Daidzein, but not genistein, has anxiolytic-liked effect on intact male Wistar rats

The phytoestrogens daidzein and genistein are ubiquitous in human food. This study aimed to elucidate their anxiety-liked effects, their effects on the reproductive organs, and the molecular mechanism behind any anxiety-liked effects in intact adult male Wistar rats. These phytoestrogens are of interest due to their posited health benefits, particularly for female, but with some effect on males as well. This study comprised two experiments: (1) Male Wistar rats received either a vehicle, daidzein, or genistein (0.25, 0.50, or 1.00 mg/kg) by subcutaneously injection for four weeks. They were then tested for anxiety-liked behaviors. Then, the brain monoamines in anxiolytic rats were determined; (2) The modulation of gamma aminobutyric acid receptors by phytoestrogens was further analyzed by administration of diazepam to phytoestrogen-treated rats before behavioral tests. In the first experiment, the biological parameters measured, including body weight, daily food intake and reproductive organ weights were unaffected by either genistein or daidzein. However, anxiolytic-like effect was observed in the low-dose daidzein (0.25 mg/kg) group. Higher doses of daidzein or genistein of all doses had no effect. Further, the low-dose daidzein did not alter brain monoamine levels. In the second experiment, the anxiolytic-like behavior of daidzein-treated rats receiving diazepam did not differ from that of the rats treated with just diazepam or just daidzein. In conclusion, 4-week exposure to daidzein or genistein had no negative effects on the reproductive organs, body weight, food intake, anxiogenic-like behavior, or monoaminergic and diazepam-modulated GABAergic neurotransmissions of intact male rats. However, beneficial anxiolytic-like effects were apparent after low-dose treatment with daidzein.