Protective effect of lafutidine, a novel H2-receptor antagonist, on reflux esophagitis in rats through capsaicin-sensitive afferent neurons

Animal model of acid-reflux esophagitis: pathogenic roles of acid/pepsin, prostaglandins, and amino acids

Esophagitis was induced in rats within 3 h by ligating both the pylorus and transitional region between the forestomach and glandular portion under ether anesthesia. This esophageal injury was prevented by the administration of acid suppressants and antipepsin drug and aggravated by exogenous pepsin. Damage was also aggravated by pretreatment with indomethacin and the selective COX-1 but not COX-2 inhibitor, whereas PGE₂ showed a biphasic effect depending on the dose; a protection at low doses, and an aggravation at high doses, with both being mediated by EP1 receptors. Various amino acids also affected this esophagitis in different ways; L-alanine and L-glutamine had a deleterious effect, while L-arginine and glycine were highly protective, both due to yet unidentified mechanisms. It is assumed that acid/pepsin plays a major pathogenic role in this model of esophagitis; PGs derived from COX-1 are involved in mucosal defense of the esophagus; and some amino acids are protective against esophagitis. These findings also suggest a novel therapeutic approach in the treatment of esophagitis, in addition to acid suppressant therapy. The model introduced may be useful to test the protective effects of drugs on esophagitis and investigate the mucosal defense mechanism in the esophagus.

Possible involvement of host defense mechanism in the suppression of rat acute reflux esophagitis by the particular histamine H2 receptor antagonist lafutidine

AIMS

Gastroesophageal reflux disease is considered to be caused primarily by gastric juice refluxed into the esophagus. Here, we investigated the possible involvement of host defense mechanisms in the development of acute reflux esophagitis using lafutidine, a histamine H(2) receptor antagonist (H(2)RA) with proven gastric mucosal protective effects.

METHODS AND RESULTS

The ligation of both the pylorus and the forestomach of SD rats under anesthesia caused hemorrhagic lesions in the esophageal mucosa at 6 h. Lesion formation was significantly inhibited by treatment with H(2)RAs, including the conventional H(2)RAs famotidine and cimetidine as well as lafutidine. The maximum suppressive abilities of these agents were similar to that of the proton pump inhibitor lansoprazole. Interestingly, unlike famotidine, lafutidine at low doses significantly suppressed esophagitis without inhibiting gastric acid secretion. Note that neither lafutidine nor famotidine inhibited hexosamine output in gastric juice samples obtained 3 h after ligation. Additionally, the protective effect of lafutidine, but not of famotidine, was partly attenuated by the denervation of capsaicin-sensitive afferent nerves with a large dose of capsaicin.

CONCLUSION

The present results indicate that esophageal host-defense via capsaicin-sensitive afferent nerves may contribute to the therapeutic action of lafutidine.

Orally administered L-arginine and glycine are highly effective against acid reflux esophagitis in rats

Background

Reflux esophagitis is caused mainly by excessive exposure of the mucosa to gastric contents. In the present study, we examined the effect of several amino acids on acid reflux esophagitis in rats.

Material/Methods

After 18 h of fasting, acid reflux esophagitis was induced by ligating both the pylorus and the transitional region between the forestomach and the corpus under ether anesthesia, and the animals were killed 4 h later. The severity of esophagitis was reduced by the oral administration of omeprazole, a proton pump inhibitor, or pepstatin, a specific pepsin inhibitor.

Results

The development of esophageal lesions was dose-dependently prevented by L-arginine and glycine, given intragastrically (i.g.) after the ligation, with complete inhibition obtained at 250 mg/kg and 750 mg/kg, respectively, and these effects were not influenced by the prior s.c. administration of indomethacin or L-NAME. By contrast, both L-alanine and L-glutamine given i.g. after the ligation aggravated these lesions in a dose-dependent manner. These amino acids had no effect on acid secretion but increased the pH of the gastric contents to 1.8~2.3 due to their buffering action.

