DOSE-RESPONSES TO INDUCERS AND INHIBITORS OF PLATELET-AGGREGATION ANALYZED VIA A MICROMETHOD

The ex vivo study of platelet function in small experimental animals t reated with anti-platelet drugs is restricted by the limited availabil ity of platelet-rich plasma (PRP). To circumvent this obstacle, a micr o-method for platelet aggregation was developed that enables ED(50) me asurements for various inducers of platelet aggregation. Fifty microli ters of human, hamster, or rabbit PRP was mixed with agonist in each w ell of a microtiter plate, and shaken at 900 rpm at 37 degrees C for i ntervals up to 5 min. After stopping the aggregation with formaldehyde in PBS, light scattering was measured vs platelet-poor plasma (PPP) a t 620 nm. Thus, aggregation in human PRP by ADP (t = 2 min) occurred w ith an ED(50) = 1.8 mu M, whereas the collagen (r = 3 min; ED(50) = 2 mu g/ml) and AA. (t = 1 min; ED(50) = 0.3 mM) induced aggregation occu rred at those concentrations that induce aggregation in classical aggr egometry. Likewise, aggregation was inhibited by the anti-GPIIb/IIIa a ntibody MA-16N7C2 and by the GPIIb/IIIa antagonists G4120 or MK-852. I n comparison with human PRP, hamster (ED(50) = 0.8 mu M at t = 2 min) and rabbit (ED(50) = 5 mu M at t = 4 min) platelet aggregation by ADP occurred with comparable sensitivities, whereas the aggregation of rab bit platelets by collagen (ED(50) = 15 mu g/ml at t = 3 min) appeared to be slightly less sensitive and subject to large interindividual var iations. The method was applied to measure plasma levels of a GPIIb/lI Ia antagonist following injection into hamsters.