Effect of phentolamine on perineal muscle EMG activity in paraplegia

The effect of the alpha-adrenergic blocking agent, phentolamine, was studied on the perineal muscle EMG in 3 paraplegic patients. The drug reduced the EMG activity in these patients. This suggests that the normal suppression of external sphincter activity during micturition might be related to a reduction in the external sphincter activity supplied by the sympathetic system.