Glucose metabolism in isolated rat adipocytes: estimate of total recovery by the product summation method.

To determine the completeness of glucose recovery into its metabolic products, adipocyte glucose utilization was compared by two different methods in a basal and in an insulin-stimulated metabolic state. One of the methods (product summation) is based on the recovery of (( U-14C ))-labeled glucose in carbon dioxide and triglyceride, together with the assay of lactate and pyruvate released into the medium from the incubated cells. The second method is a modification of a procedure by which the quantity of tritiated water that is released by metabolism from +AD5-3H+BD-labeled glucose is determined. It was found that the results of the two methods were in very close agreement. Neither method measures glucose conversion to glycogen. However, glycogenic activity is very low in adipocytes and represents only a small percentage of utilized glucose. Therefore, the finding of comparable results between the two methods suggests that the summation of the metabolic products carbon dioxide, triglyceride, lactate, and pyruvate does account for nearly all of the glucose utilized. This has important implications for the understanding of the considerable variations in rate and patterns of glucose metabolism by the fat cells under a variety of experimental conditions.