Fig. 2. Effects of increasing agonist concentration on endothelial-mediated dilations during control conditions (  solid lines ) and after inhibition of nitric oxide (NO) and prostacyclin (PGI²) (  dashed lines ). Three responses that often occur in arteries after the inhibition are shown in  A ,  B , and  C .24–26 COX = cyclooxygenase; EDHF = endothelium-derived hyperpolarizing factor; NOS = nitric oxide synthase.