The release of prostaglandins and thromboxanes from guinea-pig lung by slow reacting substance of anaphylaxis, and its inhibition.

1 Rabbit aorta contracting substance (RCS; consisting mainly of thromboxane A2) and prostaglandin-like material were released from guinea-pig isolated perfused lungs by injection of slow reacting substance of anaphylaxis (SRS-A). 2 SRS-A was resistant to boiling and proteolytic enzymes and was therefore distinguished from rabbit aorta contracting substance releasing factor (RCS-RF). 3 The release of RCS and prostaglandin-like material by SRS-A was anatagonized by indomethacin (1 microgram/ml), betamethasone and dexamethasone (4 to 50 microgram/ml). 4 Imidazole (200 microgram/ml) inhibited the formation of thromboxane A2 but not that of prostaglandins. 5 The activity of SRS-A on guinea-pig ileum and its ability to release RCS and prostaglandins were destroyed by incubation with arylsulphatase (0.83 microgram to 1 mg/ml) and with lipoxidase (16.5 to 50 microgram/ml): SRS-A lost activity on incubation with bovine serum albumin (9 microgram/ml) due to protein binding.