Estimates of food intake and body weight gain were obtained in obese (ob/ob) mice from 7 to 56 days of age. Milk intake was estimated daily from 7 to 21 days of age; there were no differences between obese and lean mice. From 14 to 21 days of age, obese mice gained more body weight than lean mice. At 21 days of age, the carcasses of obese mice contained about twice as much fat as the carcasses of lean mice did, whereas the protein content was not different. Mice were weaned at 21 days of age, and individually fed a stock diet or a high-fat diet. During the first several days after weaning, obese males consumed less food than did the lean males. After approximately 28 to 35 days of age, obese mice consumed more food and gained more weight than lean mice. At 56 days of age, obese mice contained 4 to 5 times as much body fat as did lean mice, but contained significantly less body protein than lean mice. For the 5 week post-weaning period, obese mice converted 3 to 4 times more dietary energy to body energy than did lean mice, whereas obese mice consumed only 20 to 40% more energy. At the same time, obese mice converted only about 70% as much dietary protein to body protein as did lean mice. The high-fat diet markedly enhanced the apparent energy efficiency in obese
mice. The present studies suggest that alterations in
energy metabolism, as well as in protein metabolism, may play an important role
in the development of obesity in these mice. Hyperphagia may be of secondary
impor
tance.
Male and female obese mice and their lean littermates
were killed at 21 and 56 days of age. Food residue in the stomach was removed
from the carcass. The carcass was then softened in an autoclave at 100° for 15
minutes prior to homogenization.The homogenate was heated in a water bath at
50°,mixed, and sampled. A chloroform/ methanol (2:3) mixture was used to extract
fat from the carcass homogenate. Carcass fat was determined gravimetrically. The
nitrogen content of the carcass was determined by a semi-microKjeldahl method
(12). The protein content was computed by multiplying the nitrogen con tent by
6.25. A bomb calorimeter4 was utilized to determine the energy content of mouse
carcasses. The carcass homogenates were dried (13) in a vacuum oven at 50° for
24 hours prior to combustion in the calorimeter. If you want to read full text
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