Cortisone acetate administered to mice at the same time as either the LD50 or 2 x LD50 of endotoxin significantly protected against lethality. Delaying the injection of cortisone to 1, 2, or 4 hours after that of endotoxin resulted in loss of protection with the possible exception of a 1 hour delay with the LD50 of endotoxin. Associated with this loss of protection was the failure of the hormone to induce liver tryptophan pyrrolase. Normal mice given only cortisone showed an increase in enzyme activity nearly three times that of control values when assays were carried out either 4 or 17 hours after the hormone was given. Endotoxin-poisoned mice showed normal levels of enzyme activity with concurrent injection of cortisone but depressed levels of enzyme when the cortisone injection was delayed for only 1 hour or more. Apparently, therefore, enzyme induction (or maintenance) is related to survival in endotoxin poisoning.

In line with this hypothesis was the observation that inhibitors of enzyme (protein) synthesis were found to potentiate the lethal action of endotoxin and to prevent the protective effect of cortisone. The inhibitors employed were actinomycin D, ethionine, 2-thiouracil, and 8-azaguanine. Activity of liver tryptophan pyrrolase was lowered by endotoxin and elevated by cortisone. When the two were given concurrently, normal enzyme activity was maintained. Chloramphenicol, an active inhibitor of protein synthesis in microorganisms but with limited effect in mammals, was without observable influence in these respects.

Mice 18 hours postinfection with Salmonella typhimurium, strain SR-11, given at a level that caused first deaths on the 3rd day, had a lower than normal activity of liver tryptophan pyrrolase and responded to cortisone induction with a smaller increase in enzyme level than that found in control mice. Each is characteristic of endotoxin poisoning. Animals 42 hours postinfection were free of these signs of endointoxication, an observation in agreement with earlier experiments where other measures of endotoxin were employed.

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