Aug. 3, 2001 CHAMPAIGN, Ill. — Extensive damage to cells, reduced nitric oxide production and too much calcium buildup. These negative consequences followed open-heart surgery in mice and rats in the absence of estrogen. With estrogen or a soy-based equivalent, post-operative damage is much less.
Ongoing experiments at the University of Illinois on female and male rodents are shedding light on the role of estrogen during heart surgery. Specifically, researchers are examining the impacts of estrogen during ischemia, when arterial blood flow is stopped, and reperfusion, when the flow resumes.
The latest findings, to appear in the American Journal of Physiology: Heart and Circulatory Physiology, document how the estrogen-like components of soy provide the same protection as estrogen in female rats. In two studies published last year, estrogen’s role was shown in males and females. "Under controlled, well-defined circumstances, we’ve shown that without question estrogen, whether it is natural or from soy phytoestrogens, is offering protection," said David R. Gross, a professor of physiology and head of veterinary biosciences in the UI College of Veterinary Medicine. Regardless of the repairs made to the heart, reperfusion carries risks. The level of damage that naturally occurs can dictate how well a heart restarts and recovers, Gross said.
The research is part of a departmentwide effort to understand the molecular mechanisms of estrogen in different systems of the body. "If we are able to dissect the mechanisms of estrogen’s actions on the testes, for example, those same mechanisms will probably be functional in the heart," Gross said.
"Once we find the specific proteins that are involved in the hormone’s activities, then we can develop designer drugs," he said. "We’d like to able to block undesirable actions, such as those involved in breast cancer, or stimulate activity that may help the heart function better or heal faster."
Researchers examining the heart are using mice and rats that lack estrogen. In the new study, 10 estrogen-lacking female rats ate a diet of soy rich in the isoflavones genistein, daidzein and glycitein, which bind to estrogen receptors, for three months.
The animals then went to surgery. Blood flow and hearts were stopped for 30 minutes followed by reperfusion with a standard blood substitute (oxygenated Krebs-Henseleit bicarbonate buffer). The hearts were restarted and allowed to function for two hours. The non-soy animals suffered severe damage like that in the animals not given estrogen in the earlier studies. Soy-fed rats had healthier levels of coronary blood flow, less edema, near normal nitric oxide production and no abnormal calcium accumulations.
Co-authors with Gross were doctoral student Peiyong Zhai, now at Johns Hopkins Medical Center in Baltimore; and UI colleagues Elizabeth H. Jeffery, food science and human nutrition; Janice M. Bahr, animal sciences; and Thomas E. Eurell and Robert P. Cotthaus, veterinary biosciences. The Illinois Council for Food and Agricultural Research supported the soy-related work.
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