Hypoferremia in Mice and Its Application to the Bioassay of Endotoxin

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Abstract
Baker, Phillip J. (University of Wisconsin, Madison), and J. B. Wilson . Hypoferremia in mice and its application to the bioassay of endotoxin. J. Bacteriol. 90: 903–910. 1965.—The ability of endotoxin to induce hypoferremia in mice was used for the bioassay of endotoxin. A marked depression in the serum-iron levels of mice occurred 12 hr after the intraperitoneal injection of 0.01 to 100 μg of Escherichia coli endotoxin; similar results were obtained with 1.0 to 100 μg of Brucella abortus endotoxin. This biological response to endotoxin appeared to be specific, reproducible, and dose-dependent. As heat-killed cells of B. abortus and E. coli were also able to induce hypoferremia, this bioassay could be employed for the determination of the endotoxin content of killed-cell preparations. Treatment of endotoxin by acid hydrolysis, acetylation, or pyridine-formic acid greatly diminished the hypoferremic response as well as its lethality for mice. Pretreatment of mice with Thorotrast had little effect upon the ability of endotoxin to induce hypoferremia; however, a stimulation of the activity of the reticuloendothelial system (RES) by treatment of mice with triolein markedly reduced the ability of endotoxin to induce hypoferremia. The relationship between the hypoferremic response to endotoxin and alterations in the activity of the RES are discussed.