Gender Gap Found In Pain Relief (10/30)
By DAVID PERLMAN
c.1996 San Francisco Chronicle
AN FRANCISCO - In an experiment revealing significant and unexplained differences between the sexes, researchers at the University of California at
San Francisco have discovered that a class of drugs long neglected in the treatment of severe pain is far more effective and long-lasting in women
than in men.
The unexpected results are already sending the scientists back to the laboratory in an effort to decipher the differences in the way men and women
perceive pain, and why the receptor cells in their brains appear tuned so differently to the different classes of pain relievers called opioid drugs.
The researchers agree that the results are surprising largely because virtually all past experiments on the effects of pain and pain relief have been
performed on men. That fact, the scientists say, should demand intensified research aimed at understanding more of the fundamental differences -
hormonal and physiological, as well as anatomical - between the sexes.
The new report, published Wednesday in the international journal Nature Medicine, comes from a research team headed by Dr. Jon D. Levine, professor of
medicine and oral surgery at UCSF, who for more than 20 years has been studying the complex pathways that carry signals from painful injuries and
diseases through the central nervous system to the brain as well as its natural pain-relievers, known as endorphins.
The researchers studied 48 young men and women who had undergone painful surgery to remove impacted wisdom teeth and who were treated with drugs known
as kappa opioids - a class that includes well-known prescription compounds such as Nubain, Talwin and Stadol. Past research had convinced physicians
that kappa opioids are far less effective than the more powerful class, known as mu opioids, which include morphine, Demerol, codeine and the illegal
In fact, Levine and his colleagues found, the women experienced major pain relief from the kappa opioids, while the men did not.
``The results were most dramatic,'' Levine said in an interview Tuesday. ``While the men had a very weak response to the drugs, the women not only
experienced great pain relief, but the relief lasted surprisingly long.''
As a result, Levine said, even though the kappa opioids may be of little use for relieving severe pain among men, it is time to evaluate thoroughly
their use in women with nerve injuries, labor pains, post-surgical pain, cancer and other problems.
The result, in Levine's view, is that by using the kappa opioids far more extensively, women may well be spared many of the mu opioids' difficult
side effects, which can include nausea, sedation, confusion and constipation, as well as addiction from prolonged use.
From reviewing every available record of past pain relief experiments, Levine said, he and his colleagues failed to find a single study that compared
the differing affects of painkillers on men and women - a gap in research that now seems virtually inexcusable.
Finding the reasons for the differences in pain relief between men and women will involve a whole new area of laboratory research, Levine said - first
with animals and then with human volunteers.
For example, he said, there may be significant differences in the way the sex hormones - estrogen in women and testosterone in men - mediate pain
pathways within the brain. Testosterone may react negatively to the kappa-opioids inside brain cells, while estrogen or progesterone may intensify the
effectiveness of those drugs in the brains of women.
Dr. Karen J. Berkley, a neuroscientist at Florida State University, called the Levine team's research ``significant and groundbreaking'' because it
is the first known experiment that specifically compared the differences in pain perception and pain relief between men and women.
Traditionally, Berkley said, doctors have believed that women have lower thresholds and less tolerance for pain than men, and are more likely than men
to report chronic pains that are more severe and last longer.
These are all areas that demand more thorough and unbiased research, Berkley said, to develop designs for better painkilling drugs for men and women,
and new strategies for administering them.
(The San Francisco Chronicle web site is at www.sfgate.com...