bluuebunny/crossref_metadata_2025 huggingface dataset:
Chloride-mediated junction potentials in circular muscle of the guinea pig ileum
Authors: Crist J. R. , He X. D. , Goyal R. K.
Published: December 2017

Junction potentials were recorded from circular muscle cells of the guinea pig ileum at various sites oral and anal to a transmural stimulus in the presence of atropine, apamin, and substance P antagonism (desensitization) at 30 degrees C. A short train of pulses produced an inhibitory junction potential (slow IJP), which preceded an excitatory junction potential (slow EJP). The slow IJP was observed up to 56.4 +/- 2.9 mm oral and 65.4 +/- 2.2 mm anal to the stimulus. The slow EJP was observed up to 50.4 +/- 1.9 mm oral and 58.3 +/- 2.1 mm anal to the stimulus. Hexamethonium (400 microM) decreased the amplitudes of the slow IJP and slow EJP at all sites. After hexamethonium, the slow IJP was observed up to 37.3 +/- 2.3 mm oral and 39.8 +/- 2.1 mm anal to the stimulus and the slow EJP was 44.2 +/- 2.5 mm oral and 43.3 +/- 2.6 mm anal to the stimulus. The slow IJP and slow EJP were associated with an increase and decrease in membrane resistance, respectively. Conditioning depolarizations of the circular muscle cells reduced the amplitudes of the slow IJP and slow EJP. Both were abolished at a membrane potential of approximately -25 mV. Conditioning hyperpolarizations increased the amplitude of both the slow IJP and slow EJP. Ionic substitution experiments with low external chloride solution (12.4 mM) resulted in an immediate increase in slow IJP and slow EJP amplitudes, whereas more prolonged perfusion resulted in a significant decrease in slow IJP and slow EJP amplitudes. 4,4'-Diisothiocyanostilbene-2,2'-disulfonic acid (400 microM) resulted in decreases in slow IJP and slow EJP amplitudes. These results suggest that the slow IJP and slow EJP are due to a decrease and increase in membrane chloride conductance, respectively. The noncholinergic neural pathways responsible for the slow IJP and slow EJP extend approximately 40 mm orally and anally along the longitudinal axis of the guinea pig ileum.
Mechanism of glycogenolytic action of histamine in rat hepatocytes
Authors: Mine T. , Kojima I. , Ogata E.
Published: December 2017

The mechanism by which histamine induces glycogenolysis was investigated in rat hepatocytes. Histamine induced stimulation of glucose output in hepatocytes in a dose-dependent manner. The maximal effect of the glycogenolytic action of histamine, which was approximately 60% of the maximal glucagon action, was obtained at 10(-6) M. These effects were inhibited by H1 receptor antagonists triprolidine hydrochloride and tripelennamine but not by a H2 receptor antagonist cimetidine. Histamine also increased the activity of phosphorylase a. When 10(-6) M histamine and 5 x 10(-9) M glucagon were added simultaneously, the actions of these two agents were additive. In contrast, there was no additivity when 10(-6) M histamine and 10(-8) M angiotensin II were added. Histamine did not increase adenosine 3',5'-cyclic monophosphate at any doses tested but induced a rapid increase in the cytoplasmic free calcium concentration ([Ca2+]c). Histamine increased [Ca2+]c even in the presence of 1 microM extracellular calcium, an observation suggesting that histamine caused calcium release from an intracellular calcium pool(s). When [3H]inositol-labeled hepatocytes were incubated with histamine, radioactivity in the D-myo-inositol trisphosphate fraction was rapidly increased. These results indicate that histamine acts on rat hepatocytes mainly via H1 receptors and stimulates glycogenolysis by activating the calcium messenger system.
Protection against ethanol injury in the canine stomach: role of mucosal glutathione
Authors: Victor B. E. , Schmidt K. L. , Smith G. S. , Miller T. A.
Published: December 2017

The present study determined the role that mucosal glutathione (GSH) levels play in mediating the protective effects of a prostaglandin and a mild irritant against alcohol-induced gastric injury. An in vivo canine chambered stomach preparation was used in which the exteriorized mucosa was partitioned into two equal halves, one serving as control. Animals (5-8/group) received a subcutaneous injection of either normal saline (NS) or the GSH depletor N-ethylmaleimide (NEM; 50 mg/kg) and then were assigned to one of a variety of groups based on the perfusate used to bathe the experimental side of the chamber; NS bathed the control mucosa. At completion of the studies, mucosa from each side of the chamber was assayed for total GSH (mumol/g wet wt) and evaluated for microscopic damage. Both 16,16-dimethyl prostaglandin E2 (PGE2) (1 microgram/ml) and the mild irritant 8% ethanol, when topically applied to the gastric epithelium, increased mucosal GSH levels by approximately 20% compared with control values, and elicited no deleterious effects to the mucosa. Treatment of animals with NEM prevented these GSH effects by PGE2 and 8% ethanol without damaging the mucosa. Application of 40% ethanol to the mucosa markedly reduced levels of GSH and caused significant injury to the mucosal surface, much of it extending to the level of the gastric glands. When mucosa was pretreated with PGE2 or 8% ethanol before 40% ethanol exposure, deep gastric gland injury was virtually abolished. In animals receiving NEM, the protective effects of these agents against injury by 40% ethanol were prevented. Perturbations in tissue levels of GSH under these various experimental conditions failed to correlate histologically with the status of gastric mucosal integrity.
Histamine: mercurial messenger in the gut
Authors: Rangachari P. K.
Published: December 2017

