Leukotrienes stimulate phosphatidylcholine secretion in cultured type II pneumocytes

We previously reported that arachidonic acid stimulates secretion of phosphatidylcholine in cultures of type II pneumocytes and, based on studies with cyclooxygenase and lipoxygenase inhibitors, suggested that this effect was mediated by lipoxygenase products of arachidonic acid metabolism (Gilfillan, A.M. and Rooney, S.A. (1985) Biochim. Biophys. Acta 833, 336-341). We have now examined the effect of leukotrienes on phosphatidylcholine secretion in type II cells as well as the effect of a leukotriene antagonist, FPL55712, on the stimulatory effect of arachidonic acid. Leukotrienes C4, D4 and E4 stimulated phosphatidylcholine secretion and this effect was dependent on concentration in the range 10(-12)-10(-6) M. Leukotriene E4 was the most stimulatory, followed by D4 and C4. Leukotriene B4 had no effect. Incubation of the cells with 10(-7) M leukotriene E4 for 90 min resulted in a 107% increase in the rate of phosphatidylcholine secretion. Incubation with 10(-6) M leukotrienes D4 and C4 for the same period resulted in 81% and 63% stimulation, respectively. The leukotrienes had no effect on cellular phosphatidylcholine synthesis or on lactate dehydrogenase release. The stimulatory effects of leukotrienes E4 and D4 were abolished by FPL55712. Similarly, the stimulatory effect of 6 X 10(-6) M arachidonic acid on phosphatidylcholine secretion was reduced from 74% to 25% by 10(-5) M FPL55712. Thus, the stimulatory effect of arachidonic acid on surfactant phospholipid secretion in type II cells is mediated at least in part by leukotrienes.     

Antagonism by ETYA of the effects of leukotrienes on ileum and lung parenchymal strips independent of effects on arachidonic acid metabolism

5,8,11,14-Eicosatetraynoic acid (ETYA), a compound which inhibits both the cyclooxygenase and lipoxygenase pathways of arachidonic acid metabolism, antagonized the contraction of segments of guinea-pig ileal longitudinal muscle produced by SRS-A (IC₅₀ = 2.73 μM). This activity was unaffected by pretreatment of the tissues with 10 μM indomethacin. Phenidone, another mixed cyclooxgenese-lipoxygenese inhibitor, was inactive. FPL-55712, an SRS-A antagonist, was a very potent inhibitor (IC₅₀ = 0.011 μM).BW755C and NDGA nonselectively inhibited the contractions of the guinea-pig ileal longitudinal muscle induced by SRS-A or histamine.ETYA antagonized the contraction of the guinea-pig ileal strip produced by 6 nM synthetic LTC₄ (IC₅₀ = 9.3 μM). FPL-55712 demonstrated an IC₅₀ of 0.3 μM in a similar series of experiments. ETYA, 1, 3 or 10 μM did not inhibit the contractions elicited by 0.5 μM of histamine.This was not a tissue-selective effect since 100 μM ETYA antagonized the LTC₄-induced contraction of the guinea-pig lung parenchymal strip preparation.These data demonstrate that ETYA antagonized the contractile effect of the leukotrienes on tissues from the gastrointestinal tract and lung. Furthermore, the inability of indomethacin or phenidone to inhibit the contractile response suggests that antagonism by ETYA may occur by a mechanism independent of cyclooxygenase and lipoxygenase enzymes.     

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.     

A formyl peptide contracts guinea pig lung: role of arachidonic acid metabolites

We studied the role of cyclooxygenase and lipoxygenase products of arachidonic acid metabolism in mediating N-formyl-methionyl-leucyl-phenylalanine- (FMLP) induced contractions of guinea pig lung parenchymal strips. The cyclooxygenase inhibitors indomethacin (10(-5) M) and aspirin (3 X 10(-5) to 10(-4) M), the lipoxygenase inhibitor nordihydroguaiaretic acid (10(-5) to 3 X 10(-5) M), and the combined cyclooxygenase/lipoxygenase inhibitors 1-phenyl-3-pyrazolidinone (Phenidone) (3 X 10(-5) to 3 X 10(-4) M) and BW 755C (10(-5) to 10(-4) M) each caused a decrease in the maximum force induced by FMLP (Fmax) and an increase in the concentration of FMLP required to produce 50% of Fmax (EC50). The thromboxane synthesis inhibitor imidazole (3 X 10(-3) M) also decreased Fmax. The leukotriene D4 receptor antagonist FPL 55712 (5.7 X 10(-6) to 1.9 X 10(-5) M) increased the EC50 for FMLP, whereas desensitization of lung parenchymal strips to leukotriene B4 by pretreatment with this leukotriene (10(-7) M) had no effect on FMLP-induced contraction. After exposure to FMLP (10(-6) M), guinea pig lung produced (as determined by high-performance liquid chromatography and radioimmunoassay) leukotrienes C4 and B4, thromboxane A2 (as measured by its stable degradation product thromboxane B2), and prostaglandin F2 alpha. Lung strips not exposed to FMLP showed no evidence of leukotriene production. We conclude that thromboxane A2 and leukotriene C4 generated in response to FMLP mediate a substantial fraction of the force induced by this peptide in guinea pig lung parenchymal strips.     

