Cell kinetics of rat gastrointestinal mucosa. Autoradiographic study after treatment with 15(R)15-methyl-prostaglandin E2

Involvement of cyclooxygenase-2 in gastric mucosal hypertrophy in gastrin transgenic mice

Gastrin promotes gastric mucosal growth, and hypergastrinemia induces gastric mucosal hypertrophy. Recently, it has been reported that gastrin induces cyclooxygenase-2 (COX-2) in human gastric and colorectal cancer cell lines. However, whether COX-2 is involved in gastrin-induced gastric mucosal growth in vivo is unknown. We investigated the role of COX-2 in gastrin-induced gastric mucosal hypertrophy using gastrin transgenic mice. Hypergastrinemic mice [mice with mutated gastrin under the control of the beta-actin promoter (ACT-GAS mice)] received the COX-2 inhibitor celecoxib (0, 200, or 500 mg/kg of diet) from 5 wk of age and were killed at 16 or 24 wk. Some ACT-GAS mice received celecoxib from 16 wk and were killed at 24 wk. Eighty-week-old ACT-GAS mice without celecoxib treatment were also examined. The thickness of the gastric mucosa, cell populations, COX-2 expression, and PGE(2) levels were evaluated. All ACT-GAS mice showed gastric mucosal hypertrophy, and four of six 80-wk-old ACT-GAS mice developed gastric cancer. COX-2 was expressed in interstitial cells of the hypertrophic gastric mucosa and gastric cancers. Moreover, PGE(2) levels in the gastric mucosa of ACT-GAS mice were significantly higher than those of normal mice. With treatment with celecoxib, PGE(2) levels, the gastric mucosal thickness, and the number of total gastric cells per gastric gland of ACT-GAS mice were significantly decreased. The decrease in gastric mucosal thickness was caused by a reduction of foveolar hyperplasia. The thickness of glandules and the number of Ki67-positive cells were not significantly changed. In conclusion, COX-2 contributes to gastrin-induced mucosal hypertrophy of the stomach.

Ventromedial hypothalamus lesions induce jejunal epithelial cell hyperplasia through an increase in gene expression of cyclooxygenase

BACKGROUND

We demonstrated that ventromedial hypothalamus (VMH) lesions facilitate DNA synthesis, which reflects cell proliferation in abdominal organs, including the liver, pancreas, stomach, small intestine and large intestine, all of which are amply innervated by the vagal nerve.

OBJECTIVE

To investigate which area DNA synthesis facilitates and what factors contribute to cell proliferation in the small intestine in VMH-lesioned rats.

DESIGN

At 7 days after VMH lesions or sham operations, a segment of rat jejunum was taken for histological examination. A part of the jejunum was also removed from VMH-lesioned and sham-operated rats after 3 days and examined for 5-bromo-2'-deoxyuridine (BrdU) incorporation. At 6, 12 and 24 h after VMH lesions, the proximal intestine was removed from individual rats, from the pylorus to the mid-jejunum. Total RNA was extracted from these tissues of each rat, and the levels of epidermal growth factor (EGF) and transforming growth factor (TGF)-alpha mRNA were determined using reverse-transcription polymerase chain reaction. Cyclooxygenase (COX)-1 and -2 mRNA levels were determined using Northern blotting.

RESULTS

: Jejunal villi in VMH-lesioned rats were markedly enlarged compared to those of sham-operated rats and jejunal crypts in VMH-lesioned rats more markedly incorporated BrdU. Northern blot analysis revealed an increase in COX-1 mRNA after 6, 12 and 24 h in the jejunum of VMH-lesioned rats. COX-2 mRNA was decreased 6 and 12 h after VMH lesioning; however, it was significantly increased 24 h after VMH lesions in comparison to sham-operated rats. The levels of EGF and TGF-alpha mRNA were unchanged in VMH lesioned rats.

CONCLUSION

VMH lesions induced enlargement of jejunal villi and increased the gene expression of COX-1 in the small intestine. Prostaglandins, probably E(2), induced by COX-1 may be one candidate factor responsible for the cell proliferation of the small intestinal epithelium in these rats.

