Secondary release of thromboxane A2 in aerosol leukotriene C4-induced bronchoconstriction in guinea pigs

Effect of a thromboxane synthetase inhibitor (OKY-046) on bronchoconstriction induced by aerosol leukotriene C4 and histamine was studied in anesthetized, artificially ventilated guinea pigs in order to examine whether secondary release of thromboxane A2 is produced by aerosol leukotriene C4 or not. 0.01–1.0μg/ml of leukotriene C4 and 12.5–400μg/ml of histamine inhaled from ultrasonic nebulizer developed for small animals caused dose-dependent increase of pressure at airway opening (Pao) which is considered to be an index representing bronchial response. Pretreatment of the animals with intravenous OKY-046 (100mg/kg) significantly reduced the airway responses produced by inhalation of 0.1, 0.33 and 1.0μg/ml of leukotriene C4, while the pretreatment did not affect the histamine dose-response curve. Based on these findings and previous reports (6, 7), it is suggested that aerosol leukotriene C4 activates arachidonate cyclooxygenase pathway including thromboxane A2 synthesis and the released cyclooxygenase products have bronchodilating effect as a whole     

Secondary release of thromboxane A2 in aerosol leukotriene C4-induced bronchoconstriction in guinea pigs

Effect of a thromboxane synthetase inhibitor (OKY-046) on bronchoconstriction induced by aerosol leukotriene C4 and histamine was studied in anesthetized, artificially ventilated guinea pigs in order to examine whether secondary release of thromboxane A2 is produced by aerosol leukotriene C4 or not. 0.01-1.0 micrograms/ml of leukotriene C4 and 12.5-400 micrograms/ml of histamine inhaled from ultrasonic nebulizer developed for small animals caused dose-dependent increase of pressure at airway opening (Pao) which is considered to be an index representing bronchial response. Pretreatment of the animals with intravenous OKY-046 (100mg/kg) significantly reduced the airway responses produced by inhalation of 0.1, 0.33 and 1.0 micrograms/ml of leukotriene C4, while the pretreatment did not affect the histamine dose-response curve. Based on these findings and previous reports (6,7), it is suggested that aerosol leukotriene C4 activates arachidonate cyclooxygenase pathway including thromboxane A2 synthesis and the released cyclooxygenase products have bronchodilating effect as a whole.     

Effect of a thromboxane receptor antagonist on PGD2- and allergen-induced bronchoconstriction

In this study we investigated the effect of the selective and potent thromboxane A2 (TxA2) receptor antagonist GR32191 on smooth muscle contraction induced by the TxA2 analogue U46619, prostaglandin (PG) D2, PGF2 alpha, and methacholine (MCh) in guinea pig airways in vitro and the airways response provoked by inhaled PGD2 and MCh in asthmatic subjects in vivo. GR32191 antagonized competitively the contractile responses of all three prostanoids to a similar degree but had no effect on MCh-induced contractions. In asthmatic subjects GR32191, in a single oral dose of 80 mg, did not affect base-line airway caliber or MCh-induced broncho-constriction but caused significant inhibition of PGD2-induced bronchoconstriction, displacing the concentration-response curves to the right by greater than 10-fold. The effect of the same oral dose of GR32191 on allergen-induced immediate bronchoconstriction was subsequently investigated in allergic asthmatic subjects. In individual subjects, GR32191 inhibited to varying degrees the overall bronchoconstrictor response, with the maximum effect occurring between 10 and 30 min after allergen challenge. These studies suggest that prostanoids contribute to the immediate bronchoconstriction induced by inhaled allergen in allergic asthmatics, and that this effect is mediated by stimulation of a thromboxane receptor.     

