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 (V̇O2) was measured in 2-, 4-, 6-, and 8-day-old homozygous lean (Fa/Fa) Zucker pups from each treatment. We determined minimum rate of V̇O2 at thermoneutrality and maximum V̇O2 in response to progressively colder ambient temperatures. Overfed pups were fatter than standard-fed pups (P < 0.001). But contrary to our prediction, overfed pups had a significantly increased maximum V̇O2 in response to acute cold exposure. To test the hypothesis that brown fat mediated the increased V̇O2 in the overfed pups, scapular brown fat lipectomes 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 V̇O2 were seen at thermoneutrality when brown fat is turned off. But maximum V̇O2 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 energy expenditure in response to acute cold exposure in the overfed pups.
|Original language||English (US)|
|Journal||American Journal of Physiology - Regulatory Integrative and Comparative Physiology|
|State||Published - 1986|
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