Effects of ergot alkaloids on stress-induced analgesia.

Repeated, thirty minute anticipation of unavoidable painful stimulation causes endorphin-induced analgesia in rats. This type of stress-induced analgesia (SIA) develops rapidly during the first minutes of the exposure to anticipation stress. SIA can be demonstrated during the whole period of anticipation stress. Ergot drugs (DH--ergotoxine, lisuride, trans-9,10 dihydrolisuride) administered 30 min before the onset of anticipation stress, blocked completely this form of SIA. On the other hand, no effect of ergot alkaloids in the tail-flick latency, as measured under resting conditions, was observed. Possible interactions of ergot alkaloids with opiate receptors as an important mechanism by which ergot drugs affect SIA are discussed.