[Show abstract][Hide abstract] ABSTRACT: Insulin resistance is concomitant with metabolic syndrome, oxidative stress and cardiac contractile dysfunction. However, the causal relationship between oxidative stress and cardiac dysfunction is unknown. This study was designed to determine the impact of overexpression of the cardiac antioxidant metallothionein on cardiac dysfunction induced by insulin resistance in mice.
Whole-body insulin resistance was generated in wild-type FVB and metallothionein transgenic mice by feeding them with sucrose for 12 weeks. Contractile and intracellular Ca(2+) properties were evaluated in ventricular myocytes using an IonOptix system. The contractile indices analysed included: peak shortening (PS), time to 90% PS (TPS(90)), time to 90% relengthening (TR(90)), half-width duration, maximal velocity of shortening (+dL/dt) and relengthening (-dL/dt), fura-fluorescence intensity change (DeltaFFI) and decay rate (tau).
The sucrose-fed mice displayed glucose intolerance, enhanced oxidative stress, hyperinsulinaemia, hypertriglyceridaemia and normal body weight. Compared with myocytes in starch-fed mice, those from sucrose-fed mice exhibited depressed PS, +dL/dt, -dL/dt, prolonged TR(90) and decay rate, and reduced DeltaFFI associated with normal TPS(90) and half-width duration. Western blot analysis revealed enhanced basal, but blunted insulin (15 mU/g)-stimulated Akt phosphorylation. It also showed elevated expression of insulin receptor beta, insulin receptor tyrosine phosphorylation, peroxisome proliferator-activated receptor gamma, protein tyrosine phosphatase 1B and phosphorylation of the transcription factor c-Jun, associated with a reduced fold increase of insulin-stimulated insulin receptor tyrosine phosphorylation in sucrose-fed mice. All western blot findings may be attenuated or ablated by metallothionein.
These data indicate that oxidative stress may play an important role in cardiac contractile dysfunction associated with glucose intolerance and possibly related to alteration in insulin signalling at the receptor and post-receptor levels.
[Show abstract][Hide abstract] ABSTRACT: Insulin-like growth factor-I (IGF-1) ameliorates cardiac dysfunction in diabetes although the mechanism of action remains poorly understood. This study examined the role of PI-3 kinase/Akt/mammalian target of rapamycin (mTOR) and calcineurin pathways in cardiac effects of IGF-1 against glucose toxicity. Adult rat ventricular myocytes were cultured for 8 h with either normal (NG, 5.5 mM) or high (HG, 25.5 mM) glucose, in the presence or absence of IGF-1 (10-500 nM), the PI-3 kinase/Akt inhibitor LY294002 (10 microM), the mTOR inhibitor rapamycin (20 microM) or the calcineurin inhibitors cyclosporin A (5 microM) or FK506 (10 mg/l). Mechanical properties were evaluated using an IonOptix MyoCam system. HG depressed peak shortening (PS), reduced maximal velocity of shortening/relengthening (+/- dl/dt) and prolongs time-to-90% relengthening (TR90), which were abolished by IGF-1 (100 and 500 nM). Interestingly, the IGF-1-elicited protective effect against HG was nullified by either LY294002 or rapamycin, but not by cyclosporine A or FK506. None of the inhibitors affected cell mechanics. Western blot analysis indicated that HG and IGF-1 stimulated phosphorylation of Akt and mTOR. HG also activated p70s6k and suppressed GSK-3beta phosphorylation. However, the HG-induced alterations in phosphorylation of Akt, mTOR, p70s6k and GSK-3beta were significantly reversed by IGF-1. Protein expression of Akt, mTOR, p70s6k, GSK-3beta, SERCA2a and phospholamban was unaffected by HG, IGF-1 or rapamycin. Rapamycin significantly enhanced Akt phosphorylation whereas it inhibited mTOR phosphorylation. Collectively, our data suggest that IGF-1 may provide cardiac protection against glucose in part through a PI-3 kinase/Akt/mTOR/ p70s6k-dependent and calcineurin-independent pathway.
