Thermoregulatory and metabolic changes during fever in young and old rats

• Published in: American journal of physiology. Regulatory, integrative and comparative physiology Vol. 54; no. 5; pp. R1165 - R1169
• Main Authors: BUCHANAN, Jessica B, PELOSO, Elizabeth, SATINOFF, Evelyn
• Format: Journal Article
• Language: English
• Published: Bethesda, MD American Physiological Society 01.11.2003
• Subjects: Age; Biological and medical sciences; Fever; Fundamental and applied biological sciences. Psychology; Heat; Metabolism; Rodents; Thermoregulation. Hibernation. Estivation. Ecophysiology and environmental effects; Vertebrates: anatomy and physiology, studies on body, several organs or systems; Rat; Body temperature; Rodentia; Heat production; Thermoregulation; Environmental factor; Oxygen consumption; Heat loss; ambient temperature; Fever; Vertebrata; Heat; Mammalia; Lipopolysaccharide; Calorimetry; aging
• ISSN: 0363-6119; 1522-1490

We injected old and young rats with lipopolysaccharide (LPS; 50 µg/kg ip) at two ambient temperatures (Ta; 21 and 31°C). Young rats mounted equivalent fevers at both Tas [peak body temperatures (Tb) of 38.3 and 38.7°C, respectively]. The Tb of old rats was not different from baseline (37.3°C) after LPS at Ta 21°C, whereas, at 31°C, their Tb rose to a mean peak of 38.4°C. We also measured the associated thermoregulatory responses by use of calorimetry. At 21°C, young rats developed a fever by increasing both O2 consumption and heat conservation. Old rats did not become febrile, and O2 consumption fell by 15%. Heat loss was the same in old and young rats. At 31°C, young and old rats developed similar fevers with similar increases in heat production and conservation. Our results suggest that the lack of LPS fever in old rats at 21°C is due mainly to the lowered metabolic rate.