Conclusions

The results confirmed an essential role for acid and pepsin in the pathogenesis of acid reflux esophagitis in the rat model and further suggested that various amino acids affect the severity of esophagitis in different ways, due to yet unidentified mechanisms; L-alanine and L-glutamine exert a deleterious effect on the esophagitis, while L-arginine and glycine are highly protective, independent of endogenous prostaglandins and nitric oxide.

3-Cyclo-propyl-1-(4-methyl-phenyl-sulfon-yl)piperidine-3,5-diol

In the title compound, C(15)H(21)NO(4)S, both hy-droxy groups on the piperidine ring are located in axial positions, whereas the tosyl group and the cyclo-propane ring are in equatorial positions. An intra-molecular O-H⋯O hydrogen bond occurs. In the crystal, mol-ecules form inversion dimers via pairs of O-H⋯O hydrogen bonds, generating cyclic R(4) (4)(8) motifs, as noted previously in related diols.

Prostaglandin EP receptors involved in modulating gastrointestinal mucosal integrity

Endogenous prostaglandins (PGs) play an important role in modulating the mucosal integrity and various functions of the gastrointestinal tract, and E type PGs are most effective in these actions. PGE₂ protected against acid-reflux esophagitis and prevented the development of gastric damage induced by ethanol or indomethacin, the effects mimicked by EP1 agonists and attenuated by an EP1 antagonist. Adaptive cytoprotection induced by mild irritants was also attenuated by the EP1 antagonist. On the other hand, the acid-induced duodenal damage was prevented by EP3/EP4 agonists and worsened by EP3/EP4 antagonists. Similarly, the protective effect of PGE₂ on indomethacin-induced small intestinal damage or DSS-induced colitis was mimicked by EP3/EP4 agonists or EP4 agonists, respectively. The mechanisms underlying these actions of PGE₂ are related to inhibition of stomach contraction (EP1), stimulation of duodenal HCO₃⁻ secretion (EP3/EP4), inhibition of small intestinal contraction (EP4), and stimulation of mucus secretion (EP3/EP4) or down-regulation of cytokine secretion in the colon (EP4), respectively. PGE₂ also showed a healing-promoting effect on gastric ulcers and intestinal lesions through the activation of EP4 receptors, the effect associated with stimulation of angiogenesis via an increase in VEGF expression. These findings should aid the development of new strategies for treatment of gastrointestinal diseases.

Cross-organ sensitization of thoracic spinal neurons receiving noxious cardiac input in rats with gastroesophageal reflux

Gastroesophageal reflux (GER) frequently triggers or worsens cardiac pain or symptoms in patients with coronary heart disease. This study aimed to determine whether GER enhances the activity of upper thoracic spinal neurons receiving noxious cardiac input. Gastric fundus and pyloric ligations as well as a longitudinal myelotomy at the gastroesophageal junction induced acute GER in pentobarbital-anesthetized, paralyzed, and ventilated male Sprague-Dawley rats. Manual manipulations of the stomach and lower esophagus were used as surgical controls in another group. At 4-9 h after GER surgery, extracellular potentials of single neurons were recorded from the T3 spinal segment. Intrapericardial bradykinin (IB) (10 microg/ml, 0.2 ml, 1 min) injections were used to activate cardiac nociceptors, and esophageal distensions were used to activate esophageal afferent fibers. Significantly more spinal neurons in the GER group responded to IB compared with the control group (69.1 vs. 38%, P < 0.01). The proportion of IB-responsive neurons in the superficial laminae of GER animals was significantly different from those in deeper layers (1/8 vs. 46/60, P < 0.01); no difference was found in control animals (7/25 vs. 20/46, P > 0.05). Excitatory responses of spinal neurons to IB in the GER group were greater than in the control group [32.4 +/- 3.5 impulses (imp)/s vs. 13.3 +/- 2.3 imp/s, P < 0.01]. Forty-five of 47 (95.7%) neurons responded to cardiac input and ED, which was higher than the control group (61.5%, P < 0.01). These results indicate that acute GER enhanced the excitatory responses of thoracic spinal neurons in deeper laminae of the dorsal horn to noxious cardiac stimulus.

