Endothelium-dependent and -independent vascular responses were assessed in 10 NIDDM patients and 6 normal subjects with no evidence of atherosclerotic disease. Changes in forearm blood flow and arteriovenous (AV) serum nitrite/nitrate (NO2/NO3-) concentrations were measured in response to intra-arterial infusion of acetylcholine (ACh) (7.5, 15, 30 μg/min, endothelium-dependent response) and sodium nitroprusside (SNP) (0.3, 3, 10 μg/min, endothelium-independent response). Insulin sensitivity (determined by minimal model intravenous glucose tolerance test) was lower in NIDDM patients (0.82 ± 0.20 vs. 2.97 ± 0.29 104 min · μU−1 · ml−1; P < 0.01). Baseline forearm blood flow (4.8 ± 0.3 vs. 4.4 ± 0.3 ml · 100 ml−1 tissue · min−1; NS), mean blood pressure (100 ± 4 vs. 92 ± 4 mmHg; NS), and vascular resistance (21 ± 1 vs. 21 ± 1 units; NS), as well as their increments during ACh and SNP, infusion were similar in both groups. No difference existed in baseline NO2/NO3 concentrations (4.09 ± 0.33 ]NIDDM patients] vs. 5.00 ± 0.48 μmol/1 ]control subjects]; NS), their forearm net balance (0.31 ± 0.08 ]NIDDM patients] vs. 0.26 ± 0.08 μmol/1 · 100 ml−1 tissue · min−1; NS), and baseline forearm glucose uptake. During ACh infusion, both NO2 and NO3 concentrations and net balance significantly increased in both groups, whereas glucose uptake increased only in control subjects. When data from NIDDM and control groups were pooled together, a correlation was found between the forearm AV NO2 and NO3 differences and blood flow (r = 0.494, P = 0.024). On the contrary, no correlation was evident between NO2 and NO3 concentrations or net balance and insulin sensitivity. In summary, 1) no difference existed in basal and ACh-stimulated NO generation and endothelium-dependent relaxation between uncomplicated NIDDM patients and control subjects; 2) in both NIDDM and control groups, forearm NO2 and NO3 net balance following ACh stimulation was related to changes in the forearm blood flow; and 3) ACh-induced increase in forearm blood flow was associated with an increase in glucose uptake only in control subjects but not in NIDDM patients. In conclusion, our results argue against a role of impaired NO generation and blood flow regulation in determining the insulin resistance of uncomplicated NIDDM patients; rather, it supports an independent insulin regulation of hemodynamic and metabolic effects.

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