Airway sensitivity to slow-reacting substance of anaphylaxis, histamine, and antigen in Ascaris sensitive monkeys

The role of arachidonic acid metabolites in local and systemic inflammatory processes

Leukotrienes are synthesised from arachidonic acid via the 5-lipoxygenase pathway in neutrophils, eosinophils, monocytes/macrophages, basophils and certain mast cell populations. Their synthesis is closely regulated by several known factors and the cells which contain 5-lipoxygenase do not all possess the capability to synthesise all of the leukotrienes. Neutrophils produce leukotriene B4, which attracts other neutrophils, whereas the leukotriene C4, produced by eosinophils, increases the contractile activity of smooth muscle. Monocytes/macrophages are able to produce both of these leukotrienes. Receptor sites for leukotriene B4 have been identified on monocytes and neutrophils and receptors for leukotriene D4, a cleavage product of leukotriene C4, have been defined in pulmonary tissue. In animals, sulphidopeptide leukotrienes have been shown to cause potent vasoconstriction resulting in increased blood pressure and increased vascular permeability leading to hypovolaemia. These leukotrienes also depress renal (in animals) and pulmonary (in animals and humans) function, the latter probably as a result of effects on peripheral rather than central airways. In patients with mild asthma, however, there is no differential activity of this type. The sulphidopeptide leukotrienes caused wheal and flare when administered intradermally in healthy volunteers, which was of considerably longer duration than that induced by prostaglandin D2. Conversely, leukotriene B4 caused accumulation of neutrophils in the absence of wheal and flare. Studies into the effects of dietary fish oil showed that 2 constituents, docosahexanoic acid and eicosapentaenoic acid (EPA), inhibit the conversion of arachidonic acid by cyclo-oxygenase, but not by 5-lipoxygenase. Furthermore, 5-lipoxygenase converts EPA to a pentene series of leukotrienes and the sulphidopeptide derivatives possess similar activity to their tetrameric counterparts.(ABSTRACT TRUNCATED AT 250 WORDS)

Leukotrienes, allergy and inflammation

Immunological and non-immunological injury induce as a result of the action of the enzyme lipoxygenase the release of a series of arachidonic acid metabolites known as leukotrienes. The leukotrienes play an important role in allergic and inflammatory disease. Leukotrienes C4, D4 and E4 which recently have been recognized as constituents of the allergic mediator slow reacting substance of anaphylaxis (SRS-A) induce powerful bronchoconstriction, plasma exudation and weal and flare responses. Leukotriene B4 is involved in the regulation of chemotaxis, chemokinesis and other aspects of both cellular and vascular inflammation. The development of specific lipoxygenase inhibitors may lead to a new class of drugs for the treatment of bronchial asthma and chronic inflammatory diseases.

Slow reacting substances of anaphylaxis: identification of leukotrienes C-1 and D from human and rat sources

Slow reacting substance(s) of anaphylaxis (SRS-A) was isolated from both human (lung) and rat sources and compared with three synthetic SRS-As of known structure-leukotrienes (LTs) C-1, C-2, and D. Reversed-phase liquid chromatography was used both as a final purification step and a means of comparison of biologically derived and synthetic substances. Two major peaks of SRS-A activity of both rat and human origin corresponded chromatographically with LTC-1 and LTD, respectively, and had equivalent specific activities on the guinea pig ileum. With guinea pig ileum, the specific activities (units/pmol) for synthetic leukotrienes and anaphylactic peaks were (mean +/- SEM): synthetic LTC-1, 1.93 +/- 0.13; SRS-A(rat) peak I, 1.69 +/- 0.43; synthetic LTD, 6.10 +/- 1.15; SRS-A(rat) peak II, 7.14 +/- 0.51; and SRS-A(hu) peak II, 1.90. Both synthetic LTC-1 and LTD and their SRS-A natural counterparts had a preferential contractile activity on guinea pig peripheral airway compared to central airways and were at least 200 times more active than histamine on peripheral airways on a molar basis. Leukotriene D is the major SRS-A of human lung and accounts for almost all of the biological activity. It likely is formed from leukotriene C-1 in vivo by an enzymic process of the well-known gamma-glutamyltransferase type.

Response of human isolated bronchial and lung parenchymal strips to SRS-A and other mediators of asthmatic bronchospasm

1 The responses of human isolated bronchial and lung parenchymal strips to cumulative doses of slow reacting substance of anaphylaxis (SRS-A), histamine, prostaglandin F2 alpha (PGF2 alpha) and acetylcholine have been examined, after storing the tissues overnight in Krebs solution at 4 degrees C. 2 Both tissues contracted to all four agonists. The order of potency (as determined by height of maximal contraction) was: bronchial strip: acetylcholine greater than histamine = PGF2 alpha greater than SRS-A, and parenchymal strip: PGF2 alpha much greater than histamine = SRS-A greater than acetylcholine. 3 Maximal contractions to SRS-A of both the human bronchial and parenchymal strips were approx. 30% of the maximal contractions produced by the most potent agonist on each tissue (PGF2 alpha on the parenchymal strip and acetylcholine on the bronchial strip). SRS-A, therefore, does not have a powerful direct contractile effect on either parenchymal or bronchial strip of human lung, and is approximately equipotent on both tissues. A part of the broncho-constrictor activity of SRS-A in vivo may be mediated via indirect pathways. 4 The selective SRS-A antagonist, FPL 55712, was approximately equipotent in antagonizing contractions induced by SRS-A on both human bronchial and parenchymal strips.