Comparison of Nicardipine Versus Esmolol in Attenuating the Hemodynamic Responses to Anesthesia Emergence and Extubation

OBJECTIVE

The purpose of this study was to compare the effectiveness of intravenous (IV) nicardipine versus esmolol in controlling heart rate (HR) and blood pressure (BP) responses to emergence and extubation.

DESIGN

Prospective, randomized, double blind.

SETTING

University hospital, single institution.

PARTICIPANTS

Twenty-two American Society of Anesthesiologists physical class 1 to 3 adult inpatients scheduled for general anesthesia.

INTERVENTIONS

General endotracheal anesthesia with oxygen/isoflurane and muscle relaxation. At end of surgery, with at least 2 twitches by nerve stimulator and end-tidal isoflurane <0.4%, muscle relaxant reversal was accomplished with neostigmine and glycopyrrolate. Two minutes postreversal, the IV study drug nicardipine, 0.03 mg/kg, or esmolol, 1.5 mg/kg, was administered. HR and BP were measured every minute up to 10 minutes and at minute 15 postreversal.

MEASUREMENTS AND MAIN RESULTS

There were no significant differences between groups in age, weight, gender, American Society of Anesthesiologists physical class or preoperative hemodynamics (HR, BP, mean arterial pressure [MAP]). Compared with nicardipine, 0.03 mg/kg IV, esmolol, 1.5 mg/kg IV, significantly (p < 0.05) attenuated HR more than nicardipine for the 15-minute time period poststudy drug. Compared with esmolol, nicardipine was significantly (p < 0.05) more effective in controlling MAP and systolic BP for the 1- to 3-minute and diastolic BP for the 1- to 2-minute time periods poststudy drug. There were no episodes of hypotension or adverse events.

CONCLUSIONS

Although esmolol, 1.5 mg/kg, IV was more effective than nicardipine, 0.03 mg/kg, IV for attenuating the HR response to extubation, nicardipine was more effective in controlling the BP response.

Intravenously administered vasodilatory prostaglandins increase retinal and choroidal blood flow in rats

We established an experimental system for measuring blood flow in the rat fundus and examined whether intravenously administered vasodilatory prostaglandins (PGE(1), PGE(2), and PGI(2)), 8-(4-chlorophenylthio)-cAMP (a cAMP analogue), and nicardipine (a Ca(2+)-channel blocker) increase fundus blood flow (FBF). Under artificial ventilation, rats were injected with tetrodotoxin (50 microg/kg, i.v.) to eliminate any nerve activity and prevent movement of the eye. After tetrodotoxin, the rats were infused with norepinephrine (0.3 - 0.5 microg . kg(-1) . min(-1)) and epinephrine (2.7 - 4.5 microg . kg(-1) . min(-1)) simultaneously to maintain adequate systemic circulation. We found that intravenous infusion of PGE(1) (2 - 10 microg . kg(-1) . min(-1)), PGE(2) (3 - 30 microg . kg(-1) . min(-1)), and PGI(2) (1 - 10 microg . kg(-1) . min(-1)) increased the FBF in a dose-dependent manner. The vasodilatory PGs decreased arterial pressure, whereas they did not affect heart rate. Like vasodilatory PGs, 8-(4-chlorophenylthio)-cAMP (30 micromol/kg, i.v.) increased FBF and decreased arterial pressure. While infusion of nicardipine (0.3 - 3 microg . kg(-1) . min(-1)) produced comparable depressor responses with those to vasodilatory PGs and the cAMP analogue, it did not increase FBF. These results suggest that vasodilatory PGs and cAMP act more selectively than Ca(2+)-channel blockers on retinal/choroidal blood vessels. Therefore, the vasodilatory PGs might be considered to be possible candidates for the therapeutics to treat disorders of retinal/choroidal circulation.

Assessment of the Effects of L- and N-Type Ca2+ Channel Blocking Drugs Using Canine Blood-Perfused Papillary Muscle Preparations

It is important to accurately and conveniently assess the effects of L- and N-type Ca(2+) channel blocking drugs, which are commonly used for treatment of hypertension, but no method is available to simultaneously assess the effects of them in the same preparation. We have therefore designed an ex vivo method to measure the changes in contractile response of anterior papillary muscle of right ventricle and myocardial interstitial norepinephrine (NE) level using canine blood-perfused papillary muscle preparations. Papillary muscle-developed tension (PMDT) induced by an electronic stimulator was measured with force transducer. Myocardial interstitial NE effluent was collected by microdialysis fiber, which was implanted at the base of the papillary muscle, and measured with high performance liquid chromatography. Cilnidipine, a typical L- and N-type Ca(2+) channel blocker, was used to prove the efficiency of this method. First, to assess the effects of drugs on L-type Ca(2+) channel, the changes in basal PMDT were measured. Cilnidipine and nicardipine, a selective L-type Ca(2+) channel blocker, but not omega-conotoxin GVIA (omega-CTX), a selective N-type Ca(2+) channel blocking peptide, decreased basal PMDT dose-dependently. Second, to assess the effects of drugs on N-type Ca(2+) channel, the changes in PMDT and myocardial interstitial NE level by intracardiac sympathetic ganglion stimulation were measured. Cilnidipine and omega-CTX, but not nicardipine, dose-dependently reduced sympathomimetic increases in PMDT and myocardial interstitial NE level. These results indicate that our method is efficient to assess the effects of various L- and N-type Ca(2+) channel blocking drugs in the same papillary muscle preparation.

Autoantibody-mediated Bladder Dysfunction in Type 1 Diabetes

Bladder dysfunction is a common complication of diabetic autonomic neuropathy; however, its cause remains uncertain. We have recently identified a novel IgG autoantibody (Ab) in patients with type 1 diabetes that acts as an agonist at the dihydropyridine (DHP) site of L-type voltage-gated calcium channels (VGCC), disrupting neuronal regulation of visceral smooth muscle. In the present study, passive transfer to mice of IgG from patients with type 1 diabetes was used to investigate the role of anti-VGCC Abs in mediating diabetic bladder dysfunction. Injection of mice with diabetic immunoglobulin (IgG) with anti-VGCC activity induced features of an overactive bladder, including phasic detrusor contractions and a loss of bladder wall compliance. The bladder overactivity is mimicked by the DHP agonist Bay K8644, reversed by the DHP antagonist nicardipine, but is insensitive to the motor nerve blocker tetrodotoxin, indicating that the anti-VGCC Ab acts at the level of the bladder detrusor itself. This study reports the first evidence of Ab-mediated bladder dysfunction in type 1 diabetes, which may be part of a wider spectrum of smooth muscle and cardiac abnormalities.

INDUCTION OF HEPATIC CYTOCHROME P450 ISOFORMS BY NICARDIPINE AT THERAPEUTIC DOSES IN SPONTANEOUSLY HYPERTENSIVE RATS

Nicardipine hydrochloride (Nic), a calcium channel antagonist, is used for the treatment of hypertension. In the present study, we estimated its effects on the levels and activities of hepatic cytochrome P450 isoforms in spontaneously hypertensive rats given p.o. with Nic at a dose of 0.5, 2.5, 5, or 12.5 mg/kg at 24-hr intervals for 14 days. Therapeutic effects on the development of hypertension were observed at doses of 5 and 12.5 mg/kg/day. Significant increases in the levels of mRNAs and enzyme activities of hepatic P450 isoforms, CYP1A1 and/or CYP1A2, by 14-day repetitive treatment with Nic were observed at lower therapeutic doses, whereas the increase in protein levels for CYP1A2 was observed at a higher therapeutic dose of 12.5 mg/kg/day. Likewise, the activities of hepatic CYP2B and CYP3A subfamily enzymes were increased by the 14-day-treatment of Nic only at a therapeutic dose (12.5 mg/kg/day), whereas their mRNA and protein levels were increased at lower therapeutic doses. To date, the dihydropyridine family, including Nic, has been believed to have inhibitory effects on the activity of various cytochrome P450 enzymes, especially human CYP3A4. However, the present findings demonstrate for the first time that Nic-repetitive treatments at a therapeutic dose result in significant increases in the expressions and activities of hepatic CYP1A, CYP2B, and CYP3A subfamily enzymes. Therefore, the effects of dihydropyridine family on cytochrome P450 enzymes have to be further validated to provide information on its safe and beneficial therapeutic application.

[Vasorelaxant effect of sulfur dioxide derivatives on isolated aortic rings of rats and its mechanisms]

OBJECTIVE

To investigate the vasorelaxant effect of sulfur dioxide (SO(2)) on isolated aortic rings of rats in vitro and its relaxation mechanisms.

METHODS

We perffused the isolated aortic rings of rats, and precontracted the rings with noradrenaline (NE), then observed the relaxant reactivity of SO(2) derivatives, mixture of sulfite and hydrogen sulfite [Na(2)SO(3)/NaHSO(3) 3:1(amount of substance)], to the aortic rings. Meanwhile, we studied the influence of glibenclamide and nicardipine, blockers of K(ATP) and L-calcium channels, on the vasorelaxant reactivity of SO(2) derivatives. We further incubated the aortic rings with hydroxamate (HDX), the inhibitor of SO(2) endogenous generating enzymes, and SO(2) derivatives (4 mmol/L) in vitro, then observed the contraction of the aortic rings to NE.

