.5 mm) and was completely blocked by D-600 in strontium (2.5 mm)-containing solution. It is concluded that CCK contracts the gallbladder muscle by mobilizing calcium from intracellular stores, whereas acetylcholine can utilize calcium both from intracellular or extracellular sources.
Voltage-driven, taurocholate-dependent secretion in isolated hepatocyte couplets
Authors: Weinman S. A. , Graf J. , Boyer J. L.
Published: December 2017

Bile formation by the liver is largely dependent on the transport of bile acids by hepatocytes. This process is thought to result from Na-coupled uptake of bile acids into the cell and voltage-dependent, carrier-mediated transport from cell to canaliculus. However, the dependence of bile secretion on membrane potential has not yet been observed. In this study, the effect of changes in membrane potential differences on bile secretion was tested by impaling rat hepatocyte couplets with microelectrodes, changing membrane potential by intracellular current injection, and measuring fluid secretion by optically determining canalicular size. In the presence of 50 microM taurocholate, membrane potential was -33.3 +/- 5.8 mV and canalicular area increased by 6 +/- 6%/min, corresponding to a fluid secretion rate of 2-4 fl/min. In contrast, when intracellular voltage was suddenly changed to -109.9 +/- 15.0 mV, the canalicular area increased by 20 +/- 4%/min, corresponding to a secretion rate of 19 fl/min. When these experiments were repeated in the absence of taurocholate, the negative clamp had no effect on canalicular size. Taurocholate itself did not alter membrane potential. These findings support the hypothesis that canalicular bile secretion depends on a process equivalent to electrodiffusion. We therefore conclude that membrane voltage is a driving force for taurocholate-dependent fluid secretion by the liver.
Cholecystokinin and gastrin peptides stimulate ODC activity in a rat pancreatic cell line
Authors: Scemama J. L. , De Vries L. , Pradayrol L. , Seva C. , Tronchere H. , Vaysse N.
Published: December 2017

Recent studies have demonstrated that cholecystokinin (CCK) receptors are heterologous in peripheral tissues and in the central nervous system and that CCK-gastrin (CCK-G) peptides are potent trophic factors for the gastrointestinal tract. In the present study we used 125I-labeled gastrin and 125I-labeled CCK to demonstrate the heterogeneity of CCK receptors on a rat pancreatic acinar cell line (AR4-2J) and analyze the role of these receptors in increasing the activity of ornithine decarboxylase. Pharmacological analysis of radioligand binding fit well with the presence of two different receptors: 1) a CCK-selective receptor having the characteristics of the CCK receptor present on normal pancreatic cells and 2) a high-affinity, low-selectivity CCK-G binding site that interacts with all CCK-G peptides sulfated and nonsulfated. CCK-G peptides stimulate ornithine decarboxylase activity with the following order of potencies (EC50): G-(2-17)-ds (0.1 nM) greater than or equal to CCK-9 (0.25 nM) greater than or equal to pentagastrin (0.4 nM) greater than CCK-4 (6 nM). This stimulation was not inhibited by CCK antagonist (asperlicin) at a concentration range that blocks the CCK receptor but does not compete with 125I-labeled gastrin binding to the CCK-G receptor. These results, obtained with CCK-G agonists and antagonists, demonstrate that ornithine decarboxylase stimulation in these cells is mediated via the CCK-G receptor.
Mechanics and neuropeptide responses of feline pylorus and gastric muscle in vitro
Authors: Merlo A. , Cohen S.
Published: December 2017

