title: Body temperature rhythms, cold tolerance, and fever in young and old rats of both genders.
abstract: The circadian rhythm of body temperature (CTR) of male and female rats living at 23 degrees C, as well as their body temperature response to a yeast injection or to a 2-h exposure to 0 degree C, was investigated by telemetry. Young rats had a clear CTR with a mean nocturnal peak of 38.0 +/- 0.1 degree C and diurnal trough of 36.2 +/- 0.1 degree C. Older rats, starting at about 18 months of age, tended to have poor (that is, lower amplitude) rhythms. Mean daily body temperature was 37.1 +/- 0.2 degree C at all ages. After exposure to the cold, the body temperature of young rats, old rats with a strong CTR, and old rats with a poor CTR changed in the ranges of -0.3 to +1.5 degree C, -3.1 to +0.7 degree C, and -5.2 to +0.4 degree C, respectively. This indicates that old animals, especially but not exclusively those with poor CTRs, are less resistant to cold stress. On the other hand, the capacity to develop a fever in response to a yeast injection was equivalent in the three groups of animals, although females had a smaller response than males. It is concluded that the process of aging does not have a generalized debilitating effect on temperature regulation in rats. Rather, aging seems to affect individual components of the thermoregulatory system differentially.
authors.affiliation: Department of Psychology, University of Illinois, Champaign 61820.
authors.forename: R
authors.initials: R
authors.lastname: Refinetti
authors.forename: H
authors.initials: H
authors.lastname: Ma
authors.forename: E
authors.initials: E
authors.lastname: Satinoff
mesh_terms: D000064:Acclimatization / Q000502:physiology; D000375:Aging / Q000502:physiology*; D000818:Animals; D001833:Body Temperature Regulation / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology*; D003080:Cold Temperature / Q000009:adverse effects; D005260:Female; D005334:Fever / Q000209:etiology; D008297:Male; D051381:Rats; D012441:Saccharomyces cerevisiae; D012727:Sex Characteristics