The effect of leukotriene C4 on mucin release into the cat trachea in vivo and in vitro

Airway Gland Structure and Function

Submucosal glands contribute to airway surface liquid (ASL), a film that protects all airway surfaces. Glandular mucus comprises electrolytes, water, the gel-forming mucin MUC5B, and hundreds of different proteins with diverse protective functions. Gland volume per unit area of mucosal surface correlates positively with impaction rate of inhaled particles. In human main bronchi, the volume of the glands is ∼ 50 times that of surface goblet cells, but the glands diminish in size and frequency distally. ASL and its trapped particles are removed from the airways by mucociliary transport. Airway glands have a tubuloacinar structure, with a single terminal duct, a nonciliated collecting duct, then branching secretory tubules lined with mucous cells and ending in serous acini. They allow for a massive increase in numbers of mucus-producing cells without replacing surface ciliated cells. Active secretion of Cl(-) and HCO3 (-) by serous cells produces most of the fluid of gland secretions. Glands are densely innervated by tonically active, mutually excitatory airway intrinsic neurons. Most gland mucus is secreted constitutively in vivo, with large, transient increases produced by emergency reflex drive from the vagus. Elevations of [cAMP]i and [Ca(2+)]i coordinate electrolyte and macromolecular secretion and probably occur together for baseline activity in vivo, with cholinergic elevation of [Ca(2+)]i being mainly responsive for transient increases in secretion. Altered submucosal gland function contributes to the pathology of all obstructive diseases, but is an early stage of pathogenesis only in cystic fibrosis.

Evolutionary aspects of lipoxygenases and genetic diversity of human leukotriene signaling

Leukotrienes are pro-inflammatory lipid mediators, which are biosynthesized via the lipoxygenase pathway of the arachidonic acid cascade. Lipoxygenases form a family of lipid peroxidizing enzymes and human lipoxygenase isoforms have been implicated in the pathogenesis of inflammatory, hyperproliferative (cancer) and neurodegenerative diseases. Lipoxygenases are not restricted to humans but also occur in a large number of pro- and eucaryotic organisms. Lipoxygenase-like sequences have been identified in the three domains of life (bacteria, archaea, eucarya) but because of lacking functional data the occurrence of catalytically active lipoxygenases in archaea still remains an open question. Although the physiological and/or pathophysiological functions of various lipoxygenase isoforms have been studied throughout the last three decades there is no unifying concept for the biological importance of these enzymes. In this review we are summarizing the current knowledge on the distribution of lipoxygenases in living single and multicellular organisms with particular emphasis to higher vertebrates and will also focus on the genetic diversity of enzymes and receptors involved in human leukotriene signaling.

Mammalian lipoxygenases and their biological relevance

Lipoxygenases (LOXs) form a heterogeneous class of lipid peroxidizing enzymes, which have been implicated not only in cell proliferation and differentiation but also in the pathogenesis of various diseases with major public health relevance. As other fatty acid dioxygenases LOXs oxidize polyunsaturated fatty acids to their corresponding hydroperoxy derivatives, which are further transformed to bioactive lipid mediators (eicosanoids and related substances). On the other hand, lipoxygenases are key players in the regulation of the cellular redox homeostasis, which is an important element in gene expression regulation. Although the first mammalian lipoxygenases were discovered 40 years ago and although the enzymes have been well characterized with respect to their structural and functional properties the biological roles of the different lipoxygenase isoforms are not completely understood. This review is aimed at summarizing the current knowledge on the physiological roles of different mammalian LOX-isoforms and their patho-physiological function in inflammatory, metabolic, hyperproliferative, neurodegenerative and infectious disorders. This article is part of a Special Issue entitled "Oxygenated metabolism of PUFA: analysis and biological relevance".

Proteinases release mucin from airways goblet cells

The mucin-release effect of proteinases on airways epithelium was assessed in vitro. Using explants of rabbit tracheal mucosa-submucosa we determined that elastase and alkaline proteinase from Pseudomonas aeruginosa, pancreatic trypsin and elastase and the microbial proteinases subtilisin, thermolysin and pronase, all stimulate mucin release from goblet cells. On the other hand Streptomyces caespitosus proteinase pancreatic chymotrypsin and collagenase fail to trigger mucin release. Bovine trachea and human nasal polyp epithelium also release mucins in response to proteinases. Mucin release activity is dependent on proteolytic activity of enzymes which have a fairly broad, but generally similar, substrate specificity. The cellular mechanism of action is not known. We propose that mucin secretion in response to proteinases represents a useful defence mechanism but also forms the basis for hypersecretory states and airways obstruction in chronic endobronchial inflammatory states.

Treatment of asthma with antileukotrienes: first line or last resort therapy?

Twenty five years after the structure elucidation of slow reacting substance of anaphylaxis, antileukotrienes are established as a new therapeutic modality in asthma. The chapter reviews the biochemistry and pharmacology of leukotrienes and antileukotrienes with particular focus on the different usage of antileukotrienes for treatment of asthma and rhinitis in Europe and the US. Further research needs and new areas for leukotriene involvement in respiratory diseases are also discussed.

