Heat balance and reactivity to endotoxin

¹ Division of Allergy and Infectious Disease, Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland

Shorn rabbits, supine restrained rabbits, and rabbits in the cold had relatively low body temperatures because their caloric losses were greater than normal, and they did not develop fever after endotoxin, adrenaline, or endogenous pyrogen. In such animals, mechanisms of heat conservation seemed maximally operative prior to testing; the absence of fever was related to limits imposed by ambient temperature upon heat conservation by further vasoconstriction in the ear, and shivering responses were not uniformly seen. Ordinarily appropriate late mechanisms of heat dissipation were noted after endotoxin despite the lack of fever. Febrile responses became possible when shorn animals were warmed. After repeated endotoxin injection, greater vasoconstriction over the trunk was feasible, the limitations of ambient temperature upon heat conservation became less decisive, and fever resulted. The unusual circulatory and thermal responses of chilled rabbits should be taken into consideration when performing similar experiments.