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"Biphasic" fevers often consist of more than two phases
A A Romanovsky1, C T Simons, V A Kulchitsky
1Thermoregulation Laboratory, Legacy Holladay Park Medical Center, Portland, Oregon 97208-3950, USA.
The American Journal of Physiology
|August 5, 1998
Summary
This study reveals that lipopolysaccharide (LPS) injections in rats do not cause biphasic fever as commonly believed. Instead, the fever response is consistently triphasic, regardless of LPS type or rat strain, challenging existing scientific understanding.
Area of Science:
- Immunology
- Physiology
- Pharmacology
Background:
- Lipopolysaccharide (LPS) is a potent pyrogen commonly associated with inducing biphasic fever responses in animal models.
- The prevailing assumption is that LPS doses of ≥2 µg/kg elicit a biphasic fever pattern.
Purpose of the Study:
- To investigate the actual fever pattern induced by lipopolysaccharide (LPS) in rats.
- To determine if the commonly observed biphasic fever response to LPS is accurate or if an alternative pattern exists.
Main Methods:
- Adult male rats of various strains were surgically prepared with jugular vein catheters.
- Animals were habituated to experimental conditions before intravenous injection of 10 µg/kg LPS at an ambient temperature of 30.0°C.
- Colonic and tail skin temperatures were monitored for over 7 hours post-injection, with data analyzed using time graphs and phase-plane plots.
Main Results:
- Intravenous injection of LPS consistently induced a triphasic febrile response in rats, characterized by three distinct peaks in colonic temperature and three waves of tail skin vasoconstriction.
- This triphasic pattern was observed across different LPS preparations (phenol and TCA extracts from E. coli, S. flexneri, and S. typhosa) and in multiple rat strains (Bkl:Wistar, Bkl:Sprague-Dawley, and Sim:(LE)fBR).
- Control injections of saline did not elicit any significant changes in colonic temperature.
Conclusions:
- The common belief that lipopolysaccharide (LPS) induces biphasic fever is inaccurate.
- The febrile response to LPS in rats is intrinsically triphasic, irrespective of the specific LPS preparation or rat strain used.
- This finding necessitates a re-evaluation of the established understanding of LPS-induced fever and its implications in research.