[Species difference on binding property of dilazep to erythrocytes and platelets]

The whole blood of human, rabbit and dog spiked with dilazep was fractionated by discontinuous density gradients of Ficoll-Paque, and the species difference of distribution to blood components was elucidated. In order to quantitatively evaluate its blood distribution, the binding property of dilazep to the isolated erythrocytes and platelets was also studied. Dilazep undergoes saturable binding to the erythrocytes. Therefore, the fitting of the data sets to binding models was carried out using the nonlinear least-square method, and binding parameters were calculated. This technique could be also applied to analyze directly the binding parameters for several whole blood components. In human and rabbit, dilazep was bound to the erythrocytes with a high affinity (human, KERY = 0.466 nM; rabbit, KERY = 0.0417 nM), however, the affinity to the erythrocytes in dog was very low. On the other hand, the binding affinity to the platelets decreased in the order of rabbit > dog > human.