Positive inotropic and negative chronotropic effects of (-)-cis-diltiazem in rat isolated atria

Antihypertensive Potential of Tartaric Acid and Exploration of Underlying Mechanistic Pathways

Tartaric acid is capable of balancing blood pressure. It is the main constituent of antihypertensive agents (grapes and wine) and has not been scientifically explored as an antihypertensive remedy. This study aimed to investigate the antihypertensive effect of a low-dose tartaric acid in vivo and explore underlying mechanisms in vitro. Intravenous administration of tartaric acid at the dose of 50 µg/kg caused a % fall in mean arterial pressure (MAP) in normotensive and hypertensive rats [51.5 ± 1.7 and 63.5 ± 2.9% mmHg]. This hypotensive effect was partially inhibited by atropine (1 mg/kg) and _L-NAME (100 µg/kg) pretreatment. In hypertensive rats, oral administration of tartaric acid (.1, .5, 1, 5, and 10 mg/kg) for 2 weeks resulted in 65 ± 7.3 mmHg MAP at 10 mg/kg. This antihypertensive effect was comparable to the orally administered verapamil (10 mg/kg) for 2 weeks which caused a decrease in MAP 60.4 ± 3.8 mmHg. Tartaric acid relaxed phenylephrine (PE) and High K⁺-induced contractions with EC₅₀ values of .157 (.043-.2) and 1.93 (.07-2) µg/mL in vitro. This endothelium-dependent relaxation was inhibited with atropine (1 µM) and _L-NAME (10 µM) pretreatment. Tartaric acid also suppressed phenylephrine contractions in Ca⁺² free/EGTA medium and on voltage-dependent calcium channels, causing the concentration–response curves toward right. Tartaric acid induced negative inotropic and chronotropic effects with EC₅₀ values of .26 (.14-.4) and .60 (.2-.8) in rat atria. It showed its effect by complete blockade against atropine and partially in propranolol pretreatment. These findings provide scientific basis to low-dose tartaric acid as an antihypertensive and vasodilatory remedy through muscarinic receptor-linked nitric oxide (NO) pathway and Ca⁺² channel antagonist.

Antihypertensive Activity in High Salt-Induced Hypertensive Rats and LC-MS/MS-Based Phytochemical Profiling of Melia azedarach L. (Meliaceae) Leaves

Melia azedarach L. leaves have been traditionally used but not scientifically evaluated for antihypertensive activity. The focus of the present work was to carry out the detailed phytochemical profiling and antihypertensive potential of methanolic extract and subsequent fractions of this plant. The tandem mass spectrometry-based phytochemical profiling of M. azedarach extract (Ma.Cr) and fractions was determined in negative ionization mode while molecular networking was executed using the Global Natural Product Social (GNPS) molecular networking platform. This study resulted in the identification of 29 compounds including flavonoid O-glycosides, simple flavonoids, triterpenoidal saponins, and cardenolides as the major constituents. Ma.Cr at the concentration of 300 mg/kg resulted in a fall in blood pressure (BP), i.e., 81.44 ± 2.1 mmHg in high salt-induced hypertensive rats in vivo, in comparison to normotensive group, i.e., 65.36 ± 1.8 mmHg at the same dose. A decrease in blood pressure was observed in anaesthetized normotensive and hypertensive rats treated with extract and various fractions of M. azedarach. A reasonable activity was observed for all fractions except the aqueous fraction. The highest efficacy was shown by the ethyl acetate fraction, i.e., 77.06 ± 3.77 mmHg in normotensive and 88.96 ± 1.3 mmHg in hypertensive anaesthetized rats. Ma.Cr and fractions showed comparatively better efficacy towards hypertensive rats as compared to rats with normal blood pressure. Blood pressure-lowering effects did not change upon prior incubation with atropine. In vitro testing of Ma.Cr and polarity-based fractions resulted in L-NAME sensitive, endothelium-dependent vasodilator effects on aortic tissues. Pretreatment of aorta preparations with Ma.Cr and its fractions also blocked K+-induced precontractions indicating Ca2+ channel blocking activity comparable to verapamil. The extract and polarity-based fractions did not reveal a vasoconstrictor response in spontaneously beating isolated rat aorta. Ma.Cr and fractions when used in atrial preparations resulted in negative inotropic and chronotropic effects. These effects in atrial preparations did not change in the presence of atropine. These effects of extract and fractions explained the antihypertensive potential of M. azedarach and thus provided a scientific basis for its ethnopharmacological use in the treatment of hypertension. Among the constituents observed, flavonoids and flavonoid O-glycosides were previously reported for antihypertensive potential.

