The relationship of plasma cortisol and β-endorphin immunoreactivity to surgical stress and postoperative analgesic requirement

It has been hypothesized that the endogenous opioid (endorphin) system is related to biologic stress responses. We have used general surgery as a naturalistic model for studying stress response in humans. Abdominal surgery, but not anesthesia induction, was associated with significant increases in plasma β-endorphin immunoreactivity and cortisol. Both hormones decreased significantly during post-operative morphine administration. Baseline and mean surgery levels of plasma β-endorphin immunoreactivity showed an inverse relationship with post-operative analgesic requirement. These data support involvement of the endorphin system in human stress response and in human endogenous analgesic mechanisms. Findings also support the concept that baseline or psychologically stimulated levels of arousal may also be an important determinant in the physiology of stress response and pain perception.