Latency of Pyrogen Fever. Appearance of a Fast-Acting Pyrogen in the Blood of Febrile Animals and in Plasma Incubated With Bacterial Pyrogen

Abstract

Blood from 13 rabbits given Proteus vulgaris pyrogen by intraven. injn. 3-180 min. before bleeding caused fever with much less latency than an equivalent dose of the bacterial pyrogen when the febrile blood was injected intraven into 38 test rabbits. Similarly reduced latency was seen when pyrogen was incubated before injn. with rabbit blood or plasma (tests on 52 rabbits, with heparinized and citrated plasma and control injns.). Incubation in citrated plasma also increased potency of the pyrogen 5- to 10-fold. It is concluded that pyrogen interacts with plasma in vivo and in vitro to form an "endogenous pyrogen" able to reach thermostatic centers more rapidly than the bacterial pyrogen, and that citrate promotes formation of this substance. It is not yet clear whether "endogenous pyrogen" formation is an essential step in genesis of fever.