The contribution of glucose to alanine metabolism in man.

We have studied by tracer technique the interconversion of the carbon skeleton of alanine with that of glucose. The data analysis is in terms of renewal theory rather than traditional compartmental analysis. This eliminates the need for estimation of compartment size, which is particularly difficult to determine in the case of alanine. In addition, the conversion rates between the two substances are found by considering the two components which are responsible for the determined radioactivity curves, namely, the first conversion of the labeled carbon and its subsequent movement in the product compound. The subjects of the study were for the most part underweight but had been hospitalized and eating a standard hospital diet for at least 3 days prior to the studies. Our data indicate that nearly twice as much carbon from glucose is cycled to alanine as is recycled from alanine back to glucose after a 14 hr overnight fast. Small amounts of glucose suppress the alanine-glucose arm of the cycle but probably do not change the glucose-alanine conversion. The contribution of glucose carbon to alanine metabolism is significant and appears to be immediately influenced by the magnitude of glycolysis.