Further studies on the enzymatic conversion of prostaglandin endoperoxide into prostacyclin by porcine aorta microsomes.

A simple, rapid radiochemical assay for prostacyclin synthesis has been used to characterize the enzyme in arterial walls which converts prostaglandin endoperoxides to prostacyclin. The enzyme displays a broad pH optimum, and catalyses a rapid conversion of saturating concentrations of the endoperoxide at 37 degrees C. Hydroperoxides of several unsaturated fatty acids are potent inhibitors of the enzyme, and act in a time dependent manner. The isomerase which converts prostaglandin endoperoxides to prostaglandin E2 or D2 was not detected in the arterial wall.

Influence of cholesterol feeding on the production of eicosanoids, tissue plasminogen activator and superoxide anion (O2-) by rabbit blood monocytes.

The metabolism in vitro of exogenous and endogenous arachidonic acid was studied in circulating blood monocytes obtained from control (control group) and cholesterol (0.5%)-fed (cholesterol group) rabbits. The production of superoxide anion (O2-), tissue plasminogen activator (t-PA) and adherence of monocytes were assessed in both groups of animals. The amounts of cyclooxygenase and lipoxygenase products derived from exogenously added [1-14C]AA were not significantly different in monocytes collected from both groups of animals. However, the amounts of PGD2, TXB2 and PGE2 formed from endogenous substrate were decreased significantly in monocytes obtained from the cholesterol group compared to those from the control group. The production of immunoreactive LTB4 was not suppressed significantly in monocytes collected from the cholesterol group. The production of O2- and t-PA was suppressed significantly in monocytes obtained from the cholesterol group and these cells adhered onto glass surfaces more efficiently than control cells. Since the formation of prostanoids from endogenous but not exogenous substrate is reduced, an effect of cholesterol on the liberation of AA from phospholipid pools is implicated.

Computer-aided design and synthesis of 5-substituted tryptamines and their pharmacology at the 5-HT1D receptor: discovery of compounds with potential anti-migraine properties.

The design and synthesis of a series of novel 5-substituted tryptamines with pharmacological activity at 5-HT1D and other monoamine receptors is described. Structural modifications of N- and C-linked (principally hydantoin) analogues at the 5-position were synthesized and their pharmacological activities were utilized to deduce significant steric and electrostatic requirements of the 5-HT1D and 5-HT2A receptor subtypes. Conformations of the active molecules were computed which, when overlaid, suggested a pharmacophore hypothesis which was consistent with the affinity and selectivity measured at 5-HT1D and 5-HT2A receptors. This pharmacophore is composed of a protonated amine site, an aromatic site, a hydrophobic pocket, and two hydrogen-bonding sites. A "selectivity site" was also identified which, if occupied, induced sensitivity for 5-HT1D over 5-HT2A in this series of molecules. The development and use of the pharmacophore models in compound design is described. In addition, the physicochemical constraints of molecular size and hydrophobicity required for efficient oral absorption are discussed. Utilizing the pharmacophore model in conjunction with the physicochemical constraints of molecular size and log DpH7.4 led to the discovery of 311C90 (6), a new selective 5-HT1D agonist with good oral absorption and potential use in the treatment of migraine.

6-oxo-prostaglandin F1 alpha and thromboxane B2 in uterine vein blood--a possible role in menstrual bleeding.

The role of the haemostatic system in relation to menstrual bleeding is poorly understood. Platelet retention to glass beads and plasma concentrations of 6-oxo-PGF1 alpha and thromboxane B2 were measured in uterine and peripheral venous blood obtained from 18 women undergoing abdominal hysterectomy. Concentrations of 6-oxo-PGF1 alpha were significantly (p less than 0.01) higher in uterine (1.4 +/- 0.3 ng/ml, mean +/- SEM) than in peripheral vein blood (0.2 +/- 0.1 ng/ml) as was the level of thromboxane B2 (0.5 +/- 0.1 and 0.2 +/- 0.1 ng/ml, respectively). Platelet retention in uterine vein blood (11 +/- 4%) was significantly lower than in peripheral blood (42 +/- 4%; p less than 0.01) and the degree of platelet retention correlated inversely with the plasma concentration of 6-oxo-PGF1 alpha (r -0.43; p less than 0.01). There was a significant rank correlation between time since menstruation and concentrations of 6-oxo-PGF1 alpha in uterine (tau + 0.69; p less than 0.001) and peripheral (tau + 0.56; p less than 0.05) vein blood. The results indicate that an increased local production of prostacyclin (PGI2) relative to thromboxane A2 at the time of menstruation could contribute to the mechanism of uterine bleeding.