Mechanical properties and neuropeptide responses were compared for feline pyloric and gastric muscle under isometric conditions in vitro. Total tension in antral circular muscle (0.699 +/- 0.003 kg/cm2) was less than in corpus circular (1.597 +/- 0.007 kg/cm2) or longitudinal muscle from the lesser and greater curvatures (1.256 +/- 0.009 and 1.253 +/- 0.007 kg/cm2, n greater than or equal to 55, P less than 0.05). The components of tension at optimal length were similar for all gastric muscles (P greater than 0.1). The pylorus maintained less total tension (0.335 +/- 0.003 kg/cm2) and a greater component of resting tension (75.6%) than gastric muscle (P less than 0.01). Substance P, cholecystokinin-8 (CCK-8), and neurotensin varied in potency and efficacy in circular muscle of the antrum, corpus, and inferior portion of the pyloric ring. Longitudinal muscle and the superior portion of pylorus responded poorly if at all to neuropeptides. Substance P- but not CCK-8- or neurotensin-induced contractions of gastric muscle were reduced by tetrodotoxin (TTX) and atropine (P less than 0.05). Substance P-induced pyloric contractions were TTX sensitive (P less than 0.05) but were unaffected by atropine. We concluded that 1) length-tension properties of gastric muscle are similar and distinct from the pylorus and that 2) neuropeptide efficacy varies regionally within the feline stomach and within the pylorus.
Structural analysis of a distinct subtype of CCK receptor on human gastric smooth muscle tumors
Authors: Pearson R. K. , Hadac E. M. , Miller L. J.
Published: December 2017

Human gastric smooth muscle tumors (leiomyosarcomas) have been shown to express cholecystokinin (CCK) binding sites that are functionally similar to physiologically important receptors present on their cells of origin. In this work, we have applied affinity-labeling techniques using 125I-D-Tyr-Gly-[Nle28,31]CCK-(26-33) to attempt to define the ligand-binding subunit of this receptor, and we have used the receptor antagonist L364,718 and deglycosylating enzymes to compare this molecule with well-defined CCK receptors on the classical peripheral targets (pancreas and gallbladder) of this hormone. To validate the use of 125I-D-Tyr-Gly-[Nle28,31]CCK-(26-33) for this tissue, we demonstrated that it bound to leiomyosarcoma membranes in a rapid, reversible, saturable, specific, and high-affinity manner (Kd = 0.8 nM). Although previous affinity labeling of this tissue with a CCK-33-based probe identified multiple bands, only one of those candidate proteins was predominantly labeled in the present work (Mr 100,000) by using a probe that is cross-linked through a site in greater proximity to the receptor-binding domain. Labeling was inhibited in a concentration-dependent manner by CCK-8 but not by structurally unrelated ligands. Although endo-beta-N-acetyl-glucosaminidase F digestion shifted this band by Mr 5,000, demonstrating that it was a glycoprotein, the deglycosylation product was very different from other CCK receptors studied. Also, unlike pancreatic and gallbladder CCK receptors, affinity labeling of this receptor was not affected by L364,718. These observations confirm that the gastric smooth muscle tumor CCK receptor represents a receptor subtype that is distinct from other peripheral CCK receptors, biochemically as well as functionally.
Pathogenesis of duodenal ulcer in the rat: dissociation of acid load and blood flow
Authors: Scremin O. U. , Leung F. W. , Guth P. H.
Published: December 2017

Duodenal mucosal blood flow (DMBF) and duodenal acid load were studied in nonanesthetized rats. Four groups of animals were injected with an ulcerogenic dose of mepirizole [1-(4-methoxy-6-methyl-2-pyrimidinyl)-3-methyl-5-methoxypyrazole] and were studied at 3, 6, 12, and 24 h after drug administration. Three additional groups were given an injection of the vehicle used to solubilize the drug and were studied 3, 12, and 24 h later. All animals studied 24 h after mepirizole showed ulceration of the proximal duodenum. DMBF in animals that received vehicle averaged 141 +/- 12 ml.100 g-1.min-1. A significant duodenal hyperemia was observed 3 and 6 h after mepirizole (498 +/- 113 and 377 +/- 92 ml.100 g-1.min-1, respectively). A large increase in duodenal acid load was also found at these times (47.6 +/- 2.6 and 46.4 +/- 7.3 mueq/h, respectively). DMBF declined progressively afterwards to reach subnormal levels at 24 h after mepirizole. Acid load, however, remained at a high level throughout the 24 h of observation. In contrast, no significant changes in blood flow were observed in pancreas, jejunum, ileum, or colon. In animals with a duodenal ligature 5 mm distal to the pylorus, a hyperemia was observed in the portion of duodenum in continuity with the stomach. This phenomenon was absent in the duodenum distal to the ligature. It is concluded that the high duodenal acid load observed in the face of decreasing DMBF could explain the occurrence of duodenal damage between 12 and 24 h after mepirizole administration.
Inhibition of stimulated lacrimal secretion by [D-Ala2]Met-enkephalinamide
Authors: Cripps M. M. , Patchen-Moor K.
Published: December 2017

