The role of estrogens and polyphenols in hypertension and diabetes

Menopausal women are at relatively high risk for memory loss, high blood pressure (hypertension) and diabetes.

A decade ago, the standard treatment for these problems was long-term hormone replacement therapy (HRT). Since then, studies have shown that extensive use of HRT is associated with significant adverse effects. As a result, alternatives have been sought. Certain naturally occurring edible compounds found in plants - dietary polyphenols - have been shown to have some beneficial effects similar to HRT but without the appreciable adverse effects. Grape, soy and kudzu are dietary polyphenols. One research lab investigating them through several studies has found they can blunt cognitive loss, hypertension and insulin resistance in an experimental model.

These and related studies are being led by physiologist J. Michael Wyss, Department of Cell Biology, University of Alabama at Birmingham (UAB), Birmingham, AL. Dr. Wyss will be discussing his work, entitled "The Role of Estrogens and Polyphenols in Hypertension and Diabetes," at the upcoming conference, Sex and Gender in Cardiovascular-Renal Physiology and Pathophysiology, being held August 9-12, 2007 at the Hyatt Regency Austin on Town Lake, Austin, TX. The meeting is the second scientific event to be sponsored by the American Physiological Society (APS; www.The-APS.org) this year.

Incorporated in Dr. Wyss, presentation are results from the following studies:

The research team examined whether grape polyphenols were associated with reduced cognitive dysfunction and a lower incidence of high blood pressure. They found that the effect of the polyphenols on working and reference memory errors indicated that both short-term (working memory) and long-term (reference memory) were beneficially and nearly equally enhanced by grape polyphenols.

However, a more formal test of this hypothesis, using other indices of these forms of memory, is needed before the effect can be fully interpreted.

The researchers also tested the hypothesis that grape seed polyphenols reduced salt-sensitive hypertension in young, estrogen-depleted rats. After ten weeks on specific diets, grape seed supplementation significantly reduced arterial pressure in the rats fed a high salt diet, compared to controls. The results indicate that grape seed polyphenols decrease arterial pressure in rats, probably via an antioxidant mechanism. The published results of this study are the first to demonstrate that dietary grape seed polyphenols blunt memory loss and hypertension in an animal model.

Previous studies from the Wyss lab indicate that polyphenols in soy diets protect against hypertension in estrogen-depleted/ovariectomized rats. Specifically, they have found that estrogen deprivation (by surgical removal of the ovaries) only modestly increases arterial pressure in hypertensive rats. However, in estrogen depleted rats, the removal of soy polyphenols from the diet results in a large increase in arterial pressure, putting the animal at a much greater risk of stroke and other cardiovascular complications. The precise mechanism by which soy interacts with the blood to affect hypertension is not yet known.

The UAB researchers have examined kudzu, a vine growing in the southeast United States. Their research, and others, shows kudzu root extract blunts a significant percent of the blood pressure rise that occurs in rats placed on a high salt diet. Kudzu has also been shown to reduce blood glucose, insulin and leptin in this animal model of insulin resistance (a precursor to type 2 diabetes). Glucose tolerance and sensitivity are improved some 20 percent in chronic studies and about 50 percent when kudzu and glucose are administered simultaneously.

These studies demonstrate that three polyphenols - grape, soy and kudzu - blunt hypertension, insulin resistance and cognitive decline when estrogen is not present in female rats. According to Dr. Wyss,"It is unlikely that these polyphenols could eventually provide effective stand-alone therapy for post-menopausal women, but in the future they may provide effective adjunct therapy that complements the use of lower doses of traditional pharmaceutical compounds."