Basal and exercise-induced skeletal muscle blood flow is augmented in typeI diabetes mellitus

Hyperaemia occurs early in the renal and retinal microcirculation of patien ts with type I (insulin-dependent) diabetes mellitus, and may be critical i n the development of nephropathy and retinopathy. We therefore sought to de termine whether resting and exercise-induced hyperaemia was also apparent i n the skeletal muscle circulation of young subjects with type diabetes. Blo od flow was assessed by venous occlusion plethysmography in 18 diabetic (DM ) subjects and 20 matched controls. Exercise entailed 2 min of isotonic exe rcise against no load. Endothelium-dependent and -independent vasodilator f unction was assessed following intraarterial infusion of acetylcholine and sodium nitroprusside respectively. Forearm blood flow (FBF) was higher in D M subjects than in controls (3.3 +/- 0.3 and 2.2 +/- 0.2 ml . min(-1) . 100 ml(-1) forearm respectively; P < 0.005). This was not due to differences i n forearm or body size, blood pressure, heart rate, lipid status or glycaem ic control. Peripheral insulin levels were higher in DM subjects than in co ntrols (48.5 +/- 8 and 15.5 +/- 1.5 mu-units/ml respectively; P < 0.005). R esting FBF was closely correlated with insulin levels (r(2) = 0.4; P < 0.00 5). Parameters of exercise induced hyperaemia [including peak flow (16.4 +/ - 1.4 and 12.0 +/- 0.7 ml . min(-1) . 100ml(-1) forearm in DM and control s ubjects respectively; P < 0.01) and the volume repaid to the forearm at 5 m in post-exercise (32.1 +/- 3.1 and 23.1 +/- 1.4 ml . 100 ml(-1) forearm res pectively; P < 0.05)] were also significantly greater in DM subjects, even when differences in resting FBF were taken into account. Peak hyperaemic bl ood flow and the volume repaid at 5 min were also related to insulin levels (r(2) = 0.16; P < 0.05 and r(2) = 0.27; P < 0.005 respectively). The vasod ilator response to acetylcholine was reduced in DM subjects (P < 0.05; anal ysis of variance), and the slope of this dose-flow relationship was inverse ly related to insulin levels (r(2) = 0.2; P < 0.05). These data show that b oth resting and exercise-induced skeletal muscle blood flow are augmented i n young patients with type 1 diabetes, possibly due to the vasodilatory eff ect of increased insulin levels. Diminished vasodilator responses to acetyl choline may also, in part, be a consequence of insulin-augmented resting mu scle blood flow.