Corticotropin-releasing hormone (CRH) produces analgesia in a thermal injury model independent of its effect on systemic beta-endorphin and corticosterone

Abstract

To determine separately the effect of corticotropin-releasing hormone (CRH) on analgesia and on inflammation, rats were assigned to receive CRH 60 μg/kg, CRH 300 μg/kg, morphine 4 mg/kg, or normal saline intravenously 15 min before a burn injury. Two mesh chambers that allowed collection of fluid had been previously implanted subdermally in each rat. The skin overlying the right chamber was subject to thermal injury. The left chamber served as a control. We assessed systemic analgesia, and levels of beta-endorphin and corticosterone in plasma and in chamber fluid before, 1, 4 and 24 h after drug administration. The CRH groups exhibited longer tail flick latencies than the control group ( P=0.0001) although the increase in latency was of smaller magnitude than in the morphine group. We did not observe a CRH dose response for analgesia. Plasma corticosterone levels were higher in the CRH 300 μg/kg group than in the normal saline group at 4 h ( P=0.03). Levels of beta-endorphin in plasma as well as the levels of corticosterone and beta-endorphin in chambers were similar in the CRH 300 μg/kg group and in the normal saline group (all P values>0.1). Thus, systemically administered CRH produces analgesia in thermal injury independent of its effect on these two markers of local or systemic inflammation.