Role of Estrogen in Male Reproduction

Role of Estrogen in Male Reproduction

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Estrogen is important for normal function of male reproductive organs.

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You probably recognize estrogen as a female hormone produced by women during the menstrual cycle. But men also produce estrogen, and it is important for normal male reproductive function. Although this is an active arena of biomedical research, little doubt remains that estrogen has a critical role in certain parts of the male reproductive tract.


Because exposure of the male reproductive tract to high levels of estrogen can cause reproductive problems, estrogen was considered for many years to be important for only for normal female reproductive function. A landmark study published in 1996 in the journal "Endocrinology" revealed the importance of estrogen for normal male reproduction. Researchers produced genetically engineered male laboratory animals that were incapable of responding to estrogen. Although these animals had normal levels of testosterone and other hormones required for reproductive function, their sperm were abnormal and unable to move correctly. The animals were unable to produce live offspring. This research provided the first clear indication that estrogen produced by males is important for normal fertility.


Estrogen and testosterone are two closely related chemicals called steroids. They differ only slightly in their chemical structure. An enzyme called aromatase helps convert testosterone into estrogen. Research indicates that certain cells in the testis, including those destined to become sperm, contain the aromatase enzyme and produce estrogen. Other cells that make testosterone in the testis, called Leydig cells, are also believed to make some estrogen. Although the amount of circulating estrogen in males is low compared to females, the testis itself contains a relatively high concentration of the hormone because it is made in that organ.


Estrogen made in the testis has an important role in the efferent ductules, which are tiny ducts attached to the testis that transport sperm to another duct, the epididymis, where they are stored until ejaculation. These ductules also absorb fluid that accompanies the sperm, an important function that helps keep pressure in the testis at a proper level. Specialized cells lining the ductules respond to estrogen by taking up fluid and transferring it into blood vessels in the ductule walls. The estrogen-unresponsive animals studied in the "Endocrinology" paper had extremely dilated efferent ductules, one of the problems believed to have caused their infertility.

Estrogen may have other functions in the male reproductive tract, although these are not as well understood as its role in the efferent ductules. Some research studies with laboratory animals suggest estrogen may be important for early events that occur in the testis before puberty and set the stage for normal sperm production. Estrogen may also act directly on developing sperm cells to ensure their maturation. These possibilities need further confirmation with additional human studies.

The Brain

Research with laboratory animals suggests that estrogen helps establish patterns of brain function during fetal development that are important for normal male reproductive function after puberty. During a specific time in development, the fetal testis makes testosterone that is converted to estrogen, probably by cells in the fetal brain that contain the aromatase enzyme. Brain estrogen is thought to cause changes in development that are collectively called sexual differentiation of the brain. The presence of estrogen during this fetal period is thought to set the stage for male hormonal and behavioral patterns that appear after puberty, at least in animals. Whether similar mechanisms involving estrogen exist in humans is somewhat controversial and remains under study.