Does leukotriene C4 mediate hypoxic vasoconstriction in isolated ferret lungs?

To evaluate leukotriene (LT) C4 as a mediator of hypoxic pulmonary vasoconstriction, we examined the effects of FPL55712, a putative LT antagonist, and indomethacin, a cyclooxygenase inhibitor, on vasopressor responses to LTC4 and hypoxia (inspired O2 tension = 25 Torr) in isolated ferret lungs perfused with a constant flow (50 ml.kg-1.min-1). Pulmonary arterial injections of LTC4 caused dose-related increases in pulmonary arterial pressure during perfusion with physiological salt solution containing Ficoll (4 g/dl). FPL55712 caused concentration-related inhibition of the pressor response to LTC4 (0.6 micrograms). Although 10 micrograms/ml FPL55712 inhibited the LTC4 pressor response by 61%, it did not alter the response to hypoxia. At 100 microgram/ml, FPL55712 inhibited the responses to LTC4 and hypoxia by 73 and 71%, respectively, but also attenuated the vasoconstrictor responses to prostaglandin F2 alpha (78% at 8 micrograms), phenylephrine (68% at 100 micrograms), and KCl (51% at 40 mM). At 0.5 microgram/ml, indomethacin significantly attenuated the pressor response to arachidonic acid but did not alter responses to LTC4 or hypoxia. These results suggest that in isolated ferret lungs 1) the vasoconstrictor response to LTC4 did not depend on release of cyclooxygenase products and 2) LTC4 did not mediate hypoxic vasoconstriction.     

Binding of leukotriene C4 to rat lung fibroblasts and stimulation of collagen synthesis in vitro

Arachidonate metabolites are potent biological mediators affecting multiple cellular functions. Although prostaglandins of the E series, which are products of the cyclooxygenase pathway, have been known as inhibitors or down-regulators of fibroblast proliferation and collagen synthesis, the more recently discovered products of the 5-lipoxygenase pathway have not been as extensively investigated with regard to fibroblast function. In this study, a sulfidopeptide product of the lipoxygenase pathway, leukotriene C4 (LTC4), was examined for its ability to modulate rat lung fibroblast collagen synthesis and proliferation in vitro. The data revealed the ability of LTC4 and to a lesser extent leukotriene D4 (LTD4) to stimulate collagen synthesis in a dose-dependent (10(-11)-10(-8) M) manner without affecting cellular proliferation as determined by radiolabeled thymidine incorporation; 1 nM LTC4 caused an 85% (p less than 0.02) increase above untreated controls in [3H]proline incorporation into collagenous protein in the media, which was blocked by the putative leukotriene receptor antagonist FPL55712 (10 microM) and inhibited by cycloheximide and actinomycin D. This LTC4 stimulatory effect was slightly more specific for collagen synthesis vs noncollagenous protein synthesis but was not accompanied with any change in the collagen type composition. Binding of [3H]LTC4 to these cells was specific, reversible, and saturable, with a Kd of 1.8 +/- 0.95 nM. Under equilibrium conditions, there was an estimated 2.39 X 10(4) receptors per cell. This binding was also inhibited by 10 microM FPL55712. Competitive binding studies show specificity of this binding for LTC4 relative to LTD4 and FPL55712. Furthermore, no significant conversion of LTC4 to LTD4 or leukotriene E4 was noted during the binding studies.(ABSTRACT TRUNCATED AT 250 WORDS)     

Arachidonate lipoxygenase inhibitors in guinea-pig isolated trachea. Effects on contractions to antigen and various agonists

