Thesis (M.Sc. in Pharm.)--Chulalongkorn University, 2006

Plai (Zingiber cassumunar Roxb.) is one of Thai herbal plants, which is well recognized for relieving muscle pain. In this study, the effects of plai oil on the contraction and relaxation of vascular smooth muscle in the endothelium-intact and endothelium-denuded rat aorta were investigated. The thoracic aorta was isolated from male Wistar rats (250-300 g), and the vascular tensions were measured isometrically. The results showed that plai oil (50 – 200 [micro]g/ml) significantly inhibited the PE- and KCI-induced contraction of endothelium-denuded aorta in concentration-dependent manner, but had no effects in endothelium-intact aorta. In addition, plai oil (40 and 100 [micro]g/ml) significantly inhibited the PE-induced contraction in Ca[superscript2+]-free condition, but not the caffeine-induced contraction. Furthermore, plai oil (50 and 100 [micro]g/ml) suppressed CaCl[subscript2] – induced contraction in high K[superscript+] – depolarizing solution with the apparent pD2 values of 3.76 +- 0.09 and 3.57 +- 1.35, respectively. The results also demonstrated that plai oil caused vasodilatation in endothelium-intact aorta with the apparent EC 50 values of 32.80 +- 4.43 [micro]g/m. Various compounds including methylene blue (10 [micro]M), L-NAME (10 [micro]M), glibenclamide (10 [micro]M), indomethacin (10 [micro]M), atropine (1 [micro]M), propranolol (10 [micro]M), and tetraethylammonium chloride (10 [micro]M) significantly inhibited the relaxant effect of plai oil. In conclusion, plai oil modulated the vascular tone via endothelium-dependent and endothlium-independent pathways. The direct actions on smooth muscle were possibly linked to non-specific inhibition of Ca[superscript2+] influx as well as inhibition of PE-mediated Ca[superscript2+] release from sarcoplamic reticulum. Moreover, plai oil may influences the vascular contractility through endothelium factors including NO-cGMP pathway, hyperpolarizing, cyclooxygenase, muscarinic receptors and [beta]-adrenoceptor.