Effects of single parenteral indomethacin injection in rat fundic and antral epithelial proliferation

Endogenous prostaglandins and microflora modulate DNA synthesis and neuroendocrine peptides in the rat gastrointestinal tract

BACKGROUND

Previous studies suggest that E2 prostaglandins and the microflora may participate in the regulation of endocrine cells and of gastrointestinal cell kinetics. Our aim is to examine the actions of endogenous prostaglandins and of the microflora on gastrointestinal cell proliferation and tissue levels of neuroendocrine peptides.

METHODS

Germfree and ex-germfree rats were treated with subcutaneous placebo or 1.5 mg/kg indomethacin for 3 days. All rats were labeled with 3H-methyl-thymidine, and biopsy specimens from different parts of the gastrointestinal tract were processed for autoradiography. DNA synthesis was estimated by the labeling index, except in the oxyntic mucosa, where the total number of labeled cells present in 7.5 mm mucosa was used. The concentration of neuroendocrine peptides was determined by radioimmunoassay.

RESULTS

In the germfree rat, indomethacin reduced DNA synthesis in the fundus, duodenum, and proximal jejunum (P < 0.05) and the number of villous cells throughout the small intestine (P < 0.05). Exposure to microflora increased DNA synthesis in the proximal and distal jejunum, ileum, and colon (P < 0.05 versus germfree controls) and the number of crypt cells in the distal small intestine and colon (P < 0.05) and reduced the number of villous cells in the small intestine (P < 0.05) but did not affect tissue concentrations of neuroendocrine peptides. Indomethacin increased the concentration of somatostatin in the stomach, duodenum, and colon of germfree rats (P < 0.001), the concentration of calcitonin gene-related peptide (CGRP) and enteroglucagon in the proximal and distal jejunum and ileum (P < 0.001), and the concentration of glucagon in the colon (P < 0.05). The concentrations of somatostatin, CGRP, and glucagon were lower in indomethacin-treated ex-germfree rats than in indomethacin-treated germfree rats (P < 0.01).

CONCLUSIONS

Indomethacin selectively reduced DNA synthesis in the upper gastrointestinal tract of germfree rats, indicating a basal stimulatory role for endogenous prostaglandins on cell proliferation. Endogenous prostaglandins modulate synthesis or release of gastrointestinal neuroendocrine peptides. Somatostatin may mediate indomethacin-induced reduction of DNA synthesis. The microflora stimulates cell proliferation and influences tissue levels of neuroendocrine peptides in a manner opposite to that of indomethacin.

NSAID-induced delay in gastric ulcer healing is not associated with decreased epithelial cell proliferation in rats

Nonsteriodal antiinflammatory drugs initiate gastric ulceration and delay gastric ulcer healing. This study aimed to investigate the role of epithelial cell proliferation in delayed ulcer healing and to identify the most reproducible technique for measuring cell proliferation. Rats with acetic acid-induced gastric ulcers were treated for two weeks with indomethacin (1 mg/kg), aspirin (200 mg/kg), or vehicle control. Ulcers were assessed by macroscopic measurement of ulcer area, quantitative histological measurement of mucosal regeneration, and 5-bromo-2'-deoxyuridine immunohistochemistry to assess epithelial cell proliferation. Indomethacin and aspirin significantly delayed ulcer healing and inhibited mucosal regeneration. Three techniques for assessing cell proliferation were compared, and a scoring system, designed to take into account the entire tissue, was shown to be the most reproducible technique. Indomethacin significantly enhanced cell proliferation in the fundic area of ulcer and aspirin had no effect on cell proliferation. We conclude that aspirin and indomethacin delay ulcer healing by an inhibition of mucosal regeneration, but they do not inhibit epithelial cell proliferation.

Indomethacin inhibits cell proliferation and increases cell losses in rat gastrointestinal epithelium

Gastrointestinal cell proliferation was estimated in histological sections of rats treated with low and high doses of parenteral indomethacin for 3 to 60 days. Mitoses were arrested with vincristine and cells in S phase were labeled with tritiated thymidine. Short-term, low-dose treatments reduced the mitotic activity in the oxyntic and small intestinal epithelium, whereas moderate doses restored the mitotic index and high doses increased the proliferative activity and produced epithelial hyperplasia. Long-term, low-dose treatments increased cell proliferation in the small intestine and reduced the number of villous cells. Indomethacin did not affect the proliferative response elicited by refeeding in the oxyntic mucosa, but the simultaneous administration of prostaglandin E2 analog increased the number of arrested mitoses. The turnover of labeled cells was accelerated by indomethacin, particularly in the small intestine. These findings indicate that prostaglandins are regulators of the cell kinetics of the gastrointestinal epithelium but, at the same time, they disclose the presence of trophic mechanisms that are independent of the synthesis of endogenous prostaglandins.