Aromatase activity in marsupial brain, ovaries, and adrenals

In contrast to numerous other vertebrate groups in which there is biochemical evidence for aromatase activity in brain tissues, estrogen synthesis was not detectable in the CNS of a North American marsupial, the Virginia opossum. In the present study, the occurrence of aromatase activity in marsupial brain and other tissues was reinvestigated using the Australian species, Macropus eugenii and Trichosurus vulpecula. Following incubation of tissue homogenates with [7- 3H]androstenedione and an NADH-NADPH generating system, estrogen products were isolated and finally identified by methylation and crystallization to constant specific activity. No estrogen was detectable in samples of adult brain; however, the brain of wallaby pouch young conformed to the general vertebrate pattern. Not only were small amounts of authentic estrone synthesized, but aromatization was greatest in limbic areas and activity per unit protein in all regions progressively declined with age. The ovaries of Macropus and Trichosurus as well as the adrenals of Macropus were also capable of converting labeled substrate to estrone or estradiol-17β. This study provides the first definitive evidence for synthesis of conventional eutherian estrogens in Metatheria.