Myotropic activity of leukotriene B4 on lung parenchyma strips is not necessarily attributable to thromboxane A2 release

Leukotriene B4 contracts guinea pig lung parenchymal strips by an indirect mechanism dependent upon formation of myotropic cyclooxygenase metabolites. In contrast to the prevailing notion, our data indicate that thromboxane A2 is not necessarily the sole or essential mediator involved. Several points support this conclusion. First, the quantitative and temporal aspects of thromboxane B2 release and the myotropic response to leukotriene B4 were weakly correlated (r = 0.73). Second, the dose-response curve for thromboxane A2, based on the amount of thromboxane B2 generated by lung strips contracted with leukotriene B4, was inconsistent with dose-response curves for lung strips contracted with a stable thromboxane A2 mimetic, U-46619 or with synthetic thromboxane A2 itself. Third, thromboxane synthetase inhibitors, typified by OKY-1581 and UK-37248, did not inhibit the myotropic activity of leukotriene B4 under conditions in which thromboxane B2 formation was reduced by 80 to 90%. A thromboxane A2 receptor antagonist, BM 13.177, did not inhibit the myotropic activity of leukotriene B4 under conditions in which it antagonized the effects of U-46619. Cyclooxygenase metabolites other than thromboxane A2 must contribute to the mechanism of action of leukotriene B4 or leukotriene B4 effects may be mediated directly on certain cells or receptors.     

Interaction between leukotriene D4 and adenosine or iloprost in the isolated working guinea-pig heart: prevention of the leukotriene D4 effect

The interaction between leukotriene D4 and adenosine or the prostacyclin analogue iloprost was studied in isolated guinea-pig hearts. Adenosine (1 X 10(-6) M) or iloprost (5 X 10(-8) M) abolished or greatly attenuated the vasoconstrictive effect of leukotriene D4 over a wide dose range of leukotriene D4 (0.01-1000 ng), and myocardial ischemia as a consequence of coronary insufficiency completely disappeared. Comparison of myocardial levels of reduced pyridine nucleotide fluorescence in hearts treated with leukotriene D4 and in hearts subjected to varying degrees of high-flow hypoxia, or the calcium agonist BAY-K 8644, revealed low levels of reduced pyridine nucleotides in the leukotriene D4-treated hearts, suggesting that leukotriene D4 directly suppressed myocardial contractility. These findings were supported by full restoration of cardiac work by the receptor antagonist FPL 55712 following leukotriene D4 treatment. It is concluded that adenosine and iloprost are potent inhibitors of leukotriene D4-induced reduction in coronary flow in guinea-pig hearts, and that myocardial ischaemia and suppressed cardiac work are prevented during leukotriene D4 study in adenosine or iloprost perfused hearts. Low levels of myocardial-reduced pyridine nucleotides during leukotriene D4 treatment and restoration of cardiac work by FPL 55712 indicate that leukotriene D4 may also have a direct suppressive effect on myocardial contractility.     

LY171883, 1-less than 2-hydroxy-3-propyl-4-less than 4-(1H-tetrazol-5-yl) butoxy greater than phenyl greater than ethanone, an orally active leukotriene D4 antagonist

