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.