Effect of phentolamine on the spontaneous electrical activity of responsive loci in a myofascial trigger spot of rabbit skeletal muscle

This study was designated to investigate the effect of phentolamine, a sympathetic blocking agent, on the spontaneous electrical activity (SEA) which is characteristic of a locus in the myofascial trigger point (MTrP) region. SEAs were recorded from the biceps femoris muscle of adult albino rabbits before and immediately after an injection of phentolamine hydrochloride (I mg/kg) into the external iliac artery, followed by flushing with normal saline in the experimental group. Control group was treated by the same procedure with normal saline. In the same active sensitive locus, the average integrated areas of SEA showed linear decay with time after phentolamine injection. The average integrated areas of SEA in phentolamine group was significantly lower than that of control group. The results support our hypothesis that autonomic nervous system is participated in the pathogenesis of MTrP.