The metabolic reactions responsible for the release of endogenous pyrogen from rabbit granulocytes incubated in 0.15 M NaCl are specifically inhibited by the presence of K+ (and by related alkali metal ions, Rb+ and Cs+) in the medium. The inhibitory action of K+ apparently involves penetration of the cell membrane and is directly antagonized by the cardiac glycoside, ouabain. It is concluded, therefore, that the inhibition of pyrogen release by extracellular K+ is due to transport of K+ into the cell.

Although the precise molecular mechanisms which are responsible for the release of pyrogen from granulocytes incubated in K-free saline have not been elucidated, further study of the process has revealed: (a) that it is preceded by the accumulation of pyrogen within the cell, (b) that it depends upon the catalytic action of one or more sulfhydryl-containing enzymes, (c) that it does not require energy, either from glycolysis or from reactions depending on molecular oxygen, and (d) that its inhibition by K+ and by arsenite is qualitatively similar to the depression caused by these same reagents on the release of other leucocytic proteins; i.e., lysozyme and aldolase.

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