Lafutidine, a protective H₂ receptor antagonist, enhances mucosal defense in rat esophagus

BACKGROUND

Luminal acid or CO₂ induces a hyperemic response in the esophagus, via activation of acid sensors on capsaicin-sensitive afferent nerves (CSAN). Since disruption of the hyperemic response to luminal CO₂ acidifies the interstitium of the esophageal mucosa, the hyperemic response may maintain interstitial pH (pH(int)). We hypothesized that acid-related hyperemia maintains pH(int), preventing acid-induced injury in the esophageal mucosa.

METHODS

We examined the effects of capsaicin (Cap) or lafutidine (Laf), a mucosal protective H₂ antagonist, on the regulation of pH(int) and blood flow in rat esophagus using ratiometric microimaging and laser-Doppler measurements of the lower esophageal mucosa of living rats. The esophagus was topically superfused with pH 7.0 buffer, or a pH 1.0 or pH 1.0 + pepsin (1 mg/ml) solution with or without Laf.

RESULTS

Cap (30 or 100 µM) or Laf (0.1 or 1 mM) dose-dependently increased blood flow, accompanied by increased pH(int). The pH 1.0 solution increased blood flow without pH(int) change, whereas Laf (1 mM) increased blood flow and pH(int) during acid exposure. The effects of Laf were abolished by ablation of CSAN. Perfusion of the acidified pepsin solution gradually decreased pH(int), inhibited by Laf perfusion.

CONCLUSIONS

Activation of CSAN by Laf with or without acid, accompanied by hyperemia, increased pH(int), preventing acidified pepsin-induced interstitial acidification. Stimulation of the capsaicin pathway with compounds such as Laf enhances mucosal protection from acid-related injury in the upper gastrointestinal tract.

Effect of Lonicerae Flos extracts on reflux esophagitis with antioxidant activity

AIM: To observe the effects of traditional antiinflammatory medicine Lonicerae Flos (LF) on rat reflux esophagitis (RE) induced by pylorus and forestomach ligation compared with the well-known proton antioxidant, α-tocopherol.

METHODS: Rats were pretreated with three different dosages of LF (500, 250 and 125 mg/kg) orally, once a day for 14 d before pylorus and forestomach ligation. Nine hours after pylorus and forestomach ligation, changes to the stomach and esophagus lesion areas, gastric volumes, acid and pepsin outputs, antioxidant effects, esophageal lipid peroxidation, superoxide dismutase (SOD), catalase (CAT), malondialdehyde (MDA), myeloperoxidase and glutathione (GSH) levels, and collagen contents (marker of flexibility) were observed on the esophageal and fundic histopathology. The results were compared with an α-tocopherol (once orally, 1 h before operation, 30 mg/kg) treated group in which the effects on RE were already confirmed.

RESULTS: Pylorus and forestomach ligations caused marked increases of gross esophageal and gastric mucosa lesion areas, which corresponded with histopathological changes. In addition, increases of esophageal lipid peroxidation, decreases of SOD, CAT, and GSH-free radical scavengers, increases of collagen were observed. However, these pylorus and forestomach ligation induced RE were dose-dependently inhibited by treatment of 500, 250 and 125 mg/kg of LF extract, mediated by antioxidant effects. RE at 250 mg/kg showed similar effects α-tocopherol.

CONCLUSION: The results suggest that antioxidant effects of LF could attenuate the severity of RE and prevent the esophageal mucosal damage, and validate its therapeutic use in esophageal reflux disease.

The neural regulation of the mammalian esophageal motility and its implication for esophageal diseases

