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We studied the effect of endogenous and exogenous prostaglandin E(2) (PGE(2)), a metabolite of arachidonic acid through the cyclooxygenase (COX) pathway, on interleukin (IL)-1 beta-induced COX-2 expression, using primary cultures of human bronchial smooth-muscle cells (HBSMC). Treatment with exogenous PGE(2) resulted in enhanced expression of IL-1 beta-induced COX-2 protein and messenger RNA (mRNA) as compared with the effect of the cytokine per se. Inhibition of PGE(2) production with a nonselective COX inhibitor (flurbiprofen, 10 microM) resulted in a significant reduction in IL-1 beta- induced COX-2 expression, supporting a role of endogenous COX metabolites in the modulation of COX-2 expression. None of the experimental conditions used in the study affected the expression of constitutive cyclooxygenase (COX-1). Treatment with cycloheximide to inhibit translation, and with dexamethasone or actinomycin D to inhibit transcription, linked the effect of PGE(2) to the transcriptional level of COX-2 mRNA rather than to a potential effect on protein and/or mRNA stabilization. PGE(2) increased adenylate cyclase activity in a concentration dependent manner, and forskolin, a direct activator of adenylate cyclase, caused a marked increase in IL-1 beta-dependent COX-2, suggesting the existence of a causal relationship between the two events. The same results were observed with salbutamol, a bronchodilator that acts by increasing cyclic adenosine monophosphate. The effect of PGE(2) on COX-2 expression may contribute to the hypothesized antiinflammatory role of PGE(2) in human airways, providing a self-amplifying loop leading to increased biosynthesis of PGE(2) during an inflammatory event.

Esaprazole, N-cyclohexyl-1-piperazineacetamide monohydrochloride, was studied for its activity to prevent gastric mucosal damage induced by several necrotizing agents in the rat. Its effects on acid gastric secretion and the role of gastric mucosal prostaglandin generation were also investigated. Esaprazole, given orally, dose dependently prevented the formation of mucosal damage induced by absolute ethanol, 0.2 N NaOH or 0.6 N HCl. This activity occurred at doses lower than the antisecretory doses. Esaprazole was also found to increase the gastric mucosal prostaglandin content but at doses that exceeded the cytoprotective doses. The failure of indomethacin to impair the gastric mucosal protection provided by esaprazole suggests that mechanisms other than mobilization of endogenous prostaglandins may be involved.

Cysteine-containing leukotrienes (cysteinyl-LTs) are potent bronchoconstrictors and play a key role in asthma. We found that histamine and LTD 4 markedly constrict strips of human bronchi (HB) with similar efficacy. However, in human airway smooth-muscle (HASM) cells, LTD 4 , at variance with histamine, elicited only a small, transient change in intracellular calcium ion concentration. HASM cells express both Ca 2 1 -dependent and -independent isoforms of protein kinase C (PKC) (i.e., PKC- a and PKC- « ). Western blot analysis showed that PKC- a is activated by histamine and, to a lesser extent, by LTD 4 , whereas only LTD 4 translocates PKC- « . This translocation was specifically inhibited by the LTD 4 antagonist pobilukast. Phorbol-dibutyrate ester (PDBu) (a PKC activator) contracted HB strips to the same extent in the presence as in the absence of extra- and intracellular Ca 2 1 . In the absence of Ca 2 1 , LTD 4 contracted HB strips to the same extent as did PDBu, suggesting the involvement of a Ca 2 1 -independent PKC in LTD 4 -mediated signal transduction. PDBu-induced desensitization and the PKC inhibitor H7 abolished the slow and sustained LTD 4 -triggered contraction of HB strips in the absence of Ca 2 1 , although H7 did not greatly affect the response in the presence of the ion. Thus, in human airways, we identified a novel LTD 4 transduction mechanism linked to bronchial smooth-muscle contraction, which is partly independent of Ca 2 1 and involves the activation of PKC- « .