Cardioprotective Potential of Aqueous Extract of Fumaria indica on Isoproterenol-Induced Myocardial Infarction in SD Rats

Ischemic heart disease (IHD) treatments and preventions by using plant extract and its phytochemical constituents have achieved considerable attention globally due to its cardioprotective effects. This study is aimed at investigating the cardioprotective and vascular effects of Fumaria indica (F. indica) crude extract on isoproterenol- (ISO-) induced myocardial infarction (MI) in Sprague-Dawley (SD) rats. Rats treated with isoproterenol (85 mg/kg, s.c), administered. Twice at an interval of 24 h showed a significant ST-segment elevation in ECG, edema, and necrosis in histopathology and also in troponin I (cTnI), creatine phosphokinase (CPK), lactate dehydrogenase (LDH), and aspartate aminotransferase (AST). Pretreatment with F. indica (10, 30, and 100 mg/kg, p.o) for 21 days significantly reversed the effects of isoproterenol-induced ischemic changes in the ECG, levels of cTnI, CPK, LDH, and AST, and histopathological changes. In isolated rat atrial strips, F. indica induced negative chronotropic and inotropic effects which were not affected by pretreatment with atropine, excluding role of cardiac muscarinic receptors. Cumulative addition of the extract induced a vasorelaxant effect on phenylephrine-evoked contractions in isolated rat aortic rings, which remained unchanged when challenged with _L-NAME, excluding role of endothelial NO. However, extract of F. indica concentration dependently reversed contractions evoked with high K⁺, indicating calcium entry blocking effect. In conclusion, the F. indica extract is a cardioprotective remedy that ameliorates the isoproterenol-induced cardiotoxic effects and reverses cardiac ischemia, and the calcium antagonistic effect might be of useful in the treatment of MI.

Antiplatelet Aggregation, Cardiotonic, Anti-Inflammatory, Antioxidant, and Calcium Channel Antagonistic Potentials of Nepeta ruderalis Buch

The objective of this study was to authenticate the ethnobotanical claims of the Nepeta ruderalis Buch.-Ham. (N. ruderalis) extract in the traditional system of medicine. Crude extract was prepared via a simple maceration process. DPPH free radical scavenging and carrageenan-induced rat paw edema models were used to monitor antioxidant and anti-inflammatory responses of the N. ruderalis extract. Furthermore, it was tested for antiplatelet aggregation, cardioprotective, and calcium channel antagonistic activities via standard documented protocols. The N. ruderalis extract exhibited 80.82% antioxidant activity (IC₅₀ = 207.51 ± 4.36 μg) while the anti-inflammatory response was significant (p < 0.05 to p < 0.01) at 50 mg/kg (45.58%) and 100 mg/kg (60.90%) doses. Moreover, it was found to inhibit platelet aggregation (IC₅₀ = 1.06 and 0.91 mg/mL) and, in addition, to increase the force of contraction at the concentration of 3.0-10 mg/mL with a decrease in the heart rate on isolated paired atria (EC₅₀ = 11.78 mg/mL). Relaxant activity was observed on the isolated rabbit jejunum (EC₅₀ = 0.96 mg/mL) and trachea (EC₅₀ = 0.89 mg/mL). However, in a cumulative way, an 80-millimolar potassium-induced contraction was evaluated (EC₅₀ = 1.31 mg/mL). The N. ruderalis extract exhibited antioxidant, anti-inflammatory, platelet aggregating, cardiotonic, and calcium channel antagonistic activities, therefore proving scientifically its effectiveness in the traditional system of medicine.

