Abstract The aim of this brief review is to clarify the role of aromatase in the reproduction of mammalian included animals. Aromatase (cytochrome P450 19, CYP19, P450arom) is the enzyme responsible for the production of estrogens, hormones critical for development and reproduction. In spite of its importance in reproduction, the aromatase gene has been studied in relatively few mammals and extensively only in humans, where it is thought to play significant roles also in pathophysiologies such as breast cancer and reproductive dysfunction. Aromatase cytochrome P450 is the enzyme that catalyzes the last step of estrogen biosynthesis, that is, the rate-limiting irreversible aromatization of androgens to estrogens. It is expressed in many tissues such as the gonads, brain and adipose tissue. Estrogens play many roles in the body, regulating reproduction, metabolism and behavior. In the mammalian testis, it is well known that aromatase is localized in Leydig cells. To exert a biological role, estrogens should interact with estrogen receptors (ERs) which in turn modulate the transcription of specific genes. Therefore considering the presence of at least two ERs (ERa and ERβ) in most of the testicular cells and in the other parts of the genital tract, the physiological role of estrogens in male reproduction has been extensively re-evaluated. The androgens/estrogens balance is essential for normal sexual development and reproduction in mammals. In the mammalian testis, the maintenance of this balance is under a fine tuning via endocrine and paracrine factors, but is also related to aromatase activity. Therefore the capacity of the testis and other reproductive organs to synthesize estrogens has been extensively studied during the last three decades, and the role of estrogens in male reproduction has been seriously revisited especially, taking into account the existence of specific receptors (ERa and ERβ) which are distributed all along the genital tract.
