DECLINE IN MUSCLE INSULIN-DEPENDENT AND INSULIN-INDEPENDENT GLUCOSE-UPTAKE BUT NOT GLUT-4 IN 21-DAY-OLD VS 28-DAY-OLD RATS

The most rapid age-related decrease in insulin-stimulated glucose upta ke in skeletal muscle occurs between 3 and 5 wk of age in rats. Theref ore, we studied unstimulated, insulin-stimulated, and in vitro hypoxia -stimulated 2-deoxy-D-[G-H-3] glucose (2-DG) uptake in isolated soleus , flexor digitorum brevis (FDB), and epitrochlearis muscles from rats at 21, 28, and 35 days of age. Age-related decrements in insulin- (sim ilar to 40-60%) and hypoxia-stimulated (similar to 50%) 2-DG uptake oc curred in all muscles, and most of the decline was evident by 28 days. Unstimulated 2-DG uptake declined significantly with advancing age in the epitrochlearis (73%) and FDB (60%) and tended to decrease in the soleus (38%). The time course and relative magnitude of these decremen ts were similar under unstimulated, insulin-stimulated, and hypoxic co nditions. GLUT-4 protein concentration was unaltered by age in each mu scle. These results indicate that a substantial age-related decrement in 2-DG uptake occurs in several limb muscles from rats at 21 vs. 28-3 5 days by a mechanism that is independent of GLUT-4 levels and not spe cific for the insulin-dependent pathway.