THROMBOXANE A(2) AND PLATELET-ACTIVATING-FACTOR DECREASE IN THE PLATELET-MESANGIAL CELL-INTERACTIONS

To analyze the metabolisms of platelet-activating factor (PAF) and Thr omboxane A(2) (TxA(2)) when platelets and mesangial cells (MC) interac t, immunoreactive thromboxane B-2 (TxB(2)) and PAF were measured after incubation of cultured rat MC with platelets (P) and with platelet su pernatants (PS). In both cases, TxB(2) significantly decreased with re spect to the P synthesis and to the PS content, suggesting an increase d degradation of this metabolite or even the existence of a specific e ffect of MC upon platelet TxB(2). When immunoreactive PAF was measured , results were comparable to those observed for TxB(2). Moreover, when intrinsic mesangial cell synthesis of PAF was assessed by analyzing t he [H-3]-acetate incorporation by prelabeled MC in the HPLC fraction c oeluting with cold PAF standards, it was possible to demonstrate that P or PS did not modify PAF synthesis in these cells. In summary, prese nt results support the existence of a specific effect of mesangial cel ls upon platelet TxA(2) and PAF.