Re-adaptation of the gastroduodenal mucosa to DNA synthesis during protracted stress

BACKGROUND

Previous study showed that under the influence of protracted physical stress, the DNA synthesis (DS) of the gastroduodenal mucosa rises, the highest peak being reached at 4 weeks. At 8 stress weeks, the DS decreases to values similar to those recorded at the beginning of the experiment. The possibility that this DS adaptation (DSA) could be maintained beyond 8 weeks in animals allowed to subsequent resting (stress-free) weeks, was now explored.

METHODS

Sixty-five rats were investigated. Sixty rats were transported to the stress laboratory. Thirty were water plunged and 30 sham handled once a day, 5 days a week, for 8 weeks. After 8 stress weeks, groups of 5 animals were allowed to rest for one, two, three and four weeks, ending with single water plunging or sham handling. All 65 animals received ip injection of 3H-thymidine before they were sacrificed. The ratio radioactive DNA/total DNA reflected the DS of the stomach and duodenum.

RESULTS

DSA was achieved at 8 stress weeks (stomach). The DS in the stomach of stressed rats had significantly increased at 10 weeks (P < 0.05), but at 12 weeks it had decreased to 8 weeks values. The DS in the duodenum of stressed rats had significantly increased at 9, 10 and 11 weeks (P < 0.05), but at 12 weeks DS values had decreased to those of 8 weeks.

CONCLUSIONS

The DSA at 8 stress weeks had not prevailed because the DS increased considerably in the following weeks. At 9-11 weeks, DS values had significantly increased (P < 0.05) in stressed rats, but at 12 weeks a DS re-adaptation (DSRA) had occurred. Thus, it took 8 weeks to achieve DSA (stomach), but only 4 weeks to accomplish DSRA. Animals experienced sham handling as an stressor (milder) as it also induced DS re-adjustments in the gastroduodenal mucosa. Autoradiography showed that the labelling in DNA synthesizing cells was limited almost exclusively to the mucosal layer. The model described may prove of value to studies aimed at abating the disparate fluctuations of DNA synthesis in the gastroduodenal mucosa during the various phases of protracted stress.

Indomethacin accelerates clearance of labeled cells and increases DNA synthesis in gastrointestinal mucosa of the rat

Sprague-Dawley rats treated with placebo, parenteral indomethacin, or oral prostaglandin E2 for six days were given an intraperitoneal injection of [3H] methyl-thymidine and killed at 45 min and 96 hr after labeling. Treatments were continued until death. The dpm/DNA index was determined in mucosal scrapings of the stomach, duodenum, and jejunum and used to estimate DNA synthesis (45 min) and the clearance of labeled cells (96 hr). Indomethacin increased the DNA synthesis in both the duodenal and jejunal mucosa (P less than 0.05). In comparison to the controls, the clearance of labeled cells from the antral, duodenal, and jejunal mucosa was accelerated by indomethacin treatment, whereas the elimination of labeled cells from the antral and jejunal mucosa was slowed by PGE2 treatment (P less than 0.05). DNA synthesis of the antral mucosa was significantly reduced by PGE2 (P less than 0.05). The cyclooxygenase blocker did not affect the cell kinetic parameters of the oxyntic mucosa. The plasma levels of somatostatin were significantly higher both in PGE2- and indomethacin-treated rats than in controls (P less than 0.05). It is concluded that indomethacin treatment increases the cell losses from the epithelial surface, which in turn trigger a compensatory trophic reaction. It is suggested that an important physiological action of endogenous prostaglandins is to regulate the outflow of cells from the superficial zones of the epithelium. Finally, this study disclosed the presence of hitherto unknown regulatory mechanisms that promote cell proliferation in the gastrointestinal mucosa despite inhibition of the synthesis of endogenous prostaglandins.

