19-Hydroxylation of androgens in the rat brain.

Aromatization of androgens in the central nervous system is linked with sexual differentiation of the brain and, thus, determines the nature of sexual behavior and the control of gonadotropin secretion. The process of aromatization, as determined in the human placenta, proceeds through two successive hydroxylations at C-19, the products of which are then virtually completely converted via a third hydroxylation at C-2 to estrogens. We now report that in the rat brain, 19-hydroxylation of androgens greatly exceeds aromatization and the 19-hydroxy- and 19-oxoandrogen products accumulate in quantities 5 times greater than the estrogens. This relationship implies that the aromatization sequence in the brain is deficient in the terminal hydroxylase, and the process is distinct from that in other tissues. The function of 19-hydroxy- and 19-oxotestosterone in the central nervous system is unknown but, unlike the reduced or aromatized metabolites of the male hormone, these substances cannot be delivered from the circulation and their presence in the brain is totally dependent on in situ formation, making them logical candidates for modulators of neuronal functions.