The recycling of carbon in glucose, lactate and alanine in sheep.

Pregnant ewes with catheters implanted in an artery and the uterine and recurrent tarsal veins were infused at a constant rate with U-(14)C-labelled glucose, alanine or bicarbonate. Measurements were made of the overall and local fractional contribution of glucose and alanine to CO(2) production and of the extent of interconversion of these metabolites. In the whole animal, by coupling the results with the authors' previous study of lactate metabolism, a solution was obtained to an open unrestricted 4-compartment model of the exchange of carbon between glucose, lactate, alanine and CO(2).