Research Shows That Cells Lining Blood Vessels Produce Estrogen, Estrogen Receptor

WASHINGTON, D.C. -- Pioneering research by University at Buffalo endocrinologists investigating estrogen function in humans has demonstrated for the first time that microvascular endothelial cells -- cells in the lining of the smallest blood vessels -- produce estrogen and express estrogen receptor.

In related work, the researchers have demonstrated that estrogen may derive part of its known cardiovascular protective effect by increasing production of nitric oxide in microvascular endothelial cells. Nitric oxide has been shown to relax blood vessels, thus reducing blood pressure.

Taken together, the studies provide a possible model for the development of cardiovascular disease in postmenopausal women. Results of the studies were presented here today (June 14, 1995) at the annual meeting of the Endocrine Society.

The research was conducted by a team of scientists led by Paresh Dandona, M.D., Ph.D., UB professor of medicine and chief of endocrinology at Millard Fillmore Hospital in Buffalo, a UB teaching hospital.

Their study investigating production of estrogen by human microvascular endothelial cells was based on previous research showing that stromal cells, a type of cell found in the supporting tissue of organs, produce aromatase, the enzyme that initiates the production of estrogen. Since stromal cells contain microvascular endothelial calls, Dandona's team set out to determine whether these cells, which play a role in maintaining the healthy condition of blood vessels, were the source of stromal estrogen production.

The researchers isolated microvascular endothelial cells from stromal cells in human subcutaneous fat obtained at liposuction. They then tested for the presence of the enzyme aromatase, and for estrone and estradiol, precursors of estrogen, in eight cell cultures.

All eight cultures tested exhibited aromatase activity, the findings showed. Five cultures, tested further for evidence of estrogen production, all tested positive for estrogen.

"This is the first evidence that cells from blood vessels produce their own estrogen," Dandona said.

The rapid development of atherosclerosis after menopause and its prevention by estrogen-replacement therapy has suggested that estrogen has a strong protective effect against arterial disease, but the way estrogen produces this effect has not been defined, Dandona noted.

The researchers earlier had shown that estrogen can prevent blood vessels from constricting, or narrowing -- a condition that promotes blockage. Knowing that blood-vessel constriction and dilation is modulated by nitric oxide, the researchers set out to investigate whether estrogen's effect on blood vessels derives from its ability to regulate production of nitric-oxide synthase and, by extension, nitric oxide.

In laboratory work with rabbits, the researchers compared the amount of nitric-oxide synthase in endothelial-cell cultures from animals that had their ovaries removed with cell cultures from animals with ovaries.

Results showed significantly higher amounts of nitric-oxide synthase in the preparations from animals with ovaries than in preparations from those without ovaries.

"We concluded that the concentration of nitric-oxide synthase is diminished markedly following estrogen deprivation and that estrogen has a potent modulatory effect on production of this enzyme in the blood vessel lining," Dandona said.

"This role may be important when considering the rapid development of atherosclerosis following menopause in humans and its prevention by estrogen replacement therapy."

Since cells in the endothelium responded to estrogen (by modulating the production of the nitric-oxide enzyme), the researchers hypothesized that cells lining the blood vessels also may express estrogen receptor, a previously unknown function of these cells.

To investigate this theory, they isolated and harvested human endothelial cells from tissue removed during liposuction, treated them with primary antibody against the estrogen receptor and cultured them overnight. The cultures were then treated with a second antibody that fluoresces in the presence of the activated antibody. All 15 cell cultures treated in this manner showed the presence of estrogen receptor.

"These data demonstrate for the first time the presence of estrogen receptor in human microvascular endothelial cells," Dandona said. ³These studies as a whole may provide us with a model for the origin of atherosclerosis in post-menopausal women."

Participating in these investigations were Ehad Abdel-Rahman and Sherry Mangione, doctoral candidates; Li Lin, graduate student; Nobuyuki Kadohama, Ph.D., Yoshio Osawa, Ph.D., and Carol Yarborough, Ph.D., all of the Hauptman-Woodward Medical Research Institute, Buffalo; Linda Harris, M.D., vascular fellow at Millard Fillmore Hospital, Buffalo, and John J. Ricotta, M.D., UB professor of surgery.