RESULTS

Isolated aortic rings of rats exhibited relaxant reactivity to Na(2)SO(3)/NaHSO(3) (0-12 mmol/L) in a concentration-dependent manner. IC(50) of the relaxation curve was (7.28+/-0.12) mmol/Lìand Emax was 78.79%+/-3.24%. Glibenclamide (1x10(-6) mol/L) inhibited the vasorelaxation to low dose Na(2)SO(3)/NaHSO(3) (<or=4 mmol/L), whereas it failed to inhibit the vasorelaxation to high dose of Na(2)SO(3)/NaHSO(3) (>6 mmol/L). Nicardipine (1x10(-9) mol/L) could decrease the contraction of the rings to NE, and even could inhibit the relaxation of Na(2)SO(3)/NaHSO(3) almost completely. The inhibition of the endogenous SO(2) production with HDX (1x10(-4) mol/L), resulted in an increase in the contraction of rings. The contraction curve to NE shifted to the left, and IC(50) also changed from (6.48+/-0.84)x10(-7) mol/L to (3.97+/-1.63)x10(-7) mol/L (P<0.01). However, after the incubation of aortic rings with Na(2)SO(3)/NaHSO(3) (4 mmol/L), the contraction curve to NE shifted to the right, and IC(50) changed from (6.48+/-0.84)x10(-7) mol/L to (4.93+/-0.81)x10(-5) mol/L (P<0.01).

CONCLUSION

SO(2) could relax vascular smooth muscles, and the mechanism might be associated with calcium channels and K(ATP) channels, suggesting that endogenous SO(2) could modulate the cardiovascular function.

Differential Modulation of 7-Ketocholesterol Toxicity Against PC12 Cells by Calmodulin Antagonists and Ca2+ Channel Blockers

The present study assessed the influence of intracellular Ca2+ and calmodulin against the neurotoxicity of oxysterol 7-ketocholesterol in relation to the mitochondria-mediated cell death process and oxidative stress in PC12 cells. Calmodulin antagonists calmidazolium and W-7 prevented the 7-ketocholesterol-induced mitochondrial damage, leading to caspase-3 activation and cell death, whereas Ca2+ channel blocker nicardipine, mitochondrial Ca2+ uptake inhibitor ruthenium red, and cell permeable Ca2+ chelator BAPTA-AM did not reduce it. Exposure of PC12 cells to 7-ketocholesterol caused elevation of intracellular Ca2+ levels. Unlike cell injury, calmodulin antagonists, nicardipine, and BAPTA-AM prevented the 7-ketocholesterol-induced elevations of intracellular Ca2+ levels. The results show that the cytotoxicity of 7-ketocholesterol seems to be modulated by calmodulin rather than changes in intracellular Ca2+ levels. Calmodulin antagonists may prevent the cytotoxicity of 7-ketocholesterol by suppressing the mitochondrial permeability transition formation, which is associated with the increased formation of reactive oxygen species and the depletion of GSH.

L-type calcium current reactivation contributes to arrhythmogenesis associated with action potential triangulation

INTRODUCTION

The morphology of the mammalian cardiac action potential (AP) is an important factor in the susceptibility to drug-induced early afterdepolarizations (EADs) that may initiate torsade de pointes (TdP). AP triangulation has been shown to be an important predictor of drug-induced TdP.

METHODS AND RESULTS

APs from guinea pig and rabbit left ventricular single myocytes were recorded using a microelectrode-recording technique. I(Ca-L) currents were recorded in ventricular myocytes of guinea pig and rabbit using patch-clamping technique. At a stimulus frequency of 0.5 Hz, guinea pig ventricular myocytes displayed a square-like AP, whereas rabbit ventricular myocytes exhibited a triangle-like AP. Dofetilide-induced EADs were observed only in rabbit ventricular myocytes. Under the guinea pig AP clamping condition, the normalized I(Ca-L) instant reactivation currents in guinea pig and rabbit myocytes at voltages of -40 mV were 0.13 +/- 0.01 and 0.14 +/- 0.01, respectively. However, when rabbit AP served as the first clamping voltage, the normalized I(Ca-L) reactivation currents at -40 mV in guinea pig and rabbit myocytes were 0.20 +/- 0.01, 0.21 +/- 0.01, respectively, indicating that the I(Ca-L) recovery from inactivation in the rabbit triangular AP condition was significantly faster than in the guinea pig square AP condition. Comparison of the voltage clamp using the triangular waveform with the square waveform further confirmed that triangulation accelerates I(Ca-L) recovery from inactivation.

CONCLUSIONS

In rabbit ventricular myocardium, AP triangulation accelerates I(Ca-L) channel recovery from inactivation, leading to instability of the cell membrane potential during repolarization, which is capable of initiating TdP.

Improvement of Donor Myocardial Function after Treatment of Autonomic Storm During Brain Death

BACKGROUND

In experimental brain death models, autonomic storm (AS) triggers severe myocardial dysfunction, which can be attenuated by pharmacologic treatment. The aim of this study was to determine the incidence of AS in a cohort of human organ donors and to evaluate the potential interest of AS treatment on myocardial function, cardiac harvesting and transplantation.

METHODS

The cohort consisted of 152 patients. Among them, 46 patients were initially considered as potential cardiac donors (main criteria: age < 60 years, no history of cardiac disease). AS diagnosis included increased systolic arterial pressure > 200 mm Hg associated with tachycardia >140 beats/min. Heart acceptance criteria were associated creatine kinase (CK), troponin Ic, and left ventricle ejection fraction (LVEF) estimated by echocardiography and visual inspection.

RESULTS

AS was observed in 29 patients (63%). Hypertension was treated in 12 patients (esmolol n = 6, urapidil n = 5, nicardipine). Cardiac harvesting was performed in 28 donors (61%). LVEFs were significantly higher after AS treatment (no AS: 55.4 +/- 13.4%, untreated AS: 49.0 +/- 18.8%, treated AS: 63.9+ +/- 10.3%, P = 0.049). AS treatment was found to be independently associated with LVEF in > 50% of the cases (P = 0.034). Treatment of AS or the lack of AS were associated with an increased probability of successful cardiac transplantation (OR = 8.8; 95% CI 2.1-38.3, P = 0.002).

CONCLUSIONS

Treatment of hypertension during AS may attenuate brain death-induced myocardial dysfunction and increase the number of available cardiac grafts.

Role of calcium channels in cadmium-induced disruption of cortisol synthesis in rainbow trout (Oncorhynchus mykiss)

The mechanisms of toxicity of cadmium (Cd(2+)) in adrenal steroidogenesis were investigated in vitro in adrenocortical cells of rainbow trout (Oncorhynchus mykiss). Toxicity of Cd(2+) was increased in absence of extracellular Ca(2+), but was prevented in Ca(2+)-supplemented medium. Pretreatment of cells with BAY K8644 (BAY), an agonist of voltage-dependent calcium channels, increased the Cd(2+)-mediated inhibition of ACTH-stimulated secretion but not pregnenolone (PREG)-stimulated secretion. Nicardipine, an antagonist of voltage-dependent calcium channels, also increased the inhibition of adrenocorticotropic hormone (ACTH)-stimulated secretion by Cd(2+). These results suggest that opening of voltage-dependent calcium channels with BAY may allow Cd(2+) entry at the same time as calcium, thus increasing toxicity of Cd(2+), however voltage-dependent calcium channels may not be the only way of entry into adrenocortical cells. The influx of Cd(2+), measured as intracellular Cd(2+) using Fluo-3 in PREG-stimulated adrenocortical cells, was significantly enhanced by the stimulation. These results suggest that the deleterious effect of Cd(2+) on cortisol steroidogenesis may be enhanced when the endocrine stress response is triggered.

The suppressant effect of GEA3162 on spontaneous serotonin release from human colonic mucosa in vitro

The effect of a lipophilic nitric oxide (NO)-releasing compound 5-amino-3-(3,4-dichlorophenyl) 1,2,3,4-oxatriazolium (GEA3162) on the spontaneous release of 5-hydroxytryptamine (5-HT) from human colonic mucosa was investigated in vitro. In the presence of tetrodotoxin, spontaneous outflow of 5-HT from the human colonic mucosa was measured by high-performance liquid chromatography with electrochemical detection. GEA3162 concentration-dependently suppressed the 5-HT outflow, but neither the NO-activated soluble guanylate cyclase inhibitor 1H-[1,2,4]-oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) nor peroxynitrite scavenger ebselen affected the suppressant effect of GEA3162. Moreover, neither the L-type calcium channel blocker nicardipine, NO synthase inhibitor l-N(G)-nitroarginine methyl ester nor guanylate cyclase activator guanylin affected the spontaneous 5-HT outflow. These results indicate that human colonic mucosa is capable of eliciting tetrodotoxin-resistant and nicardipine-insensitive 5-HT release, and that GEA3162 can suppress the 5-HT release via an action on colonic mucosa through mechanism independent of ODQ-sensitive cyclic GMP system or peroxynitrite generation.

