Prolonged disruption of plasma β-endorphin dynamics following surgery

The purpose of the present study was to examine the effects of surgery on plasma β-endorphin dynamics. Plasma β-endorphin levels were measured by liquid chromatography/radioimmunoassay in seven patients undergoing elective surgery. Blood samples were obtained every 4 hr for two 24-hr periods: one beginning 48 hr before surgery and the other beginning 48 hr after surgery. Computer analysis of β-endorphin levels as a function of clock time demonstrated a true circadian rhythm preoperatively with a mean of 28.0 ± 5.9 pg/ml. In the postoperative period mean β-endorphin levels were significantly elevated (85.6 ± 20.7 pg/ml, P < 0.005). Surgical procedures caused significant phase shifting in the grouped mean circadian rhythm of plasma β-endorphin (mean = 2.4 hr). When the data was analyzed individually, plasma circadian rhythms were found to be totally abolished in the three patients with the longest operative times (mean = 3.8 hr) and significantly displaced in time in the remaining four patients. These prolonged alterations in plasma endogenous opioid peptide levels following surgery have not been previously reported, and should be considered in the management of the postsurgical patient.