A comparison of the acute inflammatory response in adrenalectomised and sham-operated rats.

Carrageenin pleurisy was induced in adrenalectomised (ADX) and sham-operated (SHO) rats. The magnitude and duration of inflammation, as estimated by fluid exudation and cell migration, was greatly increased (approximately doubled) in ADX rats compared with that in their SHO controls. The content of eicosanoids (6-keto-prostaglandin F1 alpha (6-keto-PGF 1 alpha), thromboxane B2 (TXB2), and leukotriene B4 (LTB4] in inflammatory exudates from ADX rats was significantly (2-4 fold) greater than that of their SHO controls. Resident macrophages obtained from ADX rats produced more eicosanoids per cell per unit time when stimulated in vitro with zymosan, than did cells from the SHO controls. Administration of glucocorticoids blocked the inflammatory response and reduced the release of eicosanoids both in vitro and in vivo in both groups of rats. These data are consistent with the notion that physiological amounts of glucocorticoids exert a tonic inhibitory action on phospholipase activity in normal animals and that the increased secretion of these hormones during the inflammatory response serves to check and control the development of inflammation.

The source of thromboxane and prostaglandins in experimental inflammation.

Although cyclo-oxygenase products have been detected at inflammatory sites the tissue of origin remains uncertain. Inflammatory exudates were collected from rats 4, 6, 8, 12 or 24 h after subcutaneous implantation of carrageenin-impregnated sponges. Concentrations of the cyclo-oxygenase products prostaglandin E2 (PGE2), 6-oxo-PGF1 alpha and thromboxane B2 (TXB2) in inflammatory exudates and serum (obtained from blood clotted at 37 degrees C) were measured by specific radioimmunoassays. TXB2 concentrations in exudates increased to about 100 ng ml-1 at 8 h but decreased to less than 20 ng ml-1 after 24 h. PGE2 concentrations increased from 4-12 h and remained between 80 and 120 ng ml-1 from 12-24 h. 6-oxo-PGF1 alpha had the same time course as that of PGE2 but concentrations were approximately one third of PGE2 values. TXB2 concentrations in serum from thrombocytopaenic rats were less than 5% of control values. Thrombocytopaenia did not affect TXB2, PGE2 or 6-oxo-PGF1 alpha concentrations or total leukocyte numbers in inflammatory exudates. Methotrexate-induced neutropaenia did not affect serum TXB2 concentrations but cyclo-oxygenase products (including TXB2) in 6 h inflammatory exudates were reduced by 60-95%. Colchicine (1.0 mg kg-1 s.c.) prevented leukocyte accumulation in sponge exudates and this was accompanied by a reduction in TXB2, PGE2 and 6-oxo-PGF1 alpha concentrations at 6 h. These results indicate that platelets are the source of TXB2 in clotting blood but do not contribute to cyclo-oxygenase activity in experimental inflammation. The results also suggest that migrating leukocytes are the major source of thromboxane and to a lesser degree prostaglandins in acute 6 h inflammatory exudates.

The inflammatory effects of hydroperoxy and hydroxy acid products of arachidonate lipoxygenase in rabbit skin.