The calcium channel blockers, 1,4-dihydropyridines, are substrates of the multidrug resistance-linked ABC drug transporter, ABCG2

The human ATP-binding cassette transporter, ABCG2, confers resistance to multiple chemotherapeutic agents and also affects the bioavailability of different drugs. [(125)I]Iodoarylazidoprazosin (IAAP) and [(3)H]azidopine were used for photoaffinity labeling of ABCG2 in this study. We show here for the first time that both of these photoaffinity analogues are transport substrates for ABCG2 and that [(3)H]azidopine can also be used to photolabel both wild-type R482-ABCG2 and mutant T482-ABCG2. We further used these assays to screen for potential substrates or modulators of ABCG2 and observed that 1,4-dihydropyridines such as nicardipine and nifedipine, which are clinically used as antihypertensive agents, inhibited the photolabeling of ABCG2 with [(125)I]IAAP and [(3)H]azidopine as well as the transport of these photoaffinity analogues by ABCG2. Furthermore, [(3)H]nitrendipine and bodipy-Fl-dihydropyridine accumulation assays showed that these compounds are transported by ABCG2. These dihydropyridines also inhibited the efflux of the known ABCG2 substrates, mitoxantrone and pheophorbide-a, from ABCG2-overexpressing cells, and nicardipine was more potent in inhibiting this transport. Both nicardipine and nifedipine stimulated the ATPase activity of ABCG2, and the nifedipine-stimulated activity was inhibited by fumitremorgin C, suggesting that these agents might interact at the same site on the transporter. In addition, nontoxic concentrations of dihydropyridines increased the sensitivity of ABCG2-expressing cells to mitoxantrone by 3-5-fold. In aggregate, results from the photoaffinity labeling and efflux assays using [(125)I]IAAP and [(3)H]azidopine demonstrate that 1,4-dihydropyridines are substrates of ABCG2 and that these photolabels can be used to screen new substrates and/or inhibitors of this transporter.

Radix angelica elicits both nitric oxide-dependent and calcium influx-mediated relaxation in rat aorta

This study examined the vascular relaxation produced by Radix Angelica (AG; Dong Quai) and its possible mechanisms in isolated rat aortic rings precontracted with norepinephrine. The butanolic fraction (AgBt) of the crude extract of AG causes gradual endothelium-independent relaxation, which was unaffected by five different potassium channel inhibitors. AgBt attenuated the CaCl2-induced vasoconstriction in high-potassium depolarized medium; this required less than one-tenth the concentration needed to elicit vascular relaxation. An aqueous fraction (AgDw) of the crude extract induced transient acute relaxation, which was virtually abolished by endothelial ablation and pretreatment with L-NNA. L-Arginine fully reversed the action of L-NNA. Methylene blue and atropine significantly attenuated the relaxation, but indomethacin did not. Ferulic acid, the main active component in AG, relaxed both endothelium-intact and -denuded rings, while L-NNA, methylene blue, or atropine did not modify the relaxation. Ferulic acid also did not attenuate the CaCl2-induced contraction in high-potassium depolarized medium. In conclusion, Radix Angelica leads to both endothelium-dependent and -independent relaxation of isolated rat aorta. Increased formation of NO might contribute to the endothelium-mediated relaxation, while inhibition of the calcium influx might be an important mechanism in direct smooth muscle relaxation. A substance other than ferulic acid might create these effects.

The visceromotor responses to colorectal distension and skin pinch are inhibited by simultaneous jejunal distension

Noxious stimuli that are applied to different somatic sites interact; often one stimulus diminishes the sensation elicited from another site. By contrast, inhibitory interactions between visceral stimuli are not well documented. We investigated the interaction between the effects of noxious distension of the colorectum and noxious stimuli applied to the jejunum, in the rat. Colorectal distension elicited a visceromotor reflex, which was quantified using electromyographic (EMG) recordings from the external oblique muscle of the upper abdomen. The same motor units were activated when a strong pinch was applied to the flank skin. Distension of the jejunum did not provoke an EMG response at this site, but when it was applied during colorectal distension it blocked the EMG response. Jejunal distension also inhibited the response to noxious skin pinch. The inhibition of the visceromotor response to colorectal distension was prevented by local application of tetrodotoxin to the jejunum, and was markedly reduced when nicardipine was infused into the local jejunal circulation. Chronic sub-diaphragmatic vagotomy had no effect on the colorectal distension-induced EMG activity or its inhibition by jejunal distension. The nicotinic antagonist hexamethonium suppressed phasic contractile activity in the jejunum, had only a small effect on the inhibition of visceromotor response by jejunal distension. It is concluded that signals that arise from skin pinch and colorectal distension converge in the central nervous system with pathways that are activated by jejunal spinal afferents; the jejunal signals strongly inhibit the abdominal motor activity evoked by noxious stimuli.

Ca2+ channel activating action of maitotoxin in cultured brainstem neurons

The actions of maitotoxin were studied using cultured brainstem cells and adrenal chromaffin cells. Maitotoxin induced a profound increase in the Ca2+ influx into cultured brainstem cells after a brief lag period. The maitotoxin-induced Ca2+ influx was suppressed by various voltage-dependent Ca2+ channel blockers such as Co2+, Mn2+, verapamil and diltiazem. Maitotoxin-catecholamine release in brainstem cells initiated to increase after a lag period of about 1 min and the increase continued even at 4 min after treatment, while in the adrenal chromaffin cells the release started after an about 1-min lag period to attain a maximum within first 2-min and gradually decrease thereafter. These results suggest that maitotoxin acts on Ca2+ channels to increase the Ca2+ influx, accompanied by enhancement of catecholamine release in the brainstem cells with a different temporal profile from that in the adrenal chromaffin cells.

Analysis of Responses to Kava Kava in the Feline Pulmonary Vascular Bed

This study was designed to test the hypothesis that kava kava induces a depressor response in the pulmonary vascular bed of the cat and to identify the pathways involved in the mediation or modulation of these effects. In separate experiments, the effects of L-N5-(1-iminoethyl)ornithine hydrochloride (L-NIO), a nitric oxide synthase inhibitor, glibenclamide, an ATP-sensitive K+ channel blocker, meclofenamate, a nonselective cyclooxygenase inhibitor, nicardipine, a calcium channel blocker, bicuculline, a gamma-aminobutyric acid (GABA)A receptor antagonist, and saclofen, a GABAB antagonist, were investigated on pulmonary arterial responses to kava kava (kava), pinacidil, an ATP-sensitive K+ channel activator, bradykinin, an inducer of nitric oxide synthase, 3-aminopropyl(methyl)phosphinic acid hydrochloride (SKF-97541), a GABAB receptor agonist, and muscimol, a GABAA receptor agonist. Lobar arterial perfusion pressure and systemic pressure were continuously monitored, electronically averaged, and recorded. Under elevated tone conditions in the isolated left lower lobe of the feline vascular bed, kava induced a dose-dependent vasodepressor response that was not significantly altered after administration of L-NIO, glibenclamide, meclofenamate, or saclofen. Responses to kava were significantly reduced after administration of either nicardipine or bicuculline. When the calcium channel blocker nicardipine was administered in addition to the GABA blocker bicuculline, there was near complete attenuation of the kava-induced vasodepressor responses. The results of this investigation suggest that kava has potent vasodepressor activity in the feline lung bed and that this response is mediated or modulated by both a calcium channel- and GABA receptor-sensitive pathway.

Stretch-induced triphosphorylation of myosin light chain and myogenic tone in canine basilar artery

The relationship between phosphorylation of 20,000 Da myosin light chain (MLC20) and contraction in response to mechanical stretch was investigated in the canine basilar artery. A slow stretch (at a rate of 1 mm/s and a stimulus period for 15 min) increased triphosphorylated MLC20 despite lowered intracellular calcium concentration and mechanical activities, such as myogenic tone, shortening velocity and stiffness of the artery. Nicardipine, a Ca2+ channel blocker, and ML-9, a myosin light chain kinase (MLCK) inhibitor, partially inhibited the stretch-induced MLC20 phosphorylation. The remained phosphorylation was further reduced by calphostin C, a protein kinase C (PKC) inhibitor. Y-27632, a Rho-kinase inhibitor, inhibited phosphorylation of myosin light chain phosphatase and attenuated MLC20 phosphorylation. These results suggest that slow stretch induces triphosphorylation of MLC20, which is mediated by MLCK, PKC, and Rho-kinase, and that the triphosphorylation of MLC20 does not result in myogenic contraction, rather seems to counteract it.

Vasorelaxant Effects of Methyl Brevifolincarboxylate from the Leaves of Phyllanthus niruri

Methyl brevifolincarboxylate (1) isolated from the leaves of Phyllanthus niruri L. showed a vasorelaxant effect on rat aortic rings. Compound 1 exhibited slow relaxation activity against norepinephrine (NE)-induced contractions of rat aorta with or without endothelium. The compound did not affect contractions induced by a high concentration (60 mM) of K+, whereas it inhibited NE-induced vasocontraction in the presence of nicardipine. These results suggest that the inhibition of NE-induced vasocontraction by compound 1 is in part attributable to a decrease in [Ca2+]i through receptor-operated Ca2+ channels.