Prostaglandin E2-induced hyperplasia of the rat antral epithelium is followed by a secondary inhibition of the mitotic activity

The aim of the study was to examine the mitotic activity in the antral and duodenal epithelium of Sprague-Dawley rats given trophic doses of E2 prostaglandins during a prolonged period of time. Natural prostaglandin E2 (dose range: 0.2-5.0 mg.k-1) and 15 (R) 15 methyl prostaglandin E2 (dose range: 0.03-2.0 mg.kg-1) were administered for 11 days, and mitoses were arrested with vincristine for 4 h before estimation of the cumulative mitotic index. A dose-related hyperplasia of the antral glands was observed after treatment with prostaglandin E2 and the synthetic analogue (p less than 0.05). The proliferative zone was enlarged in rats treated with high doses of the analogue but natural prostaglandin E2 did not affect the limits of the proliferative zone. A dose-related reduction of the mitotic index was observed in animals treated with prostaglandin E2 despite the presence of hyperplastic changes. All doses of the analogue induced antral hyperplasia without affecting the mitotic index except in rats given the highest dose who had a significantly lower mitotic index than controls (p less than 0.05). Hyperplasia of both crypts and villi was observed in the duodenum of rats given high doses of E2 prostaglandins (p less than 0.05) whereas the mitotic index and the growth fraction were not affected by treatments. It is concluded that hyperplasia by prostaglandins is developed in absence of changes of the mitotic activity. The observed reduction of the mitotic index is interpreted as a secondary phenomenon, possibly mediated by a regulatory mechanism of cell proliferation which is triggered to reduce further epithelial growth. It is suggested that prostaglandin E2 might influence such regulatory mechanisms.

Effects of misoprostol on cell migration and transit in the dog stomach

Prostaglandins of the E series increase stomach mucosal mass by inducing hyperplasia, which could be the result either of increased cell production or of decreased cell loss. This report describes an investigation of the effect of the prostaglandin E1 analogue, misoprostol, on cell migration and transit. 3H-thymidine was used to label those cells synthesizing deoxyribonucleic acid in dogs that had been given an oral dose of 300 micrograms/kg per day misoprostol for 11 weeks. The animals were killed at timed intervals, and tissue from the gastric fundus was prepared for autoradiography. The distribution of labeled cells at various times after labeling was used to follow the movement of the wave of label and to calculate median cell migration rates and transit times. The migration rate of cells toward the gastric lumen was significantly increased from 1.4 +/- 0.3 to 3.6 +/- 0.6 cell positions per day in the misoprostol-treated group (p less than 0.001); however, the gland length (from the most basal mucous neck cell to the luminal surface) was also increased (from 52.1 +/- 1.1 to 74.0 +/- 1.6; p less than 0.001), thus there was no significant difference in the (transit) time taken for cells to reach the top of the gland (control, 17.5 +/- 9.8 days; test, 12.2 +/- 7.1 days).

Enprostil reduces the increase of gastric corpus mucosal mass induced by the hydrogen-potassium-stimulated adenosine triphosphatase inhibitor BY 831-78 in the rat

We studied whether enprostil, a synthetic prostaglandin E2 derivative, might inhibit gastrin release and the trophic effects on gastric oxyntic mucosa induced by prolonged treatment with an inhibitor of hydrogen-potassium-stimulated adenosine triphosphatase, the substituted benzimidazole BY 831-78. Rats were treated intragastrically with enprostil (1 or 15 micrograms/kg b.i.d.), BY 831-78 (15 mumol/kg once daily), the combination of enprostil and BY 831-78, ranitidine (300 mumol/kg b.i.d.), and placebo. Plasma gastrin and somatostatin levels and gastric acid secretion were measured during a 1-day treatment in animals fitted with chronic gastric fistulas and repeatedly during 9 wk of treatment in intact rats. Despite inhibiting acid secretion, enprostil did not increase plasma gastrin. When combined with BY 831-78, enprostil transiently reduced the BY 831-78-induced increase of integrated plasma gastrin (1375 +/- 206 vs. 2137 +/- 256 pmol/L.12 h, p less than 0.05) in fasted rats with fistulas, but failed to prevent the marked hypergastrinemia following 9 wk of treatment with BY 831-78 (717 +/- 80 vs. 731 +/- 56 pmol/L) in intact rats. However, enprostil reduced the BY 831-78-induced increase of oxyntic mucosal volume (458 +/- 31 vs. 567 +/- 33 mm3, p less than 0.01), whereas BY 831-78 prevented the enprostil-induced increase of antral mucosal volume (42 +/- 3 vs. 56 +/- 3 mm3, p less than 0.01). These results demonstrate that some of the trophic effects induced by a hydrogen-potassium-stimulated adenosine triphosphatase inhibitor are not exclusively governed by gastrin.

