Heat production and substrate oxidation in rats fed at maintenance level and during fasting.
A total of 36 Wistar rats were fed a commercial diet to a stipulated live weight of 75 g (Group A), 100 g (Group B) and 225 g (Group C). All rats were measured in energy balance experiments, in which the animals were fed near maintenance level, followed by a period of fasting with measurements of the gas exchange. The rats in Group A, B and C were fasted for 2, 3 and 4 days, respectively. The minimum heat production on the last day of fasting for all groups was proportional to metabolic body weight (kg0.75) with a regression: heat production, kJ day-1 = 321 x kg0.75 (R2 = 0.994). In rats fed near maintenance level, heat production was provided by oxidation of carbohydrates in 80-85%, oxidation of protein was 10-15%, while oxidation of fat contributed less than 10%. It is suggested that in the fasting period, the contribution to the total heat production from oxidized carbohydrate and fat depended on the size of the fat depots, a large fat depot giving rise to fat oxidation. On the last day of fasting, 24, 51 and 90% of the total heat originated from fat oxidation in Group A, B and C, respectively.
Royal Veterinary and Agricultural University, Department of Animal Science and Animal Health, Frederiksberg, Copenhagen, Denmark. ac@kvl.dk
A
A
Chwalibog
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Jakobsen
A H
AH
Tauson
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G
Thorbek
D000273:Adipose Tissue / Q000378:metabolism; D000818:Animals; D001522:Behavior, Animal / Q000502:physiology; D001835:Body Weight; D002151:Calorimetry; D050260:Carbohydrate Metabolism; D004032:Diet; D004435:Eating / Q000502:physiology; D004734:Energy Metabolism / Q000502:physiology*; D005215:Fasting / Q000502:physiology*; D005223:Fats / Q000378:metabolism*; D006358:Hot Temperature; D008297:Male; D010084:Oxidation-Reduction; D010101:Oxygen Consumption / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar
D005223:Fats