Determination of nifedipine in serum of women in preterm labor by high-performance liquid chromatography with diode array detection

Nifedipine (Nif) is widely used in treating cardiovascular disorders (especially hypertension) and for inhibiting preterm labor. A fully validated selective high-performance liquid chromatographic method with diode array detection, using solid-phase extraction, was developed for the determination of Nif in human serum. To assess specificity, Nif and its degradation products were separated on a Purospher RP-18 (5 microm, 125 x 4 mm) column plus a LiChrospher 100 RP-18 (5 microm, 4 x 4 mm) precolumn with a mobile phase of methanol-10 mM aqueous trifluoroacetic acid, pH 7.3 (57 + 43, v/v); chromatographic separation was followed by UV detection at 238 nm. For toxicological analysis, Nif in the presence of other calcium-channel antagonist drugs was identified under optimum chromatographic conditions. The calibration graph was constructed over the concentration range of 12.5-400 ng/mL in serum with good correlation (r = 0.9956). This method was not subject to interference by other plasma components and was successfully applied to the assay of Nif in spiked human serum and in serum of women in preterm labor after sublingual administration of 30 mg Nif per day divided into 3 equal doses. The mean recovery based on the ratio of the slopes of serum and mobile phase standard curves was 96.5%. The detection and quantification limits of the drug in spiked human serum were found to be 6 and 17.5 ng/mL, respectively. Validation of the method demonstrated good intraday and interday precision, which ranged from 2.18 to 6.67% and from 6.52 to 11.93%, respectively.

Elevated plasma nitric oxide metabolites in hypertension: synergistic vasodepressor effects of a static magnetic field and nicardipine in spontaneously hypertensive rats

The involvement of plasma nitric oxide metabolites (NO(x)) in hypertension was examined in stroke-resistant spontaneously hypertensive rats during the development of hypertension. Continuous application of a static magnetic field (SMF; a maximum magnetic flux density of 180 millitesla, a peak magnetic gradient of 133 millitesla/mm) to the left carotid sinus baroreceptors of rats was carried out for 6 weeks using a disc-shaped magnetic implant (4.4 mm in diameter, 2.2 mm in height). An L-type voltage-gated Ca2+ channel blocker, nicardipine (2 mg/kg) was administered intraperitoneally three times a week for 6 weeks, and then 15 min after each injection, mean arterial blood pressure (MAP), heart rate (HR), skin blood flow (SBF), skin blood velocity (SBV) and plasma NO(x) were monitored. The nicardipine significantly decreased MAP, and increased HR, SBF and SBV in the nicardipine-treated rats compared with the control rats (p<0.001) without changing plasma NO(x) levels. The SMF exposure alone significantly suppressed or retarded the development of hypertension in SMF-exposed rats compared with the control rats (p<0.05). The SMF significantly promoted the nicardipine-induced MAP decrease (p<0.001) and induced a significant increase in plasma NO(x) levels (p<0.01) in SMF-exposed, nicardipine-treated rats compared with the unexposed, nicardipine-treated rats. The SMF did not significantly induce any changes in the SBF and SBV in nicardipine-treated nor untreated rats. These results suggest that the SMF may enhance nicardipine-induced hypotension by more effectively antagonizing the Ca2+ influx through the Ca2+ channels compared with the nicardipine treatment alone. In addition, the enhanced antihypertensive effects of the SMF on the nicardipine-treated rats might be, at least in part, related to the increased NO(x), primarily due to the upregulation of inducible nitric oxide synthase.

Expression of the neurokinin type 1 receptor in the human colon

The distribution of the neurokinin type 1 receptor (NK1r) in human intestine, mapped in a few immunohistochemical investigations in the antrum and the duodenum, is comparable to that widely studied in rodents. Importantly, despite pharmacological evidence of their presence in mammalian intestinal muscle, their immunohistochemical visualization in smooth muscle cells remains to be determined in human digestive tract. In the present work, we studied the distribution of NK1r in the human colon, with a particular view to visualize their expression in muscle cells. With this aim, part of colonic segments were incubated with nicardipine and TTX in order to induce accumulation of the NK1r on cell membrane. NK1r were visualized by using immunohistochemistry combined with fluorescence and confocal microscopy. Without incubation, NK1r-IR was clearly observed on the membrane and the cytoplasm of myenteric and submucous neurons and interstitial cells of Cajal, but could not be clearly determined in the longitudinal and circular muscle. NK1r-IR-expressing neurons and interstitial cells were closely surrounded by substance P (SP) immunoreactive nerves. Incubation of colonic segments with nicardipine and TTX at 4 degrees C for 1 h with SP allowed to reveal a strong NK1r-IR at the surface of muscle cells. Incubation with SP (10(-6) M) at 37 degrees C for 1 min induced a relocation of NK1r-IR into the cytoplasm of muscle. This is interpreted as an internalization of NK1r induced by the binding of SP on muscular NK1r. The present data contribute to emphasize the role of NK1r in tachykinin-mediated neuronal processes regulating intestinal motility.

Intravenous Nicardipine

Nicardipine is a water soluble calcium channel antagonist, with predominantly vasodilatory actions. Intravenous (IV) nicardipine (Cardene IV), which demonstrates a relatively rapid onset/offset of action, is used in situations requiring the rapid control of blood pressure (BP). IV nicardipine was as effective as IV nitroprusside in the short-term reduction of BP in patients with severe or postoperative hypertension. A potential role for IV nicardipine in the intraoperative acute control of BP in patients undergoing various surgical procedures (including cardiovascular, neurovascular and abdominal surgery), and in the deliberate induction of reduced BP in surgical procedures in which haemostasis may be difficult (e.g. surgery involving the hip or spine) was demonstrated in preliminary studies. Preliminary studies also indicated the ability of a bolus dose of IV nicardipine to attenuate the hypertensive response, but not the increase in tachycardia, after laryngoscopy and tracheal intubation in anaesthetised patients. In large, well designed studies, IV nicardipine prevented cerebral vasospasm in patients with recent aneurysmal subarachnoid haemorrhage; however, overall clinical outcomes at 3 months were similar to those in patients who received standard management. Small preliminary studies have investigated the use of IV nicardipine in a variety of other settings, including acute intracerebral haemorrhage, acute ischaemic stroke, pre-eclampsia, acute aortic dissection, premature labour and electroconvulsive therapy.In conclusion, the efficacy of IV nicardipine in the short-term treatment of hypertension in settings for which oral therapy is not feasible or not desirable is well established. The ability to titrate IV nicardipine to the tolerance levels of individual patients makes this agent an attractive option, especially in critically ill patients or those undergoing surgery. Potential exists for further investigation of the use of this agent in clinical settings where a vasodilatory agent with minimal inotropic effects is appropriate.

Evaluation of Blood Pressure Measured by Tail-Cuff Methods (without Heating) in Spontaneously Hypertensive Rats

Conventional noninvasive blood pressure in conscious rats or mice are typically measured using the tail-cuff method after heating the animal. The goal of this study was to assess the validity of a novel tail-cuff method without animal heating when compared with the conventional heating tail-cuff method (unanesthetized rats with heating), telemetry method (unanesthetized restrained rats without heating), or carotid arterial catheter method (anesthetized rats, carotid arterial cannulation). The blood pressure and heart rate of spontaneously hypertensive rats were measured at 13:00-17:00 h for all experiments. Experiments demonstrated similar systolic blood pressure measurements when comparing the unheated-animal tail-cuff method and the telemetry method. Further, values obtained by both methods were lower than those obtained by the heated-animal tail-cuff method. Systolic blood pressure measurements obtained through carotid arterial cannulation were lower than those obtained by any other method. The heart rate was highest using the unheated-animal tail-cuff method when compared with the other methods. These data suggest that the novel unheated-animal tail-cuff method is a sensitive and accurate approach for the noninvasive measurement of blood pressure in conscious rats.

M(2) and M(3) muscarinic receptor-mediated contractions in longitudinal smooth muscle of the ileum studied with receptor knockout mice

Isometric contractile responses to carbachol were studied in ileal longitudinal smooth muscle strips from wild-type mice and mice genetically lacking M(2) or M(3) muscarinic receptors, in order to characterize the mechanisms involved in M(2) and M(3) receptor-mediated contractile responses. Single applications of carbachol (0.1-100 microM) produced concentration-dependent contractions in preparations from M(2)-knockout (KO) and M(3)-KO mice, mediated via M(3) and M(2) receptors, respectively, as judged by the sensitivity of contractile responses to blockade by the M(2)-preferring antagonist methoctramine (300 nM) or the M(3)-preferring antagonist 4-DAMP (30 nM). The M(2)-mediated contractions were mimicked in shape by submaximal stimulation with high K(+) concentrations (up to 35 mM), almost abolished by voltage-dependent Ca(2+) channel (VDCC) antagonists or depolarization with 140 mM K(+) medium, and greatly reduced by pertussis toxin (PTX) treatment. The M(3)-mediated contractions were only partially inhibited by VDCC antagonists or 140 mM K(+)-depolarization medium, and remained unaffected by PTX treatment. The contractions observed during high K(+) depolarization consisted of different components, either sensitive or insensitive to extracellular Ca(2+). The carbachol contractions observed with wild-type preparations consisted of PTX-sensitive and -insensitive components. The PTX-sensitive component was functionally significant only at low carbachol concentrations. The results suggest that the M(2) receptor, through PTX-sensitive mechanisms, induces ileal contractions that depend on voltage-dependent Ca(2+) entry, especially associated with action potential discharge, and that the M(3) receptor, through PTX-insensitive mechanisms, induces contractions that depend on voltage-dependent and -independent Ca(2+) entry and intracellular Ca(2+) release. In intact tissues coexpressing M(2) and M(3) receptors, M(2) receptor activity appears functionally relevant only when fractional receptor occupation is relatively small.

