Milk fermented with yogurt cultures and Lactobacillus casei compared with yogurt and gelled milk: influence on intestinal microflora in healthy infants.

Ingestion of fermented dairy products induces changes in the equilibrium and metabolism of the intestinal microflora and may thus exert a healthful influence on the host. We compared the effects of consumption of a traditional yogurt, a milk fermented with yogurt cultures and Lactobacillus casei (YC), and a nonfermented gelled milk on the fecal microflora of healthy infants. Thirty-nine infants aged 10-18 mo were randomly assigned to one of three groups in which they received 125 g/d of one of the three products for 1 mo. The following indexes were not modified during the supplementation period or for 1 wk after the end of supplementation: total number of anaerobes, bifidobacteria, bacteroides, and enterobacteria; pH; water content; concentrations of acetate, butyrate, propionate, and lactate; and bacterial enzyme activity of beta-galactosidase and alpha-glucosidase. In contrast, in the yogurt group the number of enterococci in fecal samples increased (P < 0.05), whereas the percentage of branched-chain and long-chain fatty acids, which are markers of proteolytic fermentation, decreased (P < 0.05). In the YC group, the percentage of children with > 6 log10 colony-forming units lactobacilli/g feces increased (P < 0.05), whereas the potentially harmful enzyme activity of beta-glucuronidase and beta-glucosidase decreased (P < 0.05). These decreases were particularly marked in those infants in the YC group in whom activity of the enzymes was initially unusually high.

Absorption balances and kinetics of nutrients and bacterial metabolites in conscious pigs after intake of maltose- or maltitol-rich diets.

Because sorbitol is poorly absorbed in the small intestine, it may be the origin of large amounts of residues reaching the large intestine and may be substrate for microbial activity. An experiment was conducted to study the quantitative appearance in the portal blood of nutrients and metabolites derived from enzymatic hydrolysis and microbial fermentation in the fore- and hindgut. Five Large White, castrated male pigs (mean BW of 61.2 +/- 1.7 kg) were fitted under anesthesia with an electromagnetic flow probe around the portal vein and with permanent cannulas in the portal vein and the carotid artery. From 10 d before surgery, they were accustomed to one of the two semisynthetic, well-balanced diets, containing a high level (53% of DM) of either a maltose-rich glucose syrup (SNat) or of a maltitol-rich hydrogenated glucose syrup (SHyd). Eight days after surgery and after an 18-h fast, each animal was given a last meal (800 g) of the diet to which it was formerly accustomed. For 12 h after this meal, blood samples were taken at 30- to 60-min intervals for glucose, sorbitol, amino N, VFA, D- and L-lactic acids, insulin, and glucagon determinations, and portal blood flow was continuously recorded. The absorption coefficients (amounts appearing for 12 h in the portal blood: amounts ingested, percentage) of glucose and of amino N were not significantly different between the two diets. The amount of sorbitol that appeared within 12 h in the portal blood after SHyd intake was 44 g (25% intake). The amount of VFA that appeared in the portal blood within 12 h was 2.7 times larger (P < .05) after intake of the maltitol-rich diet (SHyd:808 mmol) than after intake of the maltose-rich diet (300 mmol). This difference was due to an increase in absorbed amounts of propionate (SHyd 402 vs SNat 56 mmol, P < .05), butyrate (SHyd 63 vs SNat 17 mmol, P < .01), isovalerate (SHyd 17 vs SNat 5 mmol, P < .05), and acetate (SHyd 298 vs SNat 219 mmol, P < .13). There were no significant changes in insulin and glucagon production. Intake of the maltitol-rich diet resulted in less available energy (82.0%) than did intake of the maltose-rich diet (92.6%).

[Relation between food intake and oxygen consumption of organs drained by the portal vein in the conscious pig]. / Relations entre la prise alimentaire et la consommation d'oxygène des organes drainés par la veine porte chez le porc éveillé.

