Cimetidine and parietal cell regeneration in experimental wounds in rat gastric mucosa. A light and electron microscopic study

[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.

Effects of ranitidine on gastric vesicles containing H+,K(+)-adenosine triphosphatase in rats

BACKGROUND

To ascertain the mechanism for rebound acid hypersecretion after treatment with an H2-receptor blocker, we investigated the effects of ranitidine on gastric H+,K(+)-adenosine triphosphatase (ATPase) in rats.

METHODS

Male Wistar rats received ranitidine (1-50 mg/kg body weight intraperitoneally twice a day for 5 days). The rats were starved for 15 h after the last treatment and then killed, and gastric vesicles containing H+,K(+)-ATPase were prepared.

RESULTS

Treatment with ranitidine dose-dependently increased protein content in the gastric vesicular fraction purified from the gastric mucosa without changing total protein content. Ranitidine also increased the content of a 94,000-dalton protein, the catalytic subunit of H+,K(+)-ATPase. On the other hand, ranitidine did not affect the specific activity of the enzyme (mumol/min/mg of the gastric vesicular protein). Since gastric vesicles in the fasting state mainly consist of the tubulovesicular membrane, these results suggest that ranidine administration increases total tubulovesicular H+,K(+)-ATPase content (mumol/min/rat) by increasing the number of tubulovesicles per parietal cell. The ranitidine-induced increase in total tubulovesicular H+,K(+)-ATPase activity was still evident 1 week after treatment and returned to control level 1 month later.

CONCLUSIONS

All these findings suggest that the increased content and total activity of tubulovesicular H+,K(+)-ATPase after ranitidine treatment may contribute to the mechanism for acid rebound after H2-blocker therapy.

Quality of gastric ulcer healing: histological and ultrastructural assessment

It has long been assumed that the mucosa in areas of grossly 'healed' gastric or duodenal ulcers returns to normal, either spontaneously or after treatment. This assumption is based almost entirely upon visual, superficial examination by endoscopy. Few, if any, histological and ultrastructural studies examined the deeper mucosa in the areas of grossly healed ulcers. In several experimental studies, we analysed the development, evolution, and healing of acetic acid-induced gastric ulcers in rats and assessed the histological and ultrastructural features (structure and cellular composition) of the gastric mucosa in areas of grossly healed ulcers. The gastric mucosa of grossly 'healed' ulcers showed re-epithelialization of the mucosal surface at every study interval (2 weeks, 2, 3, and 4 months), but the subepithelial mucosa displayed prominent abnormalities. Two patterns of scarring were distinguished: (a) the mucosa in the area of healed ulcer was thinner (25-45% thinner than normal mucosa) with increased connective tissue and poor differentiation and/or degenerative changes in the glandular cells; and (b) the mucosa displayed a marked dilation of gastric glands with poor differentiation of the glandular cells and a reduction in the supportive microvascular network. It is theorized that these abnormalities could interfere with oxygenation, nutrient supply, and mucosal resistance and defence; therefore, they could be a basis for ulcer recurrence. These observations indicate that the quality of mucosal structural restoration rather than the speed of ulcer healing is the most important factor in determining risk of ulcer recurrence. The clinical relevance of these findings is supported by a preliminary study in which marked histological abnormalities were found in the subepithelial mucosa in patients with 'healed' duodenal ulcers.

