The role of Phospholipase A2 in Calcium-Ionophore-Mediated Injury to Rat Gastric Mucosal Cells

Although transient increases in intracellularCa²⁺ ([Ca²⁺]_i) underliea number of important physiological processes, sustainedelevations in [Ca²⁺]_i mediatedamage to a number of tissues and cell types including gastric mucosal cells. Increases in[Ca²⁺]_i can activate phospholipidhydrolysis via increases in phospholipase A₂(PLA₂) activity and subsequent cell injury.In the present study we have examined whether [Ca²⁺]_i-inducedgastric cellular injury is mediated by PLA₂activation. Gastric mucosal cells were harvested fromrat stomachs after pronase digestion. Cell integrity wasassessed using trypan blue dye exclusion and release of lysozomal enzymes.PLA₂ activity was estimated colorimetricallyby determination of thiol release from the substrate,arachidonyl thio-PC. In these studies calcium ionophore A23187 (3-25 M) resulted in an increase incell injury. The damage produced by A23187 (12.5 M)was inhibited by preincubation of cells with thePLA₂ inhibitor, quinacrine (1-100 M).Quinacrine did not reduce ethanol (10% w/v) mediated-celldamage. Similarly Ca²⁺ ionophore A23187treatment resulted in a concentration-dependent increasein PLA₂ activity in gastric cells. Theincrease in PLA₂ activity was attenuated if cells were incubated inCa²⁺-depleted medium containing EGTA (4 mM).Furthermore lysophospholipids generated byPLA₂ (lysophosphatidylethanolamine andlysophosphatidylcholine; 100 M) also increased the degree of cell injury.Pretreatment of cells with the PAF antagonist WEB 2086(10^-6 and 10^-5 M), the leukotrienesynthase inhibitor 5,6-dehydroarachidonic acid (10M), or the thromboxane synthase inhibitor furegrelate (1 M)decrease A23187-mediated cell injury. These data suggestthat Ca²⁺ ionophore-mediated increases in[Ca²⁺]_i result in gastric cellinjury and this effect is mediated in part by PLA₂ activation andsubsequent release of free fatty acids andlysophosphatides.     

Protection by Intragastric Polyethylene Glycol 400 in Rat Stomach Against Ethanol Damage Involves α2-Adrenoceptors

The aim of this study was to investigate the role of ₂-adrenoceptors in the mechanism of intragastric polyethylene glycol 400 (PEG-400) protection against ethanol-induced gastric mucosal damage. In the injury study, 0.5 hr after subcutaneous control or yohimbine (5 mg/kg), a selective ₂-adrenoceptor antagonist, rats were treated with intragastric vehicle or PEG-400 (5500 mg/kg). One hour later animals received 96% ethanol (gavage needle), 5 ml/kg, and the rats were killed after another hour. Total lengths of the gastric mucosal lesions were measured by an unbiased observer in a blinded fashion using a binocular magnifier having 5× magnification. In a separate set of experiments, 0.5 hr after subcutaneous control or yohimbine (5 mg/kg) rats received intragastric vehicle or PEG-400 (5500 mg/kg). One hour later gastric mucus volume, gastric juice volume, and gastric acid output in the gastric juice were measured. The protective effect offered by intragastric PEG-400 against ethanol-induced gastric mucosal damage was significantly diminished although not completely abolished by a selective ₂-adrenoceptor antagonist (yohimbine). Yohimbine also significantly diminished both the basal and PEG-400-stimulated increase in gastric mucus volume. These findings suggest that the protective effect afforded by intragastric PEG-400 against ethanol-induced gastric mucosal damage is partially mediated by ₂-adrenoceptors, and a mucus-dependent mechanism may be involved.     

