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Bile duct ligation was performed in germ-free and conventional rats in order to study the effects of bile deprivation on the absorption of dietary lipids and the excretion of faecal lipids in the presence or the absence of gastrointestinal flora. The main consequence of bile duct ligation in conventional rats was decrease of about 50% in the apparent absorption of dietary lipids (peanut oil). In germ-free rats, absorption decreased by only about 25%.In conventional as well as in germ-free controls, faecal lipids were mainly excreted as compounds directly soluble in organic solvents that is, free fatty acids, triglycerides, partial glycerides, cholesterol, cholesterol esters. Deprivation of bile secretion significantly increased the faecal excretion of 'insoluble' compounds-that is, calcium soaps-both in germ-free and conventional rats. Free fatty acids and sterol esters were the two main class of soluble faecal lipids both in germ-free and conventional rats deprived of bile secretion. Faecal excretion of triglycerides remained low in germ-free as well as in conventional animals. No significant difference of fatty acid absorption was observed between germ-free and conventional controls. Deprivation of bile secretion resulted in a significant decrease in the absorption of all fatty acids in germ-free as well as in conventional animals. However, the decrease was larger for saturated fatty acids-that is, 16:0 or 18:0- than for unsaturated fatty acids-that is, 18:1 or 18:2. The absorption of all fatty acids, except linoleic acid (18:2), was significantly lower in conventional rats artificially deprived of bile secretion than in their germ-free counterparts. Evidence was given for a negative digestive balance of stearic acid (18:0) in bile deprived conventional animals. This observation was correlated with a very efficient biohydrogenation of dietary unsaturated fatty acids as revealed by radio gas chromatography of faecal acids in bile deprived conventional rats fed a diet containing 1-14C oleic acid (18:1) as homogeneous triglycerides. Nevertheless, biohydrogenation of unsaturated dietary fatty acids by the gastrointestinal flora was not considered to be the only factor involved in the origin of the difference of fat absorption between bile deprived germ-free and conventional animals.

Des bilans minéraux (P, Ca, Mg, Na, K, Mn, Fe, Cu) ont été effectués sur trois lots de rats conventionnels (CV) recevant un aliment non stérilisé (CVN), autoclavé (CVA) ou irradié (CVI) et sur deux lots de rats axéniques (GF) recevant un aliment autoclavé (GFA) ou irradié (GFI). Chez les rats CV la stérilisation de l'aliment par autoclavage (CVA) ou par irradiation (CVI) modifie l'absorption apparente et la rétention de Mn, Fe, Cu, accentue l'excrétion urinaire de P et Mg et a un effet défavorable sur la rétention de Mg. La comparaison entre les rats CV et GF met en évidence un effet favorable de l'état axénique sur l'absorption apparente et la rétention de Ca, P, Mg, Mn, Cu, un effet défavorable sur l'absorption apparente de Na et K. Cependant, les différences observées sont modifiées par le mode de stérilisation de l'aliment. Ainsi, l'état axénique modifie davantage le métabolisme de Na et K, l'excrétion urinaire de P et l'absorption apparente de Mn lorsque l'aliment est irradié que lorsqu'il est autoclavé. A l'inverse, l'utilisation digestive apparente et l'excrétion urinaire de Mg, l'absorption apparente et la rétention de Fe sont modifiées davantage lorsque l'aliment est autoclavé. Chez les rats GF les effets du mode de stérilisation sur certains paramètres du métabolisme de Na, K, Fe, Mn, Mg et P sont plus grands que chez les rats CV. Le mode de stérilisation est donc susceptible de modifier le métabolisme de certains minéraux et la flore microbienne du tractus digestif est capable de modifier cette action. Minéral balances of P, Ca, Mg, Na, K, Mn, Fe and Cu were determined for three groups of holoxenic rats (CV) fed a non sterilized (CVN), steamsterilized (CVA) or irradiated (CVI) diet and for two groups of axenic (GF) rats fed a steam-sterilized (GFA) or irradiated (GFI) diet. In the group of CV rats as compared to CVN group of rats, the CVA and CVI rats retained less Cu and more Fe and Mn, their urinary excretion of P and Mg was higher and they retained less Mg. Comparison between CV and GF rats showed that the apparent absorption and retention of Ca, P, Mg, Mn, Cu were higher in GF than in CV rats. On the contrary, the apparent absorption of Na and K was lower in GF than in CV rats. However, the observed differences were modified by the mode of diet sterilization. Thus, with respect to the apparent absorption of Na, K, Mn and urinary excretion of Mg, the differences between CV and GF rats were larger when the diet was irradiated than when it was steam-sterilized. On the contrary, the apparent digestibility and urinary excretion of Mg, the apparent absorption and retention of Fe were more modified when the diet was steam-sterilized than when irradiated. For some parameters of the metabolism of Na, K, Fe, Mn, Mg, and P measured in GF rats, the differences observed between GFA and GFI rats were larger than in CV rats. Accordingly, the mode of sterilization is liable to modify the metabolism of some minerals and the microbial flora of the digestive tract is capable of modifying this action.

