Leukotrienes and lipoxins: structures, biosynthesis, and biological effects.

Arachidonic acid is released from membrane phospholipids upon cell stimulation (for example, by immune complexes and calcium ionophores) and converted to leukotrienes by a 5-lipoxygenase that also has leukotriene A4 synthetase activity. Leukotriene A4, an unstable epoxide, is hydrolyzed to leukotriene B4 or conjugated with glutathione to yield leukotriene C4 and its metabolites, leukotriene D4 and leukotriene E4. The leukotrienes participate in host defense reactions and pathophysiological conditions such as immediate hypersensitivity and inflammation. Recent studies also suggest a neuroendocrine role for leukotriene C4 in luteinizing hormone secretion. Lipoxins are formed by the action of 5- and 15-lipoxygenases on arachidonic acid. Lipoxin A causes contraction of guinea pig lung strips and dilation of the microvasculature. Both lipoxin A and B inhibit natural killer cell cytotoxicity. Thus, the multiple interaction of lipoxygenases generates compounds that can regulate specific cellular responses of importance in inflammation and immunity.

Release of slow-reacting substance of anaphylaxis in the rat: polymorphonuclear leukocyte.

The antigen-induced release of slow-reacting substance of anaphylaxis was studied in rats previously treated with different biological and pharmacological agents to deplete these animals of specific cellular elements. The polymorphonuclear leukocyte appears necessary as a crucial cell type for optimum release of the slow-reacting substance of anaphylaxis, whereas the mast cell and lymphocyte are not required.

Leukotrienes: mediators of immediate hypersensitivity reactions and inflammation.

Arachidonic acid plays a central role in a biological control system where such oxygenated derivatives as prostaglandins, thromboxanes, and leukotrienes are mediators. The leukotrienes are formed by transformation of arachidonic acid into an unstable epoxide intermediate, leukotriene A4, which can be converted enzymatically by hydration to leukotriene B4, and by addition of glutathione to leukotriene C4. This last compound is metabolized to leukotrienes D4 and E4 by successive elimination of a gamma-glutamyl residue and glycine. Slow-reacting substance of anaphylaxis consists of leukotrienes C4, D4, and E4. The cysteinyl-containing leukotrienes are potent bronchoconstrictors, increase vascular permeability in postcapillary venules, and stimulate mucus secretion. Leukotriene B4 causes adhesion and chemotactic movement of leukocytes and stimulates aggregation, enzyme release, and generation of superoxide in neutrophils. Leukotrienes C4, D4, and E4, which are released from the lung tissue of asthmatic subjects exposed to specific allergens, seem to play a pathophysiological role in immediate hypersensitivity reactions. These leukotrienes, as well as leukotriene B4, have pro-inflammatory effects.

Effects of endogenously produced leukotrienes, thromboxane, and prostaglandins on coronary vascular resistance in rabbit myocardial infarction.

In an effort to evaluate the synthesis and function of eicosanoids in myocardial infarction, we have developed a technique of in vivo myocardial infarction in rabbits followed by ex vivo cardiac perfusion. Isolated Langendorff perfused infarcted hearts (removed 1 or 4 d after infarction) responded to the inflammatory cell agonist N-formylmethionyl-leucyl-phenylalanine (fMLP) with (a) the release of leukotrienes B4, C4, and D4; (b) the release of large amounts of thromboxane (235 +/- 66 ng/5 min), prostacyclin (714 +/- 285 ng/5 min), and prostaglandin E2 (PGE2) (330 +/- 108 ng/5 min); and (c) a coronary vasoconstriction (21.1 +/- 2.5% increase in coronary perfusion pressure) that was specifically inhibited by the peptidoleukotriene receptor antagonist FPL-55712. While noninfarcted hearts challenged with fMLP also released leukotrienes B4, C4, and D4, they released only small amounts of the cyclooxygenase products (thromboxane, 30 +/- 9 ng/5 min; prostacyclin, 120 +/- 54 ng/5 min; PGE2, 27 +/- 10 ng/5 min) and showed minimal vasoconstriction (5.6 +/- 2.1% increase in perfusion pressure). Similarly, hearts challenged with fMLP 30 d following infarction released only small amounts of the cyclooxygenase products (thromboxane, 42 +/- 8 ng/5 min; prostacyclin, 386 +/- 31 ng/5 min; PGE2, 79 +/- 25 ng/5 min). When bradykinin was administered, no leukotrienes were produced, but acutely infarcted hearts released 10 times more thromboxane, prostacyclin, and PGE2 than normal hearts and significantly larger amounts of these products than 30-d infarcted hearts. Histologic analysis showed no inflammatory cells in normal hearts, a prominent polymorphonuclear leukocyte infiltration in 1-d infarcted tissue, fibroblast proliferation with mononuclear cell invasion in 4-d infarcted tissue, and a fibrotic scar with scanty mononuclear cell infiltrate in 30-d infarcted tissue. Inflammatory cell invasion was temporarily associated with augmented cyclooxygenase metabolism, suggesting that infiltrating leukocytes may be responsible for production of thromboxane, prostacyclin, and PGE2 in acutely infarcted hearts. The finding that endogenously produced peptidoleukotrienes are potent coronary vasoconstrictors in infarcted rabbit hearts suggests that these products may contribute to tissue injury in myocardial infarction.