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.     

Effects of cyclo- and lipoxygenase inhibitors on hypoxic vasoconstriction in isolated ferret lungs

To evaluate the role of leukotrienes in hypoxic pulmonary vasoconstriction, we measured steady-state pressor responses to graded hypoxia in isolated ferret lungs perfused with autologous blood containing 0.001, 0.03, 1, or 3 mM nordihydroguaiaretic acid (NDGA), 1 mM BW 755C, or 0.02-0.05 mM indomethacin. Untreated lungs served as controls. Perfusate concentrations of thromboxane B2 and 6-ketoprostaglandin F1 alpha, measured by radioimmunoassay, were markedly reduced in all treated lungs, indicating inhibition of cyclooxygenase. The maximum pressor response to hypoxia measured at a blood flow of 50 ml.min-1. kg-1 averaged 26.6 +/- 2.4 Torr in untreated lungs and was not affected by BW 755C or 0.001-0.03 mM NDGA. Because BW 755C and NDGA inhibited cyclooxygenase at concentrations that did not affect hypoxic vasoconstriction and because both agents are thought to inhibit lipoxygenase with a potency greater than or equal to that with which they inhibit cyclooxygenase, these results do not support the possibility that hypoxic pulmonary vasoconstriction was mediated by leukotrienes. At concentrations of 1 and 3 mM, NDGA inhibited the maximum hypoxic pressor response by 57 and 95%, respectively. The mechanism of this attenuation is unknown; however, it was apparently not due to cyclooxygenase inhibition, since indomethacin enhanced the maximum hypoxic pressor response by 45%. Nor was it due to blockade of calcium entry or interference with the contractile process in pulmonary vascular smooth muscle, since 1 mM NDGA did not inhibit vasoconstrictor responses to KCl or prostaglandin F2 alpha.     

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.     

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.     

Prostaglandin F2 stimulates the generation of lipoxygenase products in guinea pig isolated trachea

The generation of lipoxygenase products on the contraction elicited by prostaglandin (PG) F2 alpha was investigated in the guinea-pig isolated trachea. Indomethacin (5 x 10(-6) M) inhibited the response at low concentrations of PGF2 alpha while enhanced the response at higher concentrations of PGF2 alpha. Phenidone (10(-4) M) and nordihydroguaiaretic acid (NDGA, 3 x 10(-5) M) appeared to inhibit the PGF2 alpha response. The PGF2 alpha response augmented by indomethacin was dose-dependently inhibited by NDGA and a leukotriene (LT) antagonist, FPL55712. NDGA had no effect on the contraction elicited by histamine but markedly inhibited the contraction elicited by LTD4. The inhibition by NDGA of the LTD4-induced contraction was abolished in the presence of indomethacin (5 x 10(-6) M). FPL55712 inhibited the LTD4-induced contraction but the extent of the antagonism was not changed by indomethacin. In the presence of indomethacin PGF2 alpha (10(-8) M) did not affect the LTD4 (3 x 10(-9) M) response but significantly enhanced the arachidonic acid (AA, 6.6 x 10(-5) M)-induced contraction. FPL55712 (3 x 10(-6) M) completely inhibited the AA response augmented by PGF2 alpha. These results suggest that lipoxygenase-mediated LT-like substances are released in the response at higher concentrations of PGF2 alpha on the guinea-pig isolated trachea, and the mode of action of PGF2 alpha is different from those of histamine and LTD4.     

