Endogenous Inhibition of the Nociceptive Flexion Reflex (NFR) and Pain Ratings During the Menstrual Cycle in Healthy Women

The menstrual cycle influences pain, with symptoms often increasing during the premenstrual (late-luteal) phase. Deficiencies in endogenous inhibition of afferent nociception at the spinal level might contribute to menstrual phase-related changes in pain. This study assessed whether conditioned pain modulation (CPM) of spinal nociception differs between mid-follicular and late-luteal phases. CPM was evoked by a blood pressure cuff affixed to the right forearm and inflated to induce ischemia in 41 healthy women during both menstrual phases. Suprathreshold electric stimuli were delivered to the left sural nerve to evoke pain and the nociceptive flexion reflex (NFR) before, during, and after forearm ischemia. Forearm ischemia produced CPM of electrocutaneous pain and NFR, but inhibition did not differ across mid-follicular and late-luteal phases. Mechanisms contributing to changes in experimental pain across mid-follicular and late-luteal phases in healthy women are not due to deficits in CPM of spinal nociception.