Two-faced estrogen

The changing chemistry of estrogen could explain why its role apparently switches from protecting women from heart disease to increasing their risk later in life. Researchers Richard White and Scott Barman of the Medical College of Georgia found that estrogen targets nitric oxide synthase 1, one of three enzymes that produce the vasodilator, nitric oxide. However, normal aging leads to lowering of the enzyme's cofactors L-arginine and tetrahydrobiopterin so that in older women, increased estrogen does not boost enzyme activity but instead simply releases the vasoconstricting and damaging oxygen-free radical, superoxide. The research could lead to a new approach to hormone replacement therapy for menopausal women the researchers say.