Lappaconitine and N-deacetyllappaconitine potentiate footshock-induced analgesia in rats.

The effects of lappaconitine (LA) and N-deacetyllappaconitine (DLA) on footshock-induced analgesia (FSIA) were studied by the rat tail flick test. Rats subjected to 90 s nonescaping footshock had a significant increase in tail flick latency. Naloxone (4 micrograms, i.c.v.) partially antagonized the FSIA. After 5 consecutive exposures to footshock, rats developed a complete tolerance to the FSIA. The rats tolerant to FSIA showed a cross-tolerance to morphine- but not LA- and DLA-induced analgesia. Administrations of subanalgesic doses of LA and DLA potentiated the FSIA in both intact and adrenalectomized rats.