Estimation of the Pentose Cycle Contribution to Glucose Metabolism in Tissue in Vivo

Abstract

A method is illustrated for estimating the contribution of the pentose cycle to glucose metabolism in individual tissues in an intact animal. The method depends upon the presentation to the tissues of glucose-2-14C and the measurement of the randomization of the 14C in its conversion to glucose-6-P derivatives in the tissues. The assumptions required in making the estimations are detailed. Glucose-2-14C is infused into fasted, anesthetized rats. From the randomization of 14C in glucose from glycogen of diaphragm, skeletal muscle, heart, thyroid, brain, liver, and kidney, and in the glycerol from triglycerides of adipose tissue, the contribution in each of these tissues is estimated. In muscle, in vivo, the pentose cycle contributes no more than a few per cent to over-all metabolism; in thyroid, brain, liver, and kidney, 3–5%; and in adipose tissue, in a single determination, 34%. These estimates are generally in good agreement with estimates made in vitro. © 1967, American Chemical Society. All rights reserved.