This review considers the possibility that histamine functions as a cellular messenger in the gastrointestinal tract. Any biological messenger must be produced, received, and responded to, and must have its actions quickly terminated. Histamine is no exception. Histamine synthesis from L-histidine occurs in enterochromaffin-like cells, mucosal mast cells, and nerves. Histamine release occurs through both antibody-dependent and antibody-independent mechanisms. Released histamine interacts with a variety of cellular targets (epithelial cells, smooth muscle cells, endothelial cells, neurons, and a variety of immunocompetent cells). Occupation of H1, H2, and H3 receptors, defined by pharmacological agents, is transduced by different intracellular messengers (Ca2+, cyclic nucleotides) into diverse effects such as secretion, contraction, or modulation of other secretagogues. The responses to histamine are terminated by at least three different mechanisms: metabolic transformation by the actions of methyltransferase and diamine oxidase, desensitization at the receptor level, and cellular uptake. In addition to its well-documented effects as a mediator of inflammatory processes, histamine may also function as a neuro- and immunoregulator. While a significant pathophysiological role for histamine has been realized since the earliest description of its effects, the availability of newer pharmacological agents has permitted a finer dissection of its "physiological" effects and raised the possibility of multiple roles for histamine.
Effects of f-Met-Leu-Phe-induced inflammation on intestinal lymph flow and lymphatic pump behavior
Authors: Benoit J. N. , Zawieja D. C.
Published: December 2017

Previous studies in the literature indicate that intraenteric placement of the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (f-Met-Leu-Phe) evokes an intestinal inflammatory response characterized by an accumulation of interstitial fluid and increased lymph flow. Furthermore, it is known that movement of lymph away from the intestine is dependent on the rhythmic pumping of lymph by collecting lymphatics in the mesentery. The purpose of the present study was to determine whether the f-Met-Leu-Phe-induced increase in lymph formation is countered by an increase in lymphatic pump efficiency. Male Sprague-Dawley rats were anesthetized, and a segment of ileum with adjacent mesentery was exteriorized. The mesentery was positioned over an optical window, and a 100-microns collecting lymphatic was selected for study. The preparation was transferred to a video microscope, and the activity of the lymphatic pump was monitored under control conditions and during intraluminal infusion of 1 microM f-Met-Leu-Phe. Lymph propulsion by the lymphatic pump was calculated from the product of stroke volume and contraction frequency. In one group of animals, total lymph flow was determined by cannulating the lymphatic draining the ileal segment. Total lymph flow increased following f-Met-Leu-Phe placement in the intestine. The increased lymph flow was paralleled by a rise in lymphatic pumping. The rise in lymph propulsion by the lymphatic pump resulted exclusively from an increased stroke volume, inasmuch as contraction frequency did not change. The results of the present study suggest that activation of the lymphatic pump during acute inflammation may be important in preventing interstitial edema.
Nonadrenergic, noncholinergic inhibition and rebound excitation in canine colon depend on nitric oxide
Authors: Ward S. M. , Dalziel H. H. , Thornbury K. D. , Westfall D. P. , Sanders K. M.
Published: December 2017

Nonadrenergic, noncholinergic (NANC) nerves regulate slow waves along the submucosal border of the canine proximal colon. Experiments were performed to determine the role of nitric oxide (NO) in NANC responses. NANC responses are characterized by hyperpolarization and reduction in slow-wave amplitude and duration during the period of stimulation. This is followed by a "rebound" excitation (increase in amplitude and duration) of the slow wave immediately after the stimulus. These responses were blocked by L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthase and by tetrodotoxin (TTX). Exogenous NO mimicked NANC responses, including the poststimulus rebound excitation. Responses to NO were unaffected by L-NAME or TTX. Responses to NANC nerve stimulation and NO were blocked by oxyhemoglobin but not by methemoglobin. Rebound excitation was reduced by pretreatment with indomethacin, suggesting that an eicosanoid may mediate this phase of NANC responses. Taken together, these data suggest that NO mediates NANC nerve responses in the proximal colon. NO appears to directly cause the inhibitory response, but the rebound response may depend on release of an eicosanoid.
Neurotensin and neuromedin N stimulate mucin output from human goblet cells (Cl.16E) via neurotensin receptors
Authors: Augeron C. , Voisin T. , Maoret J. J. , Berthon B. , Laburthe M. , Laboisse C. L.
Published: December 2017

The stably differentiated human intestinal goblet cell line Cl.16E was used to study the effects of two structurally related regulatory peptides, neurotensin (NT) and neuromedin N (NN), on mucus secretion. NT and NN stimulated rapid release of mucins from filter-grown Cl.16E cells, this effect being dose related with a mean effective dose of 36 nM for NT and 422 nM for NN. The order of potency of NT, three NT fragments corresponding to the NH2-terminal part [NT-(1-11)] or to the COOH-terminal part [NT-(8-13) and NT-(9-13)], and NN in promoting mucin release and in inhibiting 125I-labeled NT binding to Cl.16E cell membranes was identical with NT greater than or equal to NT-(8-13) greater than NN greater than NT-(9-13) much greater than NT-(1-11) supporting the hypothesis that NT and NN stimulate mucin output through interaction with a common NT-preferring receptor. Scatchard analysis of equilibrium binding data showed one population of NT binding sites in Cl.16E cell membranes with the following characteristics: binding capacity (Bmax) was 141 fmol/mg of protein and dissociation constant (Kd) was 1.00 nM.(ABSTRACT TRUNCATED AT 250 WORDS)
Action of alpha 2A-adrenergic receptors in circular smooth muscle of canine proximal colon
Authors: Zhang L. , Keef K. D. , Bradley M. E. , Buxton I. L.
Published: December 2017

