WINSTON-SALEM, NC -- Postmenopausal hormone replacement therapy markedly reduces the occurrence of atherosclerosis in the internal carotid artery in monkeys, a Wake Forest University Baptist Medical Center research team reported today at an American Heart Association meeting in Santa Fe, NM.
Blockage of the internal carotid artery is a leading cause of stroke.
The team found that hormone replacement therapy from soy protein with phytoestrogens provided equivalent stroke-prevention benefits to the standard Premarin therapy prepared from mammalian estrogens.
"Phytoestrogens were as robust as Premarin," said Thomas B. Clarkson, D.V.M., professor of comparative medicine at the Wake Forest University School of Medicine.
Clarkson and his colleagues presented their findings at AHA's 38th Annual Conference of Cardiovascular Disease, Epidemiology and Prevention.
Clarkson noted that several recent studies done elsewhere had reached differing conclusions regarding the benefits of hormone replacement therapy in preventing stroke. Stroke ranks third as a cause of death for middle-aged and older women. A 50-year-old white woman has a 20 percent probability of developing a stroke sometime in her remaining lifetime.
He said that one review of seven studies of stroke deaths among postmenopausal users of estrogen replacement therapy found a reduction of risk ranging between 20 and 60 percent compared to women who were not using estrogen replacement therapy. But an English study found no benefit, and a third hinted that estrogen replacement therapy might actually be making strokes more severe.
"Given the uncertainties about the effect of estrogens on stroke and stroke risk, it seemed to us important to place a major focus on the evaluation of internal carotid artery atherosclerosis, the lesion site most commonly associated with cerebrovascular symptoms of human primates," Clarkson said.
Clarkson and Mary Anthony, research associate in the Department of Comparative Medicine, compared the effects of treatment with mammalian estrogens -- Premarin -- with treatment with soy phytoestrogens in postmenopausal monkeys, all of whom had been fed a "non-prudent diet" -- a diet high in cholesterol.
The study was part of an overall program project which is looking at the potential benefits of soy phytoestrogens as a postmenopausal therapy. The program project is financed by the National Heart Lung and Blood Institute. The soy phytoestrogen used in the study was provided by Protein Technologies International.
The results showed that both forms of estrogen replacement therapy cut internal carotid artery atherosclerosis by more than half, compared to postmenopausal monkeys who did not receive estrogens. The results were statistically significant.
But the effect on the size of the atherosclerotic plaque was much less dramatic, though both forms of estrogen did reduce the size of the plaque.
"The primary effect of the intervention is in preventing atheroscerlosis from ever occuring," Clarkson said. "Once atherosclerosis begins to develop, there is only a small effect of the two interventions."
Clarkson and Anthony also concluded that the primary way that either form of estrogen replacement therapy works is by preventing the development of what they call an "atherogenic plasma lipid profile" -- or serum cholesterol levels that lead to atherosclerosis -- despite the high cholesterol diet.
Contact: Bob Conn or Jim Steele at 336-716-4587