Labile Aggregation Stimulating Substance (LASS): the Factor from Storage Pool Deficient Platelets Correcting Defective Aggregation and Release of Aspirin Treated Normal Platelets

Abstract

Summary Mixtures of equal volumes of Hermansky‐Pudlak (HP) syndrome (adenine nucleotide storage pool deficient) and aspirin treated (AT) platelets (inhibited release of adenine nucleotides) undergo irreversible aggregation when exposed to collagen or adrenaline, whereas neither alone will do so. The present investigation has explored the basis for the mutual correction. Correction in the mixed system was accompanied by release of significant amounts of [¹⁴C]5‐hydroxy‐tryptamine from the AT platelets, whereas very little isotope was released when AT platelets alone were exposed to collagen. The correction of aggregation and the release of isotope could both be suppressed by pre‐treating HP platelets with aspirin. Labile aggregation stimulating substance (LASS) composed of two closely linked intermediates of prostaglandin (PG) E₂ and PGF_2a biosynthesis, produced using a microsomal fraction of HP platelets, could correct the aggregation and secretion defect of AT platelets exposed to collagen. These findings indicate that HP platelets when mixed with AT platelets and exposed to collagen secrete a substance which is responsible for the correction. LASS, identified as the factor involved, acted as an intercellular messenger which mediated the correction by overcoming the influence of aspirin on normal cells.