Estrogens and male reproduction.

Aromatase is the terminal enzyme responsible for estrogen biosynthesis; it is present in the endoplasmic reticulum membrane of steroidogenic cells in vertebrates. The aromatase gene is unique and its expression is regulated in a tissue- and more precisely, in a cell-specific manner via the alternative use of various promoters located in the first exons. The aromatase gene expression, and its transduction in a fully active protein not only in somatic cells but also in germ cells of rodent testes on one hand, and the widespread distribution of estrogen receptors (ER alpha and ER beta) in the genital tract of the male on the other hand, are clearly in favour of a physiological role for estrogens in the regulation of mammalian testicular functions. Moreover, the aromatase deficiency is associated for instance with severe bone maturation problems and sterility in mouse and man; but conversely, it is well known that estrogens in excess are responsible for the impairment of spermatogenesis. Therefore these female hormones (or the androgens/estrogens ratio) play a physiological role in the development and maintenance of male gonadal functions and seem to control especially the spermatid production (both qualitative and quantitative aspects) and epididymal sperm maturation.