In contrast to the tunica muscularis of the stomach, small intestine and large intestine, the external muscle layer of the mammalian esophagus contains not only smooth muscle but also striated muscle fibers. Although the swallowing pattern generator initiates the peristaltic movement via vagal preganglionic neurons that project to the myenteric ganglia in the smooth muscle esophagus, the progressing front of contraction is organized by a local reflex circuit composed by intrinsic neurons similarly to other gastrointestinal tracts. On the other hand, the peristalsis of the striated muscle esophagus is both initiated and organized by the swallowing pattern generator via vagal motor neurons that directly innervate the muscle fibers. The presence of a distinct ganglionated myenteric plexus in the striated muscle portion of the esophagus had been enigmatic and neglected in terms of peristaltic control for a long time. Recently, the regulatory roles of intrinsic neurons in the esophageal striated muscle have been clarified. It was reported that esophageal striated muscle receives dual innervation from both vagal motor fibers originating in the brainstem and varicose intrinsic nerve fibers originating in the myenteric plexus, which is called 'enteric co-innervation' of esophageal motor endplates. Moreover, a putative local neural reflex pathway that can control the motility of the striated muscle was identified in the rodent esophagus. This reflex circuit consists of primary afferent neurons and myenteric neurons, which can modulate the release of neurotransmitters from vagal motor neurons in the striated muscle esophagus. The pathogenesis of some esophageal disorders such as achalasia and gastroesophageal reflux disease might be involved in dysfunction of the neural networks including alterations of the myenteric neurons. These evidences indicate the physiological and pathological significance of intrinsic nervous system in the regulation of the esophageal motility. In addition, it is assumed that the components of intrinsic neurons might be therapeutic targets for several esophageal diseases.

Prolonged esophagitis after primary dysfunction of the pyloric sphincter in the rat and therapeutic potential of the gastric pentadecapeptide BPC 157

Seven or fourteen days or twelve months after suturing one tube into the pyloric sphincter (removed by peristalsis by the seventh day), rats exhibit prolonged esophagitis with a constantly lowered pressure not only in the pyloric, but also in the lower esophageal sphincter and a failure of both sphincters. Throughout the esophagitis experiment, gastric pentadecapeptide BPC 157 (PL 14736) is given intraperitoneally once a day (10 microg/kg, 10 ng/kg, last application 24 h before assessment), or continuously in drinking water at 0.16 microg/ml, 0.16 ng/ml (12 ml/rat per day), or directly into the stomach 5 min before pressure assessment (a water manometer connected to the drainage port of a Foley catheter implanted into the stomach either through an esophageal or duodenal incision). This treatment alleviates i) the esophagitis (macroscopically and microscopically, at either region or interval), ii) the pressure in the pyloric sphincter, and iii) the pressure in the lower esophageal sphincter (cmH2O). In the normal rats it increases lower esophageal sphincter pressure, but decreases the pyloric sphincter pressure. Ranitidine, given using the same protocol (50 mg/kg, intraperitoneally, once daily; 0.83 mg/ml in drinking water; 50 mg/kg directly into the stomach) does not have an effect in either rats with esophagitis or in normal rats.

Increases in vanilloid TRPV1 receptor protein and CGRP content during endotoxemia in rats

The aim of the present study was to determine whether the transient receptor potential vanilloid (TRPV1) receptor protein as well as the calcitonin gene-related peptide (CGRP) content could be enhanced after the i.p. administration of 5 mg/kg lipopolysaccharide (LPS) to Sprague-Dawley rats. In tongue tissue, used as a representative model of TRPV1 receptors expression, there was a significant increase in the abundance of TRPV1 receptor protein 6 h after LPS administration. In mesenteric arteries, the density of the CGRP-positive nerves as well as the release of CGRP induced by 10 microM anandamide was also significantly increased 6 h after LPS administration. The relaxant responses induced by anandamide in mesenteric beds isolated from either untreated or LPS-treated rats were abolished after a 2 h exposure to 10 microM capsaicin. Moreover, anandamide-induced relaxations of untreated mesenteries were potentiated by the protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA, 0.1 microM), but not by its inactive analogue 4alpha-phorbol (0.1 microM). The potentiation of anandamide effects caused by the PKC activator was accompanied by a significant increase in the overflow of CGRP induced by anandamide in the untreated rats. It is proposed that the overexpression of the TRPV1 receptors and the increased content of CGRP could contribute to the enhancement of anandamide effects during the endotoxemic shock. An eventual phosphorylation event linked to the overflow of CGRP could also participate in the enhanced relaxation caused by anandamide in endotoxemia.