Acute effects of prostaglandin D2 to induce airflow obstruction and airway microvascular leakage in guinea pigs: role of thromboxane A2 receptors

BACKGROUND: Although prostaglandin D2 (PGD2), a mast cell-derived inflammatory mediator, may trigger allergic airway inflammation, its potency and the mechanism by which it induces airway microvascular leakage, a component of airway inflammation, is not clear. OBJECTIVE: We wanted to evaluate the relative potency of PGD2 to cause microvascular leakage as compared to airflow obstruction, because both responses were shown to occur simultaneously in allergic airway diseases such as asthma. The role of thromboxane A2 receptors (TP receptors) in inducing these airway responses was also examined. METHODS: Anesthetized and mechanically ventilated guinea pigs were given i.v. Evans blue dye (EB dye) and, 1 min later, PGD2 (30, 100, 300 or 1,000 nmol/kg). For comparison, the effect of 150 nmol/kg histamine or 2 nmol/kg leukotriene D4 (LTD4) was also examined. Lung resistance (R(L)) was measured for 6 min (or 25 min for selected animals) and the lungs were removed to calculate the amount of extravasated EB dye into the airways as a marker of leakage. In some of the animals, specific TP receptor antagonists, S-1452 (10 microg/kg) or ONO-3708 (10 mg/kg), or a thromboxane A2 synthase inhibitor, OKY-046 (30 mg/kg), was pretreated before giving PGD2. RESULTS: Injection of PGD2 produced an immediate and dose-dependent increase in RL (peaking within 1 min), which was significant at all doses studied. At 1,000 nmol/kg, PGD2 induced a later increase in R(L), starting at 3 min and reaching a second peak at 8 min. By contrast, only PGD2 at doses of 300 and 1,000 nmol/kg produced a significant increase in EB dye extravasation. The relative potency of 1,000 nmol/kg PGD2 to induce leakage as compared to airflow obstruction was comparable to histamine at most of airway levels, but less than LTD4. Both responses caused by PGD2 were completely abolished by S-1452 and ONO-3708, but not by OKY-046. CONCLUSION: PGD2 may induce airway microvascular leakage by directly stimulating TP receptors without generating TXA2 in guinea pigs. Microvascular leakage may play a role in the development of allergic airway inflammation caused by PGD2.     

No involvement of lipid mediators in a guinea pig model of ultrasonically nebulized distilled water-induced bronchoconstriction

An inhalation of ultrasonically nebulized distilled water (UNDW) induces bronchoconstriction only in asthmatics, but the mechanism underlying the response is not fully understood. We have reported that bronchoconstriction occurs immediately after UNDW is inhaled 20 min after an antigen challenge in guinea pigs. Our aim was to examine the role of lipid mediators in this response. Passively sensitized guinea pigs were anesthetized and artificially ventilated. A sulfidopeptide leukotriene receptor antagonist, KCA-757, and platelet-activating factor antagonists, Y-24180 and E6123, were administered i.v. 15 min after an aerosolized antigen challenge, and UNDW was inhaled 5 min later. KCA-757, Y-24180, or E6123 did not, significantly alter the UNDW-induced bronchoconstriction. Together with our previous data that thromboxane A2 receptor antagonists did not influence the UNDW-induced bronchoconstriction, the present results suggest that lipid mediators are not involved in the UNDW-induced bronchoconstriction in our guinea pig model.     

A possible role for PAF in allergen-induced late responses: modification by a selective antagonist

We determined whether platelet-activating factor (PAF) plays a role in allergen-induced airway responses by studying the effects of a selective PAF antagonist WEB-2086 on antigen-induced early and late airway responses in allergic sheep. In seven sheep, inhaled Ascaris suum produced significant early (282%) and late (176%) increases in specific lung resistance (sRL). WEB-2086 (1 mg/kg iv) given 20 min before antigen challenge did not affect the early response, but the peak late increase in sRL was only 37% over base line (P less than 0.05 vs. control). To study the mechanism by which PAF contributes to antigen-induced responses, we evaluated the effects of pharmacological probes on PAF-induced bronchoconstriction. Inhaled PAF (dose range 75-700 micrograms) caused reproducible (r = 0.781, P less than 0.05) increases in sRL in eight sheep. The PAF-induced bronchoconstriction was blocked by WEB-2086 (1 mg/kg iv) and by the leukotriene antagonist FPL-55712 (30 mg by aerosol); however, neither the cyclooxygenase blocker indomethacin (2 mg/kg iv) nor the histamine H1-antagonist chlorpheniramine (2 mg/kg iv) blocked the PAF response. WEB-2086, however, did not block bronchoconstriction induced by aerosol leukotriene D4, indicating that PAF acts indirectly through leukotrienes. Finally, we determined whether PAF could induce late airway responses. Inhaled PAF produced an immediate increase in sRL in all seven sheep tested, but late airway responses were observed in only three of the seven sheep.(ABSTRACT TRUNCATED AT 250 WORDS)     

