Prolonged disruption of plasma beta-endorphin dynamics after trauma in the nonhuman primate

Recent evidence has suggested that a circadian rhythm exists for plasma beta-endorphin-like immunoreactivity. The purpose of the present study was to examine the long term effects of surgical trauma on plasma beta-endorphin dynamics. Blood samples for RIA were obtained from female baboons every 4 h for three 48-h periods: one beginning 1 week before surgical trauma, the second 30 min after surgical trauma, and the third 1 week after surgical trauma. Animals were subjected to laparotomy and 30-min anesthesia (n = 8), 5-min surgical trauma under 30-min anesthesia (low trauma; n = 8), or 20-min surgical trauma under 30-min anesthesia (high trauma; n = 8). Computer analysis of beta-endorphin levels as a function of clock time demonstrated a true preoperative circadian rhythm for all animals, with a mean of 87.9 pg/ml. In the immediate 48-h postoperative period, a postoperative alteration in circadian beta-endorphin dynamics occurred that was correlated with the severity of trauma. A disruption of circadian rhythms of plasma beta-endorphin occurred in the high trauma group only, in which it persisted for longer than 1 week after trauma. These studies establish a relationship between the alteration of circadian rhythmicity of plasma beta-endorphin-like immunoreactivity and the magnitude of trauma and injury.