Slow Reacting Substances: Comparison of Some Properties of Human Lung SRS-A and Two Distinct Fractions from Ionophore-Induced Rat Mononuclear Cell SRS

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Abstract
When mononuclear cells from the peritoneal exudates of rats are challenged with the ionophore A 23187 they produce a slow reacting substance (SRSri), and production of this activity is markedly enhanced if 0.01 M L-cysteine is also added to the incubations. Previous work from this laboratory had shown that the properties of SRSri resembled those that had been described for slow reacting substance of anaphylaxis (SRS-A) in the literature. We have now directly compared SRSri to SRS-A generated immunologically in chopped human lung. A high performance liquid chromatography separation of SRSri on Florisil has been developed by using a linear gradient of water into methanol for elution. SRSri is completely resolved into two peaks of activity, comprising approximately 33 and 67% of the total activity. SRS-A elutes at a postion that is identical to that for the smaller of the SRSri peaks. Although both peaks of SRSri activity are stable to boiling in alkali and are destroyed upon boiling in 0.1 N HCl, there are quantitative differences in the rate of destruction of the two activities and of SRS-A. Similarly, the susceptibility of the three preparations to inactivation by sulfatase from Patella vulgata was different. In addition, inhibition of contractions caused by these three preparations by the end organ antagonist of SRS-A, FPL 55712, also suggested differences between the preparations. Thus, the results suggest the existence of a family of substances that, loosely, satisfy the criteria to be referred to as SRS-A, although they differ in certain details.

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