Our hypothesis in this study was that in vitro disappearance of isoflavones from fecal or cecal contents of Golden Syrian hamsters paralleled the apparent absorption of these compounds, comparable with previous findings from in vitro human fecal incubations. Two studies were conducted to test this idea: one on in vitro fecal (study 1, n = 20/sex) and the other on in vitrocecal contents (study 2, n = 10/sex) ability to degrade isoflavones. According to HPLC analysis, urinary isoflavone excretion was significantly less by 2–4 fold in males compared with females in both studies. Fecal isoflavone excretion was not significantly different between sexes orisoflavones (study 1) and was In vitro anaerobic fecal isoflavonedegradation rate constants from study 1 were minimal with no significant correlation between urinary and fecal isoflavone excretion. However, in vitro anaerobic cecal isoflavone degradation rate constants (study 2) were greater and significantly correlated with urinary excretion ofdaidzein (R = 0.90; p = 0.01) and genistein (R = 0.93; p = 0.004), but not glycitein (R = 0.50; p = 0.3). Both male and female hamsters showed a pattern of urinary isoflavone excretion similar to that found in humans (daidzein > genistein). Hamster in vitro cecal isoflavone degradation rate constants seemed to be analogous to human in vitro fecal isoflavone degradation rate constants for genistein and daidzein. The sex difference in isoflavone excretion in hamsters and the instability in glycitein excretion across studies coupled with the paucity of human data on thisisoflavone deserve further investigation.
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