Estrogen shows promise in warding off heart disease in young rats

December 20, 1999

COLUMBUS, Ohio -- Because of its effects in reducing health risks such as heart disease, many women start taking estrogen supplements when they reach menopause. Yet new evidence in animals suggests that treatment should start before menopause begins.

Supplemental estrogen prevented hypertension -- or abnormally high blood pressure -- in 3-month-old female rats with healthy hearts who had their ovaries removed, resulting in surgical menopause.

But 17-month-old rats who had received estrogen at the beginning of natural menopause -- and after hypertension had already begun -- did not reap the same benefit.

"There still isn't a consensus on supplemental estrogen's benefits to heart health during the post-menopausal years," said Judith Radin, co-author of the study and an associate professor of veterinary sciences at Ohio State University.

"But our findings suggest that estrogen supplementation may be important for a woman nearing or going through perimenopause." Perimenopause is the three-to-five year period before menopause when estrogen levels begin to decline.

The research appeared in a recent issue of the Journal of Molecular and Cellular Cardiology.

The researchers studied a strain of rats that develops hypertension at around 4 months of age. And when these rats reach menopause -- typically around 17 months of age -- their hearts start to enlarge. Women often experience a rise in blood pressure when they reach menopause.

The researchers were also interested in the role estrogen played in the prevention of congestive heart failure (CHF). In CHF, the heart loses its ability to pump blood.

Radin and her colleagues studied two groups of female rats: 17 3-month-old rats and 16 17-month-old rats. In the first group, 12 had had their ovaries removed, and half of those received supplemental estrogen. The ovaries were removed before the rats developed signs of hypertension. The rest of the rats neither received estrogen nor had their ovaries removed. In the second group, all rats had reached menopause naturally. Eight were given estrogen supplements, and the rest were given a placebo.

In the first group, some rats received 1.5 mg of estrogen via a time-release pellet implanted under the skin. The rest of the rats received an implanted placebo pellet. The researchers took each rat's blood pressure every four weeks. Pellets were replaced every 60 days for the duration of the study.

In comparison to the rats who had their ovaries removed without supplementation, the rats who had received supplemental estrogen had significantly lower body weights (176 grams vs. 295 grams). Just as in humans, higher body weights increase the risk of hypertension. The rats receiving estrogen also had lower systolic blood pressures (130 mmHg vs. 160 mmHg) at the end of the study.

The young rats who did not have their ovaries removed and did not receive estrogen did develop hypertension (systolic reading of 155 mmHg) and weighed an average of 210 grams.

In the older group, each rat had reached menopause naturally. At this point, estrogen levels had significantly declined. Also, each rat had been hypertensive for most of her life. Half (eight) of these rats received a 1.5 mg time-release estrogen pellet implant, while the other half received placebo implants. The researchers took blood pressure readings every four weeks. Pellets were replaced every 90 days for the duration of the experiment.

Estrogen supplements did not reduce blood pressure or prevent CHF in the 17-month-old rats who already suffered from hypertension. Results showed that in these menopausal rats, estrogen supplements did not increase survival time.

"The supplemental estrogen didn't give the menopausal rats any additional health benefits," Radin said. The presence of chronic, untreated hypertension probably outweighed any benefit of the estrogen therapy.

Support for this research came from a U.S. Public Health Service grant and from the Ohio Agricultural Research and Development Center.
Contact: Judith Radin, (614) 292-4266;
Written by Holly Wagner, (614) 292-8310;

Ohio State University

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