A variety of inflammatory cells synthesize cys-leukotrienes (cys-LTs) C4, D4 and E4 in response to biological and non-biological stimuli1: eosinophils, basophils and mast cells2,3 are able to synthesize cys-LTs from arachidonic acid but cys-LTs can also be produced through transcellular metabolism from neutrophil-derived LTA4, by vascular endothelial cells4-6 and platelets7.

The purpose of this study was to determine the mechanism of enhanced prostaglandin synthesis in cultured human bronchial smooth-muscle cells challenged with interleukin-1 beta (IL-1 beta). Cells were incubated with IL-1 beta (10 to 50 U/ml) for 0 to 24 h. Prostaglandin E2 (PGE2) production was evaluated through the conversion of exogenous (14C)-arachidonic acid and specific enzyme immunoassay of endogenous products. IL-1 beta enhanced PGE2 formation in a concentration- and time-dependent manner, reaching its peak at 6 to 8 h and fading at 18 to 24 h. Immunoblot analysis showed that the inducible cyclooxygenase enzyme (COX-2) was expressed only in IL-1 beta treated cells, whereas the constitutive isoform of cyclooxygenase (COX-1) remained unaltered. COX-2 expression and PGE2 formation were inhibited by dexamethasone (2 microM), cycloheximide (10 microM), and IL-1-receptor antagonist (IL-1 ra) (250 ng/ml), independently. PGE2 synthesis was significantly reduced by compound SC-58125, a specific COX-2 inhibitor. The close parallelism between the kinetics of COX-2 protein expression and PGE2 accumulation, as well as the constitutive nature of COX-1 isoform, indicate that IL-1 beta-driven PGE2 formation in human bronchial smooth-muscle cells is mediated by de novo expression of COX-2 enzyme.

The role of mevalonate and geranylgeraniol in the control of cellular proliferation of cultured human bronchial myocytes was examined by investigating the effect of simvastatin, an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase, the rate-limiting enzyme in mevalonate synthesis. Simvastatin inhibited the rate of growth of human bronchial smooth muscle cells in a concentration-dependent manner, with an IC50 value of 0.97 +/- 0.1 microM. Mevalonate (100 microM), as well as geranylgeraniol (5 microM), at their highest non-toxic concentrations, restored cell proliferation to control levels.

The (±)-3′-hydroxyfarrerol (IdB 1031) is a new drug endowed with an interesting mucokinetic activity. In this study the effectiveness of IdB 1031 has been verified in a model of airway hyperreactivity and lung inflammation induced in anaesthetized guinea pig by active cigarette smoke exposure. IdB 1031 (500 mg/kg per os) completely inhibited the capacity of cigarette smoke to induce airway hyperreactivity. IdB 1031 also inhibited the recruitment of proinflammatory cells within the airway lumen as showed in bronchoalveolar lavage fluids. In line with these experiments IdB 1031 inhibited 5-lipoxygenase with an lC50 of 7.36×10−6 M in human leukocytes challenged by A-23187 (2 μM). A significant reduction of the above parameters was observed also in animals exposed to smoke after repeated treatment with IdB 1031 at 200 mg/kg per os for 15 days. These results show that IdB 1031 is a promising drug with a favourable spectrum of activities on the respiratory tract.

SCH 37224, 1-(1,2-dihydro-4-hydroxy-2-oxo-1-phenyl-1,8-naphthyridin-3-yl) pyrrolidinium, is a structurally novel compound that had been shown to inhibit leukotriene D 4 formation in guinea pig lung in vitro. We tested whether SCH 37224 is able to inhibit both the formation of eicosanoids from human lung parenchyma in vitro and the binding of sulfidopeptide leukotrienes to membranes of lung parenchyma and bronchi. SCH 37224, at a concentration of 30 and 100 μM, was able to inhibit antigen-induced formation of sulfidopeptide leukotrienes, measured as leukotriene E 4 , while it did not significantly affect the formation of prostaglandin D 2 . At concentrations up to 100 μM, it did not affect either the binding of [ 3 H]leukotriene C 4 to membranes of human lung parenchyma or human bronchi, or the binding of [ 3 H]leukotriene D 4 to the parenchyma. In conclusion, SCH 37224 is a selective inhibitor of leukotriene formation in human lung in vitro, which might be of potential therapeutic interest in the treatment of asthma.

