Lack of opiate receptor involvement in centrally induced calcitonin analgesia.

Calcitonin (CT) injected into the brain ventricles (ICV) of conscious rabbits induced an analgesia not reversable by naloxone which could be repeatedly elicited (for 5 days), while tolerance to morphine developed. CT and morphine synergized $\text{in vivo}$ when administered ICV in combination. CT did not alter electrically-induced contractions of guinea-pig myenteric plexus-longitudinal muscle and no displace of ³H-dihydromorphine by CT was observed in brain opiate receptor preparations. We have concluded that the mechanism of centrally induced CT analgesia may be opiate-independent.