Journal of Endocrinology 10/2005; 186(3):491-503. · 4.06 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: eNOS is expressed in cardiac myocytes and plays an important role in cardiac contractile function. This study was designed to determine whether ex vivo eNOS gene transfer in ventricular myocytes affects cardiac contractile function. Replication-incompetent adenoviral vectors encoding eNOS or marker gene beta-galactosidase (LacZ) were transduced into adult rat ventricular myocytes at an MOI of 10, 50, or 100 for 36 hours. Mechanical and intracellular Ca2+ properties of myocytes were evaluated by video-based edge detection and fura-2 fluorescence. NOS protein expression and activity were assessed by Western blot and 3H-arginine to 3H-citrulline assay. Myocytes transduced with eNOS but not LacZ displayed enhanced eNOS but not iNOS expression associated with elevated NOS activity. Myocytes transduced with eNOS exhibited significantly elevated peak shortening and velocity of shortening/relengthening associated with enhanced basal as well as electrically stimulated rise of intracellular Ca2+ compared with control or LacZ groups. The durations of shortening and relengthening were comparable in all groups. The eNOS-induced mechanical effects were paralleled with elevated phosphorylation of Akt. Furthermore, the phosphatidylinositol-3 (PI-3) kinase inhibitors wortmannin and LY294002 prevented eNOS-induced mechanical effects. These results revealed that gene transfer of eNOS directly promotes cardiomyocyte contractile function and intracellular Ca2+ handling, suggesting therapeutic potential of eNOS gene transfer.
Journal of Cardiovascular Pharmacology 03/2004; 43(2):171-7. · 2.38 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Alcoholic cardiomyopathy is manifested as ventricular dysfunction, although its specific toxic mechanism remains obscure. This study was designed to examine the impact of enhanced acetaldehyde exposure on cardiac function via cardiac-specific overexpression of alcohol dehydrogenase (ADH) after alcohol intake.
ADH transgenic and wild-type FVB mice were placed on a 4% alcohol or control diet for 8 weeks. Mechanical and intracellular Ca2+ properties were evaluated in cardiac myocytes. Levels of acetaldehyde, lipid peroxidation, and protein carbonyl formation were determined.
FVB and ADH mice consuming ethanol exhibited elevated blood ethanol/acetaldehyde, cardiac acetaldehyde, and cardiac hypertrophy compared with non-ethanol-consuming mice. However, the levels of cardiac acetaldehyde and hypertrophy were significantly greater in ADH ethanol-fed mice than FVB ethanol-fed mice. ADH transgene itself did not affect mechanical and intracellular Ca2+ properties with the exception of reduced resting intracellular Ca2+ and Ca2+ re-sequestration at low pace frequency. Myocytes from ethanol-fed mice showed significantly depressed peak shortening, velocity of shortening/relengthening, rise of intracellular Ca2+ transients, and sarco(endo)plasmic reticulum Ca2+ load associated with similar duration of shortening/relengthening compared with myocytes from control mice. Strikingly, the ethanol-induced mechanical and intracellular Ca2+ defects were exacerbated in ADH myocytes compared with the FVB group except velocity of shortening/relengthening. The lipid peroxidation end products malondialdehyde and protein carbonyl formation were significantly elevated in both livers and hearts after chronic ethanol consumption, with the cardiac lipid and protein damage being exaggerated by ADH transgene.
These data suggest that increased cardiac acetaldehyde exposure due to ADH transgene may play an important role in cardiac contractile dysfunctions associated with lipid and protein damage after alcohol intake.