Unlike other classic NSAIDs, some fenamates given at therapeutic concentrations, have been shown to inhibit, both in vitro and in vivo, the 5-lipoxygenase pathway of arachidonic acid cascade as well as the synthesis of cyclooxygenase products. This dual inhibitory property might represent an improvement in anti-inflammatory therapy. The aim of this work was to characterize the effect of morniflumate, administered at therapeutic dosages to normal human volunteers, on leukotriene B4 (LTB4) and thromboxane (TXB2) synthesis, both in purified PMNs and in whole blood. PMNs, isolated two hours after a single oral administration of morniflumate and at steady-state condition, fully retain their capacity to release LTB4 and TXB2. Since intracellular concentrations of the drug were undetectable, in spite of its elevated concentrations in platelet poor plasma, the results obtained using PMNs suggest a drug loss during the cells purification procedure. In whole blood experiments, morniflumate reduced blood LTB4 synthesis induced by Ca-ionophore A23187 Bx approximately 50%, both after single dose and at steady state; the degree of inhibition showed a pattern similar to the plasma levels of the bioactive metabolite of morniflumate (M1). The inhibition of serum TXB2 levels was higher than 85%. Hence, morniflumate is capable of reducing arachidonic acid metabolism acting both on cyclooxygenase and 5-lipoxygenase. This characteristic might provide a better approach in anti-inflammatory therapy.

Publisher Summary The chapter presents a discussion on preparation of human and animal lung tissue for eicosanoid research. A sufficient number of in vitro methods has been developed utilizing human and animal lung tissue for eicosanoid research. The chapter describes techniques that are useful in understanding the physiopathological role of eicosanoids in the pulmonary system as well as their functional effects. Eicosanoids are fatty acids of great biological significance because of their ubiquity, high potency, and multitude of other effects. Among all the organs that have been investigated, the lungs are the most active in forming and metabolizing eicosanoids; human and animal lung tissue can oxidize arachidonic acid (AA), generating cyclooxygenase as well as lipoxygenase-derived products that appear to play a role in the development of asthma, allergic reactions, and inflammation. In fact, leukotrienes (LT) have potent spasmogenic actions on human lung tissue in vitro , affect mucus production and clearance, and may be important factors in the pathogenesis of airway hyperresponsiveness. The chapter describes in detail the preparation of human lung parenchyma to produce eicosanoids, preparation of human bronchial tissue, and preparation of guinea pig isolated trachea, parenchyma, and lung.

1 The formation and release of PGE2-like material (PGE2-lm) from guinea-pig isolated trachea and human bronchi following relaxation with isoprenaline (I) was investigated. 2 When airway smooth muscle precontracted with pilocarpine is relaxed by I, PGE2-lm is released in the bathing fluid. Under conditions of β-adrenoreceptor desensitization, a greater amount of PGE2-lm is formed and the responsiveness of guinea-pig tracheal spirals to cumulative doses of I is diminished. 3 Inhibition of cyclo-oxygenase with indomethacin does not modify the relaxation induced by I but prevents the occurrence of refractoriness to I as well as formation and release of PGE2-lm. Addition of exogenous PGE2 to guinea-pig tracheas which were treated with indomethacin is able to restore the capacity of I to cause tachyphylaxis. 4 It is concluded that PGE2 which does not mediate the relaxation induced by I in airway smooth muscle, is responsible for the onset of desensitization of the β-adrenoreceptor.

Various doses of histamine, bradykinin and leukotriene C 4 caused bronchoconstriction in anaesthetized guinea-pigs which were breathing spontaneously or artificially ventilated; there was a simultaneous, dose-related increase of circulating TXA 2 . The animals were prepared for continuous recording of extracororeal circulation in order to detect the appearance in the blood of bioassayable levels of TXA 2 -like substance. Furthermore, a TXA 2 derivative, the mono-O-Me-TXB 2 , was radioimmunoassayed. Atropine, oxytropium bromide and ipratropium bromide given in μmol doses prevented both the increased airway resistance and the release of TXA 2 -like substance in the blood. Pirenzepine dihydrochloride was the least active of the drugs tested. The protecting activity of anticholinergics and the relationship with their ability to affect TXA 2 -like substance generation suggest a new site of action for these drugs besides the blockade of muscarinic receptors.

