Distinct effects of COX1 and COX2 on systemic arterial pressure. (a) The change in MAP (ΔMAP) following infusion of Ang II at 150 pmol/kg/min (between 10 and 40 minutes) and the addition of a COX2 inhibitor, SC58236 (between 40 and 70 minutes) in vehicle-treated mice (circles, n = 5); mice pretreated with SC58560, a COX1 inhibitor (triangles, n = 8); and mice pretreated with SC58236, the COX2 inhibitor (squares, n = 8). Ang II elevated MAP in vehicle-pretreated mice; the elevation was further increased upon addition of the COX2 inhibitor. Ang II increased significantly more in mice orally pretreated with the COX2 inhibitor, and significantly less in mice pretreated with the COX1 inhibitor (^#P < 0.05 vs. control). (b) Ang II induced a higher increase of MAP in COX2 knockout mice (open squares, n = 6) than in wild-type controls (filled squares, n = 5; ^#P < 0.05). Additional COX2 inhibitor infusion further elevated MAP only in wild-type mice. (c) The pressor effect of Ang II was attenuated in COX1 knockout mice (open triangles, n = 6) versus wild-type controls (filled triangles, n = 5; ^#P < 0.05). MAP was further elevated by acute infusion of the COX2 inhibitor in both COX1 knockout and wild-type mice. *P < 0.05 vs. MAP at 40 minutes.