ABSTRACT
This work was carried out on 42 albino rate to study the effect of the C.C.B [verapamil] and. H2 receptor antagonist [ranitidine] on modulation of pain threshold and morphine antinociceptive action. Our study demonstrated that C.C.B [verapamil] has antinociceptive action to thermal stimulation indicating that Ca+ is an important mediator in pain pathway. However pretreatment of rats with a single Intraperitoneal dose [I.P] of C. C.B neither potentiates nor inhibited the analgesic activity of morphine. On the other h and C.C.B [verapamil] decreased the antinociceptive action of morphine when it was given in a single [I.P] dose after morphine injection. The H2 receptor antagonist [rantidine] induced antinociceptive activity which may be through its binding to opiate receptors as the opiate antagonist naloxone blocked this effect. Pretreatment of rats with ranitidine greatly potentiated the analgesic activity of morphine, a result which may be of value in reducing the dose of morphine and hence its side effects