[The effect of estrogens on male reproduction]

One third of estrogens in the male are from the testis and the others from outside the testis. Aromatase P450 (CYP19) is an enzyme responsible for the conversion of androgens to estrogens. Estrogens regulate cell function via specific receptors--estrogen receptors (ER) which include ER alpha and ER beta. It has been found that the role of estrogens in male reproduction is complex and important, particularly during the neonatal life. Males lacking ER alpha are completely infertile because ER alpha-induced estrogens regulate the reabsorption of luminal fluid in the head of the epididymis and disruption of this essential function causes sperm to enter the epididymis diluted, rather than concentrated, resulting in infertility. Whereas males lacking aromatase or ER beta are fully fertile. Therefore, it is concluded that ER alpha, but not aromatase or ER beta, is essenitial for normal male fertility.