Flunarizine analgesia is mediated by mu-opioid receptors

We evaluated the opioid antinociceptive mechanism of the calcium channel blocker flunarizine. Flunarizine produced a dose-dependent, analgesia in the hot plate test which was antagonized by general (naloxone) and mu [beta-fualtrexamine (beta-FNA)]-opioid antagonists, indicating a role for CL receptors in flunarizine analgesia. Naltrindole (delta(1) antagonist) did not affect flunarizine analgesia. A fixed subthreshold dose of flunarizine augmented mu (morphine) analgesia and blocked delta(1) [enkephalin, [D-Pen(2,5)] (DPDPE)] analgesia. Apparently, flunarizine has mu agonistic activity and delta(1) antagonist or mixed agonistic-antagonistic activity. (C) 1997 Elsevier Science Inc.