[Stress-induced analgesia (author's transl)].

The effects of a repetitive stress (expectation of severe pain) on the threshold of a nociceptive flexion reflex of the lower limb (Rlll, Bi) were investigated in normal subjects. A progressive and significant rise of the Rlll, Bi Threshold was observed as the stress was repeated several times over a 60 to 90 minutes' period. This effect was entirely reversed by naloxone, with fall of the threshold below initial values. In a double-blind test, the injection of a placebo had no significant effect on the reflex threshold when compared with control values. These results are in agreement with those reported in animals. They provide experimental evidence for an involvement of endogenous opiate systems in the mechanism of stress in normal subjects.