IGF-I INCREASES FOREARM BLOOD-FLOW WITHOUT INCREASING FOREARM GLUCOSE-UPTAKE

Decreased insulin-mediated muscle glucose uptake is a characteristic f eature of non-insulin-dependent diabetes mellitus and other insulin-re sistant states. It has been suggested that an impairment in the abilit y of insulin to augment limb blood flow, resulting in diminished gluco se delivery to muscle, may contribute to this abnormality. In this stu dy, we used human insulin-like growth factor (IGF) I in conjunction wi th the forearm balance technique to determine whether forearm glucose uptake could be stimulated by increasing blood flow without directly s timulating the intrinsic ability of the muscle to extract glucose. IGF -I was infused intra-arterially in healthy controls at a rate of eithe r 0.4 mu g.kg(-1).min(-1) (high IGF) or 0.04 mu g.kg(-1).min(-1) (low IGF) for 140 min. With high IGF, forearm blood flow increased approxim ately twofold (34 +/- 3 vs. 64 +/- 8 ml.min(-1).l forearm volume(-1), P < 0.01), and arteriovenous glucose concentration difference (a-v dif ference) increased modestly (0.19 +/- 0.05 vs. 0.31 +/- 0.08 mM, P = 0 .32), resulting in an increased forearm glucose uptake (6.4 +/- 1.7 vs . 21.7 +/- 7.4 mu mol.min(-1).l forearm volume(-1), P = 0.09 vs. basal ). With low IGF, forearm blood flow increased by 59% (29 +/- 4 vs. 46 +/- 9 ml.min(-1).l forearm volume(-1), P < 0.05) and was associated wi th a proportional decrease in the a-v difference (0.29 +/- 0.04 vs. 0. 18 +/- 0.05 mM, P < 0.05). Forearm glucose uptake therefore was not si gnificantly different from basal values (7.6 +/- 0.6 vs. 6.9 +/- 1.8 m u mol.min(-1).kg(-1)). These data demonstrate that increasing blood fl ow without increasing the intrinsic ability of the muscle to extract g lucose does not increase forearm muscle glucose uptake.