1. The inflammatory effects of hydroperoxy (HPETE) and hydroxy (HETE) acids, synthesized by arachidonic acid lipoxygenases, have been investigated in rabbit skin. 2. High doses (10-20 micrograms) of 5-, 12- or 15-HPETE or the 5,12-di-hydroxy acid, leukotriene B4 (0.1-1 micrograms), caused small but significant increases in plasma exudation following intra-dermal injection. 3. Leukotriene B4 was equipotent with prostaglandin E2 and prostacyclin in potentiating bradykinin-induced plasma exudation, and was 100 times more active in this property than any other lipoxygenase product tested. 4. Leukotriene B4-induced plasma exudation was enhanced by prostaglandin E2. 5. The mono-HETEs were relatively inactive in causing or enhancing plasma exudation. 6. Leukotriene B4 (0.1 microgram) or prostaglandin E1 (1.0 micrograms) significantly elevated leukocyte accumulation in rabbit skin, whereas PGE2, 5-HPETE, 5-HETE, 12-HPETE or 12-HETE were inactive at doses up to 1 microgram.

Differential release of eicosanoids by bradykinin, arachidonic acid and calcium ionophore A23187 in guinea-pig isolated perfused lung.

The effects of infusions of bradykinin (0.2 microM), calcium ionophore A23187 (0.5 microM) and arachidonic acid (13 microM) on the release of eicosanoids from the guinea-pig isolated perfused lung were investigated using radioimmunoassay for thromboxane B2 (TXB2), 6-oxo-prostaglandin F1 alpha (6-oxo-PGF1 alpha), PGE2, leukotriene B4 (LTB4) and LTC4 and bioassay using the superfusion cascade. Bradykinin released more 6-oxo-PGF1 alpha than TXB2, whereas arachidonic acid and ionophore released more TXB2 than 6-oxo-PGF1 alpha. The time course of eicosanoid release varied with the stimulus: bradykinin and arachidonic acid produced an immediate release, whereas the ionophore showed a slower onset of release. Although the amounts of LTB4 and LTC4 released by the ionophore were very low according to radioimmunoassays, there was evidence from the bioassay of release of a leukotriene-like substance, thought to be LTD4. The leukotriene antagonist FPL 55712 lacks specificity in the guinea-pig trachea; at the concentration used (2 microM) it antagonized contractions of the tracheal strip to PGE2 as well as to LTC4. Our results show that in the guinea-pig perfused lung the metabolism of exogenous arachidonic acid is both qualitatively and quantitatively different from the metabolism of endogenous arachidonic acid; furthermore, the profile of eicosanoid production is stimulus-dependent.

Selective inhibition of arachidonate 5-lipoxygenase by novel acetohydroxamic acids: effects on bronchial anaphylaxis in anaesthetized guinea-pigs.

1. The effect of a novel series of orally-active acetohydroxamic acid inhibitors of arachidonate 5-lipoxygenase on 'leukotriene-dependent' anaphylactic bronchoconstriction has been investigated in anaesthetized, pump-ventilated guinea-pigs actively sensitized to ovalbumin (OA). In a complementary series of experiments, the pharmacokinetics of these compounds in the plasma compartment following oral administration to guinea-pigs has also been investigated. 2. In animals pretreated with mepyramine (2 mg kg-1, i.v.) and indomethacin (10 mg kg-1, i.v.) and challenged with antigen aerosol (OA 10 mg ml-1; 5 s) compounds BW A4C, BW A137C and BW A797C (10-200 mg kg-1, p.o., 1 h pre-challenge) markedly reduced that component of anaphylactic bronchoconstriction shown to be 'leukotriene-dependent'. 3. The maximum degree of inhibition (up to 75%) of 'leukotriene-dependent' anaphylactic bronchoconstriction by these three compounds was equivalent to that seen with the leukotriene antagonist FPL 55712 (10 mg kg-1, i.v.). 4. The peak levels of unchanged acetohydroxamic acids in the plasma compartment occurred 0.5 h after their oral administration and were as follows: BW A4C: 11.3 +/- 3.9; BW A137C: 7.6 +/- 2.4; BW A797C: 3.9 +/- 1.3 micrograms ml-1 plasma. 5. The inhibition by BW A4C and BW A137C (50 mg kg-1, p.o.) of 'leukotriene-dependent' anaphylactic bronchospasm persisted for up to 3 and 4 h respectively but did not extend to 6 h. The decline in inhibitory activity paralleled the fall in the concentration of unchanged drug in the plasma compartment over this time period. 6. The results of the present study are consistent with BW A4C, BW A137C and BW A797C attenuating 'leukotriene-dependent' bronchial anaphylaxis in anaesthetized guinea-pigs by selective inhibition of arachidonate 5-lipoxygenase.

