Intraperitoneal injection of zymosan in mice induces pain, inflammation and the synthesis of peptidoleukotrienes and prostaglandin E2

Intraperitoneal injection of zymosan in mice induced rapid extravasation and accumulation of plasma protein in the peritoneal cavity. Neutrophils began to appear in the peritoneal cavity after a lag period of approximately 3 hours. The injected mice exhibited a pain response (writhing) during the first 30 minutes after injection, but writhing ceased before protein or cell accumulation had reached maximum levels. The injection of zymosan induced synthesis of PGE2 (measured by RIA) which reached maximum levels at 30 minutes, then declined slowly. Peptido-leukotriene levels (detected by bioassay, RIA and HPLC) increased rapidly after injection, reached a peak within an hour of injection and declined to undetectable levels within 4 hours. The early peptido-LT was predominantly LTC4, while later, LTE4 was the major component. LTD4 levels remained low throughout and no LTB4 was detected at any time. Indomethacin treatment elevated levels of peptido-LTs, reduced PGE2 levels and inhibited writhing. Phenidone reduced peptido-LT levels. In vitro studies demonstrated that zymosan stimulates LTC4 synthesis by peritoneal cells whereas LTE4, LTD4, LTB4 or monoHETES were not detectable (using HPLC methods). The source of enzymes responsible for the in vivo metabolism of LTC4 to LTD4 and LTE4 could not be identified.     

Leukotriene D4 and E4 formation by plasma membrane bound enzymes

The homogenate of rat basophilic leukemia cells produces both the dihydroxy-leukotrienes and the peptido-leukotrienes (LT) C₄, D₄ and E₄. The enzymes responsible for the formation of LTA₄ and LTB₄ are in the soluble fraction while the enzymes for LTC₄, LTD₄ and LTE₄ are particulate (10, 000 × g pellet). Centrifugation of the 10, 000 × g pellet over a sucrose gradient resulted in two subfractions, a membrane fraction and a pellet (sucrose pellet.) The fractions were incubated with LTC₄, and the products were identified by bioassay, HPLC and UV spectra. The membrane fraction contained the enzymes γ-glutamyl transpeptidase and amino peptidase which convert LTC₄ to LTD₄ and LTD₄ to LTE₄, respectively. When incubated with LTC₄, the membrane fraction showed a dose dependent formation of LTD₄ and a time course which reached a plateau at 30 to 45 minutes. Addition of serine borate blocked the formation of LTD₄, and cysteine blocked LTE₄. We conclude that the γ-glutamyl transpeptidase and the amino peptidase which produce LTD₄ and LTE₄ respectively are plasma membrane bound.     

Specificity of receptors for leukotrienes A4, B4, C4, D4, E4 and histamine on the guinea-pig lung parenchyma. Effect of FPL-55712 and desensitization of the myotropic activity

The novel metabolites of arachidonic acid, leukotriene (LT) A₄, B₄, C₄, D₄ and E₄ have potent myotropic activity on guinea-pig lung parenchymal strip . The receptors responsible for their action were characterized using desensitization experiments and the selective SRS-A antagonist, FPL-55712. During the continuous infusion of LTB₄, the tissues became desensitized to LTB₄ but were still responsive to histamine, LTA₄, LTC₄, LTD₄ and LTE₄. When LTD₄ was infused continuously, the lung strips contracted to LTB₄ and histamine but were no longer responsive to LTA₄, LTC₄, LTD₄ and LTE₄. Furthermore, FPL-55712 (10 ng ml⁻¹− 10 ug ml⁻¹) produced dose-dependent inhibitions of LTA₄, LTC₄, LTD₄ and LTE₄ without inhibiting the contraction to LTB₄ and histamine. On the basis of these results, it appears that the guinea-pig lung parenchyma may have one type of receptor for LTB₄ and another for LTD₄; LTA₄, LTC₄ and LTE₄ probably act on the LTD₄ receptor.     

