Saad Lahlou

Antihypertensive effects of the essential oil of Alpinia zerumbet and its main constituent, terpinen-4-ol, in DOCA-salt hypertensive conscious rats

The present study investigated the hypotensive responses to intravenous (i.v.) treatment with the essential oil of Alpinia zerumbet (EOAZ) and its main constituent, terpinen‐4‐ol (Trp‐4‐ol), in the experimental model of deoxycorticosterone‐acetate (DOCA)‐salt hypertensive rat.

Vasorelaxant effects of the monoterpenic phenol isomers, carvacrol and thymol, on rat isolated aorta

Various essential oils are rich in carvacrol, a monoterpenic phenol isomeric with thymol. This study was undertaken to assess the vasorelaxant effects of thymol and carvacrol in rat isolated aorta and the putative mechanisms underlying these effects. Thymol and carvacrol produced a concentration‐dependent relaxation on the aortic ring preparations pre‐contracted using KCl (IC50 value of 64.40 ± 4.41 and 78.80 ± 11.91 μm, respectively) or using phenylephrine (PHE, 0.1 μm) (IC50 value of 106.40 ± 11.37 and 145.40 ± 6.07 μm, respectively) and inhibited the concentration‐response curves of aortic rings to PHE or KCl. In Ca2+‐free medium with ethylene glycol‐bis(2‐aminoethylether)‐N,N,N′,N′‐tetraacetic acid (2 mm), thymol and carvacrol both at 1000 μm completely abolished the phasic component of PHE‐induced endothelium‐containing ring contractions. At 400 μm, thymol and carvacrol significantly reduced the CaCl2‐induced contractions in Ca2+‐free medium. Furthermore, both thymol and carvacrol (300 and 1000 μm) significantly reduced the contraction evoked by phorbol dibutyrate (1 μm), an activator of protein kinase C. Magnitude of this inhibitory effect was enhanced in the presence of the Ca2+ pump inhibitor, thapsigargin (1 μm). At 1000 μm, neither thymol nor carvacrol altered the resting potential of vascular smooth muscle cells. In conclusion, thymol and carvacrol induced an endothelium‐independent relaxation in rat isolated aorta, an effect that seems mediated through some mechanisms probably involving a transduction pathway between Ca2+ release from sarcoplasmic reticulum and/or regulation of the Ca2+ sensitivity of the contractile system. Moreover, it’s conceivable that thymol and carvacrol, at low concentrations, block the Ca2+ influx through the membrane.

Arbutus unedo prevents cardiovascular and morphological alterations in L-NAME-induced hypertensive rats Part I. Cardiovascular and renal hemodynamic effects of Arbutus unedo in L-NAME-induced hypertensive rats

Hypertension induced by nitric oxide synthase inhibition is associated with functional abnormalities of the heart and kidney. The aim of the present study was to investigate whether chronic treatment with Arbutus unedo leaf (AuL) or root (AuR) aqueous extracts can prevent these alterations. Six groups of rats were used: control group received tap water; N(G)-nitro-l-arginine methyl-ester (L-NAME) group treated with L-NAME at 40 mg/kg/day; AuL and AuR groups received simultaneously L-NAME (40 mg/kg/day) and Au leaves or roots extract at the same concentration 250 mg/kg/day; l-arginine and enalapril groups received simultaneously L-NAME (40 mg/kg/day) and l-arginine at 50mg/kg/day or enalapril at 15 mg/kg/day. Treatment of rats during 4 weeks with L-NAME caused an increase of the systolic blood pressure (SBP) accompanied by a ventricular hypertrophy, an impairment of endothelium-dependent vasorelaxation, an increase of the cardiac baroreflex sensitivity and a decrease of water, sodium and potassium excretion. The co-administration of AuL or AuR extracts with L-NAME reduces the development of increased SBP, ameliorates the vascular reactivity as well as the baroreflex sensitivity and normalizes the renal function. AuR reduces the ventricular hypertrophy but AuL do not. Enalapril associated with L-NAME reverses the majority of alterations induced by L-NAME while l-arginine only lightly ameliorates the vascular reactivity. These results show that chronic treatment with Arbutus extract regress the development of hypertension and ameliorate cardiovascular and renal functions in NO deficient hypertension.