Selective inhibition of arachidonate 5-lipoxygenase by novel acetohydroxamic acids: biochemical assessment in vitro and ex vivo.

1. The chemically novel acetohydroxamic acids, BW A4C, BW A137C and BW A797C, are potent inhibitors of the synthesis of leukotriene B4 (LTB4) from arachidonic acid by human leucocyte homogenates: the concentrations required for 50% inhibition (IC50) were 0.1 microM, 0.8 microM and 0.5 microM respectively. Inhibition was less at higher concentrations of arachidonic acid. 2. These compounds also inhibited the synthesis of [14C]-5-HETE from [14C]-arachidonic acid and the calcium-dependent synthesis of LTB4 from 5-HPETE. This, therefore, suggests that they inhibit 5-lipoxygenase and LTA4 synthase. 3. Concentrations of acetohydroxamic acids required to inhibit metabolism of arachidonic acid by cyclo-oxygenase, 12-lipoxygenase and 15-lipoxygenase were 10 to 100 times higher than those required to inhibit 5-lipoxygenase. 4. The compounds were potent inhibitors of LTB4 synthesis induced by the ionophore, A23187, in human intact leucocytes. This inhibition was reversed by washing the cells. They were also potent, selective inhibitors of LTB4 synthesis induced by A23187 in whole rat blood: binding to rat plasma proteins did not greatly reduce the effectiveness of the compounds. 5. The effects of the acetohydroxamic acids, administered either intravenously or orally to rats, on the synthesis of LTB4, and thromboxane B2 (TXB2) in A23187-stimulated blood ex vivo was studied. The three compounds caused dose-dependent inhibition of the synthesis of LTB4 but not TXB2. Inhibition of LTB4 synthesis persisted for up to 6 h after a single oral dose of 50 mg kg-1. 6. The plasma concentrations of unchanged compound determined by h.p.l.c. correlated with the inhibition of LTB4 synthesis ex vivo.

Comparison of the effects of some compounds on human neutrophil degranulation and leukotriene B4 and thromboxane B2 synthesis.

The effects of aspirin, indomethacin, phenylbutazone, eicosatetraynoic acid (ETYA), nordihydroguaiaretic acid (NDGA) and 3-amino-1-[3-(trifluoromethyl)-phenyl]-2-pyrazoline (BW755C) on human neutrophil degranulation induced by A23187 and F-Met-Leu-Phe (FMLP) have been studied. These effects have been compared with those on A23187 induced leukotriene B4 (LTB4) and thromboxane B2 (TXB2) synthesis by these cells to elucidate the relationship between LTB4 formation and degranulation. All compounds inhibited TXB2 synthesis by 50% at concentrations between 0.0016 and 50 microM. The synthesis of LTB4 was inhibited by 50% by ETYA (1.9 microM) and by NDGA (0.52 microM). Degranulation induced by A23187 and FMLP was inhibited by 50% by ETYA (16 and 11 microM respectively) and by NDGA (1.5 and 6.5 microM respectively). In the case of ETYA the concentrations required to inhibit degranulation were significantly higher than those required to inhibit LTB4 synthesis. In contrast, BW755C inhibited LTB4 synthesis by 50% at 2.8 microM but did not affect A23187-induced degranulation and was only a weak inhibitor of FMLP-induced degranulation (50% inhibition at 89 microM). The effects of the above compounds on the omega-oxidation of LTB4 by human neutrophils has also been studied to investigate the mechanism of action of these compounds. None of the above compounds affected the metabolism of LTB4 by these cells suggesting that their actions are not as non-specific anti-oxidants. These data indicate that human neutrophil degranulation induced by FMLP and A23187 is independent of LTB4 synthesis.

The release of leukotriene B4 during experimental inflammation.