Inhibition by Salicylhydroxamic Acid, BW755C, Eicosatetraynoic Acid, and Disulfiram of Hypersensitive Resistance Elicited by Arachidonic Acid or Poly-l-Lysine in Potato Tuber

The hypothesis that arachidonic acid (AA) induction of sesquiterpene accumulation and browning in potato (Solanum tuberosum) is mediated by a lipoxygenase metabolite of AA was tested using lipoxygenase inhibitors. Salicylhydroxamic acid (SHAM) and 3-amino-1-(3-trifluoromethylphenyl)-2-pyrazoline hydrochloride (BW755C) delayed the response to AA. Inhibition by eicosatetraynoic acid (ETYA) was more persistent. These results are consistent with previous reports that SHAM and BW755C are reversible inhibitors of lipoxygenase and easily oxidized by potato while ETYA acts as an irreversible inhibitor. Disulfiram (tetraethylthiuram disulfide) also inhibited AA elicitor activity. SHAM was most effective if applied at the time of AA treatment, having no effect if applied 6 hours afterward. SHAM was effective in the presence of MES or MOPS buffers but not in acetate-buffered or unbuffered solutions; neither BW755C nor ETYA exhibited this restriction. However, SHAM, BW755C, and ETYA also were inhibitors of browning and sesquiterpene accumulation elicited in potato by poly-l-lysine, which, unlike AA, is not a lipoxygenase substrate. SHAM effectiveness also was restricted to 6 hours after treatment with poly-l-lysine. While the results with AA support a role for lipoxygenase, those with poly-l-lysine may be evidence that these compounds are having other effects in potato tissue.     

Glucose-stimulated protein phosphorylation in the pancreatic islet

The effect of inhibitors of the cyclo-oxygenase and lipoxygenase pathways of arachidonic acid metabolism on steroidogenesis in rat testis Leydig cells and rat tumour Leydig cells has been investigated. In the presence of nordihydroguaiaretic acid [NDGA; 4,4'-(2,3- dimethylbutan -1,4- diyl )bis[1,2- benzendiol ]], 5,8,11,14-eicosatetraynoic acid (ETYA), BW 755C [3-amino-1-[3-(trifluoromethyl)phenyl]-2-pyrazoline hydrochloride] and benoxaprofen [ Opren ; 2-(2-p-chlorophenyl- benzoxazol -5-yl)propionic acid)] (which inhibit lipoxygenase activity), but not indomethacin and aspirin (which inhibit cyclo-oxygenase activity), a dose-related inhibition of lutropin (LH)-stimulated testosterone and pregnenolone production was obtained (ID50 values of 2.5, 30, 25 and 30 microM for NDGA, ETYA, BW 755C and benoxaprofen were obtained, respectively). BW 755C and benoxaprofen had no significant effect on LH-stimulated cyclic AMP production except at the highest concentrations examined (330 and 380 microM, respectively), whereas NDGA and ETYA inhibited LH-stimulated cyclic AMP production in a dose-dependent manner (ID50 7.0 and 22 microM respectively). However, NDGA and ETYA also caused a dose-dependent inhibition of dibutyryl cyclic AMP-stimulated testosterone and pregnenolone production. The metabolism of exogenous ( 22R )-hydroxycholesterol or pregnenolone to testosterone by Leydig cells was not inhibited by either NDGA, ETYA or indomethacin. At low concentrations of NDGA and ETYA a significant increase in the conversion of both pregnenolone and ( 22R )-hydroxycholesterol to testosterone was obtained. Studies in which the metabolism of [14C]arachidonic acid by purified rat tumour Leydig cells was investigated indicate that products are formed by tumour Leydig cells that have similar mobilities in a thin layer chromatography system to 5-L-hydroxy-6,8,11,14-eicosatetraenoic acid, 12-L-hydroxy-5,8,10,14-eicosatetraenoic acid and leukotriene B4. The formation of these products was inhibited to varying degrees by NDGA, BW 755C and benoxaprofen but not by aspirin and indomethacin. These studies demonstrate for the first time that inhibition of lipoxygenase activity but not cyclo-oxygenase activity causes an inhibition of LH- and dibutyryl cyclic AMP-stimulated steroid production and suggest a stimulatory role for products of the lipoxygenase pathway of arachidonic acid metabolism in steroidogenesis. The site of this stimulation is apparently distal to the production of cyclic AMP and before the side chain cleavage of cholesterol.     

Endothelin is a potent constrictor of the lamb ductus arteriosus

Endothelin was tested on isolated ductus arteriosus preparations from mature fetal lambs. At low PO2 (18-24 Torr; 1 Torr = 133.3 Pa), the compound constricted the vessel dose-dependently over the range from about 10(-10) to 10(-7) M. The contraction was sustained and did not subside even after an extended period of washing. Endothelin was also effective on tissues (PO2,217-231 Torr; indomethacin, 2.8 X 10(-6) M) that had been completely relaxed with CO (CO/O2 ratio, 0.28). CO treatment interferes with a cytochrome P-450 mechanism, which is considered crucial for the contractile response of the vessel to oxygen. These findings are consistent with a role of endothelin in the closure of the ductus arteriosus at birth.     