We compared the effects of the leukotriene (LT) D4 receptor antagonist FPL55712 and some lipoxygenase inhibitors on contractions of isolated guinea-pig trachea induced by antigen (ovalbumin, OA) and calcium ionophore A23187 in the presence of the cyclooxygenase inhibitor indomethacin (5 microM), and by arachidonic acid (AA), melittin and LTD4. FPL55712 (0.1 and 1 microM) inhibited contractions induced by AA (100 microM) and the phospholipase A2 activator melittin (3 micrograms/ml), while the lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA, 10 microM) was a more effective inhibitor of the melittin response than the AA response. FPL55712 inhibited contractions induced by OA (100 micrograms/ml) more than by A23187 (1 microgram/ml), and these inhibitory effects of FPL55712 were much less in the presence of l-serine-borate complex (45 mM), an inhibitor of LTC4 conversion to LTD4. NDGA (10 microM) had no significant effect on the OA response, whereas the lipoxygenase inhibitors 1-phenyl-3-pyrazolidone (phenidone, 10 microM) and 5,8,11,14-eicosatetraynoic acid (ETYA, 10 microM) clearly inhibited it. In contrast, NDGA and phenidone inhibited the A23187 response, but ETYA had no effect on it. FPL55712, phenidone and ETYA, but not NDGA, had a large inhibitory effect on LTD4-induced contractions, but these inhibitors had no effect on histamine-induced contractions. These results suggest that in the guinea-pig trachea inhibitors of LTD4-induced contractions decrease antigen-induced contractions, whereas lipoxygenase inhibitors reduce the contraction to A23187.     

Pharmacology of aerosol leukotriene C4- and D4-induced alteration of pulmonary mechanics in anesthetized cynomolgus monkeys

Aerosol administration of solutions of 900 micrograms/ml of leukotriene C4 (LT) or D4 to cynomolgus monkeys produced dose-dependent, equipotent increases in pulmonary resistance (Rp) and decreases in dynamic lung compliance (Cdyn). Time to peak response was, in part, related to dose and ranged from 4 to 20 min. Both LTC4 and LTD4 were less potent than histamine. Aerosol pretreatment with the cyclooxygenase inhibitor indomethacin had no significant effect on either LTC4 or LTD4 dose-response curves; however, at the highest doses of these agonists a notable, nonsignificant inhibition of effects on both Rp and Cdyn was seen. Intravenous dl-propranolol had no effect on responses to LTD4. Aerosol pretreatment with FPL 55712 significantly (P less than 0.05) inhibited airway responses to both LTC4 and D4. In contrast, an intravenous infusion of FPL 55712 failed to block the bronchospastic activity of LTD4. In conclusion, cynomolgus monkeys are responsive to aerosol administration of LTC4 and LTD4, and the pharmacology of their responses appears to resemble that of man.     

Actions of lipoxygenase metabolites in isolated rat lungs

Leukotrienes constrict smooth muscle and could be important for the regulation of the pulmonary circulation. We examined the production and action of lipoxygenase metabolites in isolated lungs, where we controlled the perfusing fluid used. Arachidonate injected into isolated rat lungs perfused with cell- and protein-free physiological salt solution caused a transient pressor response. Following indomethacin, arachidonate caused a delayed slow pressure rise followed by edema. The lung effluent contracted the guinea pig ileum. High-pressure liquid chromatography (HPLC) analysis of the perfusate demonstrated the presence of leukotrienes (LTC4 and LTD4). Diethylcarbamazine, a leukotriene synthesis inhibitor, prevented the slow pressure rise and edema seen after indomethacin plus arachidonate. In lungs perfused with cell- and protein-free physiological salt solution, LTC4, but not LTD4, caused a transient pressure rise followed by a sustained pressure rise. The sustained rise was abolished by a leukotriene-receptor blocker (FPL 55712) but not by indomethacin. In blood-perfused lungs, LTC4 caused only the transient pressure rise that was not blocked by FPL 55712. In lungs perfused with physiological salt solution containing albumin, LTC4 had no effect. We concluded that 1) perfused nonsensitized rat lungs produced LTC4 and LTD4; 2) LTC4 may be a major pulmonary vasoconstrictor; and 3) albumin binding limits the pressor effect of LTC4.     

