Effects of antiulcer agents on healing of mepirizole-induced duodenal ulcers in rats

Emedastine difumarate: a review of its potential ameliorating effect for tissue remodeling in allergic diseases

BACKGROUND

Emedastine difumarate, a selective histamine-H1 receptor antagonist and effective antiallergic agent, inhibits various clinical symptoms of allergic rhinitis, allergic conjunctivitis, urticaria, allergic dermatitis, pruritus cutaneous, and prurigo. In addition to greater efficacy than other antihistamines, emedastine difumarate produces no adverse cardiovascular effects and exhibits minimal anticholinergic activity. Moreover, a recent study revealed that the effect of emedastine difumarate on inhibition of histamine-induced collagen synthesis in vitro was greater in dermal fibroblasts than in nasal mucosa fibroblasts. This result indicates that there are tissue-specific effects of emedastine difumarate and that it may be more effective for treating fibrosis in skin than in nasal mucosa. However, the mechanism and role of tissue remodeling is less well established for allergic skin diseases and allergic conjunctivitis, in comparison to respiratory allergic diseases.

OBJECTIVE

This review outlines the involvement of histamine in the pathogenesis of tissue remodeling in a variety of organs, and presents the evidence for the effect of antihistamines on this process. Furthermore, this review also discusses antihistamines as an intervention strategy in tissue remodeling.

METHODS

The scientific literature, published abstracts, and selected textbooks were reviewed.

RESULTS/CONCLUSION

Although additional evidence is required, emerging evidence suggests that emedastine difumarate may be of value in the prevention of excess tissue remodeling in allergic skin inflammation.

[An overview of acetic acid ulcer models and their utility for drug screening]

Since Takagi et al. reported an experimental chronic gastric ulcer model [acetic acid ulcers induced by submucosal injection of acetic acid (Type 1)], we further modified the methodology and subsequently devised three more models. The second model involves inducing ulcers by serosal application of an acetic acid solution (Type 2) and the third model achieves ulcer induction by intragastric application of an acetic acid solution (Type 3). The forth model was modification of the third model by giving the acetic acid solution and the same volume of air to make one ulcer in the stomach (Type 4). In general, animals accepted the procedures without problems and no undesirable effects were noticed. More importantly, this experimental animal model allows production of ulcers that highly resemble human ulcers in terms of both pathology and healing. Indeed, relapse is even endoscopically observed for 360 days after ulceration. The ulcers produced not only respond well to various anti-ulcer medications, such as antisecretory and mucosal protective drugs and growth factors, but also demonstrate appropriate responses to ulcerogenic agents such as NSAIDs. In addition, we have recently demonstrated that H. pylori infection resulted in delayed ulcer healing and recurrence of healed acetic acid ulcers induced in Mongolian gerbils. The present article gives a brief summary of the ulcer history before establishment of acetic acid ulcers and characteristic features of acetic acid ulcer, including both their merits and shortcomings.

Selective and competitive histamine H2-receptor blocking effect of famotidine on the blood pressure response in dogs and the acid secretory response in rats

Famotidine has been already demonstrated to be a competitive H2-receptor antagonist in the stomachs of dogs and cats. The present experiments were carried out to examine the effects of famotidine on changes in blood pressure induced by dimaprit and several other agonists in vagotomized, anesthetized dogs and on changes in gastric acid secretion induced by histamine in stomach-perfused, anesthetized rats. Famotidine caused a parallel displacement of the dimaprit dose-response curve to the right with a DR10 value of 0.059 mumols/kg, indicating that famotidine is 166 times more potent than cimetidine in vascular H2-blocking activity. On the contrary, famotidine did not affect the depressor responses to 2-pyridylethylamine and histamine that were antagonized by mepyramine. The histamine dose-response curve was displaced to the right more markedly after simultaneous administration of mepyramine and famotidine than after mepyramine alone. The effects of methacholine, phenylephrine and isoproterenol on blood pressure were not influenced by famotidine in doses up to 720 nmol/kg. In rats, famotidine also caused a parallel displacement of the acid dose-response curve to histamine to the right with a DR3 value of 24 mumols/kg/hr in stomach-perfused rats anesthetized with pentobarbital, exhibiting a potency 108 times greater than that of cimetidine. Analysis of the acid dose-response curve with the Edie-Hofstee transformation showed that famotidine, like cimetidine, was a competitive H2-receptor antagonist.