The intestinal absorption of glucose and alpha-amino nitrogen, the appearance of D-and L-lactic acids in the protal vein and the consumption of oxygen by the organs of the abdominal extrahepatic splanchnic area were studied simultaneously in pigs either during the postprandial period or during a fasting period of the same length. For this purpose, 5 growing pigs (59.4 +/- 3.5 kg live weight) were fitted with permanent catheters in the portal vein and carotid artery and with an electro-magnetic flowmeter probe around the portal vein. This device was used to measure the exchanges between the blood and the intestinal lumen. For a period of 1 wk, the animal received a semi-synthetic diet containing 6% purified cellulose (R6) and then during the next wk, a diet containing 16% purified cellulose (R16), the order of distribution being alternated from one animal to the next. During each of these 2 wk and after a fasting period of 16 h, they were subjected to 2 successive tests of 5 h, either after intake of an 800-g meal (R) (R6 or R16), or after no meal intake (J6 or J16). During these tests, blood samplings were made at 15 to 30-min intervals, the consumption of oxygen was recorded by an ABL3 radiometer and the afore mentioned nutrients and metabolites analysed in these samples. The consumption of oxygen was higher (P > 0.01) during the postprandial period (5.41 +/- 0.19 mmol/kg/h) than during the fasting period (4.64 +/- 0.19 mmol/kg/h) while the availability of oxygen only increased slightly (P < 0.05) (14.01 +/- 0.66 vs 13.08 +/- 0.76 mmol/kg/h). By contrast, the oxygen extraction coefficient did not significantly increase with meal intake. The appearance of L-lactic acid in the portal blood was higher (P < 0.001) during the postprandial period (3.83 +/- 0.32 g/h) than during the fasting period (1.23 +/- 0.23 g/h). The energy expenditure due to the aerobic metabolism of the organs drained by the portal vein ranged from 35.7 to 37.8 kcal/h after meal intake, ie 1-18% more than after fasting. The anaerobic metabolism only represented 0.3-0.4% (fasting) and 1.1-1.3% (postprandial period) of this aerobic metabolism. Oxygen consumption was not changed by the dietary cellulose content.

Quantitative measurement of endogenous amino acid absorption in unanaesthetized pigs.

The present experiment was carried out with 11 pigs (mean body weight: 53.9 +/- 1.3 kg) fitted with permanent catheters in the portal vein and carotid artery and with an electromagnetic flow probe around the portal vein. They were each subjected to 2 or 3 trials at 3 to 4-day intervals. During each trial the animals received after a previous fasting of 20 h a given amount of a protein-free diet (200 to 1200 g). The blood was collected either continuously for a quantitative determination of amino nitrogen, reducing sugars, urea and ammonia (number of meals 12, mean intake: 727 +/- 60 g) or discontinuously every 30 min between 0 and 8 h after the meal for amino acid analysis (number of meals 8; mean intake 709 +/- 105 g). A rather constant appearance (2 g/h) of amino acids in the portal blood was observed throughout the postprandial period. The intestinal absorption of each amino acid was however variable and represented between 10 and 50% of the daily requirements of the animal during the measuring period (8 h). Glutamine and to a less extent glutamic acid were exceptions as they were taken up by the gut wall from the arterial blood. There was also a marked synthesis of ornithine and citrulline by the latter. Because of the low blood level of urea, there were no apparent exchanges of urea between the blood and the intestine; in contrast, the ammonia absorption represented about 70% of that observed after ingestion of normal protein diets. Most amino acids are largely taken up by the liver and peripheral tissues, but in the case of alanine the syntheses exceed the uptake.

Absorption kinetics of dietary hydrolysis products in conscious pigs given diets with different amounts of fish protein. 1. Amino-nitrogen and glucose.

1. Concentrations of amino-nitrogen, glucose, reducing sugars and lactic acid in blood obtained from arterial and portal permanent catheters were measured together with the portal hepatic blood flow-rate during a post-prandial period of 8 h in twenty unanaesthetized pigs (initial mean body-weight 52.3 (SEM 0.9) kg) receiving experimental meals (200-1000 g) at 3-4 d intervals from 6-8 to 20 d after surgical implantation of the catheters and electromagnetic flow probe. The semi-synthetic starch-based diets contained variable amounts of fish meal given crude protein (nitrogen x 6.25; CP) concentrations (g CP/kg) of 80 (seven meals), 120 (twenty-two meals), 160 (six meals) and 240 (nine meals). 2. After the meal the concentration of amino-N increased with increasing levels of protein intake and increased more in the portal than in the arterial blood. There were significant relations between amounts of amino-N appearing in the portal blood at various time-intervals after the meal and the level of protein intake. Values for the ratio, amount absorbed within 8 h: amount ingested (absorption coefficient: 0.633 for a mean intake of 13.4 g N) decreased with increasing level of protein intake. 3. There was a rise in glycaemia after the meal, increasing with the amount of carbohydrate eaten, and this was more marked in the portal than in the arterial blood. There were also significant relations between amounts of glucose absorbed and amounts of starch ingested. However, the appearance of glucose in the portal blood was less marked than that of amino-N since the absorption coefficient within 8 h was lower (0.504 for a mean intake of 291 g reducing sugars). This was most probably due to a larger uptake of glucose by the intestinal cell wall. 4. Amounts of lactic acid appearing in the portal vein during the post-prandial period did not depend on amounts ingested; they ranged from 3 to 1.6 g/h from the 1st to the 8th hour after the meal.

