Onset of excess fat deposition in Zucker rats with and without decreased thermogenesis
Markewicz, B.; Kuhmichel, G.; Schmidt, I.
American Journal of Physiology 265(3 Pt 1): E478-E486
1993
ISSN/ISBN: 0002-9513 PMID: 8214055 Document Number: 419111
To study the first stages of excess fat deposition in Zucker rats, we artificially fed littermates with identical amounts of milk from 4 to 15-16 days of age while continuously recording oxygen consumption ( ovrhdot Vo-2) and deep body temperature. Under intermittent cold loads simulating the periodic thermoregulatory stimulation experienced in the nest, differences between the amounts of body fat deposited by artificially reared fatty (fa/fa) and lean (Fa/-) pups were as large as those seen in mother-reared pups. The decreased ovrhdot VO-2 of the cold-reared fatty pups could account for 90-100% of their extra fat deposition. At thermoneutrality, 16 day-old littermates reared with low feeding rates showed small but significant genotype differences in body fat that were not energetically accounted for by differences in ovrhdot VO-2 or lean body mass. Slightly but significantly lower fecal energy losses indicated that differences in resorption might account for the positive energy balance of thermoneutrally reared fa/fa pups. Reduced energy expenditure thus efficiently fuels excess fat deposition but is not essential for the onset of excess fat deposition in fa/fa pups. Other factors than reduced sympathetic activation of brown adipose tissue must be considered as a primary cause for the development of fa/fa obesity.