Luminal Acid Loss Research Articles

Prophylactic effect of rebamipide against the irritative and healing impairment actions of alendronate in rat stomachs

We examined the effect of rebamipide, an antiulcer drug, on the mucosal irritative and the healing impairment action of alendronate in rat stomachs. Male SD rats were used to examine the effect of rebamipide in the following 3 experiments. 1) Alendronate applied topically to the chambered stomach under urethane anaesthesia produced a decrease in the transmucosal potential difference and an increase of gastric mucosal blood flow and luminal acid loss, resulting in slight damage to the mucosa. Pretreatment with rebamipide for 3 days had no effect on the changes induced by alendronate. 2) Oral administration of alendronate caused non-haemorrhagic lesions in the stomach within 4 hr. Rebamipide, given either as a single p. o. injection or repeatedly for 7 days, did not significantly affect the lesions induced by alendronate. 3) Alendronate, given p. o. once daily for 1 week, markedly delayed the healing of acetic acid-induced gastric ulcers with the suppression of basic fibroblast growth factor (bFGF) expression. Rebamipide, given twice daily for 7 days, significantly promoted the delayed ulcer healing caused by alendronate, with the concomitant recovery of bFGF expression. These results suggest that rebamipide does not affect the direct irritating action of alendronate in the gastric mucosa, but this agent antagonizes the healing impairment action of alendronate by counteracting the downregulation of bFGF expression in the ulcerated mucosa.

Pathogenic importance of pepsin in ischemia/reperfusion-induced gastric injury

We investigated the role of pepsin in the development of ischemia/reperfusion (I/R)-induced gastric lesions in rats. Under urethane anesthesia, the pylorus was ligated, the celiac artery was clamped, and 1 ml of HCl (50–150 mM) was instilled in the stomach. Then, reperfusion was established 15 min later by removing the clamp, and 2 h later the stomach was assessed for gross mucosal damage. Pepstatin (a specific pepsin inhibitor) or pepsin was given i.g. after the pylorus was ligated while cimetidine, omeprazole, or atropine was given s.c. 30 min before the ligation. I/R produced hemorrhagic gastric injury, with a concomitant increase in the amount of pepsin secreted, and the degree of both these responses was dependent on the concentration of HCl. The formation of lesions by IR in the presence of 100 mM HCl was significantly prevented by atropine or bilateral vagotomy, but neither omeprazole nor cimetidine had any effect. Intragastric administration of pepstatin dose-dependently reduced the severity of the I/R-induced gastric lesions, the effect being significant even at 0.1 mg/kg, while that of pepsin markedly aggravated these lesions. The increased pepsin output during I/R was associated with luminal acid loss and significantly inhibited by bilateral vagotomy or pretreatment with atropine but not cimetidine or omeprazole, while pepstatin significantly inhibited the pepsin activity. In conclusion, we suggest that pepsin plays a pivotal role in the pathogenesis of I/R-induced gastric lesions, and pepsin secretion is increased during I/R, the process being associated with acid back-diffusion and mediated through a vagal-cholinergic pathway.

Prostaglandin E Receptor EP1 Subtype but Not Prostacyclin IP Receptor Involved in Mucosal Blood Flow Response of Mouse Stomachs following Barrier Disruption

Aim: We investigated the role of prostacyclin IP receptors in gastric mucosal protection as well as functional responses induced by taurocholate Na (TC) as a mild irritant using IP receptor knockout mice, in comparison with prostaglandin (PG) E receptor EP1 subtype knockout animals. Methods: Male C57/BL6 mice fasted for 18 h were used under urethane anesthesia. The stomach mounted on an ex vivo chamber was perfused with 20 mM HCl, and the transmucosal potential difference (PD), luminal acid loss, and gastric blood flow (GMBF) were simultaneously measured before and after exposure of the stomach to 20 mM TC for 20 min. Results: Mucosal exposure to TC in wild-type mice caused a marked decrease in PD, followed by an increase in H⁺ loss and GMBF. The PD gradually normalized after removal of TC from the chamber, with minimal damage in the mucosa 1 h later. The increase of GMBF following TC treatment was inhibited by indomethacin with no change in PD reduction or H⁺ loss, resulting in severe lesions in the mucosa. None of these responses induced by TC were significantly altered in IP receptor knockout mice. However, in mice lacking EP1 receptors, TC did not increase GMBF, despite causing PD reduction and acid loss, and resulted in severe damage in the mucosa. Mucosal PGE₂ levels were significantly increased after TC, similarly, in all groups of mice, while levels of 6-keto-PGF_1α showed a slight but not significant increase in all groups. Conclusion: We confirmed the importance of endogenous PGs and EP1 receptors in the adaptive protection and functional responses induced by a mild irritant in mouse stomach and further suggested that IP receptors are not actively involved in maintaining the gastric mucosal integrity under adverse conditions.