Linalool blocks excitability in peripheral nerves and voltage-dependent Na+ current in dissociated dorsal root ganglia neurons

Linalool is a terpene that occurs as a major constituent of essential oils of many plants of widespread distribution. It possesses several biological and pharmacological activities, including depressant effects on the central nervous system and olfactory receptors. The present study investigated whether linalool affects the excitability of peripheral components of the somatic sensory system. We used sciatic nerve and preparations of intact and dissociated neurons of dorsal root ganglion for extracellular, intracellular and patch-clamp recordings. Linalool concentration-dependently (0.3-2.0mM) and reversibly blocked the excitability of the sciatic nerve. It inhibited peak-to-peak amplitude of the compound action potential (IC(50) was 0.78+/-0.04 mM). At 0.8mM, it reversibly increased rheobase and chronaxy (from 3.2+/-0.1 V and 52.4+/-4.1 micros to 4.2+/-0.3 V and 71.2+/-5.5 micros (n=5), respectively) and inhibited with greater pharmacological potency the amplitude of the compound action potential components corresponding to axons with slower velocity of conduction. In a similar concentration range (0.1-6mM), linalool concentration-dependently and reversibly blocked the generation of action potentials of intact dorsal root ganglion neurons without alteration of resting membrane potential and input resistance, and inhibited the voltage-gated Na(+) current of dissociated dorsal root ganglion neurons. In conclusion, we demonstrated that linalool acts on the somatic sensory system with local anesthetic properties, since it blocked the action potential by acting on voltage-dependent Na(+) channels. This finding is important in showing the potential usefulness of linalool as a pharmacotherapeutic agent.

Essential oil of croton nepetaefolius and its main constituent, 1,8-cineole, block excitability of rat sciatic nerve in vitro.

1 The effects of the essential oil of Croton nepetaefolius (EOCN) and its major constituent, 1,8‐cineole, on the compound action potential (CAP) of nerve were investigated. 2 Experiments were performed in sciatic nerves dissected from Wistar rats, mounted in a moist chamber and stimulated at a frequency of 0.2 Hz, with electric pulses of 100 µs duration at 20–40 V. Evoked CAP were displayed on an oscilloscope and recorded on a computer. The CAP control parameters were as follows: peak‐to‐peak amplitude 8.1 ± 0.6 mV (n = 15); conduction velocity 83.3 ± 4.2 m/s (n = 15); chronaxie 58.0 ± 6.8 msec (n = 6); and rheobase 2.8 ± 0.1 V (n = 6). 3 Lower concentrations of EOCN (100 and 300 µg/mL) and 1,8‐cineole (153 and 307 µg/mL; i.e. 1 and 2 mmol/L, respectively) had no significant effects on CAP control parameters throughout the entire recording period. However, at the end of 180 min exposure of the nerve to the drug, peak‐to‐peak amplitude was significantly (P < 0.05) reduced to 27.4 ± 6.7 and 1.7 ± 0.8% of control values by 500 and 1000 µg/mL EOCN, respectively (n = 6), and to 76.5 ± 4.4, 70.0 ± 3.9 and 14.8 ± 4.1% of control values by 614, 920 and 1227 µg/mL (i.e. 4, 6 and 8 mmol/L) 1,8‐cineole, respectively (n = 6). Regarding conduction velocity, at the end of the 180 min exposure period, this parameter was significantly reduced to 85.8 ± 7.3 and 48.7 ± 12.3% (n = 6) of control values by 500 and 1000 µg/mL EOCN, respectively, and to 86.4 ± 4.5 and 76.1 ± 5.2% (n = 6) by 920 and 1227 µg/mL 1,8‐cineole, respectively. Chronaxie and rheobase were significantly increased by the higher concentrations of both EOCN and 1,8‐cineole. 4 It is concluded that EOCN and its main constituent 1,8‐cineole block nerve excitability in a concentration‐dependent manner, an effect that was totally reversible with 1,8‐cineole but not with EOCN. This suggests that other constituents of EOCN, in addition to 1,8‐cineole, may contribute to the mediation of this effect of EOCN.

