Further studies on thyrotrophin releasing hormone analgesia.

Thyrotrophin releasing hormone (TRH) administered subcutaneously produced dose dependent analgesia in acetic acid-induced writhing assay. There was no tolerance development when TRH was administered repeatedly either at 2-hr or 4-hr intervals. Furthermore, co-administration of TRH and morphine did not result in any potentiated effect. However, TRH pretreatment antagonized analgesic tolerance to morphine. On the contrary, with the dose employed, TRH failed to suppress abstinence signs in acute dependent animals. These results suggest that TRH may utilize mechanisms other than the opioid system to produce analgesia.