The coupling mechanism of P-glycoprotein involves residue L339 in the sixth membrane spanning segment

The transmembrane (TM) domains in P-glycoprotein (P-gp) contain the drug binding sites and undergo conformational changes driven by nucleotide catalysis to effect translocation. However, our understanding of exactly which regions are involved in such events remains unclear. A site-directed labelling approach was used to attach thiol-reactive probes to cysteines introduced into transmembrane segment 6 (TM6) in order to perturb function and infer involvement of specific residues in drug binding and/or interdomain communication. Covalent attachment of coumarin-maleimide at residue 339C within TM6 resulted in impaired ATP hydrolysis by P-gp. The nature of the effect was to reduce the characteristic modulation of basal activity caused by transported substrates, modulators and the potent inhibitor XR9576. Photoaffinity labelling of P-gp with [(3)H]-azidopine indicated that residue 339C does not alter drug binding per se. However, covalent modification of this residue appears to prevent conformational changes that lead to drug stimulation of ATP hydrolysis.

Electrophysiological and molecular identification of voltage-gated sodium channels in murine vascular myocytes

A voltage-gated Na+ current was characterised in freshly dissociated mouse portal vein (PV) smooth muscle myocytes. The current was found superimposed upon the relatively slow L-type Ca2+ current and was resistant to conventional Ca2+ channel blockers but was abolished by external Na+ replacement and tetrodotoxin (TTX, 1 microM). The molecular identity of the channel responsible for this conductance was determined by RT-PCR where only the transcripts for Na+ channel genes SCN7a, 8a and 9a were detected. The presence of the protein counterparts to the SCN8a and 9a genes (NaV1.6 and NaV1.7, respectively) on the individual smooth muscle myocytes were confirmed in immunocytochemistry, which showed diffuse staining around a predominantly plasmalemmal location. TTX inhibited the action potential in individual myocytes generated in the current clamp mode but isometric tissue tension experiments revealed that TTX (1 and 5 microM) had no effect on the inherent mouse PV rhythmicity. However, the Na+ channel opener veratridine (10 and 50 microM) significantly increased the length of contraction and the interval between contractions. This effect was not influenced by pre-incubation with atropine, prazosin and propranolol, but was reversed by TTX (1 microM) and completely abolished by nicardipine (1 microM). Furthermore, preincubation with the reverse-mode Na+-Ca2+ exchange blocker KB-R7943 (10 microM) also inhibited the veratridine response. We have established for the first time the molecular identity of the voltage-gated Na+ channel in freshly dispersed smooth muscle cells and have shown that these channels can modulate contractility through a novel mechanism of action possibly involving reverse mode Na+-Ca2+ exchange.

Secretory Phospholipases A2 Induce Neurite Outgrowth in PC12 Cells through Lysophosphatidylcholine Generation and Activation of G2A Receptor

We previously demonstrated that secretory phospholipase A2 (sPLA2) and lysophosphatidylcholine (LPC) exhibit neurotrophin-like neuritogenic activity in the rat pheochromocytoma cell line PC12. In this study, we further analyzed the mechanism whereby sPLA2 displays neurite-inducing activity. Exogenously added mammalian group X sPLA2 (sPLA2-X), but not group IB and IIA sPLA2s, induced neuritogenesis, which correlated with the ability of sPLA2-X to liberate LPC into the culture media. In accordance, blocking the effect of LPC by supplementation of bovine serum albumin or phospholipase B attenuated neuritogenesis by sPLA2 or LPC. Overproduction or suppression of G2A, a G-protein-coupled receptor involved in LPC signaling, resulted in the enhancement or reduction of neuritogenesis induced by sPLA2 treatment. These results indicate that the neuritogenic effect of sPLA2 is mediated by generation of LPC and subsequent activation of G2A.

Anaphylactic Shock

Background

The pathophysiology of anaphylactic shock during anesthesia is incompletely characterized. It is described as distributive by analogy with septic shock (anaerobic metabolism, high tissue oxygen pressure [Ptio2] values). The Ptio2 profile and its metabolic consequences during anaphylaxis are not known.

Methods

Ovalbumin-sensitized anaphylactic shock rats (n = 11) were compared to nicardipine-induced hypotension rats (n = 12) for systemic hemodynamics, Ptio2, sympathetic nervous system activation, skeletal muscle blood flow, and interstitial lactate and pyruvate concentrations using combined microdialysis and polarographic Clark-type oxygen probes.

Results

In both groups, the time course and the magnitude of arterial hypotension were similar. The ovalbumin group but not the nicardipine group displayed decreased skeletal muscle blood flow (from 45 +/- 6.2 ml x 100 g(-1) x min(-1) to 24.3 +/- 5 ml x 100 g(-1) x min(-1); P &lt; 0.0001) and Ptio2 values (from 42 +/- 5 to 5 +/- 2; P &lt; 0.0001). The ovalbumin group had more intense sympathetic nervous system activation with higher plasma epinephrine and interstitial norepinephrine concentrations. For the ovalbumin group, there was skeletal muscle anaerobic metabolism (lactate concentration increased from 0.446 +/- 0.105 to 1.741 +/- 0.459 mm; P &lt; 0.05) and substrate depletion (pyruvate concentration decreased from 0.034 +/- 0.01 mm to 0.006 +/- 0.002 mm; P &lt; 0.05) leading to increased interstitial lactate/pyruvate ratios (from 17 +/- 6 to 311 +/- 115; P &lt; 0.05).

Conclusions

This profile suggests decreased skeletal muscle blood flow and oxygen delivery. Persistent energy consumption results in decreased Ptio2 and substrate depletion through anaerobic glycolysis leading to complete failure of cellular energy production. This could explain rapid organ dysfunction and resuscitation difficulties.

Comparison of the direct negative dromotropic effect of a new calcium channel blocker, cilnidipine, with that of nicardipine

We encountered a 91-year-old woman with atrial fibrillation complicating bradycardia while she was receiving therapy with an L/N-type calcium channel blocker, cilnidipine, for hypertension, which is an unusual observation for the dihydropyridine class of calcium channel blockers. Therefore, we compared the dromotropic effect of cilnidipine with that of an L-type calcium channel blocker, nicardipine, which has a similar hypotensive activity. The canine isolated, blood-perfused atrioventricular node preparation was used. Cilnidipine as well as nicardipine slowed atrioventricular nodal conduction in a dose-related manner. However, the dromotropic action of cilnidipine was about five times less potent than that of nicardipine. These experimental results may suggest that we experienced an atypical clinical event of cilnidipine in a very old woman; otherwise one can speculate that the N-type calcium channel inhibitory component of cilnidipine might have played a role in exerting the negative dromotropic effect in this patient.

Inhibitory effects of nicardipine to cytochrome P450 (CYP) in human liver microsomes

To anticipate drug-drug interactions by nicardipine in vivo, cytochrome P450 (CYP) forms responsible for the metabolism of nicardipine and inhibition of CYP-dependent drug metabolism by nicardipine were investigated. Microsomes of human B-lymphoblastoid cells expressing each human CYP form were used for the metabolism of nicardipine. Inhibitory effects of nicardipine on drug metabolism were studied using human liver microsomes. CYP2C8, CYP2D6 and CYP3A4 were identified as major CYP forms for the metabolism of nicardipine in human liver microsomes. Nicardipine strongly inhibited two-pathways of triazolam hydroxylation both catalyzed by CYP3A4. Comparison of three Ca(2+) antagonists, nicardipine, nifedipine, and diltiazem revealed that only nicardipine showed such a strong inhibitory potency on the typical CYP2D6-catalyzed drug metabolism. Furthermore, nicardipine inhibited other reactions catalyzed by CYP1A, CYP2A6, CYP2C8, CYP2C9 and CYP2C19 with K(i) values ranging from 1.1 to 29.4 microM. In conclusion, nicardipine was a relatively potent inhibitor of human CYP2D6, CYP3A4 and CYP2C (especially for CYP2C8 and CYP2C19) in vitro, suggesting that drug-drug interactions between nicardipine and other drugs metabolized mainly by these CYP forms appear to occur in vivo.

Coronary Blood Flow Responses are Impaired Independent of NO and Endothelial Function in Conscious Dogs with Dilated Cardiomyopathy

BACKGROUND

Dilated cardiomyopathy (DCM) is characterized by nitric oxide (NO) deficiency and endothelial dysfunction. Whether endothelium-independent vasodilation is preserved, particularly in the coronary circulation, remains controversial.

METHODS AND RESULTS

We studied systemic and coronary flow responses to the endothelium-dependent agonist, acetylcholine, the cGMP-dependent NO-donor, nitroglycerin, the predominantly endothelium-independent agonist, adenosine, the beta-adrenergic cAMP-dependent agonist, isoproterenol, and the calcium channel antagonist, nicardipine, in conscious dogs with pacing-induced DCM. Systemic blood flow response was impaired to acetylcholine but preserved to other vasodilators in DCM. In contrast, coronary blood flow response was significantly ( P < .05) depressed to all agonists. (Peak coronary blood flow response, control versus DCM: acetylcholine: 221 +/- 14% versus 156 +/- 11%; nitroglycerin: 220 +/- 17% versus 138 +/- 9%; adenosine: 635 +/- 65% versus 376 +/- 56%; nicardipine: 338 +/- 59% versus 115 +/- 23%; isoproterenol: 219 +/- 18% versus 86 +/- 20%). The attenuation was independent of systemic hemodynamic differences.

CONCLUSION

In contrast to systemic responses, coronary blood flow responses in DCM are impaired dependent or independent of NO or second messenger mechanisms, implying either distal signaling defects or structural abnormalities in the coronary vasculature.

