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 phospholipase A1 toxin (mol. wt approximately 32,000) with a potent hemolytic activity. Subplantar injection of the toxin caused a dose-dependent swelling in the rat hind paw. Its potency was higher than those of phospholipases A2 and cardiotoxin from cobra venoms. Hind-paw edema induced by the toxin was inhibited by antiserotonin drugs (cyproheptadine and methysergide), indomethacin and betamethasone. Antihistamine (chlorpheniramine) showed a relatively weak inhibition. Intradermal injection of the toxin into back skin of the rat also induced local edema which was inhibited by chlorpheniramine and methysergide. Rats pretreated with multiple doses of compound 48/80 showed a moderate decrease in the histamine and serotonin content of rat skin, and a slight decrease in paw edema induced by the toxin, while a single dose of reserpine markedly 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 effect of the toxin. However, serotonin released by the toxin appears to be the major factor mediating the toxin-induced edema in the rat.