Exposure to the phytoestrogen daidzein attenuates apomorphine-induced penile erection concomitant with plasma testosterone level reduction in dose- and time-related manner in adult rats.

OBJECTIVES

To investigate the impact of exposure to the phytoestrogen daidzein on erectile function and sexual hormones. The negative effects of phytoestrogens on the male reproductive system, particularly on penile erection, have hardly been evaluated.

METHODS

Thirty adult male Sprague-Dawley rats were equally divided into a normal control group, three experimental groups, and one positive control group. The three experimental groups were given daidzein at doses of 2, 20, and 100 mg/kg body weight daily, and the positive control group received 0.1 mg diethylstilbestrol per animal daily for 90 days. The apomorphine-induced erection test was performed 0, 30, 60, and 90 days after daidzein administration to evaluate for erectile function or dysfunction. After each test, blood samples were collected for plasma testosterone and luteinizing hormone measurement.

RESULTS

High-dose daidzein (100 mg/kg) decreased erectile responses to apomorphine from the 30th day of daidzein treatment and lasted to the 90th day without significant differences compared with the diethylstilbestrol-treated rats. However, similar changes were observed in the medium-dose daidzein (20 mg/kg) group from the 60th day. Low-dose daidzein (2 mg/kg) had no significant effect on the erectile responses to apomorphine compared with the normal control group (P >0.05). The plasma testosterone and luteinizing hormone levels showed a declining trend similar to that of the apomorphine-induced erections.

CONCLUSIONS

The phytoestrogen daidzein has the potential to adversely affect erectile function in a dose and time-related manner that is at least partly attributable to androgen deficiency. These findings implicate that phytoestrogens, especially isoflavones, if overconsumed for a long period, might be a novel risk factor for erectile dysfunction.