Fig. 4. Concentration-response curves to levcromakalim (10−8to 3 × 10−6m) or diltiazem (10−8to 10−4m) in the presence or in the absence of apocynin (1 mm), allopurinol (10−4m), or Tiron (10 mm), obtained in the rat aorta without endothelium contracted with U46619 (3 × 10−8m). The data are expressed as percent of maximal relaxation induced by papaverine (3 × 10−4m). The data are expressed as means ± SD; n refers to the number of rats from which the aorta was taken. Difference of relaxation in response to levcromakalim between the control aorta and the aorta treated with apocynin is statistically significant (* P < 0.05).