Estrogen in the adult male: From a curiosity to absolute necessity

Androgens are considered the male hormone. However, estrogen's presence and potential importance in the male reproductive system was noted as early as the 1940's and 1950's. Reference to estrogens in the male by most scientists prior to the 1990's appeared to be more of a curiosity than serious suggestion of endocrine function in the male. One of the turning points was the discovery that P450 aromatase was present and very active in the testis. Another major discovery was the effects of diethylstilbestrol treatment during pregnancy on male mice. These discoveries opened the door to serious investigations into the potential role of estrogen in the adult male and the potential long-term effects of exposure to estrogenic compounds during development. The decade of the 90's brought new discoveries that have led us to hypothesize that estrogen not only has important functions in the adult male reproductive tract, but that estrogen and its a receptor are "essential" for normal fertility. Among these discoveries are the following: testicular germ cells and epididymal sperm synthesize estrogen; estrogen receptors are found in high concentration in the efferent ductule epithelium of all species examined; the ERa knockout (ERaKO) male is infertile and the efferent ductules are abnormal; ERa regulates fluid reabsorption by the efferent ductule epithelium; a pure antiestrogen inhibits sodium and water transport in the male tract.