Cyclooxygenase Metabolites Of Arachidonic Acid Research Articles

Acute effects of intratracheal administration of platelet-activating factor in baboons.

The bronchomotor effect of intratracheal administration of PAF-acether (60 micrograms X kg -1) was investigated in 37 curarized baboons mechanically ventilated with constant volume and frequency. PAF-acether caused an immediate bronchoconstriction as assessed by a marked increase in peak inspiratory pressure with no change in static pulmonary compliance and chest X-rays. There was a concomitant fall in arterial PO2 and a significant increase in ventilated unperfused lung zones. A decrease of circulating platelets and leucocytes was also observed. Local anesthesia with lidocaine and atropine did not prevent PAF-acether-induced bronchoconstriction although both markedly reduced the bronchial response to histamine. Albuterol significantly reduced the bronchial response to PAF-acether. Pretreatment with aspirin (80 mg X kg -1 iv) did not prevent the bronchoconstriction caused by PAF-acether, and intravenous or intratracheal arachidonic acid caused no bronchial response. Thus the role of cyclooxygenase metabolites of arachidonic acid in PAF-acether-induced bronchoconstriction is unlikely. In conclusion, an acute bronchoconstriction probably not triggered by stimulation of irritant receptors of the airways and associated with aggregation of platelet takes place subsequent to intratracheal administration of PAF-acether. These data suggest that PAF-acether might play a role in the pathogenesis of human asthma.

A role for cyclooxygenase products in the formation of phosphatidic acid in stimulated human platelets. Differential mechanisms of action of thrombin and collagen.

Human platelets prelabeled with (32P)orthophosphate or [14C]arachidonic acid (AA) were stimulated with collagen or thrombin, and platelet activation (shape change, aggregation, and release of serotonin) was determined in parallel to the formation of 32P- or 14C-labeled phosphatidic acid (PA). The results show a close correlation between the degree of platelet activation and the amount of PA formed. Activation of platelets and formation of PA induced by collagen (2 to 20 micrograms/ml) was blocked by pretreatment of platelets with trifluoperazine, indomethacin, aspirin, or N-methylimidazole. This suggests that the formation of AA by phospholipase A2 and its subsequent metabolism by cyclooxygenase and thromboxane synthetase are required for the collagen-induced formation of PA. Endoperoxide analog U-44069 induces formation of PA in human platelets that have been pretreated with or without aspirin. The action of thrombin does not follow the same pattern of collagen. Low concentrations of thrombin (0.05 units/ml) induce only platelet shape change and a small stimulation of PA, changes which are only minimally inhibited by indomethacin. However, a small increase in the thrombin concentration (to 0.1 unit/ml) induces platelet aggregation, release of serotonin, and a sharp increase in PA accumulation which are effectively inhibited by indomethacin. Even higher thrombin concentrations (0.4 to 0.8 units/ml), however, result in a further stimulation of PA formation, platelet aggregation, and release of serotonin which are insensitive to inhibition by indomethacin. The data show that cyclooxygenase metabolites of AA, produced after platelet activation, may be differentially involved in the formation of PA in platelets stimulated with collagen or thrombin. Formation of PA following collagen or intermediate concentrations of thrombin (0.1 to 0.2 units/ml) is dependent on the cyclooxygenase pathway. However, formation of PA by very low or by high concentrations of thrombin is not mediated by cyclooxygenase metabolites of AA.

C3a-induced contraction of guinea pig lung parenchyma: Role of cyclooxygenase metabolites

The complement anaphylatoxin C3a from human or porcine serum contracts isolated peripheral airways from guinea pig in a manner which is independent of histamine release. In order to evaluate the role of arachidonic acid metabolites in the C3a response, dose-response curves for C3a-induced contractions of guinea pig lung strips were compared in the presence and absence of several inhibitors which block metabolism of arachidonic acid at relatively specific steps in the pathways. The inhibitor of leukotriene activity, FPL 55712 ant the lipoxygenase inhibitor, nordihydroguiretic acid (NDGA), had no significant effect on the tissue response to C3a alone or in combination with anthistamine. The cyclooxygenase inhibitors, indomethacin and aspirin, however, both resulted in significant inhibition, causing a shift in the C3a dose-response curve to higher concentrations. When the antihistamine, pyrilamine, was included with either indomethacin or aspirin, the C3a response was inhibited further, although pyrilamine alone had no effect. Thus, C3a-induced contractions of isolated lung parenchyma are mediated primarily by cyclooxygenase metabolites of arachidonic acid. This result is in contrast to the finding that C5a anaphylatoxin mediates lung tissue contraction by release of lipoxygenase metabolites of arachidonic acid.