Leukotriene B4 (LTB4) has been detected by radioimmunoassay in inflammatory exudates obtained following the implantation of saline- or carrageenan-soaked polyester sponges in rats. The immunoreactive material was confirmed as LTB4 after extraction and purification by high pressure liquid chromatography. The peak concentration (6.9 +/- 0.5 ng/ml) was detected 6 hr after implantation of sponges soaked in 0.5% carrageenan; thereafter the level declined and was undetectable after 16-24 hr. The concentration of LTB4 during the early phase of the inflammatory response (4-8 hr) is sufficient to induce leukocyte aggregation, chemotaxis and degranulation of polymorphonuclear leukocytes (PMN) in vitro. Therefore, LTB4 may mediate, at least in part, the influx of PMN and contribute to other events which characterise the inflammatory response. The level of thromboxane B2 (TXB2) in the inflammatory exudate followed a similar time-course to that of LTB4 although the maximum concentration was higher (15-30 ng/ml). However, prostaglandin E2 (PGE2) exhibited a different time-course; the maximum level (20-30 ng/ml) was also reached 6-8 hr after implantation but remained elevated at 24 hr. The PMN count in the sponges and the concentrations of both LTB4 and TXB2, but not PGE2, were significantly reduced by prior treatment of the animals with colchicine. This suggests that PMN are the major source of LTB4 and TXB2 in the inflammatory exudate whereas PGE2 is produced in significant amounts by other tissues.

Effect of orally administered eicosapentaenoic acid (EPA) on the formation of leukotriene B4 and leukotriene B5 by rat leukocytes.

Eicosapentaenoic acid (EPA) is a poor substrate for the fatty acid cyclo-oxygenase but is a good substrate for lipoxygenase enzymes which catalyse the biosynthesis of hydroperoxy-acids, hydroxy-acids and leukotrienes. Recently, we reported that leukotriene B5 (LTB5) was at least 30 times less potent than LTB4 in causing aggregation, chemokinesis and degranulation of polymorphonuclear leukocytes in vitro. In this paper, the effect of oral administration of EPA on LTB4 and LTB5 production by rat leukocytes stimulated with the calcium ionophore, A23187, was assessed. The concentration of LTB was determined by radioimmunoassay and also by reverse-phase high pressure liquid chromatography using PGB3 as internal standard. Supplementation of a normal rat diet with EPA (240 mg/kg per day) for 4 weeks caused a significant increase in the formation of LTB5 and a decrease in the synthesis of LTB4 by stimulated leukocytes. The EPA-rich diet significantly increased the EPA content of leukocyte phospholipids without altering the content of arachidonic acid (AA) or linoleic acid. The ratio of EPA/AA in leukocytes correlated (r = 0.795, P less than 0.001) with the LTB5/LTB4 ratio produced after stimulation of leukocytes. If LTB4 has a chemotactic role during inflammation, the present data suggest that an EPA rich diet could decrease the accumulation of leukocytes at sites of inflammation.

Eicosapentaenoic acid as a modulator of inflammation. Effect on prostaglandin and leukotriene synthesis.

Products derived from arachidonic acid (AA) via both the cyclo-oxygenase and lipoxygenase pathways play a role in inflammation: prostaglandins (PGs), particularly PGE2, contribute to the formation of oedema, erythema and hyperalgesia whereas leukotriene B4 (LTB4), a product of the 5' lipoxygenase, may modulate the recruitment of leukocytes. We have previously reported that supplementation of a standard rat diet with eicosapentaenoic acid (EPA) caused a significant increase in the formation of LTB5, which is less active biologically than LTB4, and a decrease in the synthesis of LTB4 by stimulated leukocytes. Now we have assessed the effects of administration of highly purified EPA ethyl ester (79% pure), in two models of acute inflammation. Supplementation of a standard rat diet with 240 mg/kg/day EPA for 4 weeks significantly decreased the concentration of PGE2 and TXB2 in inflammatory exudate derived from implantation of carrageenin impregnated sponges: neither the concentration of LTB4 nor the cell number were reduced significantly. Triene prostaglandins were not detected in the exudate, however, significant levels of LTB5 were present. In the second model, oedema induced by injection of carrageenin into rat paws was significantly reduced in animals fed an EPA-rich diet. Supplementation of the diet with EPA could, by mainly reducing the synthesis of prostaglandins, offer a novel and non-toxic approach to the modulation of an inflammatory response.

