The effect of radiation on the secretion of von Willebrand factor by endothelial cells was studied in a three-compartment culture system. The release of von Willebrand factor was significantly increased at 48 h after a single gamma-radiation dose of 20 Gy in both the luminal and abluminal direction by 23 (P < 0.05) and 41% (P < 0.02), respectively. To establish whether the enhanced production of von Willebrand factor affected the thrombogenicity of the extracellular matrix, platelet adhesion to the matrix produced by a monolayer of cultured endothelial cells during 48 h after irradiation was analyzed in a perfusion chamber at high shear rate (1300 s-1). Platelet adhesion was significantly increased by irradiation both in the presence and in the absence of plasmatic von Willebrand factor by 65 (P < 0.05) and 34.5% (P < 0.005), respectively. Incubation of the perfusate with a monoclonal antibody that blocks the binding of von Willebrand factor to platelet GPIb (CLB-RAg 35) resulted in an almost complete inhibition of platelet adhesion. These data indicate that radiation enhances platelet adhesion to the the extracellular matrix by an increase in the release of von Willebrand factor by endothelial cells. This event may be important in early radiation-induced vascular pathology.

SummaryIt is well known that the function of platelets decreases progressively during storage of platelet concentrates at room temperature. To investigate this phenomenon in more detail, we have resuspended platelets that had been stored for 24 h or 72 h in fresh plasma, and we have measured the aggregation response and the ATP secretion. Conversely, the effect of plasma in which platelet concentrates (PC) had been stored for 24 h or 72 h, was tested on fresh platelets. Both the aggregation response to collagen and ADP and the collagen-induced ATP secretion of stored platelets partially recovered after incubation with fresh plasma (p <0.05). The same parameters measured with fresh platelets incubated in stored PC-plasma were found to be significantly reduced in comparison with the response of fresh platelets in fresh plasma (p <0.05). Finally, platelets were stored in a plasma-free medium, suitable for platelet storage and the supernatant was tested. This supernatant inhibited the function of fresh platelets in a storage time-dependent fashion. Boiling of these supernatants did not change the inhibiting capacities, whereas filtration over active charcoal did. Analysis of this supernatant revealed AMP and diadenosine tetraphosphate, which both inhibit platelet function.These data show that stored platelets release nucleotides that inhibit platelet function in a reversible manner. This phenomenon may contribute to the decrease of platelet function during storage and the recovery of platelet function after transfusion.

PCs prepared from a pool of four buffy coats can be filtered and subsequently stored for 8 days (starting +/- 24 hours after whole blood collection) without detriment to platelet function, metabolism, or activation.

SummaryThe influence of storage of platelet concentrates (PC) on the adhesion capacity of platelets was studied. Twenty-four PC, 12 prepared by the buffy coat (BC) method and 12 by the platelet-rich plasma (PRP) method, were stored for 7 days at room temperature. On days 1,3 and 7 of storage, the platelet adhesion capacity to subendothelial matrix (SEM) and collagen was studied in a rectangular perfusion system under flow conditions in conjunction with the platelet aggregation capacity after stimulation and the adenine nucleotide content. The platelet adhesion capacity to collagen was constant until day 3 of storage and decreased to about 80% of the starting value on day 7 of storage. The adhesion capacity to SEM, however, had already decreased on day 3 to about 75% of the value of day 1 and was even more decreased on day 7 to about 45% of the starting value. On day 1, platelets prepared by the BC method displayed a higher adhesion capacity to collagen and a higher aggregation capacity after stimulation by collagen alone or in combination with ADP, compared to platelets prepared by the PRP method. No other significant differences in adhesion or aggregation capacity were observed between the PC prepared by the two different methods. Both platelet adhesion and aggregation response decreased during storage, as did the total adenine nucleotide content. This study shows that platelet function, as measured by the aggregation and adhesion capacity, of platelets prepared by the PRP method is more severely impaired during the first 3 days of storage as compared to the function of platelets prepared by the BC method.