The in vitro aromatization and 5alpha-reduction of androgens to estrogens and dihydrotestosterone (DHT) were determined in incubations of microdissected brain regions of male and female gonadectomized, adrenalectomized rats. Metabolites formed from [1alpha,2alpha-3H]androstenedione or [1alpha,2alpha-3H]testosterone were purified by celite liquid-liquid partition chromatography, silica gel chromatography and recrystallization to stable 3H/14C ratios. The medial preoptic nucleus-anterior hypothalamic nucleus exhibited the highest aromatase activity and the second highest conversion to DHT. The lateral preoptic and lateral hypothalamic nuclei showed little aromatase activity yet exhibited high rates of formation of DHT. The medial basal hypothalamus showed the second highest level of aromatase activity but consistently formed the lowest amount of DHT. The discrect anatomical localization of these enzymatic conversions is suggestive of their being involved in the physiological actions of androgens.

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