An experimental model of prolonged esophagitis with sphincter failure in the rat and the therapeutic potential of gastric pentadecapeptide BPC 157

We report a simple novel rat model that combines prolonged esophagitis and parallel sphincters failure. The anti-ulcer gastric pentadecapeptide BPC 157, which was found to be stable in gastric juice, and is being evaluated in inflammatory bowel disease trials, is an anti-esophagitis therapy that recovers failed sphincters. Twelve or twenty months after the initial challenge (tubes sutured into sphincters for one week and then spontaneously removed by peristalsis), rats exhibit prolonged esophagitis (confluent hemorrhagic and yellowish lesions, thinner epithelium and superficial corneal layer, with stratification derangement); constantly lowered pressure of both sphincters (assessed by using a water manometer connected to the drainage port of a Foley catheter implanted into the stomach either through esophageal or duodenal incision); and both lower esophageal and pyloric sphincter failure. Throughout the esophagitis experiment, BPC 157 was given at either 10 micro g/kg, i.p., once a day (last application 24 h before assessment) or alternatively, it was given continuously in drinking water at 0.16 micro g/ml (12 ml/rat). This treatment recovers i) esophagitis (macroscopically and microscopically, at either region or investigated time period) and ii) pressure in both sphincters (cmH2O). In addition, BPC 157 (10 micro g/kg) or saline (1 ml/rat, 5 ml/kg) was specifically given directly into the stomach; pressure assessment was performed at 5 min thereafter. The effect of BPC 157 is specific because in normal rats, it increases lower esophageal sphincter-pressure, but decreases pyloric sphincter-pressure. Ranitidine, given as the standard drug using the same protocol (50 mg/kg, i.p., once daily; 0.83 mg/ml in drinking water; or 50 mg/kg directly into the stomach) had no effect.

Calcitonin gene-related peptide and somatostatin releases correlated with the area under the lafutidine concentration–time curve in human plasma

OBJECTIVE

To examine the effects of the histamine H(2)-receptor antagonist, lafutidine, at clinical dosage (10 mg tablet after a standardized meal) on plasma levels of the gastrointestinal peptides, calcitonin gene-related peptide (CGRP), somatostatin and gastrin.

METHODS

Six healthy male volunteers ate a standardized meal, and received either lafutidine orally at a dose of 10 mg or water only (control). Blood samples were taken before and up to 4 h after the drug administration. Plasma lafutidine concentrations were determined by high pressure liquid chromatography. Pharmacokinetic analysis of lafutidine was performed using one-compartmental model. The levels of immunoreactive substances of plasma CGRP, somatostatin and gastrin were measured by enzyme immunoassay, and the amount of peptide release was calculated by the trapezoidal method. Lafutidine significantly increased plasma CGRP levels at 1, 1.5, 2.5 and 4 h and the total amount of CGRP release (192 +/- 14.0 pg.h/mL) compared with the control group (128 +/- 21.5 pg.h/mL).

RESULTS

Lafutidine significantly increased the plasma somatostatin levels at 1 and 1.5 h, and the total amount of somatostatin released (107 +/- 18.2 pg.h/mL) compared with the control (78.4 +/- 7.70 pg.h/mL). The area under the drug concentration-time curve (AUC) from 0 to 4 h after administration correlated well with the Delta-CGRP and Delta-somatostatin release but not with total amount of gastrin released. However, plasma gastrin levels were significantly elevated at 1.5 h after drug administration.

CONCLUSION

Lafutidine at clinical dosage increases plasma CGRP and the somatostatin. The amounts released correlated with the AUC of lafutidine in humans. These results suggest that the increased release of CGRP and somatostatin may contribute to its gastroprotective and anti-acid secretory effect.