The role of leukotrienes in asthma

Leukotrienes (LT), both the cysteinyl LTs, LTC(4), LTD(4) and LTE(4), as well as LTB(4) have been implicated in the clinical course, physiologic changes, and pathogenesis of asthma. The cysteinyl LTs are potent bronchoconstrictors, which have additional effects on blood vessels, mucociliary clearance and eosinophilic inflammation. In addition, the cysteinyl LTs are formed from cells commonly associated with asthma, including eosinophils and mast cells. LTB(4), whose role is less well defined in asthma, is a potent chemoattractant (and cell activator) for both neutrophils and eosinophils. In the last 5 years, drugs have been developed which block the actions or formation of these mediators. Clinical and physiologic studies have demonstrated that they are modest short-acting bronchodilators, with sustained improvement in FEV(1) occurring in double-blind, placebo-controlled clinical trials for up to 6 months. These drugs have demonstrated efficacy in preventing bronchoconstriction caused by LTs, allergen, exercise and other agents. Additionally, there are multiple published studies which have demonstrated improvement in asthma symptoms, beta agonist use and, importantly, exacerbations of asthma in both adults and children. Comparison studies with inhaled corticosteroids (ICS) suggest that ICS are superior to leukotriene modifying drugs in moderate persistent asthma. However, several published studies now suggest that leukotriene modifying drugs are effective when added to ongoing therapy with ICS, either to improve current symptoms or to decrease the dose of ICS required to maintain control. While an anti-inflammatory effect is suggested, longer-term, earlier intervention, studies are needed to determine whether these compounds will have any effect on the natural history of the disease.

Leukotrienes as mediators of asthma

This review describes the aspects of leukotriene (LT) pharmacology and biology that are relevant to their important role in asthma. The biosynthesis and metabolism, including transcellular metabolism, of LTB4 and the cysteinyl-LTs (i.e. LTC4, LTD4 and LTE4) are described, and their transport is briefly outlined. The existence, distribution and pharmacological characterization of the receptors (BLT, CysLT1, CysLT2), as well as the transduction mechanisms triggered, are discussed in detail. We also describe their effects on airway smooth muscle tone, hyperresponsiveness and proliferation, on vascular tone and permeability, on mucus secretion, on neural fibers and inflammatory cell functions. Finally, the evidence supporting their role as asthma mediators is reviewed, including the effects of anti LT drugs (both biosynthesis inhibitors and receptor antagonists) in experimental and clinical asthma.

Biochemistry and physiology of the leukotrienes

Based on the studies that have used human subjects and materials, and a much larger body of data from animal and in vitro experiments, one can conclude that the LTs are potent bronchoconstrictors in normal and asthmatic subjects. A major part of their action is mediated directly via the cysLT-1 receptor on airway smooth muscle. There is also evidence for an effect on airway hyperresponsiveness probably via eosinophil recruitment and activation, airway edema, and possibly airway nerves. Taken together, these studies support a key role for the leukotrienes in asthma. However, additional studies are needed to further define their effects on the airway inflammatory response.

Asthma and leukotrienes: antileukotrienes as novel anti-asthmatic drugs

Antileukotriene drugs inhibit the formation or action of leukotrienes, which are potent lipid mediators generated from arachidonic acid in lung tissue and inflammatory cells. The leukotrienes were discovered in basic studies of arachidonic acid metabolism in leucocytes 20 years ago and were found to display a number of biological activities which may contribute to airway obstruction. Clinical studies with antileukotriene drugs have indeed demonstrated that leukotrienes are significant mediators of airway obstruction evoked by many common trigger factors in asthma. Moreover, treatment trials have established that this new class of drugs has beneficial anti-asthmatic properties, and several antileukotrienes have recently been introduced as new therapy of asthma. This communication presents an overview of the biosynthesis of leukotrienes, their biological effects and clinical effects of antileukotrienes in the treatment of asthama.

Effects of the cysteinyl leukotriene receptor antagonists pranlukast and zafirlukast on tracheal mucus secretion in ovalbumin-sensitized guinea-pigs in vitro

1. We investigated the inhibitory effects of the cysteinyl leukotriene (CysLT1) receptor antagonists, pranlukast and zafirlukast, on 35SO4 labelled mucus output, in vitro, in guinea-pig trachea, induced by leukotriene D4 (LTD4) or by antigen challenge of sensitized animals. Agonists and antagonists were administered mucosally, except in selected comparative experiments where drugs were administered both mucosally and serosally to assess the influence of the epithelium on evoked-secretion. 2. LTD4 increased 35SO4 output in a concentration-related manner with a maximal increase of 23 fold above controls at 100 microM and an approximate EC50 of 2 microM. Combined mucosal and serosal addition of LTD4 did not significantly affect the secretory response compared with mucosal addition alone. Neither LTC4 nor LTE4 (10 microM each) affected 35SO4 output. Pranlukast or zafirlukast significantly inhibited 10 microM LTD4-evoked 35SO4 output in a concentration-dependent fashion, with maximal inhibitions of 83% at 10 microM pranlukast and 78% at 10 microM zafirlukast, and IC50 values of 0.3 microM for pranlukast and 0.6 microM for zafirlukast. Combined mucosal and serosal administration of the antagonists (5 microM each) gave degrees of inhibition of mucosal-serosal 10 microM LTD4-evoked 35SO4 output similar to those of the drugs given mucosally. Pranlukast (0.5 microM) caused a parallel rightward shift of the LTD4 concentration-response curve with a pKB of 7. Pranlukast did not inhibit ATP-induced 35SO4 output. 3. Ovalbumin (10-500 microg ml(-1) challenge of tracheae from guinea-pigs actively sensitized with ovalbumin caused a concentration-related increase in 35SO4 output with a maximal increase of 20 fold above vehicle controls at 200 microg ml(-1). The combination of the antihistamines pyrilamine and cimetidine (0.1 mM each) did not inhibit ovalbumin-induced 35SO4 output in sensitized guinea-pigs. Neither mucosal (10 microM or 100 microM) nor mucosal-serosal (100 microM) histamine had any significant effect on 35SO4 output. 4. Pranlukast or zafirlukast (5 microM each) significantly suppressed ovalbumin-induced secretion in tracheae from sensitized guinea-pigs by 70% and 65%, respectively. 5 We conclude that LTD4 or ovalbumin challenge of sensitized animals provokes mucus secretion from guinea-pig trachea in vitro and this effect is inhibited by the CysLT1 receptor antagonists pranlukast and zafirlukast. These antagonists may be beneficial in the treatment of allergic airway diseases in which mucus hypersecretion is a clinical symptom, for example asthma and allergic rhinitis.

