Few people know that Viagra started life as a medicine which was first researched as a treatment for angina pectoris.

Researchers, Robert Furchgott, Louis Ignarro and Ferid Murad of the manufacturer Pfizer proved nitric oxide was an important signaling molecule in the body’s cardiovascular system. This chemical is released from cells and nerve endings which line the walls of blood vessels. The effect of this allows the blood vessel to relax, or dilate. The medication also prevented the formation of blood clots.  What started out as an important medicine to help people with cardiovascular problems also helped men with an entirely different problem.

When a new medicine is being developed, it is normal for many different compounds to be used in the research. This was the case for Viagra when the medication was under clinical trials for use in the treatment of angina. This way ensures that they have the safest route possible when testing on patients.

Trials and development of a medicine called Zaprinast had already taken place and whilst it was originally designed as an anti allergy treatment, it had some effects the researchers were looking for. Zaprinast inhibited the enzyme PDE, which was what the researchers were looking for in their search for an anti angina medication, a medication that dilated the blood vessels and allow a stronger flow of blood.

 It was known that the vasodilatation was caused by the actions of cGMP inside the walls of the arteries. It was therefore important that the new medication target PDE that breaks down the cGMP. It followed that the researchers had to design a molecule that had a similar structure to cGMP. When they were successful in the design of the molecule they were able to see that the medicine would block the active site of the PDE molecule and stop it breaking down the cGMP. Computers are in common use now and are used to build virtual molecules. With the aid of the computer designers can alter molecules which allow their three-dimensional shape and chemical properties to be predicted. Because of this, researchers were able to design molecules that would be good candidates as a test against the PDE enzyme. Whilst this technique allows compounds to be targeted more efficiently, development still requires many compounds to be screened in laboratory tests.

The Viagra molecule shape allows it to fit into active site of the PDE enzyme. This prevents it from breaking down and dilation of the blood vessels results.  As with most medications the chemical process used to produce Viagra is very complex and Pfizer the manufacturer, had to find a more efficient method if it was ever going to be made in the large quantities needed to be a successful treatment for impotence. That they were successful with this is testament to the success of the treatment.