[Pharmacological action of eptazocine (l-1,4-dimethyl-10-hydroxy-2,3,4,5,6,7-hexahydro-1,6-methano-1H-4-banzazonine). (II) Relationship between the analgesic action of eptazocine and brain 5-hydroxytryptamine (5-HT) (author's transl)].

The relationship between the analgesic action of eptazocine and brain 5-HT was investigated by pharmacological and neurochemical methods in comparison with pentazocine (PZC) and morphine (MOR). The analgesic effects of eptazocine, PZC, and MOR as determined by the pressure method were decreased by pretreatment with rho-chlorophenylalanine or 5,6-dihydroxytryptamine. The analgesic effects of all three drugs were also diminished by a lesion in the dorsal half of the spinal cord (C5-6) or the raphe magnus. A lesion in the central gray produced a decrease in the analgesic effects of MOR or PZC, but had a weak effect on that of eptazocine. All three drugs increased 5-hydroxyindole acetic acid (5-HIAA) levels in the brain stem, the striatum, and the spinal cord. In addition, eptazocine decreased the 5-HIAA level in the cortex and the 5-HT level in the hippocampus, but increased the 5-HT level in the spinal cord. An increase of 5-HIAA in the cortex and a decrease of 5-HT in the brain stem were observed after PZC-administration. On the other hand, MOR decreased the 5-HT level in the brain stem and striatum. These results suggest that the effects of eptazocine on 5-HT neurons are similar to those of PZC and MOR, but part of the action mechanism of eptazocine is different from those of PZC and MOR.