Long-term culture of human esophageal explants and cells

Human esophageal epithelium obtained from intermediate autopsies (less than 12 h) was maintained as cell and explant cultures. In order to develop a serum-free, defined media culture model, several medias and additives were evaluated. The viability and differentiation of the epithelial cells cultured with serum-free, Keratinocyte Growth Media (KGM, Clonetics Co., San Diego, CA) was improved over that of esophageal cells and explants cultured in either serum-supplemented CMRL 1066 (OCM), serum-free additive-supplemented CMRL 1066, or cimetidine-supplemented CMRL 1066. The KGM component EGF was determined to be trophic for esophagus cells on the basis of findings of increased 3H-TdR labelling in KGM cultures when compared to control cells grown in KGM without EGF (KBM). The morphologic pattern of the cytoskeletal proteins actin, keratin, and vimentin were characterized in isolated cell populations. The intermediate filaments, keratin, and vimentin were co-expressed in these epithelial cells. Esophageal explant viability, differentiation, and outgrowth from 15 cases were also evaluated in dishes coated with basement membrane associated proteins. Explants cultured in these dishes were equally well-preserved and differentiated. There were no significant differences in the explant histology when there was protein coating of the culture dishes, although one case showed improved outgrowth with laminin coating. A main advantage for using this culture system is that the same medium (KGM) can be used for both the culture of explants and isolated epithelial cells. Future applications of this model include determining: (1) the effect different concentrations of EGF and calcium in the media will have on esophageal proliferation and differentiation, and (2) the role of different basement membrane associated proteins on the plating efficiency of either isolated or outgrowth epithelial esophageal cells.

Aetiology of ulcers

It seems that duodenal and gastric ulcers are caused by environmental ulcerogens, which are probably infectious or chemical. The reasons for individual susceptibility to these ulcerogens have not been defined and, indeed, it is not yet certain that the effects are not essentially random. Abnormalities of function of the mucosae of the upper alimentary tract do not appear to be necessary or sufficient for the production of ulcers. The two principal clinical aspects of ulcer disease--the tendency to form chronic mucosal wounds and the tendency of the wounds to recur during many years--point to, but cannot yet be explained in terms of, failure of the processes involved in wound repair. More specifically, it is not known whether there is interference with the processes involved in normal mucosal repair or whether there is failure of the repair processes. When these problems are closer to solution, it will perhaps be possible to assess how environmental factors influence ulcerogenesis.

Parietal cell density in duodenal ulcer patients after short-term treatment with cimetidine and antacids

In a prospective study, 20 patients with endoscopically proven duodenal ulcers were randomised to be treated with cimetidine 1 g daily or with antacids 350 mmol daily. The duration of treatment was 30 days, but this was extended to three months in 3 patients in the cimetidine group and 4 patients in the antacid group. A morphological study of biopsies taken via a gastroscope from the corpus mucosa showed no change in mucosal height, parietal cell density per unit volume or changes in cellular infiltration after 30 and 90 days treatment in the two groups. Neither H-2 receptor blockers nor antacids alter mucosal height or parietal cell density. Treatment was not found to induce gastritic changes in the mucosa.

Wound healing properties of cimetidine in vitro

Cimetidine was one of a variety of drugs frequently given to surgical patients perioperatively tested for their effect on gap closure of wounded monolayers of human fascia cells in vitro. Cimetidine-treated cultures closed faster and had greater cell proliferation than controls. Closure of cimetidine-treated cultures occurred at six hours compared to ten hours in controls. Cimetidine concentrations of 1000 micrograms/ml resulted in 13.5 +/- 0.67 (SEM) X 10(4) cells/cm2 at six hours compared to 7.9 +/- 0.48 X 10(4) cells/cm2 in controls (p less than 0.05); the area covered by cells was 6.5 +/- 0.02 mm2 in treated cultures compared to 3.0 +/- 0.01 mm2 in controls (p less than 0.05). It is concluded that cimetidine stimulates fibroblast proliferation in vitro.

The structure of normal and regenerating rat oxyntic mucosa

The morphology of the normal oxyntic mucosa is described. Different animal models for the production of gastric ulcers are briefly reviewed. In a series of rats, wounds were produced by cauterisation of the oxyntic mucosa. The mucosal regeneration process was then followed by morphometrical methods using light and electron microscopy. In particular, the regeneration of the acid-producing parietal cells was followed. Initially, the ulcer area is covered by primitive epithelial cells originating from the mucosa in the wound margin. These cells form the new gastric glands. With time, all specialised epithelial cell types which normally occur in the oxyntic mucosa can be recognised and, if regeneration is allowed to continue, the structure and function of these cells will normalise. However, the amount of glands and the number of parietal cells within the glands remain subnormal.