Relationship between cold-induced thermoregulation and spontaneous
rapid body weight loss of aging fischer 344 rats.
McDonald, Roger B., Maria Florez-Duquet, Carol Murtagh-Mark, and
Barbara A. Horwitz.
Departments of Nutrition, Physiology Graduate Group and Section of
Neurobiology, Physiology, and Behavior, Division of Biological
Sciences, University of California, Davis, CA 95616
APStracts 3:0145R, 1996.
We have previously shown that although cold-induced thermoregulation
is attenuated in 26-mo-old male Fischer (F344) rats, not all rats
this age exhibit the same degree of cold-exposed hypothermia or
diminished brown adipose tissue nonshivering thermogenic capacity.
Examination of this heterogeneity suggested the hypothesis that it
was associated with differences in physiological state between aged
rats that were maintaining stable body weight versus those showing
the rapid weight loss often occurring near the end of the rat's
natural life span. To test this, we acutely exposed male F344 rats to
cold (4 hours at 6 degrees C) beginning at 24 months of age. This
exposure was weekly for the first two weeks and then on alternate
weeks as long as the rat's body weight was stable. If body weight
progressively declined for 3-5 consecutive days, the rat's response
to the acute cold exposure was again measured as was that of two
additional rats not displaying this rapid loss in body weight. If
body temperature decreased during the cold exposure to
intraperitoneal temperatures less than or equal to 32.5 degrees C,
the rat was euthanized with sodium pentobarbital and interscapular
brown adipose tissue was removed. One of the age-matched controls was
also euthanized at this time. The age at which body weight showed a
spontaneous rapid decline ranged from 24.5 to 29 months. All 8 rats
displaying spontaneous rapid weight loss had significant hypothermia
during the acute cold exposure, while none of the 8 weight stable
rats did. The development of hypothermia in the spontaneous rapid
weight loss group was not, in general, observed before their weight
loss. The weight loss and hypothermia were associated with lower
levels of brown fat uncoupling protein 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
rapid component, the latter being associated with a different
physiological state than the former.
Received 15 September 1995; accepted in final form 2 April 1996.
APS Manuscript Number R575-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 23 April 96