Infoviagra

One of the most common problem we found in Viagra is that it has an spillover effect as It blocks PDE5 and has also effect on PDE6. It turns out that PDE6 is used in the cone cells in the retina, so Viagra can temporally alter color vision. Many people who take Viagra notice a change in the way they perceive green and blue colors, for instance.

Viagra can also have side effects on people havind drugs like nitroglycerin. As Viagra, Nitroglycerin works by increasing nitric oxide, opening up the arteries that supply the heart with oxygen. Taking nitroglycerin and Viagra together, plus the blocking of PDE5, can lead to an overincrease of the nitric oxide, what could mean problems.

Other problems with Viagra can include headaches, facial flushing and upset stomach. The possibility of heart attacks is one reason why Viagra is a prescription drug. This is why before being prescribed Viagra, patients must be asessed by their doctor, who needs firstly to understand their medical history.

Sources:

http://www.howstuffworks.com/

http://www.viagra.com/

Viagra does not work as a  general smooth-muscle relaxer. On the contrary, this medicine is a drug only acting on the smooth muscle in the arteries of the penis, which is exactly what men suffering from erectile dysfunction need to treat their problem. What Viagra really does is to turn some valves on in order to pump the blood flow to the penis.

The mechanism that the body uses to “open a valve” in any part of the body involves four steps:

1. The brain sends a signal down a particular nerve fiber. This nerve fiber ends in an NANC nerve cell in an artery, somewhere near the point where blood flow needs to change. NANC stands for nonadrenergic-noncholinergic, and what it means is that the NANC nerve cell is able to create nitric oxide.
2. The NANC nerve endings inject nitric oxide into the blood and surrounding cells.
3. The nitric oxide stimulates an enzyme called guanylate cyclase in nearby cells, and this enzyme starts producing a chemical called cyclic guanosine monophosphate (cGMP).
4. cGMP tells smooth muscles that line an artery to relax. When they relax, blood flow increases.

This is the mechanism the brain uses to increase blood flow in several different parts of the body. So when the brain gets aroused, it sends a signal to the penis. Nerve cells in the penis’ corpora cavernosa start producing nitric oxide, leading to the creation of cGMP, which causes arteries in the corpora cavernosa to dilate, causing blood to flow into the penis. The extra blood flowing in causes the penis to inflate like a balloon. And then, the erection occurs.

Source: http://health.howstuffworks.com/