amlodipine Norvasc
Amlodipine inhibits doxorubicin-induced apoptosis in neonatal rat cardiac myocytes.

Yamanaka S, Tatsumi T, Shiraishi J, Mano A, Keira N, Matoba S, Asayama J, Fushiki S, Fliss H, Nakagawa M.

Second Department of Medicine, Kyoto Prefectural University of Medicine, Kyoto, Japan.

OBJECTIVES: We examined whether amlodipine, a calcium channel antagonist with potent antioxidant activity, inhibits doxorubicin-induced apoptosis in cultured neonatal rat cardiac myocytes. BACKGROUND: Recent studies have shown that doxorubicin induces apoptosis as well as necrosis in myocytes through generation of reactive oxygen species. METHODS: The effects of amlodipine and several other antioxidants on doxorubicin-induced oxidative stress and mitochondria-mediated apoptosis were examined. RESULTS: Treatment of myocytes with doxorubicin (10(-6) mol/l) for 14 h increased the number of cells with elevated peroxides, as histochemically estimated by 2',7'-dichlorofluorescin (DCF) diacetate, and the percentage of apoptotic myocytes, as estimated by Hoechst 33258 nuclear staining, compared with control myocytes (25.0 +/- 1.6% vs. 5.2 +/- 1.2%). Moreover, doxorubicin-induced myocyte apoptosis was also confirmed by annexin V-fluorescein isothiocyanate binding assay. Doxorubicin induced a reduction in myocyte adenosine 5'-triphosphate content, a loss of mitochondrial membrane potential, cytochrome c release from the mitochondria into the cytosol, and caspase-3 activation to 1.9-fold of control. Amlodipine significantly attenuated increased DCF fluorescence, inhibited the mitochondria-mediated apoptotic responses described earlier, and decreased apoptosis in the doxorubicin-treated myocytes in a dose-dependent fashion. Amlodipine at 10(-6) mol/l significantly decreased apoptosis to 15.4 +/- 0.7%, and this antiapoptotic action was more effective than that seen with other antioxidants, including probucol, ascorbic acid, and alpha-tocopherol. In contrast, the calcium channel antagonist nifedipine (10(-6) mol/l) did not inhibit apoptosis. Catalase, glutathione, and N-acetylcysteine, but not mannitol or superoxide dismutase, significantly decreased DCF fluorescence and attenuated myocyte apoptosis induced by doxorubicin to 18.7 +/- 1.2%, 19.1 +/- 1.7%, and 18.7 +/- 0.6%, respectively. CONCLUSIONS: Amlodipine significantly inhibits doxorubicin-induced myocyte apoptosis by suppressing the mitochondrial apoptotic pathway. This effect is attributed to the antioxidant properties of amlodipine, affecting mainly hydrogen peroxide.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12628736&dopt=Abstract amlodipine Norvasc



amlodipine Norvasc
Automated gas chromatographic assay for amlodipine in plasma and gingival crevicular fluid.

Monkman SC, Ellis JS, Cholerton S, Thomason JM, Seymour RA, Idle JR.

Department of Pharmacological Sciences, Medical School, University of Newcastle upon Tyne, UK.

This paper describes an automated capillary gas chromatographic method for the determination of amlodipine in plasma, and in sub-microlitre volumes of gingival crevicular fluid (GCF), in order to assess if amlodipine is present in GCF under conditions of gingival overgrowth, as has been shown for nifedipine, another dihydropyridine drug. Liquid-liquid extraction followed by derivatisation was employed to isolate amlodipine and render it suitable for gas chromatography. Amlodipine was analysed in plasma and GCF of four patients undergoing amlodipine therapy for cardiovascular disorders, three of whom had significant gingival overgrowth. Amlodipine was detected in the plasma of all patients and in massive concentrations in the GCF of those patients with overgrowth, 23- to 290-fold greater than in their plasma. Like nifedipine, amlodipine sequestration into GCF appears to be linked with gingival overgrowth.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8738044&dopt=Abstract amlodipine Norvasc



amlodipine Norvasc
Antihypertensive agents and renal protection: calcium channel blockers.

Saruta T, Kanno Y, Hayashi K, Konishi K.