The stimulation of human lung parenchymal fragments with A-23187 induces formation of leukotrienes as well as of PGD 2 : LTE 4 is the compound found in larger amount and independently of the intensity of the stimulus the % of metabolized precursor which is converted to leukotrienes or PGD 2 is remarkably similar. However, under conditions of IgE-AntilgE challenge the predominant conversion of arachidonic acid occurs to PGD 2 , LTB 4 is almost negligible and LTD 4 and E 4 together represent less Ln 30% of the oxidative products of arachidonic acid. Whether PGD 2 and leukotrienes derive from the same or different subset of cells is unresolved.

Angiotensin II (AII) induces generation of prostacyclin (PGI2) in rabbit lung in vitro at different ages, i.e., fetus, newborn and adult. Particularly, neonatal rabbit lungs display a pattern of sensitivity to AII in producing PGI2, measured as 6-oxo-PGF1 alpha, which seems to be higher than that observed in fetal lungs. The PGI2 release appears to be specific for AII stimulation since the vasoconstriction induced by noradrenaline and ergotamine was not associated with generation of this lipidic material. The inability of PGI2 to relax the extralobar pulmonary artery in the newborn suggests that the lung microcirculation is the most likely site where the vasodilating and antiaggregatory functions of PGI2 may have a physiological role.

Several naturally occurring compounds have been identified in human cerebrospinal fluid (CSF) after subarachnoid haemorrhage (SAH) as possible vasoactive agents involved in the biochemical mechanism of vasospasm. The authors have measured, in 30 patients admitted for SAH, CSF concentrations of two arachidonic acid metabolites. Prostacyclin and Prostaglandin D2, as representative of vasodilator and vasoconstrictor compounds. CSF samples were made available by lumbar punctures and intraoperative cisternal punctures. Nine patients presented with symptomatic vasospasm: lumbar CSF Prostaglandin D2 levels are significantly higher than in patients without vasospasm. The Cisternal Prostaglandin D2 level is significantly higher than the lumbar CSF concentration; CSF Prostacyclin levels do not significantly differ in the two groups of patients. These data suggest the presence of an imbalanced biochemical situation responsible for promoting vasospasm. The evaluation of cisternal levels of arachidonate metabolites support the hypothesis of the clotting phenomenon around the ruptured aneurysm wall as an important predictive pattern of vasospasm onset after SAH, as shown in computed tomography.

Ro 21-7634 has previously been shown to inhibit histamine and SRS-A release from actively-sensitized guinea pig lung fragments upon antigen challenge. In the studies described herein, it was observed that Ro 21-7634 does not decrease SRS-A release but instead acts to inhibit the synthesis of this mediator. This was confirmed by studying SRS-A synthesis in vitro in rat peritoneal cells after challenge with ionophore A23187. In the peritoneal cell system, Ro 21-7634 exhibited an IC50 of 500 microM, in comparison with 5.8,11,14-eicosatetraynoic acid, phenidone and BW755C (IC50's of 2, 100, and 100 microM, respectively). When studied at 10(-4) and 10(-3) M in perfused guinea pig lung, Ro 21-7634 inhibited antigen-induced thromboxane A2 production by 68 and 96%, respectively. In this system, antigen is believed to induce thromboxane A2 production through the release of histamine and SRS-A from lung tissue. These mediators then interact at receptor sites in the lung parenchyma to induce thromboxane A2 synthesis. Ro 21-7634 could thus be inhibiting thromboxane A2 production by preventing the release of histamine and synthesis of SRS-A in the perfused lung system. Such a mechanism is suggested by the fact that although Ro 21-7634 was effective in inhibiting antigen-induced thromboxane production, it was ineffective in inhibiting thromboxane A2 production induced in the guinea pig lung system by the direct perfusion of histamine or SRS-A through the lung.

