The release of histamine during anaphylaxis has been demonstrated in several species and various tissues, but it is well known that histamine alone cannot satisfactorily account for all the effects on smooth muscle observed during the anaphylactic reaction. The experiments presented in the present paper show that in addition to the release of histamine, the antigen-antibody reaction results in the formation of another smoothmuscle-stimulating substance which causes a slow and long-lasting contraction of the guinea-pig ileum, and which is resistant to anti-histamine drugs. This substance will be referred to as SRS-A.The existence of a slow-reacting substance in the effluent collected during shock from the perfused lungs ofthe guinea-pig was recognized by Kellaway & Trethewie (1940). They were, however, unable to separate its effect upon the guinea-pig gut from that of histamine in the effluent, and their evidence for its presence was based on the observation that the active effluent caused a more prolonged contraction of the gut than did histamine alone. The use of anti-histamine drugs now makes it possible to study SRS-A separately. METHODSThe experiments were performed on perfused lungs or minced tissue from sensitized animals.Sensitization. Young albino guinea-pigs, usually male, of 200-250 g were given an intraperitoneal and a subcutaneous injection each of 100 mg dried egg albumin, as a 10% solution in saline, containing 0-5 % phenol. The animals were killed with N20, or by dislocation of the neck, 3-5 weeks later, when they were always found to be strongly sensitized to the antigen.Young male sandy-lop or albino rabbits were used. A primary antibody response was produced by two intramuscular injections of 25 mg of the antigen, in 1 ml. of adjuvant medium (Freund & McDermott, 1942) given 7 days apart. After 6 weeks, 5 or 6 graded doses of alum-precipitated antigen, rising from 2 to 10 mg, were given intravenously at intervals of 3 days. The animals were killed by dislocation of the neck, or bled out under pentobarbitone, 6-10 days after the last injection.Rats of both sexes, of a hooded strain maintained at the National Institute for Medical Research, London, and weighing about 120 g, were sensitized similarly to rabbits but with

Mongar and Schild have demonstrated that the anaphylactic release of histamine from chopped guinea pig lung requires calcium and a heat-labile factor, and can be inhibited by metabolic inhibitors such as iodoacetate and cyanide (1-3). The effectiveness of these and other non-specific metabolic inhibitors in preventing the in ~itro anaphylactic reaction has been confirmed by other workers studying the release of histamine from chopped guinea pig and rat tissue (4) and the degranulation of mast cells in the mesentery of the guinea pig (5) and rat (6, 7).Since the metabolic inhibitors used by all these workers influence a wide range of enzymes and can alter a variety of tissue metabolic processes, they offer only limited insight into the type of enzymatic processes involved. We therefore attempted to use inhibitors which were more selective in action, and most of our studies were done with competitive rather than non-competitive inhibitors. Many of the compounds studied were synthetic substxates and were selected in the hope that they would produce inhibition by competing with the natural substrate for the enzyme involved. Our first experiments were prompted by the finding of Becket (8, 9) that the first component of guinea pig complement was an esterase which could be inhibited by diisopropylfluophosphate (DFP), and by the knowledge that DFP could also prevent the anaphylactic release of histamine and slow reacting substance SRS-A (10) from perfused guinea pig lung (11). We were also guided in our initial choice of inhibitors by the finding of Cushman, Becker, and Wirtz (12) that immune hemolysis is inhibited by thiols, esters of arginine and lysine, esters or amides of tyrosine, and peptides with a terminal aromatic amino acid having a free carboxyl group.In a preliminary report (13) we noted that amino acid ester substrates and inhibitors of chymotrypsin prevent the anaphylactic release of histamine while substrates and inhibitors of trypsin do not. The present report extends these findings. It shows that acetylation of the ester substrate so as to introduce a

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SUMMARY1. A method for the estimation of free plasma kinin and kininogen is described, which is suitable for samples of blood taken in hospital.2. The method permits the assay of very low levels of kinin and substantially eliminates errors due to the presence of amines and other interfering substances.3. In normal subjects the mean value of free kinin is 2-8 ng (bradykinin equivalent)/ml. plasma, and 6-1,ug kininogen/ml.4. In vasovagal fainting, carcinoid flush, and dumping syndrome, during the phase of peripheral vasodilatation, the free kinin exceeds 10 ng/ml., and is often in excess of 30 ng/ml.5. Sudden release of free kinin is accompanied by a fall in kininogen level.