Leukotriene D4 is a mediator of proteinuria and glomerular hemodynamic abnormalities in passive Heymann nephritis.

We assessed the role of leukotrienes (LTs) in Munich-Wistar rats with passive Heymann nephritis (PHN), an animal model of human membranous nephropathy. 10 d after injection of anti-Fx1A antibody, urinary protein excretion rate (Upr) in PHN was significantly higher than that of control. Micropuncture studies demonstrated reduced single nephron plasma flow and glomerular filtration rates, increased transcapillary hydraulic pressure difference, pre- and postglomerular resistances, and decreased ultrafiltration coefficient in PHN rats. Glomerular LTB4 generation from PHN rats was increased. Administration of the 5-LO activating protein inhibitor MK886 for 10 d markedly blunted proteinuria and normalized glomerular hemodynamic abnormalities in PHN rats. An LTD4 receptor antagonist SK&F 104353 led to an immediate reduction in Upr and to reversal of glomerular hemodynamic impairment. Ia(+) cells/glomerulus were increased in PHN rats. In x-irradiated PHN rats, which developed glomerular macrophage depletion, augmented glomerular LT synthesis was abolished. Thus, in the autologous phase of PHN, LTD4 mediates glomerular hemodynamic abnormalities and a hemodynamic component of the accompanying proteinuria. The synthesis of LTD4 likely occurs directly from macrophages or from macrophage-derived LTA4, through LTC4 synthase in glomerular cells.

Adenosine and leukotrienes have a regulatory role in lung surfactant secretion in the newborn rabbit.

Previous studies have shown that secretion of phosphatidylcholine in cultured adult rat type II pneumocytes is stimulated by purinoceptor agonists and leukotrienes. The objective of the present study was to determine if such agents have a physiological role in the regulation of surfactant secretion. We chose the newborn rabbit as the experimental model, since in this system there is a marked increase in surfactant secretion immediately after birth. We examined the effects of an inhibitor of leukotriene biosynthesis, nordihydroguaiaretic acid, two leukotriene antagonists, FPL-55712 and FPL-57231, and a P1 purinoceptor antagonist, 8-phenyltheophylline, on this increase. Newborn rabbits were delivered by Cesarean section at 30 days gestation. Some animals in each litter were killed immediately, while others were injected with test agents or solvent vehicle while still in the amniotic sacs. After breathing for 3 h in an incubator, these animals were also killed. The lungs were lavaged with saline and the phospholipid content and composition of the lung lavage liquid was measured. In control animals, there was a greater than 2-fold increase in the amounts of total phospholipid and phosphatidylcholine and in the phosphatidylcholine/sphingomyelin ratio during the 3 h period of breathing. The increases in total phospholipid and phosphatidylcholine were decreased 38-62% by the antagonists, while the increase in the phosphatidylcholine/sphingomyelin ratio was decreased 61-77%. These data show that the ventilation-induced increase in secretion of lung surfactant in the newborn rabbit is inhibited by leukotriene and P1 receptor antagonists and by an inhibitor of leukotriene biosynthesis and, when taken together with the data from the tissue culture system, support a role for leukotrienes and adenosine in the physiological regulation of surfactant secretion.

