Blood begins to lose nitric oxide shortly after it is drawn from a donor, two new studies show. The loss of this important chemical may explain earlier findings that transfusions seemed to harm rather than help some patients.
Nitric oxide (NO) dilates arteries, facilitating oxygen delivery to the tissues. In both studies, scientists tested stored red blood cells, which carry NO. They found that the cells lost at least 75 percent of their NO within 3 hours of being donated. The concentrations remained low for 42 days, after which stored blood is discarded. The researchers report their findings in the Oct. 23 Proceedings of the National Academy of Sciences.
Cardiologist Jonathan S. Stamler of Duke University Medical Center in Durham, N.C., and his team showed that it is possible to put NO back into stored blood. They then compared the effects of depleted and replenished blood on dogs by monitoring blood flow in the animals’ hearts. Blood flow was poor in dogs given blood depleted of NO but significantly better in dogs given blood with replenished NO.
Red blood cells change shape to get through narrow vessels. The other study, led by critical-care physician Timothy J. McMahon, also at Duke, found that deformability declined gradually during the 6 weeks in which blood was stored. Further research will help scientists ascertain whether the decline of NO is linked to the reduction in deformability, says McMahon.
If large trials in people confirm these results, Stamler says, hospitals should prepare to replenish stored blood with NO.