Alcoholism Clinical and Experimental Research 08/2003; 27(7):1090-8. · 3.42 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Oxidative stress is intimately involved in alcoholic cardiomyopathy. Catalase is responsible for detoxification of hydrogen peroxide (H(2)O(2)) and may interfere with ethanol-induced cardiac toxicity. To test this hypothesis, a transgenic mouse line was produced to overexpress catalase (~50-fold) in the heart, ranging from sarcoplasm, the nucleus and peroxisomes within myocytes. Mechanical and intracellular Ca(2+) properties were evaluated in ventricular myocytes from catalase transgenic (CAT) and wild-type FVB mice. Protein abundance of sarco (endo) plasmic reticulum Ca(2+)-ATPase (SERCA), phospholamban (PLB), Na(+)/Ca(2+) exchanger (NCX), dihydropyridine Ca(2+) receptor (DHPR), ryanodine receptor (RyR), Akt and phosphorylated Akt (pAkt) were measured by western blot. CAT itself did not alter body and organ weights, as well as myocyte contractile properties. Acute exposure of ethanol elicited a concentration-dependent depression in cell shortening and intracellular Ca(2+) in FVB mice with maximal inhibitions of 65.4% and 35.8%, respectively. The ethanol-induced cardiac depression was significantly attenuated in myocytes from CAT with maximal inhibitions of 42.4% and 27.3%. CAT also abrogated the ethanol-induced inhibition of maximal velocity of shortening/relengthening, prolongation of relengthening duration and intracellular Ca(2+) clearing time. Cell shortening at different extracellular Ca(2+) revealed stronger myocyte-shortening amplitude under lower (0.5 mM) Ca(2+) in CAT mice. Protein expression of NCX, RyR, Akt and pAkt were elevated in myocytes from CAT mice, while those of SERCA, PLB and DHPR were not affected. In conclusion, our data suggest that catalase overexpression may protect cardiac myocytes from ethanol-induced contractile defect, partially through improved intracellular Ca(2+) handling and Akt signaling.
Journal of Molecular and Cellular Cardiology 07/2003; 35(6):645-52. · 5.15 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Women with functional ovaries have a lower cardiovascular risk than men and postmenopausal women. However, estrogen replacement therapy remains controversial. This study examined the effect of ovarian hormone deficiency and estrogen replacement on ventricular myocyte contractile function and PKB/Akt activation. Nulliparous female rats were subjected to bilateral ovariectomy (Ovx) or sham operation (sham). A subgroup of Ovx rats received estrogen (E(2)) replacement (40 microg. kg(-1). day(-1)) for 8 weeks. Mechanical and intracellular Ca(2+) properties were evaluated including peak shortening (PS), time to PS (TPS), time to 90% relengthening (TR(90)), maximal velocity of shortening/relengthening (+/-dL/dt), fura 2 fluorescence intensity (FFI), and decay rate. Levels of sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA2a), phospholamban (PLB), and Akt were assessed by Western blot. Ovx promoted body weight gain associated with reduced serum E(2) and uterine weight, all of which were abolished by E(2). Ovx depressed PS and +/-dL/dt, prolonged TPS, TR(90), and decay rate, and enhanced resting FFI, all of which, with the exception of TPS, were restored by E(2). Ovx did not alter the levels of SERCA2a, PLB, and total Akt, but significantly reduced Akt activation [phosphorylated Akt (pAkt)], pAkt/Akt, and the SERCA2a-to-PLB ratio. These alterations in protein expression were restored by E(2). E(2) enhanced PS and +dL/dt in vitro, which was abolished by the E(2) receptor antagonist ICI-182780. Ovx reduced myocyte Ca(2+) responsiveness and lessened stimulating frequency-induced decline in PS, both ablated by E(2). These data suggest that mechanical and protein functions of ventricular myocytes are directly regulated by E(2).
