No evidence for aromatization of [3H]testosterone in oestrogen receptor containing cells of the epididymis.

Oestrogen receptors are found in the principal cells of the caput and in apical and clear cells of the epididymis of the mouse. The distribution pattern of oestrogen receptors is different from that of androgen receptors and suggests a physiological role for oestrogens in the epididymis. We examined by competition experiments and thaw-mount autoradiography to see whether aromatization of [3H]testosterone is the source of oestrogens in the epididymis. After injection of [3H]testosterone we found the same labeling pattern as after non-aromatizable [3H]dihydrotestosterone. In particular, apical and clear cells showed a low or no nuclear concentration of radioactivity as with [3H]dihydrotestosterone. Competition with oestradiol had no effect on the binding pattern of [3H]testosterone in the epididymis in contrast to its effects in the brain of the same animals. Competition with dihydrotestosterone abolished labeling in contrast to the brain, where no effect was observed. Thus no aromatization of [3H]testosterone to oestrogens but conversion to dihydrotestosterone seems to occur in the epididymis.