Voluntary exercise induces sex-specific physiological cardiac remodeling

While cardiovascular disease occurs in both men and women, it does not affect them in the same way.

Risk factors and protective factors for heart diseases are likewise unequal. The molecular mechanisms responsible for these differences are so far unknown, but some believe it is due to chromosomal linked genes or sexual hormones such as estrogen and testosterone. While the mechanisms behind the differences are unknown, the physiological differences are clear. A new study examining chronic exercise in male and female mice finds that moderate long-term exercise provokes a sex-dependent cardiac adaptation that is different for females versus males. The findings may eventually help improve treatment strategies for women and men with heart disease.

The study is entitled Voluntary Exercise Induces Sex-Specific Physiological Cardiac Remodeling." It was conduced by Sebastian Brokat, Kathleen Cantow, Nadine Ehrenberg, Arne Kuhne, Jenny Thomas, and Vera Regitz-Zagrosek, all of the Center for Cardiovascular Research in Berlin, Germany. Dr. Brokat will discuss his team's findings 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 in Austin, TX. The meeting is the second scientific event to be sponsored by the American Physiological Society (APS; www.The-APS.org) this year.

Background

Exercise is an important factor in preventing cardiovascular disease. Frequent exercise leads to the physiological remodeling (change) and hypertrophy (beneficial enlargement) of the heart. This type of hypertrophy is different from pathological hypertrophy (an abnormal enlargement that leads to problems such as heart failure). Pathological hypertrophy is also irreversible. There have been several descriptions on the effects of estradiol and testosterone (female and male hormones, respectively) on pathologic hypertrophy, but very little research has been conducted on the physiological remodeling of the heart.

Methodology

In this study, the researchers focused on chronic voluntary exercise, an important factor which protects the heart against cardiovascular diseases. The researchers observed the voluntary exercise (using a running wheel) of both male and female mice during the course of 5 weeks. They also held a control group of mice under the same conditions, but without the exercise wheel. Each mouse's daily distance, time, and average speed were recorded. Their hearts were monitored using an echocardiograph to better evaluate any cardiac changes during the course of the study. They also isolated and analyzed the RNA of each mouse to look at any changes at the molecular level.

Results

The researchers found that the female mice:

• showed a much higher level of exercise performance (9.2 km/d vs. 6.4 km/d)
• had a greater increase in LV mass (15 percent vs. five percent of left ventricular hypertrophy) compared to their sex-matched sedentary controls
• experienced a 20 percent decrease in the protein that promotes cell function while there were no changes in males
• decreased MHC ratio by 41 percent while the males experienced no change

Conclusions

According to Dr. Brokat, the lead researcher, "This study finds that exercise appears to help females more than males. The findings bring us a step closer to explaining the sex bias in physical activity that protects the heart."