Phagocytosis stimulates the release of a slow reacting substance in cultured macrophages.

1 A slow-reacting substance (SRS) was released from non-elicited mouse peritoneal macrophages during phagocytosis of zymosan particles, whereas no detectable SRS was produced by resting cells. 2 The macrophage SRS induced a delayed and slow contraction of the guinea-pig ileum but not of the chick rectum. 3 The myotonic activity was antagonized by low concentrations of FPL 55712 (sodium 7-[3-(4-acetyl-3-hydroxy-2-propylphenoxy)-2-hydroxypropoxy]-4-oxo-8-propyl-4H-1 -benzopyran-2 carboxylate) but was not affected by mepyramine or hyoscine, and was not associated with tachyphylaxis. 4 SRS release was increased by indomethacin and was abolished by the lipoxygenase and cyclooxygenase inhibitor, BW755C (3-amino-1-[m-(trifluoromethyl)-phenyl]-2-pyrazoline). 5 Addition of exogenous arachidonic acid or cysteine enhanced SRS production.