alpha-1 and alpha-2 adrenergic antagonists relieve thermal hyperalgesia inexperimental mononeuropathy from chronic constriction injury

aPhentolamine, a nonspecific alpha1- and alpha2-adrenergic antagonist, reli eves pain in patients with reflex sympathetic dystrophy We sought to determ ine whether phentolamine, prazosin (alpha1 antagonist), or SKF86466 (alpha2 antagonist) relieve thermal hyperalgesia in rats with neuropathic pain. Fo ur days after producing a chronic constriction injury (CCI), thermal hypera lgesia was tested by measuring paw withdrawal latency (PWL). After injectio n of phentolamine, prazosin, or SWF86466 each at doses of 1, 2, or 5 mg/kg, PWL tests were measured at 5 min and repeated at 15-min intervals for 1 h. Phentolamine, prazosin, and SKF864661, 2, and 5 mg/kg presided statistical ly significant analgesia in rats with CCI for at least 65 min. PWL did not return to baseline levels after 1 or 2 mg/kg of prazosin or SKF86466 but di d so after 35 min after phentolanine 2 mg/kg. After 5 mg/kg PWL returned to preoperative values between 5 and 50 min for phentolamine, at 35 and 65 mi n for prazosin, and at 50 min for SKF86466. We conclude that both alpha1 an d alpha2 peripheral receptors of the sympathetic nervous system are involve d in the thermal hyperalgesia caused by CCI and that thermal hyperalgesia c an be reversed by both alpha1 and alpha2 antagonists in a dose-dependent ma nner.