['Although the matricellular protein thrombospondin-1 (TSP1) is highly expressed in the vessel wall in response to injury, its pathophysiological role in the development of vascular disease is poorly understood. This study was designed to test the hypothesis that TSP1 stimulates reactive oxygen species production in vascular smooth muscle cells and induces vascular dysfunction by promoting oxidative stress.', 'Nanomolar concentrations of TSP1 found in human vascular disease robustly stimulated superoxide (O(2)(•-)) levels in vascular smooth muscle cells at both cellular and tissue level as measured by cytochrome c and electron paramagnetic resonance. A peptide mimicking the C terminus of TSP1 known to specifically bind CD47 recapitulated this response. Transcriptional knockdown of CD47 and a monoclonal inhibitory CD47 antibody abrogated TSP1-triggered O(2)(•-) in vitro and ex vivo. TSP1 treatment of vascular smooth muscle cells activated phospholipase C and protein kinase C, resulting in phosphorylation of the NADPH oxidase organizer subunit p47(phox) and subsequent Nox1 activation, leading to impairment of arterial vasodilatation ex vivo. Further, we observed that blockade of CD47 and NADPH oxidase 1 gene silencing in vivo in rats improves TSP1-induced impairment of tissue blood flow after ischemia reperfusion.'] Does thrombospondin-1 regulate blood flow via CD47 receptor-mediated activation of NADPH oxidase 1?