Objective: The present study was designed to determine the effects of insulin on cytosolic angiotensin II production and proliferation in cultured rat vascular smooth muscle cells.
Design and methods: Vascular smooth muscle cells were incubated with insulin for 48 h. Cytosolic angiotensin I and II were determined by radioimmunoassays of purified cell homogenates. Angiotensin II was also detected by immunohistochemistry of intact cells. Cell proliferation was determined by pulse labeling with radiolabeled thymidine. Angiotensinogen mRNA expression was determined by slot-blot analysis.
Results: Insulin significantly increased cytosolic angiotensin II concentration in vascular smooth muscle cells. Lisinopril, omapatrilat and irbesartan inhibited this increase of angiotensin II, but had no effect on angiotensin I levels. Immunohistochemical staining confirmed the presence of angiotensin II in control and insulin-treated vascular smooth muscle cells. Insulin increased cell proliferation, and addition of lisinopril, omapatrilat or irbesartan inhibited this effect. Insulin also increased expression of angiotensinogen mRNA in cultured vascular smooth muscle cells, but PD98059, a mitogen-activated protein kinase inhibitor, prevented the rise in angiotensinogen expression.
Conclusion: These results support the concept that insulin stimulates angiotensin II production in cultured vascular smooth muscle cells through a mitogen-activated, protein kinase-dependent pathway that might be a factor in the progression of atherosclerosis. Agents that block the renin-angiotensin system have direct protective effects, reducing vascular angiotensin II and growth of vascular smooth muscle cells and are thus of cardiovascular benefit.