Prolactin modulates peripheral androgen metabolism.

Although hyperprolactinemia may be associated with hyperandrogenism, if hirsutism develops, it is usually a mild form. This study was designed to investigate whether prolactin (PRL) modulates 5 alpha-reductase activity (5 alpha-RA), because 5 alpha-RA is known to be a major factor influencing the manifestation of androgenicity. Compared with normal women, euprolactinemic hirsute and both hyperprolactinemic hirsute and nonhirsute women had elevated levels of unbound testosterone (uT). Serum 3 alpha-androstanediol glucuronide (3 alpha-diol-G) was elevated only in patients who were hirsute, and serum 3 alpha-diol-G/uT ratios were elevated in euprolactinemic hirsute patients and normal in hyperprolactinemic hirsute patients. Genital skin 5 alpha-RA in vitro was elevated only in euprolactinemic hirsute women. The previously recognized positive correlation between 5 alpha-RA and the severity of hirsutism was dissociated with hyperprolactinemia. Human PRL incubated in vitro with normal genital skin also inhibited 5 alpha-RA. These data suggest that PRL modulates 5 alpha-RA and peripheral androgen metabolism and that other factors may also be involved in the evolution of hirsutism in hyperprolactinemia.