Sex differences in endogenous pain modulation by distracting and painful conditioning stimulation

Abstract

Sex differences in endogenous pain modulation were tested in healthy volunteers (32 men, 30 women). Painful contact heat stimuli were delivered to the right leg alone, and then in combination with various electrical conditioning stimuli delivered to the left forearm. Four conditioning protocols were applied to each subject in separate sessions: mild, nonpainful (control); distracting; stressfulyet-nonpainful; strongly painful. Thermal stimuli were rated on visual analog scales for pain intensity (INT) and unpleasantness (UNP). Distracting and painful conditioning stimuli significantly reduced heat pain INT and UNP ratings for both sexes, with significantly larger distraction effects on INT ratings for men than women (p=0.004). No sex differences in pain-evoked hypoalgesia were detected (p>0.05). The stress protocol did not consistently reduce heat pain ratings, possibly because the protocol was not sufficiently stressful to activate endogenous modulatory systems. Regression analysis revealed that the magnitude of pain-evoked hypoalgesia was predicted by the perceived distraction (p=0.003) and stress (p=0.04) produced by the painful conditioning stimulation, providing evidence that distraction and stress contribute to pain-evoked hypoalgesia. However, the contribution of stress to pain-evoked hypoalgesia differed by sex (p=0.02), with greater perceived stress associated with greater hypoalgesia in men and the opposite trend in women, suggesting sex differences in the mechanisms underlying pain-evoked hypoalgesia. This study provides indirect evidence that multiple neural mechanisms are involved in endogenous pain modulation and suggests that sex-specific aspects of these systems may contribute to greater pain sensitivity and higher prevalence of many chronic pain conditions among women.

Pain Levels of Examined Muscles and Gender Differences in Pain During Electromyography

“…[2,3,19,20] In our data is consistent with previous studies [2,3] and indicated greater pain levels among females compared with males.…”

Prevalência de dor nas costas e fatores associados em adultos do sul do Brasil: estudo de base populacional

“…Some epidemiological studies attribute this finding to an information bias 32 , however, it is plausible, since women, more and more, combine the execution of domestic tasks and jobs done out of home, where they are exposed to ergonomic loads, especially the repeatability, vicious positions and high velocity tasks' performance 33 . In addition, the female gender presents some anatomic functional characteristics (smaller stature, smaller muscle and bone masses, frail joints and less adapted to strenuous physical efforts as well as having a higher proportion of fat) 1,34,35 and others related to the nervous system which can collaborate to the emergence and increase of pain intensity 36,37 . The worst the health perception, the higher was the risk to have spinal pain (p<0.001).…”

Studying sex and gender differences in pain and analgesia: A consensus report

“…Psychosocial factors contribute substantially to pain perception in humans and may differentially influence pain in men and women [64,101,159,167,172]. There are welldocumented sex differences in stress responses in both animals and humans [112], and sex differences in mechanisms of stress-induced analgesia have been reported in rodents [141].…”

“…For example, changes in spinal aromatase activity dramatically and immediately affected pain thresholds in the Japanese quail, without changes in plasma levels of gonadal steroids [56,57]. Future studies in which various steroidogenic enzyme inhibitors (or hormone agonists or antagonists) are locally infused would contribute to our understanding of how local changes in hormone action result in behavioral changes in sensitivity to pain and analgesia.How do psychological factors such as stress, mood, and conditioning (expectation) contribute to sex differences in pain/analgesia?Psychosocial factors contribute substantially to pain perception in humans and may differentially influence pain in men and women [64,101,159,167,172]. There are welldocumented sex differences in stress responses in both animals and humans [112], and sex differences in mechanisms of stress-induced analgesia have been reported in rodents [141].…”