Aromatase, which is encoded by the Cyp19a1 gene, is involved in the conversion of testosterone to oestrogen, driving male sexual activity. Testosterone is the primary sex hormone in males, and oestrogen is one of two primary sex hormones in females. These findings, published in the journal Endocrinology, could lead to further research surrounding sex addiction and dysfunction.
'This is the first key finding to explain how testosterone stimulates sexual desire' said Professor Serdar Bulun, a professor of obstetrics and gynaecology and senior author of the study. 'We demonstrated conclusively that the conversion of testosterone to oestrogen in the brain is critical to maintain full sexual activity or desire in males.'
The researchers knocked out the Cyp19a1 gene from the brains of male mice, which is a genetic technique in which a gene is made inactive. This leads to approximately a 50 percent decrease in sexual activity, in terms of both number of sexual encounters and total time spent engaged.
Whilst sexual behaviour in knockout mice was partially restored by testosterone, it was only fully replenished after administering testosterone with estradiol, a form of oestrogen. This implies that, for testosterone-driven sexual activity, aromatase is a requirement.
'[Without aromatase] male mice partially lost interest in sex' said Dr Hong Zhao, research associate professor of obstetrics and gynaecology who was also involved in the study. 'Aromatase is the key enzyme for oestrogen production. Oestrogen has functions in males and females. Testosterone has to be converted to oestrogen to drive sexual desire in males.'
Aromatase deficiency, which is extremely rare, leads to chronically high testosterone levels in men and a loss of libido, and has been treated using oestrogen therapy. However, until now, it was not known how aromatase fuelled the male sex drive.
The authors suggest that these findings could have significant human implications for men who display low sexual desire, known as male hypoactive sexual desire disorder, as well as those experiencing compulsive sexual desire and sex addiction.
Next steps will include developing specific treatments to alter aromatase activity, as well as trials to ensure that the effects observed in mice can be translated into humans.