Addition of the alpha 2-adrenergic receptor agonist clonidine (1 microM) to tetrodotoxin-treated strips of canine colonic circular smooth muscle resulted in a significant increase in contractile force that was blocked by addition of the alpha 2-antagonist yohimbine (0.1 microM). The alpha 2-receptor antagonist radioligand [3H]rauwolsine bound rapidly and reversibly to a single class of saturable sites (Bmax, 38.4 +/- 6.2 fmol/mg protein) in colonic circular smooth muscle membranes with an affinity (KD = 5.1 +/- 0.9 nM) characteristic of alpha 2-adrenergic receptors in smooth muscle. Studies in cells freshly isolated from circular muscle of canine proximal colon verified the smooth muscle origin of these receptors. Rank order of potency of alpha 2-adrenergic receptor antagonists in competition for [3H]rauwolsine binding was yohimbine greater than oxymetazoline much greater than prazosin. Affinity of alpha 2-receptors for yohimbine was indistinguishable from that of its optical isomer, rauwolsine, in both competition studies (KI = 3.4 nM) and in saturation-binding experiments employing [3H]yohimbine directly (KD = 4.2 nM). The alpha-receptor agonist epinephrine, in competition studies employing [3H]rauwolsine, revealed high-affinity binding sites that were converted to low-affinity binding sites for agonist by addition of 100 microM GTP gamma S. Addition of the alpha 2 more-selective agonist clonidine (100 microM) resulted in inhibition of adenylate cyclase activity that was abolished by pretreatment of tissue strips with pertussis toxin suggesting coupling of the alpha 2-receptor in colon to adenylate cyclase via the GTP-binding protein Gi. Our data demonstrate a physiological role for adenylate cyclase-coupled receptors of the alpha 2A-subtype in canine colon circular smooth muscle.(ABSTRACT TRUNCATED AT 250 WORDS)
Adenosine A1 receptors mediate inhibition of tachykinin release from perifused enteric nerve endings
Authors: Broad R. M. , McDonald T. J. , Brodin E. , Cook M. A.
Published: December 2017

A perifused preparation of guinea pig myenteric nerve varicosities (synaptosomes) was used to determine the characteristics of evoked tachykinin release and the inhibition of such release by adenosine analogues. Release of substance P-like immunoreactivity (SP-LI) and neurokinin A-like immunoreactivity (NKA-LI) was evoked by elevated extracellular [K+] in a reversible and repeatable manner. This release was completely abolished in the absence of extracellular Ca2+. Perifusion in the presence of 5'-N-ethylcarboxamidoadenosine (NECA), a nonselective A1/A2 adenosine receptor agonist, decreased K(+)-evoked release of SP-LI and NKA-LI compared with that in the absence of the nucleoside. Similar decrements in peptide release were obtained with N6-cyclopentyl adenosine (CPA), a selective A1 agonist, and 2-[p-(2-carboxyethyl)]phenethylamino-5'-N-ethyl-carboxamidoadenosi ne (CGS 21680), a selective A2 agonist. Response to all nucleosides was graded. Potency order of adenosine analogues was CPA greater than NECA much greater than CGS 21680. Inhibition due to the nucleosides was diminished in the presence of the highly selective A1-receptor antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) while perifusion in the presence of DPCPX alone did not alter evoked release of either peptide. These findings provide direct measurements of inhibitory effects of adenine nucleosides on the release, from enteric nerve endings, of endogenous neuromediators SP and NKA. The findings also directly demonstrate the presence of functional adenosine receptors of the A1 subtype on enteric nerve endings coupled negatively to release of tachykinins. The presence of A2 receptors on enteric nerve endings is neither supported nor excluded.
Pertussis toxin-sensitive and pertussis toxin-insensitive inhibition of parietal cell response to GLP-1 and histamine
Authors: Schepp W. , Schmidtler J. , Dehne K. , Schusdziarra V. , Classen M.
Published: December 2017

We have recently shown that in rat parietal cells the glucagon-like peptide 1 (GLP-1) variants 7-36 amide, 1-37, and 1-36 amide stimulate H+ production as indirectly measured by [14C]aminopyrine (AP) accumulation. This response to the GLP-1 peptides was intracellularly mediated by activation of adenylate cyclase and by adenosine 3',5'-cyclic monophosphate (cAMP) as second messenger. In the present study, we compared prostaglandin (PG)E2, somatostatin, and the protein kinase A antagonist Rp-adenosine-3',5'-monophosphorothioate (Rp-cAMPS) with respect to their inhibitory effects on parietal cell function induced by GLP-1 or histamine. PGE2 and somatostatin noncompetitively inhibited AP accumulation and cAMP production in response to the GLP-1 variants and histamine (IC50): [mean inhibitory concn 5 x 10(-9) M PGE2; 3 x 10(-7) somatostatin]; at their maximal concentrations PGE2 (10(-7) M) and somatostatin (10(-6) M) caused 85 and 65% inhibition, respectively. Treatment with pertussis toxin (PT; 250 ng/ml; 4 h) reversed the inhibitory effect of PGE2 and somatostatin on AP accumulation and cAMP production. At 2 x 10(-3) M (IC50: 3 x 10(-4) M) Rp-cAMPS completely inhibited AP accumulation induced by the GLP-1 variants or histamine; this effect was insensitive to PT. Specificity of Rp-cAMPs as protein kinase A inhibitor is suggested by inhibition of AP accumulation in response to Sp-cAMPS and N6,O2-dibutyryl adenosine 3',5'-cyclic phosphate sodium, and forskolin, activators of protein kinase A and adenylate cyclase, respectively. We conclude that the parietal cell responses to GLP-1 and histamine are inhibited by identical mechanisms. Effects of PGE2 and somatostatin are mediated by the PT-sensitive subunit of adenylate cyclase Gi, whereas Rp-cAMPS interferes with cAMP-dependent mechanisms that are insensitive to PT.
Characterization of high-conductance anion channels in rat bile duct epithelial cells
Authors: McGill J. M. , Basavappa S. , Fitz J. G.
Published: December 2017

