Reduced cold-induced thermoregulation of aging fischer 344 rats losing body weight: a possible marker for the onset of senescence

C. M. Murtagh-Mark, M. Florez-Duguet, Barbara A Horwitz, R. B. McDonald

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We have shown that while cold-induced thermorégulation is attenuated in 26mo-old male Fischer (F344) rats, not all rats this age exhibit the same degree of cold-exposed hypothermia or diminished brown fat nonshivering thermogenic capacity. The present investigation evaluated if this heterogeneity in the cold response was associated with the loss of body weight observed near the end of the rat's natural life span. We acutely exposed male F344 rats bimonthly to cold (4 hrs at 6°C) beginning at 24 mo. of age. If body weight progressively declined for 3-5 days, the rats were again cold exposed and killed after the trial along with an age-matched, cold-exposed rat not displaying body weight loss, Interscapular brown adipose tissue was removed for measurement of mitochondria uncoupling protein (UCP). The age at which body weight showed a rapid decline in the weight unstable group ranged from 24.5 to 29 months. Rats displaying rapid weight loss had significant hypothermia during the acute cold exposure, while none of the weight stable rats did. The development of hypothermia in the weight unstable group was not observed before their weight loss. The weight loss was associated with lower rates of cold-induced oxygen consumption, lower levels of brown fat UCP, and significant changes in body fat and protein. These data suggest that the development of senescent-related hypothermia occurs rapidly and is not a simple function of chronological age or the median life span of the animals. Furthermore, these data imply that the rate of aging in terms of maintenance of thermoregulatory homeostasis has both a gradual and a rapid component, the latter being associated with a different physiological state than the former.

Original languageEnglish (US)
JournalFASEB Journal
Issue number3
StatePublished - 1996

ASJC Scopus subject areas

  • Agricultural and Biological Sciences (miscellaneous)
  • Biochemistry, Genetics and Molecular Biology(all)
  • Biochemistry
  • Cell Biology


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