Oral E2 prostaglandins affect endocrine cell populations in the gastric antrum of the rat

The aim of the present study was to investigate antral endocrine cell populations and tissue and circulating hormone levels following a 4-week oral regimen with prostaglandin E2 (25, 250 and 5000 micrograms/kg-1 b.i.d.) or a stable methyl analogue (5 and 50 micrograms kg-1 b.i.d.). Epithelial hyperplasia of the gastric antrum was observed with the highest dose of prostaglandin E2 and both doses of the analogue, as evaluated by stereological methods and conventional cell count. The treatments significantly affected the endocrine cell population. Somatostatin-immunoreactive cells were increased in proportion to the increased epithelial cellularity and plasma levels of somatostatin were increased in parallel. The tissue content of somatostatin-like immunoreactivity differed according to the extraction procedure used, and was significantly higher than controls in specimens extracted in neutral water. In the neutral extracts an immunoreactive somatostatin of unidentified molecular structure dominated quantitatively over somatostatin 14 and 28, which were the major components in acetic acid extracts. The serotonin-immunoreactive cell population was also significantly increased by natural prostaglandin E2 and the analogue but the gastrin cell population was not significantly affected by treatments. Accordingly, no significant changes were observed in tissue or plasma gastrin levels. It is concluded that the epithelial hyperplasia of the antral epithelia produced by E2 prostaglandins is associated with selective changes of endocrine cell populations. The changes were proportional to the increases of epithelial cellularity and required quantitative determination of the total antral volume to be detected.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of prostaglandins, omeprazole, and indomethacin on healing of experimental gastric ulcers in the rat

We investigated whether the trophic actions of prostaglandins, omeprazole, and indomethacin on gastric mucosa lead to accelerated healing of gastric ulcers in the rat. Cryoulcers were produced in the corpus area and treated with 16,16-dimethyl prostaglandin E2 (5 or 100 micrograms/kg b.i.d., intragastrically), omeprazole (40 mumol/kg once daily, subcutaneously), indomethacin (2 mg/kg b.i.d., subcutaneously), or placebo. At the end of the treatment, plasma gastrin, cell labeling index (autoradiography with [3H]thymidine), and the size and depth of mucosal defects were measured. Compared with placebo, omeprazole accelerated ulcer healing as indicated by a smaller ulcer area [1.1 +/- 0.2 vs. 4.8 +/- 1.2 mm2 (mean +/- SEM)] and smaller ulcer depth (383 +/- 31 vs. 488 +/- 41 microns) after 10 days of treatment. Prostaglandins did not affect ulcer healing despite thickening of gastric corpus mucosa. Indomethacin delayed ulcer healing and reduced the labeling index. Omeprazole induced a marked hypergastrinemia (208 +/- 12 vs. 66 +/- 12 pmol/L on day 5, and 469 +/- 23 vs. 58 +/- 16 pmol/L on day 10). The results indicate that abolishment of acid secretion by omeprazole accelerates healing. Trophic actions and "cytoprotective" effects by prostaglandins are not relevant for ulcer healing in this model.

Initial kinetic changes of prostaglandin E2-induced hyperplasia of the rat small intestinal epithelium occur in the villous compartments