Kinetics and balance of glucose and galactose appearance in the portal blood after intake of lactose or hydrolysed lactose in conscious pigs.

Five pigs (mean body weight: 66.2 kg) were fitted with portal and arterial catheters and an electromagnetic flow probe around the portal vein. One week after the surgical operation, each animal was successively fed, at 3-day intervals, with two experimental meals containing 392 g dry matter either from hydrolysed or non-hydrolysed lactose together with a protein-mineral-vitamin mixture (200 g). Portal and arterial blood concentrations of glucose, galactose and amino nitrogen were measured together with the portal blood flow rate during a postprandial period of 8 h after the intake of these experimental meals. Amounts of hexoses appearing in the portal blood after hydrolysed-lactose intake were 3- and 2-fold larger within 2 and 8 h, respectively, than after non-hydrolysed-lactose intake. Thus, enzymatic hydrolysis in the intestine is the limiting factor of lactose digestion in unadapted pigs. Whatever the type of lactose ingested, glucose appeared more rapidly and in larger amounts in the portal blood than galactose. After hydrolysed-lactose intake, the amount of glucose appearing in the portal blood exceeded the amount ingested already after 5 h. This means that a fraction of galactose was transformed into glucose during the transport by the enterocyte.

Comparative digestion of maltitol and maltose in unanesthetized pigs.

Four Large White pigs (mean body weight 62.8 +/- 0.6 kg) were fitted with permanent catheters in the portal vein, carotid artery and duodenum, and with an electromagnetic flow probe around the portal vein. Eight days after surgery each animal received at 4-d intervals two duodenal infusions for 1 h each of solutions (1000 mL) containing 110 g of mild enzymic milk protein hydrolysate and 440 g of either a maltose-rich glucose syrup (54.6% maltose, 5.2% free glucose) or a maltitol-rich hydrogenated glucose syrup (54.2% maltitol, 6% free sorbitol). For 8 h after the beginning of each infusion, portal blood flow rate was recorded continuously, and blood samples were collected at various intervals (15 to 30 min) for the analysis of aminonitrogen, glucose and sorbitol. Maltitol was hydrolyzed substantially in the small gut. The absorption coefficient of glucose (percentage of infused glucose appearing in the portal blood) was the same 8 h after infusion of maltitol (78.1%) and maltose (78.8%). Sorbitol was poorly absorbed, with an absorption coefficient of 7.2% after 8 h. Its presence in the gut lumen did not inhibit the absorption of glucose. Aminonitrogen from milk oligopeptides appeared more rapidly in the portal vein during the first 4 h after infusion of maltitol than after that of maltose. This was probably due to a reduced competition between absorption of glucose and oligopeptides because of the smaller amount of glucose in the digestive lumen after maltitol hydrolysis.

[Comparison of 2 technics (ninhydrin vs. TNSB) for estimating circulating amino acid nitrogen, applied to the study of the intestinal absorption of solutions of free amino acids or small peptides]. / Comparaison de deux techniques d'estimation (ninhydrine vs TNBS) de l'azote des acides aminés circulants, appliquées à l'étude de l'absorption intestinale de solutions d'acides aminés libres ou de petits peptides.

