Oestrogen is considered to be the 'female' hormone, whereas testosterone is considered the 'male' hormone. However, both hormones are present in both sexes. Thus sexual distinctions are not qualitative differences, but rather result from quantitative divergence in hormone concentrations and differential expressions of steroid hormone receptors. In males, oestrogen is present in low concentrations in blood, but can be extraordinarily high in semen, and as high as 250 pg ml −1 in rete testis fluids 1,2 , which is higher than serum oestradiol in the female 3 . It is well known that male reproductive tissues express oestrogen receptors [4][5][6][7] , but the role of oestrogen in male reproduction has remained unclear. Here we provide evidence of a physiological role for oestrogen in male reproductive organs. We show that oestrogen regulates the reabsorption of luminal fluid in the head of the epididymis. Disruption of this essential function causes sperm to enter the epididymis diluted, rather than concentrated, resulting in infertility. This finding raises further concern over the potential direct effects of environmental oestrogens on male reproduction and reported declines in human sperm counts 8,9 .Classic cellular responses to the hormone oestrogen are mediated through nuclear oestrogen receptors (ER), which function as ligand-dependent transcription factors. Efferent ductules of the testis are known to express high amounts of ER-α 10,11 , higher even than uterine tissue, and both the α and β forms of ER are present in efferent ductules and the epididymis 10 . These ductules form a series of small tubules that transport sperm from the testis to the epididymis 12 . In humans, one third of the epididymal head consists of efferent ductules 13 . In addition to ciliated cells that stir the luminal fluid, their epithelia contain nonciliated cells that resemble proximal tubule cells in the kidney. The non-ciliated cells have a reabsorptive function that results in the uptake of water, ions and proteins from the ductal lumen 12,14 . Ductules in the rat reabsorb nearly 90% of the rete testis fluid, coupling water and active ion transport in an electroneutral environment, in which Na + and water are reabsorbed at equal rates, thereby increasing the concentration of sperm as they enter the Correspondence and requests for materials should be addressed to R.A.H. (r-hess@uiuc.edu). 15,16 . This method of concentrating sperm improves their survival and maturation during epididymal storage and ensures that a large number of sperm are released upon ejaculation, increasing the randomness of fertilization and providing genetic variation 14 . These data and the observation that efferent ductules contain the highest concentrations of ER in the male led us to hypothesize that oestrogen participates in the regulation of fluid reabsorption in the male reproductive tract. HHS Public AccessTo test this hypothesis, we used the ER-α gene knockout mouse (ERKO) 17,18 . The ERKO male is infertile 18 , but its testes appear normal un...

Previous studies of the estrogen receptor-alpha knockout (alpha ERKO) in the male mouse demonstrate that the rete testis and efferent ductules are targets of estrogen. Because the alpha ERKO mouse lacks a functional estrogen receptor alpha (ER alpha) throughout development, it was not known whether the morphological and physiological abnormalities observed in the alpha ERKO male were due to developmental defects or to dysfunctions concurrent with the lack of ER alpha in the tissue. This study was designed to determine if treatment of normal wild-type (WT) mice with the pure antiestrogen, ICI 182,780, (ICI) could reproduce the morphological characteristics seen in alpha ERKO mice. Thirty-day-old male mice were treated for 35 days with either castor oil or ICI. Age-equivalent alpha ERKO mice were used for comparison. Light microscopic examinations of the reproductive tracts revealed dramatic changes in the efferent ductules of treated mice: a 1.7-fold increase in luminal diameter, a 56% reduction in epithelial cell height, a 60% reduction in brush boarder height of nonciliated cells, and an apparent reduction of the number of observable lysosomes and endocytotic vesicles. Testes of ICI-treated mice showed swollen rete testes area (6.5 times larger than control) and a 65% reduction in rete testis epithelium height. However, there were no significant changes in body and testis weights. These results indicate that ER blockage with ICI in WT mice results in morphological changes of the efferent ductules resembling those seen in alpha ERKO siblings of the same age. Based on this study, we conclude that ER alpha has a functional role in the mouse reproductive tract and the aberrant morphology observed in the efferent ductules of the alpha ERKO mouse is likely the result of a concurrent response to the lack of functional ER alpha, and not solely due to the lack of ER alpha during early developmental times.

No abstract

Oestrogen is considered to be the 'female' hormone, whereas testosterone is considered the 'male' hormone. However, both hormones are present in both sexes. Thus sexual distinctions are not qualitative differences, but rather result from quantitative divergence in hormone concentrations and differential expressions of steroid hormone receptors. In males, oestrogen is present in low concentrations in blood, but can be extraordinarily high in semen, and as high as 250 pg ml −1 in rete testis fluids 1,2 , which is higher than serum oestradiol in the female 3 . It is well known that male reproductive tissues express oestrogen receptors [4][5][6][7] , but the role of oestrogen in male reproduction has remained unclear. Here we provide evidence of a physiological role for oestrogen in male reproductive organs. We show that oestrogen regulates the reabsorption of luminal fluid in the head of the epididymis. Disruption of this essential function causes sperm to enter the epididymis diluted, rather than concentrated, resulting in infertility. This finding raises further concern over the potential direct effects of environmental oestrogens on male reproduction and reported declines in human sperm counts 8,9 .Classic cellular responses to the hormone oestrogen are mediated through nuclear oestrogen receptors (ER), which function as ligand-dependent transcription factors. Efferent ductules of the testis are known to express high amounts of ER-α 10,11 , higher even than uterine tissue, and both the α and β forms of ER are present in efferent ductules and the epididymis 10 . These ductules form a series of small tubules that transport sperm from the testis to the epididymis 12 . In humans, one third of the epididymal head consists of efferent ductules 13 . In addition to ciliated cells that stir the luminal fluid, their epithelia contain nonciliated cells that resemble proximal tubule cells in the kidney. The non-ciliated cells have a reabsorptive function that results in the uptake of water, ions and proteins from the ductal lumen 12,14 . Ductules in the rat reabsorb nearly 90% of the rete testis fluid, coupling water and active ion transport in an electroneutral environment, in which Na + and water are reabsorbed at equal rates, thereby increasing the concentration of sperm as they enter the Correspondence and requests for materials should be addressed to R.A.H. (r-hess@uiuc.edu). 15,16 . This method of concentrating sperm improves their survival and maturation during epididymal storage and ensures that a large number of sperm are released upon ejaculation, increasing the randomness of fertilization and providing genetic variation 14 . These data and the observation that efferent ductules contain the highest concentrations of ER in the male led us to hypothesize that oestrogen participates in the regulation of fluid reabsorption in the male reproductive tract. HHS Public AccessTo test this hypothesis, we used the ER-α gene knockout mouse (ERKO) 17,18 . The ERKO male is infertile 18 , but its testes appear normal un...