Intracellular mechanisms involved in leukotriene C4-stimulated adhesion of U-937 cells.

Leukotrienes C4 and D4 (LTC4 and LTD4) stimulated, 5- to 6-fold, the adhesion of the monoblastoid cell line U-937 to plastic. Half-maximal effects were observed around 1 nM. Leukotrienes E4 and B4 (LTE4 and LTB4) were less effective. The adhesive response to LTC4 was inhibited by pertussis toxin and was completely dependent on the presence of extracellular Ca2+. The LTC4-stimulated increases in inositol-phosphates and in intracellular Ca(2+)-concentration were insensitive to pertussis toxin. Activation of leukocyte adhesion is a novel action of cysteinyl-leukotrienes and the present study suggests that control of U-937-cell adhesion by LTC4 involves two pathways; one pertussis toxin insensitive pathway regulating intracellular Ca2+ in a manner partly dependent on extracellular Ca2+ and one pertussis toxin sensitive pathway not concerned with Cai(2+)-regulation.

Selective inhibition by H7 and staurosporin of phorbol ester responses in U-937 cells.

The kinase inhibitors H7 and staurosporin dose-dependently stimulate adhesion U-937 cells to plastic but fail to inhibit the CD11b/CD18-dependent adhesion of U-937 cells induced by phorbol ester. The protein kinase C activity of U-937 cells, measured as phorbol ester-stimulated phosphorylation of pep epsilon in streptolysin-O permeabilized cells, is strongly inhibited by the kinase inhibitors. H7 and staurosporin efficiently overcome the inhibitory effect of phorbol-12,13-dibutyrate (PDBu) on leukotriene D4-induced increase in intracellular Ca2+. The results suggest that U-937 cell adhesion may be controlled by a protein kinase C isoform not sensitive to the inhibitors. In addition, the data indicate that selective pharmacological interference with different protein kinase C-mediated processes is achievable.

Cysteinyl leukotrienes modulate angiotensin II constrictor effects on aortas from streptozotocin-induced diabetic rats.

Angiotensin II (Ang II) is a vasopressor peptide involved in the pathogenesis of cardiovascular diseases associated with diabetes mellitus. We have previously reported that the 5-lipoxygenase-derived products, particularly the cysteinyl leukotrienes (CysLTs), are involved in Ang II-induced contraction. In this study, we demonstrated that CysLTs contribute to the contraction elicited by Ang II in isolated aortas from streptozotocin-induced diabetic (SS) rats but not from insulin-treated diabetic rats, fructose-fed rats, or control rats. In an organ bath, pretreatment with the 5-lipoxygenase inhibitor (AA861, 10 micromol/L) reduced by 37.6+/-8.2% and 30.1+/-10.9% the Ang II-induced contractions in intact and endothelium-denuded aortic rings, respectively, from SS rats. In contrast, the CysLT(1) receptor antagonist (MK571, 1 micromol/L) or the dual CysLT(1)/CysLT(2) receptor antagonist (BAY-u9773, 0.1 micromol/L) did not affect Ang II-induced contraction. In addition, Ang II induced a 6.2+/-1.5-fold increase in CysLT release through the stimulation of the Ang II type 1 receptor. Furthermore, the urinary excretion of leukotriene E(4) was increased in SS rats (leukotriene E(4), 13.7+/-2.9 ng/24 h [SS rats, n=10] versus 1.5+/-0.5 ng/24 h [control rats, n=6]; P<0.0004). These data suggest the activation of the 5-lipoxygenase pathway in SS rats and the involvement of 5-lipoxygenase-derived products, particularly the CysLTs, in Ang II-induced contraction in aortas from SS rats through stimulation of CysLT receptors different from the well-characterized CysLT(1) or CysLT(2) receptor.

Evidence for the role of leukotrienes C4 and D4 as essential intermediates in CSF-stimulated human myeloid colony formation.

