Experimental myalgia induced by repeated infusion of acidic saline into the human masseter muscle does not cause the release of algesic substances.

摘要

Animal studies have shown that two repeated intramuscular injections of acidic saline induce mechanical allodynia that lasts for 4 weeks with spread to the contralateral side. In this study, we tested the hypothesis that two repeated intramuscular infusions of acidic saline into the human masseter muscle is associated with pain, mechanical allodynia and release of algesic substances. Eighteen healthy volunteers participated. On day 1, 2.5?mL of acidic saline (pH?3.3) was infused into one of the masseter muscles and isotonic saline (pH?6.0) into the other (randomized and single-blind). Two days later, intramuscular microdialysis was performed to sample serotonin, glutamate, pyruvate, lactate and glucose, during which the saline infusions were repeated. Pain and pressure pain thresholds (PPTs) were recorded before and after infusions on both days.Pain intensity induced by the infusions was higher after acidic than that after isotonic saline (p?