LY171883, 1-less than2-hydroxy-3-propyl-4-less than 4-(h-tetrazol-5-yl)butoxy greater than phenyl greater than ethanone, proved to be a potent antagonist of leukotriene (LT) D4 in guinea-pig ileum, trachea and lung parenchyma. The compound had little or no effect on contractions of isolated tissues to LTB4, prostaglandin F2 alpha, serotonin, histamine, bradykinin or carbamycholine. Responses of trachea to U46619, a thromboxane A2 mimetic, were antagonized by LY171883, but the doses required were approximately 10-fold higher than those necessary to produce the same degree of antagonism against LTD4. U46619 produced weak ileal contractions that were not blocked by LY171883. LY171883 antagonized both LTD4- and antigen-induced increases in total pulmonary resistance in anesthetized guinea pigs. LTD4 given intradermally to guinea pigs caused vascular leakage which was suppressed by prior administration of LY171883. LTC4-induced contractions of isolated ilea were only minimally antagonized by LY171883 whereas this agent reduced LTC4-evoked increases in total pulmonary resistance. Trachea contracted by LTD4 were relaxed by LY171883. Likewise, trachea contracted by either histamine or carbamylcholine were relaxed by LY171883 suggesting that this compound has airway smooth muscle relaxing properties. In vivo experiments supported these observations. In concert with these findings, biochemical studies showed LY171883 to be a potent inhibitor of phosphodiesterase obtained from human polymorphonuclear leukocytes and various guinea-pig tissues. This pharmacologic analysis indicates that LY171883, or a congener, may be of therapeutic value in asthma and in disease states characterized by an overproduction of LTD4.     

Mechanism of action of glucocorticosteroids. Inhibition of T cell proliferation and interleukin 2 production by hydrocortisone is reversed by leukotriene B4.

The mechanism whereby glucocorticosteroids are immunosuppressive is unknown. One potential mechanism of action of these compounds is inhibition of arachidonic acid metabolism. We found that the inhibition of lymphocyte proliferation by hydrocortisone or dexamethasone was mimicked by nonspecific lipoxygenase inhibitors and also by a specific 5-lipoxygenase inhibitor, but not by a specific cyclooxygenase inhibitor. Mitogen-stimulated cultures of T cells produce approximately 5 X 10(-9) M leukotriene B4 (LTB4) in 24 h. This production of LTB4 is completely inhibited by concentrations of hydrocortisone or lipoxygenase inhibitors that inhibit mitogen-induced [3H]thymidine incorporation. The inhibition of lymphocyte proliferation by either hydrocortisone or by the 5-lipoxygenase inhibitor was totally reversed by LTB4 but not by leukotriene C4 or leukotriene D4. LTB4 had no effect on the inhibition of lymphocyte proliferation by noncorticosteroids such as prostaglandin E2, histamine, or gamma-interferon. The inhibition of interleukin 2 (IL-2) production by hydrocortisone or dexamethasone was also completely reversed by exogenous LTB4. LTB4 alone did not cause IL-2 production or cell proliferation when added to resting lymphocytes. Thus, endogenous LTB4 production appears to be necessary but not sufficient for phytohemagglutinin-induced IL-2 production and lymphocyte proliferation. Glucocorticosteroids inhibit IL-2 production and lymphocyte proliferation by inhibiting endogenous LTB4 production.     

Acetyl glyceryl ether phosphorylcholine stimulates leukotriene B4 synthesis in human polymorphonuclear leukocytes.

Acetyl glyceryl ether phosphorylcholine (AGEPC) and leukotriene B4 (LTB4) induce concentration-dependent neutrophil aggregation. On a molar basis, LTB4 is approximately 10 to 100 times more potent than AGEPC. AGEPC-induced aggregation is attenuated by two inhibitors of arachidonate lipoxygenation, eicosatetraynoic acid and nordihydroguaiaretic acid, and to a lesser extent by the cyclooxygenase inhibitor, indomethacin. LTB4-induced aggregation is not readily reduced by the above inhibitors of arachidonic acid metabolism. Reverse phase high performance liquid chromatography, coupled with selective ion gas chromatography/mass spectrometry, shows that AGEPC stimulates neutrophils to synthesize sufficient LTB4 to account for the AGEPC response. In addition, the rate of LTB4 biosynthesis in response to AGEPC correlates well with the rate of AGEPC- and/or LTB4-induced neutrophils aggregation, and desensitization experiments indicate that AGEPC and LTB4 cross-desensitize. These data suggest that AGEPC-induced neutrophil aggregation may be mediated by LTB4.     

