Kinetics of glucose disposal in whole body and across the forearm in man.

We reevaluated the concept that the in vivo glucose disposal rate in man is determined by the activity of the glucose transport system. Rates of glucose disposal were determined in whole body and across forearm at four insulin levels (-9, -50, -160, and -1700 gU/ml) and at each insulin level at four glucose levels (-90, -160, -250, and -400 mg/dl). At the lowest insulin level, the Michaelis constants (K.:s) for glucose disposal in whole body (8.71.1 mM) and across forearm (7.41.4) mM) were compatible with a K. determined in vitro for the transport system. At higher insulin levels, the apparent K. increased significantly in whole body (16.2-37.7 mM) and across forearm (20.7-31.2 mM). We interpret the apparent increase of K. by insulin to reflect a shift in the rate-limiting step from glucose transport to some step beyond transport.