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

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 β2‐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 μg/mL) and EUG (0.006–6 mm) relaxed the phenylephrine‐induced contraction similarly with IC50 [geometric mean (95% confidence interval)] values of 226.9 (147.8–348.3) μg/mL and 1.2 (0.6–2.1) mm, respectively. Vasorelaxant effects of EOOG were significantly altered by removal of the vascular endothelium [IC50 = 417.2 (349.5–497.8) μg/mL]. In a calcium‐free medium, the CaCl2‐induced contractions were significantly reduced and even abolished by EOOG at 300 and 1000 μg/mL, respectively, whereas EOOG (1000 μg/mL) did not have any significant effect on caffeine‐induced contractions. Similar results were obtained with EUG (1.8 and 6 mm) on both CaCl2‐ 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 Ca2+ influx rather than Ca2+‐induced Ca2+ release from the sarcoplasmic reticulum.

Cardiovascular effects of the essential oil of Aniba canelilla bark in normotensive rats.

Cardiovascular effects of intravenous (i.v.) treatment with the essential oil of the bark of Aniba canelilla (EOAC) were investigated in normotensive rats. In both pentobarbital-anesthetized and conscious rats, i.v. bolus injections of EOAC (1 to 20 mg/kg) elicited similar and dose-dependent hypotension and bradycardia. Pretreatment of anesthetized rats with bilateral vagotomy significantly reduced the bradycardia without affecting the hypotension. In conscious rats, pretreatment with hexamethonium (30 mg/kg, i.v.) significantly reduced the EOAC-induced bradycardia without affecting the hypotension. The opposite effect was observed after i.v. pretreatment with the nitric oxide synthase inhibitor, NG-nitro-L-arginine methyl esther (L-NAME, 20 mg/kg). However, both EOAC-induced hypotension and bradycardia were significantly reduced by pretreatment with methylatropine (1 mg/kg, i.v.). In rat endothelium-containing aorta preparations, EOAC (1-600 μg/mL) induced a concentration-dependent reduction of potassium (60 mM)-induced contraction [IC50 (geometric mean ± 95% confidence interval) = 64.5 (45.6-91.2) μg/mL)], an effect that was significantly reduced by the addition of atropine (10 μM) in the perfusion medium [IC50 = 109.5 (72.5-165.4) μg/mL)]. Furthermore, the vasorelaxant effects of the EOAC were also but significantly reduced [IC50 = 139.1 (105.2-183.9) μg/mL)] by removal of the vascular endothelium. Furthermore, the CaCl2-induced contractions in calcium-free medium were reduced and even fully abolished by EOAC (100 and 600 μg/mL), respectively. However, EOAC (600 μg/mL) was without significant effect on caffeine-induced contractions in calcium-free medium. These data show that i.v. treatment of rats with EOAC induces dose-dependent hypotension and bradycardia, which occurred independently. The bradycardia appears mainly dependent upon the presence of an operational and functional parasympathetic drive to the heart. However, the hypotension is due to an active vascular relaxation rather than withdrawal of sympathetic tone. This relaxation seems partly mediated by an endothelial L-arginine/nitric oxide pathway through peripheral muscarinic receptor activation (endothelium-dependent relaxation) and predominantly through an inhibition of calcium inward current (endothelium-independent relaxation).

Antispasmodic effects of essential oil of Pterodon polygalaeflorus and its main constituent β-caryophyllene on rat isolated ileum.

This study investigates the effects of essential oil of Pterodon polygalaeflorus (EOPP) and β‐caryophyllene (β‐CAR). EOPP and β‐CAR relaxed the basal tone of ileum smooth muscle in a concentration‐dependent manner (IC50s = 394.35 ± 62.12 and 68.65 ± 9.51 μg/mL respectively), an effect that was unaltered by hexamethonium, L‐nitroarginine methyl ester or indomethacin. Both EOPP and β‐CAR evoked a concentration‐dependent relaxation of ileum pre‐contracted with KCl with an IC50 value of 107.78 ± 10.47 and 17.35 ± 0.75 μg/mL, respectively. EOPP and β‐CAR inhibited the contractions induced by acetylcholine (ACh) and by KCl. In ileal preparations, the CaCl2‐induced contractions were reduced by EOPP (300 μg/mL) and β‐CAR (100 μg/mL). Furthermore, CaCl2‐induced contractions were also reduced by EOPP (300 μg/mL) and β‐CAR (100 μg/mL) in ileal preparations pretreated with ACh under Ca2+‐free condition and in the presence of verapamil. EOPP (100 and 300 μg/mL) and β‐CAR (30 and 100 μg/mL) reduced the ACh‐induced contractions of isolated rat ileum under Ca2+‐free conditions. In the presence of high KCl and Ca2+‐free conditions, EOPP (300 μg/mL) and β‐CAR (100 μg/mL) reduced the contractions induced by barium. A similar effect was also observed with verapamil. It is concluded that (i) β‐CAR is an important constituent involved in the myorelaxant and antispasmodic effects induced by EOPP; (ii) the inhibitory effect on intestinal contractility is myogenic and seems mainly mediated through an intracellular mechanism. However, the ability of EOPP and β‐CAR to decrease Ca2+ influx through cytoplasmic membrane could not be discounted.

