GABA-opiates interactions in the activity of analgesics

The influence of compounds which reduce or potentiate GABA-ergic inhibition on the effect of analgesics of various structures was studied. The effect was estimated according to the analgesic activity (experiments in rats) and the suppression of the impulse summation in the central nervous system (experiments in rabbits). It was shown that GABA-negative agents (bicucullin, thiosemicarbazide) markedly decreased the effect of morphine, hydrocodone and the enkephaline analogs: Tyr-D-Ala-Gly-Phe-NH2 and Tyr-D-Ala-Gly-Phe(NO2)NH2. The action of bicuculline was close to that of naloxone, an opiate receptor blocker. GABA-positive agents (muscimol, GABA cetyl ether, valproate) potentiated the activity of the mentioned narcotic analgesics. The effect of GABA-positive agents was blocked not only by GABA-negative compounds, but also by naloxone. The obtained data are interpreted in terms of the assumed mutual complementary of GABA-ergic and opioidergic systems. It was shown that the effects of the analgesics of a different structure: phenylpiperidine derivatives (trimeperidine, fentanyl), diphenylacetic acid derivative (dimenoxadol) and 3-benzazocine tricyclic derivative (pentazocine) were unchanged by the studied GABA-ergic analyzers. The reasons for those dissimilarities between analgesics of different structures are discussed.