Extensive lesions of dermal hemorrhagic necrosis occurred in rabbits when epinephrine (or norepinephrine) was injected into the skin within 4 hours after an intravenous injection of endotoxin. As little as 5 µg. of intradermal epinephrine, and 1 µg. of intravenous endotoxin, were sufficient to produce lesions.

Similar lesions, but smaller in size and surrounded by a zone of acute inflammation, were produced by intradermal injection of a mixture of comparable amounts of endotoxin and epinephrine.

No lesions were produced by combinations of endotoxin with serotonin, pitressin, or ephedrine.

Both types of epinephrine-endotoxin lesion were prevented by pretreatment with cortisone, dibenzyline, and chlorpromazine. They were not prevented by heparin or nitrogen mustard. The lesions produced by intradermal mixtures of epinephrine and endotoxin were greatly enhanced in size and severity in animals treated with nitrogen mustard.

Both types of lesion were prevented in rabbits rendered "tolerant" by repeated injections of sublethal amounts of endotoxin.

It is concluded that endotoxin has the property of altering the reactivity of blood vessels to epinephrine in such a way that this hormone becomes a potent necrotizing agent. The possibility that this effect may represent a basic mechanism in the various intoxicating actions of endotoxin, and certain implications of this hypothesis, are discussed.

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