A novel neurotrophic role of secretory phospholipases A2for cerebellar granule neurons

Cultured cerebellar granule neurons (CGNs) require membrane depolarization or neurotrophic factors for their survival in vitro and undergo apoptosis when deprived of these survival-promoting stimuli. Here, we show that secretory phospholipases A(2)s (sPLA(2)s) rescue CGNs from apoptosis after potassium deprivation. The neurotrophic effect required the enzymatic activity of sPLA(2)s, since catalytically inactive mutants of sPLA(2)s failed to protect CGNs from apoptosis. Consistently, the ability of sPLA(2)s to protect CGNs from apoptosis correlated with the extent of sPLA(2)-induced arachidonic acid release from live CGNs. The survival-promoting effect of sPLA(2) was inhibited by depletion of extracellular Ca(2+) or by the presence of L-type Ca(2+) channel blocker nicardipine, suggesting that Ca(2+) influx occurs upon sPLA(2) treatment. Among the mammalian sPLA(2)s tested, only group X sPLA(2), but not group IB nor IIA sPLA(2)s, displayed neurotrophic activity. These results suggest a novel, unexpected neurotrophin-like role of sPLA(2) in the nervous system.

C-type natriuretic peptide inhibits L-type Ca2+ current in rat magnocellular neurosecretory cells by activating the NPR-C receptor

Magnocellular neurosecretory cells (MNCs), of the paraventricular and supraoptic nuclei of the hypothalamus, secrete the hormones vasopressin and oxytocin. As a result, they have an essential role in fundamental physiological responses including regulation of blood volume and fluid homeostasis. C-type natriuretic peptide (CNP) is present at high levels in the hypothalamus. Although CNP is known to decrease hormone secretion from MNCs, no studies have examined the role of the natriuretic peptide C receptor (NPR-C) in these neurons. In this study, whole cell recordings from acutely isolated MNCs, and MNCs in a coronal slice preparation, show that CNP (2 x 10(-8) M) and the selective NPR-C agonist, cANF (2 x 10(-8) M), significantly inhibit L-type Ca2+ current (I(Ca(L))) by approximately 50%. This effect on I(Ca(L)) is mimicked by dialyzing a G(i)-activator peptide (10(-7) M) into these cells, implicating a role for the inhibitory G protein, G(i). These NPR-C-mediated effects were specific to I(Ca(L)). T-type Ca2+ channels were unaffected by CNP. Current-clamp experiments revealed the ability of CNP, acting via the NPR-C receptor, to decrease (approximately 25%) the number of action potentials elicited during a 500 ms depolarizing stimulus. Analysis of action potential duration revealed that CNP and cANF significantly decreased 50% repolarization time (APD50) in MNCs. In summary, our findings show that CNP has a potent and selective inhibitory effect on I(Ca(L)) and on excitability in MNCs that is mediated by the NPR-C receptor. These data represent the first electrophysiological evidence of a functional role for the NPR-C receptor in the mammalian hypothalamus.

Role of l-Ca(2+) channels in intestinal pacing in wild-type and W/W(V) mice

Rhythmic contractions generating transit in the digestive tract are paced by a network of cells called interstitial cells of Cajal (ICC) found in the myenteric plexus (MP). ICC generate cyclic depolarizations termed "slow waves" that are passively transmitted to the smooth muscle to initiate contractions. The opening of l-Ca(2+) channels are believed to be primarily responsible for the influx of calcium generating a contraction in smooth muscle. However, l-Ca(2+) channels are not thought to be important in generating the pacing current found in ICC. Using intact segments of circular (CM) and longitudinal (LM) muscle from wild-type mice and mice lacking c-kit kinase (W/W(V)), we found that l-Ca(2+) channel currents are required for pacing at normal frequencies to occur. Application of 1 muM nicardipine caused a significant decrease in contraction amplitude and frequency in LM and CM that was successfully blocked with BAY K 8644. Nicardipine also abolished the pacing gradient found throughout the intestines, resulting in a uniform contraction frequency of 30-40/minute. Stimulating l-Ca(2+) channels with BAY K 8644 neither removed nor recovered the pacing gradient. W/W(V) mice, which lack ICC-MP, also exhibited a pacing gradient in LM. Application of nicardipine to LM segments of W/W(V) mouse intestine did not reduce pacing frequency, and in jejunum, resulted in a slight increase. BAY K 8644 did not affect pacing frequency in W/W(V) tissue. In conclusion, we found that l-Ca(2+) channel activity was required for normal pacing frequencies and to maintain the pacing frequency gradient found throughout the intestines in wild-type but not in W/W(V) mouse intestine.

The difference between nicardipine and its enantiomers on inhibiting vasoconstriction of isolated rabbit thoracic artery

The present study was designed to study the difference effects between nicardipine and its two enantiomers on thoracic artery of rabbit. A high-performance liquid chromatographic method was used to prepare the two enantiomers of nicardipine. The thoracic artery of rabbit was removed. The vessels were cut into 3 mm in width and 15 mm in length spiral strips and immersed into tissue baths. The concentration-response curves of nicardipine and its enantiomers were obtained by cumulative administration of the vasoconstrictors. Nicardipine and the enantiomers could shift the dose-response curves of NE, KCl or CaCl2 to right in a nonparallel manner and decrease the maximum effective in a concentration-depended manner, respectively. The pD2' value of R-(-)-nicardipine showed significantly effective than that of nicardipine and S-(+)-nicardipine (P<0.01). There was not obviouse difference between the pD2' value of nicardipine and S-(+)-nicardipine (P>0.05). The results demonstrate that the stereoselective interaction between R-(-)-nicardipine and L-calcium channel receptor is more stronger than that of S-(+)-nicardipine.

Cardiovascular effects and lethality of venom from nematocysts of the box-jellyfish Chiropsalmus quadrigatus (Habu-kurage) in anaesthetized rats

Haemodynamic effects of saline-extracted venom from nematocysts isolated from Chiropsalmus quadrigatus (Habu-kurage) were studied in anaesthetized rats. Intravenous administration of venom (0.2-5 microg protein/kg) produced immediately dose-dependent hypertension and bradycardia. Femoral blood flow transiently increased but calculated femoral vascular conductance decreased. Changes caused by 1 microg/kg of venom were reproducible, and were not affected by prazosin, atropine or BQ123 (ET(A) receptor antagonist) but were significantly attenuated by nicardipine. At doses over 2 microg/kg, hypotension and a decrease in pulse pressure were observed subsequent to transient hypertension. In 5 of 8 rats received 5 microg/kg venom and 6 of 6 rats at 10 microg/kg, death due to irreversible cardiac arrest occurred within 30 min after intravenous injection. However, during nicardipine infusion, venom (10 microg/kg) exerted only modest effects and the rats survived. Heating venom (50 degrees C for 10 min) before injection practically abolished the haemodynamic effects of 10 microg/kg venom, indicating its thermolability. Data show that C. quadrigatus venom has both vasoconstrictor and cardiodepressive effects in rats, and suggest that a calcium channel blocker can protect against the cardiovascular and lethal effects of the venom.

Factors affecting habituation of PC12 cells to ATP

Extracellular ATP triggers catecholamine secretion from PC12 cells by activating ionotropic purine receptors. Repeated stimulation by ATP leads to habituation of the secretory response. In this paper, we use amperometric detection to monitor the habituation of PC12 cells to multiple stimulations of ATP or its agonist. Cells habituate to 30 microm ATP slower than they do to 300 or 600 microm ATP. Modifying external Mg2+ affects the response of cells to 30 microm ATP, but does not affect habituation, suggesting that habituation does not necessarily correspond to either stimulus intensity or cellular response. Mg2+ affects the initial response of PC12 cells to 2MeSATP in a manner similar to ATP. Increasing external [Mg2+] to 3.0 mm, however, eliminates habituation to 2MeSATP. This habituation can be partially restored by costimulation with 100 microm UTP. Background application of UTP increases habituation to both ATP and 2MeSATP. This suggests that ATP-sensitive metabotropic (P2Y) receptors play a role in the habituation process. Finally, although Ca2+ influx through voltage-operated calcium channels does not appear to contribute to secretion during ATP stimulation, blocking these channels with nicardipine increases habituation. This suggests a role for voltage-operated calcium channels in the habituation process.

Vasorelaxant Effects of Forsythiaside from the Fruits of Forsythia suspensa

The vasorelaxant effects of forsythiaside (compound 1) from the fruits of Forsythia suspensa on isolated rat aortic rings were studied. Compound 1 showed a slow relaxation activity against norepinephrine (NE)-induced contractions of rat aorta with/without endothelium. This compound did not affect contractions induced by a high concentration of potassium (K(+) 60 mM), while it inhibited NE-induced vasocontraction in the presence of nicardipine. These results show that the inhibition by compound 1 of NE-induced vasocontraction is due to a decrease in calcium influx from the extracellular space caused by NE.