Endothelium-dependent vasorelaxant effects of the essential oil from aerial parts of Alpinia zerumbet and its main constituent 1,8-cineole in rats

Vasorelaxant effects of essential oil of Alpinia zerumbet (EOAZ) and its main constituent, 1,8-cineole (CIN) were studied. In rat isolated aorta preparations with intact endothelium, EOAZ (0.01-3000 microg/ml) induced significant but incomplete relaxation of the phenylephrine-induced contraction, an effect that was abolished by removal of vascular endothelium. However, at the same concentrations (0.01-3000 microg/ml corresponding to 0.0000647-19.5 mM), CIN induced a complete vasorelaxant effects (IC(50)=663.2+/-63.8 microg/ml) that were significantly reduced in endothelium-denuded rings (IC(50)=1620.6+/-35.7 microg/ml). Neither EOAZ nor CIN affected the basal tonus of isolated aorta. Vasorelaxant effects of both EOAZ and CIN remained unaffected by the addition of tetraethylamonium chloride (500 microM) or indomethacin (10 microM) into the bath, but were significantly reduced by N(G)-nitro-L-arginine methyl ester (100 microM). It is concluded that EOAZ induces a potent vasorelaxant effect that could not be fully attributed to the actions of the main constituent CIN, and appears totally dependent on the integrity of a functional vascular endothelium. The data is novel and corroborate the popular use of A. zerumbet for the treatment of hypertension.

Vasorelaxation induced by the essential oil of Croton nepetaefolius and its constituents in rat aorta are partially mediated by the endothelium

Previously, we reported that essential oil of Croton nepetaefolius (EOCN) decreases blood pressure in normotensive rats, an effect that seems resulting from its vasodilatory action directly upon vascular smooth muscle. In the present study, we aimed to study the role of endothelium–nitric oxide pathway in the mediation of vasodilatory effects of EOCN and two of its constituents, methyleugenol and α‐terpineol, using rat isolated thoracic aorta and mesenteric vascular bed preparations. EOCN (1–300 μg/mL), in a concentration‐dependent manner, relaxed isolated endothelium‐intact aortic rings precontracted with KCl 60 mm, with an IC50 value of 26.7 (14.7–48.2) μg/mL. Either pretreatment of the tissue with l‐NAME, a nitric oxide synthase inhibitor, or mechanical endothelium removal increased significantly the IC50 value to 66.6 (52.7–84.1) or 105.6 (91.3–122.2) μg/mL, respectively. In endothelium‐intact aortic rings precontracted with norepinephrine, EOCN (10–200 μg/mL) produced a vasorelaxant action which was decreased by the pretreatment of the aortic rings with methylene blue, a guanylate cyclase inhibitor. In mesenteric bed preparations perfused under constant pressure, EOCN reverted the reduction of mesenteric flow caused by KCl (60 mm), an effect that was attenuated by l‐NAME. Vasodilator responses to EOCN in mesenteric bed preparations were mimicked by methyleugenol and α‐terpineol, and were also significantly reduced in the presence of l‐NAME. In conclusion, EOCN has vasorelaxant effects in both a resistance vascular bed and in a conduit artery. They seem attributed, at least in part, to the actions of its main constituents methyleugenol and α‐terpineol and appear partially dependent upon the integrity of a functional vascular endothelium. Inhibition of other transduction pathways may be involved in the mediation of these effects.