Figure 4.

The mechanism of MPO-induced vasoconstriction in the SMAs. H₂O₂-evoked vasoconstriction (open circles, control) was abolished after endothelium denudation (id: 138 ± 10 μm, n = 4 arterioles from four different animals; closed diamonds, panel a). However, in the presence of MPO, and at relatively low H₂O₂ concentrations, vasoconstrictions (significant vasoconstriction at 10 μm–100 μm H₂O₂ compared to the baseline; P < 0.05) were still observed in the absence of endothelium (id: 172 ± 7 μm, n = 5 arterioles from four different arterioles; open triangles). Closed circles illustrate the effects of MPO. Asterisks denote significant differences from the action of MPO in the presence and absence of endothelium, and # indicate significant differences between the endothelium removal and the control. The MPO- and H₂O₂-induced vasoconstriction was tested in the presence of the TXA2 receptor antagonist (id: 142 ± 13 μm, n = 5 arterioles from four different animals; closed triangles, panel b) and in the presence of the COX inhibitor (id: 168 ± 8 μm, n = 5 arterioles from three different animals; open triangles, panel c). Asterisks denote significant differences from MPO.