Cardiovascular actions ofDaucus carota

Possible mechanisms of action of the aqueous extract of Artocarpus altilis (breadfruit) leaves in producing hypotension in normotensive Sprague-Dawley rats

CONTEXT AND OBJECTIVES

Artocarpus altilis (Parkinson) Fosberg (Moraceae) (breadfruit) leaves are used as an antihypertensive remedy. We investigated the possible mechanisms of action of its aqueous extract and its effect on cytochromes P450 (CYP) enzyme activities.

MATERIALS AND METHODS

Intravenous administration of an aqueous leaf extract (20.88-146.18 mg/kg) of A. altilis on mean arterial pressure and heart rate were recorded via cannulation of the carotid artery on anaesthetized normotensive Sprague-Dawley rats. Recordings of the contractile activity of the aortic rings to the extract (0.71-4.26 mg/mL) were studied using standard organ bath techniques. Inhibitions of human CYP3A4 and CYP2D6 enzyme activities were evaluated by means of a fluorometric assay in 96 well plates using heterologously expressed microsomes.

RESULTS

A. altilis caused significant (p < 0.05) hypotensive and bradycardiac responses unaffected by atropine (2 mg/kg) and mepyramine (5 mg/kg), but attenuated by propranolol (1 mg/kg) and N(G)-nitro-L-arginine methyl ester (5 mg/kg). The extract (0.71-4.26 mg/mL) significantly (p < 0.05) relaxed phenylephrine (10⁻⁹-10⁻⁴ M) and 80 mM KCl-induced contractions in endothelium intact and denuded aortic rings; and caused a significant (p < 0.05) rightward shift of the Ca²⁺ dose-response curves in Ca²⁺-free Kreb's solution. Moderate inhibitions of cytochrome P450s (CYP3A4 and CYP2D6) enzyme activities with IC₅₀ values of 0.695 ± 0.187 and 0.512 ± 0.131 mg/mL, respectively, were produced.

CONCLUSION

A. altilis exhibits negative chronotropic and hypotensive effects through α-adrenoceptor and Ca²⁺ channel antagonism. Drug adversity effects are unlikely if the aqueous leaf extract is consumed with other medications reliant on CYP3A4 and CYP2D6 metabolism. This study thus provides scientific evidence for the use of the breadfruit in the treatment of hypertension.

Antispasmodic, bronchodilator and vasodilator activities of (+)-catechin, a naturally occurring flavonoid

Catechin is a well-known flavonoid found in many food plants and often utilized by naturopaths for the symptomatic treatment of several gastrointestinal, respiratory and vascular diseases. Our aim was to explore the biological basis for the medicinal use of this flavonoid by investigating whether catechin exhibits any pharmacological activity on smooth muscle preparations. We found that catechin dose-dependently relaxes both spontaneous and high K(+) (80 mM)-induced contraction in rabbit jejunum, showing specificity for the latter by causing a right-ward shift in the Ca(2+) dose-response curve. Similar results were observed with verapamil, a standard Ca(2+) channel blocker (CCB). Catechin also inhibited high K(+)-induced contraction in intact smooth muscle preparations from rat stomach fundus, guinea-pig ileum and guinea-pig trachea. In rat aorta, catechin inhibited phenylephrine (PE, 1 microM) and K(+)-induced contractions in a similar fashion. In PE-contracted, endothelium-intact aorta, this vasodilator effect was partially blocked by Nomega-nitro-L-arginine methyl ester and atropine, indicating activity at cholinergic receptors and possibly a CCB effect at higher doses of catechin. In guinea-pig atria catechin was found inactive. These data suggest that catechin may possess Ca(2+) antagonist activity--in addition to an endothelium-dependent relaxant component in blood vessels--thus providing a pharmacological basis for the efficacy of catechin in hyperexcitability disorders of gastrointestinal, respiratory and vascular smooth muscle.

The analgesic, anti-inflammatory and calcium antagonist potential ofTanacetum artemisioides

