L-Phenylephrine hydrochloride, sodium nitroprusside, NG-nitro-L-arginine methyl ester, acetylcholine, ketamine hydrochloride and indomethacin were obtained from Sigma Chemical Co. (St. Louis, MO, USA). Polyethyleneglycol was purchased from Fluka. Plant extracts were dissolved in PEG, while methanol extract was dissolved in 0.9% normal saline. Then the solutions were further diluted by normal saline.