L'inégalité des sexes dans la douleur : un mythe devenu réalité

Women and men are not equal regarding pain. Indeed, epidemiological studies suggest that women suffer from pain more often and for a longer duration than men. These differences appear after puberty, suggesting sex hormones could play an important role. The excitatory and inhibitory mechanisms underlying pain must be examined to understand the role of these hormones in pain. The effects on pain can be demonstrated in animal models by manipulating serum levels of one or more sex hormones. Using the formalin test, a nociceptive test enabling assessment of both excitatory and inhibitory mechanisms, we were able to show that testosterone reduces excitatory nociceptive activities while estrogen and progesterone, the predominant female sex hormones, have a pronociceptive effect via the inhibitory component of pain. Moreover, this pronociceptive effect is opioidergic in females, but not in males. Interestingly, the results of animal studies also apply to humans. Human studies led to the conclusion that testoterone has protective effect, while in women; endogenous inhibitory mechanisms are significantly modulated during the menstrual cycle. The purpose of this paper is to summarize our current knowledge about the mechanisms by which sex hormones modulate between women and men the perception, prevalence and response to treatment of pain.