Pharmacological evaluation of the hydro-alcoholic extract of Campomanesia phaea fruits in rats

Campomanesia phaea (Myrtaceae), popularly known as cambuci, is one of several species of plants producing comestible fruits, largely used in human nutrition. Despite its consumption and economic potential, limited scientific research is available on the Campomanesia, especially those related to its therapeutic benefits. It is reported by traditional medicine the use of the plant in the treatment of different disorders, such as cardiovascular and nervous system disturbances. So, the aim of this study was to carry out the pharmacological evaluation of the hydro-alcoholic extract (HAE) of Campomanesia fruits in rats by screening consisting of tests: a) neuropharmacological observation, b) test on the cardiovascular system. The HAE, prepared from the extraction of fruits with water/ethanol, was concentrated and freeze-dried. Behavioral responses in rats were investigated in open field test and the cardiovascular actions were investigated by a register of indirect blood pressure and the register of spontaneous beating rate right atrium. The results revealed that HAE induced grooming, hypotension and bradycardia. So, this study identified an action on the central nervous system, represented by grooming, and a cardiovascular activity of Campomanesia. The hypotension, attributed in part to bradycardia, was not related to a cholinergic effect, discarding a possible cholinomimetic action of the plant that could justify both cardiovascular and central actions.

Antihypertensive effect of the methanolic extract from Eruca sativa Mill., (Brassicaceae) in rats: Muscarinic receptor-linked vasorelaxant and cardiotonic effects

ETHNOPHARMACOLOGICAL RELEVANCE

Eruca sativa Mill., (Brassicaceae) is a popular remedy for the treatment of hypertension in Pakistan. However, direct effect of the extract and its fractions on blood pressure and vascular tone are unknown.

AIM OF THE STUDY

This investigation was aimed to explore the pharmacological base for the traditional use of E. sativa in hypertension.

MATERIALS AND METHODS

In-vivo blood pressure study was carried out using normotensive and high salt-induced hypertensive rats under anaesthesia. The cardiovascular mechanisms were explored using rat aorta and atria in-vitro. Preliminary phytochemical analysis, spectrophotometric detection of total phenols, flavonoids and HPLC analysis of crude extract were performed using quercetin and erucin as marker compounds.

RESULTS

Intravenous injection of crude extract induced a fall in mean arterial pressure (MAP) in both normotensive (max fall: 41.79 ± 1.55% mmHg) and hypertensive (max fall: 58.25 ± 0.91% mmHg) rats. Atropine (1 mg/kg) pretreatment attenuated this effect significantly (p < 0.001), suggesting the involvement of muscarinic receptor in its antihypertensive effect. Fractions also induced atropine-sensitive antihypertensive effect. Similarly, oral administration of crude and aqueous extracts resulted a fall in MAP in the hypertensive rats. In isolated rat aortic rings from normotensive rats, crude extract and fractions induced an endothelium-dependent relaxation. This relaxation was partially inhibited with _L-NAME and atropine pretreatment and with denudation of aortic rings, indicating involvement of muscarinic receptor-linked nitric oxide (NO). In aorta from the hypertensive rats, crude extract and fractions induced endothelium-independent relaxation. This relaxation was not affected by pretreatment with _L-NAME or atropine. Crude extract and fractions also suppressed phenylephrine contractions in Ca⁺² free/EGTA medium. In isolated rat atrial preparations, crude extract and fractions induced negative inotropic and chronotropic effects with a positive inotropic effect by the n-hexane fraction, which were not affected with atropine pretreatment. Phytochemical screening and spectrophotometric analysis indicated the presence of phenols and flavonoids, whereas HPLC analysis of crude extract revealed the presence of quercetin (flavonoid) and erucin (isothiocyanate).

CONCLUSION

The results suggest that E. sativa is an antihypertensive remedy which is mainly due to its vasodilatory and partly cardiac effects. Muscarinic receptors-linked NO release and dual inhibitory effect on Ca⁺² influx and release underlie the vasodilation. This finding provides pharmacological base to the traditional use of E. sativa in hypertension. The presence of quercetin and erucin further support this finding.

