Analgesic effect of salmon-calcitonin administered by two routes. Effect on morphine analgesia

We compared the analgesia induced by intraperitoneally (i.p.) and intracerebroventricularly (i.c.v.) administered salmon-calcitonin (S-CT), using the hot-plate test and the writhing test. The influence of the route of administration on the analgesia induced by morphine was also studied. After i.p. administration the analgesic effect was observed only in the writhing test. When S-CT was administered i.c.v., analgesia was observed in both tests, although it was greater in the writhing test than in the hot-plate test. I.c.v. injected S-CT increased the analgesia of i.p. injected morphine. Our results provide new information about the analgesic effect of S-CT and suggest that central mechanisms are involved.