Acid-Independent Gastroprotective Effects of Lansoprazole in Experimental Mucosal Injury

The protective effects of the proton pumpinhibitor lansoprazole on gastric mucosal damage inducedby ethanol-HCl or hemorrhagic shock were investigated inthe present study. The morphometric analysis of gastric histological sections revealed thatlansoprazole dosedependently reduced mucosal injuryevoked by ethanol-HCl (ED₅₀ = 24.3mol/kg) or hemorrhagic shock (ED₅₀ = 38.9mol/kg), these effects being associated with markedincrements of Alcian blue recovery from gastric boundmucus (ED₅₀ = 31.4 mol/kg and 27.6mol/kg, respectively). In addition, lansoprazoleinhibited gastric acid secretion from pylorusligated rats(ED₅₀ = 9.8 mol/kg). Further experiments,performed on rats with ethanol-HCl-induced gastricinjury, indicated that the protective effects of lansoprazole were not modified by L-365,260,suramin, N^G-nitro-L-arginine, or systemicablation of capsaicin-sensitive sensory nerves, whereasthey were partly blocked by indomethacin and fullyprevented by N-ethyl-maleimide. In addition, lansoprazoledid not modify somatostatin concentrations in gastricmucosa. The present results provide evidence thatlansoprazole prevents the necrotic damage of gastric mucosa induced by ethanol-HCl or hemorrhagicshock. According to the rank order of ED₅₀values, these effects appear to depend mainly on theenhancement of the gastric mucus barrier rather than on the reduction of acid secretion. It is alsoproposed that an increased production of prostaglandins,as well as an increased availability of sulfhydrylcompounds at level of gastric mucosa may account for the gastroprotective effects oflansoprazole.     

Prostaglandin requirements are greater for protection in cold restraint-induced than alcohol-induced gastric mucosal injury

Exogenous prostaglandins inhibit visible gastric muscosal lesions produced by both absolute ethanol and cold restraint in the rat. Pretreatment with mild irritants significantly reduces the magnitude of ethanol-induced lesions presumably by stimulating endogenous prostanoid production. The effect of mild irritant pretreatment on cold restraint-induced lesion formation has not been previously reported. This study was designed to compare the protective effect of pretreatment with two mild irritants, 4% NaCl and 0.35 M HCl, and the synthetic prostanoid, 16,16 dimethyl PGE₂)16,16-dm PGE₂), on lesions produced by cold restraint or absolute ethanol. Pretreatment with both mild irritants produced complete visible protection against ethanol-induced injury but had variable effects against cold restraint-induced injury. Whereas 5 g/kg 16,16-dmPGE₂ provided complete visible protection against ethanol-induced injury, 20 g/kg 16,16-dmPGE₂ was required for complete visible protection against cold restraint-induced injury. We conclude that prostaglandin requirements for protection against cold restraint injury are greater than for protection against ethanol-induced gastric mucosal injury.This work was supported by National Institutes of Health grants BRSG 4-434400-32602, NIADDK AM 27465 and AM 17328.     

Role of capsaicin-sensitive sensory nerves in acid-induced bicarbonate secretion in rat stomach

The effect of capsaicin-sensitive afferent nerves on the alkaline secretory response induced by mucosal acidification was investigated in theex vivo stomachs of anesthetized rats. The stomach was mounted on a Lucite chamber and perfused with saline (pH 4.5) in the absence of acid secretion (omeprazole pretreatment: 60 mg/kg, intraperitoneal), and luminal pH and transmucosal potential difference (PD) were monitored simultaneously. Under these conditions the gastric mucosa responded to intravenous infection of prostaglandin E₂ (PGE₂: 300 g/kg) and mucosal acidification (0.2 N HCl for 10 min) by a significant increase of pH with a slight decrease of PD; the HCO₃ ^– output was 9.2±0.7 mol and 8.4±0.8 mol, respectively. The increased pH and HCO₃ ^– responses were significantly inhibited by prior administration of indomethacin (5 mg/kg, subcutaneously) or chemical deafferentation following capsaicin injections (total dose: 100 mg/kg, subcutaneously), whereas those induced by PGE₂ remained unchanged after either treatment. On the other hand, the mucosal application of capsaicin (0.3–6 mg/ml) increased the luminal pH and HCO₃ ^– output in a concentration-related manner, and this action was also significantly attenuated by either indomethacin or chemical deafferentation of capsaicin-sensitive sensory neurons. These results suggest that capsaicin-sensitive sensory nerves may be involved in the mechanism of acid-induced HCO₃ ^– secretion in the stomach, in addition to endogenous PGs, and these two pathways may interact somewhere in the stimulatory process.     

