Potassium channel openers and prostacyclin play a crucial role in mediating the vasorelaxant activity of Gynura procumbens

Abstract

BackgroundPrevious studies of Gynura procumbens (G. procumbens) have shown that partially purified fractions of the leaves are capable of lowering the blood pressure of rats by inhibiting angiotensin-converting enzymic activity and causing vasodilatation. The objectives of this study were therefore to further purify the active compounds that exhibited selective effects on blood vessels, determine the mechanism of actions, and to qualitatively analyse the putative compounds present.MethodsThe butanolic fraction (BU) of the crude ethanolic extract was purified using column chromatography to obtain several sub-fractions of different polarities. The in vitro effects of BU and the sub-fractions on vascular tension were subsequently determined using isolated rat thoracic aortic rings. The most potent sub-fraction (F1) alone was then investigated for its mechanisms of the vasorelaxant activity. In another experiment, thin-layer chromatography was used to qualitatively analyse the active compounds found in F1.ResultsThe BU and the sub-fractions ranging from 10-7 to 10-2 g/ml significantly (p < 0.05) inhibited the sustained tonic contractions induced by phenylephrine and potassium chloride in a concentration-dependent manner with various degree of potency. The most potent sub-fraction (F1) antagonised the calcium-induced vasocontractions (1 x 10-4 – 1 x 10-2 M) in calcium-free with high concentration of potassium as well as in calcium- and potassium-free Krebs-Henseleit solutions. Contractions induced by noradrenaline and caffeine were not affected by F1. The vasorelaxing effect caused by F1 was significantly attenuated with preincubation of potassium channel blockers (glibenclamide and 4-aminopyridine) and prostacyclin inhibitor (indomethacin) while it was not affected by preincubation with tetraethylammonium, l-nitro-arginine methyl esther, propanolol, atropine, oxadiazolo quinoxalin one and methylene blue. The qualitative phytochemical analysis of F1 indicated the presence of flavonoids.ConclusionThese results confirm previous findings that G. procumbens causes vasodilatory effects by blocking calcium channels. In addition, the present study further demonstrates that the vasodilatory effect of G. procumbens may also be due to the opening of potassium channels and the stimulation of prostacyclin production. The putative compounds are probably flavonoids in nature.

Effects of Prosopis farcta Root Extract in the Vascular Reactivity of Isolated Goat Coronary Artery

“…The affirmation of the relaxing effect of PFRE in coronary artery may implicate important implementation of the plant in patients with myocardial and coronary artery disease, that's why P. farcta has long been used as a traditional remedy for angina pectoris [22], reducing cardiac or chest pain and for managing cardiovascular disorder in Iran [19], as a therapeutic agent in treating cardiovascular disorders [23] [39] . However, the result somewhat conflicts the earlier finding of [22] Vascular contractions implicate the control of K + channels, the opening of K + channels in VSMCs results from the outward current of K + and membrane hyperpolarization which in turn results in a reduction in Ca +2 entry as a result from the closure of VDCC, and vasodilation [40].…”

Gynura procumbens: An Overview of the Biological Activities

“…Vasocontraction caused by phenylephrine, calcium and potassium chloride was shown to be antagonized by G. procumbens extracts. This was probably due to the blocking of receptor-operated and/or voltage dependent calcium channels as well as opening of potassium channel (Hoe et al, 2011; Ng et al, 2013). Therefore, G. procumbens potentially serves as an antihypertensive agent with cardioprotective activity due to its ability to target various mechanisms including the renin-angiotensin system and calcium influx which are crucial players in the pathophysiology of hypertensive conditions.…”

Gynura procumbens Improved Fertility of Diabetic Rats: Preliminary Study of Sperm Proteomic

“…This evergreen shrub grows extensively in Southeast Asia and is locally known in Malaysia as Sambung Nyawa . Several studies have reported that this herb possesses anti-inflammatory [9], antihypertensive [10], anti-cancer [11], and antihyperglycaemic [12, 13] activities and recently has been recognised as a profertility factor [14]. The administration of GP aqueous extract (GPAE) was reported to reduce blood glucose levels significantly and increased sperm quality [14].…”