Blockade of thromboxane responses in the airway of the cat by SQ 29,548

The effects of SQ 29,548, a thromboxane receptor antagonist, on airway responses were investigated in paralyzed, anesthetized, mechanically ventilated cats. Intravenous injections of the thromboxane and prostaglandin precursor, arachidonic acid (AA), and the thromboxane mimic, U 46619, produced dose-related increases in transpulmonary pressure and lung resistance and decreases in dynamic compliance. After administration of SQ 29,548 (0.5 mg/kg iv), bronchoconstrictor responses to AA were reduced by approximately 50%, whereas responses to U 46619 were reduced by approximately 90%. The cyclooxygenase inhibitor, sodium meclofenamate (2.5 mg/kg iv), blocked the component of the airway response to AA remaining after treatment with SQ 29,548. The thromboxane receptor antagonist had no significant effect on bronchoconstrictor responses to prostaglandins F2 alpha, and D2, methacholine, 5-hydroxytryptamine, histamine, or BAY K 8644, an agent that promotes calcium entry. Reductions in systemic arterial pressure in response to AA were enhanced by the thromboxane receptor antagonist and abolished by meclofenamate. SQ 29,548 had no effect on terminal enzyme activity in microsomal fractions from cat lung. These data support the hypothesis that AA-induced bronchoconstriction in the cat is mediated in large part by the actions of thromboxane A2. These data also suggest that U 46619 and U 44069 stimulate the same airway receptor as thromboxane A2 and mimic the bronchomotor effects of this hormone, which has not yet been isolated as a pure substance. These data demonstrate that SQ 29,548 is a selective thromboxane receptor antagonist in the airways of the closed-chest cat and may be a useful probe for studying responses to thromboxane A2 in physiological and pathophysiological processes in the lung.     

Leukotriene B4 induces airway hyperresponsiveness in dogs

We studied the effect of leukotriene B4 aerosols on airway responsiveness to inhaled acetylcholine aerosols and on the cellular components and cyclooxygenase metabolites in bronchoalveolar lavage fluid in dogs. Inhalation of leukotriene B4 aerosols had no effect on resting total pulmonary resistance but increased airway responsiveness, an effect that was maximum in 3 h and that returned to control levels within 1 wk. Three hours after leukotriene B4, the number of neutrophils and the concentration of thromboxane B2 recovered in lavage fluid increased markedly. Pretreatment with the thromboxane synthase inhibitor OKY-046 prevented the increases in airway responsiveness and in thromboxane B2 but did not alter neutrophil chemotaxis. Thus we speculate that leukotriene B4 causes neutrophil chemotaxis and release of thromboxane B2, which increases airway responsiveness.     

Effect of thromboxane A(2) (TXA(2)) synthase inhibitor and TXA(2) receptor antagonist alone and in combination on antigen-induced bronchoconstriction in guinea pigs

Thromboxane A(2) (TXA(2)) causes bronchoconstriction and bronchial hyperresponsiveness. Two types of TXA(2) modifiers, one synthase inhibitor and one receptor antagonist, are widely used for the treatment of asthma in Japan. Although the target of TXA(2) modifiers is to inhibit bioactivity of TXA(2), the pharmacological properties are somewhat different between these drugs. We studied the inhibitory effects of the TXA(2) synthase inhibitor CS-518 and the TXA(2) receptor antagonist S-1452 alone and in combination on antigen-induced bronchoconstriction in passively sensitized guinea pigs treated with diphenhydramine.Both CS-518 and S-1452 inhibited the antigen-induced bronchoconstriction dose-dependently with the plateau. The combination of these drugs at the maximal inhibitory doses did not have any more effect compared with each single dosing. The combination at the submaximal doses tended to show an additive effect, but the effect was not significant.These findings suggest that other prostanoids such as PGE(2), PGI(2), PGD(2) and PGF(2alpha) may not take an important role in the antiasthmatic effects of TXA(2) modifiers.     