Role of leukotriene C4 in pulmonary hypertension: platelet-activating factor vs. hypoxia

The aim of this study was to determine whether leukotriene C4 (LTC4) is a mediator of hypoxic pulmonary vasoconstriction. We hypothesized that similar increases in LTC4, detected in the lung parenchyma and pulmonary vascular compartment during cyclooxygenase blockade with indomethacin (INDO), would be observed during an equal increase in pulmonary arterial pressure caused by acute alveolar hypoxia (HYP, 100% N2) or platelet-activating factor (PAF, 10 micrograms into the pulmonary artery). Rat lungs were perfused at constant flow in vitro with an albumin-Krebs-Henseleit solution. Mean pulmonary arterial pressure (n = 6 per group) increased from a base line of 10.9 +/- 1.2 to 15.8 +/- 2.1 (HYP + INDO) and 15.5 +/- 1.9 (SE) Torr (PAF + INDO). LTC4 levels increased only in response to PAF + INDO; perfusate levels increased from 0.4 +/- 0.07 to 5.3 +/- 1.1 ng/40 ml, and lung parenchymal levels increased from 1.9 +/- 0.07 to 22.8 +/- 5.3 ng/lung. Diethylcarbamazine (lipoxygenase inhibitor) reduced PAF-induced lung parenchymal levels of LTC4 by 68% and pulmonary hypertension by 63%. We conclude that 1) LTC4 is not a mediator of hypoxic pulmonary vasoconstriction and 2) intravascular PAF is a potent stimulus for LTC4 production in the lung parenchyma.     

Arachidonate lipoxygenase inhibitors in guinea-pig isolated trachea. Effects on contractions to antigen and various agonists

We compared the effects of the leukotriene (LT) D₄ receptor antagonist FPL55712 and some lipoxygenase inhibitors on contractions of isolated guinea-pig trachea induced by antigen (ovalbumin, OA) and calcium ionophore A23187 in the presence of the cyclooxygenase inhibitor indomethacin (5 μM), and by arachidonic acid (AA), melittin and LTD₄. FPL55712 (0.1 and 1 μM) inhibited contractions induced by AA (100 μM) and the phospholipase A₂ activator melittin (3 μg/ml), while the lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA, 10 μM) was a more effective inhibitor of the melittin response than the response. FPL55712 inhibited contractions induced by OA (100 μg/ml) more than by A23187 (1 μg/ml), and these inhibitory effects of FPL55712 were much less in the presence of l-serine-borate complex (45 mM), an inhibitor of LTC₄ conversion to LTD₄. NDGA (10 μM) had no significant effect on the OA response, whereas the lipoxygenase inhibitors 1-phenyl-3-pyrazolidone (phenidone, 10 μM) and 5,8,11,14-eicosatetraynoic acid (ETYA, 10 μM) clearly inhibited it. In contrast, NDGA and phenidone inhibited the A23187 response, but ETYA had no effect on it. FPL55712, phenidone and ETYA, but not NDGA, had a large inhibitory effect on LTD₄-induced contractions, but these inhibitors had no effect on histamine-induced contractions. These results suggest that in the guinea-pig trachea inhibitors of LTD₄-induced contractions decrease antigen-induced contractions, whereas lipoxygenase inhibitors reduce the contraction to A23187.     

The role of leukotrienes in the late hemodynamic manifestations of group B streptococcal sepsis in piglets

In order to evaluate the role of leukotrienes in group B streptococcal (GBS) sepsis we studied the effect of a leukotriene receptor antagonist, FPL 57231, on the late hemodynamic changes occurring secondary to an infusion of live GBS. Paralyzed, mechanically ventilated piglets received a continuous intravenous infusion of bacteria (5 x 10(7) org/kg/min) while systemic arterial (Psa) and pulmonary artery pressures (Ppa) were measured. To separate the effects of the lipoxygenase products of arachidonic acid from those of the cyclooxygenase by-products, animals in control and treatment groups received indomethacin, a cyclooxygenase blocking agent, 15 min after the infusion of GBS was begun. In addition to GBS and indomethacin, treatment animals received a 30 min infusion of FPL 57231 starting 120 min after the bacterial infusion was begun. All study animals responded to bacteria within 15 min with marked elevation in pulmonary artery pressure (X +/- SD) (12 +/- 3 to 49 +/- 5 mmHg; p less than .01), and a decline in PaO2 (84 +/- 9 to 49 +/- 5 mmHg; p less than .01) and cardiac output (0.29 +/- 0.04 to 0.18 +/- .07 liter/min/kg; p less than .01). These changes were reversed by indomethacin. Subsequent values remained relatively stable until approximately 90 min when a gradual decrease in cardiac output (CO) and PaO2, and an increase in Ppa, and calculated systemic (SVR) and pulmonary (PVR) vascular resistances occurred. After the initial increase in TxB2 and 6-keto-PGF1 alpha, indomethacin treatment resulted in return of these values to baseline with no further increase throughout the study period.(ABSTRACT TRUNCATED AT 250 WORDS)     

