Pharmacological evidence of calcium‐channel blockade by essential oil of Ocimum gratissimum and its main constituent, eugenol, in isolated aortic rings from DOCA‐salt hypertensive rats

Abstract

Intravenous (i.v.) treatment of conscious DOCA-salt hypertensive rats with the essential oil of Ocimum gratissimum L. (Labiatae) (EOOG) induced a hypotensive effect that seems related to an active vascular relaxation rather than withdrawal of sympathetic tone. To corroborate this hypothesis, the present study examined the vascular effects of EOOG and its main constituent, eugenol (EUG) and the putative mechanisms underlying these effects. Additionally, the role of the vascular beta(2)-adrenergic mechanism in the mediation of EOOG-induced hypotension has also been investigated. In conscious DOCA-salt hypertensive rats, the EOOG-induced hypotension was reversible and remained unchanged by i.v. pretreatment with propranolol (2 mg/kg). In isolated aorta preparations with intact endothelium from DOCA-salt hypertensive rats, EOOG (1-1000 microg/mL) and EUG (0.006-6 mM) relaxed the phenylephrine-induced contraction similarly with IC(50) [geometric mean (95% confidence interval)] values of 226.9 (147.8-348.3) microg/mL and 1.2 (0.6-2.1) mm, respectively. Vasorelaxant effects of EOOG were significantly altered by removal of the vascular endothelium [IC(50) = 417.2 (349.5-497.8) microg/mL]. In a calcium-free medium, the CaCl(2)-induced contractions were significantly reduced and even abolished by EOOG at 300 and 1000 microg/mL, respectively, whereas EOOG (1000 microg/mL) did not have any significant effect on caffeine-induced contractions. Similar results were obtained with EUG (1.8 and 6 mM) on both CaCl(2)- and caffeine-induced contractions, respectively. The data suggest that hypotensive responses to EOOG in DOCA-salt hypertensive rats are due to an active vascular relaxation, which is partly dependent upon the integrity of the vascular endothelium and seems predominantly mediated through an inhibition of plasmalemmal Ca(2+) influx rather than Ca(2+)-induced Ca(2+) release from the sarcoplasmic reticulum.

Eugenol Dilates Rat Cerebral Arteries by Inhibiting Smooth Muscle Cell Voltage-dependent Calcium Channels

“…Eugenol relaxed rat aorta pre-contracted with phenylephrine and high K + 7 and K + -depolarized rat mesentery bed contracted with bolus injections of CaCl 2 23 . Acute application of eugenol also reduced systemic blood pressure in normotensive and DOCA-salt hypertensive rats, supporting the concept that the vasodilation is functional in vivo 9, 10 . Here, we show that eugenol dilates: 1) cerebral arteries and 2) arteries constricted by intravascular pressure to simulate physiological pressure, rather than receptor agonists or high K + .…”

“…Therefore, data indicate that eugenol-induced vasodilation occurs due to a combination of Ca 2+ channel pore block and augmented voltage-dependent inactivation. These mechanisms of voltage-dependent Ca 2+ current inhibition may explain previously reported relaxant effects of eugenol in the vasculature 6, 7, 9 .…”

“…Eugenol has been shown to relax rabbit ear arteries 6 and rat and rabbit aorta 7, 8 . Eugenol also reduced systemic blood pressure in both normotensive and hypertensive DOCA-salt rats 9, 10 . However, eugenol regulation of contractility in small resistance-size arteries that control regional organ blood flow has not been studied.…”

Thymol and eugenol derivatives as potential antileishmanial agents

“…22 This compound is the main constituent of essential oil of Ocimum gratissimum and Eugenia caryophyllus. 32,33 Many phenylpropanoids demonstrate growth inhibition 34,35 but there are no studies on derivatives of eugenol. Similar to the thymol derivatives, we hypothesized that the eugenol derivative could also provide greater antileishmanial activity than nonderivatized compound.…”

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

“…Dalimartha (2000) in [10] reported eugenol as one of the compounds present in S. polyanthum leaves. Eugenol, a phenolic compound abundantly found in Syzygium family [11], has reputed ability as a vasorelaxant compound that causes vasodilation in vitro [12–14] and reduces blood pressure and heart rate of rats in vivo [15]. Other major phytochemical constituents of the essential oil from S. polyanthum leaves include cis-4-decenal, octanal, α -pinene, farnesol, β -ocimene, and nonanal [16].…”