The information may help scientists develop pain treatments specifically designed for each gender, say researchers from the University of Texas at Austin.
Men typically can endure more pain than women, and painkillers seem to affect men and women differently. However, the biological reasons for those differences isn't clear.
In the first study, researchers studied pain sensitivity and responses to analgesic drugs in mutant mice that lacked a protein called GIRK2. This protein plays an important role in electrical communication between neurons.
The study found that the male mutant mice, but not the females, had lower pain thresholds than a control group of normal mice. That showed that the removal of the GIRK2 protein eliminated gender differences in baseline pain sensitivity.
The study also found that both types of analgesic tested -- clonidine and morphine -- were less effective in treating pain in mice that lacked the GIRK2 protein.
The second study used the same kind of GIRK2-deficient mice and tested their response to the analgesic effects of several kinds of drugs, including alcohol, nicotine and cannabinoids, which is the active ingredient in marijuana.
The researchers found the lack of GIRK2 eliminated the analgesic effects of some of these drugs in the mutant male mice, but not in the mutant female mice.
The combined findings of these studies indicates that the GIRK2 protein may be a critical part of the pain pathway that accounts for gender differences in pain sensitivity and response to analgesics. The protein may also offer a promising new target for pain treatment.
The U.S. National Institutes of Health has more about pain and pain control.