Women are the more sensitive sex. They experience physical pain more readily than men do, and they also respond more favorably to pain-killing drugs. Recent studies reveal that a single protein, called GIRK2, may explain the gender imbalance.
Two independent groups led by researchers at the University of Texas at Austin and the University of California at San Francisco measured how long it took mice to react when they were exposed to heat. In one test, the animals were placed on a plate that grew increasingly hot; in another, the heat was slowly applied to their tails. Genetically modified mice lacking the GIRK2 gene reacted no differently from normal mice in the control groups. Then the researchers tested how the animals reacted to the same experiments after being given various analgesic drugs such as opioids and cannabinoids. Both teams found that without GIRK2 drugged male mice experienced much less pain relief than normal. But the engineered female mice were largely or completely unaffected by the absence of GIRK2.
"Males seem mainly, if not entirely, dependent on the GIRK system. Females appear to be more complex; they seem to have evolved with additional pain-relief systems," says University of Texas neurobiologist Adron Harris, coauthor of one of the studies. The researchers say their work could guide the development of analgesic drugs that act directly on GIRK2, helping to bring more pain relief to men.