Gonadal hormones and pain modulation

In a number of animal and human studies, males and females have been shown to differ in their responsiveness to noxious stimuli [1-5]. In humans, many chronic painful syndromes are more common in women than in men. For instance, certain chronic inflammatory conditions, such as rheumatoid arthritis, complex regional pain syndrome and fibromyalgia, have a lower incidence in men than in women [6-9]. Additionally, male rodents typically have higher pain thresholds than females, and gonadectomy lowers the pain threshold in males. There is also a sex difference in the efficacy of the opioids widely used in experimental and clinical studies to test analgesia. For example, male rodents (but not humans) are more sensitive than females to the antinociceptive actions of morphine [10-13]. © Springer 2008.