[Show abstract][Hide abstract] ABSTRACT: Acute ethanol exposure depresses ventricular contractility and contributes to alcoholic cardiomyopathy in both men and women chronically consuming ethanol. However, a gender-related difference in the severity of myopathy exists with female being more sensitive to ethanol-induced tissue damage. Acetaldehyde (ACA), the major oxidized product of ethanol, has been implicated to play a role in the pathogenesis and gender-related difference of alcoholic cardiomyopathy, possibly due to its direct cardiac effect and interaction with estrogen. This study was designed to compare the effects of cardiac overexpression of alcohol dehydrogenase (ADH), which converts ethanol into ACA, on the cardiac contractile response to ethanol in ventricular myocytes isolated from age-matched adult male and female transgenic (ADH) and wild-type (FVB) mice. Mechanical properties were measured with an IonOptix SoftEdge system. ACA production was assessed by gas chromatography. The ADH myocytes from both genders exhibited similar mechanical properties but a higher efficacy to produce ACA compared to FVB myocytes. Exposure to ethanol (80-640 mg/dl) for 60 min elicited concentration-dependent decrease of cell shortening in both FVB and ADH groups. The ethanol-induced depression on cell shortening was significantly augmented in female but not male ADH group. ADH transgene did not exacerbate the ethanol-induced inhibition of maximal velocity of shortening/relengthening in either gender. In addition, neither ethanol nor ADH transgene affect the duration of shortening and relengthening in male or female mice. These data suggest that females may be more sensitive to ACA-induced cardiac contractile depression than male, which may attribute to the gender-related difference of alcoholic cardiomyopathy.
Comparative Biochemistry and Physiology - Part A Molecular & Integrative Physiology 04/2003; 134(3):607-14. · 2.17 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Cardiac resistance to IGF-1 occurs in diabetes and is attributed to cardiac dysfunction in diabetes. However, the mechanism of action responsible for cardiac IGF-1 resistance is still unknown. This study was designed to examine the impact of high glucose on IGF-1-induced contractile response and activation of serine-threonine kinase Akt as well as extracellular signal-regulated kinase (ERK1/2) in cardiac myocytes.
Isolated adult rat ventricular myocytes were cultured for 12-18 h in a serum-free medium containing either normal (NG, 5.5 mM) or high (HG, 25.5 mM) glucose. Mechanical properties were evaluated using an IonOptix MyoCam system. Myocytes were electrically stimulated at 0.5 Hz and contractile properties analyzed included peak shortening (PS), time-to-PS (TPS) and time-to-90% relengthening (TR(90)). Intracellular Ca(2+)-induced Ca(2+) release was measured as fura-2 fluorescence intensity change (DeltaFFI). Protein levels of total and phosphorylated Akt and ERK1/2, indicators of Akt and ERK1/2 activation, IGF-1 receptors (pro-IGF-1R and IGF-1Ralpha) as well as the glucose transporter GLUT4 were assessed by Western blot.
IGF-1 (10(-10)-10(-6) M) elicited a dose-dependent increase in PS and DeltaFFI in myocytes maintained in NG medium. However, IGF-1 induced a negative response on PS and DeltaFFI in HG myocytes. The IGF-1-induced responses in NG or HG myocytes were blunted by the IGF-1 receptor antagonist H-1356. Western blot analysis revealed that IGF-1Ralpha but not pro-IGF-1R was reduced in HG myocytes. While IGF-1 (10(-6) M) upregulated total Akt protein levels in both NG and HG myocytes, it only induced a significant activation of Akt in NG but not HG myocytes. IGF-1 elicited comparable ERK1/2 activation in both NG and HG myocytes.
These results suggest that the cardiac IGF-1 resistance in diabetes is likely attributed, at least in part, to reduced IGF-1R and attenuated IGF-1-induced Akt phosphorylation under elevated extracellular glucose.
