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The purpose of this work was to assess the influence of microgravity on several endogenous and microbial parameters of digestive physiology. On the occasion of two Spacelab Life Sciences missions, SLS-1 (a 9-day space flight) and SLS-2 (a 14-day space flight), Sprague-Dawley rats flown aboard the US space shuttle were compared to age-matched ground-based controls. In both flights, exposure to microgravity modified cecal fermentation: concentration and profile of short-chain fatty acids were altered, whereas urea and ammonia remained unchanged. Only in SLS-1 was there an induction of intestinal glutathione-S-transferase. Additional analyses in SLS-2 showed a decrease of hepatic CYP450 and of colonic goblet cells containing neutral mucin. After a postflight recovery period equal to the mission length, only modifications of the hepatic and intestinal xenobiotic metabolizing enzymes still persisted. These findings should help to predict the alterations of digestive physiology and detoxification potential likely to occur in astronauts. Their possible influence on health is discussed.

No information concerning the effect of weaning on intestinal cell proliferation is currently available in large species with early intestinal morphogenesis, a group including most domestic animals and humans. Changes in intestinal morphology and epithelial cell renewal were investigated in 1-, 5-, and 8-wk-old suckling and 8-wk-old weaned lambs after injection of [3H]thymidine. In suckling lambs a gradual increase in crypt depth occurred with age, especially in the proximal intestine, whereas villus height was significantly reduced in the distal regions. At 8 wk of age weaned and prolonged-suckling lambs exhibited no significant differences in crypt depth throughout the intestine and in villus height proximally. However, weaned lambs had shorter villi in the jejunum and ileum. The highest enterocyte migration rates (4.4-9.7 microns/h) were observed in 1-wk-old lambs. In suckling animals, migration rates decreased with age by 60, 51, and 11% in the duodenum, jejunum, and ileum, respectively. Weaned and prolonged-suckling 8-wk-old lambs had a similar rate of enterocyte migration in the ileum. Furthermore, ruminating animals exhibited only slightly higher migration rates in the duodenum and the jejunum (53 and 15%, respectively). In suckling lambs, epithelial cell renewal required 2.1-4.0, 4.5-6.3, and 4.0-5.3 days at 1, 5, and 8 wk of age, respectively, whereas labeled cells reached the tips of the villi within 3.0-3.1 days in weaned animals. These data suggest that the suckling period corresponds to a gradual and important phase of postnatal intestinal adaptation in the sheep, a species with early patterns of intestinal cell replacement.(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of the mode of sterilization of the diet (gamma-irradiation vs. autoclaving) on the histamine and mast cells distribution in the intestinal mucosa, was studied in germ free (GF) and conventional (CV) rats. Interactions between the diet and the digestive microflora were observed. Histamine concentration and mast cells counts are higher in CV rats small intestine than in GF's. The differences are increased with the irradiated diet. At the opposite in the hindgut, these values are higher in GF than in CV rats, especially in the rats fed the steam sterilized diet. The variations in the wall histamine contents and in the mucosal mast cells counts due to the diet and/or the microflora do not appear to be always correlated.

The length and diameter of enterocyte microvilli at mid-villus position were measured on electron-micrographs. The duodenum, jejunum and ileum of axenic (germfree) and holoxenic (conventional) inbred rats fed the same diet have been studied. The microvilli were significantly shorter in all these intestinal regions when the microflora was present. The decrease in microvillus length (due to the presence of microflora), expressed as a percentage of the length in axenic rat, was 5% in the duodenum, 9% in the jejunum and 18% in the ileum. This was not true of microvillus diameter where only the values found for the ileum of axenic rat were significantly lower, the others not differing among themselves. In conclusion, the presence of a total microflora led to a decrease in the length of enterocyte microvilli. These results have been discussed in relation with studies on renewal and enzyme activity in the intestinal epithelium.