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(Hypertension. 2003;42:569.)
© 2003 American Heart Association, Inc.

Scientific Contributions

Insulin-Stimulated Hydrogen Peroxide Increases Guanylate Cyclase Activity in Vascular Smooth Muscle

From the Division of Renal Diseases and Hypertension, Department of Medicine, The University of Texas Health Science Center, Houston, Tex.

Correspondence to Andrew M. Kahn, MD, The University of Texas Health Science Center, Houston, Medical School, 6431 Fannin St, MSB 4.148, Houston, TX 77030. E-mail Andrew.M.Kahn{at}uth.tmc.edu

Insulin resistance is associated with vascular disease. Physiological concentrations of insulin inhibit cultured vascular smooth muscle cell (VSMC) contraction and migration by increasing nitric oxide (NO)-stimulated cGMP accumulation. The failure to do so in insulin-resistant states may aggravate vascular disease. We sought to determine the mechanism of insulin’s increase in cGMP accumulation. Isobutylmethylxanthine, an inhibitor of phosphodiesterase activity, inhibited the decline in cGMP levels measured by immunoassay in cGMP-loaded cultured rat aortic VSMCs, but 1 nmol insulin did not. Thus, insulin’s increase in cGMP accumulation is due to stimulated production, not inhibited hydrolysis and/or efflux. Insulin, which increases the NADH/NAD⁺ ratio in these cells, stimulated superoxide anion (O₂^-) accumulation measured by lucigenin luminescence to 256±25% (P<0.05) by a process that was blocked by the NADH oxidase inhibitor diphenyliodonium (DPI) and enhanced by the superoxide dismutase inhibitor diethyldithiocarbonate (DETCA). Insulin also stimulated hydrogen peroxide (H₂O₂) accumulation measured by horseradish peroxidase/luminol luminescence to 221±22% (P<0.05) by a DETCA-sensitive mechanism. H₂O₂ (100 µmol/L) in the absence of insulin increased NO-stimulated cGMP accumulation to 151±11% (P<0.05). Insulin alone increased NO-stimulated cGMP accumulation to 183±17% (P<0.05), and this was blocked by either DPI or DETCA. We conclude that insulin increases NADH oxidase-derived O₂^- production in cultured rat VSMCs. This did not cause the expected scavenging of NO resulting in the reduction of NO-stimulated guanylate cyclase activity, but enough O₂^- was metabolized to H₂O₂ to increase overall NO-stimulated cGMP production.

Key Words: muscle, smooth, vascular • insulin • cyclic GMP • nitric oxide

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