Vasorelaxant and antihypertensive effects of methanolic extracts from Hymenocardia acida Tul.

ETHNOPHARMACOLOGICAL RELEVANCE: In Congolese traditional medicine, decoctions of Hymenocardia acida root bark (HaRB) and trunk bark (HaTrB) are used for the treatment of conditions assumed to be hypertension. In this work, we propose to study the vasorelaxant effect of HaRB and HaTrB methanolic extracts on isolated rat thoracic aorta, to characterize the group of molecules responsible for the observed vasorelaxant activity, to evaluate the in vitro antioxidant activity of these extracts and to determine the antihypertensive activity of the HaRB extract on spontaneously hypertensive rats (SHR). MATERIALS AND METHODS: The vasorelaxant effect of the HaRB and HaTrB methanolic extracts was studied on endothelium-intact aortic rings pre-contracted with phenylephrine (PE, 1µM). The mechanism of this vasorelaxant effect was investigated on endothelium-denuded vessels and on endothelium-intact aortic rings in the presence of three inhibitors: l-N(G)-nitroarginine methyl ester (100µM), indomethacin (10µM) and 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (10µM). To determine the nature of the compounds responsible for the vasorelaxant activity, we carried out a fractionation of the extracts and a thiolysis of the most active fraction followed by a liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS) analysis. The extracts antioxidant activity was determined by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) colorimetric assay. In vivo anti-hypertensive activity of the HaRB extract was conducted on SHR. RESULTS: HaRB and HaTrB methanolic extracts produced a concentration-dependent vasorelaxation on intact aortic rings pre-contracted with PE (1µM). The vasorelaxant responses obtained were 95.3±1.5% (5µg/ml) and 100.6±3.0% (1µg/ml), respectively. The effect was markedly attenuated by removal of endothelium or pretreatment of aortic rings with all inhibitors except indomethacin. The LC/ESI-MS analysis of the thiolysis products indicated that the fraction which caused the most important vasorelaxation (97.9±2.5% at 3µg/ml) was a mixture of procyanidins and prodelphinidins, with a predominance of procyanidins. Both extracts and all fractions from HaRB extract showed a DPPH scavenging activity, ranging from 0.4 to 0.8 quercetin-equivalents. The HaRB methanolic extract reduced the systolic blood pressure in SHR (from 214±3mmHg to 194±4mmHg) after a 5-week treatment. CONCLUSIONS: The methanolic extracts of Hymenocardia acida root and trunk bark have vasorelaxant activity. The vasorelaxant effect observed is endothelium-dependent and seems mainly mediated through the NO-cGMP pathway. The COX pathway is not involved. The vasorelaxant activity appears to be due to polymeric procyanidins and prodelphinidins. These extracts also have an antioxidant effect. The extract of Hymenocardia acida root bark shows a significant but weak antihypertensive activity in SHR.

Vascular effects and antioxidant activity of two Combretum species from Democratic Republic of Congo.

ETHNOPHARMACOLOGICAL RELEVANCE: Combretum racemosum P. Beauv (Combretaceae) leaves (CrLv) and root bark (CrRB) and Combretum celastroides subsp. laxiflorum Welw (Combretaceae) leaves (ClLv) are used in Congolese traditional medicine for several therapeutic purposes, notably for the treatment of conditions consistent with hypertension. The present study aims to investigate the vasorelaxant and in vitro antioxidant activities of these plants polar extracts and to examine the in vivo antihypertensive effect of the extract which displays the most potent vasorelaxant effect. MATERIAL AND METHODS: The vasorelaxant effect of CrLv, CrRB and ClLv methanolic extracts was studied on rat aorta rings pre-contracted with phenylephrine (PE, 1 µM) in the presence or absence of the endothelium. In some experiments, prior to the addition of the extract, rings were incubated for 30 min with either L-N(G)-nitroarginine methyl ester (L-NAME; 100 µM), a nitric oxide synthase (NOS) inhibitor, indomethacin (10 µM), a cyclooxygenase inhibitor, or 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ; 10 µM), a guanylate cyclase inhibitor. The antioxidant activity was determined by the measurement of the scavenging ability of extracts towards the stable free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH). Blood pressure was measured on normotensive Wistar rats and spontaneously hypertensive rats (SHR) treated orally with a daily dose (40 mg/kg) of the CILv extract for 5 weeks. Tested extracts have been characterised by TLC profiles targeted at flavonoids. RESULTS: All tested extracts showed an important DPPH scavenging activity, ranging from 0.6 to 1.1 quercetin-equivalents. They caused a concentration-dependent vasorelaxation on intact aortic rings pre-contracted with PE (1 µM). The responses to CrRB and CrLv methanolic extracts reached 74.0±5.1% and 62.2±8.6% at a cumulative concentration of 50 µg/ml, respectively. The ClLv (10 µg/ml) extract was more active and, in the same conditions, relaxed aortic rings by 90.3±5.8%. The vasorelaxant activity of all extracts disappeared or was significantly attenuated by removal of the endothelium or after pretreatment with L-NAME or ODQ. Indomethacin only inhibited the activity of CrLv and CrRB extracts. The ClLv extract was able to lower the systolic blood pressure in SHR rats by 7% after a 5-week treatment. CONCLUSIONS: The present study shows that methanolic extracts from ClLv, CrRB and CrLv have an antioxidant activity and an endothelium-dependent vasorelaxant effect. ClLv induces the vasorelaxant effect through the NO-cGMP pathway while CrLv and CrRB extracts also act via a prostanoid pathway. ClLv extract demonstrated a modest but significant antihypertensive activity in SHR rats.