Somatostatin effectively prevents ethanol-and NSAID-induced gastric mucosal damage in rats

The interrelationship between somatostatin and its synthetic analog, sandostatin, with neuropeptides and inflammatory mediators, as well as their protection of gastric mucosal damage, were tested in rats. Rats were treated intragastrically with 1.0 ml of 96% ethanol with or without intravenous or intraperitoneal coadministration of somatostatin (1.0 µM/kg). Mucosal damage was also induced by the administration of either indomethacin (30 mg/kg subcutaneously) with or without intravenous sandostatin (10 µg/rat), given 30 min prior to damage induction. Somatostatin levels in ethanol-damaged gastric mucosa were significantly lower than in control rats. Substance P and vasoactive intestinal peptide (VIP) levels were significantly higher in the damaged mucosa in rats treated with ethanol, as was the mucosal generation of leukotriene B₄ (LTB₄) and cysteinyl-containing leukotrienes. The coadministration of somatostatin with ethanol significantly reduced gastric mucosal injury induced by ethanol alone. The protection of the mucosa was accompanied by reduction of mucosal substance P and VIP levels, as well as the generation of leukotrienes, an effect that was reversed by intraperitoneal or intravenous coadministration of somatostatin antagonist, cyclo-(7-aminoheptanoyl-PH-E-d-Trp-Lys-THR), 1.0 µM/100 g, with somatostatin (1.0 µM/kg) and ethanol. When given by itself somatostatin significantly reduced mucosal leukotriene generation compared with their generation in saline-treated rats. Sandostatin completely abolished gastric mucosal damage induced by indomethacin administration. In rats treated with somatostatin and indomethacin, this effect was accompanied by reduction of mucosal leukotriene generation. Administration of sandostatin to pylorus-ligated rats significantly reduced gastric acid output. It is suggested that somatostatin may be involved in the pathogenesis of acute ethanol- and NSAID-induced gastric mucosal injury and that part of its protective effect involves interrelationships with the neuropeptides, substance P and VIP, as well as inhibition of mucosal leukotriene production.     

Differences in gastroprotective processes in 6- to 8- and 14- to 16-week-old rats

The gastroprotective effect of opioid peptides, prostaglandin E₂ and capsaicin against acidified ethanol-induced gastric mucosal damage in young mature rats of different (6–8 and 14–16 weeks) ages has been investigated. It was found that gastric mucosal damage was more severe in 14–16 weeks old rats. The gastroprotective effect of opioid peptides - [D-Ala², D-Leu⁵]-enkephalin (DADLE), deltorphin II, [D-Ala², Phe⁴, Gly⁵ -ol]-enkephalin (DAGO) and -endorphin - given either intracerebroventricularly (0.6, 3.3., 0.2, and 0.01 nmol/rat, respectively) or subcutaneously (825 and 960 nmol/kg, respectively) was highly reduced in 14–16 weeks old rats. The mucosal protective action of orally administered capsaicin (1600–3200 nmol/kg) and PGE₂ (280–560 nmol/kg) was also diminished in 14–16 weeks old animals. Both ACTH and corticosterone plasma levels were significantly higher in 14–16 weeks old rats. These results suggest that the gastric mucosal susceptibility to ethanol and the gastroprotective effect of opioid peptides, capsaicin and PGE₂ are age-related.     