Regional and time-dependent effects of inflammatory mediators on airway microvascular permeability in the guinea pig

1. Airway oedema resulting from increased microvascular permeability is a characteristic pathological finding of asthma. The regional effects of putative mediators involved in asthma on airway microvascular permeability have been studied. 2. The effects of histamine, leukotriene (LT) D4 and platelet-activating factor (PAF) on microvascular permeability in the nasal mucosa, larynx, trachea, main bronchi and intrapulmonary airways of the guinea pig were assessed by measuring the extravasation of intravenously administered Evans Blue dye. 3. PAF and LTD4 caused increased microvascular leakage throughout the respiratory tract, although their effects were maximal in different regions. Histamine had no significant effect on intrapulmonary airways. PAF was more potent than LTD4 and histamine at all airway levels. For example, in the trachea the doses required to cause leakage of 50% of maximal (ED50) were 10.4 nmol/kg, 138 nmol/kg and 11.2 mumol/kg, respectively, for PAF, LTD4 and histamine. 4. The effect of the three mediators was maximal 5 min after intravenous administration. Histamine, but neither LTD4 nor PAF, still caused significant leakage 30 min after administration. 5. The increased microvascular leakage induced by the mediators was inhibited by their respective specific receptor antagonists, suggesting that the effect was mediated via specific receptors. 6. Histamine, LTD4 and PAF have varying potencies in increasing microvascular permeability in the guinea-pig respiratory tract, exert their maximal effect in different regions and have varying durations of action.     

Multiple actions of the leukotriene B4 receptor antagonist SC-41930.

7-[3-(4-acetyl-3-methoxy-2-propylphenoxy)-propoxy]-3,4-dihydro-8- propyl-2H-1-benzopyran-2-carboxylic acid (SC-41930), a leukotriene B4 (LTB4) receptor antagonist with anti-inflammatory activity in animal models of colitis, was evaluated for effects on superoxide, LTB4 and prostaglandin E2 production. SC-41930 inhibited human neutrophil (PMN) superoxide generation maximally stimulated by f-Met-Leu-Phe (IC50 4 microM) and C5a (IC50 approximately 12 microM). Moreover, postreceptor stimulation of superoxide production by NaF (a G protein activator), but not by phorbol myristate acetate, was significantly inhibited by SC-41930, indicating that SC-41930 may act via attenuation of a G protein-mediated signal transduction. SC-41930 also inhibited A23187-stimulated LTB4 production (IC50 5.3 microM) in human PMN as well as LTB4 (IC50 2.1 microM) and prostaglandin E2 (IC50 2.9 microM) production in HL-60 cells. When coinjected intradermally (400 micrograms/site), SC-41930 inhibited A23187-stimulated increases in LTB4 levels in guinea pig skin. SC-41930 inhibited human synovial phospholipase A2 (IC50 72 microM), A23187-stimulated 5-hydroxy-eicosatetranoic acid production in human PMN (IC50 8.5 microM), and rat peritoneal leukotriene A4 hydrolase (IC50 20 microM), but not ram seminal vesical cyclooxygenase. The results suggest that the anti-inflammatory activity of SC-41930 could be attributed to postreceptor inhibition of inflammatory mediator production by PMN and other cells in addition to antagonism of PMN LTB4 receptors.     

Lipoxin A4 and lipoxin B4 inhibit chemotactic responses of human neutrophils stimulated by leukotriene B4 and N-formyl-L-methionyl-L-leucyl-L-phenylalanine

