"Blockade" of the RES by thorotrast so lowered the tolerance of hemorrhagic shock in rabbits and dogs that a reversible degree of hemorrhagic shock became irreversible. This was true not only in normal rabbits, but in rabbits made resistant to hemorrhagic shock by producing resistance to endotoxins.

Rabbits which had been pretreated with thorotrast and then subjected to hemorrhagic shock displayed at death the hemorrhagic lesions and the renal cortical necrosis characteristic of the Shwartzman reaction, in addition to the intramural hemorrhages in the gut which are characteristic of animals dying of hemorrhagic or of endotoxic shock. Elimination of the Shwartzman reaction by the prior administration of nitrogen mustard did not prevent the endotoxemia or the death in shock.

Rabbits made more resistant to thorotrast than normal rabbits by prior repeated administration of this substance were also more resistant than normal rabbits to endotoxin, and survived an ordinarily lethal exposure to hemorrhagic shock.

During the first few hours after its administration thorotrast induced excessive vulnerability not only to endotoxin and to hemorrhagic shock, but also to an additional small dose of thorotrast. Moreover, a non-absorbable antibiotic given by gavage shortly after thorotrast produced the same lesions as these other agents; i.e. endotoxic shock, the Shwartzman reaction, and death.

These data indicate that the lesions induced by thorotrast are produced by endotoxins which the injured or blockaded RES cannot inactivate. The presence of endotoxins in the blood of these rabbits was indicated by the lethal effect of this blood in test recipients.

The foregoing observations did not apply to rabbits with an intestinal flora free of coliform bacteria. Over 80 per cent of such rabbits were resistant to an ordinarily lethal exposure to hemorrhagic shock, and they escaped the damage caused by the usual doses of thorotrast. They did, however, develop endotoxic shock and die if given a large dose of thorotrast. These data were taken to indicate that coliform-free rabbits are not entirely free of endotoxins. (In the ordinary environment animals cannot avoid swallowing endotoxin and coliform bacteria.)

The absence of the Shwartzman reaction in the coliform-free rabbits is taken to signify that this reaction requires the participation of the endotoxins derived from the intraintestinal bacteria.

The absence of endotoxic shock in the coliform-free rabbits is taken to signify that the endotoxins of the coliform bacteria are involved in the shock and death of the coliform-bearing rabbits.

Finally the prevention by dibenamine of both the Shwartzman reaction and endotoxic shock and death in rabbits with a normal flora demonstrates that adrenergic activity plays an indispensable role in both phenomena.

The foregoing data provide strong support for the thesis that when the RES is severely disabled by any agent, endotoxins which normally and continuously enter the circulation from the gut will produce endotoxic shock and death.

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