In vivo microdialysis - A technique for analysis of chemical activators ofmuscle pain

The accurate measurement of the chemical activators of pain in skeletal mus cle has proved to be a major challenge. This study examined the applicabili ty of microdialysis to the measurement of pain-producing substances in skel etal muscle using a defined model of ischemia and reperfusion in the rat. M icrodialysis probes were placed into muscle of anesthetized rats. Ischemia was induced for 4 h, followed by reperfusion for 1 h. Perfusates were analy zed for hypoxanthine, potassium, prostaglandin (PG) E(2)and histamine. A 20 -fold increase in perfusate hypoxanthine concentration was seen prior to re perfusion (70.1 +/- 27.1 mu M for ischemic versus 3.7 +/- 1.9 mu M far cont rol; P < 005). An initial increase in PGE, concentration was seen during is chemia (7.4 +/- 2.0 nM versus 3.4 +/- 1.4 nM; P < 0.05) and immediately pos t-reperfusion (17.9 +/- 5.2 nM versus 4.0 +/- 1.1 nM; P < 0.05). Potassium concentration was significantly increased following occlusion and reperfusi on. This indicates the applicability of microdialysis to the measurement of pain-producing substances In muscle during ischemia and reperfusion. Furth er use will provide novel information on muscle pain both in defined model systems and in clinical situations in humans. (C) 1999 John Wiley & Sons, I nc.