Chez les rats qui reçoivent une flore microbienne qui fait disparaître la distension du caecum présente chez les axéniques, mais qui ne metabolise pas les acides biliaires, le pool intestinal et l'excrétion fécale se rapprochent de ceux des rats holoxéniques. La flore microbienne exerce donc une action non spécifique sur le métabolisme des acides biliaires, en modifiant les caractères de la physiologie digestive qui sont liés à la distension caecale des rats axéniques. Chez les rats qui reçoivent un aliment commercial complexe, le pool intestinal et l'excrétion fécale des acides binaires sont plus élevés que chez ceux qui reçoivent un aliment semi-synthétique qui a la même teneur en cholestérol, et la différence entre les excrétions fécales des rats axéniques et celles des rats holoxéniques est plus grande que chez les rats qui reçoivent l'aliment semi-synthétique. Cette plus grande différence est due surtout à une plus grande excrétion fécale d'acides biliaires chez les rats holoxéniques qui reçoivent le régime commercial : elle est donc en rapport avec une modification de la flore microbienne du tractus digestif sous l'action du régime alimentaire. When axenic rats are given a microflora which causes the caecum distension present to disappear but does not metabolize bile acids, the intestinal pools and fecal excretion of bile acids are intermediary between those of axenic and those of holoxenic rats. This flora acts non-specifically on bile acids metabolism by changing the physiological characters related to caecal distension in axenic rats. The intestinal pools and fecal excretion of bile acids are higher in rats given a commercial chow than in those receiving a semi-synthetic feed containing the same amount of cholesterol; the difference between axenic and holoxenic rat fecal excretions is greater than in rats given the semi-synthetic feed. This wider difference is especially due to greater fecal excretion of bile acids in holoxenic rats given the commercial diet; it is thus related to modification of the gut microbial flora due to diet.

Biotin deficiency was induced in germ-free rats using three experimental protocols. The results showed the important role of biotin during gestation and suckling. The earlier the deprivation, the earlier the deficiency and the severer the symptoms. In this vitamin deficiency, symptoms occurred that were not observed in the control rats, such as the formation of an intestinal volvulus in rats ingesting an L-isoleucine-supplemented diet. The main biochemical anomalies characteristic of propionic acidemia (ketoacidosis and increased urinary elimination of propionic acid) due to propionyl CoA carboxylase deficiency in man were not observed in the rats that were deprived of biotin for 200 days even after a dietary load of L-isoleucine. Only a small urinary excretion of propionyl-glycine and tiglylglycine was observed. We observed a drop in enzymatic propionyl CoA carboxylase activity in the liver that was proportional to the severity of the vitamin deficiency.