We have utilized patch clamp recording techniques to identify a high-conductance anion channel in the plasma membrane of rat bile duct epithelial cells. Cells were isolated from the intrahepatic bile duct 2-6 wk after bile duct ligation. Channels were present in 27% (28/102) of excised patches, and, with 150 mM Cl- in bath and pipette solutions, the slope conductance of the fully open level was approximately 364 +/- 18 pS (n = 8) with current reversal = 0 +/- 1 mV. Channel characteristics were not affected by substitution of K+ for Na+ in the pipette solution; but substitution of HCO3-, gluconate, or increased NaCl caused a shift in the reversal potential toward the new equilibrium potential for Cl-. The permeability ratios were PHCO3-/PCl- = 0.51 +/- 0.03 (n = 5), Pgluconate/PCl- = 0.12 +/- 0.04 (n = 7), and PNa+/PCl- = 0.11 +/- 0.02 (n = 3). Current transitions to a subconductance level at 72% of the fully open level were present in most studies. Channel open probability was greatest near 0 mV and decreased rapidly outside of -20 to +20 mV because of voltage-dependent channel closure. The time course for current relaxation of summed single channel currents could be described by a single exponential with more rapid channel closure as the magnitude of the voltage step away from 0 mV increased. In the cell-attached configuration, the channel was rarely open (4/35, 11%) but opening could be induced by negative pipette pressure (5/14, 35%). Possible physiological roles for this channel are discussed.
Stimulation of nitric oxide from muscle cells by VIP: prejunctional enhancement of VIP release
Authors: Grider J. R. , Murthy K. S. , Jin J. G. , Makhlouf G. M.
Published: December 2017

The source of nitric oxide (NO) and its role in neurally induced relaxation was examined in smooth muscle of the stomach and tenia coli. Field stimulation of gastric muscle strips was accompanied by frequency-dependent relaxation, vasoactive intestinal peptide (VIP) release, and NO production: the NO synthase inhibitor, NG-nitro-L-arginine (L-NNA) completely inhibited NO production and partly inhibited VIP release (52-54%) and relaxation (58-88%); inhibition of all three functions was reversed by L-arginine but not by D-arginine. In isolated gastric muscle cells, VIP caused relaxation and stimulated NO production: L-NNA completely inhibited NO production and partly inhibited relaxation; the inhibition was reversed by L-arginine but not by D-arginine. Abolition of NO production with only partial inhibition of relaxation implied that NO production from muscle cells induced by the action of VIP was partly responsible for relaxation. By contrast, field stimulation of tenia coli was accompanied by relaxation and VIP release but not by NO production. Neither VIP release nor relaxation was affected by L-NNA. In isolated muscle cells of tenia coli, VIP caused relaxation but did not stimulate NO production; relaxation in these cells was not affected by L-NNA. We conclude that 1) VIP is the primary relaxant transmitter in both gastric muscle and tenia coli, 2) the release of VIP in gastric muscle but not in tenia coli stimulates NO production from target muscle cells, and 3) NO amplifies the relaxant effect of VIP in muscle cells and acts presynaptically to enhance the release of VIP.
Postnatal development of monosaccharide transport in pig intestine
Authors: Puchal A. A. , Buddington R. K.
Published: December 2017

In vitro brush-border transport of three monosaccharides by pig intestine was studied as a function of postnatal age from immediately after birth before suckling to after weaning. Rates of transport normalized to tissue weight or surface area for glucose (Glc), galactose (Gal), and fructose (Fru) were highest at birth, with a steep decline after the onset of suckling, probably caused by any combination of three or more factors: reduced transporter site density, shifts in relative abundances of different monosaccharide transporters, and/or changes in activities of individual transporters. Whereas highest rates of Glc and Fru transport shifted from proximal to midintestine after weaning, Gal transport remained highest in proximal intestine. Postnatal increases in Km values for Gal, but not Glc, indicate there are multiple aldohexose transporters that undergo separate developmental trajectories. The presence of Fru transport in neonatal pigs may reflect a more advanced state of development than neonatal rats and rabbits, or may be an adaptation for early weaning. Changes in Fru-to-Glc and Gal-to-Glc transport ratios before weaning suggest transporter development is partly genetically hard-wired, apparently to prepare pigs for weaning. Curiously, Fru-to-Glc transport ratios were lower than those of rat and rabbit, but closely paralleled those of the carnivorous cat.
Further evaluation of the afferent nervous pathways from the rectum
Authors: Loening-Baucke V. , Read N. W. , Yamada T.
Published: December 2017

To evaluate the visceral afferents from the rectum, we recorded cerebral evoked potentials (EPs) in 26 healthy subjects after electrical stimulation of the rectum, pudendal nerve, and posterior tibialis nerve. We found two distinctly different EPs after rectal stimulation, with differences in latencies and pattern. In 13 subjects (group 1), the EP after rectal stimulation had multiple prominent peaks with early onset latencies ranging from 22 to 29 ms (mean 26 ms). In 13 subjects (group 2), the EP after rectal stimulation had a trifid configuration due to a very prominent negative peak between 97 and 108 ms (mean 101 ms) and longer onset latencies ranging from 50 to 61 ms (mean 55 ms). Latencies after pudendal nerve and posterior tibialis nerve stimulation were similar in the two groups. On further study, we found that both types of afferent pathways are present in the distal colon, since both types of EPs were found in the same subjects either in the rectum or in the rectum and sigmoid. We speculate that the early onset EP is a visceral pathway using the same afferents as the pudendal nerve because the early onset EP after rectal stimulation appears similar in number of peaks and interpeak latencies to EPs recorded after pudendal nerve stimulation, and the late onset EP is a visceral pathway using afferents along the pelvic nerve. Early onset EPs were also recorded after sigmoid stimulation, suggesting that both kinds of EPs are visceral afferents.
Immunocytochemical studies suggest two pathways for enteroendocrine cell differentiation in the colon
Authors: Roth K. A. , Kim S. , Gordon J. I.
Published: December 2017