Lipoxygenase and cyclooxygenase blockade by BW 755C enhances pulmonary hypoxic vasoconstriction

Lipoxygenase products (leukotrienes) have been proposed as the mediators of pulmonary hypoxic vasoconstriction. However, the supporting data are inconclusive because the lipoxygenase and leukotriene receptor blockers that reduce hypoxic vasoconstriction (such as diethylcarbamazine and the FPL's) have confounding effects. We investigated BW 755C, a potent inhibitor of both lipoxygenase and cyclooxygenase, in eight intact anesthetized dogs with acute left lower lobe atelectasis. We examined two manifestations of hypoxic vasoconstriction: shunt fraction, as an inverse indicator of regional constriction in response to local hypoxia, and the pulmonary pressor response to global alveolar hypoxia, as an index of general hypoxic vasoconstriction. During normoxia, shunt fraction, measured using a sulfur hexafluoride infusion, was 32.0 +/- 7.0%. The pulmonary pressor response to hypoxia, defined as the increase in pulmonary end-diastolic gradient produced by 10% O2 inhalation, averaged 4.5 +/- 1.8 mmHg. Then, during normoxia, BW 755C was administered. Shunt fraction fell in all eight dogs from the previous mean of 32% to 25.5 +/- 6.1% (t = 6.5, P less than 0.0005). The hypoxic pressor response rose in all dogs, from the previous 4.5 mmHg to 9.0 +/- 3.5 mmHg (t = 4.5, P less than 0.005). BW 755C enhances hypoxic vasoconstriction, an effect consistent with its activity as a cyclooxygenase inhibitor. These data do not support a substantive role for the lipoxygenase pathway in hypoxic vasoconstriction.     

Leukotriene and anti-IgE induced contractions of human isolated trachea: studies with leukotriene receptor antagonists and a novel 5-lipoxygenase inhibitor

The pharmacological actions of three leukotriene D4 (LTD4) receptor antagonists, FPL-55712, L-648,051, and L-649,923, and a novel inhibitor of leukotriene biosynthesis, L-651,896, have been investigated on isolated human tracheal smooth muscle. In the order of potency L-648,051 greater than FPL-55712 greater than L-649,923, these agents antagonized contractions to LTD4 and produced parallel rightward shifts in the dose-response curves. Mean -log KB values against LTD4 were 6.9 +/- 0.1, 6.5 +/- 0.3, and 6.0 +/- 0.1 for L-648,051, FPL-55712, and L-649,923, respectively. FPL-55712 also antagonized contractions to LTC4 (-log KB value, 6.4 +/- 0.3) and this activity was not decreased by the gamma-glutamyl transpeptidase inhibitor, L-serine borate. In the presence of 1 x 10(-7) M atropine, 7 x 10(-6) M mepyramine, and 1.4 x 10(-6) M indomethacin, L-648,051 at 2 x 10(-5) and 2 x 10(-6) M produced complete and partial blockade, respectively, of the contraction to goat anti-IgE. L-649,923 and FPL-55712 produced partial but significant inhibition at 2 x 10(-5) M, whereas the 5-lipoxygenase inhibitor, L-651,896, produced almost complete inhibition at 3.5 and 35 x 10(-6) M. L-Serine borate (15 mM) did not alter the the activity of FPL-55712 versus anti-IgE. These findings indicate that LTD4 receptors mediate contraction of human trachea to exogenously applied and endogenously (anti-IgE) released leukotrienes. LTD4 antagonists, such as L-648,051, may be useful in assessing the role of leukotrienes in respiratory disease.     

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.     

Binding sites for 3H-LTC4 in membranes from guinea pig ileal longitudinal muscle

Leutriene (LTC4) is one of the components of Slow Reacting Substance of Anaphylaxis (SRS-A) and is a potent constrictor of guinea pig ilea. The contraction is likely to be a receptor-mediated process. Here we report the existence of specific binding sites for 3H-LTC4 in a crude membrane preparation from guinea pig ileal longitudinal muscle. At 4 degrees C in the presence of 20 mM Serine-borate, binding increases linearly with protein concentration, reaches equilibrium in 10 minutes, and is reversible upon addition of 3 x 10(-5) M unlabelled LTC4. The dissociation curve is consistent with the existence of more than one class of binding site. Ca++ and Mg++ greatly enhance the binding of 3H-LTC4 at equilibrium. In the presence of 5 mM CaCl2 and MgCl2 not only LTC4 (IC50 10(-7)M), but also LTD4 (albeit with much lower affinity, IC50 = 6 x 10(-5) M) and the SRS-A antagonist FPL 55712 (IC50 = 10(-5) M) can compete with 3H-LTC4 for its binding sites. FPL 55712 only displaces 60-70% of the total amount bound, while LTC4 displaces 90-95%. These studies indicate that multiple classes of binding sites exist for 3H-LTC4 in guinea pig ileal longitudinal muscle, and that at least part of these binding sites might be related to the ability of LTC4 to contract guinea pig ilea.     

