Vasorelaxant property of Plectranthus vettiveroides root essential oil and its possible mechanism

Plectranthus vettiveroides (Jacob) N.P. Singh & B.D. Sharma is a traditional medicinal plant used in Siddha System of Medicine and its aromatic root is used to reduce the elevated blood pressure. The aim of the present study was to study vasorelaxant property of the root essential oil nanoemulsion (EON) of P. vettiveroides. The EON was formulated to enhance the solubility and bioavailability and characterized. The preliminary screening was performed by treating the EON with aortic rings pre-contracted with phenylephrine (1 μM) and potassium chloride (80 mM). The role of K⁺ channels in EON induced vasorelaxation was investigated by pre-incubating the aortic rings with different K⁺ channel inhibitors namely, glibenclamide (a non-specific ATP sensitive K⁺ channel blocker, 10 μM), TEA (a Ca²⁺ activated non-selective K⁺ channel blocker, 10⁻² M), 4-AP (a voltage-activated K⁺ channel blocker, 10⁻³ M) and barium chloride (inward rectifier K⁺ channel blocker, 1 mM). The involvement of extracellular Ca²⁺ was performed by adding cumulative dose of extracellular calcium in the presence and absence of EON and the concentration-response curve (CRC) obtained is compared. Similarly, the role of nitric oxide synthase, muscarinic and prostacyclin receptors on EON induced vasorelaxation were evaluated by pre-incubating the aortic rings with their inhibitors and the CRC obtained in the presence and absence of inhibitor were compared. The GC-MS and GC-FID analyses of the root essential oil revealed the presence of 62 volatile compounds. The EON exhibited significant vasorelaxant effect through nitric oxide-mediated pathway, G-protein coupled muscarinic (M₃) receptor pathway, involvement of K⁺ channels (KATP, KIR, KCₐ), and blocking of the calcium influx by receptor-operated calcium channel. It is concluded that the root essential oil of P. vettiveroides is possessing marked vasorelaxant property. The multiple mechanisms of action of the essential oil of P. vettiveroides make it a potential source of antihypertensive drug.