The synthetic enkephalin analogue, [D-Ala2]Met-enkephalinamide (DALA) was used to investigate opioid peptide modulation of lacrimal protein secretion. By use of an in vitro perifusion system, the secretion of peroxidase by rat lacrimal gland fragments was measured during continuous stimulation for up to 60 min. DALA had no effect on unstimulated secretion of peroxidase. However, the addition of DALA to the perifusion medium resulted in a dose-dependent (10 nM-10 microM) inhibition of carbachol-stimulated peroxidase release. The maximum effect of DALA was achieved at a dose of 10 microM, which resulted in a 54% inhibition of carbachol-induced secretion. The opiate antagonist naloxone (10 nM-10 microM) did not alter basal or carbachol-stimulated peroxidase release. The effect on 10 microM carbachol-stimulated secretion by the addition of 3 microM DALA, however, was reversed in a dose-dependent manner by naloxone. The extent of inhibition of vasoactive intestinal peptidergic (VIPergic) stimulation (50 nM VIP) by DALA was similar to the inhibition of cholinergic stimulation of peroxidase release by gland fragments. Neither alpha 1-adrenergic stimulation of secretion nor a synergistic stimulation by VIP and carbachol was inhibited by the enkephalin analogue. We conclude that DALA exerts an inhibitory modulation of cholinergic and VIPergic stimulation of in vitro lacrimal protein secretion and suggest a physiological role for methionine enkephalin as an inhibitory peptide involved in the regulation of lacrimal gland function.
An "epithelial" preparation from the canine gastric mucosa: responses to secretagogues
Authors: Rangachari P. K. , McWade D.
Published: December 2017

Isolated mucosal preparations from the stomach are generally obtained by removing the external muscle layers, leaving intact the muscularis mucosae. By carefully dissecting off the muscularis mucosa, we have obtained "epithelial" preparations from the canine stomach. Such preparations responded to secretagogues, histamine, pentagastrin, and a cholinergic agonist (cis-2-methyl 4-dimethylaminomethyl 1,3-dioxolane methiodide). Epithelial preparations were, in general, more sensitive than mucosal preparations. Of the three secretagogues tested, histamine was the most consistent stimulant, with well-sustained responses being noted. Responses to the other agonists were more variable. Pentagastrin produced brief but explosive increases in acid output.
Active transport of taurine in rabbit jejunal brush-border membrane vesicles
Authors: Miyamoto Y. , Tiruppathi C. , Ganapathy V. , Leibach F. H.
Published: December 2017