The intestinal absorption of nitrogen from amino acids present in a solution of small peptides or of free amino acids with the same pattern, perfused intraduodenally, has been studied using two analytical techniques [2, 4, 6 trinitrobenzene-1-sulfonic acid (TNBS) after dialysis of the blood vs ninhydrine after chromatography] to determine post-perfusion porto arterial differences and to measure blood flow rate in the portal vein. The results obtained on blood nitrogen level with the chromatographic method were always higher than those obtained using the TNBS method. The differences in the values varied from 8 to 24% according to post-perfusion time and to blood sample origin (arterial or portal). On the contrary, the absorbed amounts of nitrogen measured by either analytical technique were not very much different: no significant and systematic deviation was found between the two. The TNBS method is thus useful as a preliminary approach to very elaborate studies on intestinal absorption. In these conditions, the nitrogen of amino acids from duodenally-perfused small peptides was absorbed earlier and more rapidly than that from a perfusion of a solution of free amino acids. The amount of nitrogen appearing in the portal vein five hours after perfusion exceeded the perfused amount owing to considerable recycling of endogenous nitrogen.

[Effect of the nature of carbohydrates in pig diets on the intestinal absorption of volatile fatty acids]. / Influence de la nature des glucides présents dans le régime du porc sur l'absorption intestinale des acides gras volatils.

The appearance of nutrients (amino nitrogen and reducing sugars) and microbial metabolites (volatile fatty acids, VFA) was measured quantitatively in five pigs. After ingestion of a semi-synthetic diet (RFL) containing 22% lucerne meal (6% crude fibre), the absorption of reducing sugars (RS) in the small intestine was high (97.8%) and that of VFA low (880 +/- mmoles/24 hrs.). Ingestion of a semi-synthetic diet (RLa) containing 22% lactose and 6% purified cellulose led to lower absorption of RS (85.2%) and a higher absorption of VFA (1,180 +/- mmoles/24 hrs).

[Influence of purified cellulose level in the diet of pigs on intestinal absorption of volatile fatty acids]. / Influence du taux de cellulose purifiée dans le régime du porc sur l'absorption intestinale des acides gras volatils.

Nutrient and volatile fatty acid (VFA) absorption to portal blood was measured twice at 7 days interval in five pigs fed a semi-synthetic diet containing 6 (R6) or 16% (R16) purified cellulose for 21 or 7 days. The daily absorption (24 hrs.) of VFA in the large intestine which was larger (NS) when the cellulose level rose, increased significantly (P less than 0.05) with increasing length of adaptation (21 to 28 d.) to the diet whatever the cellulose level. The supplementary daily supply of energy in the form of VFA after increase of the cellulose level did not compensate for the corresponding deficit of absorption of reducing sugars and crude protein in the small intestine.

Kinetics of amino acid and glucose absorption following pancreatic diversion in the pig.

An experiment was conducted in the pig to determine the consequences of deprivation of exocrine pancreatic secretion on the composition and quantity of nutrients absorbed after intake of a balanced diet. Five growing pigs (53.8 kg body weight) were fitted with permanent catheters in the portal vein and the carotid artery and with an electromagnetic flow probe around the portal vein to measure the exchanges between the blood and the intestinal lumen. They were also fitted with a permanent catheter in the duct of Wirsung to educe the exocrine pancreatic secretion and another one in the duodenum in order to reintroduce it. In each animal, glucose, amino-N and amino acid absorption as well as insulin and glucagon production were measured over a period of 10 h after the meal (semi-purified diet based on purified starch and containing 180 g fish meal/kg, DM content of the meal 731 g), either in the presence of pancreatic juice (group C: immediate reintroduction), or in the absence of pancreatic juice (group D: deprivation). The deprivation of pancreatic juice provoked a marked depression in the absorption of glucose (D 67.9 (SEM 27.9) g/10 h, C 437.7 (SEM 39.5) g/10 h, P < 0.001), and of amino-N (D 7.55 (SEM 0.54) g/10 h, C 15.80 (SEM 0.79) g/10 h, P < 0.001). The composition of the mixture of amino acids in the portal blood was only slightly modified: only the levels of histidine (P < 0.05) and of valine (P < 0.06, NS) decreased in the absence of pancreatic juice. Insulin production was much lower (by 64%, P < 0.05) in the absence of pancreatic juice whereas that of glucagon was not affected.

Absorption kinetics of some carbohydrates in conscious pigs. 1. Qualitative aspects.

