The vascular effects of lethal doses of E. coli endotoxin, as observed in the mesentery of the rat, resemble the reactions of traumatic and hemorrhagic shock in the following respects: a profound inhibition of arteriolar and precapillary reactivity to topical epinephrine occurs after an initial stage of hyperreactivity; the small veins show failure to relax completely following constrictor doses of epinephrine; and the terminal vessels develop an unusual sensitivity to fluctuations in temperature of the fluid irrigating the tissue.

Rats in which tolerance to bacterial endotoxin is induced, by repeated doses given daily, become highly resistant to the lethal effects of both drum trauma and hemorrhagic shock.

However, rats in which the adaptation to traumatic shock is produced by repeated exposure to drum trauma, do not develop a significant degree of tolerance to lethal doses of endotoxin.

The injection of small non-lethal doses of bacterial endotoxin during non-lethal episodes of trauma or hemorrhage, leads to the development of irreversible shock and death.

The bearing of these findings on the problem of the relationship between endotoxin and traumatic shock is discussed.

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