Minéral balances of P, Ca, Mg, Na, K, Mn, Fe and Cu were determined for three groups of holoxenic rats (CV) fed a non sterilized (CVN), steamsterilized (CVA) or irradiated (CVI) diet and for two groups of axenic (GF) rats fed a steam-sterilized (GFA) or irradiated (GFI) diet. In the group of CV rats as compared to CVN group of rats, the CVA and CVI rats retained less Cu and more Fe and Mn, their urinary excretion of P and Mg was higher and they retained less Mg. Comparison between CV and GF rats showed that the apparent absorption and retention of Ca, P, Mg, Mn, Cu were higher in GF than in CV rats. On the contrary, the apparent absorption of Na and K was lower in GF than in CV rats. However, the observed differences were modified by the mode of diet sterilization. Thus, with respect to the apparent absorption of Na, K, Mn and urinary excretion of Mg, the differences between CV and GF rats were larger when the diet was irradiated than when it was steam-sterilized. On the contrary, the apparent digestibility and urinary excretion of Mg, the apparent absorption and retention of Fe were more modified when the diet was steam-sterilized than when irradiated. For some parameters of the metabolism of Na, K, Fe, Mn, Mg, and P measured in GF rats, the differences observed between GFA and GFI rats were larger than in CV rats. Accordingly, the mode of sterilization is liable to modify the metabolism of some minerals and the microbial flora of the digestive tract is capable of modifying this action.

β-Muricholic acid is the main bile acid in germ-free (axenic) rat but is found in smaller amounts in conventional ('holoxenic') rat. In order to study how intestinal microflora induces such a change in bile salt metabolism, the bacterial degradation of β-muricholic acid was studied in vivo and in vitro. Two conventional rats were fed a load of β-muricholic-4 ¹⁴C-acid and the distribution of radioactivity in the feces was studied by thin-layer chromatography with the following results: (1) β-muricholic-4 ¹⁴C-acid rapidly disappeared from the feces; (2) hyodeoxycholic acid was the main metabolite which was formed, together with 3α-hydroxy-6 keto-5β-cholanoic acid and several unidentified chemical species. However in vitro incubation of βmuricholic-4 ¹⁴C-acid with cecum homogenates of conventional rats did not result in the formation of hyodeoxycholic acid. The possible pathway of hyodeoxycholic acid formation in the rat is discussed. were fed a load of β-muricholic-4 ¹⁴C-acid and the distribution of radioactivity in the feces was studied by thin-layer chromatography with the following results: (1) β-muricholic-4 ¹⁴C-acid rapidly disappeared from the feces; (2) hyodeoxycholic acid was the main metabolite which was formed, together with 3α-hydroxy-6 keto-5β-cholanoic acid and several unidentified chemical species. However in vitro incubation of βmuricholic-4 ¹⁴C-acid with cecum homogenates of conventional rats did not result in the formation of hyodeoxycholic acid. The possible pathway of hyodeoxycholic acid formation in the rat is discussed. L'ingestion d'acide β-muricholique-4 ¹⁴C permet de montrer que la flore microbienne du rat possède une très grande capacité de transformer cet acide biliaire. L'acide hyodésoxycholique est le principal metabolite qui est ainsi formé. La façon dont la flore microbienne du tractus digestif réalise cette transformation demeure obscure.

When axenic rats are given a microflora which causes the caecum distension present to disappear but does not metabolize bile acids, the intestinal pools and fecal excretion of bile acids are intermediary between those of axenic and those of holoxenic rats. This flora acts non-specifically on bile acids metabolism by changing the physiological characters related to caecal distension in axenic rats. The intestinal pools and fecal excretion of bile acids are higher in rats given a commercial chow than in those receiving a semi-synthetic feed containing the same amount of cholesterol; the difference between axenic and holoxenic rat fecal excretions is greater than in rats given the semi-synthetic feed. This wider difference is especially due to greater fecal excretion of bile acids in holoxenic rats given the commercial diet; it is thus related to modification of the gut microbial flora due to diet.