Department of Internal Medicine, School of Medicine, Keio University, Tokyo, Japan.

This study defines the nature of the renal protective effects of calcium channel blockers (Ca blockers) and the effects of the Ca blocker, amlodipine, compared to those of the angiotensin-converting enzyme inhibitor (ACEI), enalapril, on the progression of renal injury in 5/6 nephrectomized spontaneously hypertensive rats (SHR) fed a high-salt diet. Furthermore, we studied the effects of various Ca blockers on the glomerular afferent and efferent arterioles using the isolated perfused hydronephrotic kidneys of six-week-old male Sprague-Dawley rats. In the first study, forty 6-week-old male SHRs which underwent 5/6 nephrectomy were equally divided into five groups. One group received no therapy. In two groups, therapy was started at four weeks post-nephrectomy, one with amlodipine and the other with enalapril. In the remaining two groups, amlodipine or enalapril therapy was started at eight weeks postnephrectomy. Amlodipine was more effective than enalapril in reducing proteinuria and glomerulosclerosis in the group that was started on drug therapy eight weeks after surgery. In the second study, at concentrations of 10(-6) to 10(-9) M, nifedipine, nicardipine and amlodipine dilated the afferent, but not the efferent, arteriole preconstricted with angiotensin II. On the other hand, efonidipine and manidipine clearly dilated angiotensin II-induced constriction of both the afferent and efferent arterioles. These results indicated that Ca blockers are effective at reducing renal injury in 5/6 nephrectomized SHR, and that they are more effective than ACEI in advanced stages of renal injury. The observation that only certain Ca blockers can dilate the efferent arteriole suggests that the renal protective effect of Ca blockers is not necessarily dependent on the dilation of the efferent arterioles.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8743511&dopt=Abstract amlodipine Norvasc



amlodipine Norvasc
Long-acting Ca2+ blockers prevent myocardial remodeling induced by chronic NO inhibition in rats.

Sanada S, Node K, Minamino T, Takashima S, Ogai A, Asanuma H, Ogita H, Liao Y, Asakura M, Kim J, Hori M, Kitakaze M.

Department of Internal Medicine and Therapeutics, Osaka University Graduate School of Medicine, Suita, Osaka, Japan.

Chronic inhibition of nitric oxide (NO) synthesis induces cardiac remodeling independent of systemic hemodynamic changes in rats. We examined whether long-acting dihydropyridine calcium channel blockers block myocardial remodeling and whether the activation of 70-kDa S6 kinase (p70S6K) and extracellular signal-regulated kinase (ERK) are involved. Ten groups of Wistar-Kyoto rats underwent 8 weeks of drug treatment consisting of a combination of NO synthase inhibitor NG-nitro-l-arginine methyl ester (L-NAME), an inactive isomer (D-NAME), amlodipine (1 or 3 mg/kg per day), or benidipine (3 or 10 mg/kg per day). In other groups, L-NAME was also used in combination with a p70S6K inhibitor (rapamycin), a MEK inhibitor (PD98059), and hydralazine. Systolic blood pressure (SBP), heart rate, and left ventricular weight (LVW) were measured, together with histological examinations and kinase assay. L-NAME increased SBP and LVW (1048+/-22 versus 780+/-18 mg, P<0.01) compared with the control, showing a significant increase in cross-sectional area of cardiomyocytes after 8 weeks. Amlodipine, benidipine, or hydralazine equally attenuated the increase in SBP induced by L-NAME. However, both amlodipine and benidipine but not hydralazine attenuated the increase in LVW by L-NAME (789+/-27, 825+/-20 mg, P<0.01, and 1118+/-29 mg, NS, respectively), also confirmed by histological analysis. L-NAME caused a 2.2-fold/1.8-fold increase in p70S6K/ERK activity in myocardium compared with the control, both of which were attenuated by both amlodipine and benidipine but not hydralazine. Both rapamycin and PD98059 attenuated cardiac hypertrophy in this model. Thus, long-acting dihydropyridine calcium channel blockers inhibited cardiac hypertrophy induced by chronic inhibition of NO synthesis by inhibiting both p70S6K and ERK in vivo.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12629037&dopt=Abstract amlodipine Norvasc



amlodipine Norvasc
Effects of an AT1 receptor antagonist, an ACE inhibitor and a calcium channel antagonist on cardiac gene expressions in hypertensive rats.