S-(+)-2-(4-Fluorophenyl)-alpha-methyl-5-benzoxazolacetic acid (flunoxaprofen, Priaxim is a new antiinflammatory compound, which in various biological systems interferes with the generation and release of arachidonic acid metabolites of the cyclo-oxygenase pathways without affecting the formation of 5- and 12-lipoxygenase products. Flunoxaprofen reduces the concentration of thromboxane (TX)B2 (ED50 = 35.4 mg/kg p.o.) and prostaglandin (PG)E2-like activity (ED50 = 39.9 mg/kg p.o.) in the inflammatory exudate of rats 8 h after implantation of sponges soaked with carrageenan, whereas the concentration of leukotriene (LT)B4 remains in the range of that of the untreated animals (3.1 ng/ml). Flunoxaprofen inhibits cell infiltration in the exudate and this suggests that LTB4 does not initiate cell recruitment but may represent a mechanism for amplifying the inflammatory response. Using human platelets challenged with collagen, flunoxaprofen only at higher concentration (10(-4) mol/l) reduces TXB2 formation without altering generation of 12-hydroxy-5,8,10,14-eicosatetraenoic acid. This suggests a low capacity of flunoxaprofen of affecting platelet aggregation regulated by arachidonic acid metabolites. Flunoxaprofen prevents pulmonary changes due to secondary release of TXA2 in the guinea-pig. In fact this drug prevents changes due to immunological reaction and antagonizes bronchoconstriction due to exogenous administration of histamine and LTC4.(ABSTRACT TRUNCATED AT 250 WORDS)

Tiaramide hydrochloride (THC) is a benzothiazoline derivative with a remarkable antianaphylactic activity: in anaesthetized guinea-pig it shows protecting effects against histamine (H)- and bradykinin (Bk)-induced bronchoconstriction, preventing increase of lung resistance and decrease of dynamic compliance. At the same time THC inhibits formation of circulating thromboxane A2 brought about by H and Bk. THC is also able to antagonize the contractions induced by CaCl2 on isolated guinea-pig tracheal spirals and its mode of action seems to be of the competitive type. Furthermore THC abolishes the "tonic" phase of K+-induced contractions of guinea-pig taenia coli which are dependent on inward movement of calcium, whereas the "phasic" component of the contractions is left unaltered. THC is a very weak inhibitor of 3'-5' cyclic adenosine monophosphate phosphodiesterase which is affected only at very high dosage (10(-2) M). The calcium antagonistic activity of THC may explain both its bronchodilating and antianaphylactic properties.

The elucidation of the structure of SRS-A (slow reacting substance of anaphylaxis) has led to the discovery of Leukotrienes (LTs), a family of arachidonate metabolites produced by the enzyme 5-lipoxygenase (1) (2). A stereospecific synthesis brings about formation of two classes of LTs, one major class composed of the sulfidopeptide leukotrienes, LTC4, LTD4 and LTE4, and another class represented solely by LTB4. A variety of stimuli, cleaving arachidonate from membrane phospholipids, provide the necessary substrate for the synthesis of prostaglandins (PGs), thromboxanes (TX) and LTs (3). PGs and to a minor extent TX are formed ubiquitarily, whereas the synthesis of LTs seems to require a considerable cellular specificity (4) (5): all of them are formed by normal and asthmatic human lung where they may play a role as potent bronchoconstrictors as well as primary mediators of airway hyperreactivity (6).