Characterization of chronic constriction of the saphenous nerve, a model of neuropathic pain in mice showing rapid molecular and electrophysiological changes

Neuropathic pain is one of the most inextricable problems encountered in clinics, because few facts are known about its etiology. Nerve injury often leads to allodynia and hyperalgesia, which are symptoms of neuropathic pain. The aim of this study was to understand some molecular and electrophysiological mechanisms of neuropathic pain after chronic constriction of the saphenous nerve (CCS) in mice. After surgery, CCS mice displayed significant allodynia and hyperalgesia, which were sensitive to acute systemic injection of morphine (4 mg/kg), gabapentin (50 mg/kg), amitriptyline (10 mg/kg), and the cannabinoid agonist WIN 55,212-2 (5 mg/kg). These behavioral changes were accompanied after surgery by an increase of c-Fos expression and by an overexpression of mu-opioid and cannabinoid CB1 and CB2 receptors in the spinal cord and the dorsal hind paw skin. In combination with the skin-nerve preparation, this model showed a decrease in functional receptive fields downstream to the injury and the apparition of A-fiber ectopic discharges. In conclusion, CCS injury induced behavioral, molecular, and electrophysiological rearrangements that might help us in better understanding the peripheral mechanisms of neuropathic pain. This model takes advantage of the possible use in the future of genetically modified mice and of an exclusively sensory nerve for a comprehensive study of peripheral mechanisms of neuropathic pain.

Carbonic anhydrases and mucosal vanilloid receptors help mediate the hyperemic response to luminal CO2 in rat duodenum

BACKGROUND & AIMS

The duodenal mucosa is exposed to PCO(2) >200 mm Hg due to the luminal mixture of gastric acid with secreted bicarbonate, which augments mucosal protective mechanisms. We examined the hyperemic response to elevated luminal PCO(2) in the duodenum of anesthetized rats luminally exposed to high CO(2) saline to help elucidate luminal acid-sensing mechanisms.

METHODS

Blood flow was measured by laser Doppler, and intracellular pH of epithelial cells by measured by ratio microimaging. The permeant carbonic anhydrase (CA) inhibitor methazolamide, relatively impermeant CA inhibitor benzolamide, vanilloid receptor antagonist capsazepine, or sodium-hydrogen exchanger 1 (NHE-1) inhibitor dimethyl amiloride were perfused with or without the high CO(2) solution.

RESULTS

The high CO(2) solution increased duodenal blood flow, which was abolished by pretreatment with methazolamide or capsazepine or by dimethyl amiloride coperfusion. Sensory denervation with capsaicin also abolished the CO(2) effects. Benzolamide dose-dependently inhibited CO(2)-induced hyperemia and at 100 nmol/L inhibited CO(2)-induced intracellular acidification. The membrane-bound CA isoforms IV, IX, XII, and XIV and cytosolic CA II and the vanilloid receptor 1 (TRPV1) were expressed in duodenum and stomach. Dorsal root ganglion and nodose ganglion expressed all isoforms except for CA IX.

CONCLUSIONS

The duodenal hyperemic response to luminal CO(2) is dependent on cytosolic and membrane-bound CA isoforms, NHE-1, and TRPV1. CO(2)-induced intracellular acidification was inhibited by selective extracellular CA inhibition, suggesting that CO(2) diffusion across the epithelial apical membrane is mediated by extracellular CA. NHE-1 activation preceding TRPV1 stimulation suggests that luminal CO(2) is sensed as H(+) in the subepithelium.

Gastro-protective action of lafutidine mediated by capsaicin-sensitive afferent neurons without interaction with TRPV1 and involvement of endogenous prostaglandins

AIM: Lafutidine, a histamine H₂ receptor antagonist, exhibits gastro-protective action mediated by capsaicin-sensitive afferent neurons (CSN). We compared the effect between lafutidine and capsaicin, with respect to the interaction with endogenous prostaglandins (PG), nitric oxide (NO) and the afferent neurons, including transient receptor potential vanilloid subtype 1 (TRPV1).

METHODS: Male SD rats and C57BL/6 mice, both wild-type and prostacyclin IP receptor knockout animals, were used after 18 h of fasting. Gastric lesions were induced by the po administration of HCl/ethanol (60% in 150 mmol/L HCl) in a volume of 1 mL for rats or 0.3 mL for mice.