Monochloramine impairs mucosal blood flow response and healing of gastric lesions in rats: relation to capsaicin-sensitive sensory neurons.

We examined the effects of monochloramine (NH2Cl) on the gastric mucosal blood flow (GMBF) response and the healing of ethanol-induced gastric lesions in rats. Rats fasted for 18 h were given the 99% ethanol p.o. for induction of gastric lesions, and were fed normally from 1 h later onwards. Monochloramine, at non-ulcerogenic doses (5 to approximately 20 mmol/L), was given p.o. twice daily for 7 days, starting 2 h after ethanol treatment. Gastric lesions caused by ethanol healed almost completely within 7 days with re-epithelialization. The repeated administration of NH2Cl significantly delayed the healing of ethanol-induced gastric lesions in a dose-dependent manner. The damaged mucosa showed a marked rise in H+ permeability, resulting in luminal acid loss, but this process was accompanied by an increase of mucosal blood flow. Monochloramine did not affect the increased mucosal H+ permeability observed in the stomach after damage by ethanol, but significantly inhibited the mucosal hyperemic response associated with luminal acid loss. Prior exposure of the mucosa to NH2Cl (20 mmol/L) did not affect the gastric hyperemic response caused by mucosal application of misoprostol (a prostaglandin E1 derivative) or NOR-3 (a nitric oxide donor), but totally attenuated the increase of GMBF in response to intragastric capsaicin. Impaired healing and GMBF responses were also observed in rats following chemical ablation of capsaicin-sensitive sensory neurons. These results suggest that NH2Cl impaired the healing of acute gastric mucosal lesions at low concentrations, and this action may be attributable, at least partly, to the impairment of gastric hyperemic response caused by the dysfunction of capsaicin-sensitive sensory neurons.

Increased susceptibility of gastric mucosa to ulcerogenic stimulation in diabetic rats--role of capsaicin-sensitive sensory neurons.

1. We examined the gastric mucosal blood flow (GMBF) and ulcerogenic responses following barrier disruption induced by sodium taurocholate (TC) in diabetic rats and investigated the role of capsaicin-sensitive sensory neurons in these responses. 2. Animals were injected streptozotocin (STZ: 70 mg kg(-1), i.p.) and used after 5, 10 and 15 weeks of diabetes with blood glucose levels of > 350 mg dl(-1). The stomach was mounted on an ex-vivo chamber under urethane anaesthesia and exposed to 20 mM TC plus 50 mM HCl for 30 min in the presence of omeprazole. Gastric transmucosal potential difference (PD), GMBF, and luminal acid loss (H+ back-diffusion) were measured before and after exposure to 20 mM TC, and the mucosa was examined for lesions 90 min after TC treatment. 3. Mucosal application of TC caused PD reduction in all groups; the degree of PD reduction was similar between normal and diabetic rats, although basal PD values were lower in diabetic rats. In normal rats, TC treatment caused luminal acid loss, followed by an increase of GMBF, resulting in minimal damage in the mucosa. 4. The increased GMBF responses associated with H+ back-diffusion were mitigated in STZ-treated rats, depending on the duration of diabetes, and severe haemorrhagic lesions occurred in the stomach after 10 weeks of diabetes. 5. Intragastric application of capsaicin increased GMBF in normal rats, but such responses were mitigated in STZ diabetic rats. The amount of CGRP released in the isolated stomach in response to capsaicin was significantly lower in diabetic rats when compared to controls. 6. The deleterious influences on GMBF and mucosal ulcerogenic responses in STZ-diabetic rats were partially but significantly antagonized by daily insulin (4 units rat(-1)) treatment. 7. These results suggest that the gastric mucosa of diabetic rats is more vulnerable to acid injury following barrier disruption, and this change is insulin-sensitive and may be partly accounted for by the impairment of GMBF response associated with acid back-diffusion and mediated by capsaicin-sensitive sensory neurons.

