From the article:
They were studying estrogen’s effects on blood vessels, focusing on its impact on the smooth muscle cells that allow blood vessels to contract, thereby regulating blood pressure and blood flow. These researchers found that estrogen targets nitric oxide synthase 1, one of three versions of the enzyme that makes the powerful vasodilator, nitric oxide.
“What we were finding is that estrogen seems to be what you might call a natural nitroglycerin; nitroglycerin also works by making nitric oxide,” Dr. White says.
Then they tried to block estrogen’s activity by blocking nitric oxide. “What surprised the heck out of me was after we blocked nitric oxide production and added estrogen, we got a contraction,” says Dr. White. “Estrogen now had turned into a constrictor agent, an agent that would increase blood pressure.”
They looked further and found that normal aging decreases levels of the cofactors L-arginine and tetrahydrobiopterin – both critical to nitric oxide synthase’s production of nitric oxide.
[…]
“Under normal conditions, such as a pre-menopausal woman, this enzyme, nitric oxide synthase, makes nitric oxide,” says Dr. White. “But if you block the production of nitric oxide, this nitric oxide synthase now has a secondary product that normally isn’t made in an appreciable form. Now it makes a compound called superoxide. It’s an oxidant, and oxidation is bad in general. It causes a lot of cellular damage. But what we also have found is that now, instead of causing relaxation, it causes constriction. So you completely flip-flop the response here.
“One of the things this means is that menopause is a good thing, a sort of revolutionary endocrinology idea,” says Dr. White.