Prostaglandin protection of rat colonic mucosa from damage induced by ethanol

The effects of pretreatment with 16,16-dimethyl prostaglandin E₂ (dmPGE₂) on ethanol-induced colonic damage were studied in the rat. Colonic damage was assessed macroscopically, histologically, and using cytoplasmic (lactate dehydrogenase) and lysosomal (acid phosphatase) enzyme markers of cell disruption. Intrarectal administration of 30% ethanol produced grossly visible regions of hyperemia and hemorrhage. Histologically, the ethanol injury was characterized by complete destruction of the surface epithelium and necrosis extending throughout most of the mucosal layer. When incubatedin vitro after challenge with ethanolin vivo, the colons released significantly more acid phosphatase and lactate dehydrogenase than did controls. Intrarectal pretreatment with dmPGE₂ caused a dose-dependent reduction in ethanol-induced damage, as measured by all three parameters. A significant (P<0.05) reduction of macroscopically visible damage was observed with 0.2 g/kg dmPGE₂, while at higher doses (20 g/kg) the histological signs of damage, including that to the colonic epithelium, were reduced or completely prevented. This dose of dmPGE₂ also reduced (P<0.01) the release of the enzymemarkers to control levels. The possibility that this protection was mediated by increased colonic fluid secretion was studied. Pretreatment with dmPGE₂ had no effect on net colonic fluid secretion (measured using the nonabsorbable marker [³H]inulin) or on the absorption of ethanol by the colon. This study demonstrates that intrarectal administration of dmPGE₂ can protect the colonic mucosa from damage induced by direct application of a potent topical irritant. With the highest dose of dmPGE₂ tested (20 g/kg), protection of the colonic epithelium from ethanol injury was observed.     

Pharmacological evidence for beta3 adrenoceptors in the control of rat gastric acid secretion

The effect of the ₃-adrenoceptor agonist BRL37344 on gastric acid secretion evoked by different secretory stimuli was investigated in anaesthetized rats with lumen-perfused stomachs in comparison with the ₂-adrenoceptor agonist clenbuterol. Intravenous injections of BRL37344 (1–10 mol/kg) and clenbuterol (0.01–1 mol/kg) dose-dependently reduced 2-deoxy-D-glucose-induced acid secretion, with BRL37344 about forty times less potent than clenbuterol. BRL37344 (0.1–3 mol/kg) inhibited pentagastrin-induced acid output, whereas clenbuterol was effective only at high doses (10–100 mol/kg). The inhibitory effect of BRL37344 on pentagastrin-induced acid secretion was not modified by the nonselective –adrenoceptor antagonist propranolol, but it was prevented by bupranolol, a ₃-adrenoceptor antagonist. Furthermore, neither BRL37344 (10 mol/kg) nor clenbuterol (100 mol/kg) modified the acid secretion induced by histamine. These data suggest that ₃ adrenoceptors have an inhibitory role in the control of rat gastric acid secretion induced by indirect stimuli.     

Cyclooxygenase-2 mediates mucin secretion from epithelial cells of lipopolysaccharide-treated canine gallbladder

Biliary mucin was regarded as a major contributing factor in formation of pigment stones as well as cholesterol ones. The aim of this study was to elucidate the mechanism of biliary mucin secretion in canine gallbladder epithelial (CGBE) cells treated by lipopolysaccharides (LPS) with special reference to cyclooxygenase (COX) -2. Confluent CGBE cells were incubated with following compounds for 8, 12, and 24 hr: (1) serum-free medium, (2) serum-free medium containing LPS (100 m/ml), (3) serum-free medium containing LPS (100 m/ml) with NS-398 (10 M), and (4) serum-free medium containing LPS (100 m/ml) with indomethacin (10 M). Mucin assay and western blots for COX-1 and COX-2 were performed. Production of PGE₂, and cAMP was also measured. Mucin secretion increased with time. At 12 hr, mucin secretion increased to 200% of control (from 100 ± 5 to 200±45%, P < 0.05). LPS treatment significantly stimulated the COX-2 expression (P < 0.05). The productions of PGE₂ and cAMP were increased from 299±68 to 524±163 pg/mg (P < 0.05) and from 0.2±0.1 to 0.92±0.4 pmol/ml (P < 0.05), respectively. NS-398, which completely inhibited COX-2 expression, significantly suppressed the level of PGE₂ and cAMP as well as mucin secretion (P < 0.05). Indomethacin, which partially inhibited COX-2 expression, suppressed the production of PGE₂, but not cAMP and mucin secretion. In conclusion, our results suggested that the PGE₂ induced by COX-2 might play a role in mucin secretion from the gallbladder epithelium through the increment of cAMP.     