Pharmacology of leukotriene receptor antagonists. More than inhibitors of bronchoconstriction

The cysteinyl leukotrienes (LTs) are chemical mediators that are thought to contribute to the pathophysiologic condition of asthma and other inflammatory diseases. The biological effects of the cysteinyl LTs in the lung are pleiotropic, including both bronchoconstrictor and a growing list of nonbronchoconstrictor activities that extend to inflammatory cell recruitment, vascular leakage, mucus production, neuronal dysfunction, and airways remodeling. This spectrum of effects of cysteinyl LTs is consistent with an expanded view of asthma that extends beyond simply bronchoconstriction and inflammation. Consequently, the clinical efficacy of cysteinyl LT receptor antagonists (LTRAs) in asthma may be related to antagonism of more than cysteinyl LT-induced bronchoconstriction. The relationship of antagonism of the multiple effects of cysteinyl LTs by cysteinyl LTRAs to their utility in the therapy of asthma is addressed, and the preclinical and clinical pharmacology of cysteinyl LTRAs is reviewed.

The importance of leukotrienes in airway inflammation in a mouse model of asthma

Inhalation of antigen in immunized mice induces an infiltration of eosinophils into the airways and increased bronchial hyperreactivity as are observed in human asthma. We employed a model of late-phase allergic pulmonary inflammation in mice to address the role of leukotrienes (LT) in mediating airway eosinophilia and hyperreactivity to methacholine. Allergen intranasal challenge in OVA-sensitized mice induced LTB4 and LTC4 release into the airspace, widespread mucus occlusion of the airways, leukocytic infiltration of the airway tissue and broncho-alveolar lavage fluid that was predominantly eosinophils, and bronchial hyperreactivity to methacholine. Specific inhibitors of 5-lipoxygenase and 5-lipoxygenase-activating protein (FLAP) blocked airway mucus release and infiltration by eosinophils indicating a key role for leukotrienes in these features of allergic pulmonary inflammation. The role of leukotrienes or eosinophils in mediating airway hyperresponsiveness to aeroallergen could not be established, however, in this murine model.

Cysteinyl leukotrienes in asthma: old mediators up to new tricks

The cysteinyl leukotrienes have long been suspected to play a role in the pathogenesis of asthma. This speculation was based largely on their release in human lung following antigen challenge as well as their potent bronchoconstrictor activity. However, there is increasing evidence that the cysteinyl leukotrienes also produce several pro-inflammatory effects and alter the activity of neuronal pathways in the airways. Douglas Hay, Theodore Torphy and Bradley Undem review these recent data and discuss the therapeutic possibilities of cysteinyl leukotriene receptor antagonists and 5-lipoxygenase inhibitors.

Effect of a new leukotriene receptor antagonist, ONO-1078, on human bronchial smooth muscle in vitro

Peptide leukotrienes (LT) have been postulated to play a major role in the etiology of bronchial asthma. The present study investigated the effect of a new peptide LT receptor antagonist, ONO-1078, on isolated human bronchial smooth muscle in vitro. Helical strips of bronchi were suspended in the organ baths filled with 37 degrees C Krebs solution and mechanical responses were recorded isometrically. ONO-1078 produced dose-dependent relaxations, which suggested that the spontaneous basal tone was in part mediated by LT. ONO-1078 caused dose-dependent relaxations of the tissues which were precontracted with LTC4 or LTD4 (3 x 10(-8) M). Pretreatment of bronchi with ONO-1078 (10(-8) M, 10(-7) M) significantly inhibited dose-dependent contractions induced by LTC4 and LTD4. ONO-1078 (10(-6) M) also significantly reduced the antigen-induced contractions in bronchi passively sensitized with atopic serum from mite-allergic patients. Moreover the combination of an H1-receptor antagonist, diphenhydramine (10(-5) M), and ONO-1078 (10(-6) M) completely abolished the antigen-induced contractions. The present findings demonstrate that ONO-1078 is a potent antagonist of exogenous and endogenous LT in the human airway. The selective LT antagonist such as ONO-1078 may be valuable in the therapy of allergic asthma.