Effect of thromboxane A2 (TXA2) synthase inhibitor and TXA2 receptor antagonist alone and in combination on antigen-induced bronchoconstriction in guinea pigs

Thromboxane A2 (TXA2) causes bronchoconstriction and bronchial hyperresponsiveness. Two types of TXA2 modifiers, one synthase inhibitor and one receptor antagonist, are widely used for the treatment of asthma in Japan. Although the target of TXA2 modifiers is to inhibit bioactivity of TXA2, the pharmacological properties are somewhat different between these drugs. We studied the inhibitory effects of the TXA2 synthase inhibitor CS-518 and the TXA2 receptor antagonist S-1452 alone and in combination on antigen-induced bronchoconstriction in passively sensitized guinea pigs treated with diphenhydramine. Both CS-518 and S-1452 inhibited the antigen-induced bronchoconstriction dose-dependently with the plateau. The combination of these drugs at the maximal inhibitory doses did not have any more effect compared with each single dosing. The combination at the submaximal doses tended to show an additive effect, but the effect was not significant. These findings suggest that other prostanoids such as PGE2, PGI2, PGD2 and PGF2alpha may not take an important role in the antiasthmatic effects of TXA2 modifiers.     

A PAF receptor antagonist inhibits acute airway inflammation and late-phase responses but not chronic airway inflammation and hyperresponsiveness in a primate model of asthma

We have examined the effects of a PAF receptor antagonist, WEB 2170, on several indices of acute and chronic airway inflammation and associated changes in lung function in a primate model of allergic asthma. A single oral administration WEB 2170 provided dose related inhibition of the release of leukotriene C(4) (LTC(4)) and prostaglandin D(2) (PGD(2)) recovered and quantified in bronchoalveolar lavage (BAL) fluid obtained during the acute phase response to inhaled antigen. In addition, oral WEB 2170 treatment in dual responder primates blocked the acute influx of neutrophils into the airways as well as the associated late-phase airway obstruction occurring 6 h after antigen inhalation. In contrast, a multiple dosing regime with WEB 2170 (once a day for 7 consecutive days) failed to reduce the chronic airway inflammation (eosinophilic) and associated airway hyperresponsiveness to inhaled methacholine that is characteristic of dual responder monkeys. Thus, we conclude that the generation of PAF following antigen inhalation contributes to the development of lipid mediators, acute airway inflammation and associated late-phase airway obstruction in dual responder primates; however, PAF does not play a significant role in the maintenance of chronic airway inflammation and associated airway hyperresponsiveness in this primate model.     

Inhibition of antigen-induced airway hyperresponsiveness, but not acute hypoxia nor airway eosinophilia, by an antagonist of platelet-activating factor

The role of platelet-activating factor (PAF) in Ag-induced airway hyperresponsiveness was evaluated in a guinea pig model using the PAF antagonist SDZ 64-412. Repeated OVA challenge by aerosol (twice weekly x 4 wk) of previously sensitized guinea pigs produced striking airway hyperresponsiveness as determined by pulmonary resistance changes to increasing doses of inhaled acetylcholine given 3 days after the last OVA challenge. Each OVA challenge produced significant hypoxia that was unaffected by oral pretreatment with 20 mg/kg SDZ 64-412, 2 h before each challenge (pO2 = 35 +/- 2 mm Hg for OVA alone vs 40 +/- 6 mm Hg for SDZ and OVA groups, respectively). SDZ 64-412 pretreatment abolished the airway hyperresponsiveness resulting from repeated Ag challenge. Morphometric analysis revealed that SDZ 64-412 treatment had no effect on the increased numbers of eosinophils that infiltrated the airways of OVA-challenged guinea pigs. These results suggest that PAF may be a primary mediator of airway hyperresponsiveness, but not acute bronchoconstriction, induced by repeated Ag challenge. This activity of PAF appears independent of eosinophil recruitment to airways.     

