The relationship between the analgesic action of eptazocine and brain catecholamine was investigated by pharmacological and neurochemical methods in comparison with pentazocine (PZC) and morphine (MOR). The analgesic action. of eptazoeine as determined by the pressure method was decreased by pretreatment with 6-hydroxydoparnine (6-0HDA) or disulfirarn. Eptazocine increased the norepinephrine (NE) level in the brain stem, but decreased the dopamine (DA) level in the cortex. Eptazocine decreased the rates (ADA turnover in the cortex and the brain stem and NE turnover in the spinal cord. The analgesic action of PZC was decreased by α-methyl-p-tyrosine (α-MT), disulfirarn 6-0HDA or reserpine. PZC decreased NE levels in the cortex and the brain stem, and DA level in the striatum. The turnover rates of NE in the brain stem and the spinal cord were increased by PZC. The analgesic action of MOR was potentiated by α-MT and attenuated by reserpine or 6-0HDA. MOR decreased NE and DA levels in the cortex and NE level in the brain stem, but increased DA level in the brain stem and NE level in the spinal cord. The turnover rates of NE in the cortex and the brain stem were increased at low doses of MOR, but those of DA in the striatum and NE in the spinal cord were decreased at high doses of MOR. These results suggest that the mechanism of eptazocine-induced analgesia is different from those of PZC and MOR in terms of the relationship to catecholamine neurons.
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