Defibrotide, a polydeoxyribonucleotide obtained from mammalian lungs, reduced in a dose-dependent fashion the ischemic contracture due to low perfusion (0.2 ml/min) of isovolumic left heart of rabbit and abolished the irregular rhythm of the heart, thereby restoring the cardiomechanical activity upon reperfusion (20 ml/min). Defibrotide stimulated the release of PG-like material from the heart in a dose-dependent manner without modifying the basal contractility. Both PGE2 and PGI2 (10 ng/ml) have an antiischemic activity on this preparation as shown by the partial reduction of the ischemic contracture and by the improvement of heart contractility upon reperfusion. Indomethacin infusion (1 microgram/ml) completely removed both the antiischemic activity of Defibrotide (400 micrograms/ml) and its ability to increase the generation of prostaglandins in the rabbit heart. These results suggest that Defibrotide has a beneficial influence on ischemic rabbit heart through an increase in prostaglandin synthesis. However other mechanisms not necessarily related to prostaglandin generation, such as a direct effect on membrane function deactivation and mitochondrial Ca2+ overload, should be considered in explaining the antiischemic activity of Defibrotide in the rabbit heart.

Summary Tiaramide hydrochloride (THC), a benzothiazolinone derivative, displays a direct bronchodilating activity associated with anti-anaphylactic properties. The smooth muscle relaxing capacity of this compound is not related to increased levels of cyclic AMP. The anti-anaphylactic activity has been investigated using isolated lungs from ovoalbumin sensitized guinea-pigs. THC prevents histamine and TXA 2 release from lungs during antigen exposure. In addition to this THC antagonizes the direct effect of histamine on TXA 2 generation in guinea-pig lungs without affecting the cyclo-oxygenase system. Our results indicate that THC can control the anphylactic reaction through at least two different mechanisms: 1) inhibition of mediator release, 2) direct antagonism of their spasmogenic activity.

Defibrotide, a polydeoxyribonucleotide extracted from mammalian organs (laboratory code Fraction P), displays antithrombotic activity after oral administration on different animal species. This activity is also demonstrated in a typical local thrombonecrotic hemorrhagic lesion caused by endotoxin in rabbit (Shwartzman reaction). Defibrotide prevents and antagonizes this kind of lesion in a dose dependent and in a long lasting way. The ability of Defibrotide to increase generation of PGI2 from vascular tissue following oral administration, is demonstrated and the mechanism of this phenomenon discussed.

Histamine 2.5, 5, 10 or 20 μg/kg i.v. induce a pronounced bronchospasm in guinea-pigs, accompanied by a dose-related increase of TXA 2 in arterial blood, as revealed by contraction of rabbit isolated aorta and by radioimmunoassay. Aspirin 10 mg/kg prevented formation of TXA 2 like material without significantly modifying the severity of the bronchospasm. Bradykinin 0.5, 1 or 2 μg/kg i.v. acted similarly, except that pretreatment with aspirin blocked both the increased airway resistance and release of TXA 2 . Aspirin also blocked the increase in blood pressure and heart rate caused by histamine or bradykinin.

Experimental and clinical studies indicate that cerebral vasospasm following subarachnoid hemorrhage (SAH) may be caused by changed biochemical properties of the endothelium and vascular smooth muscle cell exposed to vasoactive substances synthetized by cerebral arteries and released in clotted blood. Many compounds have been identified in CSF from SAH patients: Thromboxanes A2 and B2, Prostaglandins F2 alpha, E2 and D2 are the major prostanoids incriminated in the causation of cerebral arterial spasm. We have monitored the CSF PGD2 concentrations with serial lumbar punctures at different intervals from the hemorrhage in 16 patients admitted for SAH: PGD2 was measured with radioimmunoassay as its 9-methoxy derivative. The lumbar CSF PGD2 concentration ranges from 0.11 to 1.53 ng/ml. In 7 cases vasospasm was angiographically demonstrated. 9 patients presented no clinical or radiological evidence of vasospasm. In 5 cases cisternal CSF samples were available at the operation by cisternal punctures. There was no correlation between CSF PGD2 concentration and clinical course. In the 7 cases with evidence of vasospasm a significant increase of CSF PGD2 corresponded to neurological deterioration. In all 9 cases without evidence of vasospasm CSF PGD2 concentration trend was in a steady-state. The cisternal CSF PGD2 concentration was higher than lumbar CSF concentration in cases with arterial spasm. This suggests the importance of the clotting phenomenon in vasospasm onset after SAH. PGD2 is one of the most important spasmogens in clotted blood. Although its role in the genesis of vasospasm onset remains to be defined, its vasospastic action, in addition to that of other analogous compounds, seems to be relevant.