Interactions between airway epithelium and mediators of inflammation

Epithelial cells lining the respiratory airways classically are considered to be "target" cells, responding to exposure to a variety of inflammatory mediators by altering one or several of their functions, such as mucin secretion, ion transport, or ciliary beating. Specific responses of epithelial cells in vivo or in vitro to many of these inflammatory mediators are discussed. Recent studies have indicated that airway epithelial cells also can act as "effector" cells, responding to a variety of exogenous and/or endogenous stimuli by generating and releasing additional mediators of inflammation, such as eicosanoids, reactive oxygen species, and cytokines. Many of these epithelial-derived substances can diffuse away and affect neighboring cells and tissues, or can act, via autocrine or paracrine mechanisms, to affect structure and function of epithelial cells themselves. Studies dealing with airway epithelium as a source of inflammatory mediators and related compounds also are discussed.

Stimulation of leukotriene production and membrane translocation of 5-lipoxygenase by cross-linking of the IgE receptors in RBL-2H3 cells

Recent studies in rat basophilic leukemia cells (RBL-2H3) have shown that two pharmacological agents, ionomycin and thapsigargin, induce leukotriene C4 production and translocation of 5-lipoxygenase from cytosol to membrane, primarily by causing an influx of extracellular calcium. In the present study, we investigate the induction of these events by receptor activation. Cross-linking of high-affinity IgE receptors (Fc epsilon RI) by antigen in RBL-2H3 cells leads to leukotriene C4 production and membrane translocation of 5-lipoxygenase. As in the ionomycin-stimulated cells, leukotriene C4 production in antigen-stimulated cells is calcium-dependent since the amount of leukotriene C4 produced correlates quantitatively with the increase in intracellular free calcium concentration ([Ca2+]i). However, the increase in [Ca2+]i required for equivalent leukotriene C4 production by antigen is not as high as it is using ionomycin. In addition, no threshold [Ca2+]i level is required for leukotriene production by antigen, which is in contrast to the ionomycin stimulation that a [Ca2+]i level of 300-400 nM is required. Furthermore, antigen causes an additive increase in leukotriene C4 production in cells stimulated by the ionomycin. These results suggest that another as yet unidentified intracellular pathway acts in conjunction with Ca2+ for leukotriene synthesis in antigen-stimulated cells. Antigen stimulation causes 20-30% of the total cell 5-lipoxygenase to associate with membranes (compared with 10% in unstimulated cells) as demonstrated by enzyme activity assay and by Western Blot using antibodies to 5-lipoxygenase.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased secretion of glandular-kallikrein in the bronchial washings induced by intravenous injection of leukotriene C4 in guinea-pigs

1. Intravenous administration of leukotriene C4 (LTC4) and LTD4 (1-10 nmol kg-1) caused a dose-dependent increase in secretion of glandular-kallikrein in the bronchial washings of guinea-pigs, as measured by cleavage of a synthetic substrate and the formation of kinin. LTC4 was more potent than LTD4 and pilocarpine was much less potent than peptide leukotrienes on a molecular basis. 2. The increases in levels of glandular-kallikrein in the bronchial washings that were induced by LTC4 (3 nmol kg-1, i.v.) were almost completely inhibited by pretreatment with an antagonist of leukotrienes (ONO-1078), with an antagonist of thromboxane (S-1452), with an inhibitor of thromboxane synthetase (OKY-046), with indomethacin, with atropine or with scopolamine. These results indicate that the LTC4-induced increase in levels of glandular-kallikrein may have been mediated by the formation of thromboxane and the release of acetylcholine. 3. The increases in levels of glandular-kallikrein in the bronchial washings induced by STA2 (20 pmol kg-1, i.v.), a stable analogue of thromboxane A2, were completely blocked by pretreatment with atropine, whereas increases induced by pilocarpine (41 mumol kg-1, i.v.) were not blocked by pretreatment with indomethacin, although such increases were inhibited by atropine. This result indicates that secretion of kallikrein stimulated by LTC4 may have been mediated by the successive formation of thromboxane A2 and release of acetylcholine. 4. Intravenous administration of bradykinin (3-30 nmol kg-1) caused a dose-dependent increase in levels of glandular-kallikrein in the bronchial washings. This increase was completely inhibited by pretreatment with atropine, with indomethacin or with an antagonist of thromboxane.5. The increases in levels of glandular-kallikrein in the bronchial washings induced by LTC4 (3 nmol kg'- , i.v.) and pilocarpine (41 flmol kg- 1, i.v.) were significantly inhibited by pretreatment with an antagonist of bradykinin. These results suggest that intravenous LTC4 may increase secretion of glandular-kallikrein via formation of thromboxane A2 and release of acetylcholine in that order, and kinin released by kallikrein may enhance the rate of secretion of glandular-kallikrein.

