Endothelium nitric oxide-independent vasorelaxant effects of the aqueous extract from Stephania abyssinica on the isolated rat thoracic aorta.

BACKGROUND: Stephania abyssinica (Dillon & A. Rich) Walp (Menispermaceae) is a medicinal plant used in the west region of Cameroon to treat arterial hypertension. The present study evaluated the vasorelaxant effects of the aqueous (AESA) and methanol (MESA) extracts from the fresh leaves of S. abyssinica on aorta rings isolated from Wistar rats. METHODS: Aorta rings with intact endothelium were contracted with KCl (60 mM) or phenylephrine (10-5 M) and exposed to cumulative concentrations of each extract, ranging from 10 to 1,000 µg/mL. The vasorelaxant effects of AESA were further evaluated in presence of Nω-nitro-L-arginine methyl ester (L-NAME, 10-4 M), tetraethylammonium (TEA, 5 µM), glibenclamide (5 µM), propranolol (5 µM), and the association glibenclamide-propranolol (AGP). In another set of experiments, the effect of AESA was evaluated on calcium-induced contraction in a hyperpotassic milieu. RESULTS: AESA and MESA exhibited a concentration-dependent vasorelaxation on KCl-contracted aortic rings with respective EC50 of 160.10 and 346.50 µg/mL. AESA similarly relaxed aortic rings contracted with phenylephrine (EC50, 176.80 µg/mL). The vasorelaxant activity of AESA was not significantly affected by L-NAME but was markedly reduced by TEA, glibenclamide, propranolol, and AGP. AESA strongly inhibited the Ca2+-induced contraction by 95%. CONCLUSIONS: These results support the use of S. abyssinica against arterial hypertension and suggest that the vasorelaxant effect of AESA is not mediated via the endothelium/nitric oxide pathway. AESA relaxant properties might be due to an inhibition of Ca2+ influx and/or the activation of ATP-sensitive K+ channels probably via the stimulation of ß-adrenergic receptors.

Acute and chronic antihypertensive effects of Cinnamomum zeylanicum stem bark methanol extract in L-NAME-induced hypertensive rats.

BACKGROUND: Previous study showed that the aqueous extract of the stem bark of Cinnamomum zeylanicum possesses antihypertensive and vasodilatory properties. The present work investigates the acute and chronic antihypertensive effects of the methanol extract of Cinnamomum zeylanicum stem bark (MECZ) in L-NAME-induced hypertensive rats. METHODS: The acute antihypertensive effects of MECZ (5, 10 and 20 mg/kg) administered intravenously were evaluated in rats in which acute arterial hypertension has been induced by intravenous administration of L-NAME (20 mg/kg). For chronic antihypertensive effects, animals were treated with L-NAME (40 mg/kg/day) plus the vehicle or L-NAME (40 mg/kg/day) in combination with captopril (20 mg/kg/day) or MECZ (300 mg/kg/day) and compared with control group receiving only distilled water. All drugs were administered per os and at the end of the experiment that lasted for four consecutive weeks, blood pressure was measured by invasive method and blood samples were collected for the determination of the lipid profile. The heart and aorta were collected, weighed and used for both histological analysis and determination of NO tissue content. RESULTS: Acute intravenous administration of C. zeylanicum extract (5, 10 and 20 mg/kg) to L-NAME-induced hypertensive rats provoked a long-lasting decrease in blood pressure. Mean arterial blood pressure decreased by 12.5%, 26.6% and 30.6% at the doses of 5, 10 and 20 mg/kg, respectively. In chronic administration, MECZ and captopril significantly prevented the increase in blood pressure and organs' weights, as well as tissue histological damages and were able to reverse the depletion in NO tissue's concentration. The MECZ also significantly lower the plasma level of triglycerides (38.1%), total cholesterol (32.1%) and LDL-cholesterol (75.3%) while increasing that of HDL-cholesterol (58.4%) with a significant low atherogenic index (1.4 versus 5.3 for L-NAME group). CONCLUSION: MECZ possesses antihypertensive and organ protective effects that may result from its ability to increase the production of the endogenous NO and/or to regulate dyslipidemia.

In vivo antioxidant and vasodilating activities of Gmelina arborea (Verberaceae) leaves hexane extract.

The present study investigated the effects of Gmelina arborea hexane leaves extract on markers of oxidative stress and its vasorelaxant effects on isolated rat aorta, in order to postulate the possible mechanisms involved in the antihypertensive properties of the plant. To evaluate the antioxidant effects of the extract, rats were randomly divided into four groups of five rats each. With the exception to the group receiving Tween (2.5%), the other groups were treated either with NaCl (900mg/kg/day) alone, NaCl (900mg/kg/day) combined with vitamin C (5mg/kg/day) or Gmelina arborea extract (150mg/kg/day). At the end of eight weeks of treatment, animals were sacrificed and some organs as well as blood samples were collected for biochemical analysis. The in vitro vasodilating effects of the extract (0.5-1.5mg/ml) were evaluated using intact and denuded rat thoracic aortic rings or aorta pre-incubated in L-NAME (2µM), indomethacin (2µM) or glibenclamide (2µM) and contracted with phenylephrine (1µM). The in vivo effects of G. arborea hexane extract prevented both left ventricular and vascular hypertrophy, it also modulated lipid metabolism. Moreover, the extract prevented lipid peroxidation, increased superoxide dismutase and catalase activity as well as NO level. On isolated rat aortic rings, the extract induced concentration-dependent vasorelaxant effects. Extract-induced vasodilation was reduced by mechanical denudation of the endothelium as well as pre-treatment with L-NAME, indomethacin or glibenclamide. These results indicate that Gmelina arborea hexane extract possesses bioactive compounds with antioxidant and vasorelaxant properties.

Antihypertensive and vasorelaxant effects of Cinnamomum zeylanicum stem bark aqueous extract in rats.

The present study was undertaken to evaluate the antihypertensive and vasorelaxant effects of Cinnamomum zeylanicum Blume stem bark aqueous extract in rats. The in vivo activities of the extract were evaluated on normotensive and three rat models of hypertension while the in vitro tests were assayed on rat isolated aorta rings. Acute intravenous injection of the extract (5, 10 and 20mg/kg) induced a significant reduction in mean arterial blood pressure in anaesthetised normotensive Wistar rats, salt-loaded hypertensive, L-NAME hypertensive and spontaneously hypertensive rats. Pre-treatment of rats with either propranolol or atropine significantly inhibited the hypotensive effects of the plant extract suggesting its possible action through the interferences with both cholinergic and sympathetic transmissions. Moreover, pre-treatment of rats with L-NAME inhibited the sustained plant antihypertensive effects, suggesting a possible active vasodilatation, which might be partly mediated by an endothelial l-arginine/nitric oxide pathway. In isolated rat aortic rings pre-contracted with KCl (60mM), the extract exhibited cumulative vasodilating effects, which were attenuated with either L-NAME, vascular endothelium removal or both tetraethylammonium and glibenclamide pre-treatments. The vasorelaxant effects may be involved in the extract antihypertensive mechanism, partially by increasing the endothelial nitric oxide and by activating the KATP channels in vascular smooth muscle.