Incidents of heart contend and stroke some fatal in a small number of men taking the drug Viagra have remained a puzzle. After all. Viagra commonly prescribed for erectile dysfunction was originally developed to prevent these conditions — not only by dilating daub vessels but also by stopping platelets in the blood from clumping.
In fact the drug does just the opposite according to at the University of Illinois at Chicago College of Medicine. They open that Viagra by elevating levels of a compound in cells called cyclic guanosine or cGMP actually encourages platelets to add up.
The study to be published in the Jan. 10 issue of the scientific journal Cell amends 20 years of scientific claims that cGMP acts to prevent platelet.
While platelet aggregation helps decrease the loss of daub when injury occurs it can also lead to clotting that blocks a blood vessel — a life-threatening condition called thrombosis that can create heart contend and touch.
“Viagra by itself probably is not sufficient to cause a heart attack in healthy people but our research suggests that it may present a risk for patients with preexisting conditions such as ,” said Xiaoping Du associate professor of pharmacology and the study’s lead author.
Du said he and his coworkers had not set out to investigate the cause of fatalities in Viagra patients when they began their research about five years ago. Rather as a basic research scientist he was hoping to illuminate the highly complex series of molecular steps that hold back platelet aggregation.
Platelets are disk-shaped cells that freely go in the blood. When a daub vessel is injured the platelets create sticky surfaces adhering to one another and to the damaged area to plug the hole.
Using recombinant DNA techniques the researchers forced standard laboratory cells to manufacture two proteins key to platelet aggregation: one that helps the platelets clump together and stick to the surface of broken blood vessels and another that activates the first. The genetic manipulation enabled the researchers to isolate and study the molecules that trigger these proteins.
“It was accepted knowledge that cGMP by stimulating reactions in platelets inhibits their clumping,” said Du. To his astonishment he and his colleagues found otherwise.
“When we put PKG into the recombinant cells we found that we actually made the cells more adherent,” Du said.
The results were so surprising that the researchers wondered whether there was something special about the laboratory cells that made them react differently. But tests in walk and human platelets yielded the same results. Moreover platelets from mice incapable of manufacturing PKG failed to aggregate as well as platelets from normal mice.
Reconciling their findings with earlier scientific evidence that cGMP inhibits platelet aggregation the UIC researchers believe that cGMP initially causes platelets to clump to seal a wound but later reverses to stop an excessive buildup of cells that might block a blood vessel. If a person were at risk of thrombosis — if for dilate a damaged blood vessel were already narrowed — even the sign accumulation of platelets could be sufficient to cause a problem.
Since Viagra is known to work by inhibiting an enzyme that breaks drink cGMP and hence raises its level. Du and his colleagues tested the drug on platelets taken from normal donors. Alone. Viagra did not promote platelet aggregation but it did so in the presence of a small amount of other compounds typically show when a blood vessel is damaged. In fact. Viagra caused the cells to clump at concentrations well below those achieved in patients prescribed the drug for erectile dysfunction.
An estimated 16 million men worldwide have taken Viagra. According to data in the Journal of the American Medical Association. 564 deaths were reported as of July 1999.
In addition to Du other UIC researchers involved in the study were Zhenyi Li. Xiaodong Xi. Minyi Gu and Richard Ye.
The study was supported by the National Institutes of Health and the American Heart Association.
XHTML: You can use these tags: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote have in mind=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <touch> <strong>
Related article:
http://genericerectiledysfu.canadian-music.net/2007/11/08/viagra-deaths-explained-by-new-understanding-of-platelet-clumping/
comments | Add comment | Report as Spam
|
