Viagra-for Heart Disease?
November 1, 2005
Viagra may offer more than just a relatively quick-fix for men's sex lives. A new study suggests that Viagra (sildenafil) may also slow the progress of some types of heart disease.
Researchers at Johns Hopkins claim to have found evidence that Viagra effects the human heart, according to a study published in the 25 October 2005 issue of journal Circulation and reported by MedPage Today on 25 October.
"The main thing we've found is that sildenafil essentially blunts the cardiac-stimulating effects of a synthetic catecholamine, dobutamine," said David Kass, MD, according to MedPage Today.
Dr. Kass and colleagues have previously shown that sildenafil can reverse or prevent cardiac hypertrophy in mice. (See previous report in MedPage Today.) The more recent study published in Circulation suggests that sildenafil has a similar effect on humans, although more clinical studies are needed to prove it, according to Dr. Kass.
The findings may also explain why the "heart-pounding excitement of Viagra-enhanced sex" seems to be relatively safe for men who have heart disease, according to MedPage Today.
Dr. Kass said that the results "would suggest that all along there has been some sort of blunting effect, so that heart is not racing as much as would have been. In retrospect, it may explain why the drug has been so well-tolerated even in patients with coronary disease." He believes that the study results should prompt further clinical research into potential additional therapeutic uses of Viagra and similar drug-compounds.
Recent Study
The Circulation study included 35 healthy volunteers in a randomized, controlled, double-blind placebo format. Researchers tested heart function four times: at baseline, after a dobutamine challenge, at a second baseline, and after dobutamine challenge combined with either Viagra (sildenafil) (100 mg) or placebo.
Results showed that dobutamine's effects on patients taking Viagra at the second challenge were significantly less pronounced than in the initial response. In contrast, volunteers receiving placebo group showed similar reactions to those seen in the initial response:
- In volunteers not taking Viagra, the peak power index rose 254 mmHg per second from the baseline of about 300; in volunteers taking Viagra, it rose only 164 mmHg.
- In volunteers not taking Viagra, the ejection fraction rose by 15%; in patients taking Viagra, it rose only 4%.
- Ventricular end-systolic elastance in volunteers not taking Viagra rose 2.52 mmHg/mL; in volunteers in whom Viagra was co-administered, the measurement was only 0.84.
All of these differences had high statistical significance.
Viagra works by inhibiting the enzyme phosphodiesterase 5 (PDE5), which breaks down cyclic GMP (cGMP). This inhibition leads to increased levels of cGMP, which in turn causes the vasodilation that accounts for Viagra's positive effect on erectile function.
However, although cGMP also regulates cardiac function and counters beta-adrenergic stimulation, scientists until now believed that not enough PDE5 was present in the heart-muscle significantly to affect its metabolism.
These study results overturn that view, according to Dr. Kass, who reportedly said, "The enzyme really is in there and sildenafil really does have an effect on the human heart."
Sources:
Little
Blue Pill May Put Brakes on Some Heart Disease, MedPage Today,
25 October 2005.
Sildenafil
Inhibits Beta-Adrenergic-Stimulated Cardiac Contractility in
Humans. Borlaug BA et al., Circulation, volume 112,
pages 112:2642-2649, 2005.
Chronic inhibition of cyclic GMP phosphodiesterase 5A prevents and
reverses cardiac hypertrophy. Takimoto E et al., Nature
Medicine, volume 11(2), pages 214-222, February 2005.
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