Effect of different modifications of a semi-synthetic diet on bile acid metabolism in axenic and holoxenic rats

Axenic (germfree) and holoxenic (conventional) rats were fed diets which were different as to (a) the mode of sterilization : autoclaving or gamma-irradiation ; (b) the absence or presence of 10 p. 100 lactose added before sterilization.In addition, the autoclaved diet was offered to the rats in the form of pellets and the irradiated diet in the form of a paste.Important changes in bile acid metabolism were induced by these dietary modifications.1) The bile acid intestinal pools were much larger in the rats fed the irradiated diet than in those fed the autoclaved one.They were unmodified by the addition of lactose when the diet was irradiated, but increased when it was autoclaved.The variations were observed both in axenic and holoxenic rats, and are therefore considered as not mediated by the intestinal bacterial flora.2) Bile acid fecal excretions varied conversely to the pools.3) In axenic rats, the percentage of cholic acid decreased when the bile acid pool increased.4) In holoxenic rats, the bacterial transformation of bile acids was lower with the irradiated diet than with the autoclaved diet, and with the lactose-containing diet than with the lac- tose-free one.The formation of m-muricholic acid at the expense of hyodeoxycholic acid increased when the bacterial transformation of bile acids decreased.Hypotheses are proposed to explain these variations in bile acid metabolism induced by the diet.