Glucose metabolism in the lactating beagle dog

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Abstract
A study was made of the role of glucose as an oxidizable substrate and as a source of C for the synthesis of milk using lactating beagle dogs. Uniformly C14-labeled glucose was used as a tracer of these metabolic pathways. Our data indicate that the labeled glucose was completely eliminated from the dog's body within 24 hr after injection. Sixty percent of the injected dose appeared in the expired CO2, 40% in the various milk products. Comparison of the integrated specific activity of plasma glucose with that of expired CO2 indicates that 36% of the dog's energy requirement is met by the oxidation of glucose. This presumably means that the catabolism of noncarbohydrate substances must be of considerable importance to the energy metabolism of not only the fasted dog and the diabetic dog, as has been demonstrated earlier, but also of the fed dog. We have also shown that 68–100% of the C required for the synthesis of lactose is derived from plasma glucose. In addition, plasma glucose contributes 7.2–12% of milk protein C and 5.1–8.7% of milk fat C. These results are compared with similar data obtained earlier in our laboratory using lactating cows and sows.