Enteroendocrine cells represent the most heterogeneous population of terminally differentiated cells in the mouse intestinal epithelium. Each of the approximately 15 different enteroendocrine cell subpopulations shows characteristic distributions along both the cephalocaudal and crypt-to-villus (in the small intestine) or crypt-to-surface epithelial cuff (in the colon) axes of the gut. These cells provide a sensitive model for studying how the continuously renewing gut epithelium is able to establish and maintain its spatial differentiation. Enteroendocrine cells are derived from the same multipotent stem cell that gives rise to enterocytes and goblet and Paneth cells. Regional differences in enteroendocrine cell number and type reflect positional differences in the differentiation programs of this lineage. To better understand the nature of these programs, we used multilabel immunocytochemical methods to examine the accumulation of endogenous neuroendocrine products as well as the product of a liver fatty acid binding protein/human growth hormone transgene in enteroendocrine cells located in proximal colonic glands. The results suggest that serotonin, substance P-, glucagon-like peptide-1 (GLP-1)-, peptide tyrosine tyrosine (PYY)-, neurotensin-, and cholecystokinin (CCK)-producing cells can all arise from a single stem cell located within a given gland. Based on pairwise comparison of the coexpression of each of these six products in individual cells as well as their ability to support transgene expression, it appears that the enteroendocrine lineage has two branches; one branch produces substance P and serotonin cells while the other yields GLP-1, PYY, neurotensin, and CCK cells.
Role of adenosine in postprandial and reactive hyperemia in canine jejunum
Authors: Sawmiller D. R. , Chou C. C.
Published: December 2017

The role of adenosine in postprandial jejunal hyperemia was investigated by determining the effect of placement of predigested food into the jejunal lumen on blood flow and oxygen consumption before and during intra-arterial infusion of dipyridamole (1.5 microM arterial concn) or adenosine deaminase (9 U/ml arterial concn) in anesthetized dogs. Neither drug significantly altered resting jejunal blood flow and oxygen consumption. Before dipyridamole or deaminase, food placement increased blood flow by 30-36%, 26-42%, and 21-46%, and oxygen consumption by 13-22%, 21-22%, and 26-29%, during 0- to 3-, 4- to 7-, and 8- to 11-min placement periods, respectively. Adenosine deaminase abolished the entire 11-min hyperemia, whereas dipyridamole significantly enhanced the initial 7-min hyperemia (45-49%). Both drugs abolished the initial 7-min food-induced increase in oxygen consumption. Dipyridamole attenuated (14%), whereas deaminase did not alter (28%), the increased oxygen consumption that occurred at 8-11 min. Adenosine deaminase also prevented the food-induced increase in venoarterial adenosine concentration difference. In separate series of experiments, luminal placement of food significantly increased jejunal lymphatic adenosine concentration and release. Also, reactive hyperemia was accompanied by an increase in venous adenosine concentration and release. This study provides further evidence to support the thesis that adenosine plays a role in postprandial and reactive hyperemia in the canine jejunum.
Connexins and glucagon receptors during development of rat hepatic acinus
Authors: Berthoud V. M. , Iwanij V. , Garcia A. M. , Saez J. C.
Published: December 2017

Levels (by immunoblotting) and cell distribution (by immunofluorescence) of connexins (Cxs) and glucagon receptors (GRs) were studied during the ontogeny of the rat liver. Cx32, the main rat liver gap junction protein, was present in fetal hepatocytes, and its abundance increased between the 19th and 21st gestational days. The major increase in Cx32 levels occurred between the 7th and 21st postnatal days, after which adult levels were reached. The adult pattern of distribution of Cx26 and Cx32 was established by the 21st postnatal day. Cx43 was present in the liver capsule and perisinusoidal cells, and its levels did not show significant variations throughout development. Levels of GRs were much lower in fetal than in adult livers. After birth, GRs increased progressively, reaching adult levels at about the 28th postnatal day. In adults, GR immunoreactivity on the plasma membrane of hepatocytes was localized to the region facing the sinusoid and showed a density gradient of distribution along the hemiacinus: high in pericentral regions and decreasing toward more glucogenically active cells located in periportal regions. Because cells of the hepatic acinus communicate via gap junctions, which are permeable to second messengers, we propose that signals transduced by GRs in cells expressing high levels of receptor might spread to cells expressing low levels of receptor, thus maximizing metabolic activation.
Intestinal absorption and lymphatic transport of peroxidized lipids in rats: effect of exogenous GSH
Authors: Aw T. Y. , Williams M. W.
Published: December 2017

