Effects of glucose and insulin on development of impaired insulin action in muscle

Rat hindquarters were perfused for 2 h with either 0, 5, or 25 mM glucose in combination with either 0, 50, or 20,000 microU insulin/ml, whereupon responsiveness of glucose uptake to 20,000 microU insulin/ml and 25 mM glucose was measured. Perfusion with 25 mM glucose and 20,000 microU insulin/ml resulted in an initial glucose uptake of 43.6 +/- 3.9 mumol.g-1.h-1, which decreased to 18.7 +/- 1.6 mumol.g-1.h-1 after 2 h (P less than 0.001). Omission of glucose from the perfusate prevented the decrease in responsiveness, whereas 5 mM glucose caused a lesser decrease (to 28.3 +/- 2.2 mumol.g-1.h-1). At 0 and 50 microU insulin/ml the effects of glucose were present but were less pronounced. The decrease in insulin responsiveness of glucose uptake (55%) was accompanied by a lesser decrease (29%) in muscle glucose transport, whereas glucose transport in muscle membrane vesicles, muscle insulin binding, and insulin receptor tyrosine kinase activity were unchanged. Muscle glycogen synthase activity decreased (P less than 0.005) during perfusion with 25 mM glucose and 20,000 microU insulin/ml but did not decrease during perfusion with no glucose and 20,000 microU insulin/ml. It is concluded that insulin responsiveness of glucose uptake in muscle is decreased by exposure to glucose in a dose-dependent manner and the inhibitory effect of glucose is enhanced by simultaneous insulin exposure. The mechanism behind this insulin resistance could partly be explained by a decrease in muscle membrane glucose transport, possibly caused by changes in intracellular milieu.