Cyclo-oxygenase isozymes in mucosal ulcergenic and functional responses following barrier disruption in rat stomachs.

1. We examined the effects of selective and nonselective cyclo-oxygenase (COX) inhibitors on various functional changes in the rat stomach induced by topical application of taurocholate (TC) and investigated the preferential role of COX isozymes in these responses. 2. Rat stomachs mounted in ex vivo chambers were perfused with 50 mM HCl and transmucosal potential difference (p.d.), mucosal blood flow (GMBF), luminal acid loss and luminal levels of prostaglandin E2 (PGE2) were measured before, during and after exposure to 20 mM TC. 3. Mucosal application of TC in control rats caused a reduction in p.d., followed by an increase of luminal acid loss and GMBF, and produced only minimal damage in the mucosa 2 h later. Pretreatment with indomethacin (10 mg kg[-1], s.c.), a nonselective COX-1 and COX-2 inhibitor, attenuated the gastric hyperaemic response caused by TC without affecting p.d. and acid loss, resulting in haemorrhagic lesions in the mucosa. In contrast, selective COX-2 inhibitors, such as NS-398 and nimesulide (10 mg kg[-1], s.c.), had no effect on any of the responses induced by TC and did not cause gross damage in the mucosa. 4. Luminal PGE2 levels were markedly increased during and after exposure to TC and this response was significantly inhibited by indomethacin but not by either NS-398 or nimesulide. The expression of COX-1-mRNA was consistently detected in the gastric mucosa before and after TC treatment, while a faint expression of COX-2-mRNA was detected only 2 h after TC treatment. 5. Both NS-398 and nimesulide significantly suppressed carrageenan-induced rat paw oedema, similar to indomethacin. 6. These results confirmed a mediator role for prostaglandins in the gastric hyperaemic response following TC-induced barrier disruption, and suggest that COX-1 but not COX-2 is a key enzyme in maintaining 'housekeeping' functions in the gastric mucosa under both normal and adverse conditions.

Role of nitric oxide in mucosal blood flow response and the healing of HCl-induced lesions in the rat stomach.

The role of nitric oxide (NO) in the gastric mucosal blood flow response and the healing of HCl-induced gastric lesions was investigated in rats. After 18 h fasting rats were given 0.6 N HCl p.o. for the induction of gastric lesions, and 1 h later they were fed normally. After induction of gastric lesions, they were repeatedly administered the NO synthase inhibitors NG-nitro-L-arginine methyl ester (L-NAME 5-20 mg/kg p.o. twice daily) or aminoguanidine (20 mg/kg s.c. once daily) for 7 days. Gastric lesions caused by HCl healed almost completely within 5 days with granulation and to an extent with re-epithelialization. Repeated administration of L-NAME but not aminoguanidine significantly delayed the healing of gastric lesions in a dose-dependent manner. The damaged mucosa secreted less acid, but showed a marked rise in H+ permeability, resulting in luminal acid loss accompanied by an increase of mucosal blood flow. Aminoguanidine did not significantly affect any of these functional changes observed in the stomach after damage by HCl, whereas L-NAME treatment slightly reversed the decreased acid response, increased the luminal H+ loss, and totally inhibited the mucosal hyperemic response associated with luminal acid loss in the damaged mucosa. In addition, the deleterious influences of L-NAME on the mucosal blood flow response and the healing of gastric lesions were significantly antagonized by co-administration of L-arginine but not of D-arginine (500 mg/kg x 2, i.p.). Luminal output of NO2-/NO3- was significantly increased in pylorus-ligated stomachs in control rats on days 3 and 5 after damage, and such increases in gastric NO output were completely attenuated by L-NAME treatment. These results suggest that endogenous NO may contribute to the healing of acute gastric injury by mediating the mucosal hyperemic responses associated with acid back-diffusion and by facilitating acid disposal in the damaged mucosa. NO mediating such responses and participating in the healing aspect of gastric lesions may be produced by the constitutive type of NO synthase.

