A COMPARISON OF ANALGESIC ACTIVITIES PRODUCED BY INTRACEREBRAL INJECTIONS OF SEVERAL SYMPATHOMIMETIC AMINES

In mice, the analgesic ED₅₀ of intracerebral injection of adrenaline, noradrenaline, ephedrine, amphetamine, and tyramine was 0.84, 1.2, 18.2, 4.8, and 31.5μg respectively as determined by the method of i.p. tartar emetic induced writhing. It indicates that the analgesic activity of sympathomimetic amines requires certain structural specificity. Employing the method of radiant heat focusing on the rabbit nose, only a part of the animals with intraventricular injection of 0.5 mg of noradrenaline showed an analgesic action of very short duration. Since the analgesic effect of intraventricular noradrenaline is so weak, the present results support the view that morphine analgesia is not an indirect action via central noradrenaline liberation.