Figure 2: Effect of betulinic acid (BA, 2.0 μM) on acetylcholine (ACh)-induced vasorelaxation in endothelium-intact rat aortic rings previously contracted by 1 μM phenylephrine (PE) after exposure to pyro gallol (500 μM) for 15 min. Tension was measured and calculated as a percentage of the contraction in response to PE. Con: rings without any pretreatments; BA: rings preincubated with BA for 30 min; Pyrogallol: rings preincubated with pyrogallol for 15 min; BA+pyrogallol: rings incubated with BA for 30 min, and pyrogallol for the last 15 min; L-NAME/Indo/MB+BA+pyrogallol: rings preincubated with L-NAME (100 μM), indomethacin (Indo, 10 μM), or methylene blue (MB, 10 μM) for 30 min and then washed before incubating with BA for another 30 min, and pyrogallol for the last 15 min. All data are expressed as mean ± SD; n = 8 rings from the eight rats per group. *P < 0.05, **P < 0.01 vs. Con; ##P < 0.01 vs. pyrogallol; +P < 0.05, ++P < 0.01 vs. BA+pyrogallol