Exposure to a moderate intensity static magnetic field enhances the hypotensive effect of a calcium channel blocker in spontaneously hypertensive rats

We investigated the combined effects of a moderate intensity static magnetic field (SMF) and an L-type voltage-gated Ca(2+) channel blocker, nicardipine in stroke-resistant spontaneously hypertensive rats during the development of hypertension. Five-week-old male rats were exposed to SMF intensity up to 180 mT (B(max)) with a peak spatial gradient of 133 mT/mm for 14 weeks. Four experimental groups of 14 animals each were examined: (1) sham exposure with intraperitoneal (ip) saline injection (control); (2) SMF exposure with ip saline injection (SMF); (3) sham exposure with ip nicardipine injection (NIC); (4) SMF exposure with ip nicardipine injection (SMF + NIC). A disc-shaped permanent magnet or a dummy magnet was implanted in the vicinity adjacent to the left carotid sinus baroreceptor region in the neck of each rat. Nicardipine (2 mg/kg ip) was administered three times a week for 14 weeks, and then 15 min after each injection, arterial blood pressure (BP), heart rate (HR), baroreflex sensitivity (BRS), skin blood flow (SBF), skin blood velocity (SBV), plasma nitric oxide (NO) metabolites (NO(x) = NO(2) (-) + NO(3) (-)), plasma catecholamine levels and behavioral parameters of a functional observational battery were monitored. The action of nicardipine significantly decreased BP, and increased HR, SBF, SBV, plasma epinephrine and norepinephrine in the NIC group compared with the control respective age-matched group without changing plasma NO(x) levels. Neck exposure to SMF alone for 5-8 weeks significantly suppressed or retarded the development of hypertension together with increased BRS in SMF group. Furthermore, the exposure to SMF for 1-8 weeks significantly promoted the nicardipine-induced BP decrease in the SMF + NIC group compared with the respective NIC group. Moreover, the SMF induced a significant increase in plasma NO(x) in the nicardipine-induced hypotension. There were no significant differences in any of the physiological or behavioral parameters measured between the SMF + NIC and the NIC groups, nor between the SMF and the control groups. These results suggest that the SMF may enhance nicardipine-induced hypotension by more effectively antagonizing the Ca(2+) influx through the Ca(2+) channels compared with the NIC treatment alone. Furthermore, the enhanced antihypertensive effects of the SMF on the nicardipine-treated group appear to be partially related to the increased NO(x). Theoretical considerations suggest that the applied SMF (B(max) 40 mT, 0 Hz) can be converted into a changing magnetic field (B(max) 30-40 mT, 5.7-6.5 Hz or 7.5-8.3 Hz) in the baroreceptor region by means of the carotid artery pulsation. Therefore, we propose that the moderate intensity changing magnetic field, i.e., the magnetic field modulated by the pulse rate, may influence the activity of baroreceptor and baroreflex function.

Long-Term Anti-Hypertensive Therapy with Benidipine Improves Arterial Stiffness over Blood Pressure Lowering

Pulse wave velocity (PWV) reflects arterial stiffness and is an independent predictor of cardiovascular mortality and morbidity. However, because it is closely related to blood pressure (BP), PWV is an imperfect measure for evaluating the effects of anti-hypertensive drugs on arterial wall properties. To clarify the effect of benidipine on arterial properties, we first derived the regression line between BP and PWV changes in a short-term experiment. Using this line, we evaluated the long-term effect of benidipine on PWV changes. In the short-term experiment, 29 participants were intravenously administered nicardipine for 90 min. Maximum decreases of brachial-ankle PWV (baPWV) were plotted against the corresponding decreases in BP. In the long-term experiment, 9 hypertensive patients were treated with benidipine for 1 year, during which BP and baPWV were monitored. After 1 year, benidipine was suspended for 2 weeks, and BP and baPWV were reevaluated. In the short-term experiment, PWV was dependent on BP only, and the equation of the regression line was deltaPWV (cm/s) =10.114 x deltaMBP (mmHg) (r=0.913) or deltaPWV (%) =0.719 x deltaMBP (%) (r=0.926). In the long-term therapy, benidipine treatment achieved stable BP control within 3 months; the real PWV decreases (r-PWV) were almost identical to the PWV decrease estimated (e-PWV) from BP lowering at 3 months. However, r-PWV exceeded e-PWV after 6 months. Relative BP and PWV improvements compared to the control were maintained 2 weeks after suspension of benidipine. In conclusion, long-term benidipine administration improves arterial wall properties beyond what can be accounted for by changes in BP.

Alteration of cyclopiazonic acid-mediated contracture of mouse diaphragm after denervation

As a major Ca(2+) source for muscle contraction, the sarcoplasmic reticulum (SR) of skeletal muscle maintains its Ca(2+) content by uptake of myoplasmic Ca(2+) and by replenishment with extracellular Ca(2+). Since transection of motor nerve alters the functions of SR Ca(2+) pump and sarcolemma ion channels, this study explored the effect of denervation on the contracture evoked by cyclopiazonic acid (CPA), an inhibitor of SR Ca(2+) pump. In innervated hemidiaphragm, CPA elicited a bimodal elevation of muscle tone, which was dependent on extracellular Ca(2+) and differentially inhibited by pretreatment with 2-aminoethoxydiphenylborane (APB) and U73122. Activation of muscle Na(+) channels to simulate denervation-induced membrane depolarization did not change the contracture profile. After denervation for 5-14 days when the contracture induced by caffeine was not yet depressed, CPA elicited only APB-sensitive monophasic contracture. Stimulation of ATP-regulated K(+) channels with lemakalim hyperpolarized muscle membrane and attenuated CPA contracture in denervated, but not innervated, hemidiaphragm. The effects of lemakalim were antagonized by glybenclamide. It is inferred that the bimodal CPA contracture is resulted from distinct recruitments of Ca(2+) entry and that denervation alters the voltage dependence and down-regulates CPA-mediated Ca(2+) influx.

Ionic mechanism for contractile response to hyposmotic challenge in canine basilar arteries

A hyposmotic challenge elicited contraction of isolated canine basilar arteries. The contractile response was nearly abolished by the removal of extracellular Ca(2+) and by the voltage-dependent Ca(2+) channel (VDCC) blocker nicardipine, but it was unaffected by thapsigargin, which depletes intracellular Ca(2+) stores. The contraction was also inhibited by Gd(3+) and ruthenium red, cation channel blockers, and Cl(-) channel blockers DIDS and niflumic acid. The reduction of extracellular Cl(-) concentrations enhanced the hypotonically induced contraction. Patch-clamp analysis showed that a hyposmotic challenge activated outwardly rectifying whole cell currents in isolated canine basilar artery myocytes. The reversal potential of the current was shifted toward negative potentials by reductions in intracellular Cl(-) concentration, indicating that the currents were carried by Cl(-). Moreover, the currents were abolished by 10 mM BAPTA in the pipette solution and by the removal of extracellular Ca(2+). Taken together, these results suggest that a hyposmotic challenge activates cation channels, which presumably cause Ca(2+) influx, thereby activating Ca(2+)-activated Cl(-) channels. The subsequent membrane depolarization is likely to increase Ca(2+) influx through VDCC and elicit contraction.

Calcium influx pathways in rat CNS pericytes

In central nervous system (CNS), pericytes have been proposed to play a role in broad functional activities including blood-brain barrier, microcirculation, and macrophage activity. However, contractile responses and Ca2+ signaling in CNS pericytes have not been elucidated. The aim of the present study is to investigate contractility and Ca2+ influx pathway in CNS pericytes. CNS pericytes were cultured from rat brain. Contraction of the pericytes in response to various stimuli was evaluated by the change in surface area measured by a light microscope with a digital camera. Reverse transcription and polymerase chain reaction (RT-PCR) was performed to examine the expression of mRNA of alpha-smooth muscle actin. Intracellular Ca2+ was measured using fura-2 fluorescence spectroscopy. A23187 (Ca2+ ionophore), high external K+ (4 x 10(-2) mol/l), endothelin-1, and serotonin induced contraction of CNS pericytes. RT-PCR analysis revealed the expression of alpha-smooth muscle actin in CNS pericytes. Cytosolic Ca2+ ([Ca2+]i) increased after application of high concentration of external K+, tetraethylammonium, and charybdotoxin, which was inhibited by nicardipine and removal of external Ca2+. Angiotensin-II, serotonin, acetylcholine, ATP, and endothelin-1 caused biphasic response in [Ca2+]i. In response to these agents, [Ca2+]i rapidly increased and then decayed to a relatively constant Ca2+ plateau. The Ca2+ plateau was partially inhibited by nicardipine and completely abolished by omission of external Ca2+. After intracellular Ca2+ store was depleted by the removal of external Ca2+ and addition of thapsigargin, reapplication of external Ca2+ evoked increases in [Ca2+]i. These results indicate that CNS pericytes express mRNA of alpha-smooth muscle actin and possess contractile ability. In CNS pericytes, resting membrane potential is regulated by large conductance Ca2+-activated K+ channels and Ca2+ enters into the cells via L-type voltage-dependent Ca2+ channels, agonist-activated Ca2+ permeable channels, and capacitative Ca2+ entry pathways.

Comparison of the Effects of Nicardipine and Sodium Nitroprusside for Control of Increased Blood Pressure after Coronary Artery Bypass Graft Surgery

We compared the haemodynamic effects of nicardipine and sodium nitroprusside after coronary artery bypass graft surgery. When post-surgery systolic blood pressure reached > 150 mmHg, patients were randomly given nicardipine (N group, n = 26) or sodium nitroprusside (S group, n = 21). The drugs were infused at a rate of 2 μg/kg per min for 10 min. If the target blood pressure (120-140 mmHg) was not achieved, the infusion rate was increased by 1 üg/kg per min every 10 min. Cardiac and stroke volume indices had increased significantly in the N group after 10 min and in both groups after 60 min. The infusion duration and total dose of drug were significantly lower in the N group compared with the S group. Nicardipine infusion controlled post-operative hypertension more rapidly and was superior to sodium nitroprusside in maintaining left ventricular performance immediately after drug infusion.

