This gender difference in pain response makes sense in light of what is already known about women and pain, says Zubieta, an associate professor of psychiatry and radiology at the U-M Medical School. "Women experience chronic pain syndromes more frequently, often in tandem with stress-related mood disorders, and they are also more sensitive to the effects of opiate drugs," he explains. "This may be due to a difference in their capacity to activate their pain-response systems when estrogen or progesterone are low."
But to understand women and pain, it turns out, one must look at the influences that hormones may have on these pain-control systems. For the 2002 paper, the researchers had only studied women in the early follicular phase of their menstrual cycles, when estrogen levels are lowest, in order to make sure results were as consistent as possible from woman to woman. None of the women in the study was taking hormonal birth control, and all had ovulated the previous month.
For their latest pilot study, the team scanned healthy women once during their early follicular phase, and again during that same phase in another month -- after they had been wearing an estrogen-releasing skin patch for a week. The patch made their levels of estrogen rise to levels normally seen during later parts of the menstrual cycle. This allowed the team to study estrogen's effect without the effects of other hormones, such as progesterone, that normally increase along with it.
Scans made without the painful jaw stimulus showed that under high estrogen conditions, the number of available mu-opioid receptors, where endorphins would dock in case of pain, increased in several pain- and stress-controlling areas of the brain.
When the painful jaw injection was given, the effect of the estrogen on the capacity to activate thi
Contact: Sally Pobojewski
University of Michigan Health System