Integrin binding by Arg-Gly-Asp (RGD)-containing peptides has been shown to alter vascular tone in a variety of blood vessels and has been implicated as a mechanism of vasoregulation during tissue injury. However, the effect of these peptides in the coronary circulation has not been examined. Thus the purpose of our study was to test the hypothesis that integrins act as receptors linked to the regulation of coronary vasomotor function. In particular, the ability of RGD-containing peptides to influence vascular tone by interacting with the α_vβ₃- and α₅β₁-integrins was studied in isolated pig coronary arterioles. All vessels developed basal tone and dilated in a concentration-dependent manner to soluble peptides cyclic GPenGRGDSPCA (cyclic RGD), an α_vβ₃-cyclic-binding peptide (XJ735), DMP7677, an α₅β₁-binding peptide, and to protease-generated (neutrophil elastase) fragments of denatured collagen type I (a major RGD-containing extracellular matrix protein). The vasodilations to cyclic RGD, XJ735, and collagen fragments were almost completely blocked by endothelial removal or by the cyclooxygenase inhibitor indomethacin. In contrast, after endothelial removal and incubation with indomethacin, coronary arterioles showed concentration-dependent constriction to the α₅β₁-integrin ligand DMP7677 but not to cyclic RGD or XJ735. Collectively, our results indicate that activation of endothelial α_vβ₃- and α₅β₁-integrins mediates coronary arteriolar dilation via the endothelial production of cyclooxygenase-derived prostaglandins. These data support a role for integrins in the regulation of coronary vascular tone that may be particularly important during myocardial injury.