Aromatase activity in adult guinea pig brain is androgen dependent

Androgen metabolism in target tissues constitutes an important step for understanding hormone action. The in situ aromatization of androgen represents one of these metabolic events. We characterized aromatase activity (AA) in a microsomal preparation of brain tissue from adult guinea pigs since earlier reports questioned its presence in neural tissues of this species. Analyses revealed an apparent substrate affinity (≃17 nM) that was equivalent in adult males and females. However, adult male brains contained greater quantities of AA than female brains. Specifically, AA in the preoptic area (POA: p < 0.05) and the medial basal hypothalamus (MBH;p < 0.01) was greater in males than in females. AA was concentrated in the limbic system and hypothalamus (amygdala>POA>septum>MBH), whereas low levels were consistently measured in cortical tissue. In vitro estrogen formation was significantly lower in POA (p < 0.05) and MBH (p < 0.01) after castration. After dihydrotestosterone treatment, AA returned to levels equal to or greater than those observed in intact males. These data indicate that AA does exist in the guinea pig brain and is modulated by androgens through the androgen receptor. The presence of high levels of aromatase activity may suggest a role for locally formed estrogens in brain function in this species.