Quantitative analysis of arachidonic acid metabolites in complex biological fluids using capillary gas chromatography/negative ion chemical ionisation mass spectrometry

Capillary column gas chromatography and negative ion chemical ionisation mass spectrometry (GC/NICIMS) was combined to develop an assay for the simultaneous measurement of seven cyclo-oxygenase metabolites of arachidonic acid (prostanoids). This assay has been used to analyse prostanoids in stimulated human platelet-rich plasma and guinea-pig lung perfusate.

Coronary vasoconstriction induced by leukotrienes in the anaesthetized dog

In the anaesthetized dog LTC 4, LTD 4 (0.3–10 μg, injected into the coronary artery) and the thromboxane-mimetic U46619 (5–10 μg) decreased coronary blood flow. LTE 4 (1–10 μg), however, did not affect coronary blood flow. The vasoconstrictor responses to LTC 4, LTD 4 or U46619 were not altered by the cyclo-oxygenase inhibitor indomethacin (5 mg/kg i.v.). LTC 4 and LTD 4 did not stimulate the release of any prostaglandin-like substance into the pericardial fluid. It is concluded that LTD 4 and LTD 4 are able to produce coronary vasoconstriction in vivo independent of the production of any cyclo-oxygenase metabolites of arachidonic acid.

Anaphylactic release of thromboxane A2, prostaglandin D2, and prostacyclin from human lung parenchyma.

Antigen challenge of passively sensitized chopped human lung resulted in the generation of several arachidonic acid cyclooxygenase metabolites (AACM): thromboxane A2 (TxA2) as measured by its stable metabolite TxB2, prostaglandin D2 (PgD2), prostacyclin (PgI2) as measured by its stable metabolite 6-keto-PgF1 alpha, prostaglandin F2 alpha (PgF2 alpha), and prostaglandin E (PgE). The kinetics of AACM release after antigen challenge paralleled histamine release. All AACM were released in an antigen dose-dependent manner and reached maximal release at antigen concentrations lower than those required for maximal histamine release. Quantitatively, of the AACM measured, PgD2 and PgI2 were found to predominate in anaphylactic reactions of human lung parenchyma. Generation of PgD2 and PgI2 were 3- to 7-fold greater than that of other AACM measured. Thromboxane B2 was generated in quantities comparable to PgE and PgF2 alpha. Studies were designed to test the hypothesis that lung smooth muscle contraction per se can account for the generated AACM that are released during anaphylaxis of the lung. The studies compared antigen-induced AACM generation with methacholine-induced (10(-4) M) AACM generation. The failure to confirm this hypothesis was especially evident for PgD2 where release was dependent on mast cell activation. Thromboxane A2, PgD2, and PgI2 have been reported to have potent effects on smooth muscle. Our data suggested that these AACM are generated in such sufficient quantities that they may function in important aspects of the modulation of hypersensitivity responses in human lungs.

Platelet-lung in vivo interactions: an artifact of a multi-purpose model?

The simultaneous evaluation of platelet behaviour in vivo and of the accompanying bronchoconstriction in the guinea pig is described. Arachidonic acid induces bronchoconstriction, accompanied by, but independent from, thrombocytopenia, whereas collagen induces bronchoconstriction also accompanied by, but dependent from, thrombocytopenia. In both cases bronchoconstriction is due to cyclo-oxygenase metabolites of arachidonic acid. Use of potential inhibitors of thromboxane synthetase failed to reveal which of prostaglandin endoperoxides or thromboxane A2 is responsible for aspirin-inhibitive bronchoconstriction and thrombocytopenia. In contrast to PGE1 prostacyclin failed to interfere with bronchoconstriction by serotonin or by arachidonic acid, even though thrombocytopenia by the latter was suppressed. Bronchoconstriction by collagen, in contrast, was inhibited by nanogram doses of prostacyclin, confirming platelet-dependency. The combined bronchoconstriction/thrombocytopenia test in guinea pigs can discriminate sites of action of anti-inflammatory drugs, of agents which block specific platelet and/or bronchial receptors, which stimulate the cyclic AMP system, or generically which interfere with the mechanisms of bronchoconstriction and of thrombocytopenia.