Nitric Oxide-Mediated Regulation of Gastric H+, K+-ATPase and Alcohol Dehydrogenase Following Ethanol-Induced Injury in Rats

The mucosal protective effect of nitric oxide(NO) was examined by usingN^G-nitro-L-arginine methyl ester (L-NAME) asnitric oxide synthase (NOS) inhibitor and nitroprusside(NP) as NO donating agent, in ethanol-induced rat gastric lesion model.The results are summarized as follows: (1) As gastrictissue samples were examined by light microscopy,intragastric exposure of ethanol was demonstrated to induce gastric injury, which was more prominentin female rats. The depletion of NO by L-NAME treatmentexacerbated the ethanol-induced gastric lesion but NPtogether with ethanol promoted repair of the mucosal injury, especially in female rats. (2)Gastric H⁺, K⁺-ATPase enzymeactivity, which was responsible for acid secretion,seemed not to be effected by ethanol treatment. Togetherwith ethanol, L-NAME treatment activated, whereas NP treatmentinhibited, the enzyme activity in female rats. (3)Ethanol treatment inhibited gastric alcoholdehydrogenase (ADH) activity, which was responsible forthe first-pass metabolism of ethanol. Together with ethanol,L-NAME did not effect the enzyme activity whereas NPtreatment disappeared the inhibitory effect of ethanolin both gender. Hydroxyl radical (OH) scavenger activity was found to increase in ethanol andethanol + NP groups in both sexes, but superoxideradical (O₂ ^-) scavengeractivity did not change. The results indicate that NOmay ameliorate the damaging effect of ethanol possibly by regulating acidsecretion, ethanol metabolism, and antioxidant contentin rat gastric mucosa.     

Role of histamine H3 receptors in control of mouse intestinal motility in vivo and in vitro: comparison with alpha2-adrenoceptors

We tested drugs acting at histamine H₃ receptors in mice on the gastrointestinal transit of a charcoal meal in vivo and on neurogenic contractions of isolated ileal preparations. The agonist (R)--methylhistamine (100 mol/kg) caused a maximum 25% reduction of gastrointestinal transit, an effect mimicked by immepip (100 mol/kg) and antagonized by thioperamide (20 mol/kg) or clobenpropit (20 mol/kg). In the isolated ileum, (R)--methylhistamine (10–100 M) caused a slight, thioperamide-insensitive, reduction (maximum 15%) of electrically evoked cholinergic contractions. In comparison, the ₂-adrenoceptor agonist clonidine (0.1 mol/kg) caused a 35.2% inhibition of the gastrointestinal transit and almost completely reduced (maximum 82% at 1 M) the cholinergic contraction of the isolated ileum, both effects being antagonized by idazoxan (0.4 mol/kg and 1 M, respectively). These results suggest that histamine H₃ receptors, located outside the myenteric plexus, mediate an inhibition of the gastrointestinal transit in vivo. Conversely, the presence of ₂-adrenoceptors in the cholinergic nerve endings and their inhibitory role in the control of gastrointestinal propulsion is confirmed.     