In vivo airway eosinophil accumulation does not enhance antigen- or propranolol-induced bronchoconstriction in guinea pigs

BACKGROUND: Chronic airway eosinophil accumulation is characteristic of asthma. However, it remains unclear whether airway eosinophils enhance or reduce release of chemical mediators and/or action of the released mediators in the airways in vivo, because previous investigators have indicated that eosinophil-derived factors such as histaminase and arylsulfatase may alter the allergic reaction by metabolizing chemical mediators. Recently, we have developed a guinea pig model of propranolol-induced bronchoconstriction (PIB), which is mediated by lipid mediators such as thromboxane A2 (TxA2), cysteinyl leukotrienes (cLTs) and platelet activation factor (PAF). This study was conducted to explain the influence of airway eosinophil accumulation on antigen-induced bronchoconstriction and the following PIB, both of which are mediated by lipid mediators. METHODS: Guinea pigs were transnasally treated with 75 microg/kg of polymyxin-B or vehicle twice a week for a total of 3 weeks. Guinea pigs were anesthetized and treated with diphenhydramine hydrochloride, and then artificially ventilated 24 h after the last administration of polymyxin-B or vehicle followed by passive sensitization. Propranolol at a concentration of 10 mg/ml was inhaled 20 min after an aerosolized antigen challenge. RESULTS: The proportion of eosinophils in bronchoalveolar lavage fluid obtained 15 min after the propranolol inhalation was significantly increased in guinea pigs treated with polymyxin-B compared with the vehicle. The polymyxin-B treatment did not affect antigen-induced bronchoconstriction or the following PIB. CONCLUSIONS: We conclude that eosinophils accumulated in the airways by polymyxin-B does not affect release of chemical mediators induced by antigen or propranolol inhalation, or action of released mediators in vivo.     

Effect of a peptide leukotriene antagonist, ONO-1078 on antigen-induced airway microvascular leakage in actively sensitized guinea pigs.

We examined the effect of ONO-1078, a peptide leukotriene antagonist, on antigen-induced airway microvascular leakage in ovalbumin-sensitized guinea pigs. When guinea pigs were pretreated with mepyramine, ovalbumin challenge increased vascular permeability to Evans blue dye in trachea, main bronchi and intrapulmonary airways. Oral administration of ONO-1078 significantly reduced microvascular leakage in intrapulmonary airways at doses more than 3 mg/kg, but not in trachea. Moreover, oral administration of ONO-1078 significantly reduced SRS-A mediated microvascular leakage into all airway tissues and was more effective in intrapulmonary airways at 3 mg/kg. Simultaneously, ONO-1078 also inhibited SRS-A mediated bronchoconstriction. On the other hand, azelastine (10 mg/kg, p.o.), an anti-asthma agent, failed to inhibit microvascular leakage into the airways. These results suggest that peptide leukotrienes may be important mediators of airway microvascular leakage, and that the inhibitory effect of ONO-1078 on antigen-induced airway microvascular leakage in addition to the blockade of bronchoconstriction may have therapeutic implications for bronchial asthma.     

Bronchoconstrictor and antibronchoconstrictor properties of inhaled prostacyclin in asthma

Prostacyclin (PGI2) is generated in appreciable amounts during allergic reactions in human lung tissue. To define its activity on human airways we have studied the effects of doubling concentrations of inhaled PGI2 and its hydrolysis product 6-oxoprostaglandin F1 alpha (6-oxo-PGF1 alpha) on specific airway conductance (sGaw), maximum expiratory flow at 30% vital capacity (Vmax30), forced expiratory volume in 1 s (FEV1), and static lung volumes in subjects with mild allergic asthma. In a second study the effect of inhaled PGI2 on bronchoconstriction provoked by increasing concentrations of inhaled prostaglandin (PG) D2 and methacholine was observed. Inhalation of PGI2 up to a concentration of 500 micrograms/ml had no significant effect on sGaw but produced a concentration-related decrease in FEV1 and Vmax30 in all subjects. In two of four subjects inhalation of PGI2 also increased residual volume and decreased vital capacity but had no effect on total lung capacity. PGI2, but not 6-oxo-PGF1 alpha, protected against bronchoconstriction provoked by either PGD2 or methacholine whether airway caliber was measured as sGaw, FEV1, or Vmax30. The apparent disparity between the bronchoconstrictor and antibronchoconstrictor effects of PGI2 might be explained by its potent vasodilator effect in causing airway narrowing through mucosal engorgement and reducing the spasmogenic effects of other inhaled mediators by increasing their clearance from the airways.     

