Eicosanoids最新文献

Arachidonate 15-lipoxygenase (an n-6 lipoxygenase) has been purified to homogeneity, cloned and expressed and appears to be a highly regulated enzyme showing pronounced tissue specificity. The enzyme is expressed prominently in the reticulocyte where it appears to be under posttranscriptional control and may play a key physiological role in reticulocyte maturation by initiating mitochondrial breakdown. 15-Lipoxygenase is also expressed in significant quantities in airway epithelial cells and eosinophils although no clear role for this enzyme in these cell types has been defined. The enzyme catalyzes the conversion of free arachidonic acid to 15-HPETE, free linoleic acid to 13-HPOD and can also oxygenate polyenoic acids esterified in phospholipids. A number of potential physiological and pathological roles for products of this enzyme have been postulated. These include a physiological role in prolactin secretion from pituitary cells and in the initiation of the acrosome reaction in spermatozoa. An important pathological role in the oxidation of LDL by macrophages has also been proposed, indicating that the enzyme could be a pharmacological target for the treatment of atherosclerosis.

New Zealand white rabbits were fed a diet enriched with cholesterol (0.25%) for 4 months. At that time, the aortae and coronary vessels of the cholesterol-fed rabbits were extensively covered with atherosclerotic lesions while those of age-matched control rabbits were normal. Langendorff-perfused hearts from the rabbits were compared for their ability to release PGI2 and PGE2 into the coronary sinus effluent during basal perfusion and after exposure to a bolus injection of 50 mumoles of arachidonic acid. No differences were detected in prostaglandin production between the cholesterol-fed and control animals. Nor were any differences in coronary hemodynamics observed. Aortic arachidonic acid metabolism was studied in an intimal en-face preparation. No differences were observed in the basal release of the PGI2 metabolite, 6-keto-PGF1 alpha, or PGE2. PGI2 and PGE2 production increased in response to arachidonic acid and to the calcium ionophore, A23187, but no differences were observed between cholesterol-fed or control tissues. Using minced aortic tissue, the production of 5-, 11-, 12- and 15-hydroxyeicosatetraenoic acids (HETE) were quantified by GC/MS. Differences in basal or A23187-stimulated HETE biosynthesis were not detected between the normal and atherosclerotic rabbit tissues. The data demonstrate that alterations in vascular prostaglandin and HETE are not prominent in rabbits with stable atherosclerosis produced by 4 months of cholesterol feeding.

Vascular bed reactivity to exogenous LTD4 and blockade of these responses by a selective LTD4 receptor antagonist, SK&F 104353, were studied. Yorkshire pigs (N = 13; 25.8 +/- 1.4 kg) were anesthetized with isoflurane, and monitored for cardiac output (CO), mean pulmonary artery pressure (MPAP), pulmonary capillary wedge pressure (PCWP), right ventricular stroke work (RVSW), mean arterial pressure (MAP), renal artery blood flow (RABF), pulmonary vasculature resistance (PVR), renal vascular resistance (RVR), and systemic vascular resistance (SVR). LTD4 (0.03, 0.1, 0.3, 1, 3 and 10.0 micrograms/kg) was given intravenously. The MPAP, MAP, and RABF were recorded at baseline and for 20 min after the injection of LTD4. SK&F 104353 was infused (3 mg/kg/h, i.v.) and the dose-response to LTD4 was repeated. LTD4 induced changes in the MPAP, PCWP, MAP, and RABF. SK&F 104353 attenuated LTD4 induced changes in the MPAP, PVR, RABF and RVSW. MPAP was increased 123 +/- 24% and 115 +/- 10%, respectively, in pigs given 3.0 and 10 micrograms/kg doses, and increased to only 36 +/- 9% at a 10 micrograms/kg dose of LTD4 in animals pretreated with SK&F 104353 (P less than 0.05). MPAP was not increased at the 3.0 micrograms/kg dose, and increased to only 36 +/- 9% at a 10 micrograms/kg dose of LTD4 in animals pretreated with SK&F 104353 (P less than 0.05). These changes were paralleled by a reduction in PVR. RABF was decreased 76 +/- 5% and 83 +/- 7%, respectively, at the 3.0 and 10 micrograms/kg dose of LTD4.(ABSTRACT TRUNCATED AT 250 WORDS)

This study investigates the action of nitrovasodilators on f-metleu-phe (FMLP)-stimulated LTB4 release and intracellular cyclic nucleotide levels in human polymorphonuclear leukocytes (PMN). Sodium nitroprusside, and the molsidomine (MOL) metabolites SIN-1 and SIN-1A potently inhibited LTB4 release and increased cGMP levels. No significant effects on LTB4 release or cGMP accumulation were observed in the presence of molsidomine or glyceryl trinitrate. None of the compounds tested affected cAMP levels. It is suggested that nitrovasodilators (i) inhibit LTB4 release from human PMN via enhanced cGMP and (ii) that this inhibition requires the presence of an active metabolite, probably nitric oxide.