Evidence for apical Na+/H+ exchanger in bovine main pancreatic duct

The finding of a high Pco ₂ in basally secreted pancreatic juice of man and dog raises the hypothesis of proton secretion from ductal epithelial cells presumably through a Na⁺/H⁺ exchanger. To test this possibility, H⁺ luminal secretion and Na⁺ movements were measuredin vitro on samples of bovine pancreatic ducts mounted in Ussing-type chambers. The rate of luminal acidification measured by the pH stat method, using bicarbonate-free media gassed with 100% O₂, reached 2.75 Eq/cm²/hr. Proton secretion was blocked in the presence of 1 mM amiloride or in the absence of Na⁺ (replaced by choline) in the mucosal solution. Study of transepithelial²²Na fluxes in short-circuited tissue, bathed on both sides by control Ringer solution, gassed by 95% O₂-5% CO₂ demonstrated a net sodium transport from the mucosal to the interstitial side of the duct (net²²Na flux=3.23±0.8 Eq/cm²/hr). This net sodium transport was electroneutral and blocked by mucosal amiloride (0.5–1 mM/liter) or by interstitial ouabain (1 mM/liter). These results are consistent with the existence of a Na⁺/H⁺ exchanger on the luminal side of the bovine main pancreatic duct.     

Inhibition of canine gastric acid secretion by an H-1 receptor antagonist to histamine

Histamine H-2 receptors are thought to mediate gastric acid secretory responses, where-as H-1 receptors supposedly regulate mucosal vascular responses to histamine. In an in vivo chambered canine stomach flap preparation, the H-1 receptor antagonist, tripelennamine, injected intraarterially (22.1 mol/kg) into the stomach flap reduced histamine-stimulated (1.25 /kg/min intravenously) acid secretion by approximately two thirds with a secondary reduction in gastric mucosal blood flow. This antisecretory action does not appear to be due to nonspecific mucosal damage. The H-2 receptor antagonist, metiamide, injected intraarterially (2.5 mol/kg) also inhibited gastric acid secretion by about two thirds as did intravenously injected metiamide (4.5 mol/kg), whereas intravenously administered tripelennamine (40.8 mol/kg) was ineffective as an acid secretory inhibitor. Intraarterial tripelennamine reduced the secretory actions of the H-2 agonist, 4-methyl-histamine (2.2 g/kg/min intravenously), while intravenous metiamide depressed the gastric mucosal dilator responses to the H-1 agonist, 2-methylhistamine (5 g/kg/min intravenously). Both histamine-receptor antagonists also reversed the systemic circulatory depressor effects of histamine and its analogs. These results suggest the need for reevaluation of inferences based upon the assumed specificity of H-2 and H-1 agonists and antagonists.     

Role of calcium in thromboxane B2-mediated injury to rabbit gastric mucosal cells

A sustained increase in cytosolic Ca²⁺ can damage gastric mucosal cells. The present study has examined the role of Ca²⁺ in thromboxane B₂ (TXB₂)-mediated damage of rabbit isolated gastric mucosal cells. Cells were isolated from rabbit oxyntic mucosa by collagenase-EDTA digestion. Cell metabolic activity and cell damage were estimated by alamar blue dye absorbance and trypan blue uptake, respectively. Cellular Ca²⁺ was monitored by indo-1 dye fluorescence. Addition of TXB₂ (10^–6 and 10^–8 M) to the cell suspension resulted in a decrease in metabolic activity, and this effect was reduced when Ca²⁺ was removed from the incubation Ca²⁺ and incubation of cells with the intracellular Ca²⁺ chelator, BAPTA-AM (20 M), reduced cell injury in response to TXB₂. Incubation of cells with the Ca²⁺ ionophore A23187 (1–25 M) resulted in a dose-dependent increase in trypan blue uptake and a reduction in cell metabolism. Cell unjury in response to A23187 were exacerbated by addition of TXB₂ (10^–8 M) to the cell suspension. TXB₂ treatment reduced cellular content of reduced glutathione (GSH), while exogenous GSH addition (10 mM) reduced TXB₂-mediated cell injury. These data demonstrate that TXB₂ can directly injure gastric mucosal cells. Gastric mucosal cellular damage in response to TXB₂ is mediated in part by a disruption of Ca²⁺ homeostasis as well as a reduction in cellular GSH content.This work was supported by a grant from the Medical Research Council of Canada MT6426.     

