Mouse paw oedema induced by Habu snake (Trimeresurus flavoviridis) venom: inhibition by morphine, naloxone and methylnaloxone alone or in combinations.

The oedema produced in the mouse by intraplantar injection of the venom of Trimeresurus flavoviridis was inhibited by morphine (Mo) and by naloxone (Nx); the action of Mo increased with the dose, whereas that of Nx first progressed and thereafter regressed with the dose; very small doses of Nx antagonized Mo. Methylnaloxone (MeNx), a quaternary ammonium derivative of Nx was much less effective than Nx by the subcutaneous route but almost as effective by the intraplantar route. Peripheral opioidergic receptors are thus likely to be involved. Very high doses of Mo acted an synergistically with an optimal dose of EDTA or zymosan; complex interactions occurred between lower doses of Mo or Nx and EDTA or zymosan.