The combined use of isolated strips of guinea-pig lung parenchyma and ileum as a sensitive and selective bioassay for leukotriene B4

The biological effects of leukotriene (LT)B₄ were compared, on a molar basis, with those LTC₄, LTD₄, LTE₄, 5-hydroxyeicosatetraenoic acid (5-HETE), PGD₂, PGE₁, PGF_2α, PGI₂, 6-oxo-PGF_1α, bradykinin (BK) and angiotensin II (Ang II) on isolated strips of guinea-pig lung parenchyma (GPP) and ileum smooth muscle (GPISM) superfused in series.LTB₄ similar to LTC₄ and LTD₄ on GPP, in relation to potency and contractions induced, but differed from LTE₄ in being ten times more active and causing contractions of a much shorter duration of action on this tissue. However, unlike the other LTs, LTB₄ produced contractions which were resistant to FPL 55712 (1.9μM) and, when given repeatedly, caused tachyphylaxis in GPP,LTB₄ was considerable more active on GPP than the other substances investigated. Further, PGD₂, PGF_2α and PGI₂ contracted GPP, the order of potency being PGD₂ > PGF_2α ? PGI₂ whereas PGE₁ and PGE₂ relaxed this tissue. In contrast to all other agonists tested which contracted GPISM, LTD₄ displaying the highest activity, LTB₄ was inactive on this tissue. 5-HETE and 6-oxo-PGF_1α were inactive on both GPP and GPISM.On the basis of differential effects of LTB₄ on GPP and GPISM, this assay repressents a simple and selective means to distinguish LTB₄-like materials from other naturally-occuring substances likely to be generated in inflammatory fluids.     

Quantitation of luekotrienes C4, D4 amd E4 released by pathophysiological stimuli

In order to examine the modulation of leukotriene (LT) release, the PAF-acether-mediated stimulation of these compounds in rat lung was studied. Release of LTC₄, LTD₄ and LTE₄ in both perfused and chopped lung preparations was measured using HPLC and radioimmunoassay. Pre-incubation or pre-infusion of the tissue with indomethacin and PGE₂ was conducted to investigate the effect of cyclooxygenase inhibitors and products on the lipoxygenase pathway. In addition, the effects of LT levels of pre-incubation with vasoactive intenstinal polypeptide (VIP) in chopped lung were observed.In perfused rat lung, indomethacin reduced the levels of LTC₄ relative to LTD₄ as measured in the first 2 min after stimulation of the lung by PAF-acether. Chopped lung preparations, incubated for 15 min. exhibited higher levels of LTC₄ and LTD₄ in indomethacin-treated samples, this increases being effectively reversed by PGE₂.In the VIP pre-incubation experiments clear inhibition of peptido -leukotriene synthesis was observed, with no LTC₄ and only low levels of LTD₄ and LTE₄ observed in VIP-incubated samples. In preliminary experiments using rabbit C5a des arg and PAF-acether on rabbit lung parenchyma strips to stimulaet LT release, disodium cromoglycate pre-incubation was observed to inhibit this release.Inhibition of the 5-lipoxygenase pathway of PGE₂ is supported by these experiments. VIP appears to act as an inhibitor of LTC₄ and LTD₄ biosynthesis or release in this model. Too little is known that peptidergic actions to postulate a mechanism by which a neuroendocrine peptide exerts control of release of arachidonate metabolites; however, VIP is associated with muscarinic stimulation (1) and has been found in mast cells (2).     

Leukotriene-induced contraction is mediated by cysteinyl leukotriene receptor CysLT1 in guinea pig fundus but by CysLT1 and CysLT2 in antrum

AimsLeukotriene D₄ (LTD₄) causes contraction of the stomach through unclear receptors. The aim of the present study is to characterize the cysteinyl leukotriene receptor (CysLT) mediating leukotriene-induced muscle contraction in the stomach.Main methodsWe measured contraction of gastric muscle strips isolated from the guinea pig fundus and antrum caused by cysteinyl leukotrienes, including LTC₄, LTD₄ and LTE₄, as well as the dihydroxy leukotriene LTB₄ in vitro.Key findingsIn both fundic and antral muscle strips, LTC₄ and LTD₄ caused marked whereas LTE₄ caused moderate, concentration-dependent contractions. In contrast, LTB₄ caused only small contraction. The relative potencies for cysteinyl leukotrienes to cause contraction in both fundus and antrum were LTC₄ = LTD₄ > LTE₄. The LTD₄-induced contraction was not affected by tetrodotoxin or atropine, suggesting that the action is not neurally mediated. The LTD₄-induced contraction in the fundus was almost abolished by the CysLT₁ selective antagonist montelukast. In contrast, the LTD₄-induced contraction in the antrum was only partially inhibited by montelukast or the dual CysLT₁ and CysLT₂ antagonist BAY u9773. This antral contraction was almost abolished by the combination of montelukast and BAY u9773, indicating enhancement of inhibition.SignificanceThe results of the present study demonstrate that cysteinyl leukotrienes LTC₄, LTD₄ and LTE₄ cause moderate to marked whereas the dihydroxy leukotriene LTB₄ causes small muscle contraction in the stomach in vitro. The leukotriene-induced contraction is mediated by CysLT₁ in fundus but by CysLT₁ and CysLT₂ in antrum.     

