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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]