Concentrations of reducing sugars, glucose, fructose and lactic acid in blood obtained from arterial and portal catheters were measured for periods of 8-24 h in twenty-three unanaesthetized pigs (mean body-weight 50 kg). From 6 to 8 d after implantation of catheters, the animals received experimental meals containing different levels (400, 800, 1200, 1600 g respectively) of different sugars (glucose ten meals, sucrose eighteen meals, lactose nine meals, maize starch sixteen meals) as well as a protein-mineral-vitamin premix. After each meal the reducing sugars appeared in the portal blood in successive waves. The porto-arterial differences in the concentration of reducing sugars, representing the real appearance of sugar-hydrolysis products in the animal, varied greatly according to the sugar ingested and its level of intake. For each level of intake, these differences were larger, but of shorter duration, for glucose and sucrose than for maize starch. For these three carbohydrates, the higher the level of ingestion, the larger and the more persistent the porto-arterial differences. Lactose represented a special case, as the porto-arterial differences of reducing sugars were always much lower than those obtained with the other sugars and they did not vary with the level of intake. Our findings show that the products formed by feeding glucose and sucrose appear more rapidly in the portal blood than those formed by feeding lactose. Accordingly, the length of time of digestion of glucose and sucrose is shorter than that of maize starch and lactose.

Absorption kinetics of some carbohydrates in conscious pigs. 2. Quantitative aspects.

Concentrations of reducing sugars, glucose, fructose and lactic acid in blood obtained from arterial and portal catheters were measured together with the portal hepatic blood flow-rate for periods of 8-24 h in twenty-six unanaesthetized pigs (mean body-weight 51 kg). The animals received experimental meals containing different amounts (100-1600 g) of different sugars (glucose fifteen meals, sucrose twenty-four meals, lactose fourteen meals, maize starch nineteen meals) together with a protein-mineral-vitamin mixture (150 g) 6-8 after implantation of the catheters and an electromagnetic flow probe. Because the portal blood flow pattern did not differ between test meals, net absorption followed the same trends as for porto-arterial concentration differences (R erat et al. 1984). Apart from lactose, the amounts of reducing sugars appearing in the portal vein correlated with the intake of the test meal, but the absorption pattern was different for each sugar. The appearance of reducing sugars was faster and earlier after intake of glucose than after sucrose and the same was the case for sucrose relative to maize starch. The differences between the three carbohydrates tended to increase with the level of intake. With a test meal containing 1 kg carbohydrate, i.e. a normal meal in a 50 kg pig, digestion of sucrose and maize starch was not finished 8 h after the meal since only 60 and 52% respectively of their hydrolysis products were recovered in the portal blood. In the case of lactose, the amounts of reducing sugars appearing in the portal blood were always very small and constant (113-118 g within 8 h) whatever the level of intake, i.e. 30 and 15% of their hydrolysis products for intakes of 400 and 800 g respectively. Depending on the carbohydrate ingested, the uptake of glucose by the gut cell wall ranged from 14 to 21 g/h and the production of lactic acid from 2.5 to 3.5 g/h.

[Comparative kinetics of appearance in the portal vein of alpha-aminated nitrogen from mixtures of small peptides of free amino acids of the same composition introduced in the duodenum of conscious pigs]. / Cinétique comparée d'apparition dans la veine porte de l'azote alpha-aminé provenant de mélanges de petits peptides ou d'acides aminés libres de même composition introduits dans le duodenum chez le porc éveillé.

The quantitative kinetics of appearance of amino acids (a.a.) in the pig portal vein was studied in 6 animals for 5 hrs. after duodenal perfusion of an enzymatic hydrolysate of milk proteins or a solution of free a.a. of the same composition. Each product was given in two quantities (55 and 110 g). The quantities of a.a. appearing in the portal vein were higher after perfusion of the hydrolysate than after that of the free a.a., independently of the time after the perfusion. Thus, nitrogen present in the small intestine as small peptides is absorbed more quickly than when it is present as free amino acids.

Splanchnic fluxes of amino acids after duodenal infusion of carbohydrate solutions containing free amino acids or oligopeptides in the non-anaesthetized pig.