Leukotrienes cause eosinophil emigration into conjunction tissue

The ability of LTB₄, LTC₄, the 5S,6R and 5R,6S LTD₄ stereoisomers, and LTE₄ to evoke leukocyte infiltration into the conjunctiva was demonstrated in the guinea pig by histological andl ight microscopy techniques. LTD₄ and LTE₄ demonstrated a dose-dependent and predominantly eosinophilic infiltrate over the selected dose range (10ng to 1000ng), while there was only a minimal response to LTC₄. LTB₄ produced marked eosinophil inflitrates only at the highest dose; scattered neutrophil infiltrates were also noted at the high dose of LTB₄. The 5R,6S LTD₄ stereoisomer did not evoke any leukocyte infiltrantion. The SRS-A antagonist, FPL 55712, abolished pre-treatment had no inhibitory effect, indicating direct mediation of this response by LTs. Histamine caused a comparable eosinophilia over a dose range of 10μg to 1000μg. LT-induced eosinophil emigration was directed to the conjunctival epithelium; the cells appeared intact and no tissue damage was observed. These results may have relevance in the areas of allergic conjunctivitis and asthma research.     

Contraction of guinea pig gail bladder strips by leukotrienes and other agonists

In the presence of indomethacin, Leukotriene C₄ (LTC₄), LTD₄ and LTE₄ were shown to be contractile agents on guinea pig gall bladder strips. The respective pD₂ values for LTC₄, LTD₄ ad LTE₄ were 9.1, 9.1 and 7.7. The contractile effects of LTD₄ were not mediated through the generation of cyclooxygenase products and were antagonized by the SRS-A antagonist FPL-55712. The effects of PGE₁, PGF_2α, the endoperoxide analogue U44069 and histamine on gall bladder strips were also examined. All these agents caused dose-related contractions but were considerably less potent than the leukotrienes. Leukotrienes are therefore potent contractile agents on the guinea pig gall bladder and may contribute to gall bladder contractions or spasms .     

Antinociceptive activity of filenadol on inflammatory pain

The novel analgesic filenadol (d,1-erythro-1-(3′,4′-methylenedioxyphenyl)-1-morpholinopropan-2-ol) inhibited phenyl-p-benzoquinone-induced writhing in mice with ID₅₀ values of 68.8 (p.o.), 1.67 (i.v.) and 0.48 (i.c.v.) mg/kg. Hyperalgesia induced by arachidonic acid, PGE₂ or LTB₄ in this test was also decreased by filenadol (ID₅₀ = 24.4, 3.7 and 50.1 mg/kg p.o., respectively). This compound was effective on PGE₂, LTB₄, bradykinin, PAF or IL-1μ-induced decrease in pain threshold in the rat paw pressure model and almost totally suppressed the writhing induced by zymosan in mice, while peritoneal production of 6-ketoPGF_1α was inhibited by 48.5–62 % and only at 100 mg/kg significant inhibition of LTC₄ was achieved. The late phase of formalin-induced pain response in mice was prevented by filenadol, without affecting the oedema. Filenadol is an antinociceptive agent that reduces the hyperalgesic effects of inflammatory mediators besides inhibiting partially the synthesis of eicosanoids.     