The characteristics of taurine uptake in rabbit jejunal brush-border membrane vesicles were investigated. Taurine was transiently accumulated inside the vesicles against a concentration gradient when an inwardly directed NaCl gradient was imposed across the membrane. Uptake of taurine showed an absolute requirement for both Na+ and Cl-. The NaCl gradient-dependent taurine uptake was stimulated by a valinomycin-induced, inside-negative, K+-diffusion potential, suggesting that the uptake process was electrogenic. The uptake system exclusively interacted with beta-amino acids of small size, but had no affinity for alpha-amino acids. Kinetic analysis revealed that the system exhibited high affinity for taurine (Kt = 14.4 +/- 0.5 microM). Taurine uptake was greatly influenced by extravesicular concentrations of Na+ and Cl-. The Cl- stoichiometry was found to be one. In the presence of Cl-, taurine uptake was sigmoidally related to Na+ concentration, and the Na+ stoichiometry was calculated to be three. Thus three Na+ and one Cl- were involved per transport of one taurine molecule. The uptake process was not affected by other transport inhibitors such as amiloride, harmaline, furosemide, and 4,4'-diisothiocyanostilbene-2,2'-disulfonate.
Properties of receptors for gastrin and CCK on gastric smooth muscle cells
Authors: Menozzi D. , Gardner J. D. , Jensen R. T. , Maton P. N.
Published: December 2017

Previous studies have demonstrated that cholecystokinin (CCK), gastrin, and structurally related peptides can interact with various types of receptors that can be distinguished by their relative affinities for agonists and antagonists. In the present study we examined the effect of gastrin, the COOH-terminal octapeptide of CCK (CCK-8), and the tetrapeptide of CCK (CG-4) on contraction of dispersed gastric smooth muscle cells from guinea pig and tested the ability of various CCK receptor antagonists to affect agonist-induced muscle cell contraction. For purposes of comparison we tested the effect of each antagonist on CCK-stimulated amylase secretion by pancreatic acini from guinea pig. On gastric smooth muscle cells, CCK-8, gastrin, and CG-4 were all full agonists. CCK-8 and gastrin were equipotent and CG-4 was 6,000-fold less potent. Each antagonist caused inhibition of CCK-stimulated contraction with relative potencies (IC50): L364,718 (4 microM) = CBZ-CCK-(27-32)-NH2 (3 microM) greater than proglumide analogue 10 (90 microM). Inhibition by each of the antagonists was competitive in nature, specific for CCK peptides, and each had the same IC50 whether contraction was stimulated by CCK-8, gastrin, or CG-4. Relative potencies (IC50) of the three antagonists for inhibiting CCK-stimulated amylase release from pancreatic acini were L364,718 (3 nM) greater than proglumide analogue 10 (200 nM) greater than CBZ-CCK-(27-32)-NH2 (3 microM). These results demonstrate that gastric smooth muscle cells possess receptors that differ from CCK receptors on pancreatic acini in terms of affinities for both agonists and certain antagonists.(ABSTRACT TRUNCATED AT 250 WORDS)
Effects of fish oil on gastric mucosal 6-keto-PGF1 alpha synthesis and ethanol-induced injury
Authors: Faust T. , Redfern J. S. , Lee E. , Feldman M.
Published: December 2017

Fundic mucosal content and synthesis of 6-ketoprostaglandin F1 alpha, the major prostanoid in the rat gastric mucosa, were determined after rats had ingested a diet containing 10% fish oil or 10% corn oil for 4 wk. 6-Ketoprostaglandin F1 alpha content and synthesis in rats fed a fish oil-supplemented diet were reduced significantly compared with rats receiving a corn oil-supplemented diet (P less than 0.05). However, rats receiving 10% fish oil for 8 wk sustained significantly less gastric mucosal injury after intragastric challenge with 15% and then with absolute ethanol than rats receiving 10% corn oil or regular chow for 8 wk (P less than 0.05). Thus fish oil ingestion protected the gastric mucosa even though fish oils reduced mucosal prostaglandin synthesis.
Gastric H+-K+-ATPase in situ: evidence for compartmentalization
Authors: Hersey S. J. , Perez A. , Matheravidathu S. , Sachs G.
Published: December 2017