We previously found that mucosal glutathione (GSH) plays an important role in the intestinal metabolism of luminal peroxidized lipids [T. Y. Aw, M. W. Williams, and L. Gray. Am. J. Physiol. 262 (Gastrointest. Liver Physiol. 25): G99-G106, 1992]. To determine the effects of exogenous GSH on lipid hydroperoxide elimination under conditions in which mucosal GSH was initially depleted with buthionine sulfoximine (BSO), we infused peroxidized lipid solutions without or with GSH into the proximal intestine of rats and monitored the steady-state output of hydroperoxides in lymph and recovery of luminal hydroperoxides. GSH supplementation in BSO-treated rats resulted in a concentration-dependent attenuation of lymphatic output of peroxidized lipids that was correlated with increases in mucosal GSH. Compared with BSO control, the luminal lipid hydroperoxide contents were significantly lower in GSH-supplemented rats, consistent with enhanced elimination of peroxidized lipids by exogenous GSH. The effect of GSH was ameliorated by the inhibitors of GSH uptake, suggesting that the uptake of GSH is required for promotion of intestinal removal of luminal hydroperoxides. Other thiols, either at comparable or higher concentrations than GSH, were without significant effects on lymphatic transport or luminal recovery of lipid hydroperoxides, indicating that these thiols are poor substitutes for GSH. Overall, the data are consistent with exogenous GSH being a source for cellular reduction of peroxidized lipids. Results from these studies could directly impact on future consideration of therapeutic means to increase cellular antioxidant systems to promote intestinal hydroperoxide detoxication.
Histamine receptors on submucous neurons in guinea pig colon
Authors: Frieling T. , Cooke H. J. , Wood J. D.
Published: December 2017

Intracellular microelectrodes were used to investigate the actions of histamine in the submucous plexus of the distal colon of the guinea pig. Three effects resulted from application of histamine to submucous neurons. The first was membrane depolarization associated with increased input resistance and augmented excitability. The second was presynaptic suppression of acetylcholine release at nicotinic synapses. The third occurred during long-term application and consisted of recurrent trains of action potentials associated with periodic depolarization of membrane potential. Pharmacological analysis, with selective agonists and antagonists, suggested mediation of the first and third response by postsynaptic histamine H2 receptors. The second response was mediated by presynaptic histamine H3 receptors. These actions of histamine represent a mechanism for neuroimmune signaling between mucosal mast cells and submucous neurons in gastrointestinal type 1 hypersensitivity reactions to allergens.
Vagal regulation of gastric prostaglandin E2 release by central TRH in rats
Authors: Yoneda M. , Tache Y.
Published: December 2017

The central action of the stable thyrotropin-releasing hormone (TRH) analogue, RX 77368, to induce vagal release of gastric prostaglandin E2 (PGE2) was investigated in urethan-anesthetized rats. Intracisternal RX 77368 (1.5-1,000 ng) dose dependently increased gastric PGE2 levels measured for 3 h in the perfusate of dialysis fibers implanted into the corpus submucosa. RX 77368 injected intravenously (1,000 ng) had no effect. The stimulatory action of RX 77368 (1.5 ng) on gastric PGE2 release was blocked by indomethacin and bilateral cervical vagotomy. Omeprazole did not alter the PGE2 response to 3 ng of RX 77368 and reduced by 39% PGE2 release induced by the 1,000-ng dose. RX 77368 (1.5 ng) by itself did not influence acid secretion but increased acid output to 117 +/- 18 mumol/2 h in indomethacin-pretreated rats. Indomethacin also increased by 97% the acid response to the 3-ng dose of RX 77368, but the effect of a maximal effective dose of RX 77368 was not modified. These results indicate that RX 77368 acts in the brain to induce a vagal-dependent stimulation of gastric PGE2 secretion which is biologically active to reduce the acid response to submaximal doses of TRH analogue. These data suggest a possible role of medullary TRH in the central vagal regulation of gastric PGE2 release.
Stilbenes stimulate T84 Cl- secretion by elevating Ca2+
Authors: Brayden D. J. , Krouse M. E. , Law T. , Wine J. J.
Published: December 2017

Basolateral but not apical application of 10-200 microM 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS) or 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS) to T84 monolayers produced a transient increase in short-circuit current (Isc), followed by a sustained inhibition. 4,4'-Dinitrostilbene-2,2'-disulfonic acid (DNDS) had no effect. The increase in Isc produced by DIDS represents Cl- secretion and appears to result from Ca2+ elevation, because in all respects except time course the response to DIDS mimicked the response to the Ca(2+)-elevating agent thapsigargin. Fura-2 measurements established that thapsigargin elevates Ca2+ in T84 cells, but Ca2+ responses to DIDS could not be established directly because DIDS absorbs strongly at the critical wavelengths. Responses to DIDS and thapsigargin were 1) blocked by bumetanide; 2) not blocked by basolateral Ba2+; 3) completely nonadditive; 4) strongly synergistic with basal levels of Isc or with Isc increases produced by elevating adenosine 3',5'-cyclic monophosphate (cAMP; with forskolin) or guanosine 3',5'-cycxlic monophosphate (with heat-stable enterotoxin); and 5) reversibly abolished by removal of basolateral Ca2+. Interactions between Ca2+ and cAMP-elevating agents strongly support a model of Cl- secretion in which apical Cl- conductance is activated by cyclic nucleotides but not by Ca2+ while basolateral K+ channels are activated by Ca2+. In contrast with this mechanism, whole cell patch-clamp recordings of nonconfluent T84 cells indicated that DIDS and other Ca(2+)-elevating agents stimulated an increase in Cl- conductance. Thus increases in cytosolic free Ca2+ in nonconfluent T84 cells activate conductances that differ from those in confluent monolayers.
Polyamines are necessary for cell migration by a small intestinal crypt cell line
Authors: McCormack S. A. , Viar M. J. , Johnson L. R.
Published: December 2017

