Mitotic activity in the gastric mucosa of the rat after fasting and refeeding

The effects of feeding on cell morphology and proliferation of the gastrointestinal tract of juvenile Burmese pythons (Python molurus)

The gastrointestinal tract of Burmese pythons ( Python molurus (L., 1758)) exhibits large morphological and physiological changes in response to feeding and extended periods of fasting. In this study the mucosa of the stomach, small intestine, and colon were examined for changes in structure and cellular proliferation. The mucosa of fasting pythons exhibited low levels of cellular replication, but after feeding, cellular replication was evident as early as 12 h in the small intestine and colon and 24 h in the stomach. Replication peaked 3 days postfeeding for the small intestine and colon, but was still increasing at 6 days postfeeding in the stomach. Interestingly, cell proliferation was still evident after 45 days in the colon. In these tissues, a stock of “ready-to-use” primary lysosomes is found in the mucosal cells of fasting animals, whereas profound intracellular recycling is typical of animals that have been fed. These findings indicate that during the postprandial period, the intestinal mucosa undergoes extensive remodelling in anticipation of the next fasting and feeding period. One key adaptive factor for the python’s ability to cope with infrequent feeding is a well-prepared digestive system in fasting animals that can quickly start functioning again when food becomes available.

Feeding manipulation elicits different proliferative responses in the gastrointestinal tract of suckling and weanling rats

Food deprivation has been found to stimulate cell proliferation in the gastric mucosa of suckling rats, whereas the weanling period has been reported to be unresponsive in terms of proliferative activity. In the present study we analyze regional differences in the effect of milk or food deprivation on cell proliferation of the epithelia of the esophagus and of five segments of small intestine in suckling, weanling and newly weaned Wistar rats of both sexes. DNA synthesis was determined using tritiated thymidine to obtain labeling indices (LI); crypt depth and villus height were also determined. Milk deprivation decreased LI by 50% in the esophagus (from 15 to 8.35%) and small intestine (from 40 to 20%) of 14-day-old rats. In 18-day-old rats, milk and food deprivation decreased LI in the esophagus (from 13 to 5%) and in the distal segments of the small intestine (from 36-40 to 24-32%). In contrast, the LI of the epithelia of the esophagus (5%) and of all small intestine segments (around 30%) of 22-day-old rats were not modified by food deprivation. Crypt depth did not change after treatment (80 to 120 microns in 14- and 22-day-old rats, respectively). Villus height decreased in some small intestine segments of unfed 14- (from 400 to 300 microns) and 18-day-old rats (from 480 to 360 microns). The results show that, contrary to the stomach response, milk deprivation inhibited cell proliferation in the esophagus and small intestine of suckling rats, demonstrating the regional variability of each segment of the gastrointestinal tract in suckling rats. In newly weaned rats, food deprivation did not alter the proliferation of these epithelia, similarly to the stomach, indicating that weanling is a period marked by the insensitivity of gastrointestinal epithelia to dietary alterations.

LHRH and somatostatin effects on the cell proliferation of the gastric epithelium of suckling and weaning rats

The aim of this study was to investigate the effects of LHRH and somatostatin on the cell proliferation of the gastric epithelium of suckling and weaning rats after fasting treatment. Previous studies on the cell proliferation of the gastric epithelium have shown that fasting stimulates this process in suckling, but not in weaning and adult rats. As milk is the most important source of nutrients and hormones during the suckling phase, and luteinizing hormone-releasing hormone (LHRH) and somatostatin are found in milk, their possible inhibitory roles on the gastric epithelium were investigated. Metaphasic index was achieved by vincristine blockade in 18- and 22-day-old treated and non-treated rats. The results showed that at 18 days, both hormones inhibited the enhanced proliferation activity due to fasting treatment, while at 22 days, no effect was detected. Therefore, LHRH and somatostatin were considered to have inhibitory roles on the cell proliferation of the gastric epithelium in suckling rats only.