Leukotriene D4 (LTD4) induces mucus secretion from goblet cells in the guinea pig respiratory epithelium

To study the potential role of leukotriene (LTD4) as a mucus secretagogue, anesthetized and spontaneously breathing guinea pigs were intubated and challenged with various concentrations of an LTD4 aerosol. The resulting changes in airway resistance and compliance were then observed for 20 min, after which the animals were euthanized and the lower respiratory tract airways fixed for morphometric evaluation. Sections for these airways were stained with alcian blue-periodic acid Schiff (AB-PAS), photographed, and the content of AB-PAS positive granules in the epithelium of the extrapulmonary bronchi quantified. The fractional volume of mucus granules in the respiratory epithelial volume. Aerosol LTD4 produced a dose-dependent decrease in the granule fractional volume (GFV) over the range of 0.1 to 1 microgram/ml when compared with epithelia challenged with saline aerosols. Increasing the concentration of administered LTD4 from 1 microgram to 3 micrograms/ml produced further bronchoconstriction but had no further effect on the GFV. Decreases in GFV did not appear to be secondary to smooth muscle contraction since aerosols of other agonists (0.05% histamine and 1% acetylcholine), which yielded resistance changes similar to those of LTD4, did not effect the GFV. Pretreatment with an aerosol of the specific LTD4 receptor antagonist SK&F 104353-Z2 produced a dose-dependent inhibition of the changes in both the airway resistance and GFV. The data suggest that LTD4 mediates epithelial mucus secretion as well as bronchoconstriction in the guinea pig airway and may provide an additional therapeutic use for specific LTD4 receptor antagonists in the treatment of obstructive pulmonary disease.

Platelet activating factor and tracheobronchial respiratory glycoconjugate release in feline and human explants: involvement of the lipoxygenase pathway

It has been suggested that platelet activating factor (PAF) may participate in many aspects of bronchial asthma, including stimulation of mucus secretion. Feline tracheal and human bronchial explant production of respiratory glycoconjugates (RGC) in response to platelet activating factor (PAF) was investigated, in order to differentiate the actions of this putative mediator on mucus secretion. PAF caused a dose-dependent increase in RGC release in concentrations ranging from 100-0.5 microM during a 1-2 hours incubation with either feline or human explants, and the effect was inhibited by the PAF receptor antagonists Ro 19-3704. Several lines of evidence suggest that PAF enhances RGC release indirectly through stimulation of the production of lipoxygenase metabolites of arachidonic acid. 1) Incubation of 10 microM PAF together with arachidonic acid (100 micrograms/ml) enhances PAF's stimulatory effect on RGC release in cats. 2) The cyclooxygenase inhibitor ibuprofen (65 and 420 microM) either failed to effect or slightly enhanced PAF induced RGC release in both species. 3) The combined cyclooxygenase and lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA) as well as the putatively specific 5-lipoxygenase inhibitor L-651,392 (both at 50 microM) inhibited the response to PAF in both species. 4) The putative LTD4 receptor antagonists (L-660,711, 100 microM) slightly reduced the PAF secretory response in human bronchi. We conclude that PAF causes specific receptor mediated RGC release. This response is indirectly mediated through the generation of lipoxygenase metabolite formation including 5-lipoxygenase pathway metabolites.

The influence of leukotrienes and platelet activating factor on mucociliary activity in the rabbit maxillary sinus

Inflammatory mediators released in the airways during allergic reactions can affect the mucociliary system. Leukotrienes and platelet activating factor have been shown to affect the mucociliary activity in various cell preparations. The in vivo effects of these inflammatory mediators on mucociliary activity in rabbit maxillary sinus were investigated using a photoelectric technique. Leukotrienes C4 and D4 in the dose range 0.01-10.0 nmol/kg did not alter mucociliary activity significantly, either when given as bolus injections or as intraarterial infusions. Platelet activating factor had no effect in the dose range 0.001-0.1 nmol/kg. A dose of 1.0 nmol/kg increased mucociliary activity by 20.2 +/- 5.5% but produced adverse respiratory and circulatory effects at the same time. It is concluded that the inflammatory mediators leukotrienes C4, D4 and platelet activating factor have no essential regulatory influence on mucociliary activity in the upper airways of the rabbit.

The effects of local anaesthetic agents upon mucus secretion in the feline trachea in vivo

The actions of lignocaine and tetrodotoxin (TTX) in a tracheal segment of the cat were tested on secretion of mucus macromolecules radiolabelled with 35S and 3H. Lignocaine, 4.3-43 mM, given into the segment, caused a concentration dependent increase of secretion of 3H-and 35S-labelled macromolecules. At 43 mM, lignocaine increased secretion: delta 3H = +433 +/- 191%, delta 35S = +327 +/- 34.5% (n = 8). This effect lessened over 15-45 min. Atropine (1 mg/kg) had little effect on these responses. All concentrations of lignocaine tested (4.3-43 mM) abolished the effect of vagus nerve stimulation on secretion and diminished the effect of a submaximal concentration of pilocarpine (5 microM) in the segment in a dose-dependent manner. TTX in the segment did not alter the resting secretion. At 50 microM it abolished, and at 10 microM diminished, vagal control of secretion without affecting the secretory response to pilocarpine. The study shows that lignocaine, in concentrations which block vagal control of secretion (greater than or equal to 4.3 mM), stimulates the release of mucus macromolecules. Resting secretion is unaltered by TTX, and so does not appear to be under neurogenic inhibition. Larger concentrations of lignocaine (greater than or equal to 13 mM) also diminish pilocarpine-induced secretion, whereas TTX may inhibit nervous control of mucus secretion selectively. The results suggest that clinical anaesthesia of the airways with lignocaine may stimulate mucus secretion.

