Isoflavones from Tofu are absorbed and metabolized in the isolated rat small intestine

Studies suggest a variety of biological effects of soybean isoflavones, bur there is little information regarding small intestinal absorption and meta bolism. The aim of this study was to investigate intestinal handling of lum inally administered soybean-based tofu in an isolated preparation of the lu minally and vascularly perfused rat small intestine (male Sprague-Dawley, s imilar to 45 d old). A synthetic emulsion free from blood components was us ed as vascular medium, with a perfluorocarbon as oxygen carrier. Luminal me dia consisted of tofu, predigested with pepsin and pancreatin and emulsifie d with bile acids, containing 39.5 mu mol/L genistein compounds and 19.1 mu mol/L daidzein compounds. Viability of the organ preparation was maintaine d during the entire perfusion, confirmed by lack of significant differences between tofu and control perfusion experiments for arterial pressure, gluc ose consumption, oxygen uptake, lactate-pyruvate ratio and acid-base homeos tasis. Daidzein (8.9%) and genistein (8.0%) compounds from tofu exhibited a lmost the same (P > 0.05) absorption rate during small intestinal passage. The majority of the absorbed genistin appeared vascularly as genistein (4.4 %), in addition to minor amounts of unchanged genistin (2.1%) and genistein glucuronide (1.5%). In the luminal effluent, a considerable increase of ge nistein (338%) as well as daidzein (190%) as cleavage products of the gluco sides and malonyl-glucosides was observed. The distribution of daidzein com pounds in the small intestine was not different from that of genistein comp ounds (P > 0.05), except for the blood vessels, which had extremely low tot al amounts. Sulfate derivatives of genistein and daidzein compounds were no t detectable. An effect of tofu ingredients was observed on absorption rate of genistin, on glucuronidation and on distribution of genistein glucuroni de in the intestine.