Endogenous angiotensin II suppresses insulin signaling in vascular smooth muscle cells from spontaneously hypertensive rats

Background Angiotensin II (Ang II) has been reported to inhibit insulin signaling at multiple levels in vascular smooth muscle cells (VSMC) in vitro. We have demonstrated that VSMC from spontaneously hypertensive rats (SHR) produce Ang II in a homogenous culture. Objective In the current study, we investigated influences of endogenous Ang II on insulin signaling in VSMC from SHR. Design and methods Phosphatidylinositol 3-kinase (PI3-kinase) activity, insulin receptor substrate-1 (IRS-1) associated tyrosine phospholyration, and p85 subunit of PI3-kinase were measured in VSMC from SHR and normotensive Wistar-Kyoto (WKY) rats in the absence and presence of Ang II type 1 receptor antagonist RNH6270 and mitogen-activated protein kinase/extracellular signal-regulated kinase (MEK) inhibitor U01 26. Results Insulin treatment increased PI3-kinase activity in VSMC from WKY rats in a dose-dependent manner. In contrast insulin treatment of VSMC from SHR did not affect PI3-kinase activity. However, co-treatment of VSMC from SHR with RNH6270 and insulin, increased PI3-kinase activity. PI3-kinase activity, IRS-1-associated tyrosine phosphorylation and p85 subunit of PI3-kinase in VSMC from WKY rats decreased in response to treatment with Ang II and returned to control levels upon co-treatment with U01 26. Basal levels of PI3-kinase activity, IRS-1-associated tyrosine phosphorylation, and p85 subunit of PI3-kinase were significantly lower in VSMC from SHR than in cells from WKY rats. U01 26 treatment of VSMC from SHR significantly increased levels of PI3-kinase activity, IRS-1-associated tyrosine phosphorylation, and p85 subunit of PI3-kinase. Conclusion These results indicate that endogenous Ang II suppresses insulin signaling in VSMC from SHR by activating extracellular signal-regulated kinase. These findings suggest that tissue Ang II may play a role in insulin resistance in hypertension. (C) 2001 Lippincott Williams & Wilkins.