Histological effect of (R)-alpha-methylhistamine on ethanol damage in rat gastric mucosa: influence on mucus production

Influence of the Novel Histamine H3 Receptor Antagonist/Inverse Agonist M39 on Gastroprotection and PGE2 Production Induced by (R)-Alpha-Methylhistamine in C57BL/6 Mice

The role of histamine H3 receptors (H3Rs) in the regulation of gastroprotection and production of prostaglandin E2 (PGE2) as well as somatostatin remains contradictory. Therefore, the effects of the H3R antagonist/inverse agonist M39 on in vivo acidified ethanol-induced gastric ulcers and gastric acid secretion in the C57BL/6 mice were assessed. Results showed that acute systemic administration of H3R agonist (R)-α-methylhistamine (RAMH, 100 mg/kg, i.g.) significantly reduced the severity of ulcer index, increased gastric acid output, and increased mucosal PGE2 production without any alteration of somatostatin concentration in gastric juice. However, only acute systemic administration of the H2R agonist dimaprit (DIM, 10 mg/kg, p.o.) significantly decreased the level of somatostatin measured in gastric juice. Moreover, acute systemic administration of M39 (0.3 mg/kg, i.g.) abrogated the RAMH-induced increase of acid output as well as PGE2 production, but not the DIM (10 mg/kg, i.g.)-stimulated acid secretion, indicating that RAMH as well as M39 modulate the gastroprotective effects through interactions with histamine H3Rs. The present findings indicate that agonistic interaction with H3Rs is profoundly involved in the maintenance of gastric mucosal integrity by modulating PGE2 as well as gastric acid secretion, with no apparent role in the regulation of the inhibitory influence of somatostatin.

Campomanesia lineatifolia Ruiz & Pav. as a gastroprotective agent

ETHNOPHARMACOLOGICAL RELEVANCE

Campomanesia lineatifolia Ruiz and Pav. (Myrtaceae) is a native edible species found in the Amazon Rainforest, commonly known as gabiroba. In Brazil, Campomanesia species are frequently used in traditional medicine for gastrointestinal disorders.

MATERIALS AND METHODS

The present study performed phytochemical analyses and determined both the in vitro antioxidant activity of the ethanolic extract of Campomanesia lineatifolia leaves (EEC) as well as its ethyl acetate fraction (EAFC). In this analysis, quercetin was used as a positive control. Gastroprotective activity was also investigated at different oral doses in two experimental models in rats - gastric lesion induced by ethanol and gastric lesion induced by indomethacin. In this analysis, cimetidine and sucralfate were used as positive controls. The area of gastric lesion underwent macroscopic and histomorphometric evaluations, while the mucus content was estimated by applying the periodic acid-Schiff stain. Oral acute toxicity was also assessed.

RESULTS

Phytochemical studies revealed the presence of flavonoids and tannins. Catechin and quercitrin were isolated by bioguided chromatographic fractionation of EAFC. EEC and EAFC presented in vitro antioxidant activity. The oral administration of EEC and EAFC at doses 100-400 mg/kg (ethanol model) and at doses of 400-1200 mg/kg (indomethacin model) proved to be effective in preventing gastric ulcerations in rats. Pretreatment with EAFC (400mg/kg) significantly increased the gastric mucus content in the ethanol model. No animals died during the acute oral toxicology test.

CONCLUSIONS

Results confirm the Brazilian ethnopharmacological use of Campomanesia lineatifolia as a gastroprotective agent and indicate that the anti-ulcer effect is most likely mediated by scavenging free radicals due to the polyphenol content and, at least in part, by increasing the mucus secretion and the mucosal defense. In addition, EEC and EAFC were found to be safe when applied to a 2000 mg/kg single oral dose.

Ligands for histamine H(3) receptors modulate cell proliferation and migration in rat oxyntic mucosa

1. (R)-alpha-methylhistamine, a selective agonist of histamine H(3) receptors, promotes mucus secretion and increases the number and volume of mucus-secreting cells. The hypothesis that the increased number of mucous cells could reside in an alteration of homeostasis in the gastric epithelium was investigated. 2. (R)-alpha-methylhistamine was administered to rats 1 h (10-100 mg kg(-1) by intragastric and by intraperitoneal route) and 24 h (100 mg kg(-1) by intragastric route) prior to killing. The (S)-isomer of alpha-methylhistamine (55.4 mg kg(-1)), 100 times less potent than the (R)-isomer at H(3) receptors, and the H(3)-receptor agonist FUB 407 (9.14-91.35 mg kg(-1)) were intragrastically administered 1 h prior to killing. The H(1)-receptor antagonist mepyramine (30 mg kg(-1)), the H(2)-receptor antagonist famotidine (3 mg kg(-1)), and the H(3)-receptor antagonists ciproxifan (3 mg kg(-1)) and clobenpropit (30 mg kg(-1)) were intragastrically administered 30 min before (R)-alpha-methylhistamine. Gastric tissue was processed for histology and immunohistochemistry. 3. Within 1 h, (R)-alpha-methylhistamine and FUB 407 dose-dependently increased the number of BrdU-positive cells and of apoptotic cells. (S)-alpha-methylhistamine failed to modify proliferation and apoptosis. The increase in proliferation by (R)-alpha-methylhistamine was reversed by ciproxifan and clobenpropit, but not by mepyramine and famotidine. 4. (R)-alpha-methylhistamine accelerated the differentiation towards pit cells and their outward migration 24 h after its administration. These effects were counteracted by ciproxifan. The apoptosis rate was unaffected at 24 h. 5. These findings reveal a primary role of histamine H(3)-receptor ligands in modulating cell proliferation and migration in rat fundic mucosa.