Endothelium-independent vasorelaxant activity of Trachyspermum ammi essential oil on rat aorta

Several pharmacological activities of the essential oil of Trachyspermum ammi seeds (TAEO) have been previously studied. These include antitussive, antihypertensive, and antispasmodic effects. However, its action on isolated aorta has not yet been studied. This study was aimed to investigate the vasorelaxant activity of TAEO and characterize its mechanism of action. Extraction of TAEO was performed using Clevenger-type apparatus with the final content of 4.5% (v/w). To evaluate some probable mechanisms of action of TAEO, the action isometric tension was then measured in the aortic rings from Wistar rats which were precontracted with phenylephrine (PHE) (1 µM) or KCl (60 mM). The major constituents of TAEO included Thymol (38.1%), gamma-terpinene (33.3%), and p-cymene (23.1%), as was analyzed by GC-MS. The cumulative concentrations of TAEO reduced precontraction caused by PHE and KCl (p < 0.05) significantly, which was dose dependent. The vasorelaxation caused by TAEO was not influenced in the presence of methylene blue and L-NAME in the endothelium-intact and denuded aorta ring. The inhibitory effect of TAEO on the aortic rings precontracted with KCl and PHE was considerably reduced by nifedipine. These findings hypothesized that the vasorelaxation caused by TAEO is completely endothelium independent and the extracellular Ca²⁺ influx was also inhibited by TAEO.

Calcium influx inhibition is involved in the hypotensive and vasorelaxant effects induced by yangambin

The pharmacological effects on the cardiovascular system of yangambin, a lignan isolated from Ocotea duckei Vattimo (Lauraceae), were studied in rats using combined functional and biochemical approaches. In non-anaesthetized rats, yangambin (1, 5, 10, 20, 30 mg/kg, i.v.) induced hypotension (−3.5 ± 0.2; −7.1 ± 0.8; −8.9 ± 1.3; −14 ± 2.3, −25.5% ± 2.6%, respectively) accompanied by tachycardia (5.9 ± 0.5; 5.9 ± 1.6; 8.8 ± 1.4; 11.6, 18.8% ± 3.4%, respectively). In isolated rat atria, yangambin (0.1 µM–1 mM) had very slight negative inotropic (Emax = 35.6% ± 6.4%) and chronotropic effects (Emax = 10.2% ± 2.9%). In endothelium-intact rat mesenteric artery, yangambin (0.1 µM–1 mM) induced concentration-dependent relaxation (pD₂ = 4.5 ± 0.06) of contractions induced by phenylephrine and this effect was not affected by removal of the endothelium. Interestingly, like nifedipine, the relaxant effect induced by yangambin was more potent on the contractile response induced by KCl 80 mM (pD₂ = 4.8 ± 0.05) when compared to that induced by phenylephrine. Furthermore, yangambin inhibited CaCl₂-induced contractions in a concentration-dependent manner. This lignan also induced relaxation (pD₂ = 4.0 ± 0.04) of isolated arteries pre-contracted with S(−)-Bay K 8644. In fura-2/AM-loaded myocytes of rat mesenteric arteries, yangambin inhibited the Ca²⁺ signal evoked by KCl 60 mM. In conclusion, these results suggest that the hypotensive effect of yangambin is probably due to a peripheral vasodilatation that involves, at least, the inhibition the Ca²⁺ influx through voltage-gated Ca²⁺ channels.