Enhancement of antibiotic concentrations in gastric mucosa by H2-receptor antagonist

We measured the effects of cimetidine on antibiotic concentrations in the luminal portion of gastric mucosa. Guinea pigs were premedicated with cimetidine 4 mg/kg intramuscularly. Clindamycin, an antibiotic previously characterized under physiologic pH conditions, was administered intramuscularly and levels measured in serum and tissue using a high-pressure liquid chromatography (HPLC) technique. The luminal mucosa concentration of clindamycin at 1 hr (pH 5.9) was fivefold greater compared to the concentrations seen under physiologic (pH 2.0) conditions (81.5g/g vs 15.9g/g;P<0.05) and 10-fold greater at 2 hr (82.7g/g vs 8.09g/g;P<0.05). There was no difference in peak serum levels between the groups. The finding that an antibiotic with characteristics of a base is thus affected by a nonconservative acid inhibitor such as cimetidine supports the presence of an acidic storage pool as proposed by other investigators. H₂-receptor antagonists may be useful therapeutic adjuncts inH. pylori infections by virtue of increasing gastric concentrations of antibiotics that behave as weak bases.Sponsored in part by Public Health Service grant RR05870 from the National Institutes of Health and by Upjohn Company.     

Cyclic GMP-Mediated Activation of a Glibenclamide-Sensitive Mechanism in the Rabbit Sphincter of Oddi

We investigated whether glibenclamide-sensitive potassium channels are involved in cyclic GMP (cGMP)-mediated relaxation of the rabbit Oddi's sphincter. Changes in isometric tension were measured in the presence of atropine (1 M) and guanethidine (4 M). Concentration–response curves for nitroglycerin, vasoactive intestinal polypeptide (VIP), and sodium nitroprusside (SNP) were shifted to the right in the presence of (p-chloro-d-Phe⁶, Leu¹⁷)-VIP (VIPa), a VIP receptor antagonist. Glibenclamide (1 M) attenuated the relaxations to VIP, nitroglycerin, or 8-bromo cGMP. In the presence of tetrodotoxin (TTX), glibenclamide attenuated relaxations to VIP without effect on those to nitroglycerin. Furthermore, nitroglycerin increased both cAMP and cGMP concentrations, however, it failed to increase the tissue cAMP concentration in the presence of TTX. VIPa also blocked the increase in content of either cyclic nucleotide. VIP increased cAMP with a TTX-sensitive increase in cGMP content. 8-Bromo cGMP (1 M) significantly increased the tissue cAMP content. This was blocked by either TTX or VIPa (both 1 M). We conclude that ATP-sensitive potassium channel (K_ATP) activation contributes to cGMP-mediated relaxation of the Oddi's sphincter of the rabbit. Activation of K_ATP results from a cyclic AMP-mediated process due to cGMP-dependent VIP release from neurons.     

Serum and tissue zinc concentrations in patients with endoscopic esophagitis

Because zinc is an important metabolic requirement for growth and repair of squamous tissue, we questioned whether changes in serum and esophageal tissue zinc were present in patients with reflux esophagitis. To investigate this question, we prospectively studied 49 patients undergoing upper gastrointestinal endoscopy for symptoms of abdominal pain and discomfort; 19 patients were taking H₂ antagonists at the time of the study. Blood was obtained to measure serum zinc concentrations prior to endoscopy and tissue zinc levels were obtained from esophageal biopsies from the distal, middle, and proximal esophagus in patients who were either endoscopically normal or who exhibited endoscopic esophagitis. Serum zinc concentrations were significantly lower in patients with endoscopic esophagitis compared to the endoscopically normal group (77±3.8 g/dl vs 88±2.4 g/dl,P<0.02). Distal esophageal tissue concentrations were significantly higher in patients with endoscopic esophagitis compared to the endoscopically normal group (200±30 g/liter vs 135±15 g/liter,P<0.05); whereas there were no differences between values obtained in the proximal or middle esophagus. Serum and tissue zinc concentrations in patients with esophagitis receiving H₂ antagonists were more similar to values obtained in patients who were endoscopically normal than to patients with endoscopic esophagitis without treatment. This study suggests that in endoscopic esophagitis: (1) greater amounts of zinc are concentrated in the rapidly proliferating distal esophageal epithelium, (2) the serum zinc pool may serve as a major zinc source, and (3) decreasing esophageal mucosal inflammation with H₂ antagonists may decrease zinc loss via the esophageal epithelium.This protocol (WR-1471) was approved by the WRAMC Human Use Committee/Institutional Review Board and suported by Department of Clinical Investigation FundingThe opinions and assertions contained herein are the private ones of the authors and are not to be construed as official policy of reflecting the views of the Army of the Department of Defense     