Seriate histomorphometry of whole rat stomach: an accurate and reliable method for quantitative analysis of mucosal damage

The evaluation of mucosal damage in experimental models of gastric injury is commonly based on macroscopic detection of gross lesions and/or histological examination of tissue samples and is limited by the subjectivity of the examiner and by the paucity of nonrepresentative samples. This study proposes a novel method for the histomorphometric analysis of gastric damage, based on the examination of seriate parallel strips taken from whole rat stomachs. Strips were cut perpendicular to the lesser curvature, placed on a glass slide, with the side of each strip distal to the pylorus upward, and processed for routine histology. Sections were then observed by light microscopy: the length of damaged mucosa divided by the total length of mucosa, measured on a micrometric scale and expressed in percentage values, was indicated as the lesion index. Furthermore, to evaluate the severity of the damage, three types of lesions were discriminated depending on their depth: type I, lysis of luminal cells; type II, damage involving the cells lying on both surface mucosa and gastric pits; and type III, damage involving the lower part of the lamina propria with injury of glands associated with detachment of whole mucosal layers. Three models of acute gastric damage (ethanol, hemorrhagic shock, and indomethacin) were examined and treatment was also carried out with the antiulcer drugs omeprazole, ranitidine, and misoprostol, to show the advantages of this histomorphometric approach. The results indicate that this method allows an accurate quantitative analysis of gastric damage, and the effects of different antiulcer drugs can be better discriminated.

Involvement of gastrin in gastric secretory and protective actions of N-alpha-methyl histamine

N alpha-methylhistamine (N alpha-MH) is one of an unusual metabolite of histamine that was found in Helicobacter pylori-infected stomachs and is believed to interact with specific histamine H(1), H(2) and H(3)-receptors to stimulate gastric acid secretion and gastrin release from isolated G-cells but the effects of N alpha-MH on gastric mucosal integrity have been little studied. This study was designed; (1) to compare the effect of exogenous N alpha-MH with that of standard histamine on gastric secretion and plasma gastrin levels in rats equipped with gastric fistula (series A); and (2) to assess the action of N alpha-MH on gastric lesions induced by 100% ethanol (series B) in rats with or without removal of antral portion of the stomach (antrectomy). Rats of series B were pretreated intragastrically (i.g.) or intraperitoneally (i.p.) with N alpha-MH or histamine (0.1-2 mg/kg) 30 min prior to 100% ethanol (1.5 ml, i.g.) with or without: (1) vehicle (saline); (2) RPR 102681 (30 mg/kg i.p.), to block CCK-B/gastrin receptors; and (3) ranitidine (40 mg/kg s.c.) to inhibit histamine H(2)-receptors. The area of gastric lesions was determined planimetrically, gastric blood flow (GBF) was assessed by H(2)-gas clearance method and venous blood was collected for determination of plasma gastrin levels by radioimmunoassay (RIA). N alpha-MH and histamine dose-dependently increased gastric acid output (series A); the dose increasing this secretion by 50% (ED(50)) being 2 and 5 mg/kg i.g or i.p., respectively, and this effect was accompanied by a significant rise in plasma gastrin levels. Both, N alpha-MH and histamine attenuated dose-dependently the area of gastric lesions induced by 100% ethanol (series B) while producing significant rise in the GBF and plasma immunoreactive gastrin increments. These secretory, protective, hipergastrinemic and hyperemic effects of N alpha-MH and histamine were completely abolished by antrectomy, whereas pretreatment with RPR 102681 attenuated significantly the N alpha-MH and histamine-induced protection against ethanol damage and accompanying hyperemia. Ranitidine, that produced achlorhydria and a further increase in plasma gastrin levels, failed to influence the N alpha-MH- and histamine-induced protection and accompanying rise in the GBF. We conclude that (1) N alpha-MH stimulates gastric acid secretion and exhibit gastroprotective activity against acid-independent noxious agents in the manner similar to that afforded by histamine; and (2) this protection involves an enhancement in the gastric microcirculation and release of gastrin acting via specific CCK-B/gastrin receptors but unexpectedly, appears to be unrelated to histamine H(2)-receptors.

Rapid onset of (R)-alpha-methylhistamine protection in response to ethanol-induced histologic damage in rat gastric mucosa

The influence of pretreatment with (R)-alpha-methylhistamine, selective agonist of histamine H3 receptors, has been investigated on gastric mucosal lesions at different time intervals, from 5 to 60 minutes, after administration of absolute ethanol in the rat. The amount and depth of lesions were quantitatively evaluated by light microscopy. In rats pretreated with (R)-alpha-methylhistamine, the integrity of the mucosa was preserved in approximately 80% of the total mucosal length measured despite ethanol challenge. Prevention of lesion formation was as great at 5 min after ethanol administration as at 60 min. When present, damage involved mainly superficial mucosa and lesions extending deeply into the gland region were evident in 1-2.5% of the total mucosa. Present findings indicate that mechanisms by which (R)-alpha-methylhistamine operates enable the mucosa to counteract damage just from the moment of exposure to ethanol and that protection is exerted both on surface and pit cells and on gastric glands.