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SYMPATHETIC NERVOUS SYSTEM AND PAIN

The intravenous phentolamine test. Phentolamine is an α1 and α2 adrenergic antagonist. It prevents excitation of noradrenaline-sensitive nociceptors. Phentolamine in normal saline (30 mg 100 ml-1) is infused over 20 min. If pain is relieved, it is believed that the pain is sympathetically maintained.