Gastric glands, isolated from rabbit, were permeabilized with digitonin to permit measurement of H+-K+-adenosinetriphosphatase (ATPase) activity and proton transport in situ. Measurement of proton gradient formation using acridine orange fluorescence showed two phases of ATP-driven proton accumulation; one phase occurs spontaneously in KCl medium and one phase requires the K+ ionophore valinomycin. Valinomycin was found to increase H+-K+-ATPase activity, indicating that the second phase is because of increased proton transport rather than a decrease in proton leak rate. The acid-activated, irreversible inhibitor, omeprazole, was used to selectively eliminate the H+-K+-ATPase molecules associated with the spontaneous component of proton transport. After omeprazole treatment a residual, valinomycin-dependent component of proton transport could be demonstrated. These results are interpreted as evidence for two compartments of H+-K+-ATPase, separated by a barrier that prevents K+ diffusion and pH equilibration. The two compartments may be separated also on the basis of anion selectivity. The spontaneously active compartment was found to be functional with various anions, including sulfate and isethionate, whereas the valinomycin-dependent component is highly selective for chloride. The proportion of H+-K+-ATPase that exists in each compartment was quantitated by measuring the fraction of total ATPase activity that could be inhibited by omeprazole in the absence and presence of valinomycin. For glands that were preconditioned with cimetidine, approximately 30% of the inhibitable enzyme was found associated with the spontaneous compartment, and this fraction increased to approximately 70% with histamine preconditioning.(ABSTRACT TRUNCATED AT 250 WORDS)
TRH-induced vagal stimulation of duodenal HCO-3 mediated by VIP and muscarinic pathways
Authors: Lenz H. J. , Vale W. W. , Rivier J. E.
Published: December 2017

The central nervous system effects of thyrotropin-releasing hormone (TRH) on proximal duodenal bicarbonate secretion were studied in freely moving rats. Cerebroventricular administration of TRH (0.5-5.0 nmol) significantly stimulated basal duodenal bicarbonate secretion, whereas intravenous administration of TRH did not. Ganglionic blockade with chlorisondamine and truncal vagotomy abolished TRH-induced bicarbonate secretion, whereas atropine significantly attenuated the response. The vasoactive intestinal peptide (VIP) receptor antagonist, (4Cl-D-Phe6, Leu17) VIP given intravenously completely prevented the stimulatory effect of central TRH on duodenal bicarbonate secretion. In contrast, hypophysectomy, adrenalectomy, opiate and noradrenergic blockade, or indomethacin did not affect the TRH-induced bicarbonate response. Intravenous administration of VIP and carbachol significantly stimulated bicarbonate outputs, and these responses were blocked by the VIP antagonist and atropine, respectively. These results indicate that TRH may serve as a central nervous system mediator that stimulates duodenal bicarbonate secretion in rats by increasing vagal outflow. Vagal stimulation induced by TRH increases duodenal bicarbonate secretion by the release of VIP and, in part, by activation of a muscarinic pathway but not by pituitary, adrenal, and noradrenergic pathways or endogenous opiates and prostaglandins. The actions of peripheral VIP and carbachol appear to be mediated by specific VIP and muscarinic receptors, respectively.
Intracellular pH dependence of buffer capacity and anion exchange in the parietal cell
Authors: Wenzl E. , Machen T. E.
Published: December 2017