RESULTS: Both lafutidine and capsaicin (1-10 mg/kg, po) afforded dose-dependent protection against HCl/ethanol in rats and mice. The effects were attenuated by both the ablation of CSN and pretreatment with N^G-nitro-L-arginine methyl ester, yet only the effect of capsaicin was mitigated by prior administration of capsazepine, the TRPV1 antagonist, as well as indomethacin. Lafutidine protected the stomach against HCl/ethanol in IP receptor knockout mice, similar to wild-type animals, while capsaicin failed to afford protection in the animals lacking IP receptors. Neither of these agents affected the mucosal PGE₂ or 6-keto PGF_1α contents in rat stomachs. Capsaicin evoked an increase in [Ca²⁺]i in rat TRPV1-transfected HEK293 cells while lafutidine did not.

CONCLUSION: These results suggest that although both lafutidine and capsaicin exhibit gastro-protective action mediated by CSN, the mode of their effects differs regarding the dependency on endogenous PGs/IP receptors and TRPV1. It is assumed that lafutidine interacts with CSN at yet unidentified sites other than TRPV1.

Essential role of pepsin in pathogenesis of acid reflux esophagitis in rats

Pepsin, a protease activated by gastric acid, is a component of the refluxate, yet the role of pepsin in the pathogenesis of reflux esophagitis has not been well studied. In the present study, we examined the effect of pepstatin, a specific inhibitor of pepsin, on acid reflux esophagitis. Acid reflux esophagitis was induced in rats by ligating both the pylorus and the forestomach for 3 or 4 hr. Pepstatin, ecabet Na (the anti-ulcer drug), and L-glutamine were administered intragastrically after the ligation. Pepstatin or ecabet Na, given intragastrically, significantly prevented esophageal lesions, even though they did not affect basal acid secretion in pylorus-ligated rats. Pepstatin significantly inhibited pepsin activity in vivo and in vitro, while ecabet Na inhibited this activity in vitro. By contrast, L-glutamine given intragastrically aggravated the lesions in a dose-dependent manner, but even in the presence of L-glutamine the development of esophageal lesions was totally prevented by coadministration of pepstatin or ecabet Na. L-Glutamine increased the pH of gastric contents to approximately 2.0, the optimal pH for the proteolytic activity of pepsin in vitro. In addition, intragastric administration of exogenous pepsin worsened the severity of esophageal damage. These results suggest that pepstatin is highly effective against acid reflux esophagitis, without influencing acid secretion, while L-glutamine aggravated these lesions by increasing the pepsin activity by shifting the intraluminal pH to the optimal pH range for proteolytic action. It is assumed that pepsin plays a major pathogenic role in the development of acid reflux esophagitis.

Lafutidine, a newly developed antiulcer drug, elevates postprandial intragastric pH and increases plasma calcitonin gene-related peptide and somatostatin concentrations in humans: comparisons with famotidine

Lafutidine, a newly developed histamine H(2)-receptor antagonist, inhibits daytime (i.e., postprandial) as well as nighttime gastric acid secretion in clinical studies. It also has gastroprotective activity that particularly affects mucosal blood flow in rats. This study focused on the efficacy of lafutidine on plasma concentrations of gastrointestinal peptides in humans. Six healthy male volunteers aged 23-32 years without Helicobacter pylori infection were orally administered either 10 mg lafutidine, 20 mg famotidine, or water only (control) 30 min after a standard meal (650 kcal). Plasma concentrations of lafutidine and famotidine were highest from 90 to 150 min after administration. Intragastric pH was elevated after both lafutidine and famotidine compared with the control. Plasma concentrations of calcitonin gene-related peptide (CGRP) and somatostatin were significantly increased after lafutidine at 60 and 90 min. We concluded that lafutidine increases plasma concentrations of CGRP and somatostatin in humans, which may result in inhibition of postprandial acid secretion and gastroprotective activity.