Increased susceptibility of rat gastric mucosa to ulcerogenic stimulation with aging

We examined the influences of aging on gastric damage and gastric mucosal blood flow (GMBF) responses induced by acid back-diffusion, following the barrier disruption, and investigated the relation of capsaicin-sensitive sensory nerves to these changes. Male Fischer rats 3, 13, and 24 months old were used. Under urethane anesthesia, a rat stomach was mounted on a chamber, and gastric potential difference (PD), luminal H+ loss, and GMBF were measured before, during, and after exposure to 20 mM sodium taurocholate (TC) for 30 min, in the presence of 50 mM HCl. Mucosal exposure to TC caused surface cell damage, PD reduction, and acid back-diffusion (luminal H+ loss) in all groups of rats; delta PD reduction and the amount of H+ loss were not significantly different between young and aged rats. In young rats, a marked increase of GMBF was observed with luminal acid loss following TC treatment, yet it resulted in less damage in the gastric mucosa. In aged rats, however, such GMBF responses were apparently mitigated, leading to a significant worsening of gastric mucosal lesions induced by TC. Mucosal application of capsaicin (0.1 mg/ml) caused an increase of GMBF in young rats, but this response was significantly attenuated in aged rats. In addition, the amount of calcitonin gene-related peptide (CGRP) released in the isolated stomach in response to capsaicin (1 X 10(-5) M) was significantly lower in aged animals when compared to young rats. These findings suggest that the gastric mucosa of aged rats is more vulnerable to acid back-diffusion following the barrier disruption, partly because of dysfunction of GMBF responses mediated by capsaicin-sensitive sensory neurons in the acidic conditions.

The role of capsaicin-sensitive sensory neurons in healing of HCl-lnduced gastric mucosal lesions in rats

Background/Aims: Capsaicin-sensitive sensory neurons are important in protecting the stomach against damage. This study investigated the role of these sensory neurons in the healing of gastric lesions. Methods: Rats fasted for 18 hours were given 1 ml of 0.6N HCI orally for induction of gastric lesions; they were then fed normally from 1 hour later. On various days after HCI treatment, the area of lesion, acid secretion, mucosal DNA synthesis, mucosal H+ permeability, and blood flow responses were measured. Results: Ablation of sensory neurons by capsaicin pretreatment did not affect the development of gastric lesions in response to HCI but significantly delayed the healing of these lesions. The damaged mucosa secreted less acid and had minimal changes in DNA synthesis but showed a marked increase in H+ permeability, resulting in luminal acid loss accompanied by an increase of mucosal blood flow. Sensory deafferentation did not have any influence on such changes in the damaged stomach, except the mucosal hyperemic response to acid. Conclusions: Capsaicin-sensitive sensory neurons may contribute to the healing of gastric lesions by mediating the mucosal hyperemic responses associated with acid back-diffusion and by facilitating acid disposal in the mucosa.

The potentiation of taurocholate-induced rat gastric erosions following parenteral administration of cyclo-oxygenase inhibitors.

Subcutaneous administration of anti-inflammatory doses of aspirin, indomethacin, naproxen and flurbiprofen inhibited prostacyclin formation ex vivo in the luminally-perfused gastric mucosa of anaesthetized rats. These doses of anti-inflammatory compounds potentiated the formation of gastric mucosal erosions following 3 h luminal perfusion of the topical irritant, acidified sodium taurocholate (2 mM in 100 mM HCl). The increase in luminal acid-loss during gastric perfusion of acidified taurocholate was not significantly enhanced by these anti-inflammatory agents. A correlation was found between the increase in gastric erosion formation and the inhibition of mucosal prostacyclin formation ex vivo by intravenous injection of aspirin or ketoprofen during acid-taurocholate perfusion. BW755C, which failed to inhibit mucosal prostacyclin formation ex vivo, did not significantly augment acid-taurocholate induced gastric damage. The present findings support the potentiating interactions between topical irritation and inhibition of gastric cyclo-oxygenase in the genesis of the gastric lesions.

