Role of phosphatidylinositol 3-kinase/Akt pathway in angiotensin II and insulin-like growth factor-1 modulation of nitric oxide synthase in vascular smooth muscle cells.

The aim of this study was to examine the role of the phosphatidylinositol 3-kinase (PI3K)/serine/threonine kinase Akt signaling pathway in mediating interactions between angiotensin II (Ang II) and insulin-like growth factor-1 (IGF-1) in regulation of inducible nitric oxide synthase (iNOS) in vascular smooth muscle cells (VSMCs). Exposure to 100 nM IGF-1 for 10 min resulted in increased insulin-receptor substrate-1 associated PI3K activity and Akt kinase activity, whereas 100 nM Ang II pretreatment for 5 min strikingly decreased these IGF-1 effects. NOS activity was also increased in VSMCs following exposure to IGF-1 (10 min up to 24 h). Pretreatment with Ang II for 5 min reduced IGF-1-induced NOS activity. IGF-1 treatment for 24 hr increased iNOS gene transcription, and Ang II pretreatment reduced this stimulation of iNOS gene expression by attenuating PI3K/Akt signaling. These results implicate PI3K/ Akt pathways in Ang II/IGF-1 regulation of iNOS in VSMCs.