Polyphenols from Parabarium huaitingii and their positive inotropic and anti-myocardial infarction effects in rats

Eight phenolic compounds, including (-)-epicatechin (1) and seven proanthocyanidins (2-8), were obtained from the butanol extract of Parabarium huaitingii (PHB). Their chemical structures were identified based on analyses of mass spectra (MS), NMR, CD spectra, and partial acid catalyzed thiolytic degradation. The observation made by laser scanning confocal microscope found a significant increase of the concentration of intracellular Ca²+ ([Ca²+](i)) in single myocytes when the PHB was added, while compounds 1 and 3 had the same physiological effect. Further investigations showed PHB had a dose-dependent positive inotropic effect on isolated right atria and papillary muscle of left ventricle of the rat, while having no significant influence on the spontaneous beating rate of the isolated right atria. The inotropic effect of PHB could be greatly abolished by pretreating the myocardium in Ca²+-free solution. These findings indicated that PHB could significantly increase [Ca²+](i) in myocytes, which was greatly dependent on the influx of extracellular Ca²+. Compounds 1 and 3 might be the effective ingredients of the inotropic effect of PHB. In addition, PHB could also significantly decrease the infarct size of the heart on acute myocardial infarction (AMI) model rats, which suggested its myocardial protective effect on ischemic myocardium. The positive inotropic effect of PHB, together with its myocardial protective effect on AMI, suggested that PHB had a promising potential for the prevention and treatment of heart failure, especially the one that was caused by AMI.

Hypotensive and endothelium-independent vasorelaxant effects of methanolic extract from Curcuma longa L. in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Curcuma longa L. (CL) is a yellow rhizome that is used in African traditional medicine to treat palpitation, hypertension or other related blood circulation disorders.

AIM OF THE STUDY

To justify the use of CL in ethnomedicine, we investigated the vasorelaxant effect of methanolic extract of CL (CLME) and its underlying mechanisms in isolated rat mesenteric artery.

MATERIALS AND METHODS

The effect of CLME on the mean arterial pressure (MAP) and heart rate (HR) (pulse interval) were determined in vivo in non-anaesthetized rats. Superior mesenteric rings were isolated, suspended in organ baths containing Tyrode solution at 37 degrees C and gassed with 95% O(2)+5% CO(2), under a resting tension of 0.75 g. The vasorelaxant effects of CLME were studied by means of isometric tension recording experiments.

RESULTS

In normotensive rats, CLME (10, 20 and 30 mg/kg, i.v.) induced dose-dependent hypotension (2.0+/-0.5%; 27.1+/-5.0% and 26.7+/-4.6%, respectively), and pronounced bradycardia (5.8+/-1.2%, 19.3+/-3.2% and 22.9+/-4.6%, respectively). CLME (1-1000 microg/mL) induced concentration-dependent relaxation of tonic contractions evoked by phenylephrine (Phe) (10 microM) and KCl (80 mM) in rings with intact-endothelium (E(max)=82.3+/-3.2% and 97.7+/-0.7%) or denuded-endothelium (E(max)=91.4+/-1.0% and 97.8+/-1.1%). Also, in a depolarized, Ca(2+) free medium, CLME inhibited CaCl(2) (1 microM-30 mM)-induced contractions and caused a concentration-dependent rightward shift of the response curves, indicating that CLME inhibited the contractile mechanisms involving extracellular Ca(2+) influx. In addition, in Ca(2+) free media containing EGTA (1 mM), CLME inhibited the transient contraction of denuded rings constricted with Phe, but not those evoked by caffeine (20 mM). In contrast, neither glibenclamide, BaCl(2), tetraethylammonium nor 4-aminopyridine affected CLME-induced relaxation.

CONCLUSIONS

These results demonstrate the hypotensive and bradycardic effects of CLME, as well as its potent vasodilation of rat mesenteric arteries. These effects, may in part, be due to the inhibition of extracellular Ca(2+) influx and/or inhibition of intracellular Ca(2+) mobilization from Phe-sensitive stores.