Cardiovascular Research 04/2003; 57(3):738-48. · 5.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This study characterized the cardiac contractile function and IGF-I response in a transgenic diabetic mouse model. Mechanical properties were evaluated in cardiac myocytes from OVE26 diabetic and FVB wild-type mice, including peak shortening (PS), time to PS (TPS), time to 90% relengthening (TR(90)) and maximal velocity of shortening/relengthening (+/-dL/dt). Intracellular Ca(2+) was evaluated as Ca(2+)-induced Ca(2+) release [difference in fura 2 fluorescent intensity (Delta FFI)] and fluorescence decay rate (tau). Sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA)2a, phospholamban (PLB), Na(+)-Ca(2+) exchanger (NCX), GLUT4, and the serine-threonine kinase Akt were assessed by Western blot. RhoA and IGF-I/IGF-I receptor mRNA levels were determined by RT-PCR and Northern blot. OVE26 myocytes displayed decreased PS, +/-dL/dt, and Delta FFI associated with prolonged TPS, TR(90), and tau. SERCA2a, NCX, and Akt activation were reduced, whereas PLB and RhoA were enhanced in OVE26 hearts. GLUT4 was unchanged. IGF-I enhanced PS and Delta FFI in FVB but not OVE26 myocytes. IGF-I mRNA was increased, but IGF-I receptor mRNA was reduced in OVE26 hearts and livers. These results validate diabetic cardiomyopathy in OVE26 mice due to reduced SERCA2, NCX, IGF-I response, and Akt activation associated with enhanced RhoA level, suggesting a therapeutic potential for Akt and RhoA.
AJP Endocrinology and Metabolism 03/2003; 284(2):E366-76. · 4.51 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Chronic peritoneal sepsis in a rodent model produces myocardial dysfunction characterized by decreased rates of ventricular contraction and relaxation in the isolated heart preparation. However, it remains controversial whether the ventricular contractility is altered during sepsis. In the present study, we determined the effect of chronic peritoneal sepsis on the mechanical properties and intracellular Ca2+ handling of cardiac myocytes isolated from septic rats at 24 or 48 h. Mechanical properties were evaluated by use of an IonOptix MyoCam system. Myocytes were electrically stimulated at 0.5 Hz. The contractile properties analyzed included peak shortening (PS), time-to-peak shortening (TPS), time-to-90% relengthening (TR90), and maximal velocities of shortening and relengthening (+/-dL/dt). Intracellular Ca2+ handling was evaluated with fura-2 fluorescent dye. Myocytes obtained from 24-h postseptic animals exhibited a depressed PS (85% of control), normal TPS, prolonged TR90 (147% of control), and reduced +/-dL/dt (both 79% of control). Myocytes from 48-h postseptic animals also exhibited a reduced peak of intracellular Ca2+ sequestration (55% of control), but resting intracellular Ca2+ and Ca2+-transient decay were comparable with the values seen in myocytes from untreated rats. Myocytes from septic and control animals were equally responsive over a range of stimulation frequencies (0.1-5 Hz). Myocytes from septic animals were unresponsive (5% of control) to increase of extracellular Ca2+ (0.5-3 mM). These results demonstrate that sepsis produces substantial deficits in cardiac myocytes function that can be attributed to altered calcium transient properties.
[Show abstract][Hide abstract] ABSTRACT: Growth hormone (GH) plays a key role in cardiac growth and function. However, excessive levels of GH often result in cardiac dysfunction, which is the major cause of death in acromegalic patients. Transgenic mice with GH over-expression serve as useful models for acromegaly and exhibit impaired cardiac functions using echocardiography, similar to those of human acromegaly. However, the mechanism underscoring the impaired ventricular function has not been well defined. This study was designed to evaluate the cardiac excitation-contraction coupling in GH over-expressing transgenic mice at the single ventricular myocyte level. Myocytes were isolated from GH and age-matched wild-type mouse hearts. Mechanical properties were evaluated using an IonOptix MyoCam system. The contractile properties analyzed included peak shortening (PS), time-to-peak shortening (TPS) and time-to-90% relengthening (TR(90)), and maximal velocities of shortening/relengthening (+/-dL/dt). Intracellular Ca2+ properties were evaluated by fura-2. GH transgenic mice exhibited significantly increased body weights and enlarged heart and myocyte size. Myocytes from GH transgenic mice displayed significantly enhanced PS and+/-dL/dt associated with similar TPS and TR(90) compared with the wild-type littermates. Myocytes from GH transgenic mice displayed a similar resting intracellular Ca2+ level and Ca2+ removal rate but exhibited an elevated peak intracellular Ca2+ level compared with the wild-type group. Myocytes from both groups were equally responsive to increases in extracellular Ca2+ concentration and stimulating frequency. These results suggest that GH over-expression is associated with enhanced contractile function in isolated myocytes and that the impaired cardiac function observed in whole hearts may not be due to defects at the myocyte level.
