Expression of aromatase and oestrogen receptors in reproductive tissues of the stallion and a single cryptorchid visualised by means of immunohistochemistry.

Androgen metabolism may proceed to amplify the action of testosterone by its aromatisation to oestradiol. Recently, a growing body of evidence suggests a role of oestrogens in the male reproductive tract via their specific oestrogen receptors (ERs). In order to check whether androgens are converted to oestrogens in the testis, epididymis and prostate of the stallion, the expression of aromatase was visualised by means of immunohistochemistry. Moreover, to show the cellular targets for oestrogens the presence of oestrogen receptor alpha (ERalpha) and oestrogen receptor beta (ERbeta) was demonstrated in these tissues. Finally, to show whether naturally occurring cryptorchidism has any influence on the localisation of aromatase and distribution of ERs, the reproductive tissues of a single horse, bilaterally cryptorchid, were also taken for this study. The results demonstrated that aromatase and ERs are ubiquitously distributed throughout the male reproductive tract, what indicates a putative role of oestrogens in modulating the function of the reproductive tissues of the stallion. In the cryptorchid horse the increase in conversion of androgen to oestrogen was observed as manifested by aromatase overexpression. This is the first report showing the cellular site of oestrogen biosynthesis not only in the testis but also in the epididymis and prostate of sexually mature stallion and a single, adult cryptorchid.