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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[sub 2]) replacement (40 μg·kgsup -1]. day[sup -1]) for 8 weeks. Mechanical and intracellular Ca[sup 2+] properties were evaluated including peak shortening (PS), time to PS (TPS), time to 90% relengthening (TR[sub 90]), maximal velocity of shortening/relengthening (±dL/dt), fura 2 fluorescence intensity (FFI), and decay rate. Levels of sarco(endo)plasmic reticulum Ca[sup 2+]-ATPase (SERCA2a), phospholamban (PLB), and Akt were assessed by Western blot. Ovx promoted body weight gain associated with reduced serum E[sub 2] and uterine weight, all of which were abolished by E[sub 2]. Ovx depressed PS and ±dL/dt, prolonged TPS, TR[sub 90], and decay rate, and enhanced resting FFI, all of which, with the exception of TPS, were restored by E[sub 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 SERCA2ato-PLB ratio. These alteration in proton expression were restored by E[sub 2]. E[sub 2] enhanced PS and +dL/dt in vitro, which was abolished by the E[sub 2] receptor antagonist ICI-182780. Ovx reduced myocyte Ca[sup 2+] responsiveness and lessened stimulating frequency-induced decline in PS, both ablated by E[sub 2]. These data suggest that mechanical and proton functions of ventricular myocytes are directly regulated by E[sub 2]. [ABSTRACT FROM AUTHOR]

Objective: 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. Methods: 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 (TR90). Intracellular Ca2+-induced Ca2+ release was measured as fura-2 fluorescence intensity change (ΔFFI). 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-1Rα) as well as the glucose transporter GLUT4 were assessed by Western blot. Results: IGF-1 (10−10–10−6 M) elicited a dose-dependent increase in PS and ΔFFI in myocytes maintained in NG medium. However, IGF-1 induced a negative response on PS and ΔFFI 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-1Rα 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. Conclusion: 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. [Copyright &y& Elsevier]

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[SUB90]) and maximal velocity of shortening/relengthening (±dL/dt). Intracellular Ca[SUP2+] was evaluated as Ca[SUP2+]-induced Ca[SUP2+] release [difference in fura 2 fluorescent intensity (ΔFFI)] and fluorescence decay rate (τ). Sarco(endo)plasmic reticulum Ca[SUP2+]-ATPase (SERCA)2a, phospholamban (PLB), Na[SUP+]-Ca[SUP2+] 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 ΔFFI associated with prolonged TPS, TR[SUB90], and τ. SERCA2a, NCX, and Akt activation were reduced, whereas PLB and RhoA were enhanced in OVE26 hearts. GLUT4 was unchanged. IGF-I enhanced PS and AFFI 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. [ABSTRACT FROM AUTHOR]

Presents information on a study which examined the impact of cardiac overexpression of alcohol dehydrogenase on ethanol-induced cardiac contractile defect in rats. Materials and methods; Results and discussion.

— 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 (RT90/TR90), and maximal velocities of contraction/shortening and relaxation/re-lengthening (±VT and ±dL/dt). Intracellular Ca2+ 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 RT90. Muscles from both groups exhibited comparable responses to post-rest potentiation, increasing extracellular Ca2+ concentration, noradrenaline and acute ethanol challenge. Ventricular myocytes from both the control and ethanol groups possessed similar PS, TPS, TR90 and ±dL/dt. Both resting and peak intracellular Ca2+ levels were elevated in myocytes from the ethanol group. Additionally, acute ethanol application depressed caffeine-induced intracellular Ca2+ 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 Ca2+ loading and apoptosis. [ABSTRACT FROM PUBLISHER]