Failure of Naloxone to Improve Spinal Cord Blood Flow and Cardiac Output after Spinal Cord Injury

It has been reported that the narcotic antagonist, naloxone, can improve spinal cord blood flow (SCBF) and clinical recovery after experimental spinal cord injury produced by the weight-dropping technique. The purpose of the present study was to determine the effect of naloxone on SCBF, cardiac output (CO) and blood flow to other organs following clip compression injury. Rats were anesthetized, paralyzed and ventilated, with mean systemic arterial pressure (MSAP) recorded continuously, After a C-7-T-1 laminectomy and a 1-minute acute compression injury with a 50-g clip at T-1, rats were given injections of radioactive microspheres for measurement of SCBF, CO, and blood flow to other organs. The first determination was made 15 minutes after injury and a second was made after a 1-hour treatment with naloxone. Treated animals each received an intravenous bolus injection of naloxone (10 mg/kg) followed by a 1-hour intravenous infusion (2 mg/kg/hour). Naloxone failed to improve posttraumatic SCBF in the injured spinal cord. In addition, naloxone did not prevent posttraumatic hypotension or the progressive decline in CO seen between 15 and 75 minutes after injury. Thus, this study does not support the previous claims of a beneficial effect of naloxone on posttraumatic SCBF and MSAP.