ESTIMATION OF GLUCOSE TURNOVER WITH STABLE TRACER GLUCOSE-1-C-13

Abstract

Glucose turnover was measured in normal and diabetic dogs by dilution of 1-13C-glucose and 1-14C-glucose tracers infused simultaneously at constant rates. In order to quantify the stable isotope, an enzymatic assay for the analysis of 1-13C-glucose was developed and evaluated. CO2 from C-1 of glucose was evolved by coupling hexokinase, glucose-6-phosphate dehydrogenase, and 6-phosphogluconic dehydrogenase activities. The 13C/12C ratio of the CO2 was measured with a high-precision magnetic-deflection double-collector mass spectrometer, and the radioactivity of 14CO2 was quantified by liquid scintillation. The ratio of 13C/12C was reproducible in assays of CO2 evolved from either naturally occurring or 13C-enriched glucose. Systemic glucose production rates measured with 13C- and 14C-labeled tracers were similar over a wide range from 2-12 mg/kg per min. 1-13glucose may be employed as a tracer for glucose metabolism in human subjects without incurring the risk of radiation.