Submandibular glands and the regulation of gastric proliferation and TGFα distribution during rat postnatal development

Rodent gastric mucosa grows and differentiates during suckling-weaning transition. Among the molecules in rat milk, EGF and TGFβ are important peptides in the control of cell proliferation, and together with TGFα, they are also produced by submandibular glands. We aimed to determine the effect of saliva and milk on epithelial cell proliferation in the stomach of rat pups. We also examined the distribution of TGFα in the gastric mucosa after sialoadenectomy (SIALO) and fasting in order to determine whether this growth factor is affected by the deprivation of molecules derived from saliva and milk. SIALO was performed at 14 days and fasting was induced 3 days later. Cell proliferation was evaluated through metaphasic index and TGFα was detected by immunohistochemistry. We observed that whereas SIALO did not alter cell division, since the metaphasic index (MI) was unchanged, fasting stimulated cell proliferation (P < 0.05). After SIALO and fasting, MI was reduced when compared to the fasted group (P < 0.05). We found that TGFα is distributed along gastric gland and SIALO did not interfere in the localization and number of immunolabeled cells, but fasting increased their density when compared to the control (P < 0.05). The association of SIALO and fasting reduced TGFα immunostaining (P < 0.05). Therefore, during fasting, high MI was parallel to increased TGFα in gastric epithelium, but interestingly, this effect was found only in the presence of submandibular glands. We suggest that during suckling, peptides derived from saliva and milk are important to regulate gastric growth.

Goblet cell number in the ileum of rats denervated during suckling and weaning

The enteric nervous system plays a role on the stimulation of secretory cells of intestinal epithelia. We have demonstrated that ablation of ENS stimulates epithelial cell proliferation. As goblet cells are important constituents of the epithelial sheet, it is mandatory to investigate separately this cell type. The myenteric plexus of the ileum of rats in postnatal development was partially removed by the serosal application of benzalkonium chloride (BAC). Three groups of animals were used: those where BAC application was at 13 days and sacrifice was at 15 (13/28-day-old) or 23 days after treatment (13/36-day-old), and those where BAC was applied at 21 days and rats were killed 15 days after treatment (21/36-day-old) . The number of goblet cells in the ileum was estimated in sections stained by periodic acid-Schiff (PAS) histochemistry. In the 13/28 and 21/36 groups, the number of goblet cells was significantly higher after BAC treatment. These results suggest that the myenteric denervation may have an acute effect on the number of goblet cell in suckling and weanling rats, probably through submucous plexus.

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 percent in the esophagus (from 15 to 8.35 percent) and small intestine (from 40 to 20 percent) of 14-days-old rats. In 18-days-old rats, milk and food deprivation decreased LI in the esophagus (from 13 to 5 percent) and in the distal segments of the small intestine (from 36-40 to 24-32 percent). In contrast, the LI of the epithelia of the esophagus (5 percent) and of all small intestine segments (around 30 percent) of 22-day-old rats were not modified by food deprivation. Crypt depth did not change after treatment (80 to 120 mum in 14- and 22-day-old rats, respectively). Villus height decreased in some small intestine segments of unfed 14- (from 400 to 300 mum) and 18-day-old rats (from 480 to 360 mum). 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.

Cell proliferation and migration in the jejunum of suckling rats submitted to progressive fasting

Cell proliferation and migration in the intestinal crypts, and cell migration in the villus are controlled by different mechanisms in adult rats. In the present study, weanling rats and fasting rats were used to quantitatively study the correlation of cell cycle parameters and epithelial cell migration in crypts and intestinal villi. Eighteen-day-old rats received a single injection of tritiated thymidine[3H]T dR (23:00 h); half of the pups were submitted to fasting 5 h earlier. Cell proliferation was determined in radioautographs of jejunal crypts, on the basis of the labeling indices (LI) taken 1,8,13 and 19 h after [3H]TdR. The results showed that the labeling index did not differ 1 h or 19 h after [3H]TdR between the fed (38.7 percent or 48 percent) and fasting groups (34.6 percent or 50.4 percent). The modified method of grain count halving indicated that cell cycle time did not differ between fed (16.5 h) and fasting rats (17.8 h); the growth fraction, however, had lower values in fasting (59 percent) than in fed rats (77 percent). Cell migration in the crypt, estimated by the LI obtained for each cell position, did not change with treatment. As for the villi, the cell migration rate was significantly retarded by 3 cell positions (8 percent). These results suggest that the cell migration in the villi of weanling pups does not depend directly on the cell proliferation and migration in the intestinal crypt, but is directly affected by the absence of food in the lumen.

Fasting enhances cell proliferation of gastric epithelium during the suckling period in rats

The effect of fasting on cell proliferation was studied during the postnatal development of the maturing stomach. Metaphase indices were obtained after counting mitotic cells blocked by vincristine. The indices were examined at different times of day (10:00 a.m. and 6:00 p.m.) in 16 Wistar rats for each age (10, 18, 22 and 30 days) with different dietary patterns: only milk; weaning with milk and chow; recently weaned, with only chow, and fully weaned, respectively. Metaphase indices (mean +/- SEM) for both periods taken together for 10 and 18-day old animals were significantly higher in fasted (2.25 +/- 0.22 per cent and 2.49 +/- 0.28 per cent , respectively) than in control fed animals (1.67 +/- 0.09 per cent and 1.84 +/- 0.05 per cent , respectively), even if not significantly different for one period alone (18 h). No significant difference in indices was observed for 22-day old rats (fasted = 1.65 +/- 0.28 per cent ). The metaphase index of 30-day old rats was significantly higher in fed (1.02 +/- 0.16 per cent ) than in fasted animals (0.20 +/- 0.03 per cent ). We conclude that fasting enhances cell proliferation in stomach epithelium during the milk intake period, in contrast to the inhibitory effect observed in adult animals. The weaning period marks a transition to the opposite effect of fasting, i.e., a decrease in cell proliferation in 30-day old animals

The effect of fasting on cell proliferation in the gastric mucosa of the 14-day old suckling rat

The effect of fasting on cell proliferation in the gastric mucosa was investigated in 14-day old suckling Wistar rats. The renewal of the epithelial cells of the corpus of the stomach was evaluated by DNA labelling and counting arrested metaphases in fifty 14-day old rats fasted for 18 to 21 h and in fifty 14-day old rats fasted for 18 to 21 h and in fifty control suckling rats of the same age. The animals were sacrificed at 3 h intervals over a 24-h period. The metaphase arrest method was also used to estimate the rate of entry of cells into mitosis in the gastric glands of 26 rats under both feeding and fasting conditions. In addition to the proliferation indiices, the number of epithelial cells, and the heights of the glands and mucosa were measured morphometrically in 20 rats. No significant differences in the rate of entry of cells into mitosis (number of cells in fasted = 0.49 ñ 0.077 cells 100 cells -1 h-1), in the number of epithelial cells (fasted = 241.2 ñ 24.3 cells/0.023 mm2) or in the height of the gastric glands (fasted = 194 ñ 5.4 um) of fasted and control rats were observed. Both labelling and metaphase indices (means ñ SEM) were significantly higher (P<0.01) in the fasted (13.9 ñ 0.57% and 1.3 ñ 0.07%, respectively) suckling rats than in the controls (7.9 ñ 0.39% and 0.9 ñ 0.05%, respectively). These data indicate that fasting stimulates cell proliferation in the gastric mucosa of suckling rats rather than decreasing proliferation, as the case for adult rats