The effect of gonadal hormones on the sensation of pain : Quantitative sensory testing in women

Sammanfattning: Accumulating evidence points to sex differences in pain sensitivity and many chronic pain conditions preferentially affect women. Sex hormones, and in particular estrogens, have been shown to affect pain processing and pain sensitivity in animals, although the findings are divergent. The aim of the research on which this thesis is based was to examine the effect of gonadal hormones on the sensation of pain in women who either presented normal variations in hormonal levels over time or who had been given hormone treatment.Different quantitative sensory tests (QST) examining temperature thresholds, cold, heat and pressure pain thresholds, as well as tolerance thresholds for heat and cold, were performed during different hormonal conditions: During hormonal fluctuations throughout the ovulatory cycle (papers I, II); in women undergoing in vitro fertilization (IVF), a treatment associated with extremely low and high 17β-estradiol levels (paper III); and before and after hormonal substitution treatment in postmenopausal women suffering from fibromyalgia (paper IV).The results showed little changes in pain sensitivity during the ovulatory cycle, with an interaction between 17β-estradiol and progesterone on cold pressor pain as the major finding. No significant changes in pain sensitivity were seen even with the extreme variations in 17β-estradiol levels that occurred during the IVF-treatment. Also, the use of hormonal substitution treatment did not affect pain thresholds or tolerance in postmenopausal women suffering from fibromyalgia.Session-to-session effects were reported in several studies and seem to be an important factor when using repeated sessions design. Additionally, the present work also emphasizes the use of actual hormonal values as essential instead of tentative calendar methods when evaluating hormonal effects on the sensation of pain during the menstrual cycle. The present studies thus indicate that changes in gonadal hormone levels have little effect on experimental pain in women, contrary to what has been reported in animal studies.