Variation of pain and vasomotor responses evoked by intramuscular infusion of hypertonic saline in human subjects: influence of gender and its potential neural mechanisms

The aim of current study was to explore role of gender in pain and cutaneous vasomotor responses during the condition of intramuscular (i.m.) hypertonic (HT, 5.8%) saline induced muscle pain. In 20 healthy human subjects (10 females), 2-4.8. ml of either HT or isotonic (IT, 0.9%) saline was infused into the left tibialis anterior muscle to elicit muscle pain, during which the intensity and distribution of pain together with skin vasomotor responses were investigated. Cutaneous blood flow was assessed using laser-Doppler flowmetry in 4 different skin areas: ipsilateral infusion area (5. cm × 5. cm), ipsilateral referred pain area (5. cm × 10. cm), contralateral area to the infusion site (5. cm × 5. cm), and contralateral area to the referred pain site (5. cm × 10. cm). Among the different i.m. infusions, 4.8. ml HT saline evoked the highest pain intensity, the longest pain duration, and the largest pain distribution area in different subjects (P