Kim S, Ohta K, Hamaguchi A, Yukimura T, Miura K, Iwao H.

Department of Pharmacology, Osaka City University Medical School, Japan.

1. This study was undertaken to determine whether the AT1 receptor directly contributes to hypertension-induced cardiac hypertrophy and gene expressions. 2. Stroke-prone spontaneously hypertensive rats (SHRSP) were given orally an AT1, receptor antagonist (losartan, 30 mg kg-1 day-1), an angiotensin converting enzyme inhibitor (enalapril 10 mg kg-1 day-1), a dihydropyridine calcium channel antagonist (amlodipine, 5 mg kg-1 day-1), or vehicle (control), for 8 weeks (from 16 to 24 weeks of age). The effects of each drug were compared on ventricular weight and mRNA levels for myocardial phenotype- and fibrosis-related genes. 3. Left ventricular hypertrophy of SHRSP was accompanied by the increase in mRNA levels for two foetal phenotypes of contractile proteins (skeletal alpha-actin and beta-myosin heavy chain (beta-MHC)), atrial natriuretic polypeptide (ANP), transforming growth factor-beta-1 (TGF-beta 1) and collagen, and a decrease in mRNA levels for an adult phenotype of contractile protein (alpha-MHC). Thus, the left ventricle of SHRSP was characterized by myocardial transition from an adult to a foetal phenotype and interstitial fibrosis at the molecular level. 4. Although losartan, enalapril and amlodipine lowered blood pressure of SHRSP to a comparable degree throughout the treatment, losartan caused regression of left ventricular hypertrophy of SHRSP to a greater extent than amlodipine (P < 0.01). 5. Losartan significantly decreased mRNA levels for skeletal alpha-actin, ANP, TGF-beta 1 and collagen types I, III and IV and increased alpha-MHC mRNA in the left ventricle of SHRSP. Amlodipine did not alter left ventricular ANP, alpha-MHC and collagen types I and IV mRNA levels of SHRSP. 6. The effects of enalapril on left ventricular hypertrophy and gene expressions of SHRSP were similar to those of losartan, except for the lack of inhibition of collagen type I expression by enalapril. 7. Unlike the hypertrophied left ventricle, there was no significant difference between losartan and amlodipine in the effects on non-hypertrophied right ventricular gene expressions of SHRSP. 8. Our results show that hypertension causes not only left ventricular hypertrophy but also molecular transition of myocardium to a foetal phenotype and interstitial fibrosis-related molecular changes. These hypertension-induced left ventricular molecular changes may be at least in part mediated by the direct action of local angiotensin II via the AT1, receptor.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8762077&dopt=Abstract amlodipine Norvasc



amlodipine Norvasc
Quantitative determination of amlodipine in serum by liquid chromatography with atmospheric pressure chemical ionization tandem mass spectrometry.

Yasuda T, Tanaka M, Iba K.

Research Center, Sumitomo Pharmaceuticals Co. Ltd., Osaka, Japan.

A sensitive and specific liquid chromatographic method coupled with tandem mass spectrometry was developed for the quantification of amlodipine in human and rat serum, which is a dihydropyridine derivative with calcium antagonist activity. An atmospheric pressure chemical ionization interface was used as the ion source and the analysis was performed in the selected reactive monitoring (SRM) mode. Deuterated amlodipine was used as the internal standard, and serum samples were treated with diethyl ether extraction prior to analysis. Serum levels in the range 0.014-7.2 ng ml-1 were measured accurately by this method, and the lower limit of quantitation (LOQ) was 0.014 ng ml-1 using 1 ml of human serum. The accuracy was within 7% of the expected values. The intra-assay precision was less than 3% and the inter-assay precision was less than 6%. The method was applied to a pharmacokinetic study of amlodipine in rats, in which the measurable range was 0.14-72 ng ml-1 using 0.1 ml of serum because of a limitation on the sample volume.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8799314&dopt=Abstract amlodipine Norvasc



amlodipine Norvasc
Low protein diet mediated renoprotection in remnant kidneys: Renal autoregulatory versus hypertrophic mechanisms.