Seven non-anaesthetized pigs (mean body-weight 64.6 kg) were used to study the intestinal absorption and hepatic metabolism of glucose and amino acids (AA) using carbohydrate solutions (maltose dextrin; 440 g/2 I), containing 110 g of either an enzymic milk-protein hydrolysate (PEP) with a large percentage of small peptides (about 50% with less than five AA residues) and very few free AA (8%) or a mixture of free AA (AAL) with an identical pattern, infused intraduodenally. Each pig was previously fitted under anaesthesia with electromagnetic flow probes around the portal vein and the hepatic artery, and with permanent catheters in the portal vein, carotid artery, one hepatic vein and the duodenum. Each solution was infused for 1 h after a fasting period (18 h) and each pig received both solutions at 8 d intervals. The observation period lasted 8 h. For most AA (his, lys, phe, thr, arg, tyr, pro) the absorption rate after infusion of PEP was significantly higher than after that of AAL during the 1st hour, but the differences quickly disappeared. After 8 h, the only differences concerned his and tyr (PEP > AAL) and met, glu and asp (AAL > PEP). There was a large uptake of blood AA by gut-wall cells, higher after AAL infusion than after PEP infusion, particularly for branched-chain AA (BCAA). The absorption of ammonia-nitrogen after both infusions was equivalent to two-thirds of urea-N passing from blood to intestinal tissues and lumen. Glucose absorbed within 8 h represented only 76% (PEP) or 69% (AAL) of the infused amounts. The cumulative hepatic total AA (TAA) uptake increased from 13 to 27% of the infused amounts between the 1st and the 8th hour after PEP infusion, and from 8 to 31% after AAL infusion. Most essential AA were largely taken up by the liver, with the exception of met (PEP) and thr and of BCAA, which were poorly retained for both solutions; there was a high uptake of ala and gly, and a release of asp, glu, and gln. Urea-N released by the liver within 8 h was equivalent to 23-25% absorbed amino-N and to around 1.5 times ammonia-N taken up by the liver within 8 h. Glucose was highly taken up by the liver during the first hours then released, the total uptake within 8 h representing about half the absorbed amount.(ABSTRACT TRUNCATED AT 400 WORDS)

Metabolic and hormonal effects of test meals with various protein contents in pigs.

The postprandial release of immunoreactive insulin, glucagon, gastrin, somatostatin, pancreatic polypeptide (PP), and gastric inhibitory polypeptide (GIP) was studied in parallel with the absorption of sugars and amino acids in conscious pigs. Six pigs fitted with permanent catheters in the portal vein and arterial blood system as well as within an electromagnetic flow probe around the portal vein received successively at 3-day intervals, three meals of 800 g each containing 0, 14, or 28% protein (semisynthetic diets based on fish protein). Blood samples were collected and portal blood flow was recorded during a postprandial period of 8 h. For the same level of feed intake, an increase in the dietary protein concentration led to a higher alpha-amino nitrogen absorption and to a lower appearance of reducing sugars in the portal vein; in addition, the carbohydrate absorption efficiency (amounts absorbed as a percentage of amounts ingested) was reduced, showing the competition between the absorption of amino acids and glucose. The largest absorption occurred during the first 4 h after the meal, but neither the digestion of proteins nor that of carbohydrates were finished 8 h after the meal since portoarterial differences could still be observed. All test meals induced a rise of portal and peripheral concentrations of insulin, gastrin, somatostatin, and PP, and of the systemic level of GIP. Glucagon increased after the 28% protein meal only. The rise of plasma insulin paralleled that of blood glucose, and bore a significant positive relationship to the systemic GIP level in the early postprandial period. In terms of absolute amounts, portoarterial concentration gradients increased postprandially. Insulin release was significantly the highest after intake of the 14% protein diet. The gastrin response was significantly correlated to the amount of protein. Similarly the release of glucagon and somatostatin tended to increase with increasing dietary amount, but differences failed to reach significance (P less than 0.05), except for glucagon 2 h after the meal. There were very close relationships between the hourly amounts of alpha-amino nitrogen absorbed and gastrin and glucagon production, as between insulin and PP secretions. From the present results, the induction of physiological increments of plasma peptide concentration in 60-kg pigs would require infusion rates of about 50-250 micrograms/h for insulin, 1-4 micrograms/h for gastrin 17, 5-10 micrograms/h for glucagon and somatostatin, and 5-50 micrograms/h for PP.

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 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.