Activities of enzymes of acetoacetate metabolism in rat brown adipose tissue during development.

The activities of two mitochondrial enzymes concerned in the utilization of acetoacetate, namely 3-oxoacid CoA-transferase and acetoacetyl-CoA thiolase, were high throughout the suckling and weanling period in brown adipose tissue of the rat. In contrast, 3-hydroxybutyrate dehydrogenase activity was comparatively low during this period. The activity of cytosolic acetoacetyl-CoA synthetase (involved in lipogenesis) declined after birth and remained low until the pups were weaned. Experiments with brown-adipose-tissue slices from weanling rats indicated that 70% of the [3-14C]acetoacetate utilized was oxidized to 14CO2, and this value was not altered appreciably by the addition of glucose and insulin.