1. Lipoxin A4 (LXA4) and lipoxin B4 (LXB4) have been evaluated for their capacities to modulate neutrophil (PMN) migration and endothelial cell adherence using compounds prepared by total chemical synthesis. 2. Increased PMN migration was seen with concentrations of LXA4 from 10(-9) mol/l to 10(-7) mol/l. LXA4 was 100-fold less potent than leukotriene B4 (LTB4) and it elicited only one-half of the maximal response of LTB4. 3. The (5S,6S,15S)-isomer of LXA4 induced only a weak migratory response and LXB4 was inactive, suggesting that the activity of LXA4 was stereospecific. 4. Modified chequerboard analysis indicated that LXA4 was a chemokinetic agent. 5. Preincubation of PMN with increasing concentrations of LXA4 induced a very similar dose- and time-dependent inhibition of the subsequent response to 10(-7) mol/l LTB4 or 10(-7) mol/l N-formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP). The inhibition was observed at 10(-10) mol/l LXA4; the concentration which produced 50% inhibition was 10(-8) mol/l and 100% inhibition of PMN locomotion occurred at 10(-6) mol/l LXA4. 6. The (5S,6S,15S)-isomers of LXA4 and LXB4 were 5- and 100-fold less potent than LXA4, respectively, in suppressing LTB4- or FMLP-induced PMN migration. 7. Preincubation of PMN with LXA4 led to a suppression of calcium mobilization, as assessed by Quin2-AM fluorescence, when the cells were subsequently stimulated under optimal conditions by LTB4 or FMLP. 8. These results suggest that the inhibitory activity of lipoxins may be related to the capacity of these molecules to regulate calcium ion mobilization.     

An examination of the influence of the epithelium on contractile responses to peptidoleukotrienes and blockade by ICI 204,219 in isolated guinea pig trachea and human intralobar airways

The influence of the epithelium on antagonism by ICI 204,219 of contractile responses to peptide leukotriene (LT) agonists was examined in guinea pig tracheal and human bronchial rings. The -log molar KB values for ICI 204,219 were found to be independent of the epithelium in both tissues. Even though uninfluenced by the epithelium, the -log molar KB values for ICI 204,219 were about 10-fold smaller in human airways than in guinea pig trachea. Removal of the epithelium from guinea pig trachea resulted in small leftward shifts of the concentration-response curves to LTC4 and LTD4 and rightward shifts of the concentration-response curves to LTE4 when examined in the presence of indomethacin. The potentiation of LTC4 and LTD4 by epithelium removal was not seen in the presence of inhibitors of the transformation of LTC4 to LTD4 and LTD4 to LTE4. The influence of the epithelium on responses to LTE4 remained in the presence of these metabolic inhibitors. The lipoxygenase inhibitors nordihydroguaiaretic acid, B755C, Rev 5901 and AA861 antagonized responses to LTE4 in the presence, but not in the absence of epithelium. In human airways, epithelium removal resulted in a small leftward shift of the concentration-response curve to LTD4 whereas responses to LTC4 and LTE4 were unaltered. This effect was not observed in the presence of indomethacin, relating it to reduced release of cyclooxygenase products. These data suggest that contractile responses of guinea pig trachea to LTE4 are modulated by LTE4-induced release of 5-lipoxygenase product(s) only when the epithelium is present.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pharmacologic analysis of two novel inhibitors of leukotriene (slow reacting substance) release

LY83583 , a quinolinedione , and LY151364 , a quinoxalinedione , were developed as inhibitors of leukotriene (slow reacting substance of anaphylaxis) release. They preferentially inhibited the release of leukotrienes over histamine from fragmented guinea-pig lung and rat peritoneal cells in vitro, regardless of whether the mediators were released immunologically by antigen or chemically by the divalent cationic ionophore, A23187. Similar results were obtained with rat peritoneal cells in vivo. In that system, comparison of LY83583 with disodium cromoglycate showed the former to preferentially inhibit release of leukotrienes, whereas the latter favored inhibition of histamine release. LY83583 did not significantly decrease antigen-induced bronchospasm in guinea pigs after i.v. administration of doses that approached toxic levels. In addition, LY83583 did not antagonize contractions to carbachol or histamine on guinea-pig trachea, prostaglandin F2 alpha-elicited contraction on guinea-pig ileum or contractions produced by serotonin on guinea-pig aorta. This agent, at 1 X 10(-5) M, reduced the maximal responses to bradykinin on ileum and caused a rightward displacement with a reduction in the maximal response to norepinephrine on guinea-pig aorta. In summary, LY83583 and LY151364 have interesting pharmacologic profiles which make them useful as tools in understanding the role of the leukotrienes in isolated tissue systems.     