Lipoxygenase and cyclooxygenase blockade by BW755C does not prevent the secondary phase of septic pulmonary hypertension

The infusion of Group B beta hemolytic streptococci (GBS) in newborn animals generates a dual phase pulmonary hypertensive response. The initial, acute phase responds to cyclooxygenase or thromboxane inhibition, and appears to be thromboxane mediated. The second phase is characterized by a more moderate rise in pulmonary vascular resistance, accompanied by an increase in microvascular permeability. It has been speculated that this phase may be leukotriene mediated. In an attempt to clarify this, we have studied and compared the effects of the thromboxane synthetase inhibitor, Dazmegrel (DAZ), and the combined cyclooxygenase/lipoxygenase inhibitor, BW755C, on the cardiopulmonary hemodynamics of the secondary phase of GBS induced pulmonary hypertension in newborn piglets. Ten piglets were infused with GBS, and all animals developed a significant increase in pulmonary artery pressure (to 39 +/- 5 and 36 +/- 5 mmHg for DAZ and BW755C animals respectively). After one hour of GBS, either DAZ or BW755C was administered. Data were collected for another two hours following drug administration. GBS infusion was continued throughout. Both DAZ and BW755C were associated with transient, acute reductions in pulmonary artery pressure (to 22 +/- 5 and 22 +/- 8 mmHg, respectively). However, after 60 minutes, PAP again began to rise in both groups (PAP 30 +/- 5 and 30 +/- 11 mmHg respectively by 240 minutes). There were no differences between the groups at any time. These data do not support a significant role for lipoxygenase products in mediating the secondary phase of septic pulmonary hypertension.     

Placental vascular responses to leukotriene receptor antagonist FPL 55712

We have previously shown that FPL 55712, a specific leukotriene receptor antagonist, potentiates estrogen induced uterine hyperemia in nonpregnant rabbits. We therefore chose to investigate the vascular responses of pregnant rabbits to leukotriene blockade. Nine unanesthetized animals carrying 46 viable fetuses were used in this study. Regional blood flows were measured by the radioactive microsphere technique. In 5 rabbits control blood flows were measured after vehicle administration and FPL 55712, 1 mg/kg bolus, followed by infusion of 100 micrograms/kg/min was given via the jugular vein. Regional blood flows were measured again after 10 minutes of infusion. The procedural order was reversed in the remaining 4 animals. Resistance was calculated as mean arterial pressure divided by total flow to an organ. FPL 55712 decreased the blood pressure from 83 +/- 2 to 76 +/- 3 mmHg (P less than .001). Uterine resistance was not significantly changed (387 +/- 44 to 362 +/- 42 mmHg X ml-1 X min X gm), but renal resistance fell from 18.5 +/- 1.1 to 15.1 +/- 1.2 mmHg X ml-1 X min X gm (P less than .01). FPL 55712 induced maternal placental vasodilatation with resistance decreasing from 291 +/- 33 to 261 +/- 31 mmHg X ml-1 X min X gm (P less than .04). Vehicle administration did not cause dilation in any vascular bed. FPL 55712 appears to be a placental vasodilator whose action is most likely due to receptor blockade of the vasoconstrictive endogenous leukotrienes.     