Antisecretory and antiulcer effect of the H2-receptor antagonist famotidine in the rat: comparison with ranitidine

1 The effects of the new H2-receptor antagonist famotidine, administered orally, on gastric secretion and emptying as well as on experimentally-induced gastric and duodenal ulcers were studied in the rat. Ranitidine was used as a reference compound. 2 Both compounds inhibited acid secretion in a dose-dependent manner. Calculated ED50 values were 0.80 and 6.84 mg kg-1 for famotidine and ranitidine, respectively. However, the duration of the antisecretory action was the same for both drugs. 3 The effect of the two drugs, administered at equiactive antisecretory doses, on gastric emptying was different. Ranitidine significantly accelerated the emptying rate whereas famotidine had no effect. 4 Famotidine reduced, in a dose-dependent manner, ulcer incidence in stomachs of dimaprit-treated rats and in duodena of cysteamine-treated animals with a potency respectively 2 and 7 times higher than that of ranitidine. 5 Famotidine is therefore an effective antisecretory and untiulcer compound. Its potency, but not its efficacy, is higher than that of ranitidine. Moreover, the duration of the antisecretory action is virtually the same for both drugs.

Development and significance of cysteamine and propionitrile models of duodenal ulcer

Cysteamine is widely used in rodents to induce duodenal ulcer. Herein, the pathogenesis of duodenal ulceration in its earliest stages was reviewed using findings from cysteamine- and propionitrile-induced duodenal ulcer in rodent models, especially taking into account changes in the secretion of gastric acid, duodenal and pancreatic bicarbonate as well as gastroduodenal motility. The effect of cysteamine-HCl in inducing ulcers in rats is circadian rhythm-dependent. The effect is greatest from just before the end of diurnal rest to just after the start of nocturnal activity. The chronobiologic effect may be in part due to the circadian rhythm-dependent increased gastric acid production from cysteamine. Titratable acidity was found to be twice as great in the gastric juice of rodents when cysteamine was given by injection at 2000 (just after the start of nocturnal activity) in comparison to when given at 0800 or 1200 (at the beginning or middle span of daily rest). Further studies have shown that adrenalectomy of rats 7 days before cysteamine administration obliterated the observed circadian susceptibility to ulcer formation. Duodenal ulceration, at least in the cysteamine model, appears to be under chronobiologic neuroendocrine control or influence, seemingly mediated by the adrenal glands.

Effect of antisecretory agents and vagotomy on healing of "chronic" cysteamine-induced duodenal ulcers in rats

Penetrated cysteamine-induced duodenal ulcers in rats have a very prolonged course of healing. In this study, it was investigated how much the healing of these ulcers is accelerated by some treatments. The treatments included omeprazole, cimetidine, and truncal vagotomy. In addition, the effect of omeprazole and cimetidine on gastric acid secretion was investigated in chronic gastric fistula rats. After 25 days of treatment, significantly more rats in the treated groups had healed ulcers than in the control group. There was little further improvement up to 100 days of treatment, and the difference between treated and untreated groups decreased. The morphology of healing ulcers in treated and untreated rats was also compared. In controls, there was a simultaneous regeneration of mucosa and the submucosal Brunner's glands from the edges of the ulcer, the slow proliferation rate of the latter probably being decisive for the prolonged healing. In the treated rats, the mucosa first regenerated with formation of crypts and low villi and subsequently, the Brunner's glands were formed by proliferation from the bottom of the crypts.

Healing of cysteamine-induced duodenal ulcers in the rat

The mechanism and time for healing of cysteamine-induced duodenal ulcers in rats were investigated. Cysteamine induces a mixture of erosions, ulcers, and penetrating ulcers. These three stages of ulcerations healed in different ways and in different times. Erosions healed within three days by formation of new mucosa from the epithelium of the remaining parts of the crypts of Lieberkühn. The mucosa became completely normal within 15 days. Ulcers healed primarily by a contraction of the circular layer of the external muscle coat, thereby approaching the ulcer edges and reestablishing a complete layer of Brunner's glands in the submucosa. Healing was complete within 15 days. Penetrated ulcers healed very slowly by formation of new epithelium and Brunner's glands from the ulcer edges. The newly formed epithelium was desquamated unless protected by underlying Brunner's glands and the regeneration of these therefore determined the healing of the ulcer. Only a few of these ulcers had healed after 50 days. After 100 and 150 days, approximately 50% had healed, and after 200 days still only 64% had healed. Thus the cysteamine ulcer with destroyed muscle coat has a very prolonged healing and thereby represents a model for a chronic duodenal ulcer which may be of value as a model for testing treatments of duodenal ulcers.