Catecholamines abrogate antimitogenic effects of 2-hydroxyestradiol on human aortic vascular smooth muscle cells

Catechol-O-methyltransferase (COMT)-mediated methylation of 2-hydroxyestrad iol (endogenous estradiol metabolite) to 2-methoxyestradiol (angiogenesis i nhibitor) may be responsible for the antimitogenic effects of 2-hydroxyestr adiol on vascular smooth muscle cells (VSMCs). Catecholamines are also subs trates for COMT, and increased levels of catecholamines are associated with vasoocclusive disorders. We hypothesize that catecholamines may abrogate t he vasoprotective effects of 2-hydroxyestradiol by competing for COMT and i nhibiting 2-methoxyestradiol formation. To test this hypothesis, we investi gated the antimitogenic effects of 0.001 to 0.1 mu mol/L of 2-hydroxyestrad iol on human aortic VSMC proliferation (cell number and DNA synthesis), col lagen synthesis, and migration in the presence and absence of catecholamine s. Norepinephrine, epinephrine, and isoproterenol concentration-dependently abrogated the inhibitory effects of 2-hydroxyestradiol on cell number, DNA synthesis, collagen synthesis, and cell migration. These modulatory/attenu ating effects of catecholamines were not abrogated in the presence of the a lpha- and beta -adrenergic receptor antagonists, phentolamine mesylate and propranolol, respectively. In contrast to 2-hydroxyestradiol, the antimitog enic effects of 2-methoxyestradiol (0.1 mu mol/L) were not attenuated by is oproterenol (1 mu mol/L) or quercetin (competitive inhibitor of COMT, 10 mu mol/L). Norepinephrine, epinephrine, and isoproterenol concentration-depen dently (10 to 500 mu mol/L) inhibited the metabolism of 2-hydroxyestradiol (0.25 to 2 mu mol/L) to 2-methoxyestradiol, and the potency of the catechol amines to reverse 2-hydroxyestradiol-induced inhibition of VSMC proliferati on, collagen synthesis, and migration was correlated with their ability to inhibit 2-methoxyestradiol formation. Our findings suggest that catecholami nes within the vasculature may abrogate the anti-vaso-occlusive effects of estradiol and 2-hydroxyestradiol by blocking 2-methoxyestradiol formation.