Increased excretion of leukotriene E4 during aspirin-induced asthma.

The etiology of aspirin-sensitive asthma is unknown, but a plausible hypothesis is that the inhibitory effect of aspirin on the cyclooxygenase enzyme increases formation of bronchoconstrictor leukotrienes via "shunting" of unmetabolized arachidonic acid into metabolism by the 5-lipoxygenase enzyme. The severity and rapidity of bronchospasm that is induced by cyclooxygenase-inhibiting drugs in aspirin-sensitive asthmatics is directly related to the dose and to the potency of the drug to inhibit the cyclooxygenase enzyme. Since increased leukotriene synthesis has recently been shown to occur during allergen-induced asthma, we have examined whether altered leukotriene synthesis correlates with the degree of either cyclooxygenase inhibition or bronchospasm during asthma that is induced by doses of aspirin that range from 30 to 365 mg in individual patients. Excretion of leukotriene E4 was increased by a mean of 361% +/- 76% (p less than 0.05) during aspirin-induced asthma episodes, but the degree of increase for individual patients did not correlate with the degree of bronchospasm or inhibition of platelet thromboxane B2 formation. Thus although the endogenous synthesis of potent bronchoconstrictor leukotrienes increases during aspirin-induced bronchospasm, it appears unlikely that a direct "shunting" of unmetabolized arachidonate into leukotriene synthesis represents the mechanism of aspirin-induced asthma.     

Differential effects of methacholine and leukotriene D4 on cyclic nucleotide content and isoproterenol-induced relaxation in the opossum trachea

The effects of leukotriene D4 and methacholine on cyclic nucleotide content and isoproterenol-induced relaxation were examined in the isolated opossum trachea. Although leukotriene D4 (-log EC50 = 6.70) was a more potent contractile agent than methacholine (-log EC50 = 5.78), the maximal response to leukotriene D4 was only 65% of the maximum response to methacholine. Contraction of tracheal strips with leukotriene D4 was accompanied by a 3-fold increase in cyclic GMP accumulation. Methacholine-induced contraction was not associated with an increase in cyclic GMP. Neither agent altered basal cyclic AMP content. Additional experiments were carried out to examine functional inhibitory interactions between bronchoconstricting and bronchodilating pathways. In these studies, cumulative isoproterenol concentration-response curves were constructed in tracheal strips contracted with three different concentrations of methacholine and in tissues contracted with three corresponding equieffective concentrations of leukotriene D4. Although the relaxant response to isoproterenol decreased as tissues were contracted with higher concentrations of either agent, the inhibitory effect of methacholine on isoproterenol-induced relaxation was much greater than the inhibitory effect of leukotriene D4. Previous studies from our laboratory suggested that a potential explanation for the greater inhibitory effect of methacholine on the mechanical response to isoproterenol was that methacholine may inhibit isoproterenol-stimulated cyclic AMP accumulation whereas leukotriene D4 may not. However, neither methacholine nor leukotriene D4 inhibited isoproterenol-stimulated cyclic AMP accumulation in the opossum trachea. The results of this study indicate that the sensitivity of airway smooth muscle to beta adrenoceptor agonists is influenced both by the initial contractile state of the tissue and by the type of agent used to induce tone.     

