Effets hypotenseurs de l'extrait aqueux des écorces du tronc de Lophira lanceolata (Ochnaceae) chez le rat.

Abstract

Lophira lanceolata is a plant used in Cameroon folk medicine for treatment of many diseases like hypertension. The aim of this study was to evaluate the hypotensive effects and some mechanisms of action of the aqueous extract of the stem bark of Lophira lanceolata. The heart rate and blood pressure were recorded by direct method, before and after intravenous administration of the extract at doses of 5, 10, 15 or 20 mg/kg. The dose of extract having the most hypotensive effect was used to evaluate the mechanisms of action of this plant namely when combine to atropine (1 mg/kg), yohimbine (100 μg/kg), propanolol (100 μg/kg), cimetidine (15 mg/kg), indometacine (5 mg/kg) and reserpine (5 mg/kg). The aqueous extract of the stem bark of Lophira lanceolata induced an immediate fall of blood pressure at doses of 10, 15 and 20 mg/kg. The dose of 20 mg/kg shows a hypotensive effect most important reason and induced immediate and significant decrease in heart rate, why it was used to study the action mechanisms of the extract. Pretreating rats with atropine (1 mg/kg) and reserpine (5 mg/kg) has significantly reduced the immediate hypotensive effect of aqueous extract of the stem bark of Lophira lanceolata respectively by17,58% (P < 0,05) and by 13,33% (P < 0,05). Pretreating rats with yohimbine (100 μg/kg), propanolol (100 μg/kg), cimétidine (15 mg/kg), and l'indometacine (5 mg/kg) did not significantly alter the previous effect. The significant negative chronotropic effect of the extract, at the dose of 20mg/kg was significantly inhibited by all pharmacological antagonist used. These results suggest that the hypotensive effects of aqueous extract of the stem bark of Lophira lanceolata involve muscarinic receptor and reduce the release of catecholamine aqueous extract of the stem bark of Lophira lanceolata would not act by the cyclooxygenase pathway, the H2-histamine receptors, the α2-adrenergic and the β1-adrenergic receptor. The propanolol and cimetidine respectively induced immediate and hypotensive effects of the extraction. The .aqueous extract of the stem bark of Lophira lanceolata showed hypotensive activity that would justify its empirical use in the management of hypertension.