This study was performed to further identify the sequence of cell kinetics that occurs in the development of gastric and intestinal epithelial hyperplasia after orally administered prostaglandins of the E series. A high-dose, short-treatment schedule was used to examine the initial effects on kinetic parameters in the rat small intestinal epithelium. Groups of rats were killed after a single dose of oral prostaglandin E2 at 1 h after in vivo labeling with [methyl-3H]thymidine and during continued treatment at 6, 12, 24, 48, 72, and 96 h. As evidenced by autoradiography, the earliest change produced by prostaglandin E2 was an increased cellularity of the villous compartment (p less than 0.05 after 24 h). There was no change of labeling index of the villous compartment or of the leading edge of labeled cells within 24 h. At 48 h, the increased cellularity was accompanied by a significantly elevated labeling index of the villi. Throughout the study period no significant differences were observed between groups in the number of cells or labeling indices in the jejunal crypts, or in cellular input from the crypts to the villi. Epithelial turnover time in the placebo and treatment groups was 69 and 71 h, respectively. To exclude the possibility that prostaglandin E2 initially affects cell birth rate and mean cell cycle time, a metaphase blocker was given after 4 days of treatment in a second study. Animals were killed after 0, 0.5, 1.0, 1.5, and 2.5 h. The rate of entry into mitoses was 8.1% cells/h in controls compared with 8.2% cells/h in treated rats. The distribution of mitoses within crypts was identical in the two groups and the mean cell cycle time was 13.6 and 13.2 h, respectively. Also in this study there were trophic changes of the villi. It is concluded that the hyperplasia produced by oral prostaglandin E2 starts in the villi of the small intestine and is initiated by reduced cell exfoliation from the villous tips. Previously recorded retention of cellular elements in villi and crypts, increased cellularity of the proliferative compartments, and reduced mitotic index are secondary events.

Alternating proliferative capacity in the rat gastrointestinal mucosa. Effects of E2 prostaglandins and indomethacin

Having previously observed an apparent uneven distribution of proliferating cells in the gastric corporic mucosa of the rat, we examined the mitotic distribution along 8-mm sections of gastric and jejunal epithelia. Metaphases were arrested with vincristine to facilitate mitotic count, and the effects of treatment with a prostaglandin E2 analogue and a cyclooxygenase blocker were examined. Clusters of mitotic figures alternating with non-proliferating areas were observed in the gastric corporic epithelium of control rats. During 4 h mitotic activity was absent over 21% of the corporic mucosa. Extending the examined area to about 240 glands reduced substantially the error of mitotic counts. An uneven distribution of mitoses was found in the antral and jejunal epithelium, but areas without proliferating cells were uncommon. Treatment with the prostaglandin E2 analogue reduced the number of mitosis-free areas in the gastric corpus to 13%, and clusters were less easily identified. The total mitotic count was unaffected by treatment. In the jejunum prostaglandin increased the absolute number of mitoses. The mitotic span was also increased, reflecting the uneven distribution. Indomethacin produced the opposite effects to the prostaglandin analogue, including reduction of epithelial height. Of the gastric corporic mucosa 35% was non-proliferating during the observation period, but the clustering phenomenon was still apparent. Absence of dose relationship was attributed to ulcerogenic actions of high doses of indomethacin. It is concluded that mitoses are unevenly distributed in the upper gastrointestinal epithelium of the rat and that safe estimates of mitotic count require examination of large corporic areas.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell cycle distribution of proliferative and functional cells of the rat jejunum after treatment with oral E2 prostaglandins

Proliferative and functional epithelial cells were isolated from jejunal specimens of the rat by means of vibrational treatment combined with differential air insufflation. This method gave a good separation between superficial cells of the villi and the crypt cells, as evaluated by flow cytometry, morphology, cytology, and incorporation of radioactive thymidine into DNA. Groups of Sprague-Dawley rats (260 g) were treated twice daily for 11 days with oral placebo, 15(R)15-methyl-prostaglandin E2 in the range of 0.125-2 mg X kg-1, or 5 mg X kg-1 natural PGE2. Isolated crypt cells and superficial cells of the jejunal villi were then analysed by flow cytometry. Morphometric measurements were performed on sections of some jejunal specimens not submitted to vibrational treatment. The cell cycle distribution of crypt cells was unaffected by treatment with the prostaglandin analogue despite the presence of trophic changes. The proportion of crypt cells in G2/M phase was slightly but significantly reduced in rats given natural PGE2 compared with controls. The cell cycle distribution of villus cells was not affected by prostaglandin treatment. Trophic changes in the absence of increased DNA synthesis (S phase) or increased mitotic activity suggests that the hyperplasia observed after prostaglandin treatment is due to a reduced cell loss and/or slower migration time of epithelial cells.

Effect of prostaglandins on the adult rat stomach and intestine

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