Relation between essential fatty acid metabolism and gastrointestinal symptoms in cystic fibrosis

Studies in our laboratory have supported the hypothesis, that the basic defect in cystic fibrosis increases the metabolism of essential fatty acids and thereby gradually gives rise to essential fatty acid deficiency, which is a well documented finding in most cases with this disease. Both the increased metabolism--giving high liberation of arachidonic acid and its metabolic products, i.e. different eicosanoids--and the subsequent essential fatty acid deficiency will cause gastrointestinal symptoms and the sequence of this development will mirror the natural history of the disease. Clinical data and results from animal research are discussed in relation to gastrointestinal symptoms and signs of cystic fibrosis.

Lipoxygenase metabolites of arachidonic acid do not induce mucus secretion from rabbit intestinal goblet cells in vitro

Lipoxygenase metabolites of arachidonic acid are effective mucus secretagogues in the respiratory tract but their efficacy in the intestinal tract was unknown. Mucosal explants and sheets of epithelial cells isolated from rabbit small and large intestine were exposed to leukotrienes B4, C4, and D4 and monohydroxyeicosatetraenoic acids 5-HETE, 12-HETE, and 15-HETE. Light and electron microscopic inspection of goblet cells in treated tissues failed to detect evidence of recent compound exocytosis of mucin granules or other morphological evidence of secretory activity. These results indicate that lipoxygenase metabolites are not directly responsible for the increased mucus secretion observed in ulcerative colitis.

The physiology of stress and its relationship to mechanisms of disease and therapeutics

Although stress reactions are organized to protect the homeostatic state of animals, they contain elements that may either enhance or diminish susceptibility to disease processes; in many instances, however, stress reactions themselves may induce pathologic change. It is important, therefore, that the veterinary clinician recognize the elements of a stress reaction and understand the mechanisms of disease with which they interact. This article provides a classification of stress stimuli that can be applied when considering interactions between stress reactions and disease processes.

Neonatal adaptation to stress of parturition and dystocia

The fetal animal undergoes a tremendous transition from intrauterine to extrauterine life at parturition. In this article, the maternal-fetal interactions of parturition are discussed with the aim of examining the normal stress reactions of parturition. Dystocia is discussed from the standpoint of additional distress of the newborn, with an aim toward the development of rational therapeutic support.

Inhibition of cysteinyl-leukotriene production by azelastine and its biological significance

Azelastine is a phthalazinone derivative with a wide spectrum of pharmacological activities. Actively sensitized guinea pigs were used to examine the broncholytic effect of azelastine in vivo. Furthermore, the influence of azelastine on the production of arachidonic acid (AA) metabolites was investigated in vitro and compared to the effects of nordihydroguaiaretic acid (NDGA), indomethacin and ketotifen. In vivo, azelastine protected actively sensitized guinea-pigs against ovalbumin-induced bronchospasm with an ID50 of 0.08 mg/kg orally. Ketotifen was similarly active (ID50 = 0.05 mg/kg). Antigen-induced contraction of isolated tracheal rings of sensitized guinea-pigs was concentration-dependently inhibited by azelastine and NDGA with IC50-values of 94.1 and 34.2 mumol/l, respectively. Ketotifen exerted only weak inhibitory activity (18% at 100 mumol/l). The arachidonic acid-induced contraction of isolated guinea-pig tracheal rings was also inhibited both by azelastine (IC50 = 92.6 mumol/l) and NDGA (IC50 = 20.4 mumol/l). Ketotifen was inactive on this model. Antigen challenge of chopped lung tissue from sensitized guinea-pigs resulted in the release of cysteinyl-leukotrienes (LT) which were identified by reversed phase high pressure liquid chromatography (HPLC) as LTD4 and LTE4. The release of cysteinyl-LT from sensitized guinea-pig lung tissue induced by antigen challenge was concentration-dependently inhibited by azelastine (IC50 = 35.2 mumol/l) and NDGA (IC50 = 8.4 mumol/l) but not by ketotifen and indomethacin. By contrast, indomethacin caused a pronounced augmentation of cysteinyl-LT release. The concentration of indomethacin, which augmented cysteinyl-LT release by 50% was 0.19 mumol/l.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of the 5-lipoxygenase pathway with piriprost (U-60,257) protects normal primates from ozone-induced methacholine hyperresponsive small airways

Weekly exposure to ozone in seven normal Rhesus monkeys led to induction of methacholine hypersensitive airways (RL increases 242 +/- 60% and Cdyn decreases 68 +/- 13% of baseline methacholine responses). It took 19 weeks to establish this hyperresponse that persisted for greater than 15 weeks once ozone was stopped. A second exposure led to similar response peaks in 6 weeks. At the peak of the second response, weekly 1% piriprost exposure before ozone led to a return to baseline that was not different between placebo and piriprost treated animals (9.4 +/- 1.0 and 4.3 +/- 2.9 weeks, placebo and treated, respectively P = 0.09 NS). A statistical difference in the mecholyl response in placebo and piriprost treated groups while on ozone was shown only in the Cdyn measurement (Cdyn% change 68 +/- 13 vs 24 +/- 14, placebo and piriprost, respectively P = 0.03). Off ozone (or return to baseline), a statistical difference could be detected both in RL and Cdyn (RL% changed 151 +/- 41 vs 31.1 +/- 49, P = 0.03, and for Cdyn 62.7 +/- 8 vs 9 +/- 10, P = 0.0006, placebo and piriprost, respectively). We conclude tha the primate provides a chronic model of airways reactivity in which the role of lipoxygenase is implicated because of the beneficial role of piriprost, and further that the ozone lesion is primarily in the smaller airways (possibly and alveolitis).

