Increased life expectancy of human immunodeficiency virus (HIV)-positive patients has led to evidence of complications apparently not directly related to immunodeficiency or opportunistic infection, including increased cardiovascular risk. We tested the hypothesis that vascular dysfunction occurs in the murine acquired immune deficiency syndrome (AIDS) model and evaluated potential mechanisms in murine AIDS tissues and relevant human HIV/AIDS vascular tissues. We also investigated endothelial activation and/or endothelial protein nitration and their association with time-dependent vascular dysfunction. At 1 and 5 wk of murine AIDS, statistically significant decreases in KCl contractility and time-dependent contractile deficits in response to phenylephrine were observed. The maximal response (E(max)) was reduced by approximately 40% at 10 wk, and EC(50) values were significantly changed: 102 +/- 7.3 ng for control vs. 190 +/- 37 and 130 +/- 22 ng at 5 and 10 wk, respectively (P < 0.05). Endothelium-dependent relaxation to ACh was decreased (EC(50) = 120 +/- 27 and 343 +/- 94 nM for control and at 10 wk, respectively), whereas the response to an exogenous nitric oxide donor, sodium nitroprusside, remained unchanged, suggesting a specific endothelial dysfunction. Histochemical investigations of the same vascular tissues as well as corresponding coronary endothelium showed an increase in protein 3-nitrotyrosine, intercellular adhesion molecule, and nitric oxide synthase isoforms 2 and 3. These findings were corroborated in concurrent experiments in a cohort of well-cataloged human cardiac microvascular tissues. We have demonstrated, for the first time, a specific functional vasculopathy with endothelial involvement in a murine model of AIDS that was also associated with and correlated to increased oxidative stress and specific endothelial activation. This finding was echoed in a relevant population of human HIV/AIDS patients. Research into sources and intracellular targets of oxidants in this disease could provide important mechanistic insights and may reveal new therapeutic opportunities for this increasingly important cardiovascular disease state.