Pharmacology of peptide leukotrienes on ferret isolated airway smooth muscle

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

Functional expression of single-chain antibody to leukotriene C4

Leukotriene C₄ (LTC₄) is synthesized by binding of glutathione to LTA₄, an epoxide derived from arachidonic acid, and further metabolized to LTD₄ and LTE₄. We previously prepared a monoclonal antibody with a high affinity and specificity to LTC₄. To explore the structure of the antigen-binding site of a monoclonal antibody against LTC₄ (mAbLTC), we isolated full-length cDNAs for heavy and light chains of mAbLTC. The heavy and light chains consisted of 461 and 238 amino acids including a signal peptide with molecular weights of 51,089 and 26,340, respectively. An expression plasmid encoding a single-chain antibody comprising variable regions of mAbLTC heavy and light chains (scFvLTC) was constructed and expressed in COS-7 cells. The recombinant scFvLTC showed a high affinity with LTC₄ comparable to mAbLTC. The scFvLTC also bound to LTD₄ and LTE₄ with 48% and 17% reactivities, respectively, as compared with LTC₄ binding, whereas the antibody showed almost no affinity for LTB₄.     

Contraction of guinea pig uterus by synthetic leukotrienes

Synthetic leukotrienes (LT) C₄ and D₄ elicited concentration-dependent contractions of the guinea pig uterus between 10^?8-10^?6M, whereas LTE₄ appeared 1000-fold weaker. The potencies of LTC₄ and LTD₄ were similar to that of acetylcholine and PGF_2α but weaker than that of PGE₂. The maximal contractions elicited by LTC₄ and LTD₄ were 66.0 ± 2.1% and 63.8 ± 4.6% that elicited by acetylcholine. FPL 55712 (10^?5M) antagonized the uterine contractile activity of LTD₄, while meclofenamic acid at 10^?5M but not at 10^?6M also antagonized the LTD₄-induced contration. Radioimmunoassay of the uterine tissue bathing fluid following LTD₄ indicated the variable presence of low concentrations of PGE₂, PGF_2α and TXB₂. These results demonstrate the LTC₄ and LTD₄ possess significant uterine contractile activity, which may only partially be mediated indirectly via prostaglandin products.     

And THP-1 cells do not release LTB4, LTC4, or LTD4 in response to A23187

U937 and THP-1 cells possess some characteristics of human mononuclear phagocytes, cells which synthesize and release LTB₄, LTC₄, and LTD₄. Incubation of these cells with recombinant human interferongamma (IFN-gamma) or Phorbol Myristate Acetate (PMA) induces a more differentiated cell state. We hypothesized that U937 and THP-1 cells would release LTB₄, LTC₄, and LTD₄ in response to stimulation with the non-physiologic agonist, calcium ionophore A23187 and that preincubation with IFN-gamma or PMA might alter leukotriene release by thes cells. We cultured both cell lines for 48 hours in the presence and absence of IFN-gamma (10000 units/ml)n and for 120 hours in the presence and absence of PMA (160 nM) and then challenged them with A23187 (5uM) for 30 minutes at 37°C. The supernatants were deproteinated and assayed by RIA for LTB₄ and LTC₄ and by RP-HPLC for LTB₄, LTC₄, and LTD₄. Neither U937 nor THP-1 cells released quantities of leukotrienes detectable by RIA, <0.3ng/5 × 10⁶ cells. Peripheral blood mononuclear phagocytes from normal volumteers, cultured and challenged in vitro at under identical conditions, released 11.3 ± 2.9 ng LTB₄ and 2.0 ± 1.5 ng LTC₄/10⁶ viable monocytes. The lack of leukotriene production by U937 and THP-1 cells was not altered by preincubation for 48 hours with IFN-gamma (n=3) nor by preincubation with PMA for 120 hours (n=3). We conclude 1) U937 and THP-1 cells do not appear to be appropriate in vitro models for the examination of leukotriene release from normal mononuclear phagocytes. 2) Pre-incubation of U937 and THP-1 cells with IFN-gamma or PMA under the conditions tested, does not induce the ability of these cell lines to release leukotrienes.     

Generation of leukotriene B4 and leukotriene E4 from porcine pulmonary artery

When chopped porcine pulmonary arteries were incubated with calcium ionophore A23187 (1) in the presence of indomethacin there was a time dependent generation of a substance which produced contractions of superfused strips of guinea-pig ileum smooth muscle (GPISM) which were indistinguishable from those induced by LTD₄. This material however had a different retention time from LTD₄ when subjected to HPLC and co-chromatographed with synthetic LTE₄. In addition to LTE₄ a substance which had properties indistinguisable from those of LTB₄ when assayed on a combination of guinea-pig lung parenchymal strips (GPP) and GPISM (2) was generated from the pulmonary artery. This substance co-chromatographed with synthetic LTB₄. The adventitia and intima were the richest source of LTE₄, the adventitia releasing slightly more than the intima. The output of LTB₄ and LTE₄ was inhibited by 6,9-deepoxy-6,9-(phenylimino)-Δ^6,8 prostaglandin I₁ (U-60,257). Nordihydroguaiaretic acid (NDGA) inhibited the generation of LTE₄.     

