Estrogens and Spermatogenesis
For many years androgens were thought to be the primary hormones required for proper functioning of the male reproductive system, and testes were shown to be the major producers of the hormone. In the 1970s it was recognized that in addition to androgens testes were also a source of estrogens, and the intratesticular concentration of estrogens was higher than levels present in the serum of females of reproductive age. Since then there has been an interest in the study of the role of estrogens in the male. However, in recent years a great interest has been regenerated to decipher the role of estrogens in the control of male fertility because of various developments. For example, discovery of the estrogen receptor b (ERb) in the male was an important development ,and the evidence emerging from mice with targeted disruption of estrogen receptors showing defects in male fertility was another provocative evidence of the importance of estrogens in male reproduction. In addition, the description of reduction in sperm counts and increase in the incidence of testicular tumors in men to which environmental estrogens were causally linked were also important observations on pathology-inducing effects of estrogens. It is now established that estrogens are involved in numerous physiological processes in the male, for example, bone turnover, behavior and the cardiovascular system, but controversy exists as to whether male fertility over the past five decades has truly shown a decline due to the relatively low levels of estrogens in the environment that humans are exposed to. As a result of this renewed interest, the role of estrogens in male reproductive physiology is rapidly being redefined. It is therefore pertinent that a comprehensive evaluation of the data on the role of estrogens in the male is made. However, because of the ambiguity in the definition of precise function of the estrogens in the male, extensive research into the effects of the hormone on the male reproductive system is warranted.