When chopped human lung is stimulated with the Ca++ ionophore A23187 (0.25-10 microM) leukotriene (LT) B4, LTD4 and LTE4 are found in the incubation medium according to different patterns. LTD4 is released promptly and its levels increase up to 45 min after the stimulus (A23187, 10 microM) and decline later (120 min); LTE4 formation follows a sigmoidal shape and continues to accumulate even 2 hr after the challenge; LTB4 levels reach a plateau at 45 min. LTC4 was undetectable in most experiments but it was found to accumulate when reduced glutathione (10 mM) was added. Addition of exogenous LTC4 to unstimulated fragments of human lung shows that an effective interconversion to LTD4 and LTE4 takes place: A23187 stimulates formation of LT and cyclo-oxygenase products dose dependently; a statistically significant formation of LT occurs at A23187 concentration of 1 microM whereas thromboxane B2 (TXB2) and 6-K-prostaglandin F1 alpha levels increased significantly only at 2.5 microM A23187. Pretreatment with U-60257 (100 microM) prevented formation of LT without a concomitant increase of TXB2 levels. Indomethacin (1.5 microM) blocked the release of 6-K-prostaglandin F1 alpha and TXB2 without a shift of arachidonic acid towards LT-like activity. Addition of exogenous LTC4 did not trigger synthesis of TXB2 or 6-K-prostaglandin F1 alpha. Our results indicate that reduced glutathione levels and the activity of the enzymes involved in LT biosynthesis and/or metabolism play an important role in controlling the pattern of LT release from human lung.

Ca++-ionophore and antigen challenge of human lung fragments caused a massive release of leukotrienes, whose relative proportions varied considerably and were dependent on the experimental conditions. A broncho-selective beta 2-adrenoceptor agonist fenoterol was able to prevent the antigen-induced leukotriene release completely, whereas the Ca++-ionophore induced leukotriene release was only moderately inhibited. The HPLC data were confirmed by SRS-A bioassay.

A central role of polyunsaturated fatty acids as precursors of various substances which can act as mediators or modulators of different cellular functions is widely recognized. The recent discovery that some arachidonic acid metabolites, derived from 5-1ipoxigenase pathway, can display potent biological actions which are similar to that of slow reacting substance of anaphylaxis (SRS-A), stimulated a fresh interest in the field of asthma and other allergic diseases (1) (2). These compounds, first discovered in polymorphonuclear leukocites obtained from peritoneal cavity of rabbits, possess a conjugated triene in their molecular structure and have been therefore named leukotrienes (LTs) (3). Among them, the dihydroxy acid leukotriene B4 (LTB4) causes chemotaxis and chemochinesis (4), responses which are involved in inflammation, whereas the peptidolipids leukotriene C4 (LTC4), D4 (LTD4) and E4 (LTE4) induce alterations occurring in immediate type hypersensitivity reactions (5). Several investigators have demonstrated that LTC4, LTD and LTE4 bring about a severe cons-triction in guinea-pig and LTE4 peripheral airways with a poten- cy greater than histamine (6) (7). Studies performed in conscious guinea-pigs pointed out that the modifications in dynamic compliance (CD vn) and lung resistance (RL) due to cysteine-containing LTs are associated with a fall in mean systemic arterial pressure: these effects, both on airway and cardiovascular systems were interpreted as direct in nature (7). Beside causing constriction of gastrointestinal and respiratory smooth muscle, LTs have been reported to cause a marked vasoconstriction in the microvasculature of guinea-pig skin and in the coronary circulation. SRS-A and LTC4 are also able to increase formation and release of thromboxane A2 (TXA2) in guinea-pig perfused lungs, an effect which is prevented by cyclo-oxygenase inhibitors and by FPL-55712, a SRS-A receptor antagonist (8). These observations and the early evidence of Berry and Collier (9), emphasizing the ability of aspirin to antagonize SRS-A induced bronchoconstriction in guinea-pig, prompted us to examine whether the biological activity of LTC4 is actually direct or merely mediated by other arachidonic acid metabolites. Bronchodilators currently employed in the treatment of asthma have been also considered in view of their ability to protect guinea-pig from pulmonary and cardiovascular actions of LTC4.

