The role of morphine in a rat model of hypoxic-ischemic injury.

We investigated whether morphine plays a neuroprotective role in a neonatal rat pup model of bilateral carotid artery occlusion with hypoxia. At postnatal day 10, rats received either morphine (n = 7), naloxone (n = 7), or saline placebo (n = 15) after hypoxic-ischemic injury. Survival (days), weight gain and animal testing (negative geotaxis, surface righting, and rotarod) were compared between treatment groups. Lesion volume was delineated with magnetic resonance imaging at days 7 and 28-57 after injury. Survival in rats treated with morphine, naloxone, or saline was, respectively, 14, 29, and 73%. Median number of days of survival after bilateral carotid artery occlusion with hypoxia treated with morphine was 4 (95% confidence interval 4 to 22), with naloxone was 3 (95% confidence interval -1.4 to 21), and with placebo was 28 (95% confidence interval 18 to 28). There were no statistically significant differences in magnetic resonance imaging-derived ischemic lesion volumes, weight gain, or behavioral testing measures between the groups. Morphine was ineffective as a neuroprotectant in rat pups with severe hypoxic-ischemic injury and may have contributed to their decreased survival.