INTRODUCTION:Gynura procumbens has been shown to decrease blood pressure via inhibition of the angiotensin‐converting enzyme. However, other mechanisms that may contribute to the hypotensive effect have not been studied.OBJECTIVES:To investigate the cardiovascular effects of a butanolic fraction of Gynura procumbens in rats.METHODS:Anaesthetized rats were given intravenous bolus injections of butanolic fraction at doses of 2.5–20 mg/kg in vivo. The effect of butanolic fraction on vascular reactivity was recorded in isolated rat aortic rings in vitro.RESULTS:Intravenous administrations of butanolic fraction elicited significant (p<0.001) and dose‐dependent decreases in the mean arterial pressure. However, a significant (p<0.05) decrease in the heart rate was observed only at the higher doses (10 and 20 mg/kg). In isolated preparations of rat aortic rings, phenylephrine (1×10‐6 M)‐ or potassium chloride (8×10‐2 M)‐precontracted endothelium‐intact and ‐denuded tissue; butanolic fraction (1×10‐6–1×10‐1 g/ml) induced similar concentration‐dependent relaxation of the vessels. In the presence of 2.5×10‐3 and 5.0×10‐3 g/ml butanolic fraction, the contractions induced by phenylephrine (1×10‐9–3×10‐5 M) and potassium chloride (1×10‐2–8×10‐2 M) were significantly antagonized. The calcium‐induced vasocontractions (1×10‐4–1×10‐2 M) were antagonized by butanolic fraction concentration‐dependently in calcium‐free and high potassium (6×10‐2 M) medium, as well as in calcium‐ and potassium‐free medium containing 1×10‐6 M phenylephrine. However, the contractions induced by noradrenaline (1×10‐6 M) and caffeine (4.5×10‐2 M) were not affected by butanolic fraction.CONCLUSION:Butanolic fraction contains putative hypotensive compounds that appear to inhibit calcium influx via receptor‐operated and/or voltage‐dependent calcium channels to cause vasodilation and a consequent fall in blood pressure.

Objectives: To investigate the hypotensive and angiotensin-converting enzyme (ACE) inhibitory activities of a partially purified fraction (FA-I) of the leaves of Gynura procumbens and to qualitatively analyse the putative compounds present in the fraction. Materials and Methods: The hypotensive effect of FA-I was tested in both spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY) by an intravenous administration of 0–10 mg/kg of the FA-I. Administration of captopril (20 µg/kg) served as the control. In vitro 0.0–2.0 mg/ml FA-I was added to a mixture of ACE and hippuryl-L-histidyl-L-leucine and assayed by a modification of the colourimetric method of Hurst and Lovell-Smith. All blood pressure measurements were monitored by the Macintosh MacLab set-up. ACE activity was measured by an in vitro assay in which the enzymatic cleavage of hippuryl-L-histidyl-L-leucine to form histidyl-leucine and hippurate was determined colourimetrically by a cyanuric chloride/dioxane reagent. Results: The FA-I produced a marked dose-dependent reduction in mean arterial pressure (MAP) in SHR and WKY rats, with an ED₅₀ of 1.09 and 1.05 mg/kg, respectively (p < 0.01). Furthermore, FA-I at 10 mg/kg strongly inhibited the angiotensin I-induced rise in MAP (p < 0.01). This response was comparable to that of captopril at 20 µg/kg. In the in vitro assay, ACE activity was inhibited with an IC₅₀ of 0.8 mg/ml. The qualitative phytochemical analysis of FA-I indicated the presence of glycoconjugates and peptides. Conclusion: These results suggest that the hypotensive effect of G. procumbens may be due, in part, to the glycoconjugated or peptidal substances found in FA-I that exhibit an inhibitory effect on ACE.