Exclusion of linkage between bipolar affective disorder and chromosome 16 in 12 Australian pedigrees.

Several recent reports of possible susceptibility loci for bipolar affective disorder (BAD) have identified sites on a number of chromosomes. Specifically, two Danish studies have suggested the presence of a susceptibility locus for BAD on chromosome 16p13. As the first step of a whole genome scan, we screened 12 Australian families with markers at 16p13 and also a number of markers spanning the entirety of chromosome 16. Linkage analysis was undertaken using both the parametric lod score method (two- and multipoint) with different models and diagnostic thresholds, and the nonparametric affected pedigree member (APM) method. Results of lod score analysis convincingly excluded the 16p13 region from linkage to BAD in these families, while APM provided no support for linkage. Furthermore, using the broad definition of BAD, with individuals affected by bipolar I and II and recurrent unipolar disorders included, the entire chromosome was excluded from linkage to BAD with autosomal-dominant transmission at a maximum age-specific penetrance of 60%, and with autosomal-dominant and recessive modes of transmission at a maximum age-specific penetrance level of 90%. Diagnostic thresholds which did not include unipolar affected individuals were somewhat less informative. However, a majority (between 63-96%, depending upon the model) of the chromosome was clearly excluded using narrow diagnostic thresholds. Moreover, no positive lod scores were obtained at theta = 0.00 for any tested model or diagnostic threshold. Our results indicate that no linkage exists between BAD and chromosome 16 markers in this group of Australian families.

Nonparametric simulation-based statistical analyses for bipolar affective disorder locus on chromosome 21q22.3.

Straub et al. [1994: Nat Genet 8:291-296] reported a candidate bipolar affective disorder (BAD) locus on chromosome 21q22.3. As a replication study, we analyzed 12 Australian BAD pedigrees for the presence of excess allele sharing and cosegregation with the putative chromosome 21q22.3 BAD locus, using six microsatellite markers. The nonparametric simulation-based statistic SimAPM produced positive results for the marker PFKL (P < 0.001) and D21S198 (P = 0.007). PFKL also demonstrated linkage (P < 0.001) when analyzed using the more conservative statistic, SimIBD. Comparable results were obtained when using the original APM statistic (P = 0.02 for D21S198). However, other nonparametric analyses such as GENEHUNTER and model-free linkage (MFLINK) analysis did not yield significant results. Combined LOD scores for the 12 families were strongly negative for all six markers under six genetic models. Two-point and multipoint analyses of individual families revealed one family, family 17, with maximal LOD scores greater than 1.41 for the 10.5-cM region between PFKL and D21S198. This report provides additional support for the suggestive linkage of a susceptibility locus for BAD on chromosome 21q22.3.

Gastric ulcer formation and cyclo-oxygenase inhibition in cat antrum follows parenteral administration of aspirin but not salicylate.

The ulcerogenic actions of aspirin and sodium salicylate in cat gastric antrum following intravenous injection, and their effects on the synthesis of two major cyclo-oxygenase products by antral mucosa have been determined. Near-maximal rates of gastric acid secretion were stimulated by histamine, infused i.v. for 1 h prior to bolus injection of aspirin or salicylate and throughout the subsequent 4 h. The area of lesions in the cat gastric antrum were then assessed macroscopically and the generation of both 6-oxo-PGF1 alpha and PGE2 from strips of antral mucosal tissue following 1 min vortex-incubation was determined by radioimmunoassay. The plasma and mucosal-tissue levels of both aspirin and salicylate were determined using HPLC techniques. Aspirin (0.2 mmol. kg-1 i.v.) induced substantial deep antral ulceration during the 4 h histamine infusion, whereas sodium salicylate (0.2 mmol. kg-1 i.v.) caused no significant macroscopic damage. Sodium salicylate likewise caused no significant inhibition in the ex vivo generation of either 6-oxo-PGF1 alpha or PGE2, whereas aspirin induced 92 +/- 3 and 97 +/- 1% inhibition of generation of these prostanoids respectively. The levels of total salicylate in plasma and mucosal tissue were comparable following bolus i.v. injection of aspirin or sodium salicylate. These observations support the concept that cyclo-oxygenase inhibition is an important mechanism underlying deep gastric ulceration induced by aspirin, when administered parenterally in the cat.

