Viagra, the drug best known for treating impotence, may prove effective for treating an enlarged heart.
A study showed that sildenafil citrate (Viagra) successfully treated enlargement and thickening of the heart in male mice—not only stopping further growth of the heart muscle, but also actually reversing the growth and damage that had already taken place.
"If, indeed, what works in mice works in humans, this will become a standard part of care," says Dr. Richard Stein, a national spokesman for the American Heart Association.
THE EXPERIMENTS
In one experiment, researchers separated male mice into two groups—one was fed Viagra and one received a regular diet. The scientists then constricted the main artery in the mice, causing the heart to pump harder. This resulted in a condition essentially the same as hypertrophy, the enlargement and thickening of the heart muscles.
The mice who received Viagra developed hypertrophy at half the rate of the mice who were not getting the drug. The Viagra mice also showed 67% less muscle stiffening, had smaller hearts and improved heart function.
In another experiment, the researchers gave Viagra to some mice in a group of males that already had hypertrophy. After two weeks, muscle growth almost completely disappeared in the mice given Viagra, while the hearts of the control mice continued to grow.
"By treating mice with Viagra in doses that would be similar to what a person would get, we found that we could block hypertrophy and could prevent progression to heart failure," explains study co-author Dr. Hunter Champion, an assistant professor of medicine at Johns Hopkins University School of Medicine.
IMPLICATIONS
The findings are important because they reveal mechanisms that are involved in heart thickening and the progression to heart failure.
Prior to this study, experts did not know that PDE5A, the enzyme involved in sexual function, was also involved in heart function.
Interestingly, Viagra was originally developed to dilate coronary blood vessels in people who had angina. It didn't work for angina, but while being tested, was found to be effective for the treatment of erectile dysfunction.
Champion believes that the effect on the heart may actually be seen in the entire class of drugs, not just Viagra. "It could very well be that Levitra or Cialis would do the same thing," he says, referring to Viagra's two competitors in the erectile dysfunction marketplace.
It may be a while, though, before using these drugs as heart therapy becomes a possibility. Heart failure drug trials take time to prove measurable results.
