Exposure of juvenile rats to the phytoestrogen daidzein impairs erectile function in a dose-related manner in adulthood

Health benefits of isoflavones such as genistein and daidzein have led to an increasing interest in consuming soybeans or soy-containing food. However, possible adverse effects of such plant estrogens on the male reproductive system, particularly penile erection, have not been sufficiently evaluated. In previous research, we observed that exposure of adult rats to daidzein could attenuate apomorphine-induced erections. To identify the impact of daidzein exposure in early life on erectile function, we evaluated erectile capacity using an apomorphine-induced erectile test and determining intracavernous pressure after exposure of juvenile rats to daidzein at a dose of 2, 20, or 100 mg/kg for 90 days. Meanwhile, the levels of sex hormones, including testosterone, luteinizing hormone, and follicle-stimulating hormone, were determined. Both subtypes of the estrogen receptor (alpha and beta) in the corpora cavernosa were also detected immunohistochemically. When the rats were examined at adulthood, we observed that those animals treated with a medium (20 mg/kg) or high (100 mg/kg) dose of daidzein, but not with a low dose (2 mg/kg), showed lower plasma testosterone levels and attenuated erectile parameters, including apomorphine-induced erections and intracavernous pressure concomitant with markedly decreased expression of estrogen receptor beta in the corpora cavernosa. However, the penis still grew to its normal size, as in controls. Thus, these results suggested that exposure of juvenile rats to daidzein in a relatively large amount could adversely affect penile erection in adulthood.