The effects of ingestion of poorly digestible carbohydrates on bacterial transformations of cholic acid and p-muricholic acid were studied in rats fed on increasing levels of lactose, lactulose, amylomaize or potato starches. Each level was given for 3 weeks and, at the end of each dietary treatment, bile acid faecal composition was analysed and a group of six rats was killed every 4 h during 24 h to determine the amounts of fermented carbohydrate and fermentation characteristics (caecal pH, volatile fatty acids (VFA) and lactic acid concentrations). Fermentation of carbohydrates decreased caecal pH and enhanced caecal VFA and lactic acid concentrations. Irrespective of the poorly digestible carbohydrate, the variation of bacterial transformation always occurred in the same way : the bacterial transformation of /?-muricholic acid into hyodeoxycholic acid was the first to disappear, while o-muricholic acid formation increased ; second, cholic acid transformation decreased and finally all bile acid transformations were strongly affected. There was a significant correlation between bile acid transfer and the minimal caecal pH in vivo. This effect of pH was similar in vitro. To determine whether the levels of bacteria which transformed bile acids were modified, rats fed on the highest amounts of poorly digestible carbohydrates were introduced into isolators and carbohydrate feeding was stopped. Caecal pH recovered its initial value but bile acid transformations remained changed, suggesting that the intestinal microflora were modified by ingestion of fermentable carbohydrates.
The 0-glucuronidase activities of bacterial strains isolated from the rat intestinal tract were studied both in vitro in culture media and in vivo in the intestinal contents of gnotobiotic rats. Only 50 of 407 strains tested were found to be positive in vitro. They belonged to the three genera Clostridium, Peptostreptococcus, and Staphylococcus. The in vitro-negative strains were also negative in vivo. The I-glucuronidase activities of the positive strains were generally greater in vivo than in vitro. The highest in vivo activities were found in the intact bacterial cells and in the soluble fractions prepared from disrupted pellets. There was a discrepancy between the activities obtained from both conventional and gnotobiotic rats harboring selected positive strains, suggesting that the main 0-glucuronidase-positive strains have not yet been isolated from the intestines of conventional rats. Glucuronidation together with sulfation are the most usual forms of conjugation observed during the metabolism processes in mammals and also represent the major pathway for detoxification mechanisms. Thus, hydrolysis of glucuronides by ,-glucuronidase enzymes have been considered by pathologists to be an important enzyme reaction in the digestive tract. The 3-glucuronidase enzymes were detected both in intestinal tissues and in intestinal bacteria. The activity in the intestinal tissues was found to be optimal at pH 4.5, whereas that of bacteria was best at around pH 6.5 to 7.0 (13). Williams et al. (16) and Rod and Midtvedt (13) clearly
The activities of UDP-glucuronyl transferase(s) in homogenates and microsomal preparations of human liver, kidney and intestine were tested with hyodeoxycholic acid (HDC). The various kinetic parameters of the UDC-glucuronidation were determined from time course experiments. In both liver and kidney preparations, HDC underwent a very active metabolic transformation: liver K, = 78 PM, V,, = 3.3 nmol*min -l.rng -i protein; kidney K, = 186 PM, I',, = 9.9 nmol.min -l.rng -l protein. To our knowledge this is the first observation of both an extensive and comparable bile acid glucuronidation occurring in renal and hepatic tissues.
Summary. 1.5 and 3 % of Maillard's reaction products (MRP), prepared by heating glycine and glucose, were incorporated into a semi-synthetic diet. The diet was sterilized by irradiation. MRP caused a change in apparent absorption of calcium and magnesium in germfree (GF) and conventional (CV) rats. The absorption of these minerals was reduced in the small intestine of CV and GF, perhaps due to the action of MRP on enterocyte metabolism. This effect was compensated for only in CV rats by increased absorption of these minerals in the cecum and the colon. The presence of microflora and the increase in cecal volume in CV rats suggested that MRP fermentation increased mineral absorption in the cecum and colon. However, although total apparent absorption of magnesium and phosphorus was higher in CV rats ingesting MRP, the urinary excretion of these minerals was also higher and their retention was not better. The effect of MRP in GF rats was not compensated for in the cecum, and mineral retention was significantly reduced in GF rats ingesting MRP. Introduction.
Summary. Germfree and conventional rats were given a semi-synthetic diet containing either normal cornstarch or an amylomaize starch. The experimental groups thus formed were compared to assess the effects of these two types of starch and to determine if digestive tract microflora was involved in these effects.The presence of amylomaize starch decreased body growth in germfree and conventional rats, increasing food intake in the former and decreasing it in the latter. In conventionals, amylomaize starch decreased the apparent digestibility of the ration only slightly, while in germfrees it diminished apparent digestibility considerably. The cecal weight of germfree animals was not modified by amylomaize starch but that of conventional rats was increased fourfold.In both types of rat, amylomaize starch largely decreased the plasma concentration of cholesterol, largely increased the total amount of bile acids in the small intestine but slightly modified the fecal elimination of cholesterol and bile acids. It augmented the cholesterol concentration in the liver of germfrees and decreased it in conventionals while, on the contrary, it diminished the total amount of bile acids in the hind gut in the former and augmented it in the latter. This starch did not change bile acid deconjugation in conventional rats but considerably decreased other bacterial transformations of cholesterol and bile acids.Digestive tract microflora was undoubtedly involved in the action of amylomaize starch on cecal weight, ration digestibility, food intake, hepatic cholesterol concentration, the amount of bile acid in the hind gut and obviously in the transformation of cholesterol and bile acids. It did not play a role in the other effects of this starch : the strong decrease in the concentration of plasma cholesterol was the direct effect of amylomaize starch on rat metabolism.Introduction.
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