Interactions between personal expectations and naloxone: effects on tolerance to ischemic pain.

Sixteen healthy subjects participated in an investigation of the interactive effects of naloxone and personal expectations of control, stress, and anxiety, on time tolerance to ischemic pain. Control and anxiety levels provided no significant naloxone-saline discriminations, but there was a significant interaction between stress levels and naloxone-induced reduction in tolerance to ischemia. This finding suggests that activity in the opiate system may be a function of the modifying influences of variable attitudes to environmental stress. A primary analgesic role for the endorphins is challenged, however, by the findings that tolerance levels failed to reveal naloxone reactors and stress levels were not significantly associated with differences in tolerance. The latter, on the other hand, correlated significantly with control and anxiety levels, indicating that further research is needed to clarify the complex relationship between these three variables and their effects on the modulation of pain perception.