AJP - Regulatory, Integrative and Comparative Physiology, Vol 251, Issue 3 518-R524, Copyright © 1986 by American Physiological Society
Brown fat mediates increased energy expenditure of cold-exposed overfed neonatal rats
B. J. Moore, J. S. Stern and B. A. Horwitz
Genetically lean rat pups, overfed by being raised in small litters of
three from day 1 postpartum, rapidly become obese compared with pups raised
in standard sized litters of eight. Because of the rapid onset of their
obesity, we expected that overfed pups would exhibit defective brown fat
thermogenesis as is seen in neonatal genetically obese rodents. O2
consumption (VO2) was measured in 2-, 4-, 6-, and 8-day-old homozygous lean
(Fa/Fa) Zucker pups from each treatment. We determined minimum rate of VO2
at thermoneutrality and maximum VO2 in response to progressively colder
ambient temperatures. Overfed pups were fatter than standard-fed pups (P
less than 0.001). But contrary to our prediction, overfed pups had a
significantly increased maximum VO2 in response to acute cold exposure. To
test the hypothesis that brown fat mediated the increased VO2 in the
overfed pups, scapular brown fat lipectomies were performed on a new group
of overfed pups at 2 days of age and compared with sham-operated littermate
controls. On day 8, no differences in minimum VO2 were seen at
thermoneutrality when brown fat is turned off. But maximum VO2 in response
to cold, when brown fat is turned on maximally, was significantly reduced
in the lipectomized overfed pups compared with sham-operated overfed
littermates. These data suggest that manipulations of diet, accomplished by
raising pups in small litters, can increase brown fat thermogenic function.
The results of the lipectomy experiment imply that brown adipose tissue is
a primary mediator of the increased energy expenditure in response to acute
cold exposure in the overfed pups.
