H<sub>2</sub>O<sub>2</sub>-induced vasoconstriction is mediated by COX-1.

<p>Arteriolar constrictions (control, as given in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0103858#pone-0103858-g001" target="_blank">Fig. 1A</a>, closed symbols) were prevented in the presence of the non-specific COX inhibitor indomethacin (10 µM, n = 5 arterioles from 4 different animals, preincubation for 30 min, id: 111±3 µm, open symbols; panel A). Panel B: The roles of COX isoforms in H<sub>2</sub>O<sub>2</sub>-evoked responses were studied by comparing vascular diameters in the absence of COX inhibitors (dotted line) with those in the presence of COX-1 inhibitor SC-560 (1 µM, n = 5 arterioles from 3 different animals, id: 113±14 µm; open squares) or with COX-2 inhibitor celecoxib (3 µM, n = 4 arterioles from 4 different animals, id: 146±13 µm; open triangles). Asterisks denote significant differences from the control.</p>