Hypoxia-induced activation in small isolated pulmonary arteries from the cat

Effects of hypoxia on force development and membrane potential were studied in isolated small (less than 300 microns diam) and large (greater than 500 microns diam) pulmonary arteries from cats. There was a consistent and reproducible hypoxic constrictor response in small pulmonary arteries that began at PO2 values between 350 and 300 Torr and reached a maximum at PO2 between 50 and 30 Torr. In the small artery smooth muscle cell the membrane potential, which was -51 +/- 1.4 mV at a PO2 of 400 Torr, was depolarized to -37 +/- 2 mV at a PO2 of 50 Torr. In contrast, larger arteries did not exhibit significant hypoxic constriction or depolarization upon exposure to low PO2. Constriction in small arteries was not blocked by phentolamine. Treatment with a low dose of indomethacin (10(-9) M) augmented the response; however, a larger dose of indomethacin (10(-3) M) blocked the constriction to hypoxia but not to 30 mM KCl. Depolarization during hypoxia was not blocked by ouabain. Results of this study suggest that the hypoxic response of these isolated small pulmonary vessels may be like that seen in the intact lung. Furthermore, these data suggest that hypoxic vasoconstriction may be mediated by electrical events occurring at the pulmonary arterial muscle cell membrane either directly or via mediators released from the vessel wall.     

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.     

Effects of antioxidants on cyclooxygenase and lipoxygenase activities in intact human platelets: Comparison with indomethacin and etya

Five antioxidative agents (BW755C, 1-naphtol, NDGA, propylgallate and quercetin) were compared with indomethacin and ETYA for their effects on (¹⁴C) arachidonic acid metabolism by cyclooxygenase (CO) and lipoxygenase (LPO) enzymes in intact human platelets. All tested compounds inhibited CO activity in a concentration-dependent manner. LPO activity was suppressed by NDGA, propylgallate, quercetin and ETYA but strongly enhanced by BW755C, 1-napthol and indomethacin. Whereas NDGA and ETYA showed almost equipotent inhibitory effects towards both fatty acid oxygenases, propylgallate and quercetin were found to be respectively 6.5 and 4 times better inhibitors of LPO than of CO activities.These data indicate that antioxidants affect arachidonic acid metabolism in intact human platelets in different ways: BW755C and 1-naphtol exerted the same activity as indomethacin, a selective CO blocker, whereas NDGA, propylgallate and quercetin behaved as ETYA, a dual CO-LPO inhibitor. Considering their inhibition selectivity, propylgallate and quercetin may serve as prototypes for more specific blockers of LPO activity.     

Involvement of intramural prostaglandin E2 in prenatal patency of the lamb ductus arteriosus

Release of prostaglandin E2 (PGE2) was studied in isolated ductus arteriosus preparations from immature (103 or 104 days gestation; term, 147 days) and near-term fetal lambs. Mature preparations produced measurable amounts of the compound in most cases and the release rate was 19 +/- 2 pg/(100 mg wet weight X min) at a PO2 of 3-8 Torr (1 Torr = 133.3 Pa). PGE2 release increased with the PO2 of the medium, peak values (about 125 pg/(100 mg X min)) being attained at 106-276 Torr when the oxygen-induced contraction was still submaximal. Experiments in which tissues were either contracted with excess potassium or relaxed with CO proved that PGE2 formation is independent from the contractile state. PGE2 was also released from ductus preparations lacking the adventitia, the intima, or both; however, release values were maximal when the adventitia was preserved. The magnitude of the intrinsic tone in these stripped preparations was inversely related to the rate of PGE2 formation. Reduced glutathione increased PGE2 release from the mature ductus, whole or stripped, and also relaxed hypoxic preparations; both effects were reversed by concomitant treatment with indomethacin. PGE2 synthesis tended to be greater in the immature than the mature ductus, maximal values (115 +/- 27 pg/(100 mg X min)) being observed at 6-8 Torr. We conclude that the ductus arteriosus is endowed with an enzyme system for the synthesis of PGE2 whose function accords with an effector role of the compound in the regulation of tone. These findings, together with the potent relaxation exerted by PGE2 at low PO2, indicate that the locally generated prostaglandin is well suited for keeping the ductus patent in the fetus.