Slow reacting substance as a preformed mediator from human lung.

Homogenates from human lung contained a preformed slow reacting substance (pSRS). The pattern of contraction on the guinea-pig ileum by pSRS was indistinguishable from that of SRS-A. The activity of pSRS could not be attributed to the presence of K+, Na+, Ca2+ and Mg2+ ions, or any prostaglandin including PGF2 or its 15-oxo derivative. As with SRS-A, pSRS could be absorbed onto Amberlite XAD-2 and silicic acid. Both were eluted from the former with 80 per cent ethanol and from the latter with a mixture of ethanol, ammonia and water. Both pSRS and SRS-A were resistant to the action of NaOH whereas their activities were destroyed by boiling in HCl. Arylsulphatase II B destroyed the activities of both pSRS and SRS-A. An antagonist of SRS-A, FPL55712, inhibited the action of pSRS at comparable concentrations to that of SRS-A. These experiments suggest that pSRS and SRS-A are identical. Thus SRS joins histamine and ECF-A as a preformed mediator. Although SRS was present in a preformed state the amount of material extractable was more than doubled by the anaphylactic reaction. The extraction of slow reacting substance from human lung without apparent requirement for antigen or antibody points to a possible role of this mediator in inflammatory reactions evoked by mechanisms independent of IgE and other tissue-sensitizing antibodies.