Analgesic Action of Chlorpromazine and Reserpine in Relation to that of Morphine

Abstract

An analgesic action of reserpine is reported in mice. This effect, detected by the hot-plate method, is of little, or only of moderate intensity, in the first 2 hr. after injection; maximal intensity is obtained 48–72 hr. after the injection of the drug, and then decreases gradually; after 144 hr. injected animals behave again like controls. The analgesic effect of reserpine seems to differ from that shown by morphine or that shown by chlorpromazine which is quicker in onset and disappears in a few hours. Reserpine potentiates the analgesic action of morphine. This potentiation can be observed 2 hr. after the injection of reserpine. The early potentiating period is followed by a later period of summation of effects. Since a short interval after the injection, reserpine does not exert any analgesic effect, but is able to potentiate morphine analgesia, this action has been regarded as a direct one; the later period of analgesia and summation of effects with morphine has been interpreted as an indirect action of the drug