Increased histamine sensitivity in mice after administration of endotoxins.

CFW mice given submicrogram doses of endotoxins intravenously became highly susceptible to the lethal effects of 0.5 mg of histamine given intraperitoneally 1 to 2 h later. The histamine-sensitizing effects of the endotoxins were transitory and disappeared within 6 to 8 h. L-Epinephrine administered intravenously immediately after histamine challenge protected mice from death, but aterenol and isoproterenol were ineffective. The histamine-sensitizing effect in endotoxins was precipitated by anti-endotoxin sera with a concomitant eightfold loss in activity. However, dissociation of the immune complex in 0.25 M acetic acid fully restored histamine-sensitizing activity. The transitory nature of the hypersensitivity produced by endotoxin and the high heat resistance of the active material prove that it is different from the histamine-sensitizing effects of pertussigen.