The synthesis of eicosanoids induced by anaphylaxis in guinea-pig isolated lungs perfused via the trachea.

We have monitored the release of prostanoids and leukotrienes from isolated lungs taken from previously sensitized guinea-pigs perfused either via the pulmonary artery or via the trachea. The eicosanoids were monitored by direct radioimmunoassay and further identified by bioassay and radioimmunoassay following separation by RP-HPLC. When ovalbumin is delivered via the trachea it releases more cyclo-oxygenase products (3-fold) and lipoxygenase products (10-fold) than when delivered via the pulmonary circulation. Indomethacin enhanced leukotriene release whereas BW755C did not affect the release of leukotrienes induced by ovalbumin. These results suggest that perfusing the lungs via the trachea might be relevant for the study of anaphylaxis and other conditions in which the pathophysiological development is determined by cells closer to the alveolar surface in the lung.

Release of eicosanoids from isolated lungs of guinea-pigs exposed to pure oxygen: effect of dexamtethasone.

The effect of dexamethasone on bradykinin-induced release of eicosanoids from isolated lungs of guinea-pigs exposed to pure oxygen (O2) is described. Pathological changes were induced in the lungs of guinea-pigs exposed to pure O2 for 72 and 96 h. Bradykinin-induced release of 6-oxo-PGF1 alpha and thromboxane B2 (TXB2) was increased in lungs from guinea-pigs exposed to 72 and 96 h of O2. Removal of PGI2 and PGE2 was not affected by the exposure to O2, but the removal of bradykinin was significantly reduced after 96 h of O2 exposure. Dexamethasone did not reduce bradykinin-induced release of eicosanoids from lungs of control animals, but it did inhibit the release from lungs of guinea-pigs exposed to O2. Dexamethasone had no effect on the metabolism of Bk by the inflamed lungs.

Biotransformation and cardiovascular effects of arachidonic acid in the dog.

The biotransformation and cardiovascular effects of arachidonic acid (AA) were studied in the circulation of anaesthetized dogs. Arterial blood was continuously bioassayed for arachidonate metabolites using the blood-bathed organ technique of Vane. AA (5-10 microgram/ml) infused into an incubation coil of flowing blood was converted into a labile substance which contracted the vascular tissues (rabbit aorta, RbA; rabbit coeliac and mesenteric arteries, RbCA and RbMA; bovine coronary artery, BCA) and the gastrointestinal smooth muscle strips (rat stomach strip, RSS; rat colon, RC). These effects could be mimicked by exogenously generated thromboxane A2 (TXA2). Conversion of AA was inhibited by indomethacin and the selective thromboxane synthetase inhibitor, imidazole (100 microgram/ml). The half-life of TXA2 in blood was 30-47 sec, a similar value to that found in aqueous solutions at 37 degrees C. PGH2 was also converted in blood to other product(s) which contracted RSS and RC, relaxed RbCA and RbMA but had little effect on RbA. Intravenous infusion of AA (50-800 microgram kg-1 min-1) caused effects on the bioassay tissues which could be mimicked by prostacyclin. The AA infusion also induced falls in pulmonary and systemic arterial pressures and bradycardia. All effects were abolished by indomethacin (5 mg/kg) or aspirin (200 mg/kg). Radioimmunoassay confirmed that the major product of intravenously infused AA was 6-oxo-PGF1alpha, the chemical degradation product of prostacyclin. Thus, although AA is transformed to the vasoconstrictor TXA2 when incubated for sufficient time with blood alone, on rapid pulmonary transit it is transformed into a prostacyclin-like substance.