LOCAL INCREASES OF SUBCUTANEOUS BETA-ENDORPHIN IMMUNOACTIVITY AT THE SITE OF THERMAL-INJURY

To examine interactions between exogenous opioid analgesia and endogen ous opioid generation at a site of bum-induced tissue injury, we measu red beta-endorphin (BE) and corticosterone (C) in aliquots of plasma a nd wound fluid withdrawn from subcutaneous wire mesh chambers beneath the site of a 3-5% surface area burn. After brief inhalational anesthe sia at the time of thermal injury, rats received morphine (4 mg/kg, si ngle dose), fentanyl (0.02 mg/kg hourly for 4 h), or no opioid. System ic hormone responses and behavioral changes were minimal as expected f or the minimal percentage bum. In all three groups intrachamber BE and C rose above baseline at 1, 2 and 4 h postburn, then returned to base line at 24 h. Systemic opioid treatment produced analgesia (by tail fl ick latency testing) but did not reduce intrachamber hormone responses . Thus local BE and C responses at the site of thermal injury are regu lated differently from systemic pituitary-adrenal responses.