The roles of oestrogen in the male

Roles for oestrogens in brain masculinization/sexual behaviour, regulation of follicles-stimulating hormone (FSH) secretion and Leydig cell development and function are well established. However, the widespread distribution of oestrogen receptors alpha and beta in reproductive and other tissues of the male, and findings from human males or transgenic animals in which the genes coding for these receptors or for aromatase are non-functional, are changing our perception of the roles of estrogen in the male. Aspects of pubertal development in boys (growth of the long bones, their mineralization and epiphyseal closure) attributed to the actions of androgens are now recognized as being mediated in part by oestrogens. Oestrogens also play a role (probably vasodilatory) in the cardiovascular system of the male. Within the reproductive system, oestrogens have been shown to play a role in the regulation of fluid resorption from the efferent ducts and appear to be important in the structural and functional development of the Wolffian/excurrent duct system, as well as that of the prostate; inappropriately low or high oestrogen exposure during development can cause permanent changes to these tissues, which may lead to disorders of permatogenesis and infertility. Sertoli cells and certain germ cells in the testis are also for oestrogen action. Many other tissues (adipose, kidney, thymus/immune system, skin, gut and muscle) are oestrogen targets in the male. Based on these findings and the widespread distribution of aromatase, it is argued that many of the effects of oestrogens in the male might stem from its local production and action and, furthermore, that the balance in action between androgens and oestrogens might be of central importance at many oestrogen target sites.