The impotence drug Viagra may also help prevent the abnormal growth of the heart seen in some types of heart disease, researchers reported on Sunday.

The drug, originally tested but rejected as a heart drug, stopped the overgrowth of hearts in mice with surgically induced heart failure, the researchers said.

“A larger-than-normal heart is a serious medical condition, known as hypertrophy and is a common feature of heart failure that can be fatal,” said cardiologist Dr. David Kass of The Johns Hopkins University School of Medicine, who led the study.

Viagra, known generically as sildenafil and made by Pfizer, was the first of the new impotence drugs. It works by affecting a molecule called nitric oxide, which expands blood vessels.

It increases blood flow to the genitals, but was originally tested to see if it could help hearts function better. However, it had little effect on resting heart rates.

Viagra blocks an enzyme called phosphodiesterase-5A.

Phosphodiesterase-5 or PDE5A is involved in the breakdown of another molecule called cyclic GMP. Cyclic GMP in turn serves as a natural brake to heart overgrowth.

Working with mice, Kass and colleagues showed that blocking PDE5A prevents and reverses the growth associated with heart failure, a chronic heart condition caused by infections, high blood pressure and other heart diseases.

Often the hearts of heart failure patients grow to abnormal sizes as they struggle harder and harder to pump blood. About half of heart failure patients die within five years of being diagnosed.

“We thought we could more strongly apply the brake on hypertrophy in the heart if we used sildenafil to prevent the breakdown of cyclic GMP,” Kass said.

Writing in the journal Nature Medicine, Kass and colleagues said Viagra improved heart function in mice with surgically induced heart failure and also reversed hypertrophy.

“This study shows that sildenafil can make hypertrophy go away,” said Kass, whose work was not funded by Pfizer.

“Its effects can be both stopped in their tracks and reversed. Overall, the results provide a better understanding of the biological pathways involved in hypertrophy and heart dilation, leading contributors to heart failure,” he added in a statement.

“They suggest possible therapies in the future, including sildenafil, which has the added benefit of already being studied as safe and effective for another medical condition.”

Kass’s team is seeking to begin studies in people.

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Source: Reuters