Previous studies showed that Gynura procumbens reduced blood pressure by blocking calcium channels and inhibiting the angiotensin-converting enzyme activity. The present experiments were to further explore the effects and mechanisms of a purer aqueous fraction (FA-I) of G. procumbens on angiotensin I (Ang I)-induced and angiotensin II (Ang II)-induced contraction of aortic rings and also on the bradykinin (BK) effect on cardiovascular system. Rat aortic rings suspended in organ chambers were used to investigate the vascular reactivity of FA-I. Effect of FA-I on BK was studied by in vitro and in vivo methods. Results show that FA-I significantly (P < 0.05) decreased the contraction evoked by Ang I and Ang II. In the presence of indomethacin (10 µM) or N-nitro-L-arginine methyl ester (0.1 µM), the inhibitory effect of FA-I on Ang II-induced contraction of aortic rings was reduced. Besides, FA-I potentiated the vasorelaxant effect and enhanced the blood pressure-lowering effect of BK. In conclusion, FA-I reduced the contraction evoked by Ang II probably via the endothelium-dependent pathways, which involve activation of the release of nitric oxide and prostaglandins. The inhibition of angiotensin-converting enzyme activity by FA-I may contribute to the potentiation of the effects of BK on cardiovascular system.

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.

27An increase in blood pressure (BP) by a high-salt (HS) diet may involve the 28 changes in the expression of epithelium sodium channels (ENaCs) and aquaporins 29 (AQPs) in the kidney which affect the sodium-and water-handling mechanisms. In the 30 present study, spontaneously hypertensive rats (SHRs) and Wistar Kyoto (WKY) rats 31 were exposed to HS and regular-salt (RS) diets for 6 weeks and fluid intake was 32 monitored. After 6 weeks, mean arterial pressure (MAP) and plasma hormonal activity 33 of atrial natriuretic peptide (ANP), levels of angiotensin II (Ang II), aldosterone and 34 arginine vasopressin (AVP) were determined. The expression of mRNA and protein 35 levels of ENaC and AQP subunits in kidneys were quantified by real-time PCR and 36 Western blotting. High-salt diet caused higher MAP only in SHRs and higher fluid 37 intake in both strains of rats when compared with their respective controls on RS diet.38 The plasma levels of Ang II and aldosterone were low in both SHRs and WKY rats fed 39 with HS diet. Meanwhile, plasma ANP activity was high in both strains of rats on HS 40 diet; whilst the AVP showed vice versa effects. The renal expression of mRNA and 41 protein levels of α-and γ-ENaCs was lowered by HS diet in both SHRs and WKY rats.42 Although β-ENaC mRNA and protein expression levels were depressed in SHRs but 43 they were enhanced in WKY rats. On the other hand, AQP-1, 2 and 7 mRNA and 44 protein expression levels were lowered in both strains of rats fed with HS diet, while 45 that of AQP-3, 4 and 6 showed no significant changes. The suppression of mRNA and 46 protein expression levels of ENaC and AQP subunits suggests that the HS-induced 47 increase in the MAP of SHRs may not be due to the renal sodium and water retention 48 solely. 49 3 50 Introduction 51 Dietary salt (i.e. sodium chloride, NaCl) intake is the most remarkably modifiable 52 environmental risk factor that attracts many studies on hypertension (HPN). It has been 53 acknowledged as an important contributing factor of the aetiology and progression of 54 HPN [1]. Despite the abundant experimental, interventional and epidemiological 55 observations demonstrating an association between dietary salt and HPN, scepticism 56 remains as to how high salt (HS) intake can be mechanistically linked to the increase in 57 blood pressure (BP). Knowing the heterogeneity of HPN, it is likely to involve the 58 intricate integration of multiple regulatory systems and the kidneys have long been 59 implicated to play a central role in regulating BP. Defects in the kidneys sodium-and 60 water-handling mechanisms have been mooted as one of the primary causes of HPN in 61 HS intake [2]. 62The kidneys have the capacity to return altered BP to baseline level by 63 increasing or decreasing sodium and water excretion in response to elevated or reduced 64 BP [3]. This is accomplished in the kidney by the presence of renal membrane-bound 65 protein i.e. epithelial sodium channel (ENaC) that fine-tune sodium reabsorption [4] 66 and aquaporins (AQPs) that ...