Arachidonic acid metabolism in respiratory epithelial cells

1. Arachidonic acid metabolism by respiratory epithelial cells either freshly isolated or maintained in culture is discussed. 2. A comparison is made between rat, rabbit, canine and human cells and illustrates the considerable variation in the metabolism between various species. 3. The relationship between arachidonic acid metabolism and ion movement in these cells is reviewed.

An alternate mechanism for regulation of leukotriene production in leukocytes: studies with an anti-inflammatory drug, sodium diclofenac

Sodium diclofenac, a potent cyclooxygenase inhibitor, was recently shown to inhibit arachidonic acid conversion to leukotriene products in human leukocytes. This activity was confirmed by radioimmunoassay in calcium ionophore A 23187-stimulated leukocytes isolated from the rat peritoneal cavity and human peripheral blood. Studies with rat peritoneal leukocytes revealed that this effect was not mediated by inhibition of 5-lipoxygenase or phospholipase A2, but rather through modulation of arachidonic acid uptake and release. The potency of this effect was dependent upon cell type; macrophages being more sensitive to the drug than neutrophils. In leukocytes treated with sodium diclofenac, arachidonic acid released from phospholipids in response to A 23187 challenge was reincorporated into triacylglycerols. The drug enhanced the spontaneous uptake of arachidonic acid into the cellular triacylglycerol pool and, in this manner, decreased the availability of intracellular arachidonic acid. Therefore, sodium diclofenac, in addition to inhibition of cyclooxygenase, regulates leukotriene production of inflammatory cells by a mechanism mediated in part through the redistribution of arachidonic acid in lipid pools.

Leukotrienes and lipoxins: structures, biosynthesis, and biological effects

Arachidonic acid is released from membrane phospholipids upon cell stimulation (for example, by immune complexes and calcium ionophores) and converted to leukotrienes by a 5-lipoxygenase that also has leukotriene A4 synthetase activity. Leukotriene A4, an unstable epoxide, is hydrolyzed to leukotriene B4 or conjugated with glutathione to yield leukotriene C4 and its metabolites, leukotriene D4 and leukotriene E4. The leukotrienes participate in host defense reactions and pathophysiological conditions such as immediate hypersensitivity and inflammation. Recent studies also suggest a neuroendocrine role for leukotriene C4 in luteinizing hormone secretion. Lipoxins are formed by the action of 5- and 15-lipoxygenases on arachidonic acid. Lipoxin A causes contraction of guinea pig lung strips and dilation of the microvasculature. Both lipoxin A and B inhibit natural killer cell cytotoxicity. Thus, the multiple interaction of lipoxygenases generates compounds that can regulate specific cellular responses of importance in inflammation and immunity.

SRS-A leukotrienes decrease the activity of human respiratory cilia

We have studied the effects of the slow reacting substance of anaphylaxis (SRS-A) constituents leukotrienes (LT) C4 and D4 on the ciliary activity of human respiratory cells. The ciliary beat frequency on human nasal cells harvested by cell scraping from the inferior turbinate was measured in a blind design by a microphoto-oscillographic technique. A total of 740 ciliated cells from seventy-four cell scrapings were studied. Mean baseline of ciliary beat frequency was 10.2 Hz. The ciliary beat frequency exhibited a pronounced variability in the spontaneous changes between the cell scrapings, yet less so within cell samples from the cell scrapings. We, therefore, evaluated the effect of the test solutions relative to the spontaneous decrease found during simultaneous perfusion with control solution of samples from the same cell scrapings. LTC4, 3-300 nmol/l, caused a highly significantly dose-related decrease in the ciliary beat frequency by up to approximately 20% as compared to the corresponding control solution. The effect of LTC4 was significantly inhibited by the SRS-A receptor antagonist FPL 55712 (10 mumol/l), but not by indomethacin (10 mumol/l). LTD4, 300 nmol/l, also decreased the ciliary beat frequency. LTB4, which is a leukotriene, although without the sulphidopeptide side chain of the SRS-A leukotrienes, did not affect the ciliary beat frequency in a concentration of 100 nmol/l. This would seem to confirm the structure specificity of the elucidated effect of the SRS-A leukotrienes. Histamine (100 mumol/l) did not affect the ciliary beat frequency.(ABSTRACT TRUNCATED AT 250 WORDS)

