Autonomic Nervous System Mediates the Hypotensive Effects of Aqueous and Residual Methanolic Extracts ofSyzygium polyanthum(Wight) Walp. var.polyanthumLeaves in Anaesthetized Rats

Syzygium polyanthum(Wight) Walp. var.polyanthumleaves are consumed as a traditional Malay treatment of hypertension. This study investigates hypotensive potential of aqueous (AESP) and residual methanolic (met-AESP) extracts ofS. polyanthumleaves and possible involvement of autonomic receptors. AESP and met-AESP (20 to 100 mg/kg) were intravenously administered into anaesthetized Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats. Blood pressure and heart were monitored for 20 min. AESP and met-AESP induced significant dose-dependent hypotension, but only 100 mg/kg AESP caused mild bradycardia (n=5). AESP-induced hypotension was more potent than that of met-AESP in WKY. AESP has a faster onset time than that of met-AESP in both WKY and SHR. However, met-AESP-induced hypotension was more sustained than that of AESP in SHR. Blockages of autonomic ganglion andα-adrenergic receptors using hexamethonium and phentolamine (n=5for each group) partially attenuated AESP-induced hypotension, suggesting involvement ofα-adrenergic receptors. Blockages of autonomic ganglion,β-adrenergic, cholinergic receptors, and nitric oxide production using hexamethonium, propranolol, atropine, and N-ω-nitro-l arginine methyl ester (L-NAME) (n=5for each group) partially attenuated met-AESP-induced hypotension, suggesting involvement ofβ-adrenergic and cholinergic receptors via nitric oxide production.