Effects of NAC (a), apocynin (b) and VAS2870 (c) on phenylephrine-induced contraction of RTA strips. Two cumulative concentration-responses were constructed in RTA strips stimulated with α1-adrenoceptor agonist phenylephrine. For the second contraction, RTA strips were preincubated for 30 min with NAC (10~20 mM), apocynin (0.3~3 mM), VAS2870 (1~10 μM) or vehicle, then were stimulated with agonist in the continuous presence of the inhibitor. Data are mean ± S.E.M. of 6 independent experiments. Force is expressed as the percentage of maximal force obtained in the first contraction.