TECHNIQUES FOR ASSESSING PROTEIN AND GLUCOSE KINETICS

Isotopic labelling techniques can lead to a better understanding of th e changes in substrate flow resulting from trauma and other pathologic al conditions. This article describes the basic approaches used to mea sure rates of substrate flow, especially those using stable isotopes, and their application to the study of glucose and protein kinetics. Me thods for measuring glucose turnover and gluconeogenesis in the whole body by constant infusion of different labelled forms of glucose are e xplained. The advantages of measuring regional rates of glucose metabo lism, using arteriovenous balance of tracer and tracee, are illustrate d with results demonstrating the role of gluconeogenesis by the kidney . Similar approaches are used to measure protein turnover rates in the whole body and in specific regions, with labelled amino acids such as [1-C-13]leucine. In addition, rates of protein synthesis in individua l tissues can be assessed by measuring the incorporation of tracer int o protein of a biopsy sample. The relative merits of two methods of gi ving the tracer, by constant infusion or by flooding injection, are ex plained, with examples of studies of muscle protein synthesis in surgi cal patients.