MODULATION OF THE BIOLOGICAL EFFECTS OF GLUCOSINOLATES BY INULIN AND OAT FIBER IN GNOTOBIOTIC-RATS INOCULATED WITH A HUMAN WHOLE FECAL FLORA

The influence of dietary fibre on the biological effects of glucosinol ates was investigated in gnotobiotic rats harbouring a human whole fae cal flora. Animals were fed for 6 wk with diets containing 12% rapesee d meal (RSM) supplemented or not supplemented with 10% inulin (INL) or oat fibre. Both fibre types enhanced the liver hypertrophy due to RSM to equal extents, but had different effects on the other glucosinolat e-related toxic effects. INL partially restored a normal thyroid hormo ne status whereas kidney weight, goitre and growth deficit wt:re incre ased on exposure to the diet containing oat fibre. Oat fibre and, to a lesser extent, INL modulated the alterations of digestive xenobiotic- metabolizing enzymes (XME) induced by RSM. They counter-balanced the i nduction of hepatic cytochrome P-450 and lessened the induction of uri dine diphosphate-glucuronosyltransferase in the liver but did not modi fy depletion of its activity in the small intestine. On the other hand , they enhanced the induction of glutathione S-transferase in the live r and the large intestine but not in the small intestine. These findin gs give new evidence that the biological effects of naturally occurrin g non-nutrient compounds are closely dependent on the composition of t he diet. Two mechanisms are proposed to explain the different influenc e of INL and oat fibre on RSM toxicity. Their different fermentative c haracteristics could lead to a modulation of the bacterial metabolism of glucosinolates in the caecum. Alternatively, their own action on th e digestive XME could modify the subsequent metabolism of bacterial gl ucosinolate derivatives. Copyright (C) 1996 Elsevier Science Ltd.