FRIDAY, Jan. 10 (HealthScoutNews) -- Platelet clumping caused by Viagra may be the cause of heart attack and stroke in some men who take the impotence drug.
That's what researchers from the University of Illinois at Chicago College of Medicine have found. Their study appears in today's issue of Cell.
Cases of heart attack and stroke in a small number of men who take Viagra have puzzled medical researchers. That's because Viagra was originally developed to prevent heart attack and stroke by dilating blood vessels and by stopping platelets from clumping.
However, this new study says Viagra actually causes platelet clumping. It does that by elevating levels of a compound in cells called cyclic guanosine monophosphate (cGMP). This compound actually encourages platelets to clump.
The researchers used laboratory cells and mouse and human platelets in their research.
The study contradicts 20 years of claims that cGMP prevents platelet clumping. That clumping can lead to clotting that blocks blood vessels, resulting in a condition called thrombosis that can cause heart attack and stroke.
The researchers note that Viagra alone is probably not sufficient to cause a heart attack or stroke in healthy people. However, their findings suggest that taking Viagra may be a risk for people who have health problems such as hardening of the arteries.
Platelets are disk-shaped cells that circulate in the blood. In response to blood vessel injuries, platelets form sticky surfaces and attach to one another and the damaged area of the blood vessel. That plugs the hole in the blood vessel.
About 16 million men around the world have taken Viagra, which is used to treat erectile dysfunction. Data in the Journal of the American Medical Association (news - web sites) says 564 deaths of men taking Viagra were reported as of July 1999.
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