Products of the lipoxygenation of arachidonic acid have been shown to induce a variety of effects on cells of myeloid lineage. Colony-stimulating factor causes release of arachidonic acid from cell membranes, which then undergoes oxygenation via the cyclooxygenase and lipoxygenase pathways. Nordihydroguaiaretic acid (NDGA) and 3-amino-1-[m(trifluoromethyl)-phenyl]-2-pyrazoline (BW 755C), compounds that inhibit both the cyclooxygenase and lipoxygenase pathways, cause dose-dependent inhibition of CSF-induced human granulocyte-monocyte colony formation in vitro, with complete inhibition at 20 and 50 microM, respectively. Indomethacin, which inhibits cyclooxygenase but not lipoxygenase, has no effect on colony growth at 50 microM, which is well in excess of the dose needed for complete inhibition of cyclooxygenase. Leukotrienes (LTs) C4 and D4 (5-100 ng/ml) reverse NDGA inhibition of colony growth. At similar concentrations, neither leukotriene B4 or 5-HETE caused reversal of NDGA inhibition. These results support a role for LTC4 and LTD4 as essential intermediates in CSF-stimulated myeloid colony formation.

Cysteinyl leukotrienes are involved in angiotensin II-induced contraction of aorta from spontaneously hypertensive rats.

OBJECTIVE: Non specific lipoxygenase inhibitors have been reported to reduce the in vitro constrictor response and the in vivo pressor effect of angiotensin II in rats. The aim of this study was to assess the role of cysteinyl leukotrienes, in the vascular response to angiotensin II in spontaneously hypertensive rats (SHR). METHODS: Rings of thoracic aorta from SHR and normotensive Wistar-Kyoto rats (WKY) were compared in terms of contractile responses and release of cysteinyl leukotrienes in response to angiotensin II. RESULTS: Pretreatment with the specific 5-lipoxygenase inhibitor AA861 10 microM reduced the efficacy of angiotensin II in intact and endothelium-denuded aorta from SHR (% inhibition vs. control: 65+/-12.6% with endothelium (n=6), P<0.05; 43+/-7.2% without endothelium (n=6), P<0.05) but not in aorta from WKY. In addition, in aorta from SHR, the CysLT(1) receptor antagonist MK571 1 microM reduced by 55+/-6.1% (n=6, P<0.05) the contractile effects of angiotensin II in rings with endothelium but not in endothelium-denuded rings. Angiotensin II induced a 8.6+/-2.1-fold increase in cysteinyl leukotriene production in aorta rings from SHR with endothelium which was prevented by the AT(1) receptor antagonist losartan 1 microM but not by the AT(2) receptor antagonist PD123319 0.1 microM. In aorta rings from WKY, cysteinyl leukotriene production remained unchanged after exposition to angiotensin II. The cysteinyl leukotrienes (up to 0.1 microM) induced contractions in aorta rings from SHR but not from WKY. CONCLUSIONS: These data suggest that cysteinyl leukotrienes, acting at least in part on endothelial CysLT(1) receptors, are involved in the contractile response to angiotensin II in isolated aorta from SHR but not from WKY.

Rabbit uterine oxytocin receptors and in vitro contractile response: abrupt changes at term and the role of eicosanoids.

We examined the relation between increased uterine oxytocin receptor concentration and increased in vivo sensitivity of the rabbit uterus to oxytocin at the end of gestation. We determined oxytocin receptor concentrations in myometrium and decidua on different days near term of gestation and postpartum. We also examined the in vitro contractile response to oxytocin on days 30 and 5 days postpartum, when the uterus is unresponsive in vivo, and on day 31 (term), when the uterus is exquisitely sensitive to this hormone in vivo. In addition, we tested the role of endogenous eicosanoids and decidual oxytocin receptors in the myometrial contractile response to oxytocin by examining the contractile response in the presence of the cyclooxygenase/lipoxygenase inhibitor sodium meclofenamate or in muscle strips from which the decidua had been removed by scraping. The concentration of specific binding sites for [3H]oxytocin in myometrial and also decidual membrane preparations was determined. We demonstrate that contractile sensitivity to oxytocin increases at least 4-fold between days 30 and 31 (term) of gestation, and this is accompanied by a nearly 10-fold increase in the concentration of oxytocin-binding sites in both decidua and myometrium. The lesser sensitivity to oxytocin on day 30 was, however, only apparent in the presence of meclofenamate, which suggests that endogenous eicosanoids contribute to the preterm response to oxytocin measured in vitro. The maximal response to oxytocin (integrated area) increased 2-fold between day 30 and term. Thus, an increase in both sensitivity and maximal response to oxytocin could be demonstrated at term in vitro. Five days after parturition, maximal response and uterine sensitivity measured in the presence of meclofenamate had returned to those of the preterm uterus, and the concentration of oxytocin-binding sites had declined. In contrast, sensitivity and maximal response to the cholinergic agonist carbamylcholine declined between day 30 and term. These results support a highly regulated physiological role for oxytocin in parturition which depends primarily on changes in receptor concentration.