Responses to leukotriene C4 in the perfused rat lung

The isolated rat lung was used to study both the effect of leukotriene C4 on pulmonary perfusion pressure and the synthesis and release of cyclooxygenase products in the pulmonary circulation. A cell-free perfusate was passed only once through the pulmonary circulation or was recirculated. During single transit, leukotriene C4 produced dose-dependent increases in pulmonary perfusion pressure that were abolished by FPL-55712, a leukotriene receptor antagonist, but were not altered significantly by indomethacin. The duration of the pulmonary pressor response to leukotriene C4 was markedly prolonged during recirculation compared to single transit. Leukotriene C4 also induced dose-dependent increases in effluent levels of 6-keto-prostaglandin F1 alpha and thromboxane B2 that were attenuated by indomethacin or FPL-55712 pretreatment. We conclude that leukotriene C4 directly constricts the pulmonary vasculature independent of cyclooxygenase products, is not rapidly degraded by the pulmonary circulation and stimulates the release of cyclooxygenase products in the pulmonary circulation that can be attenuated by pretreatment with indomethacin or FPL-55712.     

Pharmacologic profile of SK&F 104353: a novel, potent and selective peptidoleukotriene receptor antagonist in guinea pig and human airways

In this report, we describe the in vitro and in vivo pharmacologic profile of 2(S)-hydroxy-3(R)-[(2-carboxyethyl)thio]-3-[2-(8-phenyloctyl)pheny l]- propanoic acid (SK&F 104353) in guinea pig and human airways. In the isolated guinea pig trachea, SK&F 104353 was a potent, competitive antagonist of leukotriene (LT) D4-induced contractions (pA2 = 8.6). In contrast, SK&F 104353 produced little effect on LTC4 concentration-response curves under conditions where the bioconversion of LTC4 to LTD4 was inhibited. LTE4-induced contractions in guinea pig trachea were sensitive to inhibition by SK&F 104353 (pKB greater than 8.9). SK&F 104353 (10 microM) had no intrinsic contractile activity and was without effect on contractions produced by KCl, histamine, prostaglandin D2, platelet-activating factor or U-44069 in guinea pig trachea. Furthermore, unlike other purported LT antagonists, LT 171883 and FPL 55712, SK&F 104353 (30 microM) did not inhibit cyclic nucleotide phosphodiesterase activity measured in homogenates from canine tracheal smooth muscle. In the isolated human bronchus, SK&F 104353 produced concentration-dependent rightward shifts in LTD4 concentration-response curves and, unlike in guinea pig trachea, was an effective antagonist of LTC4-induced contractions with a pKB of 8.0 to 8.4. This provides further evidence that, in contrast to guinea pig airways, responses produced by LTC4 and LTD4 in human bronchus appear to be mediated via the same LT receptor population. SK&F 104353 was also an effective antagonist of LTE4-induced responses in human bronchus (pKB greater than 8.2).(ABSTRACT TRUNCATED AT 250 WORDS)     

Chemotactic peptide stimulation of leukotrienes from healthy and inflamed rabbit colons

Prostaglandins, thromboxanes and leukotrienes are increased in human and experimental colitis. To evaluate the biosynthesis of these eicosanoids, colon inflammation was induced in rabbits by formalin enema followed by i.v. immune complexes, and the distal colon was perfused ex vivo. Bradykinin increased synthesis of prostaglandin E2 and thromboxane B2 more from colitis than from control colons (both P less than .001) but had no effect on leukotriene synthesis. The inflammatory cell agonist N-formylmethionyl-leucyl-phenylalanine (30 ng) also induced greater synthesis of prostaglandin E2 (70 +/- 13 vs. 14 +/- 6) and thromboxane B2 (84 +/- 22 vs. 20 +/- 11) from colitis than from control colons (P less than .01), but leukotriene B4 (416 +/- 68 vs. 438 +/- 128 ng/5 min) and leukotriene C4 (171 +/- 50 vs. 203 +/- 25 ng/5 min) synthesis were greatly augmented in both colitis and control colons. In vitro incubations demonstrated similar dose-dependent stimulation of leukotriene B4 by N-formylmethionyl-leucyl-phenylalanine in both colitis and control colons. These studies demonstrate that healthy colon tissue as well as colitis tissue can produce proinflammatory leukotrienes in response to bacterial peptides. Leukotriene production may contribute to the induction or mediation of colon inflammation.     