Differential activity of leukotrienes upon human pulmonary vein and artery

Responses to leukotrienes B4, C4, D4 and E4 were examined in human pulmonary artery and pulmonary vein preparations from surgical specimens. Leukotrienes C4 (LTC) and D4 (LTD) were potent contractants of pulmonary vein over the dose range of 10(-10) M to 10(-6) M, whereas they produced minimal contractions of human pulmonary artery only at concentrations of 10(-8) M or greater. Leukotriene E4 was less potent than LTC or LTD, and leukotriene B4 (LTB) at concentrations up to 10(-6) M had no effect upon either pulmonary veins or pulmonary arteries. Contractions of pulmonary vein by LTD were inhibited in a competitive manner by FPL 55712. Dose response characteristics of LTD and inhibition by FPL 55712 were similar for pulmonary venous and bronchial smooth muscle. We conclude that pulmonary vein smooth muscle has leukotriene receptors comparable to those of bronchial smooth muscle whereas pulmonary artery does not.     

Leukotrienes C4, D4, and E4 in fetal lamb tracheal fluid

Previously, we demonstrated that either putative leukotriene receptor antagonists or a synthesis inhibitor markedly decreased pulmonary vascular resistance in the near-term fetal lamb and concluded that leukotrienes may play a role in maintaining the high pulmonary vascular resistance in the fetus. To further investigate the role of leukotrienes, we measured concentrations of leukotriene (LT) C4, LTD4, and LTE4 in 17 tracheal fluid samples from 8 of 9 near-term (129-139 days, term = 145 days), chronically-catheterized, fetal lambs during normoxia to evaluate their possible role in regulating resting tone and in seven of the nine before and during hypoxia to evaluate their possible role in hypoxic vasoconstriction. The tracheal fluid samples collected by gravity over 1-3 min, on ice, were immediately treated with cold ethanol, centrifuged, and the supernatant covered with N2 and stored in a -70 degrees C freezer for a maximum of 3 weeks. Purification and separation of leukotrienes was done by reverse-phase high performance liquid chromatography using a gradient elution method, and fractions corresponding to LTC4, LTD4, and LTE4 standards were quantified immediately by radioimmunoassay. During normoxia (descending aortic PaO2 2.9 +/- 0.3 kPa [21.5 +/- 2.5 mmHg]; mean +/- SD), all 3 leukotrienes were detected in 16 of the 17 samples: LTC4 29 +/- 28 pg/ml (range 0-119 pg/ml); LTD4 66 +/- 51 pg/ml (range 9-177 pg/ml); and LTE4 43 +/- 50 pg/ml (range 0-204 pg/ml).(ABSTRACT TRUNCATED AT 250 WORDS)     

The effects of platelet-activating factor on flow rate and eicosanoid release in the isolated perfused rat gastric vascular bed

In the isolated rat stomach perfused via the vasculature in situ under constant pressure bolus injections of platelet-activating factor (PAF, 3, 16, or 50 ng) induced dose-dependent, long-lasting reductions of flow rates and simultaneously significant increases in the release of cysteinyl-leukotrienes (cys-LT), thromboxane (TX) B2 and 6-keto-prostaglandin (PG) F1 alpha. Reversed phase high pressure liquid chromatography demonstrated the release of a mixture of comparable amounts of LTC4, LTD4 and LTE4 by PAF. Inhibition of cys-LT synthesis by the lipoxygenase inhibitors nordihydroguaiaretic acid (NDGA) and L-651,896 did not significantly affect PAF-induced flow reduction indicating that endogenous cys-LT are of minor importance for the PAF effect on gastric vascular flow. This conclusion is supported by the fact that the cys-LT receptor antagonist FPL 55712 in a concentration (1 x 10(-6) M) that completely antagonized gastric flow reduction by exogenous LTC4 (1 x 10(-7) M) had no effect on the PAF-induced reduction of flow. The cyclooxygenase inhibitor indomethacin aggravated the PAF-induced flow reduction suggesting that the endogenous vasodilator PGI2 might act as a functional PAF antagonist in the rat gastric vascular bed. In contrast to FPL 55712 the PAF antagonist BN 52021 significantly and concentration-dependently antagonized the PAF effect on gastric vascular flow. The results demonstrate that PAF and LTC4 induce flow reductions in the rat gastric vascular bed by activating different receptors and that endogenous eicosanoids released by PAF do not contribute significantly to the PAF effect on gastric vascular flow.     