Determination of lafutidine in human plasma by high-performance liquid chromatography-electrospray ionization mass spectrometry: application to a bioequivalence study

A rapid, sensitive and specific high-performance liquid chromatography-electrospray ionization mass spectrometry (LC/ESI-MS) method was developed and validated for the first time to determine the concentration of lafutidine in human plasma. After the addition of diazepam (the internal standard, IS) and 1 M sodium hydroxide solution to 0.5-ml plasma sample, lafutidine was extracted from plasma with n-hexane : isopropanol (95 : 5, v/v). The organic layer was evaporated and the residue was redissolved in 200-microl mobile phase. The analyte was chromatographically separated on a prepacked Shimadzu Shim-pack VP-ODS C(18) column (250 x 2.0 mm i.d.) using a mixture of methanol-water (20 mM CH(3)COONH(4)) = 80 : 20 (v/v) as mobile phase. Detection was performed on a single quadrupole mass spectrometer using an electrospray ionization interface and the selected-ion monitoring (SIM) mode. The method showed excellent linearity (r = 0.9993) over the concentration range of 5-400 ng/ml and had good accuracy and precision. The within- and between-batch precisions were within 10% relative standard deviation. The limit of detection was 1 ng/ml. The validated LC/ESI-MS method has been successfully applied to the bioequivalence study of lafutidine in 24 healthy male Chinese volunteers.

Distribution of the vanilloid (capsaicin) receptor type 1 in the human stomach

Vanilloid receptor type 1 (TRPV1) is expressed in a capsaicin-sensitive and peptide-containing sub-population of primary sensory nerves that in the rat stomach seems involved in regulation of chlorhydropeptic secretion and gastroprotection. Our aim was to identify which cell types express TRPV1 in the human stomach in order to gain a better insight in the role of this receptor in the regulation of HCl secretion. Immunohistochemistry, by using three different commercially available anti-capsaicin antibodies, in situ hybridisation and Western blot analysis were performed on fragments surgically obtained from the gastric body on the large curvature. TRPV1 labelling was found in the parietal cells at the level of intra-cytoplasmatic granules matching mitochondrial features and distribution. Immunolabelled neurons and nerve fibres were also seen, the latter numerous in the submucosa and mucosa and often ending close to the parietal cells. TRPV1 presence was confirmed by Western blot analysis and in situ hybridisation. TRPV1 presence in nerve structures and parietal cells suggests the possibility of a combined effect of both neuronal and epithelial TRPV1 on chlorhydropeptic secretion. The presumed TRPV1 mitochondrial location inside parietal cells is in favour of the existence of a local pathway of auto-regulation of HCl secretion. Therefore, TRPV1 might modulate chlorhydropeptic secretion in the human stomach through more complex pathways than previously thought.

Behavioral, pharmacological and molecular characterization of the saphenous nerve partial ligation: A new model of neuropathic pain

The saphenous partial ligation (SPL) model is a new, easily performed, rodent model of neuropathic pain that consists of a unilateral partial injury to the saphenous nerve. The present study describes behavioral, pharmacological and molecular properties of this model. Starting between 3 and 5 days after surgery, depending on the modality tested, animals developed clear behaviors indicative of neuropathic pain such as cold and mechanical allodynia, and thermal and mechanical hyperalgesia compared with naive and sham animals. These pain behaviors were still present at 1 month. Signs of allodynia also extended to the sciatic nerve territory. No evidence of autotomy or bodyweight loss was observed. Cold and mechanical allodynia but not thermal and mechanical hyperalgesia was reversed by morphine (4 mg/kg i.p.). The cannabinoid receptor agonist WIN 55,212-2 (5 mg/kg i.p.) improved signs of allodynia and hyperalgesia tested except for mechanical hyperalgesia. Gabapentin (50 mg/kg i.p.) was effective against cold and mechanical allodynia but not hyperalgesia. Finally, amitriptyline (10 mg/kg i.p.) failed to reverse allodynia and hyperalgesia and its administration even led to hyperesthesia. Neurobiological studies looking at the expression of mu opioid receptor (MOR), cannabinoid CB(1) and CB(2) receptors showed a significant increase for all three receptors in ipsilateral paw skin, L3-L4 dorsal root ganglia and spinal cord of neuropathic rats compared with naive and sham animals. These changes in MOR, CB(1) and CB(2) receptor expression are compatible with what is observed in other neuropathic pain models and may explain the analgesia produced by morphine and WIN 55,212-2 administrations. In conclusion, we have shown that the SPL is an adequate model that will provide a new tool for clarifying peripheral mechanisms of neuropathic pain in an exclusive sensory nerve.