Estrogens--male hormones?

The cytochrome P450 aromatase is the terminal enzyme responsible for the irreversible transformation of androgens into estrogens; it is present in the endoplasmic reticulum membrane of cells and rather ubiquitous in its localization. The aromatase gene is unique in humans and its expression is regulated in a cell-specific manner via the alternative use of various promoters located in the first exon I of the CYP19 gene. The aromatase gene expression and its translation into a fully active protein have been shown in most of the testicular cells including germ cells as well as in the epithelial cells of the epididymis in mammals. Together with the widespread distribution of estrogen receptors (ERalpha and ERbeta) in the genital tract of the male, a physiological role for estrogens in the regulation of mammalian reproductive functions including the regulation of gonadotropin feedback, is now well recognized. Moreover, in men the aromatase deficiency is associated with severe bone maturation problems, alterations of lipid and sugar metabolism and sterility; but conversely an excess of estrogens is responsible for the impairment of spermatogenesis. In addition, estrogens play an important role in the control of osteoporosis and of atherosclerosis, especially in elderly men. Consequently, estradiol seems to be a critical factor not only for normal reproduction (at least for maturation and survival of germ cells) but also for various physiological processes and thus, estrogens should be now considered as "male hormones".