In vitro activity-guided vasodilatory effect of Orthosiphon stamineus leaves

Objective: To investigate the vasodilatory effect of Orthosiphon stamineus leaves using the activity-guided approach. Methods: Leaves of O.stamineus were serially extracted to obtain the petroleum ether (PE), chloroform (CE), methanol (ME) and water (WE) extracts. The extracts were screened for in vitro inhibition of noradrenaline (NA)-induced contraction of rat aorta. The active CE was fractionated and the fractions further tested. The active fraction was screened for chemical composition. Results: The PE and WE were found to inhibit the NA-induced contractions only at low doses of the agonist, while ME showed no effect. However, the CE inhibited the NA-induced contractions, dose-dependently. At 0.25, 0.5 and 1 mg/ml, CE respectively inhibited the NA contractions by 8.5, 29 and 48%. Of the 5 fractions obtained from CE (C 1-5), C 1-3 fractions showed effective dose-dependent inhibition of NA-induced aortic contractions. However, C 2 was the most effective; at 0.5 and 1 mg/ml, it inhibited the maximum NA-induced contractions by 16.5 and 49.0%, respectively. Qualitative phytochemical screening of C 2 indentified flavonoids as the predominant chemical group in the fraction. Conclusion: Orthosiphon stamineus possesses potent vasodilatory effects in vitro, exerted via a possible endothelium-independent mechanism and the flavonoids contained therein, may be responsible. [J Exp Integr Med 2012; 2(3.000): 255-261]