Relationship between analgesia and turnover of brain biogenic amines

The analgesic activity of morphine, delta9THC, and sodium salicylate was studied concomitantly with changes in brainstem and cortex turnover of dopamine (DA), noradrenaline (NA), and serotonin (5HT). The results show that a correlation exists between the presence of analgesia and the increased turnover rates of the three biogenic amines. Morphine and sodium salicylate induced analgesia is accompanied by an increased turnover rate of all three biogenic amines; delta9THC-induced analgesia is accompanied by an increased turnover rate of DA and 5HT only. There is, however, no consistent relationship between the degree of analgesia and the degree of change in the turnover rates. The existence of the endogenous morphine-like substances, endorphines, may explain why morphine analgesia is distinct from that of delta9THC and sodium salicylate. The possible relationship between this morphine-like substance and biogenic amines is discussed.