Increased leukotriene C4 in ethchlorvynol-induced acute lung injury in dogs

We investigated whether ethchlorvynol (ECV)-induced acute lung injury (ALI) is associated with an increase in leukotriene C4 (LTC4) production. In six pentobarbital sodium-anesthetized dogs, ECV (15 mg/kg iv) introduced into the pulmonary circulation resulted in a 164 +/- 31% increase in extravascular lung water 120 min after ECV administration. Concomitantly, the mean (+/- SE) concentration of LTC4 in arterial plasma measured by radioimmunoassay following 80% EtOH precipitation, XAD-7 extraction and high-pressure liquid chromatography purification was 5.0 +/- 1.3 pg/ml, unchanged from control (pre-ECV) values. In contrast, in pulmonary edema fluid 120 min post-ECV, the LTC4 concentration was 35.2 +/- 10.8 pg/ml, sevenfold greater than those values found in the arterial plasma (P less than 0.01). In six additional dogs, 120 min after unilateral ALI had been induced with ECV (9 mg/kg iv), LTC4 in the bronchoalveolar lavage (BAL) of the uninjured lung was 12.1 +/- 1.5 pg/ml, unchanged from pre-ECV values, whereas, LTC4 in the BAL of the injured lung increased from a control value of 10.2 +/- 1.6 to 24.2 +/- 3.5 pg/ml (P less than 0.01) 120 min after ECV administration. These results demonstrate that, in ECV-induced acute lung injury, LTC4 concentrations in pulmonary edema fluid are considerably greater than those found in arterial plasma in the case of bilateral acute lung injury and significantly greater in the BAL of the injured lung compared with the uninjured lung in the case of unilateral acute lung injury. The results are a necessary first step in support of the hypothesis that leukotrienes participate in the altered permeability of ECV-induced acute lung injury.     

Comparative study of the pulmonary effects of intravenous leukotrienes and other bronchoconstrictors in anaesthetized guinea pigs

Pulmonary responses to intravenous leukotrienes C4, D4 and E4 administered as a bolus injection and by continuous infusion were studied in anesthetized guinea pigs. LTD4, LTC4 and LTE4 (respective ED50 of 0.21 +/- .1, 0.64 +/- .2 and 2.0 +/- .1 microgram kg-1) produced dose-dependent increases in insufflation pressure when given as a bolus injection to anesthetized guinea pigs (Konzett-R?ssler). Bronchoconstriction was antagonized by FPL-55712 (50-200 micrograms kg-1), and indomethacin (50-200 micrograms kg-1) but was not significantly altered by mepyramine (1.0 mg kg-1), methysergide (0.1 mg kg-1), intal (10 mg kg-1) mepacrine (5 mg kg-1) or dexamethasone (10 mg kg-1). The beta adrenoceptor blocker, timolol (5 micrograms kg-1) produced a significantly greater potentiation of the responses to the leukotrienes than to arachidonic acid, histamine and acetylcholine. Responses to bolus injection of LTE4 but not LTD4 or LTC4 were partially antagonized by atropine (100 micrograms kg-1) and bilateral vagotomy. In experiments of a different design, continuous infusion of LTD4 and LTE4 (2.8-3.2 micrograms kg-1 min-1) into indomethacin-treated animals produced slowly developing increases in pulmonary resistance and decreases in compliance. The increase in resistance produced by LTE4 and LTD4 was partly reversed by intravenous FPL-55712 (1.0 mg kg-1) and atropine (100 micrograms kg-1) but was almost completely reversed by FPL-55712 (3 - 10 mg kg-1). These findings indicate that leukotrienes can produce bronchoconstriction in guinea pigs through cyclooxygenase-dependent and cyclooxygenase independent mechanisms both of which are blocked by FPL-55712. Cholinergic mechanisms are involved in the mediation of part of the response to bolus injection of LTE4 as well as a small part of the initial response to continuous infusion of LTD4 and LTE4. Intrinsic beta adrenoceptor activation serves to down modulate responses to the leukotrienes to a greater extent than responses to arachidonic acid, histamine and acetylcholine.     

