The risk of cardiovascular disease is markedly elevated in individuals with diabetes, representing the primary cause of morbidity and mortality in these diabetic patients (1). More specifically, individuals with diabetes display dysfunctions in the regulation of blood flow in coronary arterioles (2,3). Importantly, impairments in the appropriate vasodilatory response of myocardial arterioles to various pharmaceutical and physical stimuli can be present even if there is no discernible atherosclerotic blockage in these blood vessels (4,5). Moreover, increased flow-mediated dilation (FMD) in coronary arterioles is an important regulatory mechanism for controlling arteriolar diameter and blood flow in response to changes in wall shear stress, and this mechanism is also impaired in conditions of glucose dysregulation (6,7).While the underlying etiology for the dysfunctions in the coronary microcirculation in diabetes is certainly multifactorial, the contribution of impairments in the endothelial nitric oxide (NO)-generating system and their association with the excess generation of reactive oxygen species (ROS) appears to be crucial in the development of these vascular abnormalities. For example, the impairment of the induction of vasodilation in coronary arterioles in the db/db mouse, a model of obesity-associated insulin resistance and type 2 diabetes, is related to limitations in NO availability (8,9). It is of great interest that NO availability can be compromised by interactions with superoxide anion, with a by-product of this reaction being the generation of peroxynitrite (OONO 2 ), an ROS that itself is known to mediate deleterious effects on the cardiovascular system in diabetes (10). However, prior to the study of Cassuto et al. (11), which appears in this issue, the specific impact of OONO 2 on the endothelial caveolae, which is required for the proper functionality of endothelial NO synthase (eNOS) (12), and the subsequent effect of this interaction on NO-regulated FMD in response to changes in wall shear stress in conditions of human diabetes had not been rigorously addressed in the scientific literature.The study of Cassuto et al. (11) convincingly advances the concept that, in human diabetes, defects in the ability of NO to facilitate vasodilation in coronary arterioles under conditions of increased OONO 2 exposure are related to the impaired expression of the caveloin-1 (Cav-1), an important structural component of caveolae in the endothelial membrane. Using tissue isolated from older nondiabetic subjects and subjects with either type 1 or 2 diabetes, the authors demonstrated that in vitro increases in FMD due to enhanced wall shear stress were severely reduced in coronary arterioles from diabetic subjects compared with coronary arterioles from nondiabetic subjects. Moreover, these vasomotor defects were associated with augmented OONO 2 production, as reflected by 3-nitrotyrosine levels (a biomarker of OONO 2 -mediated protein nitration), and were reproduced by direct incubation of arterioles with OONO...