Novel structural determinants of the human neutrophil chemotactic activity of leukotriene B

A specific 5(S),12(R)-dihydroxy-eicosa-6,8,10(trans/trans/cis), 14(cis)-tetraenoic acid, designated leukotriene B, is generated by the lipoxygenation and subsequent enzymatic hydration of arachidonic acid in a variety of leukocytes. Leukotriene B elicits a maximal human neutrophil chemotactic response in vitro which is similar in magnitude to those evoked by the chemotactic fragment of the fifth component of complement, C5a, synthetic formyl-methionyl peptides, and 5-hydroxy-eicosatetraenoic acid (5-HETE). The neutrophil chemotactic potency of purified leukotriene B, assessed by the 50% effective concentration of 6 x 10(-9) M, is equivalent to that of C5a, but is up to 100-fold greater than that of 5-HETE and of other natural di-HETE isomers. 5(S),12(R)-di-hydroxy-eicosa-6,8,10(all-trans),14(cis)-tetraenoic acid, which differs from leukotriene B only in having a trans-double bond in place of a cis-double bond in the triene portion of the molecule, and acetyl-leukotriene B are significantly less potent neutrophil chemotactic factors than leukotriene B, which indicates that both the conjugated double bonds and the free hydroxyl-group(s) are functionally critical determinants. The capacity of acetyl-leukotriene B to inhibit competitively and selectively the human neutrophil chemotactic response to equimolar concentrations of leukotriene B suggests the existence of a specific subset of receptors for this potent lipid mediator.     

Leukotriene B4 stimulates polymorphonuclear leukocyte adhesion to cultured vascular endothelial cells.

Adhesion of polymorphonuclear leukocytes (PMN) to the endothelial lining of blood vessels is an essential component of the inflammatory response. We have examined the effects of various lipoxygenase metabolites of arachidonic acid on PMN adhesion to cultured vascular endothelial cells, using a quantitative monolayer adhesion assay. Our results indicated that leukotriene B4 (LTB4) could effectively stimulate PMN adhesion to endothelial cell surfaces, in contrast to the sulfidopeptide leukotrienes C4, D4, and E4, and the monohydroxyacid lipoxygenase products of leukocytes and platelets, 5S-hydroxy-6-trans-8,11,14-cis-eicosatetraenoic acid and 12S-hydroxy-5,8-cis,10-trans,14-cis-eicosatetraenoic acid, respectively. LTB4-stimulation of PMN-endothelial adhesion did not appear to be dependent upon the generation of cyclooxygenase metabolites, nor was it inhibited by exogenous prostacyclin. Enhanced PMN adhesion was observed with endothelial cells that were cultured from different types of large vessels (arteries and veins) in several species. These findings suggest an important pathophysiologic role for LTB4 in regulating leukocyte-vessel wall interactions.     

Influence of epithelium on guinea pig airway responses to tachykinins: role of endopeptidase and cyclooxygenase

We have studied the effect of epithelium removal on the contractile responses to exogenous tachykinins and to endogenous tachykinins released by capsaicin in guinea pig trachea. We also studied the effects of inhibition of endopeptidase (by phosphoramidon, 10 microM, and thiorphan, 100 microM), and of inhibition of cyclooxygenase (by indomethacin, 5 microM) on these responses. The order of potency of exogenous tachykinins was neurokinin A (NKA) greater than neurokinin B (NKB) greater than substance P (SP). Epithelium removal enhanced the sensitivity and magnitude of the contractile response to SP, and to a lesser extent NKA and NKB. Capsaicin induced only a weak contractile response in guinea pig trachea. Phosphoramidon and thiorphan increased the sensitivity to SP, but had no effect on acetylcholine responses. The leftwardshift due to epithelium removal was reduced, but not abolished, by phosphoramidon and thiorphan. NKA- and NKB-induced contractions were also enhanced significantly by phosphoramidon. The effect of epithelium removal was abolished for NKA, but not for NKB. Phosphoramidon also increased significantly the contraction to capsaicin in the presence of epithelium, without altering the response obtained in the absence of epithelium. Indomethacin potentiated the sensitivity and maximal contractile response to all the tachykinins with the greatest effect on SP responses, and to capsaicin. The combination of indomethacin with phosphoramidon or thiorphan abolished the effect of epithelium removal for all the tachykinins. We conclude that the effects of exogenous and endogenous tachykinins are enhanced by removal of epithelium and by inhibition of metalloendopeptidase and cyclooxygenase, suggesting that tachykinins may be degraded by epithelial enzymes, and may release relaxant prostanoids in airways.(ABSTRACT TRUNCATED AT 250 WORDS)     