We have developed a method for measurement of urinary 2,3-dinor-TXB2, which is a reflection of the actual rate of TXA2 synthesis by platelets in vivo. This determination was based on purification by high-pressure liquid chromatography and on measurement by RIA. After validation of the assay, we established the range of urinary Tx metabolites in healthy infants born at full-term during their first week of life. The 2,3-dinor-TXB2 levels were higher than in adults and declined gradually during the first seven days of life.

The PGE2 level in the rat resting stomach, dropped into liquid nitrogen after removal, was 44.6 +/- 8.3 ng/stomach, when determined by radioimmunoassay, but cutting of the greater curvature with scissors after removal caused an approximately sixfold increase in the PGE2 level. Compression of the stomach in situ with metal tongs refrigerated in liquid nitrogen markedly reduced the PG levels, and further purification by reversed-phase high performance liquid chromatography reduced the PGE2 and 6-keto-PGF1 alpha levels to 4.7 +/- 0.6 and 4.8 +/- 0.8 ng/stomach, respectively. Pretreatment of the rats with indomethacin (10 mg/kg, i.v.) did not decrease the PGE2 level, but the 6-keto-PGF1 alpha level was reduced slightly. The lowest level of PGE2 in the resting state was significantly increased after administration of 1.0 M NaCl solution into the gastric lumen. The peak value was 70.0 +/- 21.8 ng/stomach at 30 min, after which the level decreased gradually. The level of 6-keto-PGF1 alpha was not significantly increased during the administration of 1.0 M NaCl solution.

Antisera to 16-carboxytetranordihydro leukotriene E4 (tetranor LTE4), a major urinary oxidative metabolite (via omega- and beta-oxidation) of leukotriene E4 (LTE4) in primates, were obtained by immunisation of rabbits with a related, non-naturally occurring synthetic metabolite (16-carboxytetranordihydro leukotriene C4 ester) conjugated to Keyhole Limpit haemocyanin. Material which competed with [11, 12-3H]tetranor LTE4 for binding to this antisera was isolated from urine from allergic asthmatics by reversed-phase HPLC. This material eluted with the retention time of synthetic standards, and its mean urinary excretion was elevated during both the first three hours (6.13 +/- 2.15 ng/h) and 3-6 h (5.87 +/- 1.99 ng/h) after antigen inhalation, compared with baseline values (3.42 +/- 1.49 ng/h), in 5 allergic mild asthmatics. A much greater and statistically significant increase in urinary leukotriene E4 (LTE4) excretion, occurring in all subjects, was seen during acute antigen-induced bronchoconstriction (baseline, 1.62 +/- 0.66 ng/h; 0-3 h, 19.58 +/- 8.79 ng/h; p less than 0.05) in these subjects. These data support the suggestion that endogenous peptide leukotrienes are metabolised by omega- and subsequent beta-oxidation in man, but emphasize the relative importance of urinary LTE4 excretion after allergen elicited leukotriene generation, further substantiating a pathological role for peptide leukotrienes in allergic asthma.

To assess whether thromboxane A2 (TXA2) exerts a direct electrophysiological effect on cardiac muscle, the effects of STA2 (10 micrograms/l), a stable TXA2 analogue, on the action potentials were examined in isolated guinea pig ventricular muscles using conventional microelectrode techniques. STA2 failed to induce any significant changes in the action potential characteristics in both normal Tyrode's solution and the hyperkalemic (K+ = 10.8 mM) solution. 15 min of superfusion with the "ischemic" solution, which consisted of hyperkalemia (K+ = 10.8 mM), hypoxia (pO2 less than 50 mmHg), acidosis (pH = 6.4) and substrate deprivation (glucose-free), progressively shortened the action potential duration and reduced the resting membrane potential, action potential amplitude and Vmax. STA2 did not affect the changes in the action potential during such "ischemic" superfusion. These results indicate that STA2 exerts no direct electrophysiological effects on both the normal and the "ischemic" myocardium. The arrhythmogenic effects of TXA2 observed in in vivo studies might reflect the ability of TXA2 to induce platelet aggregation and vasoconstriction resulting in an exacerbation of myocardial ischemia.

High affinity binding sites for LTC4 have been identified in various tissues, including guinea-pig ileal longitudinal muscle. More recently, it has been shown that LTC4 binds to non-receptor sites as well, particularly to glutathione transferases. In the present study, LTC4 and 9 chemically synthesized analogues, as well as the SRS-A antagonist FPL 55712 and S-decyl-glutathione, were tested for their ability to inhibit 3H-LTC4 binding in membranes from guinea-pig ileal longitudinal muscle and to affect the tone of the ileum in vitro. A significant correlation between binding and contractile activities was found for the LTC4 analogues and FPL 55712. However, S-decyl-glutathione, although possessing some affinity for LTC4 binding sites, was devoid of any effect on guinea-pig ileum tone at least up to 10(-5) M, thus indicating that these sites cannot be functional receptors, although they may represent other units involved in leukotriene action, e.g. uptake sites.