Antinociceptive activity of salmon calcitonin injected intraventricularly in mice: modulation of morphine antinociception.

Salmon calcitonin (sCT) was tested i.v.t. for its ability to produce antinociception in mice as quantitated by the tail-flick, hot-plate and p-phenylquinone (PPQ) writhing tests. sCT from two sources, Bachem (Torrance, CA) and Armour Pharmaceutical Co. (Chicago, IL), was shown to have naloxone reversible antinociceptive activity in the tail-flick and hot-plate tests. However, the sCT analgesic activity in the PPQ test was only partially naloxone reversible. sCT produced a naloxone reversible potentiation of doses of morphine that had low analgesic activity, but sCT failed to potentiate higher doses of morphine in the tail-flick test. sCT has a similar biphasic effect on morphine in the PPQ test in that low doses of morphine were selectively potentiated. However, the potentiation in the PPQ test was not naloxone reversible. sCT was shown not to be cross-tolerant to morphine in the PPQ test. Thus, sCT appears to produce its antinociceptive effects via interaction with both opiate and nonopiate mechanisms.