How sildenafil（昔多芬） , the active ingredient in Viagra, can alleviate¹（减轻，缓和） heart problems is reported by Bochum's researchers in cooperation with colleagues from the Mayo Clinic in Rochester (Minnesota) in the journal Circulation. They studied dogs with diastolic（心脏舒张的） heart failure, a condition in which the heart chamber² does not sufficiently³ fill with blood. The scientists showed that sildenafil makes stiffened⁴ cardiac walls more elastic⁵（有弹性的） again. The drug activates⁶ an enzyme⁷ that causes the giant protein titin in the myocardial（心肌的） cells to relax. "We have developed a therapy in an animal model that, for the first time, also raises hopes for the successful treatment of patients" says Prof. Dr. Wolfgang Linke of the RUB Institute of Physiology⁸.

"Rubber band proteins" can be influenced

Sildenafil inhibits⁹ a specific enzyme (phosphodiesterase 5 A), which causes the increased formation of a messenger substance (cGMP). The messenger substance activates the enzyme protein kinase G, which attaches phosphate groups to certain proteins. This so-called phosphorylation causes blood vessels¹⁰ to relax, which was why the "potency¹¹ pill" Viagra originally came onto the market. The Bochum and Rochester researchers found that the cardiac muscle protein titin is also phosphorylated through the same mechanism¹². "The titin molecules¹³ are similar to rubber bands" explains the Bochum physiologist¹⁴. "They contribute decisively to the stiffness of the cardiac walls." The activity of the protein kinase G causes titin to relax. This makes the cardiac walls more elastic. The effect occurs within minutes of administering the drug.

Heart failure drugs currently not sufficient

"Of all the patients aged¹⁵ over 60 who are in hospital because of a weak heart, half suffer from diastolic heart failure" explains Linke. "Although we know that the decreased distensibility¹⁶ of the cardiac walls is the cause, the disease cannot be treated properly with today's medicines." In the so-called "Relax" study of the Heart Failure Network, the efficacy of sildenafil in people is already being tested. "If, for the first time, the drug is found to have a positive effect on heart failure, we would already have a molecular¹⁷ mechanism on hand to explain the effect" says Linke.