Abstract-Vascular smooth muscle cell (VSMC) migration participates in atherosclerosis and arterial restenosis after balloon angioplasty. Because these processes are enhanced in insulin-resistant states, our goal was to determine whether insulin affects VSMC migration and, if so, how. The migration of primary cultured VSMCs from canine femoral artery was measured with the use of a wound migration assay and related to cGMP levels. Insulin (1 nmol/L) did not affect migration or cGMP production in control cells. When inducible nitric oxide synthase (iNOS) was induced by 24-hour preincubation with lipopolysaccharide and interleuken-1, basal migration decreased, cGMP production increased, and insulin inhibited migration by Ͼ90% and stimulated cGMP production by 3-fold. The nitric oxide synthase inhibitor N G -monomethyl-L-arginine blocked the affect of insulin on the migration of VSMCs with iNOS. 8-Bromo-cGMP inhibited VSMC migration in control cells, and 1-H-1[1,2,4]oxadiazolo- [4,3a]quinoxolin-1-one, a selective inhibitor of guanylate cyclase, blocked the inhibition by insulin of migration of cells with iNOS. We conclude that insulin does not normally affect cGMP production or the migration of these VSMCs. However, after the induction of iNOS, insulin stimulates cGMP production and inhibits migration via an NOS-and a cGMP-dependent mechanism. (Hypertension.
2000;35[part 2]:303-306.)Key Words: cyclic 3Ј,5Јguanosine monophosphate Ⅲ muscle, smooth, vascular Ⅲ nitric oxide Ⅲ insulin I nsulin resistance, which occurs in obesity, non-insulindependent diabetes mellitus, and essential hypertension, is associated with increased atherosclerosis and restenosis after balloon angioplasty, 1-3 but the reasons for this are obscure. The migration of vascular smooth muscle cells (VSMCs) from the arterial media through the internal elastic membrane into the neointima is an integral part of the pathogenesis of atherosclerosis and restenosis. 4 The insulin-resistant conditions noted are marked by hyperinsulinemia as the pancreas attempts to maintain plasma glucose concentration at a normal level. 1 Because hyperinsulinemia has been thought to aggravate atherosclerosis or restenosis, 5 several investigators have studied the effects of insulin on VSMC migration. 6 -8 Although some studies have shown a small stimulation of VSMC migration with insulin, the results are controversial. In some studies, the concentrations of insulin that were used were supraphysiological, 8 such that the insulin-like growth factor-1 pathway may have been activated. Insulin-like growth factor-1 is known to stimulate VSMC migration. 9 In other studies, insulin alone had no effect on VSMC migration 6 but increased it when it was stimulated by another agent. 7 We have reported that physiological concentrations of insulin stimulated cGMP production in primary cultured VSMCs from canine femoral artery. 10,11 These cells were cultured under conditions such that they expressed the inducible isoform of nitric oxide synthase (iNOS), 11 and an inhibitor of NOS blocked ...