When parietal cells (PC) are stimulated with histamine, the anion exchanger rate increases three to five times to compensate for alkaline loading induced by H+-K+ adenosinetriphosphatase (ATPase) and to provide Cl for acid secretion. It has been hypothesized that this increased activity is caused by the increase in intracellular pH (pHi) that often occurs in stimulated PC (from 7.1 to a maximum of 7.3). The dependence of the anion exchanger on pHi was studied using microspectrofluorimetry of the pH-sensitive dye 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF). N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES)-buffered solutions were used because the anion exchanger can transport OH- (or HCO3) in exchange for Cl- even with [HCO3]o = 200 microM. It was found that when solutions were changed either from NaCl to Cl- free or Cl- free to NaCl, rates of change of pHi (delta pH/delta t) were strongly dependent on pHi: nearly 0 at pHi 6.6 and 1.25 pH/min at pHi 8.0. To convert these pHi changes into anion flux rates, the intrinsic buffer capacity (beta i) was determined over the same pHi range by making small changes of [NH4]o to determine the resulting changes of [NH4]i and pHi (i.e., beta i = delta[NH4]i/delta pHi) in PC that had been pretreated with 1 mM amiloride and 200 microM [H2]4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) [to block Na+-H+ and Cl- -OH-(HCO3-) exchange]. beta i was also strongly dependent on pHi: at pHi 6.5 beta i = 48 mM/pH, and this decreased as pHi increased; at pHi 7.75 beta i = 8 mM/pH. The derived anion fluxes (i.e., JOH = beta i x delta pH/delta t) were roughly linearly related to pHi between 6.6 (JOH near 0) and 8.1 (JOH = 13 mM/min). Between pHi 7.1 and 7.3, the range normally observed during stimulation of PC, rates of anion exchange increased by 75%. This pHi sensitivity cannot explain the 300-500% increase in anion exchanger activity observed during secretagogue stimulation of PC.
Rapid frequency rhythmic postprandial motility in the canine ileum
Authors: Fich A. , Phillips S. F. , Hanson R. B. , Zinsmeister A. R.
Published: December 2017

We report here a novel motor phenomenon that we recorded from the canine terminal ileum in the postprandial period. In chronic models that allowed us to monitor myoelectrical activity and intraluminal pressure from the jejunum and distal ileum, we regularly saw in the ileum, but not in the jejunum, a rhythmic sequence of intraluminal pressure waves at a frequency of 19-24 cycles/min. This unusual motor pattern was rarely seen in the first 2 h after food and was essentially absent during fasting; it appeared reproducibly 1-4 h after food, at the time when chyme reached the ileum. The phenomenon was accompanied by spike bursts that were usually at the same rapid, rhythmic frequency, but the rate of the ileal slow wave persisted at the preprandial level (13-15/min). These findings further exemplify differences in the regulation of the motility between jejunum and ileum; moreover, the phenomenon highlights the capacity of the distal small intestine to response specifically to the nature of its luminal contents. This reaction of the ileum to the arrival of dietary residues is deserving of further study in the evaluation of the small bowel's response to a meal.
Cobalamin release from intrinsic factor and transfer to transcobalamin II within the rat enterocyte
Authors: Ramasamy M. , Alpers D. H. , Tiruppathi C. , Seetharam B.
Published: December 2017

To ascertain the mechanism of release of cobalamin (Cbl) from intrinsic factor (IF) and subsequent formation of transcobalamin II (TC-II)-Cbl complex, we studied the intracellular distribution of 57Co-labeled Cbl after its uptake in suckling and adult rats. The amount of Cbl bound to IF, to the IF-Cbl receptor via IF, and to TC-II was determined by immunoprecipitation with monospecific antisera raised to these proteins. IF-Cbl receptor activity was found to be very low in suckling rats up to 12 days after birth. Oral administration of leupeptin in amounts known to alter protein turnover had no effect on the release of Cbl from IF nor did it inhibit the formation of the TC-II-Cbl complex in either adult or suckling animals. However, oral administration of chloroquine resulted in a transient increase in the intestinal concentration of Cbl in both adult and suckling rats and in total inhibition of Cbl released from IF in adults rats. Chloroquine prevented completely the transfer of Cbl to TC-II in adult rats and inhibited the transfer by 50% in suckling rats. These data demonstrate that in adult mucosa utilizing receptor-mediated endocytosis, Cbl is transferred from IF to TC-II. This transfer does not require the IF-Cbl receptor, as it occurs in suckling rats. Finally, transfer of Cbl to TC-II is decreased by a drug that alters vesicular pH. Because Cbl can be released at acid pH from IF, it is proposed that release of Cbl from IF and its transfer to TC-II occurs in an acidic vesicle.
Effects of quinacrine on calcium active transport by rat intestinal epithelium
Authors: Favus M. J. , Tembe V. , Tanklefsky M. D. , Ambrosic K. A. , Nellans H. N.
Published: December 2017

