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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
Author(s) -
Interaminense Leylliane Fátima Leal,
Jucá Davi Matthews,
Magalhães Pedro Jorge Caldas,
LealCardoso José Henrique,
Duarte Gloria Pinto,
Lahlou Saad
Publication year - 2007
Publication title -
fundamental and clinical pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.655
H-Index - 73
eISSN - 1472-8206
pISSN - 0767-3981
DOI - 10.1111/j.1472-8206.2007.00514.x
Subject(s) - eugenol , phenylephrine , medicine , nifedipine , caffeine , contraction (grammar) , endocrinology , aorta , propranolol , vascular smooth muscle , essential hypertension , vasoconstriction , pharmacology , calcium , blood pressure , chemistry , smooth muscle , organic chemistry
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 β 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 μ g/mL) and EUG (0.006–6 m m ) relaxed the phenylephrine‐induced contraction similarly with IC 50 [geometric mean (95% confidence interval)] values of 226.9 (147.8–348.3) μ g/mL and 1.2 (0.6–2.1) m m , respectively. Vasorelaxant effects of EOOG were significantly altered by removal of the vascular endothelium [IC 50 = 417.2 (349.5–497.8) μ g/mL]. In a calcium‐free medium, the CaCl 2 ‐induced contractions were significantly reduced and even abolished by EOOG at 300 and 1000 μ g/mL, respectively, whereas EOOG (1000 μ g/mL) did not have any significant effect on caffeine‐induced contractions. Similar results were obtained with EUG (1.8 and 6 m m ) 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.