Acute intravenous antihypertensive and in vitro vasorelaxant effect of the hydroalcoholic stem bark extract of Hymenaea rubriflora Ducke in spontaneously hypertensive rats

OBJECTIVES: The cardioprotective potential of Hymenaea rubriflora Ducke's stem bark hydroalcoholic extract (HR-HAc) has not yet been investigated. This study aimed to quantify HR-HAc's antioxidant capacity and evaluate its effects on blood pressure (BP) and vascular reactivity in spontaneously hypertensive rats (SHR). METHODS: SHR and normotensive Wistar Kyoto (WKY) rats received intravenous HR-HAc (2.5-60 mg/kg). Mean arterial pressure (MAP) and heart rate (HR) were measured with or without atropine and propranolol. Isolated aortas from SHR and WKY rats were exposed to HR-HAc (0.1-729 μg/ml), with or without endothelium and K+ channel blockers. Phenolic content and antioxidant activity were quantified using standard colorimetric and chromatographic methods. KEY FINDINGS: In SHR rats, HR-HAc produced dose-dependent hypotension and bradycardia. MAP reduction in WKY rats was similar, while HR was unaffected. Atropine significantly attenuated HR-HAc-induced reductions in MAP and HR in SHR rats. HR-HAc induced potent endothelium-independent relaxation in SHR rat aortas, which was significantly reduced by tetraethylammonium or 4-aminopyridine. In WKY rats, vasorelaxant effects were endothelium-dependent. CONCLUSIONS: HR-HAc lowers MAP and induces bradycardia in SHR via muscarinic receptors, while also promoting vasodilation through activation of voltage- and calcium-activated K+ channels. These distinct mechanisms highlight HR-HAc as a promising preclinical antihypertensive candidate.