Pharmacology of peptide leukotrienes on ferret isolated airway smooth muscle

The contractile activities of peptide leukotrienes (LT) on isolated spiral strips of ferret trachea were characterized pharmacologically. LTC4 and LTD4 contracted ferret tracheal strips in a concentration-related manner and were 3- to 8-fold more potent than carbachol. In contrast, high concentrations of LTE4 evoked either weak contractions or none at all, whereas LTC4 and D4 were partial agonists compared to carbachol. In tissues which were unresponsive to LTE4, this compound antagonized contractile responses to LTC4 and D4 in an apparently competitive manner: Carbachol-induced contractions were not altered by LTE4. The cyclooxygenase inhibitor, indomethacin (5 microM), LT antagonist, FPL55712 (10 microM), atropine (1 microM), phenoxybenzamine (10 microM), and LTB4 (10 microM) failed to alter LTC4 and D4 concentration-response curves. The results indicate that ferret trachea is sensitive to the contractile activity of LTC4 and LTD4 but not LTE4. The LT-induced contractions appear to be mediated by a direct action of the LT rather than indirectly through release of secondary mediators such as thromboxane, prostaglandin, or acetylcholine. LT receptors in ferret trachea are insensitive to FPL55712 but are antagonized by LTE4.     

Contraction of isolated airway smooth muscle by synthetic leukotrienes C4 and D4

The pharmacology of leukotrienes (LT) C4 and D4 in isolated airway smooth muscle was investigated. In rat trachea, neither LTC4 or D4 elicited a response. In contrast, LTC4 was a potent contractile agonist in guinea-pig trachea, bronchus and parenchymal lung strip. Similar effects were obtained with LTD4 in trachea and parenchyma. In trachea and bronchus, the concentration-response curve to LTC4 was biphasic: indomethacin converted the biphasic response curve to a simple sigmoidal shape and enhanced the maximum contractile response. The SRS-A antagonist FPL 55712 antagonized the effect of LTD4 in both trachea and parenchyma. As regards LTC4-induced contraction of trachea and bronchus, FPL 55712, depending on concentration, either antagonized, or antagonized and enhanced the maximum contractile response. The enhancement of the maximum contractile response by FPL 55712 was not apparent when indomethacin was present. FPL 55712 failed to antagonize the effect of LTC4 in parenchyma.     

Hyperbaric oxygen toxicity: role of thromboxane.

Exposing rabbits for 1 h to 100% O2 at 4 atm barometric pressure markedly increases the concentration of thromboxane B2 in alveolar lavage fluid [1,809 +/- 92 vs. 99 +/- 24 (SE) pg/ml, P less than 0.001], pulmonary arterial pressure (110 +/- 17 vs. 10 +/- 1 mmHg, P less than 0.001), lung weight gain (14.6 +/- 3.7 vs. 0.6 +/- 0.4 g/20 min, P less than 0.01), and transfer rates for aerosolized 99mTc-labeled diethylenetriamine pentaacetate (500 mol wt; 40 +/- 14 vs. 3 +/- 1 x 10(-3)/min, P less than 0.01) and fluorescein isothiocyanate-labeled dextran (7,000 mol wt; 10 +/- 3 vs. 1 +/- 1 x 10(-4)/min, P less than 0.01). Pretreatment with the antioxidant butylated hydroxyanisole (BHA) entirely prevents the pulmonary hypertension and lung injury. In addition, BHA blocks the increase in alveolar thromboxane B2 caused by hyperbaric O2 (10 and 45 pg/ml lavage fluid, n = 2). Combined therapy with polyethylene glycol- (PEG) conjugated superoxide dismutase (SOD) and PEG-catalase also completely eliminates the pulmonary hypertension, pulmonary edema, and increase in transfer rate for the aerosolized compounds. In contrast, combined treatment with unconjugated SOD and catalase does not reduce the pulmonary damage. Because of the striking increase in pulmonary arterial pressure to greater than 100 mmHg, we tested the hypothesis that thromboxane causes the hypertension and thus contributes to the lung injury. Indomethacin and UK 37,248-01 (4-[2-(1H-imidazol-1-yl)-ethoxy]benzoic acid hydrochloride, an inhibitor of thromboxane synthase, completely eliminate the pulmonary hypertension and edema.(ABSTRACT TRUNCATED AT 250 WORDS)     