Ion Selective Effects of Salicylate on Antral Mucosa

The effects of luminal salicylate, 5mM, were measured on rates of ion transport by isolated antral mucosa. At neutral luminal pH, salicylate increases Na and decreases Cl permeability. Salicylate does not alter net Na transport but decreases net Cl secretion. At luminal pH 4, the effects of salicylate can be arbitrarily divided into two phases. The intitial phase is associated with an increase in Na and marked decrease in Cl permeability. Subsequently, a greater increase in Na permeability and a marked increase in Cl permeability occurs. Active Na transport persists in the presence of salicylate at pH 4. Indirect evidence also suggests that Cl secretion persists under these conditions, buy at a reduced rate. The rate of luminal acid acid loss also increases in the presence of salicylate. A 4-fold increase in salicylate concentration or decrease in luminal pH from 4 to 3 did not appear to intensify the effects observed for 5 mM salicylate at pH 4. The increase in cation and decrease in anion permeability observed at pH 7 and initially at pH 4 are compatible with an influence of a negative charge of the salicylate anion. The subsequent changes observed in the presence of acid also are compatible with the concept that as the mucosa becomes overwhelmed with acid, a nonspecific increase in permeability occurs. However, the effect of salicylate on active Cl transport is largely independent of acid diffusing into the mucosa.

Histamine Effects on H+ Permeability by Isolated Gastric Mucosa

This study examines the effects of histamine on mucosal permeability to acid by isolated stomach of rabbits. Histamine (9 X 10(-5) M) decreased antral luminal acid loss which could not be accounted for by active H+ secretion or appearance of organic acid. Histamine also increased antral electrical resistance and decreased the unidirectional luminal to serosal flux (Jls) of (14)c-erythritol. Histamine, theophylline, and N(6),O(2)-dibutyryl adenosine 3',5'-monophosphate did not significantly alter secretion by fundus in the presence of salicylate (5 X 10(-3)M). However, after removal of salicylate, these agents stimulated acid secretion. Histamine decreased luminal acid loss by both antrum and fundus treated with salicylate, increased the electrical resistance of these tissues, and decreased Jls erythritol of fundic mucosa. Burimamide (1 X 10(-3) M) inhibited the permeability effects of histamine on antrum and fundus. The data indicate that histamine decreases spontaneous antral mucosal permeability as well as salicylate-induced increase in mucosal permeability of both antrum and fundus. The effects of burimamide suggest that antrum contains H2 receptor sites urelated to acid secretion and that fundus contains H2 receptor sites which also govern permeability but are independent of those related to acid secretion.

Effects of Alcohol on Ion Transport by Isolated Gastric and Esophageal Mucosa

The effects of ethyl alcohol, 20%, were measured on steady state rates of ion transport by isolated mucosa. Luminal, but not serosal, addition of alcohol altered ion transport. Alcohol caused a sustained reduction in apparent basal acid secretion by fundic mucosa. These tissues were resistant to ordinarily effective stimulants of acid secretion (histamine, theophyline, dibutyryl cyclic AMP, and gastrin) by rabbit mucosa. Across antral mucosa, net Na transport was inhibited, and net Cl transport was reduced in the presence of alcohol. The unidirectional fluxes of both ions were increased as was permeability to erythritol. These effects of alcohol did not require the presence of acid in the lumen. The rate of luminal acid loss by antrum was increased by alcohol. Addition of ouabain alone, which inhibits net Na and Cl transport, did not alter the rate of luminal acid loss by antrum. Alcohol, however, still increased the rate of luminal acid loss by antral mucosa treated with ouabain. Alcohol reduced the electrical resistance of fundic and antral mucosa but had no effect on the rate of luminal acid loss or electrical resistance of esophageal mucosa. Luminal application of alcohol inhibits active ion transport in addition to increasing cation and anion permeability. However, inhibition of active transport per se is not necessarily associated with an increase in mucosal permeability.