Implications of gastric topical bioactive peptides in ammonia-induced acute gastric mucosal lesions in rats

Response of blood endothelin-1 and nitric oxide activity in duodenal ulcer patients undergoing Helicobacter pylori eradication

AIM: To investigate the effect of Helicobacter pylori eradication on endothelin-1 (ET-1) and nitric oxide (NO) in duodenal ulcer (DU) patients.

METHODS: Sixty-six H pylori-infected active DU patients were consecutively enrolled to receive one-week triple therapy (rabeprazole, amoxicillin and metronidazole) and then one-month rabeprazole therapy. They were asked back to determine ulcer and H pylori status using endoscopy one month later. Thirty-seven healthy controls (H pylori +/-: 17/20) were enrolled for comparison. Blood samples were collected in each visit to measure plasma ET-1 and nitrate/nitrite levels using an enzyme immunoassay kit.

RESULTS: Sixty DU patients finished trial per protocol. The ulcer healing and H pylori-eradication rates were 86.7% and 83.3%, respectively. Plasma ET-1 level in DU patients was higher than that of H pylori-negative and positive controls (3.59±0.96 vs 0.89±0.54 vs 0.3±0.2 pg/mL, P<0.01), while nitrate/nitrite levels among them were also significantly different (8.55±0.71 vs 5.27±0.68 vs 6.39±0.92 µmol/L, P<0.05). H pylori eradication diminished ET-1 levels (3.64±0.55 vs 2.64±0.55 pg/mL, P<0.01) but elevated nitrate/nitrite level (8.16±0.84 vs 11.41±1.42 µmol/L, P<0.05).

CONCLUSION: Both plasma ET-1 and nitrate/nitrite levels increase in active DU patients. After an effective H pylori eradication, DU healing is associated with diminished blood ET-1 level and elevated nitrate/nitrite level.

Changes in endothelin-1 gene expression in the gastric mucosa of rats under cold-restraint-stress

OBJECTIVE

To investigate in rats the role of endothelin (ET)-1 gene expression in the development and progression of acute gastric mucosal lesions (AGML) induced by stress, and the effect of BQ-123 (a special ETA receptor antagonist) on the AGML.

METHODS

A rat model of gastric ulcer induced by cold-restraint-stress (CRS) was used. ET-1 concentrations in the plasma and gastric mucosa were determined by radioimmunoassay (RIA), gastric mucosa blood flow (GMBF) was measured with a laser Doppler flow meter, the ulcer index (UI) was used to estimate the degree of gastric mucosa damage and the expression levels of ET-1 mRNA in the gastric mucosa were measured using dot blot and reverse transcription polymerase chain reaction (RT-PCR). Different doses of BQ-123 were administered via the left femoral vein prior to the stress in order to observe the effects of BQ-123 on the ET-1 concentrations in the plasma and gastric mucosa, the GMBF and the UI.

RESULTS

Compared with the normal controls, the ET-1 concentrations in the plasma and gastric mucosa of the stressed rats were increased significantly (P < 0.05), the GMBF was decreased markedly (P < 0.01), and the UI increased dramatically (P < 0.01). There was a significant positive correlation between the gastric mucosal EF-1 concentration and the UI (r = 0.98, P < 0.01), and a significant negative correlation between the gastric mucosal ET-1 concentration and GMBF (r = -0.89, P < 0.01) and also between the UI and GMBF (r = -0.98, P < 0.01). The expression level of ET-1 mRNA in the gastric mucosa of the stressed rats increased significantly compared with that of the normal controls (P < 0.01), and there was a positive correlation between the expression of ET-1 mRNA and the ET-1 concentration in the gastric mucosa (r = 0.93, P < 0.01). Compared with the untreated animals, the GMBF was increased (P < 0.01) and the UI decreased significantly (P < 0.01) in the BQ-123-treated rats, and the dose of BQ-123 correlated with the degree of change in the GMBF and UI; however, the ET-1 concentrations of either the plasma or the gastric mucosa did not change markedly in the BQ-123-treated animals (P > 0.05).

CONCLUSION

The present study showed that the level of expression of ET-1 mRNA and the synthesis of ET-1 in the gastric mucosa both increased significantly, which suggests that the increased concentration of endogenous ET-1 may be involved in the development and progression of stress ulcer (acute gastric mucosa lesion). The mechanism of action may be associated with a reduction of GMBF induced by ETAR-mediated vasoconstriction. BQ-123 can dose-dependently attenuate significantly the degree of damage to the gastric mucosa induced by stress, and may have therapeutic benefits for stress ulcer.

Intraportal nicotine infusion in rats decreases hepatic blood flow through endothelin-1 and both endothelin A and endothelin B receptors

Smoking has been demonstrated to aggravate liver injury. Nicotine, a major pharmacological component of tobacco smoke, affects a multitude of functions. Smoking and nicotine induce synthesis of endothelin (ET)-1. The effect of intraportal infusion of nicotine on hepatic circulation and an involvement of ET-1 and ET receptor in the action of nicotine were investigated in rats. Nicotine (0-100 microg/kg/h) was infused into the portal vein of urethane-anesthetized rats, and changes of hepatic blood flow were evaluated. Intraportal infusion of nicotine dose-dependently decreased hepatic blood flow and increased portal pressure without any alteration of heart rate or arterial blood pressure. This action of intraportal nicotine was completely abolished by pretreatment of ET-1 antibody. Either BQ485 (ET(A) receptor antagonist) or BQ788 (ET(B) receptor antagonist) partially reversed the effect of nicotine, and combination of BQ788 and BQ485 completely abolished it. These findings suggest that nicotine inhibits hepatic circulation through ET-1, and ET(A) and ET(B) receptor.

