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A study was conducted with conventional and germ-free broiler chicks to obtain more information on the role of the intestinal microflora in the anti-nutritive effects of NSP in broiler chicks. As the NSP source, highly methylated citrus pectin (HMC) was used at a dose level of 30 g/kg in a maize-based diet. The diets fed to the germ-free chicks were gamma-irradiated, whereas those fed to the conventional chicks were not. Feeding the HMC diet to conventional birds depressed weight gain and food utilization (P < 0.05), whereas in germ-free birds only weight gain was reduced (P < 0.05). Feeding the HMC diet to conventional birds reduced digestibilities of energy and starch at the end of the jejunum. Ileal digestibilities of starch and energy were not strongly affected when birds were fed on the HMC-containing diet. Faecal digestibilities of organic matter, crude fat, starch and amino acids, N retention and metabolizable energy were reduced when conventional chicks were fed on the HMC diet. Feeding the HMC diet to germ-free birds hardly affected faecal digestibility of nutrients and N retention, whereas metabolizable energy was increased. Feeding the HMC diet to conventional or germ-free birds increased the viscosity of the digesta in the small intestine. This increase in digesta viscosity was more pronounced in conventional than in germ-free birds. The pH of ileal digesta was reduced when HMC was added to the diet of conventional chicks, but not in germ-free chicks. Feeding the HMC diet to conventional birds markedly affected morphology of the gut wall, whereas in germ-free chicks very little effect was found on gut morphology. Based on the results of the present study, it is concluded that the gastrointestinal microflora mediates the magnitude of the anti-nutritive effects of HMC in broiler chicks. However, the exact role of the microflora in chicks in the magnitude of the anti-nutritional effects of HMC could not be derived from the present study, since the results might have been influenced by gamma-irradiation of the diets fed to the germ-free chicks.

The aim of the present work was to investigate the influence of the intestinal microflora on the changes in hepatic cytochrome P450 apoproteins induced by dietary glucosinolates. Ten rats harbouring a conventional digestive microflora were offered either a diet containing 390 g myrosinase-free rapeseed meal/kg (n 5) or a control diet devoid of glucosinolates (n 5). A similar trial was performed using germ-free rats. After 4 weeks of exposure to the dietary regimens, animals were slaughtered and their livers removed for preparation of microsomes and analysis of cytochrome P450 (EC 1.14.14.1). The glucosinolate-rich diet decreased the concentration of total cytochrome P450 in conventional rats only (-34%). The bacterial status did not modify the concentration of apoproteins CYP1A2 and CYP2B1/B2, but greatly decreased the concentration of the male constitutive isoform CYP2C11 (-53 and -45% respectively in conventional and germ-free rats). Germ-free rats fed on the glucosinolate-rich diet had a greater concentration of CYP3A (+139%) and a lower concentration of CYP2E1 (-32%) than their counterparts fed on the control diet. However, these differences were absent in conventional animals. On the whole, the influence of the intestinal microflora on the changes in hepatic cytochrome P450 due to the consumption of cruciferous vegetables is very complex and obviously involves different mechanisms according to the apoprotein.

We questioned whether polyamines coming from the diet or produced by intestinal microflora or by intracellular metabolism influence intestinal functions. Therefore, we compared pathogen-free rats and germ-free rats receiving a diet with low polyamine content and either treated or not treated with difluoromethylornithine (DFMO) and/or methylglyoxal bis (guanylhydrazone) (MGBG). Wet weight, protein content, DNA content, sucrase (EC 3.2.1.48), maltase (EC 3.2.1.20) and lactase (EC 3.2.1.23) specific activities, amounts of putrescine, spermidine and spermine were measured in the mucosa of the proximal and distal intestine. Body weight was also determined. Rats without microflora had a higher specific activity of maltase and higher amounts of spermidine and spermine but lower lactase specific activity than pathogen-free animals; the low-polyamine diet given to germ-free rats had little effect on the functional variables measured (decrease of maltase and lactase specific activities) and did not modify the amounts of polyamines. DFMO and/or MGBG administered to germ-free rats receiving a low-polyamine diet induced modifications of most of the variables studied. Body weight and wet weight of proximal and distal intestine decreased, disaccharidase specific activities decreased, and amounts of polyamines changed according to the inhibitor used. Thus, our results showed that the deprivation of polyamine supply from microflora or from the diet failed, under our experimental conditions, to affect the intestinal properties analysed but exogenous and endogenous polyamine restriction altered general properties of the organism as well as intestinal functions.

The metabolism of maltitol (4-alpha-D-glucosylsorbitol) was assessed in fasting conventional (C) rats, C mice and germ-free (GF) mice, using [U-14C]maltitol. The radiorespirometric patterns of 14CO2 collected for 48 h after the administration of labelled maltitol were characterized by a constant rate of 14CO2 production lasting 4 h for both C rats and mice. The pattern for the GF mice showed a peak at the second hour followed immediately by a slow decrease. The percentage recovery of 14CO2 was significantly lower for the GF mice (59%) compared with C animals (72-74%). Urine, faeces and intestinal contents after 48 h totalled 19% of the administered radioactivity in the C rats and mice and 39% in the GF mice. The digestibility of maltitol and the absorption of sorbitol in GF mice was also assessed. The caecum and small intestine of GF mice, 3 h after administration of equimolar quantities of maltitol (140 mg/kg body-weight) or sorbitol (70 mg/kg body-weight), contained 39 and 51% of the ingested dose respectively, present mostly in the caecum as sorbitol. The alpha-glucosidase (maltase) (EC3.2.1.20) activity of the small intestine was appreciably higher (1.5-1.7 times) in the GF mice than in the C mice. These results suggest that the enzymic activities in the small intestine of mice and rats are sufficient to hydrolyse maltitol extensively. Consequently, the slow absorption of sorbitol seems to be an important factor limiting the overall assimilation of maltitol in the small intestine.