Journal of Endocrinology 06/2002; 173(2):257-64. · 4.06 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Alcoholic cardiomyopathy is characterized by impaired ventricular function although its toxic mechanism is unclear. This study examined the impact of cardiac overexpression of alcohol dehydrogenase (ADH), which oxidizes ethanol into acetaldehyde (ACA), on ethanol-induced cardiac contractile defect. Mechanical and intracellular Ca(2+) properties were evaluated in ventricular myocytes from ADH transgenic and wild-type (FVB) mice. ACA production was assessed by gas chromatography. ADH myocytes exhibited similar mechanical properties but a higher efficiency to convert ACA compared with FVB myocytes. Acute exposure to ethanol depressed cell shortening and intracellular Ca(2+) in the FVB group with maximal inhibitions of 23.3% and 23.4%, respectively. Strikingly, the ethanol-induced depression on cell shortening and intracellular Ca(2+) was significantly augmented in the ADH group, with maximal inhibitions of 43.7% and 40.6%, respectively. Pretreatment with the ADH inhibitor 4-methylpyrazole (4-MP) or the aldehyde dehydrogenase inhibitor cyanamide prevented or augmented the ethanol-induced inhibition, respectively, in the ADH but not the FVB group. The ADH transgene also substantiated the ethanol-induced inhibition of maximal velocity of shortening/relengthening and unmasked an ethanol-induced prolongation of the duration of shortening/relengthening, which was abolished by 4-MP. These data suggest that elevated cardiac ACA exposure due to enhanced ADH expression may play an important role in the development of alcoholic cardiomyopathy.
[Show abstract][Hide abstract] ABSTRACT: Ethanol causes vasoconstriction and contributes to the development of hypertension. Acetaldehyde (ACA), the primary metabolite of ethanol, elevates blood pressure by releasing endogenous catecholamines. In vitro, ACA leads to vasorelaxation, although the response may vary among various vascular beds. This study examined the influence of hypertensive state on the ACA-induced vasorelaxant responsiveness. Ring segments of thoracic aorta were isolated from Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) and isometric tension development was measured. In aorta with or without intact endothelium, the contractile responses to KCl and norepinephrine were greatly attenuated, whereas vasoconstrictive response to 5-HT was enhanced, by hypertension. Vasorelaxant response to histamine was similar between WKY and SHR groups. ACA (1-30 mM) elicited endothelium-intact as well as -denuded vasorelaxation in a dose-dependent manner in aorta from both WKY and SHR groups. Interestingly, the ACA-induced endothelium-intact vasorelaxation was significantly diminished, whereas the ACA-induced endothelium-denuded vasorelaxation was significantly augmented, by hypertension. These data indicated that the ACA-induced vasorelaxant response, either endothelium-intact or-denuded, is altered by the hypertensive state.
Pharmacological Research 04/2002; 45(3):195-9. · 4.35 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To assess the teratogenic action of ethanol on cardiac contractile function in offspring exposed to ethanol in utero, pregnant Sprague-Dawley rats were fed with ethanol during gestation. Left-ventricular papillary muscles and myocytes were isolated from the offspring of the ethanol-ingesting and control pregnant rats. Mechanical parameters measured were peak tension development (PTD, indicating the myocardial force-generating capacity), peak cell shortening (PS), time-to-PTD/PS (TPT/TPS), time-to-90% relaxation/re-lengthening (RT(90)/TR(90)), and maximal velocities of contraction/shortening and relaxation/re-lengthening (+/- VT and +/- dL/dt). Intracellular Ca(2+) levels and apoptosis were evaluated with fura-2 fluorescent dye and Caspase-3 activation assay, respectively. Offspring of the ethanol group displayed decreased heart weight associated with comparable body, liver and kidney weight, and papillary muscle weight/size, compared to the control group. However, prenatal ethanol exposure depressed myocardial PTD and +/- VT. The myocardium from the ethanol group also exhibited slightly but significantly shortened TPT, accompanied with normal RT(90). Muscles from both groups exhibited comparable responses to post-rest potentiation, increasing extracellular Ca(2+) concentration, noradrenaline and acute ethanol challenge. Ventricular myocytes from both the control and ethanol groups possessed similar PS, TPS, TR(90) and +/- dL/dt. Both resting and peak intracellular Ca(2+) levels were elevated in myocytes from the ethanol group. Additionally, acute ethanol application depressed caffeine-induced intracellular Ca(2+) rise in myocytes from both groups. Myocytes from the ethanol group displayed an enhanced Caspase-3 activation, compared to control myocytes. These results suggest that prenatal ethanol exposure alters myocardial contractile function and may contribute to the development of postnatal cardiac dysfunction through, in part, increased intracellular Ca(2+) loading and apoptosis.
