In the brain, aromatase transforms testosterone, a hormone that drives sexual activity in males, into estradiol, which is a type of estrogen.
Scientists have shown that estrogens are important for the control of reproductive function in both sexes. In addition, estrogens are critical for functional and organizational roles in brain development and adult behavior.
To determine whether brain aromatase is essential for normal male sexual activity, the Northwestern researchers developed mice that lacked aromatase in the brain.
In these male mice, sexual activity was reduced by approximately 50%. This decrease in activity occurred even in the presence of strikingly higher levels of testosterone in their blood compared with the control group of male mice. Mice that could not produce aromatase in any area of the body, including the brain, showed no sexual activity at all.
“Male mice partially lost interest in sex,” states study author Dr. Hong Zhao, research associate professor in obstetrics and gynecology at Northwestern University Feinberg School of Medicine.
Dr. Zhao further emphasizes the key role of aromatase in the production of estrogen. “Estrogen has functions in males and females. Testosterone has to be converted to estrogen to drive sexual desire in males,” she explains.
Senior author Dr. Serdar Bulun, chair of obstetrics and gynecology at the Feinberg School of Medicine and Northwestern Medicine, explains vividly how a male mouse would usually react in the company of a female mouse:
“It would chase after her and try to have sex with her.”
However, Dr. Bulun notes: “If you knock out the aromatase gene in the brain, their sexual activity is significantly reduced. There is less frequency of mating. The male mice are not that interested.”
He concludes: “This is the first key finding to explain how testosterone stimulates sexual desire.”
“[F]or the first time, we demonstrated conclusively that the conversion of testosterone to estrogen in the brain is critical to maintain full sexual activity or desire in males. Aromatase drives that.”
– Dr. Serdar Bulun
The study authors believe that their findings suggest that “sexual behavior may be modified though inhibition or enhancement of brain aromatase enzyme activity.” This knowledge could potentially lead to new treatments for disorders of sexual desire.
According to the scientists, it is possible to use drugs to target aromatase to control the sexual desires of a male.
For example, hypoactive sexual desire disorder, more commonly known as low sexual desire, is a common condition.
Low sexual desire is a common side effect of many widely used medications, including a group of antidepressants called selective serotonin reuptake inhibitors (SSRIs).
The team states that a treatment focused on increasing aromatase might boost sexual desire in those who experience this side effect.
On the other hand, doctors can also treat hypersexuality disorder, or compulsive sexual desire, using an existing aromatase inhibitor. However, a side effect of this treatment is osteoporosis, a type of bone disease in which bones become weak and may break.
The researchers hope that the results of the new study will help guide the development of new selective drugs that block only the brain promoter region of aromatase.
If scientists could achieve this specificity, the medications would not cause some of the unpleasant side effects of existing aromatase inhibitors.