Role of granulocytes in endothelial injury in coronary heart disease in humans.

Recent studies suggest that granulocytes (PMNs) play a role in the pathogenesis of acute and chronic myocardial ischemia and extension of myocardial injury. A positive correlation was also found between leukocyte count and severity of coronary artery disease. Rabbit derived antiserum dependent-reduction of circulating PMNs in the dog or using monoclonal antibody anti-CD11b/CD18 of PMNs resulted in smaller myocardial infarcts. Granulocytes can release a variety of mediators tissue injury and synergize with these different mediators and other cells resulting in amplification of neutrophil stimulation and rising to additional products with enhanced endothelial injury. This paper reviews "in vivo" studies that have been instrumental in demonstrating this role of granulocytes as a mediator of myocardial ischemia. Experience in humans shows the modification of PMNs function in angina and during myocardial ischemia, and data from our group demonstrated that their aggregability is increased in the coronary sinus of patients with angiographically documented coronary disease. Upon re-perfusion PMNs accumulate and produce an inflammatory response resulting in endothelial injury. Free radicals formed during ischemia or re-perfusion produce deleterious effects on cell membranes, endothelial cell and myocardium. On the other hand the PMNs activation occurring during coronary angioplasty (PTCA) by the release of proteolytic enzymes and the generation of oxygen-free radicals, may aggravate the endothelial damage induced by PTCA and further stimulate platelets having potential implications in subsequent development of restenosis. An other aspect of PMNs function is related to leukotriene C4 release; the vasoconstrictor effect of this leukotriene on coronary arteries is synergistic with that induced by platelet-released thromboxane A2, as well as the decrease in coronary flow produced by the combination of both substances is greater than the sum of changes caused by the two eicosanoids separately administered. The potential role of leukocytes, oxygen radicals, leukotrienes and granulocyte enzymes in pathophysiology of myocardial injury due to a regional ischemia and reperfusion is an area of intense investigation. Experimental and clinical studies to elucidate these events should not only provide insights into acute and chronic pathologic tissue damage, but may also lead to the identification of important new targets of pharmacologic intervention.

Inflammatory mechanisms and nocturnal asthma.

The results of recent research strongly suggest that airway inflammation, which may increase at night as a result of circadian troughs in blood epinephrine and cortisol concentrations, underlies the bronchial hyperresponsiveness that is almost certainly a major contributor to the pathogenesis of nocturnal asthma. This article reviews what is known about the nature and complex interactions of the inflammatory cells and mediators that may be involved in asthma, with particular emphasis on nocturnal asthma. The roles of platelet-activating factor antagonists, corticosteroids, and theophylline in suppressing this response also are discussed.

Prostaglandins and the mechanism of action of anti-inflammatory drugs.

Aspirin and a large number of nonsteroidal anti-inflammatory drugs act primarily through the inhibition of prostaglandin synthesis by inhibiting the enzyme cyclooxygenase. Other groups of biologically active polyunsaturated fatty acid derivatives including the leukotrienes, are generally not inhibited by this class of drugs in the same concentration ranges. Inhibition of the vasodilator prostaglandins, prostaglandin E2 and prostacyclin, as well as the leukotrienes, may reduce their inflammatory effects in several disease states. In addition, prostaglandin synthesis is also inhibited by glucocorticoids even though their mode of action may involve other effects as well. Prostaglandin E2 stimulates the osteoclastic reabsorption of juxtaarticular bone; its inhibition by nonsteroidal anti-inflammatory agents may, therefore, retard the process of bone erosion in rheumatoid arthritis and in other inflammatory processes. Inhibition of prostaglandin synthesis by these drugs accounts for many of their major toxic effects, including gastritis, which is the most common side effect; precipitation or aggravation of renal failure; fluid retention; hyperkalemia; antiplatelet effects with hemorrhagic phenomena; and aggravation of asthma and rhinosinusitis. Inhibition of prostaglandin synthesis can, therefore, account for most of the therapeutic as well as toxic effects of the nonsteroidal anti-inflammatory agents. Inhibition of pathways of synthesis of other important mediators, such as leukotrienes, are currently under investigation and may provide another approach for the development of new therapeutic agents.

