CELL-CELL INTERACTION BETWEEN PLATELETS AND IL-1-BETA STIMULATED VASCULAR SMOOTH-MUSCLE CELLS IN SYNTHESIS OF THROMBOXANE A(2)

Transcellular biosynthesis of thromboxane (Tx) A(2) between vascular s mooth muscle cells (SMC) and platelets has been investigated by using C-14-arachidonic acid (AA) radiolabeled rat SMC (or platelets) and the fate of the label in phospholipids and eicosanoid fractions was studi ed using radioimmunoassay (RIA) and thin-layer chromatography (TLC). S timulation of SMC with interleukin-1 beta (IL-1 beta) resulted in prod uction of cyclooxygenase metabolites (e.g. 6-keto-PGF(1 alpha), PGE(2) , PGF(2 alpha), PGD(2)), 15-, 11-, 5-HETE, and free AA, with a coincid ent decline of phosphatidylcholine (PC) in SMC. IL-1 beta did not indu ce TXB(2) production, a stable metabolite of TXA(2) measured by TLC an d radioimmunoassay, either in human platelets from 0.01-100 U/ml for 1 h or in SMC for 24 h. However, human platelets converted exogenous PG H(2) to TXA(2) despite cyclooxygenase inhibition or PGH(2) receptor bl ockade. Furthermore, TXB(2) was produced in large quantities during co -incubation of IL-1 beta-stimulated SMC with human platelets for 30 mi n in concert with a significant decrease of 6-keto-PGF(1 alpha) and ei cosanoids (PGE(2), PGF(2 alpha) and PGD(2)) compared with control (P < 0.01). Pretreatment of SMC with cycloheximide and actinomycin not onl y inhibited IL-1 beta-induced eicosanoid synthesis and phospholipid br eakdown but also diminished TXB(2) production when co-incubated with p latelets. These data suggest that a cell-cell interaction, i.e. platel et utilizing SMC-derived endoperoxides for its TXA(2) production, migh t cause an excess thromboxane A(2) synthesis.