In vivo microdialysis—A technique for analysis of chemical activators of muscle pain

The accurate measurement of the chemical activators of pain in skeletal muscle has proved to be a major challenge. This study examined the applicability of microdialysis to the measurement of pain-producing substances in skeletal muscle using a defined model of ischemia and reperfusion in the rat. Microdialysis probes were placed into muscle of anesthetized rats. Ischemia was induced for 4 h, followed by reperfusion for 1 h. Perfusates were analyzed for hypoxanthine, potassium, prostaglandin (PG) E2 and histamine. A 20-fold increase in perfusate hypoxanthine concentration was seen prior to reperfusion (70.1 ± 27.1 μM for ischemic versus 3.7 ± 1.9 μM for control; P < 0.05). An initial increase in PGE2 concentration was seen during ischemia (7.4 ± 2.0 nM versus 3.4 ± 1.4 nM; P < 0.05) and immediately post-reperfusion (17.9 ± 5.2 nM versus 4.0 ± 1.1 nM; P < 0.05). Potassium concentration was significantly increased following occlusion and reperfusion. This indicates the applicability of microdialysis to the measurement of pain-producing substances in muscle during ischemia and reperfusion. Further use will provide novel information on muscle pain both in defined model systems and in clinical situations in humans. © 1999 John Wiley & Sons, Inc. Muscle Nerve 22: 1047–1052, 1999