Prostaglandins, thromboxanes, and leukotrienes in inflammation.

Arachidonic acid undergoes two metabolic pathways in leukocytes. The first, catalysis by prostaglandin cyclo-oxygenase, yields the prostaglandin endoperoxides G2 and H2 and thromboxane A2, which induce rapid irreversible aggregation of human platelets and are potent inductors of smooth muscle contraction. The second pathway, catalysis by lipoxygenase, yields various hydroperoxy acids. In platelets, 12-hydroperoxyeicosatetraenoic acid is the predominant product; in polymorphonuclear leukocytes, 5-hydroperoxyeicosatetraenoic acid is formed. These are primarily reduced to 12-hydroxyeicosatetraenoic acid and 5-hydroxyeicosatetraenoic acid. 5-Hydroperoxyeicosatetraenoic acid may also be dehydrated to leukotriene A4. Enzymatic hydrolysis of leukotriene A4 yield leukotriene B4, a potent mediator of leukocyte function. Prostaglandins, thromboxanes, and some hydroxyeicosatetraenoic acids exert chemotactic effects on polymorphonuclear leukocytes. In this respect, leukotriene B4 is the most active compound derived from arachidonic acid. In vivo, adherence of leukocytes to the endothelium of microvessels near inflammatory areas and the sticking phenomenon of these cells are the initial hallmarks of an inflammatory response. In vitro, these responses seem to correspond with leukocyte aggregation and adherence. Leukotriene A4 may also react to form leukotriene C4 (a natural component of slow-reacting substance of anaphylaxis), leukotriene D4, leukotriene E4, and the 11-trans-isomers. All three leukotrienes are virtually unable to induce chemotaxis, enzyme release, or leukocyte aggregation, but they possess biologic properties previously attributed to slow-reacting substances, such as a potent effect on smooth muscle in the peripheral airway and an ability to markedly increase macromolecular permeability in venules. In addition to prolonging bleeding time and causing gastric ulcers, aspirin and other nonsteroidal anti-inflammatory drugs can trigger or aggravate an asthmatic attack. Aspirin can also trigger or aggravate urticaria, probably as a direct effect of thioether leukotrienes rather than from antibody mediation. Many nonsteroidal anti-inflammatory drugs increase formation of slow-reacting substance-A after challenge with allergen, perhaps by inhibiting cyclo-oxygenase, thereby releasing more arachidonic acid for metabolism by lipoxygenase. Alternatively, certain prostaglandins inhibit liberation of arachidonic acid from phospholipids; inhibiting their formation causes release of more arachidonic acid, which must be metabolized by different lipoxygenase pathways, since the cyclo-oxygenase pathway is closed.

Co-participation of thromboxane A2 and leukotriene C4 and D4 in mediating cyclosporine-induced acute renal failure.

The relative role of thromboxane (TxA2) and sulfidopeptide leukotrienes C4 (LTC4) and D4 (LTD4) in the acute renal failure induced by cyclosporine was studied in the rats. Bolus i.v. administration of 20 mg/kg of CsA but not vehicle to adult male Sprague-Dawley rats resulted in a significant fall in glomerular filtration rate from 0.85 +/- 0.10 and renal plasma flow (RPF) 2.45 +/- 0.14 ml/min/100 g body wt to values at 20 min of 0.47 +/- 0.03 and 1.01 +/- 0.12 ml/min/100 g body wt (P less than 0.01), respectively, without a fall in mean arterial pressure. This hemodynamic effect was maintained for the following 40-min period. Pretreatment of rats with the TxA2 receptor antagonist GR32191 (3 mg/kg i.v.) allowed a partial but significant preservation of GFR (0.60 +/- 0.05 ml/min/100 g body wt) and RPF (1.55 +/- 0.12 ml/min/100 g body wt). In addition, the antagonism of endogenously produced LTC4 and LTD4 with the putative receptor antagonist L-649,923 (1 mg/kg i.v.) partially prevented the fall in GFR (0.65 +/- 0.07 ml/min/100 g body wt) and RPF (1.80 +/- 0.18 ml/min/100 g body wt) at 20 min after CsA injection. The combined administration of GR32191 and L-649,923 completely abolished the CsA-induced decline in GFR (0.80 +/- 0.09 ml/min/100 g body wt) and RPF (2.40 +/- 0.12 ml/min/100 g body wt). These findings suggest that TxA2 and LTC4/LTD4 participate in mediating renal function deterioration induced by acute CsA administration in the rat.

