Oestrogen-androgen crosstalk in the pathophysiology of erectile dysfunction

Ageing in man is associated with a decline in testosterone following changes in the hypothalamo-pituitary-testicular axis. This may offset the physiologic equilibrium between oestrogen and androgen and at some point when the ratio of free testosterone to oestradiol reaches a critical level, the oestrogenic gonadotropin suppressive effect predominates with decreased release of FSH and LH. Adding to this endocrinal complexity is the continued peripheral conversion to oestradiol through aromatisation. Although the androgen deficiency is not the sole cause for impotence in the elderly, there is a gradual decrease in nocturnal penile tumescence (NPT) and spontaneous morning erections with ageing. Despite the age related increase in oestrogen levels, the information on the pathophysiological role of the "female hormone" in erectile dysfunction has been scanty. Together with our identification of oestrogen receptors within the penile cavernosum, we have delineated dysfunctional changes on male erection mediated by oestradiol. These findings parallel the recent concerns over environmental oestrogens on fertility declines in young men. Oestrogenic activity is also present in plants and thereby in human diet. These phytoestrogens are structurally and functionally similar to oestradiol and more potent than the environmental oestrogenic chemicals such as organochlorine and phenolic compounds. Thus in the light of growing concerns of possible compromising effects on sexuality by endogenous and environmental oestrogens, we are faced with the scientific need to delineate their role on the mechanism of male erectile pathway in health and disease for clinical correlates and prognostics.