Soon after collection, banked blood begins losing nitric oxide, and since nitric oxide opens the body's small blood vessels, oxygen is prevented from reaching the body's tissues, according to the results of two studies published in the October 8th Early Edition of the Proceedings of the National Academy of Sciences.
"The ability of red blood cells to deliver oxygen is principally determined by how well they can open blood vessels (the role of nitric oxide) rather than by how much oxygen they carry. If nitric oxide can't be released, then vessels won't open and by inference, less oxygen is delivered," Dr Jonathan S. Stamler, senior author of one of the studies, told Reuters Health.
"No one had previously examined the nitric oxide content of stored blood or assessed its ability to open blood vessels," noted Stamler, a researcher at Duke University in Durham, North Carolina. The findings indicate that "nitric oxide is rapidly depleted during storage. Thus all of the blood in blood banks - millions of units transfused each year into millions of patients - is evidently defective."
In their animal study, Stamler's team evaluated blood taken from pigs and found that concentrations of S-nitrosohemoglobinm declined by 70 percent in one day and by 83 percent after one week. The team went on to show that the ability of banked blood to promote vasodilation is directly related to the concentration of S-nitrosohemoglobin.
"Rapid losses in S-nitrosohemoglobin were also seen in human whole blood," the researchers add.
Blood flow reduced
In another experiment, they observed that blood flow to the heart was reduced in dogs when nitric oxide-depleted red blood cells were infused. Conversely, use of red blood cells imparted with nitric oxide increased in perfusion.
Stamler said that his team hopes to start a clinical trial in the near future looking at the benefits of reintroducing nitric oxide into banked blood.
In the second study, Dr Timothy J. McMahon, also from Duke University, and colleagues examined the changes that took place over six weeks in red blood cells obtained from 15 healthy volunteers.
The findings echoed those from the first study. A rapid and sustained drop in S-nitrosohemoglobin levels was noted soon after collection. At the same time, the ability of the stored red blood cells to open blood vessels declined.
The "clinical concern," say the researchers, is that "even 'fresh' blood may have developed adverse biological characteristics."
SOURCE: Proceedings of the National Academy of Sciences, October 8th Early Edition. – (Reuters Health)
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