EDEMA-INDUCING ACTIVITY OF A LETHAL PROTEIN WITH PHOSPHOLIPASE A1 ACTIVITY ISOLATED FROM THE BLACK-BELLIED HORNET (VESPA-BASALIS) VENOM

The lethal protein of the hornet (Vespa basalis) venom is a phospholip ase A1 toxin (mol. wt approximately 32,000) with a potent hemolytic ac tivity. Subplantar injection of the toxin caused a dose-dependent swel ling in the rat hind paw. Its potency was higher than those of phospho lipases A2 and cardiotoxin from cobra venoms. Hind-paw edema induced b y the toxin was inhibited by antiserotonin drugs (cyproheptadine and m ethysergide), indomethacin and betamethasone. Antihistamine (chlorphen iramine) showed a relatively weak inhibition. Intradermal injection of the toxin into back skin of the rat also induced local edema which wa s inhibited by chlorpheniramine and methysergide. Rats pretreated with multiple doses of compound 48/80 showed a moderate decrease in the hi stamine and serotonin content of rat skin, and a slight decrease in pa w edema induced by the toxin, while a single dose of reserpine markedl y diminished the toxin-induced edema in association with depletion of serotonin in rat skin. The edema-inhibitory action of amine-depleting agents appeared to correlate with their potencies to deplete serotonin in the skin. It is suggested that serotonin, prostaglandin E2, and to a lesser extent of histamine are involved in producing the local effe ct of the toxin. However, serotonin released by the toxin appears to b e the major factor mediating the toxin-induced edema in the rat.