Objective: To assess the effects of drug-induced changes in mean transit time (MTT) on the activity of human fecal¯ora in vitro. Methods: The activity of fecal¯ora was estimated by the ability of a fecal inoculum to ferment a substrate (beet ®ber) in vitro in a batch system for 24 h. The inoculum was collected from 8 healthy volunteers studied during three 3-week randomized periods, who received a controlled diet alone (control period) or the same diet with either cisapride or loperamide. Cisapride and loperamide were adjusted in order to halve and double MTT measured during the control period. At the end of each period, the percentage disappearance of the initial added substrate and the concentration and the pro®le of short-chain fatty acids (SCFAs), were determined. Results: In the control period, the pH of the inoculum and SCFA concentration were inversely related to MTT (P 0.0001). Individual SCFA production was also signi®cantly related to MTT (P`0.01). Cisapride-reduced transit time was associated with a signi®cant rise in the concentrations of total SCFAs (P`0.05), propionic and butyric acids (P`0.05) and the percentage substrate disappearance (P`0.05). Inverse relations were observed during the loperamide period. Moreover, MTT was inversely related to the percentage substrate disappearance (P`0.001), SCFA production (P`0.001) and butyrate production (P`0.0005). Conclusion: Changes in MTT alter bacterial activity and modify the bacterial pathways affecting the proportion of individual SCFAs. Sponsorship:

(SCFA: 95 ± 22 mmol/g FM; pH 6.9 ± 0.1 ).In conclusion, the supplementation of a diet with 5% algal fibre changes the physicochemical characteristics of the digesta according to the algal fibre properties in the digestive compartment considered. The extent of 5% algal fibre fermentation at different sites of large intestine influences significantly the production of SCFA and consequently the pH of digestive contents.

(INRA, laboratoire de technologie appliquée à la nutrition, BP 527, 44026 Nantes cedex 03, France)

Fermentation in vitro de fibres alimentaires à l'état natif et dans des contenus iléaux de porc : étude préliminaire. V Salvador C Cherbut, J-L Barry (INRA,