Alcohol and Alcoholism 01/2002; 37(1):30-7. · 1.96 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 1. Panax ginseng is used to enhance stamina and relieve fatigue as well as physical stress. Ginsenoside, the effective component of ginseng, regulates cardiovascular function. This study was to examine the effect of ginsenosides Rb1 and Re on cardiac contractile function at the cellular level. Ventricular myocytes were isolated from adult rat hearts and were stimulated to contract at 0.5 Hz. Contractile properties analysed included: peak shortening (PS), time-to-90%PS (TPS), time-to-90% relengthening (TR90), and fluorescence intensity change (DeltaFFI). Nitric oxide synthase (NOS) activity was determined by the 3H-arginine to 3H-citrulline conversion assay. 2. Both Rb1 and Re exhibited dose-dependent (1-1000 nM) inhibition in PS and DeltaFFI, with maximal inhibitions between 20-25%. Concurrent application Rb1 and Re did not produce any additive inhibition on peak shortening amplitude (with a maximal inhibition of 24.9+/-6.1%), compared to Rb1 or Re alone. Pretreatment with the NOS inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME, 100 microM) abolished the effect of Rb1 and Re. Both Rb1 and Re significantly (P<0.05) stimulated NOS activity concentration-dependently. 3. This study demonstrated a direct depressant action of ginsenosides on cardiomyocyte contraction, which may be mediated in part through increased NO production.
British Journal of Pharmacology 12/2001; 134(6):1159-65. · 5.07 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Diabetes and hypertension both produce myocardial dysfunction that accelerates cardiovascular morbidity and mortality. Coexistence of the two often results in a more severe cardiomyopathy than either process alone. The purpose of this study was to characterize the contractile function of diabetic hypertensive cardiomyopathy at the single myocyte level. Adult spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats were made diabetic with a single injection (55 mg/kg) of streptozotocin (STZ). Contractile properties of ventricular myocytes were evaluated, including peak shortening (PS), time-to-peak shortening (TPS), time-to-90% relengthening (TR90) and maximal velocities of shortening/relengthening (+/-dL/d t). The experimental animals exhibited enlarged heart size, elevated blood glucose and systolic blood pressure. PS was unchanged (SHR), enhanced (WKY-STZ) or depressed (SHR-STZ) compared to control (WKY). Myocytes from all experimental groups displayed prolonged TPS and TR90 compared to the WKY group, although only those from the hypertensive groups (SHR, SHR-STZ) were associated with reduced +/-dL/d t. Additionally, myocytes from the WKY-STZ but not the SHR or the SHR-STZ groups exhibited impaired responsiveness to increased extracellular Ca2+. Myocytes from the SHR-STZ group displayed a leftward shift of the stimulus frequency-peak shortening response curve compared to the WKY group. These results confirmed observations at the multicellular levels that combination of diabetes and hypertension results in a greater impairment of cardiac contractile function than is seen with either disease alone.
Journal of Molecular and Cellular Cardiology 10/2001; 33(9):1719-26. · 5.15 Impact Factor