Bronchial effects of leukotriene D4 inhalation in normal human lung

The aim of the study was to investigate whether inhaled leukotriene (LT) D4 could mimic the characteristics of asthmatic patients after allergen-induced attack, i.e. a prolonged subclinical bronchial obstruction, an increased reactivity of the airways and a late reaction. The effects of LTD4 were compared with those of histamine and the mechanism of action sought. Thirty-three non-atopic individuals participated in the study. The two drugs were inhaled as an aerosol of small particles causing a relative peripheral deposition pattern in order to mimic the preferential involvement of peripheral airways in asthmatic patients out of attack. LTD4 caused a dose-dependent obstruction of the airways as measured by partial flow-volume curves and volume of trapped gas, yet only minor changes in forced expiratory volume in 1 s (FEV1) and peak expiratory flow rate. LTD4 was 1900-7000 times more potent than histamine. LTD4 inhalations were almost symptomless as opposed to the irritative and dyspnoeic symptoms seen after inhalation of histamine. The time duration for the induced change in partial flow-volume curves was the same for the two drugs. Approximately 30 min elapsed until the bronchial obstruction had decreased by 50% of the maximum effect, and no delayed reaction was observed within 10 h. The reactivity of the airways did not change during 10 h after inhalation of LTD4 as tested by repeated exercise challenges. Pretreatment with ipratropium bromide prevented the effect of LTD4 on FEV1, yet not on partial flow-volume curves. Pretreatment with either cimetidine and mepyramine or with indomethacin, did not affect the bronchial obstruction after LTD4.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of removal of epithelium on antigen-induced smooth muscle contraction and mediator release from guinea pig isolated trachea

We examined the effect of removal of the epithelium on antigen-induced smooth muscle contraction and the release of mediators of inflammation from superfused, sensitized guinea-pig tracheal spirals in vitro. The epithelium was stripped from one-half of each trachea by mechanical means, and immunologic responses were evaluated by paired analysis. Removing the epithelium potentiated antigen-induced contraction, as reflected by a 5-fold leftward shift in the antigen dose-response curve, but the maximum response to antigen was not altered. This potentiation was not inhibited by pretreating the tissues with indomethacin (5 X 10(-6) M). At maximum concentrations of antigen removing the epithelium had no effect on the magnitude or kinetics of release of immunoreactive sulfidopeptide leukotrienes, prostaglandin (PG) D2, PGF2 alpha or thromboxane B2. Removing the epithelium did, however, significantly decrease the release of PGE and 6-keto-PGF1 alpha, a prostacyclin metabolite. Antigen-induced histamine release was enhanced by removing the epithelium; this effect varied inversely with antigen concentration. Selectively exposing either the luminal or serosal surface of an intact, superfused trachea to antigen resulted in the release of less than 5% of the total tissue histamine. Removing the epithelium from the intact trachea increased histamine release to approximately 25% following luminal but not serosal exposure to antigen. These studies demonstrate that the tracheal epithelium can act to inhibit antigen-induced airway contraction in vitro. This may in part reflect the role of the intact epithelium as a diffusion barrier which can limit the rate of influx of antigen molecules and thereby influence tissue mast cell activation.