Several species of the genus Tanacetum are traditionally used in a variety of health conditions including pain, inflammation, respiratory and gastrointestinal disorders. In the current investigation, we evaluated the plant extract of T. artemisioides and some of its pure compounds (flavonoids) for analgesic, anti-inflammatory and calcium antagonist effects in various in-vivo and in vitro studies. Using the actetic acid induced writhing test, intraperitoneal (i.p) administration of the plant extract (25-50 mg/kg) and its flavonoid compounds TA-1 and TA-2 (1-5 mg/kg ) exhibited significant analgesic actvity. The maximum analgesic effect observed with the crude extract of the plant was 71% at 50 mg/kg, while that of compounds TA-1 and TA-2 (5 mg/kg i.p) was 75 and 47%, respectively. The plant extract and its pure compounds caused inhbition of formalin induced paw licking in mice predominatly in the second phase of the test. Diclofenac sodium, a standard reference compound, showed a simlar effect in these chemical induced pain models. In the carrgeenan induced rat paw edema assay, the plant extract (50-200 mg/kg i.p) demonstrated significant (P< 0.01) anti-inflammatory activity which was comparable to that obtained with diclofenac sodium and indomethacin. In isolated rabbit jejunum preprations the plant extract showed an atropine sensitive dose-dependent (0.10-1.0 mg/mL) spasmogenic activity followed by a spasmolytic effect at the next higher doses (3-5 mg/mL). The crude extract of the plant also inhibited the high K+-induced contractions, indicating a calcium channel blocking (CCB) activity, which was further confirmed when the plant extract caused a rightward shift in the Ca++ concentration response curves in the isolated rabbit jejunum preparations, similar to that seen with verapamil. The flavonoid compounds isolated from the plant were devoid of any activity in the isolated tissue preparations. These results indicate that the plant extract of T. artemisioides possesses analgesic, anti-inflammatory and CCB activities. The flavonoid compounds of the plant may have a role in its observed analgesic and antiinflammatory activities, while the CCB activity of the plant may be attributed to some other chemical constituents present. Moreover the findings support the traditional reputation of the genus Tanacetum for its therapeutic benefits in pain and inflammatory conditions.

Studies on cardio-suppressant, vasodilator and tracheal relaxant effects ofSarcococca saligna

Sarcococca saligna is a shrub that is traditionally used for its medicinal properties in Pakistan. In this study we report the cardio-suppressant, vasodilator and tracheal relaxant activities of the aqueous-methanolic extract (Ss.Cr) of the plant. Ss.Cr, that tested positive for the presence of saponins, flavonoids, tannins, phenols, and alkaloids, exhibited a dose-dependent (0.3-5 mg/mL) negative inotropic and chronotropic effect on the isolated guinea-pig atrium which was resistant to atropine (1 microM) and aminophylline (10 microM) pretreatment. In rabbit thoracic aorta, Ss.Cr dose-dependently (0.1-3 mg/mL) relaxed the high K+ (80 mM) and phenylephrine (PE, 1 microM)-induced contractions, indicating a possible Ca++ channel blocking (CCB) effect. When tested against PE (1 microM) control peaks in normal Ca++ and Ca++-free Kreb's solution, Ss.Cr exhibited dose-dependent (0.1-3 mg/mL) inhibition, being more potent in relaxing the PE responses in Ca++-free Kreb's solution, thus indicating specific blockade of Ca++ release from the intracellular stores. Ss.Cr also relaxed the agonist-induced contractions in: a) rat aorta irrespective of the presence of endothelium or nitric oxide synthase inhibitor L-NAME and b) rabbit and guinea-pig tracheal strips. The data shows that Ss.Cr possesses possible Ca++ channel blocking activity which might be responsible for its observed cardio-suppressant, vasodilator and tracheal relaxant effects though more tests are required to confirm this Ca++ channel blocking effect.

Cardiovascular effects of ginger aqueous extract and its phenolic constituents are mediated through multiple pathways

Ginger is a world known food plant which is equally reputed for its medicinal properties. We report here the hypotensive, endothelium-dependent and independent vasodilator and cardio-suppressant and stimulant effects of its aqueous extract (Zo.Cr). Zo.Cr, which tested positive for saponins, flavonoids, amines, alkaloids and terpenoids, induced a dose-dependent (3.0-10.0 mg/kg) fall in the arterial blood pressure (BP) of anaesthetized rats which was partially blocked by atropine (1 mg/kg). In isolated endothelium-intact rat aorta, Zo.Cr (0.01-5.0 mg/ml) relaxed the phenylephrine (1 microM)-induced contractions, effect partially blocked by atropine (1 microM). Zo.Cr inhibited the K+ (80 mM)-induced contractions and also shifted the Ca++ dose-response curves to the right, similar to verapamil, indicating Ca++ antagonist activity. An atropine-resistant and l-NAME-sensitive vasodilator activity was also noted from ginger phenolic constituents 6-, 8- and 10-gingerol, while 6-shogaol showed a mild vasodilator effect. In guinea-pig atria, Zo.Cr (0.1-5.0 mg/ml) inhibited the force and rate of atrial contractions. Pretreatment with atropine blocked the inhibitory effect and a stimulatory effect was unmasked which was resistant to propranolol and verapamil but sensitive to ryanodine, blocker of Ca++ release from intracellular stores. Later at doses >or=1.0 mg/ml, the extract completely suppressed the atrial tissue, effect resistant to glibenclamide, pyrilamine, aminophylline and L-NAME. These data indicate that the aqueous ginger extract lowers BP through a dual inhibitory effect mediated via stimulation of muscarinic receptors and blockade of Ca++ channels and this study provides sound mechanistic basis for the use of ginger in hypertension and palpitations.

