Endogenous Opioid Function Differs Between Men and Women Women appear to be more sensitive than men to the effect of endogenous opioid blockade on hypothalamic-pituitary-adrenocortical responses to pain, findings of a new study suggest. Women tend to exhibit higher pain sensitivity and larger HPA responses to stress, according to a research team led by Dr. Mustafa Al'Absi, at the University of Minnesota School of Medicine in Duluth. The endogenous opioid system modulates HPA activity, but there has been little research addressing sex differences in the effects of opioid blockade on HPA responses, pain perception and cardiovascular reactivity. Dr. Al'Absi's group administered thermal pain stimuli and cold pressor tests to 11 women and 15 men during two sessions in which placebo or 50 mg of the opioid blocker naltrexone was administered. They measured pain thresholds, pain tolerance, blood pressure responses, emotional responses, and blood hormone levels during both sessions. Naltrexone significantly attenuated changes in blood pressure and decreased pain responses during the cold pressor test in women only. However, "naltrexone did not alter subjective mood measures, suggesting that its effects on the HPA axis were specific to its opioid antagonistic impact rather than other nonspecific or metabolic factors," the authors write in their report, published in the March/April issue of Psychosomatic Medicine. Both men and women exhibited increased blood levels of cortisol, adrenocorticotropin and beta-endorphin in response to pain, which were significantly higher after naltrexone. Prolactin levels were also increased after naltrexone, more so in women than men. The authors speculate that "sex differences may in part be caused by effects of steroids on opiate receptors in several areas of the brain and to differences in the role of the opioid system in the stress response." They also suggest that these gender effects in endogenous opioids are involved in the differential responses to drugs, severity of substance abuse, and outcomes of treatment. Psychosom Med 2004;66:198-206. Thanks to Reuters Health Remember we are NOT Doctors and have NO medical training. This site is like an Encylopedia - there are many pages, many links on many topics. Support our work with any size DONATION - see left side of any page - for how to donate. You can help raise awareness of CAM.