The effect of leukotrienes C4 and D4 on the microvasculature of guinea-pig skin

The effects of chemically-synthesised leukotrienes C₄ and D₄ (5(S) hydroxy-6(R)-δ-glutamylcysteinylglycinyl-7,9,11,14-eicosa-⁴tetraenoic acid, LTC₄; 5(S) hydroxy-6(R)-cysteinylglycinyl-7,9,11,14-eicosatetraenoic acid, LTD₄) on the microvasculature have been measured in guinea-pig skin using [¹²⁵I]-albumin accumulation to measure plasma exudation and ¹³³Xe clearance to measure blood flow changes. As previously shown using biosynthetic material, LTD₄ caused vasoconstriction resulting in reduced blood flow. Similarly, LTC₄ was found to have vasoconstrictor activity but was more potent and had a steeper dose-response curve than LTD₄. There was no evidence of conversion of exogenous arachidonic acid to vaso-constrictor activity in the skin $\text{in vivo}$ (in the absence of another stimulus): intradermally injected arachidonic acid produced vasodilatation, but induced little change in blood flow in animals pretreated with indomethacin. The vasodilator effect of arachidonic acid is presumed to be due to conversion to either PGE₂ or PGI₂. These results suggest that cyclo-oxygenase is normally active in the skin, whilst lipoxygenase requires activation in some way. As reported in a previous study, LTD₄ induced plasma exudation when injected into the skin, but pronounced responses could only be induced by LTD₄ mixed with a vasodilator prostaglandin such as PGE₂. In contrast, LTC₄ induced no exudation when tested alone and little when PGE₂ was added. However, evidence was obtained that LTC₄ has some permeability-increasing activity which is marked by its potent vasoconstrictor activity.     

Melanocyte-Stimulating Properties of Arachidonic Acid Metabolites: Possible Role in Postinflammatory Pigmentation

Normal human epidermal melanocytes became swollen and more dendritic with an increase in the amount of tyrosinase and immunoreactive b-locus protein when they were cultured for 2 days with the following arachidonic acid metabolites: prostaglandin (PG) D₂, leukotriene (LT) B₄, LTC₄, LTD₄, LTE₄, thromboxane (TX) B₂ and 12-hydroxy eicosatetraenoic acid (12-HETE). The effect of LTC₄ was particularly strong compared to that of PGE₂, about which we have previously reported. On the other hand, PGE₁, PGF_2α and 6-ketoPGF_1α did not show any significant stimulatory effect. These data suggest that arachidonate-derived chemical mediators, especially LTC₄, may be responsible for the induction of post-inflammatory hyperpigmentation of the skin.     

Leukotriene F4: Comparison of its pharmacological profile with that of the other cysteinyl-containing leukotrienes in guinea-pig ileum and lung parenchyma in vitro

The biological effects of leukotriene (LT)F₄ were compared, on a molar basis, with those of LTC₄, LTD₄ and LTE₄ on isolated superfused strips of guinea-pig ileum smooth muscle (GPISM) and lung parenchyma (GPP). LTF₄ was 1–2 orders of magnitude less active than the other leukotrienes on GPISM (LTD₄ > LTC₄ > LTE₄ > LTF₄) whereas, in the GPP, the activity of LTF₄ was comparable with that of LTE₄, both leukotrienes being about one order of magnitude less active than LTC₄ or LTD₄ (LTC₄=LTD₄ > LTE₄=LTF₄). Further, LTF₄ caused protracted contractions of the GPP which were indistinguishable from those due to LTE₄ and of a much longer duration than responses elicited by either LTC₄ or LTD₄.FPL 55712 (1.9μM) antagonised actions of LTF₄ in both tissue preparations. Indomethacin (2.8μM) inhibited contractions induced by LTF₄ in GPP indicating that part of the bronchoconstriction due to LTF₄, like that elicited by the other leukotrienes, is mediated via release of cyclo-oxygenase products.     