Calcium antagonism and the vasorelaxation of the rat aorta induced by rotundifolone

The vasorelaxing activity of rotundifolone (ROT), a major constituent (63.5%) of the essential oil of Mentha x villosa, was tested in male Wistar rats (300-350 g). In isolated rat aortic rings, increasing ROT concentrations (0.3, 1, 10, 100, 300, and 500 microg/ml) inhibited the contractile effects of 1 microM phenylephrine and of 80 or 30 mM KCl (IC50 values, reported as means +/- SEM = 184 +/- 6, 185 +/- 3 and 188 +/- 19 microg/ml, N = 6, respectively). In aortic rings pre-contracted with 1 microM phenylephrine, the smooth muscle-relaxant activity of ROT was inhibited by removal of the vascular endothelium (IC50 value = 235 +/- 7 microg/ml, N = 6). Furthermore, ROT inhibited (pD2 = 6.04, N = 6) the CaCl2-induced contraction in depolarizing medium in a concentration-dependent manner. In Ca2+-free solution, ROT inhibited 1 microM phenylephrine-induced contraction in a concentration-dependent manner and did not modify the phasic contractile response evoked by caffeine (20 mM). In conclusion, in the present study we have shown that ROT produces an endothelium-independent vasorelaxing effect in the rat aorta. The results further indicated that in the rat aorta ROT is able to induce vasorelaxation, at least in part, by inhibiting both: a) voltage-dependent Ca2 channels, and b) intracellular Ca2+ release selectively due to inositol 1,4,5-triphosphate activation. Additional studies are required to elucidate the mechanisms underlying ROT-induced relaxation.

Endothelium-dependent hypotensive and vasorelaxant effects of the essential oil from aerial parts of Mentha x villosa in rats

Cardiovascular effects of an essential oil from the aerial parts of Mentha x villosa (OEMV) were tested in rats using a combined in vivo and in vitro approach. In non-anesthetized normotensive rats, OEMV (1, 5, 10, 20, 30 mg kg(-1) body wt., i.v.) induced a significant and dose-dependent hypotension (-3 +/- 1.8%; -6 +/- 0.7%; -40 +/- 6.7%; -58 +/- 3.8%; -57 +/- 2.1%, respectively) associated with decreases in heart rate (-1 +/- 0.3%; -9 +/- 0.9%; -17 +/- 3.2%; -72 +/- 3.1%; -82 +/- 1.4%, respectively). The hypotensive and bradycardic responses evoked by OEMV were attenuated and blocke by pre-treatment of the animals with atropine (2 mg kg(-1) body wt., i.v.). In isolated rat atrial preparations, OEMV (10, 100, 300, 500 microg ml(-1)) produced concentration-related negative chronotropic and inotropic effects (IC50 value = 229 +/- 17 and 120 +/- 13 microg ml(-1), respectively). In isolated rat aortic rings, increasing concentrations of OEM (10, 100, 300, 500 microg ml(-1)) were able to antagonize the effects of phenylephrine (1 microM), prostaglandin F2alpha (10 microM) and KCl (80 mM)-induced contractions (IC50 value = 255 +/- 9, 174 +/- 4 and 165 +/- 14 microg ml(-1), respectively). The vasorelaxant activity induced by OEMV was attenuated significantly by either endothelium removal (IC50 value = 304 +/- 9 microg ml(-1)), NG-nitro L-arginine methyl ester (L-NAME) 100 microM (IC50 value=359 +/- 18 microg ml(-1)), L-NAME 300 microM (IC50 value = 488 +/- 20 microg ml(-1)) or indomethacin 10 microM (IC50 value = 334 +/- 18 microg ml(-1)). However, it was not affected by atropine 1 microM (IC50 value = 247 +/- 12 microg ml(-1)). Furthermore, the hypotensive response induced by OEMV was attenuated significantly after nitric oxide (NO) synthase blockade (L-NAME, 20 mg kg(-1) body wt., i.v.), while bradycardia was not altered. The results suggest that the hypotensive effect induced by OEMV is probably due to its direct cardiodepressant action and peripheral vasodilation, which can be attributed to both endothelium-dependent (via EDRFs, at least NO and prostacyclin) and endothelium-independent mechanisms (such as Ca2+ channel blockade).