Indomethacin inhibits cell proliferation in the oxyntic epithelium of the rat

The aim of this investigation was to examine the action of parenteral indomethacin and oral prostaglandin E2 on cell proliferation in the rat oxyntic mucosa. Groups of Sprague Dawley rats were treated with either 1.5 mg/kg indomethacin subcutaneously, 5 mg/kg oral prostaglandin E2 or placebo, twice daily during 5 days. All rats were killed exactly 4 hours after mitotic arrest with vincristine, and a biopsy specimen from the oxyntic mucosa was processed for routine microscopic evaluation. Mitotic figures were distributed cluster-like along the oxyntic mucosa alternating with mitosis-free areas. The total number of mitotic figures in 8 mm of mucosa was significantly reduced by administration of indomethacin (p < 0.05). In rats given indomethacin, 32.5% of the examined mucosa did not have mitotic figures, which is significantly higher than 14.3% as observed in placebo-treated rats (p < 0.05). Both rats treated with indomethacin and with prostaglandin E2 had fewer microscopic fields containing 5-6 mitotic figures than placebo-treated animals (p < 0.05). The maximal length of mitosis-free areas was 0.6 (0.6-0.9) mm in rats given indomethacin which is significantly larger than 0.4 (0.2-0.4) mm observed in controls (p < 0.05). Indomethacin produced epithelial atrophy as shown by a significant reduction of the epithelial height observed in those rats compared to controls (p < 0.05). The inhibition of cell proliferation observed in the oxyntic mucosa of rats treated with the cyclooxygenase blocker indicates that an important physiological role of endogenous prostaglandin is to maintain the proliferative activity of the epithelium at a high level.

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)

Digestive tract cell proliferation and food consumption patterns of Ha/ICR mice

The relationship between the daily pattern of food consumption and the proliferation rate of the oesophagus, stomach, forestomach, small intestine and colon of Ha/ICR mice was examined. Proliferative activity was determined by [3H]TdR incorporation on a wet weight tissue basis, along with selective counting of labelled nuclei. Under conditions of ad libitum feeding with a 12 hr light cycle (lights on at 0600) mice eat most of their food during the dark period. A distinct circadian rhythm was observed in the oesophagus, stomach, forestomach and colon with the peak of [3H]TdR incorporation between 0400 and 0600 and the nadir between 1600 and 1800. Although a circadian fluctuation was observed in the small intestine, its amplitude was much less than in other areas. This rhythmic change in proliferation rate could be phase shifted by allowing the mice to feed only between 0800 and 1600 for 14 days. Under these conditions the peak in proliferative activity occurred between 1800 and 2000. Fasting reduced the daily level of proliferative activity in all of the digestive tract sites studied, and for all areas except the oesophagus greatly reduced or eliminated the circadian fluctuation. The forestomach and colon were the most influenced by fasting with 24 hr [3H]TdR incorporation reduced to 30-40% of the control value. Refeeding following a 48 hr fast produced a rapid increase in proliferative activity peaking at levels well above the control value at 16 hr after the onset of refeeding. The major exception to this was the small intestine which slowly returned to the control value during the first 24 hr. Partial refeeding produced a diminished refeeding response. Once the normal pattern of food consumption was re-established following refeeding the normal proliferative fluctuations were again observed.

Deglycyrrhizinised liquorice (DGL) and the renewal of rat stomach epithelium

Deglycyrrhizinised liquorice (DGL) stimulated proliferation in the forestomach of the rat but did not stimulate and possibly even inhibited proliferation in the glandular part. DGL increased the number of fundus glands in which labelled mucus secreting cells occur as well as the total number of labelled mucus cells per gland. The mechanism of action proposed for DGL is that DGL stimulates and/or accelerates the differentiation to glandular cells as well as mucus formation and secretion. The accelerated proliferation observed in the forestomach is ascribed to an improved environment in the stomach as a consequence of the enhanced mucus secretion under the influence of DGL.

Glycoprotein synthesis in the mucous cells of the vascularly perfused rat stomach. II. Differentiating mucous cells

Labeled leucine, serine, galactose, glucosamine and sulphate were administered to rat stomachs in a perfusion system. Sections of the gastric fundus were studied by light microscopic autoradiography. Five categories of mucous cells were distinguished and their glycoprotein synthetic activity was measured in autoradiographs by counting silver grains over each category. During their differentiation, while migrating from the isthmus of the fundic glands to the free luminal surface, the surface mucous cells (SMC) showed an increase in incorporation of all precursors used. Differences between the incorporation patterns of the various precursors, in cells of different ages, suggest that structural development runs ahead of functional activity, and that the latter continues up to the very moment the cell is shed from the surface. Sulphate was incorporated at a considerably lower rate by the SMC of the free surface than by the foveolar SMC, in which by cytochemical staining strongly acidic glycoproteins were shown. Since the mucous neck cells incorporated all precursors at a low rate, these cells apparently do not play an important role in gastric mucus synthesis. They did not incorporate sulphate, which is consistent with histochemical observations.

Differentiation of immature mucous cells into parietal, argyrophil, and chief cells in stomach grafts

Microscopic and submicroscopic studies on regenerating gastric mucosa neonatally grafted in the subcutaneous tissue of littermate mice have revealed that immature mucous cells are totipotent; ultimately they transform into mature mucous, parietal, argyrophil, and chief cells in the gastric glands.