Studies from our laboratory have shown that polyamines are essential for the normal repair of duodenal erosions induced in vivo in a rat stress-ulcer model. In that model, the inhibition of ornithine decarboxylase, a rate-limiting enzyme of polyamine biosynthesis, with alpha-difluoromethylornithine (DFMO) almost entirely prevented healing. Healing could be restored by oral polyamines. In this paper, we have investigated whether the polyamines are required for the early stages of epithelial restitution using an IEC-6 cell culture model of cell migration. Treatment of the cells with DFMO for 4 days reduced cell migration 80%. Migration could be restored to normal by concomitant treatment with putrescine (PUT), spermidine (SPD), or spermine (SPM), but not by their addition during the migration period (6 h) only. If DFMO treatment was not begun until the migration period, it still reduced cell migration 20%, and this deficit could not be restored by concomitant addition of the polyamines. Intracellular polyamine levels at these times, i.e., 6 h or 4 days, were an important factor in these results. Only PUT was undetectable after 6 h of DFMO. SPD and SPM were still at normal levels at 6 h. SPD was undetectable at 4 days, but SPM was still at 40% of normal. These data give added importance to PUT because its absence reduced cell migration after only 6 h, while SPD and SPM were still present in normal amounts. Perhaps exogenous SPD and SPM restored cell migration when present with DFMO for 4 days treatment primarily because they contributed to intracellular PUT through the acetyltransferases.(ABSTRACT TRUNCATED AT 250 WORDS)
Thyrotropin-releasing hormone: an inhibitory regulatory peptide of feline lower esophageal sphincter
Authors: Parkman H. P. , Reynolds J. C. , Ogorek C. P. , Kreider M. S.
Published: December 2017

The functional role of thyrotropin-releasing hormone (TRH) at the lower esophageal sphincter (LES) was examined in the cat. The specific aims of this study were to determine: 1) the relative distribution of TRH throughout the feline gastrointestinal tract and 2) the effect of TRH on LES basal pressures and its response to exogenously induced contractions. TRH concentrations were determined by radioimmunoassay in tissue extracts from 12 sites. The mean concentration of TRH at the manometrically determined LES was 240 +/- 85 pg/g wet wt tissue, and the maximal concentration was just distal to the LES (659 +/- 189 pg/g wet wt). TRH concentration was higher in the mucosa than the underlying muscle layer of the fundus, antrum, duodenum, and ileum. In physiological studies, TRH given selectively via the left gastric artery had no effect on basal LES or esophageal pressures. TRH (2.8 x 10(-8) mol/kg) decreased the LES response to the D50 of substance P by 47.2% (34.8 +/- 3.1 to 18.4 +/- 2.9 mmHg, P < 0.01). In the presence of tetrodotoxin, TRH gave a similar inhibition of substance P-induced contractions (53.5%). TRH also decreased bombesin-induced contractions by 47.5% (29.6 +/- 6.0 to 15.8 +/- 3.9 mmHg, P < 0.025). TRH, however, had no effect on bethanechol-induced contractions. We conclude that 1) TRH is present throughout the gastrointestinal tract, with highest concentrations in the region distal to the LES; 2) TRH has no effect on basal LES tone; and 3) TRH inhibits the LES response to endogenously released and exogenous substance P but not the LES response to bethanechol.(ABSTRACT TRUNCATED AT 250 WORDS)
Chloride channels in myocytes from rabbit colon are regulated by a pertussis toxin-sensitive G protein
Authors: Sun X. P. , Supplisson S. , Mayer E.
Published: December 2017

Because of the high intracellular Cl- concentration ([Cl-]i) in gastrointestinal smooth muscle, receptor-mediated opening of Cl- channels at the cell resting potential could represent a plausible mechanism for initial receptor-mediated cell depolarization. To test this hypothesis, we characterized activation of large-conductance Cl- channels by the neurokinin-1 (NK-1) receptor agonist [Sar9,Met(O2)11]-substance P, by specific second messengers, and by direct G protein activation in myocytes isolated from the rabbit colon longitudinal muscle layer. In excised inside-out patches, large-conductance ion channels selective for Cl- over Na+ could be induced by holding the patch at pipette potentials values > 60 mV. The channel showed multiple smaller conductance states (< or = 20) but could open and close via a main gate. When the channel was fully open, its slope conductance was 300 pS, with substates as small as 15 pS, comparable to the predominant conductance observed in cell-attached patches. The voltage-activation profile for full conductance was bell-shaped with maximal open probability (Po) for channel opening of approximately 0 mV. In cell-attached patches, addition of the NK-1 agonist to pipette solution activated a channel that corresponded to a subconductance state of the maxi Cl- channel. The voltage-activation profile for this subconductance state showed a maximal Po value for membrane potentials of approximately 0 mV, with rapid inactivation at more positive and partial inactivation at more negative membrane potentials. In excised inside-out patches, both the full and smaller conductance states of the Cl- channel were activated by the nonhydrolyzable guanosine triphosphate analogue guanosine 5'-O-(3-thiotriphosphate) and inhibited by pertussis toxin (PTX), whereas [Ca2+]i increased channel activity only in concentrations > 1 mM. In cell-attached patches, addition of different Ca2+ ionophores resulted in channel activation in 10% of cells, and activators of protein kinase A or protein kinase C had no effect. These findings are consistent with the hypothesis of a possible role of G protein-coupled Cl- channels in receptor-mediated initial cell depolarization in longitudinal colonic smooth muscle.
Complement activates Kupffer cells and neutrophils during reperfusion after hepatic ischemia
Authors: Jaeschke H. , Farhood A. , Bautista A. P. , Spolarics Z. , Spitzer J. J.
Published: December 2017