Calcium mobilization as the endothelium-independent mechanism of action involved in the vasorelaxant response induced by the aqueous fraction of the ethanol extract of Albizia inopinata G. P. Lewis (AFL) in the rat aorta

In a previous work, we demonstrated that, in normotensive rats, AFL induced a marked hypotension due to a decrease in total peripheral resistances (TPR), partially secondary to the release of NO by the endothelium. NO did not, however, account for the total vasodilation produced by AFL in these rats. The aim of this study was to determine the involvement of the intracellular calcium mobilization in the vasorelaxant action induced by AFL in the rat aorta. In aorta of normotensive rats AFL (10, 20, 40 and 80 microg/ml) inhibited the sustained contractions induced by KCl (80 and 30 mM) and phenylephrine (Phe, 1 microM) with similar IC50 values (54 +/- 6, 52 +/- 4 and 65 +/- 4 microg/ml, respectively). The relaxing response induced by AFL against Phe-induced contractions was modified significantly by the endothelium removal (IC50 = 132 +/- 23 and 65 +/- 4 microg/ml, endothelium removed and intact endothelium aortic rings, respectively). Nevertheless, removal of the endothelium did not significantly change IC50 values when KCl (30 and 80 mM) was used as the contractile agent. The inhibitory effect induced by AFL on high (64.5 mM) K+-induced contraction was potentiated slightly (p < 0.05) by the decrease (from 2.5 to 0.3 mM, Ca2+) and attenuated by the increase (from 2.5 to 7.5 mM Ca2+) in the external [Ca2+]. In addition, in aortas from normotensive rats, AFL antagonized transient contractions induced in Ca2+-free media induced by 1 microM noradrenaline in a concentration-dependent manner, but not those induced by 20 mM caffeine. It is suggested that the remaining vasodilator effect of AFL in normotensive rats is probably due to an inhibition of Ca2+ influx and/or inhibition of intracellular Ca2+ mobilization from the noradrenaline-sensitive stores.

Endothelium-derived nitric oxide is involved in the hypotensive and vasorelaxant responses induced by the aqueous fraction of the ethanolic extract of the leaves of Albizia inopinata (Harms) G. P. Lewis in rats

The acute cardiovascular effects of an aqueous fraction of the ethanolic extract of the leaves (AFL) of Albizia inopinata (Harms) G. P. Lewis (Leguminosae) were studied in rats using a combined in vivo and in vitro approach. In conscious, unrestrained rats, AFL (5, 10 and 20 mg/kg(-1) body wt. i.v., randomly) produced a significant and dose-dependent hypotension associated with increases in heart rate and cardiac output, and with a strong reduction in total peripheral resistances. The hypotensive response to AFL (20 mg/kg(-1) body wt.) was attenuated significantly after nitric oxide (NO) synthase blockade (L-NAME, 20 mg/kg(-1) body wt. i.v.). Furthermore, under these conditions, the associated tachycardia was inhibited completely. In isolated rat aortic rings, increasing concentrations of AFL (10, 20, 40 and 80 microg/ml(-1)) were able to antagonize the effects of phenylephrine- (1 microM) and KCl- (80 mM) induced contractions (IC50 value 65 +/- 4 and 54 +/- 6 microg/ml(-1), respectively). The smooth muscle-relaxant activity of AFL was inhibited similarly either removal of the vascular endothelium or by L-NAME (10 and 100 microM), but was not affected significantly by atropine (1 microM) or indomethacin (10 microM). In isolated rat atrial preparations, AFL (30, 100, 300 and 500 microg/ml(-1)) produced concentration-related negative inotropic and chronotropic effects (IC50 value = 274 +/- 53 and 335 +/- 23 microg/ml(-1), respectively). These results suggest that in rats, the hypotensive effect of AFL is due to a peripheral vasodilation, at least partly secondary to the release of NO by the vascular endothelium. The direct cardio-depressant actions of AFL are of little importance in the systemic effects of the extract.