Characterization of the conjunctival vasopermeability response to leukotrienes and their involvement in immediate hypersensitivity.

The microvascular permeability response of the guinea pig conjunctiva to sulfidopeptide leukotrienes (LTs) was quantified as extravasation of radiolabeled bovine serum albumin. The LTs were potent inducers of increased microvascular permeability, with relative potencies LTE4 greater than or equal to LTD4 greater than LTC4. The response to LTs was unaffected by indomethacin or a pyrilamine/cimetidine combination, but the LT antagonists FPL 55712 and SKF 102922 significantly inhibited the response to LTC4, LTD4 and LTE4. In guinea pigs actively sensitized to ovalbumin, topical ocular administration of ovalbumin markedly increased conjunctival microvascular permeability; this response was reduced by approximately 50% following histaminergic blockade by pyrilamine/cimetidine. FPL 55712 and SKF 102922 and the 5-lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA) had no effect on the response to antigen when used alone. However, each agent significantly reduced the non-histaminergic component of the response when given in conjunction with pyrilamine/cimetidine. Thus, it appears that the immediate hypersensitivity response in guinea pig conjunctiva has a possible non-histaminergic component which is at least partly mediated by LTs.

An in vivo model for measuring antigen-induced SRS-A-mediated bronchoconstriction and plasma SRS-A levels in the guinea-pig.

1 Pharmacological modulation of antigen-induced anaphylaxis in actively sensitized guinea-pigs with intravenously administered indomethacin (10 mg/kg), pyrilamine (2.0 mg/kg) and propranolol (0.1 mg/kg) resulted in a delayed onset, slowly developing bronchoconstriction indicative of a slow-reacting substance of anaphylaxis (SRS-A) response. 2 Measurements of pulmonary mechanics on the drug-pretreated animals challenged with ovalbumin demonstrated a more prominent effect on dynamic compliance than resistance. This is consistent with the more potent effects of SRS-A on peripheral rather than central airways. 3 The slowly developing bronchoconstriction obtained after treatment with indomethacin, pyrilamine and propranolol was inhibited by the standard SRS-A antagonist, FPL 55712 and the SRS-A synthesis inhibitors, phenidone, BW 755C and nordihydroguaiaretic acid. 4 Plasma SRS-A levels were determined in guinea-pigs following antigen challenge. The appearance of SRS-A in the plasma preceded the onset of bronchoconstriction and SRS-A levels remained elevated throughout its development. Coincident with the inhibition of bronchoconstriction by the SRS-A synthesis inhibitor, phenidone, was a dose-dependent reduction in plasma SRS-A. The intravenous ED50 in each case was 4 mg/kg. 5 This model of antigen-induced SRS-A-mediated bronchoconstriction should prove useful for the in vivo evaluation and development of therapeutics which regulate the synthesis of SRS-A.

Involvement of SRS-A in the Schultz-Dale response of the guinea-pig small intestine.

1 The anaphylactic reaction of the guinea-pig ileum, the so called Schultz-Dale reaction, shows a biphasic response: a short rapid contraction followed by a partial relaxation and a slow contractile response. 2 Dose-response curves with ovalbumin as an antigen were obtained for the quick and slow contraction of this anaphylactic reaction. 3 Mepyramine (1 microgram/ml) blocked the rapid first contraction, but failed to abolish the slow one in about 50% of the animals studied. 4 The SRS-A antagonist, FPL 55712, significantly depressed the slow sustained contraction during the Schultz-Dale reaction. Disodiumcromoglycate was without effect on both phases when it was added 5 min before addition of the antigen. However, when added simultaneously with the antigen it produced a 30% suppression of the slow phase in the highest concentration used.