1. Metformin is an activator of AMP-activated protein kinase (AMPK). Recent studies suggest that pharmacological activation of AMPK inhibits cardiac hypertrophy. In the present study, we examined whether long-term treatment with metformin could attenuate ventricular hypertrophy in a rat model. The potential involvement of nitric oxide (NO) in the effects of metformin was also investigated. 2. Ventricular hypertrophy was established in rats by transaortic constriction (TAC). Starting 1 week after the TAC procedure, rats were treated with metformin (300 mg/kg per day, p.o.), N(G)-nitro-L-arginine methyl ester (L-NAME; 50 mg/kg per day, p.o.) or both for 8 weeks prior to the assessment of haemodynamic function and cardiac hypertrophy. 3. Cultured cardiomyocytes were used to examine the effects of metformin on the AMPK-endothelial NO synthase (eNOS) pathway. Cells were exposed to angiotensin (Ang) II (10⁻⁶ mol/L) for 24 h under serum-free conditions in the presence or absence of metformin (10⁻³ mol/L), compound C (10⁻⁶ mol/L), L-NAME (10⁻⁶ mol/L) or their combination. The rate of incorporation of [³H]-leucine was determined, western blotting analyses of AMPK-eNOS, neuronal nitric oxide synthase (nNOS) and inducible nitric oxide synthase (iNOS) were undertaken and the concentration of NO in culture media was determined. 4. Transaortic constriction resulted in significant haemodynamic dysfunction and ventricular hypertrophy. Myocardial fibrosis was also evident. Treatment with metformin improved haemodynamic function and significantly attenuated ventricular hypertrophy. Most of the effects of metformin were abolished by concomitant L-NAME treatment. L-NAME on its own had no effect on haemodynamic function and ventricular hypertrophy in TAC rats. 5. In cardiomyocytes, metformin inhibited AngII-induced protein synthesis, an effect that was suppressed by the AMPK inhibitor compound C or the eNOS inhibitor L-NAME. The improvement in cardiac structure and function following metformin treatment was associated with enhanced phosphorylation of AMPK and eNOS and increased NO production. 6. The findings of the present study indicate that long-term treatment with metformin could attenuate ventricular hypertrophy induced by pressure overload via activation of AMPK and a downstream signalling pathway involving eNOS-NO.
Estrogen exerts vascular protective effects, but the underlying mechanisms remain to be understood fully. In recent years, hydrogen sulfide (H(2)S) has increasingly been recognized as an important signaling molecule in the cardiovascular system. Vascular H(2)S is produced from L-cysteine, catalyzed by cystathionine γ-lyase (CSE). In our study, apolipoprotein E (ApoE)-deficient mice were ovariectomized and implanted with placebo (OVX mice) or 17β-estradiol (E(2)) pellets (OVX + E(2) mice). Compared with OVX mice, OVX + E(2) mice showed increased plasma H(2)S levels (P = 0.012) and decreased aortic lesion area (P = 0.028). These effects were largely reversed when supplementing with the irreversible CSE inhibitor DL-propargylglycine (PPG) in the OVX + E(2) + PPG mice. Meanwhile, the nitric oxide and prostacyclin-resistant responses to cumulative application of acetylcholine (ACh) were studied among all the three groups of femoral arteries. Compared with the arteries in the OVX group, the vasodilator sensitivity of arteries to ACh was increased in the OVX + E(2) group and attenuated in the OVX + E(2) + PPG group. E(2) and estrogen receptor (ER) α agonist 4',4″,4'″-(4-propyl-[1H]-pyrazole-1,3,5-triyl) trisphenol rapidly increased H(2)S release in human endothelial cells, but not partially selective ERβ agonist 2,3-bis-(4-hydroxyphenyl)-propionitrile. These effects were inhibited by ER antagonist ICI 182780 or by protein kinase G (PKG) inhibitor KT5823. Furthermore, endothelial PKG activity was increased by E(2) (P = 0.003) and E(2)-induced vasodilation was inhibited by KT5823 (P = 0.009). In conclusion, the endothelial CSE/H(2)S pathway is activated by E(2) through PKG, which leads to vasodilation. These actions may be relevant to estrogen's anti-atherogenic effect.
1. Growth hormone (GH) has been demonstrated to overcome the inappropriate deceleration of growth rate in children with central precocious puberty treated with gonadotropin-releasing hormone analogue (GnRHa). However, the underlying mechanisms remain largely unclear. In the present study, we investigated the potential involvement of the epidermal growth factor receptor (EGFR) pathway in the growth promotion by GH using in vitro cultured growth plate chondrocytes isolated from adolescent rats treated with GnRHa. 2. Chondrocytes were stimulated with GH in the presence or absence of the Janus tyrosine kinase (JAK) 2 inhibitor AG490 (1, 10 and 100 nmol/L), the EGFR kinase inhibitor AG1478 (0.1, 1 and 10 nmol/L), U0126 (an inhibitor of extracellular signal-regulated kinase (Erk) activation; 10 μmol/L) or a neutralizing antibody against epidermal growth factor (EGF Ab; 0.1, 1 and 10 μg/mL). The proliferation of chondrocytes was assessed by the 3-(4,5-dimethyl-2 thiazoyl)-2,5-diphenyl-2H-tetrazolium bromide assay and immunostaining for proliferating cell nuclear antigen (PCNA). Phosphorylation of Erk1/2 and EGFR was detected by western-blotting. Intracellular mRNA and extracellular protein levels of EGF were detected using reverse transcription-polymerase chain reaction and ELISA, respectively. 3. Growth hormone promoted the proliferation of chondrocytes, which was correlated with increased phosphorylation of Erk1/2 and EGFR and enhanced expression of EGF. Pretreatment with AG490, AG1478, U0126 or EGF Ab completely or partially inhibited the proliferation of chondrocytes and activation of Erk1/2 and EGFR. Pretreatment with AG490, AG1478, or U0126 partially inhibited the expression of EGF. 4. The findings indicate that GH promotes chondrocyte proliferation by activating EGFR signalling.
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