Hyperglycemia induced cell growth and gene expression via the serum response element through RhoA and Rho-kinase in vascular smooth muscle cells.

The impressive correlation between cardiovascular disease and alterations in glucose metabolism has raised the likelihood that atherosclerosis, heart failure, and type 2 diabetes may share common antecedents. Postprandial hyperglycemia has been shown to play an important role on the onset and development of heart failure and cerebral infarction in several large-scale clinical trials. Recently, chronic hyperglycemia has been reported to enhance the vasoconstrictor response by Rho-kinase. We have previously reported that phenylephrine enhanced the vasoconstrictor response in a spontaneous diabetes mellitus OLETF (Otsuka-Long-Evane-Tokushima fatty) rat model. However, the mechanism of hyperglycemia in these reactions, particularly the influence of hyperglycemia on the signal transduction pathway, is still not well understood. We, therefore, examined the effect of hyperglycemia on the cell growth and gene expression of rat aortic smooth-muscle cells (RASMCs). Hyperglycemia accelerated the growth of RASMCs in a concentration-dependent manner. Furthermore, the c-fos gene expression was also increased by hyperglycemia. Phenylephrine activated the c-fos gene expression. Hyperglycemia augmented the phenylephrine-induced c-fos gene expression synergistically in a dose dependent manner. The deletion analysis revealed that the c-fos serum response element (SRE) accounts for the c-fos gene expression. RhoA, and Rho-kinase were involved in hyperglycemia-induced c-fos gene expression. An HMG-CoA reductase inhibitor, Pitavastatin, inhibited these hyperglycemia-augmented reactions by inhibiting RhoA. Hyperglycemia itself increased the cell growth and gene expression. Furthermore, it modifies and augments the cell growth and gene expression by alpha1-AR-mediated stimulation. Statin might therefore be effective for the treatment of hyperglycemia-induced cardiovascular dysfunction.

Effects of endothelium-derived hyperpolarizing factor and nitric oxide on endothelial function in femoral resistance arteries of spontaneously hypertensive rats.

In hypertension, endothelium-dependent relaxation is attenuated and this attenuation contributes to the increased peripheral resistance. However, the role of endothelium-derived hyperpolarizing factor (EDHF) in the arteries of hypertensive rats remains unclear. Therefore, the aim of this study was to evaluate the role of EDHF in the femoral resistance arteries of hypertensive rats. The femoral resistance arteries were isolated from 5-, 15- and 25-week-old spontaneously hypertensive rats (SHR) and age-matched Wistar Kyoto rats (WKY). Changes in internal diameter were examined with videomicroscopy. EDHF-mediated dilatation was determined by differences between the degree of acetylcholine (ACh)-induced dilatation in the presence of NG-monomethy-L-arginine (L-NMMA) plus a prostaglandin I2 inhibitor (indomethacin) and the degree of such dilatation in the presence of L-NMMA, indomethacin and KCl. Charybdotoxin (CTx) and apamin (a Ca2+-activated K+ channel [KCa] inhibitor)-sensitive EDHF dilatation was also compared between in 5-, 15- and 25-week-old SHR and WKY. ACh-induced vasodilatation was not different between 5-week-old SHR and WKY. There was no difference between NO- and EDHF-mediated vasodilatation in 5-week-old rats. ACh-induced vasodilatation was weaker in 15-week-old SHR than in WKY. NO-mediated vasodilatation did not differ between the two groups. EDHF-mediated dilatation was attenuated in SHR but not in WKY. ACh-induced dilatation was weaker in 25-week-old SHR than in WKY. NO- and EDHF-mediated vasodilatation were attenuated in SHR but not WKY. EDHF-mediated vasodilatation was attenuated before the loss of NO-mediated vasodilatation in the femoral resistance arteries of SHR. The attenuation of this vasodilatation was mediated by the CTx plus apamin-sensitive EDHF.