Variations in digestive physiology of rats after short duration flights aboard the US space shuttle

The purpose of this work was to assess the influence of microgravity on sev eral endogenous and microbial parameters of digestive physiology. On the oc casion 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: concentratio n and profile df short-chain fatty acids were altered, whereas urea and amm onia 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. Aft er a postflight recovery period equal to the mission length, only modificat ions of the hepatic and intestinal xenobiotic metabolizing enzymes still pe rsisted. These findings should help to predict the alterations of digestive physiology and detoxification potential likely to occur in astronauts. The ir possible influence on health is discussed.