Ketogenesis in Rats on High Carbohydrate and High Fat Diets

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Abstract
Rats were adapted to isocaloric high fat and high carbohydrate diets for 4-6 weeks and ketogenesis was studied at 4 levels of organization: the intact animal, the surviving liver slice, "octanoate oxidase" activity of washed liver particles and whole, fortified liver homogenates. Significant differences between the diet groups were found at all levels. The fat-fed rats showed higher blood ketone concentrations in the fed state than did the CHO group and a much smaller elevation after a 24 hour fast. Ketone body production by surviving liver slices was higher in the fat diet group in the fed state and lower after a fast. Washed liver particles prepared from fat diet rats showed a "defect" in octanoate oxidation which was partially corrected by the addition of a sparking concentration of alpha-ketoglutarate. Differences consistent with those described were found in whole fortified liver homogenates. These findings are discussed in the light of other attempts to elucidate the cellular mechanisms involved in mammalian adaptations.