Protection by nitecapone against sodium taurocholate-induced damage to cultured gastric cells

The goal of this study was to observe if nitecapone protected against taurocholate-induced damage in primary cultured rat gastric mucosal cells, as well as in a well-differentiated human gastric epithelial cell line (MKN 28). Prostaglandins were measured to analyze the protection mechanism. In primary rat gastric mucosal cell culture, nitecapone 125–250 M protected the cells significantly against damage induced by sodidum taurocholate, increasing cell viability by 31–38%. In the human gastric epithelial cell line, in which mitochondrial activity was measured as an indication of cell viability, nitecapone (62.5–250 M) protected the cells against sodium taurocholate-induced damage by 12–20%. Prostaglandin E₂, thromboxane B₂, and 6-keto-prostaglandin F₁ measurements in the primary cultured rat gastric mucosal cells showed that nitecapone (125 M and 250 M) significantly stimulated prostaglandin E₂ production (84.7% and 61.0%, respectively), and inhibited thromboxane B₂ formation (50% at 250 M), while the 6-keto-prostaglandin F₁ formation was unaffected. Nitecapone had no effect on prostaglandin E₂ production in the MKN 28 epithelial cell line. Indomethacin or aspirin, at concentrations that did not affect cell viability, antagonized the stimulative effect of nitecapone on prostaglandin E₂ formation in the primary cultured rat gastric mucosal cells. Although the prostaglandin E₂ synthesis was blocked, nitecapone still protected against cell damage induced by taurocholate. These results demonstrated the direct and efficacious protection of nitecapone on gastric cell level and suggest that the cytoprotection by nitecapone against taurocholate may not be mediated through the mechanism of stimulated synthesis of prostaglandin E₂.     

Role of prostaglandins in the early phases of experimental gastric carcinogenesis in the rat

Summary The study was initiated to evaluate the effect of N-methyl-N-nitro-N-nitrosoguanidine (NG) on gastric intraluminal prostaglandin release during a 30-day treatment period and to investigate the effect of a stable prostaglandin E¹ analogue (misoprostol) on NG-induced gastric mucosal damage during the same time period. Samples of gastric juice (1 h) were obtained from 40 male Sprague-Dawley rats with chronic gastric fistulas, in basal conditions and after 5, 15 and 30 days of continuous oral administration of NG (120 mg/l) or tap water. Aliquots of gastric juice were titrated with 0.1 M NaOH. Other aliquots were extracted with ethyl acetate and subjected to specific radioimmunoassay for prostaglandin E₂. The severity of gastric mucosal lesions was evaluated in 60 rats after 5 days and 30 days of continuous oral administration of NG (120 mg/l) or NG plus misoprostol (200 g/kg^-1/day^-1) or tap water, and a histological study was carried out. Administration of NG induced a significant decrease of gastric intraluminal prostaglandin E₂ concentration at 15 and 30 days. Oral administration of misoprostol, at non-antisecretory doses, protected the rats against NG-induced gastric mucosal damage. Prostaglandins may be involved in the early phases of experimental gastric carcinogenesis.This work was supported by grants from the Ministry of Education (MPI)