Both D-cis- and L-cis-diltiazem attenuate hydrogen peroxide-induced derangements in rat hearts

The effects of D-cis- and L-cis-diltiazem on the hydrogen peroxide (H2O2)-induced derangements of mechanical function and energy metabolism, and accumulation of intracellular Na+ were studied in isolated rat hearts. The intracellular concentration of Na+ ([Na+]i) in the myocardium was measured using a nuclear magnetic resonance technique. H2O2 (600 microM) increased the left ventricular end-diastolic pressure, decreased the tissue level of ATP, and increased the release of lactate dehydrogenase from the myocardium. These alterations induced by H2O2 were significantly attenuated by D-cis-diltiazem (15 microM) or L-cis-diltiazem (15 microM). H2O2 (1 mM) produced a marked increase in the myocardial [Na+]i, which was effectively inhibited by tetrodotoxin (3 microM), D-cis-diltiazem (15 microM) or L-cis-diltiazem (15 microM). These results suggest that both D-cis- and L-cis-diltiazem protect the myocardium against the H2O2-induced derangements in the isolated, perfused rat heart. The protective action of D-cis- and L-cis-diltiazem may be due to their ability to inhibit the H2O2-induced increase in [Na+]i, at least in part.

Palmitoyl-L-carnitine modifies the myocardial levels of high-energy phosphates and free fatty acids

Long-chain acylcarnitines, such as palmitoyl-L-carnitine (PALCAR), are known to accumulate in the myocardium during ischemia. We examined whether exogenous PALCAR modifies the myocardial levels of high-energy phosphates (HEP) and free fatty acids (FFA) in the heart, and whether d-cis-diltiazem and l-cis-diltiazem, an optical isomer having less potent Ca2+ channel blocking action than d-cis-diltiazem, attenuate the PALCAR-induced myocardial changes. Rat hearts were perfused aerobically at a constant flow according to the Langendorff's technique, while being paced electrically. PALCAR (5 microM) decreased the tissue levels of adenosine triphosphate and creatine phosphate and increased the tissue level of adenosine monophosphate, and produced mechanical dysfunction. In addition, PALCAR (5 microM) increased markedly the tissue levels of FFA, especially those of arachidonic and palmitoleic acids, and the release of creatine kinase (CK) from the myocardium. These alterations in the myocardial levels of HEP and FFA induced by PALCAR were significantly attenuated by d-cis-diltiazem (15 microM) or l-cis-diltiazem (15 microM). Both drugs also attenuated the PALCAR-induced CK release. The present study demonstrates that PALCAR modifies the tissue levels of HEP and FFA in the heart and that both d-cis- and l-cis-diltiazem protect the myocardium against the PALCAR-induced changes through mechanisms other than Ca2+ channel blocking action.

A non-invasive vibrating calcium-selective electrode measures acetylcholine-induced calcium flux across the sarcolemma of a smooth muscle

To determine possible sources of Ca2+ during excitation-contraction coupling in smooth muscle, a vibrating Ca2(+)-selective electrode was used to measure Ca2+ flux during the process of contraction. The smooth muscle model was the longitudinal muscle of the body wall of a sea cucumber Sclerodactyla briareus. Because acetylcholine caused slow contractions of the muscle that were inhibited by Ca2+ channel blockers diltiazem and verapamil in earlier mechanical studies, we chose a vibrating Ca2(+)-selective electrode as our method to test the hypothesis that acetylcholine may be stimulating Ca2+ influx across the sarcolemma, providing a Ca2+ source during excitation-contraction coupling. Acetylcholine treatment stimulated a net Ca2+ efflux that was both dose and time dependent. We then tested two L-type Ca2+ channel blockers, diltiazem and verapamil, and two non-specific Ca2+ blockers, cobalt (Co2+) and lanthanum (La3+) on acetylcholine-induced Ca2+ flux. All four Ca2+ blockers tested potently inhibited Ca2+ efflux induced by physiological doses of acetylcholine. We propose that the acetylcholine-induced Ca2+ efflux was the result of, first, Ca2+ influx through voltage-sensitive L-type Ca2+ channels, then the rapid extrusion of Ca2+ by an outwardly directed carrier such as the Na-Ca exchanger as suggested by Li+ substitution experiments. The vibrating Ca2+ electrode has provided new insights on the active and complex role the sarcolemma plays in Ca2+ homeostasis and regulating Ca2+ redistribution during excitation-contraction coupling.