Aim 1: To investigate the effects of blood processing and storage (using standard FDA-approved conditions) on NO production and scavenging by human RBCs/Hb in vitro. Using sensitive biochemical assays (electron spin resonance [ESR]) and a rat aortic ring in vitro bioassay, the investigators will test the effects of RBC storage time, leukoreduction, and irradiation on NO synthesis and/or scavenging by intact RBCs and free Hb. Modifications such as washing and rejuvenation will be investigated as possible approaches to correct abnormalities in NO bioavailability.