The effects of KB-2796 and BAY K 8644 on fentanyl-induced analgesia in rats.

We investigate the modulatory effects of subcutaneous administration of different doses of KB-2796 (1, 5 and 15 mg/kg), a new calcium channel blocker, and BAY K 8644 (0.25, 0.5 and 1 mg/kg), a calcium agonist, on fentanyl-induced analgesia (20 micrograms/kg) in rats. The drugs were tested individually as well as in combination with fentanyl. Dimethyl sulfoxide (DMSO) was used as a control. Nociceptive sensitivity was assessed by the tail-flick technique. When KB-2796 and BAY K 8644 were used alone, only KB-2796 at the dose of 15 mg/kg produced an effect that was significantly different from that of DMSO (p < 0.01). The effect was antinociceptive. When administered with fentanyl, KB-2796 at 5 and 15 mg/kg potentiated the analgesic effect of fentanyl (p < 0.05), but suppression of fentanyl analgesia by BAY K 8644 was not significant at any of the doses tested. Our data supports the hypothesis that the calcium ion is partially involved in fentanyl-induced analgesia.