Persistent effects of exercise on skeletal muscle glucose transport across the life-span of rats.

Very young rats (< 2 mo) have a persistent increase in insulin-stimulated glucose transport rate in skeletal muscle for several hours after completing a bout of exercise. We studied the effect of exercise on the glucose transport activity of isolated epitrochlearis muscles from male Fischer 344/Brown Norway F1 hybrid rats across a wide range of the life-span (at 3.5, 13, and 25 mo). The stimulation of 3-O-methylglucose (3-MG) accumulation by a submaximally effective insulin concentration (100 microU/ml) was enhanced (50-75%) 4 h after exercise, regardless of age. In contrast, the 3-MG transport rate with 20,000 microU/ml insulin was enhanced after exercise only in the youngest rats (35%), and this increased responsiveness occurred despite no changes in muscle total GLUT-4 levels. In addition, epitrochlearis GLUT-4 levels were reduced by 29% between 3.5 and 13 mo of age in sedentary rats but did not decline further between 13 and 25 mo of age. GLUT-4 levels were moderately but significantly (P < 0.05) related (r = 0.554) to epitrochlearis muscle capacity for insulin-stimulated 3-MG transport.