Additive effect of coexistent type 2 diabetes and arterial hypertension on endothelial dysfunction in resistance arteries of human forearm vasculature

Population studies suggest that vascular complications accumulate when arterial hypertension supervenes on diabetes mellitus. Although it has been demonstrated that endothelial function is impaired in patients with either diabetes mellitus or arterial hypertension it is unknown whether or not both diseases exert additive effects on endothelial dysfunction. The authors therefore investigated endothelium-dependent and endothelium-independent vasodilation in the forearm vasculature of 44 individuals: in 10 type 2 diabetic patients (DM), in 12 patients with arterial hypertension (HT), in 10 patients with both DM and HT (DM+HT), and in 12 healthy control subjects (C). Forearm blood flow (FBF) was measured by venous occlusion plethysmography at rest and following intraarterial infusion of acetylcholine (ACh) and the NO-donor sodium nitroprusside (SNP) at increasing doses. FBF at rest was significantly lower in diabetic patients: 2.2 +/- 0.1 (DM) and 2.6 +/- 0.2 (DM+HT) versus 3.1 +/- 0.1 (HT) and 3.4 +/- 0.2 (C) mL/min per 100 mL of tissue. ACh and SNP both increased FBF dose-dependently in each group. The maximum response to ACh was progressively decreased in DM and HT: 13.7 (C) > 8.1 (DM) > 7.6 (HT) > and 5.7 (DM+HT) mL/min per 100 mi of tissue. Reduction of the endothelium-dependent flow reserve assessed as percent increase in maximum FBF was also impaired following the same rank order: 349 (C) > 268 (DM) > 160 (HT) > 126 (DM+HT) %. The flow response to the NO-donor SNP amounted to: 327 (C), 306 (DM), 200 (HT), and 194% (DM+HT). In DM+HT the reduction of endothelium-dependent flow response was more pronounced compared with the endothelium-independent flow response. The present data provide evidence that type 2 diabetes and arterial hypertension impair endothelium-dependent dilation of resistance arteries in an additive manner suggesting that this progressive endothelial dysfunction might contribute to the increased incidence of cardiovascular complications when both diseases are coexistent.