The reliability of rates of glucose appearance in vivo calculated from single tracer injections

Abstract

The rate of appearance of unlabeled glucose was calculated from changes in plasma glucose specific radioactivity after a single i.v. injection of labeled glucose and compared with the actual constant infusion rate of unlabeled glucose into an anesthetized dog with all sources of endogenous glucose production surgically removed. The mean steady-state rate of appearance of unlabeled glucose calculated from the area under the specific radioactivity vs time curve was 7% higher than the actual infusion rate (n = 4), but the difference was not statistically significant. The variability in the rate calculated in this manner was, however, greater than the variability reported with rates determined from a primed constant infusion of tracer. Using 15-60 or 60-120 min specific radioactivity data the mean rate of appearance of glucose, calculated on the assumption of a 1-pool model for glucose turnover in vivo, was .apprx. 60% higher than the actual infusion rate. The results also indicate that it is possible to construct multi-pool models, but it is difficult to equate specific physiological events with the individual terms of the multi-exponential equation which describes the changes in plasma glucose specific radioactivity.