Summary The selectivity of procaterol for β 2 -adrenoceptors vs β 1 -adrenoceptors in animals has been already described. In these studies the ability of procaterol to protect guinea-pig against bronchoconstriction induced by various spasmogens such as histamine, LTC 4 and acetylcholine is demonstrated. The results obtained both in anaesthetized animals and in perfused lungs clearly show that procaterol antagonizes not only the direct effect of the bronchoconstrictors quoted above but also their ability to activate arachidonic acid metabolism and to augment the generation of TXA 2 . Procaterol (0,3-3 μg/Kg i.v.) is more potent than salbutamol in protecting passively sensitized guinea-pig from massive bronchoconstriction following antigen challenge: a phenomenon which is paralleled by an increment of the circulating TXA 2 . The possibility that the adenylate-cyclase-stimulating properties of procaterol may explain its antiasthmatic activity is discussed.

1 Histamine (0.5 to 5 micrograms) and slow reacting substance of anaphylaxis (SRS-A, 0.05 to 0.3 u), injected in the isolated, perfused lungs of normal and ovalbumin-sensitized guinea-pigs, promote formation and release of thromboxane A2(TXA2) and other arachidonate metabolites, the effect being more pronounced in sensitized lungs. 2 Carbachol injected (1 to 10 micrograms) or perfused (1 micrograms ml-1 min-1) through normal or sensitized lungs does not elicit formation of TXA2 and prostaglandins. Furthermore the increased generation of arachidonate metabolites due to histamine is not altered by carbachol. 3 Atropine and ipratropium bromide (1 microgram ml-1 min-1) reduce significantly the increased rate of production of TXA2 caused by histamine and SRS-A both in normal and sensitized lungs, whereas hexamethonium (10 to 25 micrograms ml-1 min-1) is ineffective. 4 The mechanism of action of atropine in inhibiting the increased generation of TXA2 is clearly not related to its antimuscarinic or antihistaminic properties. The drug might act at the early events, involved in the activation of arachidonic acid metabolism. The results suggest new sites of action for atropine which, besides the control of the vagal bronchomotor tone, interferes directly with the primary mediators of anaphylaxis.

A wide literature exists about the pathogenesis of cerebral arterial spasm following subarachnoid haemorrhage: several compounds have been identified in human cerebrospinal fluid as possible vasoactive agents involved in the biochemical mechanism of vasospasm onset. Many experimental evidences exist for a major involvement of arachidonate metabolites. The present work represents a review of experimental data supporting the hypothesis of cerebral arterial spasm as a result of an imbalanced vascular regulatory mechanism involving arachidonate metabolites. The authors have also monitored, in 25 cases of aneurysmal subarachnoid haemorrhage, lumbar and cisternal CSF levels of prostacyclin and PGD2, as representative of vasodilating and, respectively, vasoconstrictor compounds. In all cases CSF arachidonate metabolite levels after SAH were significantly higher than in control cases. Ten patients presented with symptomatic vasospasm: lumbar CSF PGD2 levels show fluctuations with superimposed peaks related to the neurological deterioration due to vasospasm, while lumbar CSF prostacyclin concentration-trend suggest a decreasing synthesis. In 15 patients presenting without vasospasm, lumbar CSF concentration of arachidonate metabolites are in a 'steady-state'. These data confirm the existence of an imbalanced biochemical situation promoting vasospasm, markedly in cisterns near to the ruptured aneurysmal wall. The evaluation of cisternal CSF levels of arachidonate metabolites supports the hypothesis of the clotting phenomenon around the ruptured aneurysm as an important predictive pattern of vasospasm, as shown in CT findings.