Griffin KA, Picken M, Giobbie-Hurder A, Bidani AK.

Department of Internal Medicine, Loyola University Medical Center; and Edward Hines, Jr., Hospital, Maywood and Hines, Illinois 60141, USA. Martha.Prado med.va.gov

BACKGROUND: The mechanism of low protein diet conferred renoprotection in the ablation model remains controversial. Blockade of glomerular hypertrophy, reduced preglomerular vasodilation, and preserved autoregulation have all been postulated. The potential differential impact of calcium channel blockers on these mechanisms and glomerulosclerosis was examined. METHODS: Rats with 5/6 renal ablation received either a 25% standard protein diet, an 8% low protein diet and a low protein diet with either verapamil or amlodipine. Renal autoregulatory and morphometric studies were performed at 3 weeks before the development of significant injury, and the assessment of glomerulosclerosis after 7 weeks of continuous blood pressure radiotelemetry in additional rats. RESULTS: The preserved renal autoregulation in low protein rats was abolished by both calcium channel blockers, with the impairment being either comparable to (low protein + verapamil) or greater than the standard protein rats (low protein + amlodipine). Neither calcium channel blocker blocked the inhibitory effects of low protein diet on renal blood flow, kidney weight, and glomerular volume. Results (mean +/- SE) for glomerular volume (microm-3x 10(-6)): low protein (N = 11), 1.6 +/- 0.1; low protein + verapamil (N = 10), 1.7 +/- 0.1; low protein + amlodipine (N = 12), 1.7 +/- 0.2; versus standard protein (N = 10), 2.2 +/- 0.1; P < 0.05. Only amlodipine, but not verapamil, reduced average systolic blood pressure (143 +/- 2 mm Hg versus low protein rats, 168 +/- 5 mm Hg, and standard rats, 170 +/- 6 mm Hg; P < 0.01). Nevertheless, the glomeruloprotection seen in low protein (N = 15) as compared to standard protein (N = 14) rats (9%+/- 3% versus 28%+/- 6% glomerulosclerosis; P < 0.01) was abolished in both low protein + verapamil (N = 14, 32%+/- 7%) and low protein + amlodipine rats (N = 16, 27%+/- 7%). CONCLUSIONS: Preservation of renal autoregulation and not inhibition of hypertrophy is the critical component in low protein diet-conferred glomeruloprotection.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12631125&dopt=Abstract amlodipine Norvasc



amlodipine Norvasc
Amlodipine inhibits the development of right ventricular hypertrophy and medial thickening of pulmonary arteries in a rat model of pulmonary hypertension.

Takahashi T, Kanda T, Imai S, Suzuki T, Kobayashi I, Nagai R.

Second Department of Internal Medicine, Gunma University School of Medicine, Japan.

This study was designed to evaluate the effects of amlodipine, a new calcium channel blocker, on the development of right ventricular hypertrophy and thickening of the media of the pulmonary arteries in a rat model of pulmonary hypertension. Pulmonary hypertension was induced in rats by administering a single injection of monocrotaline, 80 mg/kg. The oral administration of amlodipine, 3, 10, or 30 mg/kg/day, was initiated 24 hours later (day 1). On day 28 of therapy, we determined the right ventricular systolic pressure (RVSP), the mass ratio of the right ventricle (RV) to the left ventricle, the thickness of the wall of the RV, the diameter of myocardial fibers in the RV, the percent thickness of the media of the pulmonary artery, and the percent area of smooth muscle in the pulmonary arteries. The magnitude of all parameters was significantly less in the rats administered amlodipine, 30 mg/kg/day, vs. the control group given monocrotaline alone. RVSP, the percent medial thickness, and the percent smooth muscle area, were significantly lower in rats administered a dose of amlodipine, 30 mg/kg/day vs. 10 mg/kg/day. The oral administration of amlodipine, 30 mg/kg/day, inhibited the development of RV hypertrophy and medial thickening of the pulmonary arteries in rats exposed to monocrotaline significantly more effectively vs. the untreated control exposed only to monocrotaline.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8824928&dopt=Abstract amlodipine Norvasc