Electric field stimulation of precision-cut lung slices

The precision-cut lung slice (PCLS) technique is widely used to examine airway responses in different species. We developed a method to study nerve-dependent bronchoconstriction by the application of electric field stimulation (EFS) to PCLS. PCLS prepared from Wistar rats were placed between two platinum electrodes to apply serial rectangular impulses (5-100 Hz), and bronchoconstriction was studied by videomicroscopy. The extent of airway contractions increased with higher frequencies. Stable repeated airway contractions were obtained at a frequency of 50 Hz, a width of 1 ms, and an output of 200 mA for 2.5 s each minute. Larger airways showed stronger responses. The EFS-triggered contractions were increased by the acetylcholine esterase inhibitor neostigmine (10 μM) and reversed by the muscarinic antagonist atropine (10 μM), whereas the thromboxane protanoid receptor antagonist SQ29548 (10 μM) had no effect. Magnesium ions (10 mM) antagonized airway contractions induced by EFS, but not by methacholine, indicating that nerve endings remain intact in PCLS. Our data further show that the electrically evoked airway contractions in PCLS are mediated by cholinergic nerves, independent of thromboxane and more prominent in larger airways. Taken together these findings show that nerve endings remain intact in PCLS, and they suggest that the present method is useful to study neurogenic responses in airways of different size.     

Pharmacological model for airway hypersensitivity produced by propranolol and reserpine in guinea pigs

Combined treatment with propranolol and reserpine enhanced acetylcholine-induced doseresponse curves for bronchoconstriction in guinea pigs in vivo. This airway hyperreactivity model was investigated pharmacologically. (1) Increased capillary permeability and increases in leukocytes in bronchoalveolar lavage fluid (BALF) were not observed after this combined treatment. (2) The increased airway sensitivity to acetylcholine produced by propranolol and reserpine was inhibited by ketotifen and theophylline, reported in clinical studies to inhibit airway hyperreactivity. (3) Two leukotriene (LT) receptor antagonists, MCI-826 and FPL-55712, clearly inhibited this increased airway reactivity. (4) A thromboxane A₂ (TXA₂) receptor antagonist, ONO-3708, and TXA₂ synthetase inhibitor, OKY-046, also inhibited this increased airway reactivity.These results suggest that the airway hyperreactivity model produced by propranolol and reserpine in guinea pigs is a valuable pharmacological tool for investigating a remedy and LT and TXA₂ may be involved in the onset of this airway hyperreactivity.     

Lower leukotriene C(4) levels in bronchoalveolar lavage fluid of asthmatic subjects after 2.5 years of inhaled corticosteroid therapy

Long-term treatment with inhaled corticosteroids has been shown to result in improvement of symptoms and lung function in subjects with asthma. Arachidonic acid (AA) metabolites are thought to play a role in the pathophysiology of asthma. It was assessed whether differences could be found in bronchoalveolar lavage (BAL) AA metabolite levels between subjects with asthma who were treated for 2.5 years with inhaled bronchodilators alone or in combination with inhaled corticosteroids. Prostaglandin (PG)D(2), PGF(2alpha), 6-keto-PGF(1alpha), thromboxane B(2), leukotriene (LT)C(4) and LTB(4) levels and cell numbers were assessed in BAL fluid from 22 non-smoking asthmatic subjects. They were participating in a randomized, double-blind multicentre drug trial over a period of 2.5 years. Results of the group treated with inhaled corticosteroids (CS(+): beclomethasone 200 mug four times daily) were compared with the other group (CS(-)) which was treated with either ipratropium bromide (40 mug four times daily) or placebo. BAL LTC(4) levels of asthmatic subjects were significantly lower after 2.5 years inhaled corticosteroid therapy (CS(+), 9(1-17) pg/ml vs. CS(-), 16(6-53) pg/ml; p = 0.01). The same trend was observed for the PGD(2) levels. The results suggest that inhaled corticosteroids may exert their beneficial effect on lung function via a mechanism in which inhibition of LTC(4) synthesis in the airways is involved.     

