The circle has closed

Viagra analogue saved sheep from heart failure

Polina Loseva, "The Attic"

In the 90s, Pfizer employees began clinical trials of a new drug sildenafil, designed to cope with angina and high blood pressure. According to the results of the first phase of trials, the drug failed to achieve its goal, but suddenly it turned out to be effective against impotence. Now we know this drug as Viagra. But recently, the original idea of Pfizer employees got a new chance. The analogue of viagra – tadalafil (cialis) – is again being tried against diseases of the cardiovascular system. However, so far the results have been obtained only on sheep.

The history of Viagra has become a classic example of how the drug has completely changed the direction of its action. Initially, its active ingredient – sildenafil – was tested as a remedy for high blood pressure. Sildenafil should be blocking the work of the phosphodiesterase signaling enzyme in the muscles. When the enzyme is active, muscle cells contract, the lumen of the vessels narrows and blood pressure increases.

However, in the course of testing, it turned out that sildenafil mainly acts on type 5 phosphodiesterase. This variant of the enzyme is found in the muscles of the walls of blood vessels, but it is much more in the muscles of the cavernous bodies. Therefore, sildenafil was ineffective against hypertension, but it perfectly relaxed the muscles of the penis, causing an erection. As a result, this drug, already under the name "Viagra", entered the market as a cure for impotence.

Over the past time, Viagra has had many analogues. In 2003, tadalifil (which we know as cialis) entered the market in the USA. It acts on the same principle as sildenafil – it blocks phosphodiesterase type 5, and binds to it much more strongly than its predecessors. And scientists from Manchester decided to arrange a rematch of tadalifil against cardiovascular diseases.

To do this, they took 69 adult sheep and simulated heart failure in them, stimulating the heart with an artificial pacemaker and making it beat too fast. Under the influence of the increased load, the chambers of the heart expanded, and their walls became thicker. At the same time, muscle cells began to perceive external signals for contraction worse.

Then the animals received tadalifil for three weeks in the same doses prescribed to patients suffering from erectile dysfunction. As a result, many of the symptoms of heart failure disappeared: the heart began to contract more actively, respond better to hormonal stimulation (for example, adrenaline), and some of the chambers of the heart restored the original thickness of the walls. At the same time, the peripheral vessels did not change in any way and the blood pressure remained unchanged.

Thus, tadalifil was able to reverse heart failure without having side effects. So, he got a new chance to become a cure for heart disease. The circle has closed.

However, so far doctors do not recommend people to self-medicate. Although the heart of a sheep is similar to a human heart, it is too early to draw conclusions about the absolute safety of the drug.

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