Figure 7. Effects of tempol, a reactive oxygen species scavenger and apocynin, the NADPH oxidase inhibitor on S1P–induced afferent arteriolar vasoconstriction.

(a): afferent arteriolar responses to increasing concentrations of S1P in the absence (diamonds) and presence of tempol (10⁻³ mol L⁻¹, squares) or apocynin (10⁻⁴ mol L⁻¹, triangles). Data represent the actual diameters from each group. The S1P alone data are taken from Figure 2. Con, control diameters averaged from the last 5-min incubation period in the absence or presence of tempol or apocynin but prior to administration of S1P. (b): the same data normalized as a percentage of the control diameter for each group. Values are expressed as mean ± SEM. *P < 0.05 vs. control diameter in the same group. †P < 0.05 vs. vasoconstriction with S1P alone at the same concentration.