Bradykinin generation in RC-MAP during storage at 4 degrees C and leukocyte removal filtration

We investigated contact system activation in red cell concentrate in mannitol-adenine-phosphate (MAP) solution (RC-MAP) during storage and leukocyte removal filtration. The contact system activation was assessed in terms of bradykinin (BK) generation. The BK level in the RC-MAP transiently but significantly (p < 0.05) increased at 7 to 14 days of storage. Moreover, the BK level in 21-day-stored RC-MAP was approximately 10 times higher than that in other blood components. The BK level in mannitol-containing MAP solutions, but not that in mannitol-free MAP solution, saline or whole blood, increased during storage. The plasma angiotensin-converting enzyme (ACE) activity decreased significantly only in mannitol-containing MAP solutions. These findings suggest that mannitol plays an essential role in the increase in BK level in RC-MAP. Furthermore, the BK level in RC-MAP increased 10 minutes after the start of filtration through a negatively charged filter, either a BPF-4 or an RN-40, and reached a maximum of 6,000 pg/ml. Hypotensive reactions are rare in RC-MAP transfusion in comparison to their incidence in platelet concentrate (PC) transfusion in spite of the higher BK level in RC-MAP than in PC. Therefore, BK generation in various blood components is not likely to be the main cause of hypotensive reactions. However, the level of BK in RC-MAP is sufficiently high to cause site pain. Further investigation on the clinical significance of a high BK level in blood components is necessary.