A dose of nicotine equivalent to a single cigarette is enough to block the production of estrogen in women, according to a study by a team of researchers from Uppsala University in Sweden. These results may explain why women find it more difficult to stop smoking than men. This work was presented at the 35th European College of Neuropsychopharmacology annual conference, which took place in Vienna, Austria.
The team worked with a group of ten healthy female volunteers. The participants received a dose of nicotine intranasally and were injected with a radioactive tracer connected to a molecule that binds to an enzyme called aromatase. This enzyme is responsible for the production of estrogen. Using PET and MRI scans, the authors examined the activity of aromatase and where it was located in the brain. Results showed that a single dose reduced the amount of aromatase in the brain.
“For the first time, we can see that nicotine works to shuts down the estrogen production mechanism in the brain of women. We were surprised to see that this effect could be seen even with a single dose of nicotine, equivalent to just one cigarette, showing how powerful the effects of smoking are on a woman’s brain. This is a newly-discovered effect, and it’s still preliminary work,” said lead researcher, Associate Professor Erika Comasco (Uppsala University, Sweden). “We’re still not sure what the behavioural or cognitive outcomes are; only that nicotine acts on this area of the brain; however, we note that the affected brain system is a target for addictive drugs, such as nicotine.”
Researchers have known for a while that women and men respond differently to nicotine. Women tend to find it harder to quit, don’t react as well to nicotine replacement therapy, and are more likely to relapse than men. The biological basis for these differences is unclear, but this is the first study to suggest how aromatase may be involved.
“This discovery leads us to believe that nicotine’s effect on estrogen production has a significant impact on the brain, but perhaps also on other functions, such as the reproductive system – we don’t know that yet. There are significant differences in the way men and women react to smoking. Women seem to be more resistant to nicotine replacement therapy; they experience more relapses, show greater vulnerability for heritability of smoking, and are at greater risk of developing primary smoking-related illnesses, such as lung cancer and heart attacks. We need now to understand if this action of nicotine on the hormonal system is involved in any of these reactions,” said Professor Comasco. “Of course, this is a comparatively small group of women, we need a larger sample to confirm these findings. Nevertheless, the message is that nicotine has various effects on the brain, including on the production of sex hormones such as estrogen”.