Changes in airway resistance by simultaneous exposure to TNF-alpha and IL-1beta in perfused rat lungs

Tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta are formed simultaneously under inflammatory conditions such as asthma and acute respiratory distress syndrome. Here we investigated the effects of TNF-alpha (10 ng/ml) and/or IL-1beta (10 ng/ml) in isolated blood-free perfused rat lungs. In lungs precontracted with methacholine, IL-1beta alone and IL-1beta/TNF-alpha decreased airway resistance 10 min after administration, whereas TNF-alpha alone had no effect. In untreated lungs, airway resistance was unaltered by either cytokine alone but started to increase 40 min after treatment with both cytokines together, indicating bronchoconstriction. The bronchoconstriction was accompanied by a steroid-sensitive increase in cyclooxygenase (COX)-2 mRNA expression and thromboxane formation. The cytokine-induced bronchoconstriction was blocked by the thromboxane receptor antagonist SQ-29548, indomethacin, the selective COX-2 inhibitor NS-398, and the steroid dexamethasone. We conclude that IL-1beta has an early bronchodilatory effect (after 10 min) that is unchanged by TNF-alpha. However, at later time points (after 40 min), IL-1beta and TNF-alpha in concert cause a COX-2- and thromboxane-dependent bronchoconstriction. Our findings show that TNF-alpha and IL-1beta exert complex and time-dependent effects on lung functions that cannot be predicted by studying each cytokine alone.     

Stimulation of thromboxane release by extracellular UTP and ATP from perfused rat liver. Role of icosanoids in mediating the nucleotide responses

1. In isolated perfused rat liver, infusion of UTP (20 microM) led to a transient, about sevenfold stimulation of thromboxane release (determined as thromboxane B2), which did not parallel the time course of the UTP-induced stimulation of glucose release. An increased thromboxane release was also observed after infusion of ATP (20 microM). Although the maximal increase of portal pressure following ATP was much smaller than with UTP (4.2 vs 11.5 cm H2O), the peak thromboxane release was similar with both nucleotides. 2. Indomethacin (10 microM) inhibited the UTP-induced stimulation of thromboxane release and decreased the UTP-induced maximal increase of glucose output and of portal pressure by about 30%. The thromboxane A2 receptor antagonist BM 13.177 (20 microM) completely blocked the pressure and glucose response to the thromboxane A2 analogue U-46619 (200 nM) and decreased the ATP- and UTP-induced stimulation of glucose output by about 25%, whereas the maximal increase of portal pressure was inhibited by about 50% and 30%, respectively. BM 13.177 and indomethacin inhibited the initial nucleotide-induced overshoot of portal pressure increase, but had no effect on the steady-state pressure increase which is obtained about 5 min after addition of ATP or UTP. 3. The leukotriene D4/E4 receptor antagonist LY 171883 (50 microM) inhibited not only the glucose and pressure response of perfused rat liver to leukotriene D4, but also to leukotriene C4 by about 90%. This suggests that leukotriene D4 (not C4) is the active metabolite in perfused liver and the effects of leukotriene C4 are probably due to its rapid conversion to leukotriene D4. LY 171883 also inhibited the response to the thromboxane A2 analogue U-46619 by 75-80%, whereas the response of perfused liver to leukotriene C4 was not affected by the thromboxane receptor antagonist BM 13.177 (20 microM). The glucose and pressure responses of the liver to extracellular UTP were inhibited by LY 171883 and by BM 13.177 by about 30%. This suggests that the inhibitory action of LY 171883 was due to a thromboxane receptor antagonistic side-effect and that peptide leukotrienes do not play a major role in mediating the UTP response. 4. In isolated rat hepatocytes extracellular UTP (20 microM), ATP (20 microM), cyclic AMP (50 microM) and prostaglandin F2 alpha (3 microM) increased glycogen phosphorylase a activity by more than 100%.(ABSTRACT TRUNCATED AT 400 WORDS)