Ginger lowers blood pressure through blockade of voltage-dependent calcium channels

Ginger (Zingiber officinale Roscoe), a well-known spice plant, has been used traditionally in a wide variety of ailments including hypertension. We report here the cardiovascular effects of ginger under controlled experimental conditions. The crude extract of ginger (Zo.Cr) induced a dose-dependent (0.3-3 mg/kg) fall in the arterial blood pressure of anesthetized rats. In guinea pig paired atria, Zo.Cr exhibited a cardiodepressant activity on the rate and force of spontaneous contractions. In rabbit thoracic aorta preparation, Zo.Cr relaxed the phenylephrine-induced vascular contraction at a dose 10 times higher than that required against K (80 mM)-induced contraction. Ca2+ channel-blocking (CCB) activity was confirmed when Zo.Cr shifted the Ca2+ dose-response curves to the right similar to the effect of verapamil. It also inhibited the phenylephrine (1 microM) control peaks in normal-Ca2+ and Ca2+-free solution, indicating that it acts at both the membrane-bound and the intracellular Ca2+ channels. When tested in endothelium-intact rat aorta, it again relaxed the K-induced contraction at a dose 14 times less than that required for relaxing the PE-induced contraction. The vasodilator effect of Zo.Cr was endothelium-independent because it was not blocked by L-NAME (0.1 mM) or atropine (1 microM) and also was reproduced in the endothelium-denuded preparations at the same dose range. These data indicate that the blood pressure-lowering effect of ginger is mediated through blockade of voltage-dependent calcium channels.

Hypotensive action of coumarin glycosides from Daucus carota

Daucus carota (carrot) has been used in traditional medicine to treat hypertension. Activity-directed fractionation of aerial parts of D. carota resulted in the isolation of two cumarin glycosides coded as DC-2 and DC-3. Intravenous administration of these compounds caused a dose-dependent (1-10 mg/kg) fall in arterial blood pressure in normotensive anaesthetised rats. In the in vitro studies, both compounds caused a dose-dependent (10-200 microg/ml) inhibitory effect on spontaneously beating guinea pig atria as well as on the K+ -induced contractions of rabbit aorta at similar concentrations. These results indicate that DC-2 and DC-3 may be acting through blockade of calcium channels and this effect may be responsible for the blood pressure lowering effect of the compounds observed in the in vivo studies.

The presence of cholinomimetic and calcium channel antagonist constituents in Piper betle Linn

The crude aqueous extract of Piper betle leaves (Pb.Cr) was studied for the possible presence of cholinomimetic and calcium channel antagonist constituents. Pb.Cr at doses of 1-10 mg/mL caused a moderate spasmogenic effect in isolated guinea-pig ileum and this activity was concentrated in the aqueous fraction, which was found to be about 5 times more potent. Pretreatment of the tissue with atropine (1 microM) but not hexamethonium (100 microM) completely abolished the contractile effect of the aqueous fraction indicating a cholinergic (muscarinic) mechanism. In isolated rabbit jejunum preparations Pb.Cr did not produce a significant increase in the spontaneous contractions, but instead produced a dose-dependent (0.03-3.0 mg/mL) inhibition of spontaneous activity. Activity-directed fractionation revealed that the spasmolytic action was concentrated in the ethyl acetate fraction. When tested against K(+)-induced contractions, both Pb.Cr and its ethyl acetate fraction (Pb.EtAc) caused a dose-dependent inhibition, suggesting calcium channel blockade (CCB). The potent CCB effect of the crude extract and its ethyl acetate fraction was confirmed when pretreatment of the tissue with Pb.Cr or Pb.EtAc shifted the Ca(++) dose-response curves to the right in a dose-dependent manner. These data indicate that the plant contains cholinomimetic and possible calcium channel antagonist constituents, which are concentrated in the aqueous and ethyl acetate fractions respectively. It is suggested that some of the traditional uses of this plant may be explained on the basis of these activities.

The antiplatelet aggregatory activity of Acacia nilotica is due to blockade of calcium influx through membrane calcium channels

1. The extract of Acacia nilotica (A. nilotica) blocked platelet aggregation mediated by platelet agonists, arachidonic acid (0.75 mM), ADP (4.3 microM), platelet activating factor (800 nM) and collagen (638 nM) in a dose-dependent manner. 2. The extract (0.21-1.4 mg/ml) blocked the platelet aggregation induced by Ca2+ ionophore, A-23187 (6 microM), in a dose-dependent manner, indicating that the Ca2+ influx is involved in aggregation. 3. The plant extract also inhibited aggregation in platelets pretreated with phorbol, 12-myristate, 13-acetate (196 nM) alone or in combination with ADP (4.3 microM), indicating an effect on protein kinase C. 4. These results indicate that the antiplatelet aggregatory activity of the extract of A. nilotica is mainly due to blockade of Ca2+ channels, although evidence also suggests the involvement of protein kinase C.