To determine the possible role of acidic lysosomal vesicles in the transcellular transport of Ca, bidirectional Ca fluxes were measured across intestinal segments in vitro in the absence of electrochemical gradients. Mucosal addition of the weak base quinacrine (0.2 mM) caused a 67% decline in the mucosal-to-serosal Ca flux (Jm----s) across duodenum (175 +/- 34 vs. 58 +/- 9 nmol.cm-2.h-1, P less than 0.007) and reduced cecal Ca Jm----s (177 +/- 15 vs. 45 +/- 4, P less than 0.0001). Higher concentrations of up to 2.0 mM caused no further decline in cecal Ca Jm----s. Inhibition of cecal Ca Jm----s by mucosal chloroquine (0.1 mM) or ammonium chloride (10 mM) varied from 37 to 50%. Addition in vitro of quinacrine to enterocyte basolateral membrane vesicles failed to inhibit ATP-dependent Ca uptake. The present studies demonstrate that agents that collapse lysosomal pH gradients inhibit transcellular Ca transport. These observations are consistent with the hypothesis that Ca destined for transcellular transport is functionally associated with acidic lysosomes and that these organelles play an important role in transepithelial Ca translocation.
Accumulation of weak base in gastric mucosa provides evidence for an acidic storage compartment
Authors: Ekblad E. B. , Warnock D. G. , Licko V.
Published: December 2017

Uptake and release of acridine orange (AO), a fluorescent weak base that accumulates in acidic spaces, were studied in perfused frog gastric mucosa. Tissue was mounted between two flow-through chambers and loaded with AO on the mucosal side. AO washout and acid secretion rate were monitored simultaneously by a flow-through fluorescence detector and a pH-stat, respectively. Data were displayed on a computer screen, stored, and analyzed. AO, in concentrations as high as 0.02 mM, does not affect the acid secretion rate. Nonlinear least-squares analysis of AO washout curves resolved two exponential components: a faster component associated mainly with AO washout from the chamber and a slower component reflecting primarily AO washout from the tissue. The slower exponential declines more slowly at higher concentrations and/or longer duration of AO loading, whereas the faster exponential is unaffected. AO washout is unaffected by the level of the steady-state acid secretion rate. Nitrite inhibits the acid secretion rate but does not affect the AO washout. When nitrite is removed, acid secretion rate and fluorescence (AO concentration in the mucosal medium) increase simultaneously and transiently. The net amount of AO released from the tissue is proportional to the net amount of acid released. Stimulation by secretagogue in basally secreting tissue causes synchronous transient increases in acid secretion rate and fluorescence. We conclude that accumulation of AO provides evidence for the existence of an intracellular storage pool of free protons within the transporting epithelium.
Effects of platelet-activating factor on ion transport in isolated rat jejunum
Authors: Hanglow A. C. , Bienenstock J. , Perdue M. H.
Published: December 2017

In isolated normal rat jejunum, platelet-activating factor (PAF) induced a dose-dependent increase in short-circuit current (Isc) that was reduced in chloride-free buffer and inhibited by the Cl- channel blocker, diphenylamine-2-carboxylate. An immediate rise in Isc (early phase) occurred that fell to a new elevated base line by 15 min (late phase). These responses to PAF occurred only when experiments were conducted at or before approximately 9 A.M. Early phase responses were blocked by the specific PAF antagonists, BN52021 and WEB2086, and were inhibited by the neurotoxin, tetrodotoxin. Early and late phases were also reduced by cyclooxygenase inhibitors and by doxantrazole, a mast cell stabilizing drug. However, histamine and serotonin antagonists were ineffective. We conclude that PAF causes changes in ion transport that include Cl- secretion and acts on the epithelium possibly via an intermediate cell and enteric nerves. In addition, known PAF receptors are involved in one component of the response that appears to follow a circadian rhythm.