A simple and sensitive radioreceptor assay for leukotrienes

A simple and sensitive radioreceptor assay (RRA) for leukotrienes (LTs) was developed using a highly specific [³H]leukotriene D₄ (LTD₄) binding to guinea pig lung membrane homogenates. The assay can detect down to 0.15 pmol of LTD₄. The values for fifty percent inhibition of bound [³H]LTD₄ was 1.5 nM for LTD₄, 45 nM for LTC₄ and 24 nm for LTE₄. LTB₄ at 3.0 × 10⁻⁵ M had no effect on [³H]LTD₄ binding. The RRA for LTs in the absence of serine-borate complex was bi-specific for both LTC₄ and LTD₄. However, in the presence of 20 nM serine-borate this method was highly specific for LTD₄. Recovery rate averaged 87.2% after ethanol extraction and evaporation of known amounts of LTD₄. When the radioreceptor assay and radioimmunoassay data for leukotriene levels in the samples were compared to each other, an excellent correlation was observed with a correlation coefficient ‘r’ of 0.992. The assay was also validated by quantitation of LTs released from human granulocytes stimulated with calcium ionophore, A23187. The method is simpler, less expensive, and more specific for LTD₄ than the other methods such as high pressure liquid chromatography and radioimmunoassay and is suitable for routine measurement of either LTD₄ specifically or LTC₄ plus LTD₄ simultaneously in one cell system.     

formation of leukotriene E5 by murine peritoneal cells

Resident mouse peritoneal cells, stimulated with opsonized zymosan, produced leukotriene C₄ and E₄, with LTE₄ being the major (80–90%) product. When mice were placed on diets containing increasing amounts of fish oil, four additional sulfidopeptide leukotrienes (SP-LT), LTC₅, LTE₅, 11-trans LTC₅ and 11-trans LTE₅, were identified. The identity of LTE₅ was confirmed by spectrophotometric, chromatographic and enzymatic methods. When equivalent amounts of n-6 and n-3 polyunsaturated fatty acids (PUFA) were included in the diet, the stimulated peritoneal cells ( ) produced higher quantities of LTE₅ (30.2 ± 5.4 ng/10⁶ cells) than LTE₄ (22.8 ± 7.3 ng/10⁶ cells). In addition, studies demonstrated a 60% reduction in LTC₄ (42.0 ± 10.8 ng/10⁶ cells to 16.7 ± 6.2 ng/10⁶ cells) and the appearance of LTC₅ (2.1 ± 0.9 ng/10⁶ cells) in resident macrophages (stimulated with A23187) from mice maintained on a fish oil diet compared to mice fed the control diet. This study demonstrated that formation of the pentaenyl SP-LT , in particular LTE₅, by peritoneal cells can significantly contribute to the endogenous SP-LT pool in response to an inflammatory stimulus following a dietary regimen containing fish oil.     

Inflammation and pain sensitivity: Effects of leukotrienes D4, B4 and prostaglandin E1 in the rat paw

Leukotrienes (LT's) and prostaglandins (PG's) have been proposed as mediators of vascular permeability change in inflammatory reactions. Also, prostaglandins, especially of the E-type, have been shown to enhance pain responses. In the present studies in rat, the effects of LTB₄ and LTD₄ on edema and pain thresholds were examined in combination with PGE₁ and/or brewer's yeast. Subplantar injections of LTD₄ or LTB₄ induced small increases in paw thickness which were potentiated by the co-administration of PGE₁. LTD₄ alone had no significant effect on the development of the yeast paw edema. LTB₄ was found to reduce significantly the yeast edema and this reduction could be reserved by administration PGE₁. A small but significant decrease in pain threshold was caused by PGE₁ and this was significant enhanced in the presence of LTD₄. LTB₄, like PGE₁, was found to cause slight hyperalgesia but no synergy between the two agents was observed. LTD₄ was found to have no effect on the initial hypoalgesia or subsequent development of hyperalgesia caused by brewer's yeast. Both LTB₄ and PGE₁, however, prevented the initial hypoalgesia and significantly reduced tha latency for development of yeast induced hyperalgesia. These effects of LTB₄ are discussed in terms of possible release of cyclooxygenase products.