The hypothesis that complement factors may be involved in the postischemic activation of Kupffer cells (KC) and polymorphonuclear neutrophils (PMN) was investigated in a model of hepatic ischemia (45 min) and reperfusion in male Fischer rats in vivo. Depletion of serum complement before ischemia resulted in a significant attenuation of the KC-induced oxidant stress (enhanced oxidation of plasma glutathione) and also prevented the accumulation of PMNs in the liver during the initial reperfusion period of 1 h. Complement activation through injection of cobra venom factor (CVF; 75 micrograms CVF/kg) also induced enhanced oxidation of plasma glutathione and accumulation of PMNs in the liver. Isolation of KC and PMNs from the liver 1 h after CVF treatment demonstrated a similar priming effect for stimulation with phorbol myristate acetate and opsonized zymosan as was observed in the postischemic liver. Complement-depleted animals and animals pretreated with the soluble human complement receptor type 1 (BRL 55730; 22.5 mg/kg) accumulated significantly less PMNs in the postischemic livers during longer reperfusion periods (24 h) and sustained significantly less injury. It is concluded that complement is involved in the induction of a KC-induced oxidant stress, the priming of KC and PMNs for enhanced reactive oxygen generation, and the continuous accumulation of PMNs in the liver during reperfusion.
Secretin receptors mediating rat forestomach relaxation
Authors: Steiner T. S. , Mangel A. W. , McVey D. C. , Vigna S. R.
Published: December 2017

Frozen sections of the rat stomach were incubated with 125I-labeled porcine secretin, and then secretin binding sites were localized by autoradiography. Saturable binding was observed only in the muscularis externa (circular and longitudinal smooth muscle layers) of the proximal nonglandular forestomach. Saturable binding was quantitated by densitometry. 125I-porcine secretin bound to a single class of high-affinity binding sites with a dissociation constant of 0.6 nM. Porcine and rat secretins were nearly equipotent in inhibiting saturable 125I-porcine secretin binding, and vasoactive intestinal polypeptide, peptide histidine-isoleucine, and glucagon were much weaker. Carbachol (100 microM) stimulated a sustained increase in tension in forestomach muscle in vitro, and porcine secretin caused relaxation of this stimulated contraction. We conclude that rat forestomach smooth muscle expresses a high-affinity specific secretin binding site that mediates relaxation. This putative secretin receptor may mediate some of the actions of secretin on gastric motility.
On the coupling of membrane digestion with intestinal absorption of sugars and amino acids
Authors: Pappenheimer J. R.
Published: December 2017

An hypothesis is advanced to account for the large paracellular component of absorption of nutrients by the small intestine. High concentrations of hexoses and amino acids in the immediate vicinity of transporters and cell junctions are generated by membrane-bound saccharases and peptidases. After saturation of membrane carriers, the concentrations of monomers in the microenvironment increase until paracellular plus transcellular absorption equals rates of formation. During hydrolysis of maltose, the concentration of glucose at which rates of absorption and formation are equal is 200-300 mM, and at these concentrations paracellular transport accounts for 60-80% of total absorption. Transcellular concentrative transport provides the force for osmotic flow and at the same time triggers contraction of perijunctional actomyosin, thereby increasing transjunctional coefficients of osmotic flow and solvent drag. Paracellular absorption requires no oxidative energy other than that required to maintain the transjunctional concentration gradient and to energize contraction of cytoskeletal elements controlling junctional permeability and functional surface of lateral membranes. Almost all glucose generated by membrane hydrolysis is absorbed, but some may diffuse from high concentration in the microenvironment to the lumen thus accounting for the small amounts of free glucose found in macrosamples of chyme. Unstirred layers adjacent to the brush border retard backdiffusion to lumen, thus maintaining high concentrations for passive paracellular absorption. Coupling of membrane digestion with paracellular transport provides almost perfect matching of absorption to digestive loads because transport by solvent drag is proportional to concentration at cell junctions and this in turn is proportional to rate of hydrolysis.(ABSTRACT TRUNCATED AT 250 WORDS)
Nitric oxide regulates migrating motor complex cycling and its postprandial disruption
Authors: Sarna S. K. , Otterson M. F. , Ryan R. P. , Cowles V. E.
Published: December 2017

We investigated the role of nitric oxide (NO) in the regulation of migrating motor complex (MMC) cycling during the fasting state and its postprandial disruption. Intravenous infusion of Nohgr-nitro-l-arginine methyl ester (l-NAME) first produced a premature MMC and then disrupted MMC cycling for the rest of the day. The cycle length of the MMCs was significantly shorter than the control on the 2nd, 3rd, and 4th day after l-NAME infusion. The gastric cyclic motor activity (CMA) did not usually exhibit a premature cycle on the day of l-NAME infusion but was disrupted by l-NAME infusion; the duration of CMA disruption in the stomach was significantly longer than that of MMC disruption in the small intestine. Infusion of Nohgr-nitro-l-arginine (l-NNA) exhibited similar effects. The intravenous infusion of l-NAME also significantly shortened the duration of MMC disruption by a meal. l-Arginine alone had no significant effect on gastrointestinal motor activity during the fasting or the fed state, but when infused with l-NAME, it blocked the effects of NO synthase inhibition. Angiotensin II increased the mean arterial pressure to a level similar to that produced by l-NAME but had no significant effect on the fasting or the fed pattern of gastrointestinal motor activity. We conclude that NO containing nonadrenergic noncholinergic (NANC) neurons play a significant role in regulating MMC and CMA cycling during the fasting state and their disruption by a meal. However, NO may not be the only NANC neurotransmitter to inhibit contractions in the gut; phase I activity in the small intestine persisted during NO synthase inhibition by l-NAME or l-NNA.

nonadrenergic noncholinergic neurons; cyclic motor activity: Nohgr-nitro-l-arginine methyl ester; Nohgr-nitro-l-arginine; vasoactive intestinal peptide; cholecystokinin

Submitted on November 30, 1992

Accepted on June 3, 1993