Protective effects of endothelin-1 antibody on stress induced lesion of gastric mucosa in rats

AIM

To explore the protective effects of endothelin-1 antibody (ET-1Ab) on acute gastric mucosa lesions induced by stress in rats.

METHODS

Stress ulcer induced by cold-restraint-stress(CRS) was used as model in this study, different dose ET-1Ab were administered by left femoral vein prior to stress so as to observe the effects of the drug on ET-1 levels in plasma and gastric mucosa, gastric mucosa blood flow(GMBF)and ulcer index(UI) of CRS rats.

RESULTS

(1) Compared with the normal control group, ET-1 levels of plasma and gastric mucosa and UI were increased significantly in the stress groups (116.2±4.7 mv and 125.1±4.2 mv vs 49.1±9.7 mv, 113.8±9.3 mv and 122.9±19.6 mv vs 52.3±10.3 mv, 28.6±1.85 mv and 51.2±5.93 mv vs 0, P<0.01), while GMBF were decreased markedly in stress groups (227.8±13.5 mv and 150.8±11.5 mv vs 405.8±23.3 mv, P<0.01).There was significantly positive correlation between ET-1 and UI (r = 0.96, P<0.01), and significantly negative correlation between ET-1 and GMBF(r = -0.91, P<0.01). (2) However, compared with the single-stress groups, ET-1 levels of plasma and gastric mucosa and UI were decreased significantly in ET-1Ab-stress groups (69.2±7.3 mv vs 116.2±24.7 mv, 80.6±12.3 mv vs 125.1±24.2 mv, 58.5±6.3 mv vs 113.8±29.3 mv, 68.9±9.6 mvvs 122.9±19.6 mv, 13.2±2.05 mv vs 28.6±1.85 mv, 25.8±3.62 mv vs 51.2±5.93 mv, P<0.01), GMBF were increased dramatically (329.8±16.3 mv vs 227.8±13.5 mv, 251.9±11.3 mv vs 150.8±1.5 mv, P<0.01), ET-1Ab can dose-dependently reduce levels of the ET-1 and UI, and improve GMBF significantly in cold-restraint-stress.

CONCLUSION

In the course of CRS-induced ulcers, endogenous ET-1 levels of plasma and gastric mucosa were increased significantly, and there were close relationship between ET-1 levels and UI. The increased ET-1 may involve in the pathogenesis of CRS-induced ulcers in rats by its vasoconstriction and marked reduction of GMBF. ET-1Ab can dose-dependently attenuate the degree of gastric mucosa lesions induced by CRS significantly. So it may have therapeutic effect for SU.

Effect of intragastric ammonia on gastrin-, somatostatin-and somatostatin receptor subtype 2 positive-cells in rat antral mucosa

Somatostatin suppresses gastrin and somatostatin secretion via somatostatin receptors (SSTRs). Ammonia produced by Helicobacter pylori has been reported to modify gastric gastrin and somatostatin levels. We investigated the distribution of SSTR-subtype 2 (SSTR-2) in relation to gastrin- and somatostatin-containing cells and the effect of ammonia solution (0.01%-0.1%) administered orally for 2 to 4 weeks on these cells in rat antral mucosa by immunohistochemistry. The majority of SSTR-2 peptide [31-41]-positive cells were located in the basal third of the glands. Double staining experiments revealed that SSTR-2 peptide [31-41]-positive cells are co-localized in 85.0 +/- 2.2% of the gastrin-containing cells and in 34.4 +/- 4.8% of the somatostatin-containing cells. Ammonia solution significantly decreased the number of somatostatin-containing cells and increased the proportion of SSTR-2 peptide [31-41]-labeling in the somatostatin-containing cells in a duration-dependent manner. Maximum changes were observed in rats treated with ammonia solution at the lowest level of 0.01% accompanied by an increase in serum gastrin levels in the portal vein. Sodium hydroxide at the similar pH to 0.01% ammonia solution had no effect. These findings suggest that SSTR-2 are localized in antral endocrine cells and that ammonia solution mainly decreases somatostatin-containing cells without SSTR-2 expression, resulting in an increase in gastrin secretion into the portal vein.

Intraluminal thyrotropin-releasing hormone affects gastric somatostatin and acid secretion through its specific receptor in rats

BACKGROUND

Although thyrotropin-releasing hormone (TRH) is present in the gastric mucosa and juice, the pathophysiologic significance of TRH is poorly understood at the peripheral level of the stomach. In the present study we analyzed the TRH-induced secretion profiles of somatostatin, histamine, and acid in the rat stomach.

METHODS

The effects of intraluminal perfusion of TRH on somatostatin, histamine, and acid and the influence of the specific anti-TRH receptor antibody were investigated by using the rat gastric intraluminal perfusion model.

RESULTS

Intraluminal TRH caused an immediate decrease in somatostatin secretion in a dose-dependent manner, and this change occurred preceding an increase in acid secretion. In contrast, this treatment did not yield any significant changes in histamine contents in the effluent. Pretreatment of the gastric lumen with the anti-TRH receptor antibody caused a complete inhibition of TRH-induced changes in somatostatin and acid secretion.

CONCLUSIONS

These findings suggest that intraluminal TRH affects somatostatin and acid secretion in a paracrine manner via its specific receptor in the rat stomach.