Leukotriene synthesis by human gastrointestinal tissues

The prostaglandin and leukotriene synthesizing capacity of human gastrointestinal tissues obtained at surgery was investigated using radioimmunoassay for prostaglandin E2, leukotriene B4 and sulfidopeptide leukotrienes. The leukotriene immunoassay data were validated by high-pressure liquid chromatography (HPLC). During incubation at 37 degrees C, fragments of human gastric, jejuno-ileal and colonic mucosa released considerably larger amounts of prostaglandin E2 than of leukotriene B4 and sulfidopeptide leukotrienes. Gastrointestinal smooth muscle tissues released even larger amounts of prostaglandin E2, but smaller amounts of leukotrienes than the corresponding mucosal tissues. Adenocarcinoma tissue released larger amounts of leukotriene B4, sulfidopeptide leukotrienes and prostaglandin E2 than normal colonic mucosa. Ionophore A23187 (5 micrograms/ml) did not stimulate release of prostaglandin E2 from any of the tissues investigated, but enhanced release of leukotriene B4 and sulfidopeptide leukotrienes. HPLC analysis demonstrated that immunoreactive leukotriene B4 co-chromatographed almost exclusively with standard leukotriene B4, while immunoreactive sulfidopeptide leukotrienes consisted of a mixture of leukotrienes C4, D4 and E4. Leukotriene synthesis by human gastrointestinal tissues was inhibited by the lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA) and the dual enzyme inhibitor BW755C (3-amino-1-(trifluoromethylphenyl)-2-pyrazoline hydrochloride). Synthesis of prostaglandin E2 was inhibited by the cyclooxygenase inhibitor indomethacin as well as by BW755C. Incubation of gastrointestinal tissues in the presence of glutathione decreased the amounts of leukotrienes D4 and E4, while release of leukotriene C4 was simultaneously increased. On the other hand, incubation of tritiated leukotriene C4 with incubation media from human gastric or colonic mucosa resulted in conversion of the substrate to [3H]leukotriene D4 and [3H]leukotriene E4. The results indicate the capacity of human gastrointestinal tissues to synthesize the 5-lipoxygenase-derived products of arachidonate metabolism, leukotriene B4 and sulfidopeptide leukotrienes, in addition to larger amounts of prostaglandin E2. Furthermore, considerable activities of the sulfidopeptide leukotriene-metabolizing enzymes gamma-glutamyl transpeptidase and dipeptidase were detected in human gastrointestinal tissues. These enzymes might play an important role in biological inactivation and/or change of biological profile of sulfidopeptide leukotrienes generated in the human gastrointestinal tract.

Leukotrienes cause eosinophil emigration into conjunctival tissue

The ability of LTB4, LTC4, the 5S,6R and 5R,6S LTD4 stereoisomers, and LTE4 to evoke leukocyte infiltration into the conjunctiva was demonstrated in the guinea pig by histological and light microscopy techniques. LTD4 and LTE4 demonstrated a dose-dependent and predominantly eosinophilic infiltrate over the selected dose range (10 ng to 1000 ng), while there was only a minimal response to LTC4. LTB4 produced marked eosinophil infiltrates only at the highest dose; scattered neutrophil infiltrates were also noted at the high dose of LTB4. The 5R,6S LTD4 stereoisomer did not evoke any leukocyte infiltration. The SRS-A antagonist, FPL 55712, abolished peptidoleukotriene-induced eosinophil emigration, and indomethacin pre-treatment had no inhibitory effect, indicating direct mediation of this response by LTs. Histamine caused a comparable eosinophilia over a dose range of 10 micrograms to 1000 micrograms. LT-induced eosinophil emigration was directed to the conjunctival epithelium; the cells appeared intact and no tissue damage was observed. These results may have relevance in the areas of allergic conjunctivitis and asthma research.

Metabolism of arachidonic acid by hamster trachea lack of stimulation by A23187

The metabolism of arachidonic acid has been studied using hamster trachea in short-term organ culture. To study endogenous substrate utilization, tissue lipids were labeled with [3H]-arachidonic acid, whereas exogenous substrate turnover was assessed by the addition of 100 microM [14C]-arachidonic acid to the medium. Both exogenous and endogenous arachidonate were converted primarily to 6-keto-PGF1 alpha and PGE2, with varying amounts of an unidentified non-polar product noted. Production of the prostanoids increased steadily with time up to 24 hours. No significant generation of lipoxygenase products was found. Release of incorporated labeled arachidonic acid was nearly linear with time, resulting in the transfer of about 10% of the total label into the medium after 24 hours. About 3% of the total label was converted to prostaglandins. In the presence of 10 microM A23187, release of label was increased by only 25 to 60% relative to the control. Analysis of labeled compounds in the medium showed that this increase resulted from increased release of unchanged arachidonic acid, and that the yield of oxygenated products was the same as from the control incubations.

Intravenous SRS-induced increases in tracheal mucous gel layer thickness: evidence for thromboxane involvement

Intravenous (IV) slow reacting substance (SRS) challenge produces bronchoconstriction that can be reduced by cyclooxygenase inhibitors. This report shows that IV SRS challenge also produces significant increases in tracheal mucous gel thickness and that the increases are inhibited by pretreatment with indomethacin (4 mg/kg, PO) or imidazole (10 mg/kg, IV). The increase in gel thickness is preceded by increases in plasma thromboxane B2 (TXB2) levels and the inhibition of gel thickening by imidazole is paralleled by decreases in plasma TXB2 levels. Aerosolized SRS produces increases in tracheal mucous gel thickness which are not inhibited by either indomethacin or imidazole, but are significantly inhibited by FPL-55712. These findings indicate that SRS acts, not only directly to stimulate mucous secretion but also indirectly through an indomethacin and imidazole sensitive mechanism.