Current applications for nicardipine in invasive and interventional cardiology

Interventional coronary procedures, such as rotational atherectomy and coronary artery bypass graft (CABG) stenting, are associated with a risk of postoperative vasoconstriction, which can lead to sequelae that produce morbidity and even death. Vasodilators, such as calcium channel blockers, sodium nitroprusside and adenosine, are often administered to prevent or reverse these sequelae, and have proven effective for this purpose. The injectable dihydropyridine calcium channel blocker, nicardipine, has several unique properties that make it an effective option for preventing and/or reversing microvascular or conductance vessel vasoconstriction. In this review, we describe the evidence-based uses of nicardipine injection in interventional cardiology and cardiac catheterization procedures. In comparison to other calcium channel blockers, nicardipine injection appears to be potentially safer, easier to administer and capable of producing a more predictable response. This drug has potential advantages in preventing or reversing the no-reflow phenomenon that sometimes occurs after interventions in coronary bypass grafts. Nicardipine may also be effective when administered in a flush solution with other drugs during rotational atherectomy and clot debulking with or without distal protection devices. It also can control the hypertension that occurs after sternotomy and cardiac surgery, and in the cardiac catheterization laboratory. In summary, the dihydropyridine calcium channel blocker, nicardipine, has a wide range of useful applications during cardiovascular interventions.

Interactions of phospholipase D and cytochrome P450 protein stability

Previous studies have suggested a relationship between cytochrome P450 (P450) 3A (CYP3A) conformation and the phospholipid composition of the associated membrane. In this study, we utilized a novel microsomal incubation system that mimics many of the characteristics of CYP3A degradation pathway that have been observed in vivo and in cultured cells to study the effects of phospholipid composition on protein stability. We found that addition of phosphatidylcholine-specific phospholipase D (PLD) stabilized CYP3A in this system, but that phosphatidylinositol-specific phospholipase C (PLC) was without effect. Addition of phosphatidic acid also stabilized CYP3A protein in the microsomes. The use of 1,10-phenanthroline (phenanthroline), an inhibitor of PLD activity, decreased CYP3A stability in incubated microsomes. Similarly, 6-h treatment of primary cultures of rat hepatocytes with phenanthroline resulted in nearly complete loss of CYP3A protein. Treatment of rats with nicardipine or dimethylsulfoxide (DMSO), which have been shown to affect CYP3A stability, altered the phospholipid composition of hepatic microsomes. It did not appear, though, that the changes in phospholipid composition that resulted from these in vivo treatments accounted for the change in CYP3A stability observed in hepatic microsomes from these animals.

Changes in calcium signalling, gravitropism, and statocyte ultrastructure in pea roots induced by calcium channel blockers

The effect of Ca2+ channel blockers (D600 and nicardipine) were investigated in our experiments on 5-day seedlings of pea. Nicardipine had more inhibiting effect on root elongation than D600. The Ca2+ channel blockers (CCB) depressed gravitropic response in roots. In root statocytes, the destruction of the polar arrangement of cell organelles and other changes were induced by 10(-5) M D600 or nicardipine treatment for 12 h. At ultrastructural level, there were observed a lack of polarity, pronounced vacuolization, and changes in dictyosome structure in treated statocytes. Cytochemical study indicated that Ca2+ ions were concentrated in the intracellular organelles and cell walls in statocytes treated with CCB similar to untreated control. The data suggest that the effects of the CCB that demonstrated the correlation between the loss of polarity in statocytes and altered root gravitropism may be functionally related to systems that regulate Ca2+ homeostasis, particularly Ca2+ channels.

Treatment with Nicardipine Protects Brain in an Animal Model of Hypertension‐Induced Damage

Control of blood pressure protects from the development of cerebrovascular lesions and vascular dementia (VaD). This study has assessed the influence of treatment with the dihydropyridine-type Ca2+ antagonist nicardipine on brain microanatomical changes in spontaneously hypertensive rats (SHR). SHR were treated from 16th to 26th week of age with hypotensive (3 mg/Kg/day) or non-hypotensive (0.1 mg/Kg/day) doses of nicardipine, with the non-dihydropyridine-type vasodilator hydralazine (10 mg/kg/day) or with vehicle (control group). Untreated age-matched Wistar Kyoto (WKY) rats were used as a normotensive reference group. Brain volume, number of neurons, glial fibrillary-acidic protein (GFAP)-immunoreactive astrocytes and neurofilament 200 KDa (NFP)-immunoreactivity (IR) were assessed in frontal and occipital cortex, hippocampus and striatum. A decrease of volume and number of nerve cells and a loss of NFP-IR was found in the frontal and occipital cortex and in the CA1 subfield of hippocampus and in the striatum of SHR. Treatment with nicardipine countered microanatomical changes occurring in SHR, whereas hydralazine displayed a less pronounced effect. Comparatively, the non-hypotensive dose of nicardipine was less active than the hypotensive one. The observation that equihypotensive doses of nicardipine or hydralazine did not protect brain in the same way from hypertensive brain damage suggests that lowering blood pressure is per se not enough for affording neuroprotection. The demonstration of neuroprotective effect of nicardipine suggests an use of the compound in situations in which hypertension is accompanied by the risk of brain damage.

Vasodilation increases the threshold for bupivacaine-induced convulsions in rats

Bupivacaine affects the vascular resistance by peripheral and central nervous system (CNS) mechanisms. As vasoconstrictors increase the CNS toxicity of IV bupivacaine, vasodilators may decrease its CNS toxicity. We examined the hypothesis that vasodilators decrease the CNS toxicity of bupivacaine in awake, spontaneously breathing rats. Male Sprague-Dawley rats were randomly divided into control (C), nicardipine (N), and phentolamine (P) groups (n = 12 in each group). Racemic bupivacaine was administered IV at 1 mg/kg/min until tonic/clonic convulsions occurred. Saline, nicardipine (0.4 microg/min), and phentolamine (10 microg/min within 5 min, 50 microg/min thereafter) were simultaneously administered with bupivacaine in groups C, N, and P, respectively. Mean arterial blood pressure was significantly increased by infusion of bupivacaine in group C and was maintained at baseline levels before the onset of convulsions in groups N and P. The convulsive dose of bupivacaine in group C was 5.8 +/- 1.5 mg/kg, but was significantly larger in groups N and P (7.6 +/- 1.5 and 8.1 +/- 1.1 mg/kg, P = 0.02 and 0.001, respectively). However, there were no differences in total or protein-unbound plasma concentration of bupivacaine or in concentration of bupivacaine in the brain at the onset of convulsions among the 3 groups. We conclude that nicardipine and phentolamine increase the cumulative dose but do not affect the threshold plasma or brain concentrations required for bupivacaine-induced convulsions.

IMPLICATIONS

Bupivacaine, a long-acting local anesthetic, induces central nervous system toxicity when its plasma concentration is increased. Nicardipine and phentolamine increased the cumulative dose but did not affect the threshold plasma concentrations, required for bupivacaine-induced convulsions, suggesting that both nicardipine and phentolamine inhibited the increase in the plasma concentration of bupivacaine by inducing peripheral vasodilation.

ICC pacing mechanisms in intact mouse intestine differ from those in cultured or dissected intestine

Pacing of mouse intestine is driven by spontaneous activity of a network of interstitial cells of Cajal in the myenteric plexus (ICC-MP). So far, highly dissected circular muscle (CM) strips from control and mutant mice lacking ICC-MP and isolated, cultured ICC from newborn control mice were used to analyze its properties. Using intact circular and longitudinal segments of intestine, we recently reported that there were both significant similarities and differences between pacing studied in segments and from isolated, dissected tissues. Here, we report additional similarities and differences in our model from those in highly reduced systems. Similar to cultured or dissected intestine, blockade of sarcoplasmic-endoplasmic reticulum Ca(2+) pumps with thapsigargin or cyclopiazonic acid reduced pacing frequency, but thapsigargin was less effective than in isolated, cultured ICC. Moreover, inhibition of inositol 1,4,5-trisphosphate (IP(3)) receptors with xestospongin C, a putative inhibitor of IP(3) receptors, failed to affect pacing but successfully blocked increased pacing frequency by phorbol ester. 2-Aminoethoxy-diphenylborate, a putative blocker of IP(3)-mediated calcium release, caused a significant decrease in the amplitude and frequency of contractions. The mitochondrial uncoupler carbonyl cyanide p-trifluormethoxyphenylhydrazone blocked pacing and KCl-induced contractions at a concentration of 1 microM. The cyclic nucleotide agonists sodium nitroprusside (SNP), forskolin, and 8-bromo-cGMP inhibited pacing in CM. In longitudinal muscle (LM), SNP and forskolin had little effect on pacing. Furthermore, dibutyryl-cAMP did not affect pacing in CM or LM. These results suggest that pacing in intact intestine is under partly similar regulatory control as in more reduced systems. However, pacing in intact intestine is not affected by xestospongin C, which abolishes pacing in isolated, cultured ICC and exhibits attenuated responses to thapsigargin. Also, major differences between LM and CM suggest a separate pacemaker may drive LM.