Pharmacological evidences for the blood pressure lowering and cardiovascular inhibitory actions of the essential oil of Thymus serrulatus hochst. Ex benth

Background: T. serrulatus is used in folk medicine for the treatment of cardiovascular disorders, including hypertension. This study investigates its hypotensive, cardiac-depressant, and vasodilatory activities. Methods: The hypotensive effect of Thymus serrulatus essential oil was evaluated in vivo in anesthetized rats by measuring changes in mean arterial blood pressure following intravenous administration. Ex vivo, cardiac-depressant activity was assessed in isolated guinea-pig atrial preparations, and vasodilatory effects were examined in rat aortic rings. Results: Intravenous administration of T. serrulatus essential oil produced a dose-dependent (1–10 mg/kg) reduction in arterial blood pressure. In spontaneously beating guinea-pig atrial tissues, the oil exerted negative chronotropic and inotropic effects at concentrations of 0.1–5 mg/mL. In rat aorta, it caused complete relaxation of phenylephrine (PE, 1 μM)-induced contractions, with an EC₅₀ of 1.27 mg/mL, while partial relaxation (59% ± 3%) was observed against high K⁺ (80 mM). The vasodilatory effect against PE was not significantly altered by endothelium removal or atropine pretreatment, indicating an endothelium- and muscarinic-independent mechanism. Preincubation with a lower concentration (0.1 mg/mL) produced a rightward shift in PE-mediated concentration–response curves (CRCs) without reducing maximal response, similar to prazosin-like competitive antagonism. A higher concentration (0.3 mg/mL) suppressed the maximal PE response, consistent with non-competitive antagonism comparable to verapamil. In Ca⁺⁺-free medium, preincubation with T. serrulatus (0.3 and 1 mg/mL) shifted Ca²⁺ CRCs to the right with reduced maximal response, further supporting Ca⁺⁺ channel–blocking activity. Conclusion: T. serrulatus essential oil exhibits hypotensive, cardiac-depressant, and vasodilatory effects, likely mediated through α-adrenergic antagonism and Ca⁺⁺ channel blockade. These findings provide pharmacological support for its traditional use in cardiovascular disorders, including hypertension.