Lecithins enhance leukotriene production from white cells

36 x 10(7) WBC were isolated from 120 ml heparinized venous blood by 5% dextran T-500 sedimentation. 20 mg egg lecithin and 20 mg dipalmitoyl lecithin were respectively pretreated in 2 ml 0.15 M Tris buffer by vibration and sonication. WBC were incubated with the pretreated lecithins for 20 min. Leukotrienes (LTs) were identified by HPLC and bioassay, and quantified with an RIA Kit. Crude incubation medium of both lecithin groups caused guinea pig ileum contractions which were antagonized with FPL55712. Incubation media were partially purified with Bond elut C18. Purified samples of both lecithin groups showed LTC4 and LTD4 peaks on HPLC. LTC4 production (pg/10(7) WBC, M +/- SD) was 194.5 +/- 61.7 (n = 5) in control group, 348.9 +/- 95.4 (n = 6) in dipalmitoyl lecithin group, 543.8 +/- 105.6 (n = 6) in egg lecithin group and 105.62 +/- 63.2 (n = 6) in AA-861 + dipalmitoyl lecithin group. LTC4 production of both lecithin groups was significantly higher than that of control group (P less than 0.01 in dipalmitoyl lecithin group and P less than 0.001 in egg lecithin group). Both egg lecithin and dipalmitoyl lecithin enhanced LT production from WBC. LT production was suppressed in the presence of AA-861. The mechanism of the enhancement in LT production is unclear, but these lecithins are apparently not substrates because dipalmitoyl lecithin contains no arachidonic acid.     

Cyclooxygenase pathway mediates lung injury induced by phorbol and platelets

The role of platelets in lung injury has not been well defined. In the present study of isolated perfused rat lungs, phorbol myristate acetate (PMA; 0.15 microgram/ml) or platelets (6.7 X 10(4)/ml) alone did not discernibly change the pulmonary arterial pressure (PAP) or lung weight (LW). However, the combination of platelets and PMA drastically increased the PAP and LW (delta PAP 26.2 +/- 1.0 mmHg, delta LW 2.7 +/- 0.4 g). delta PAP was positively correlated with the increase in thromboxane B2 produced by infusion of platelets and PMA (thromboxane B2 = 35.6 + 0.97 delta PAP, r = 0.67, P less than 0.01). The hypertension and edema formation induced by PMA and platelets were strongly attenuated by indomethacin, an inhibitor of platelet cyclooxygenase (delta PAP 5.6 +/- 2.0 mmHg, P less than 0.001; delta LW 0.0 +/- 0.1 g, P less than 0.001), and by imidazole, an inhibitor of thromboxane A2 synthase (PAP 8.0 +/- 2.5 mmHg, P less than 0.001; LW 0.0 +/- 0.3 g, P less than 0.01). Inactivation of platelet lipoxygenase with nordihydroguaiaretic acid mildly depressed pulmonary pressure but did not affect delta LW (delta PAP 18.9 +/- 1.6 mmHg, P less than 0.05; delta LW 3.1 +/- 0.3 g, P greater than 0.05). In vitro experiments showed that the capacity of platelets to release oxygen radicals was only 2.6% of that found for granulocytes. These results suggest that platelets may be activated by PMA to increase PAP and vascular permeability.(ABSTRACT TRUNCATED AT 250 WORDS)