Degradation of porstaglandin F2alpha in the human pulmonary circulation

Mechanism of BLIMP1/TRIM66/COX2 in human decidua participates in parturition†

The mechanism underlying the initiation of parturition remains unclear. Cyclooxygenase 2 and prostaglandins in decidual membrane tissue play an important role in the "parturition cascade." With the advancement of gestation, the expression of the transcriptional suppressor B lymphocyte-induced maturation protein 1 in the decidual membrane gradually decreases. Through chromatin immunoprecipitation sequencing, we found that B lymphocyte-induced maturation protein 1 has a binding site in the distal intergenic of PTGS2(COX2). Tripartite motif-containing protein 66 is a chromatin-binding protein that usually performs transcriptional regulatory functions by "reading" histone modification sites in chromatin. In this study, tripartite motif-containing protein 66 exhibits the same trend of expression as B lymphocyte-induced maturation protein 1 in the decidua during gestation. Moreover, the co-immunoprecipitation assay revealed that tripartite motif-containing protein 66 combined with B lymphocyte-induced maturation protein 1. This finding indicated that tripartite motif-containing protein 66 formed a transcription complex with B lymphocyte-induced maturation protein 1, which coregulated the expression of COX2. In animal experiments, we injected si-Blimp1 adenoviruses (si-Blimp1), Blimp1 overexpression plasmid (Blimp1-OE), and Trim66 overexpression plasmid (Trim66-OE) through the tail vein of mice. The results showed that B lymphocyte-induced maturation protein 1 and tripartite motif-containing protein 66 affected the initiation of parturition in mice. Therefore, the present evidence suggests that B lymphocyte-induced maturation protein 1 and tripartite motif-containing protein 66 partially participate in the initiation of labor, which may provide a new perspective for exploring the mechanism of term labor.

Pathogenic Mechanisms of Pulmonary Arterial Hypertension: Homeostasis Imbalance of Endothelium-Derived Relaxing and Contracting Factors

Pulmonary arterial hypertension (PAH) is a progressive and fatal disease. Sustained pulmonary vasoconstriction and concentric pulmonary vascular remodeling contribute to the elevated pulmonary vascular resistance and pulmonary artery pressure in PAH. Endothelial cells regulate vascular tension by producing endothelium-derived relaxing factors (EDRFs) and endothelium-derived contracting factors (EDCFs). Homeostasis of EDRF and EDCF production has been identified as a marker of the endothelium integrity. Impaired synthesis or release of EDRFs induces persistent vascular contraction and pulmonary artery remodeling, which subsequently leads to the development and progression of PAH. In this review, the authors summarize how EDRFs and EDCFs affect pulmonary vascular homeostasis, with special attention to the recently published novel mechanisms related to endothelial dysfunction in PAH and drugs associated with EDRFs and EDCFs.

PGE2 vs PGF2α in human parturition

Prostaglandin E2 (PGE2) and F2α (PGF2α) are the two most prominent prostanoids in parturition. They are involved in cervical ripening, membrane rupture, myometrial contraction and inflammation in gestational tissues. Because multiple receptor subtypes for PGE2 and PGF2α exist, coupled with diverse signaling pathways, the effects of PGE2 and PGF2α depend largely on the spatial and temporal expression of these receptors in intrauterine tissues. It appears that PGE2 and PGF2α play different roles in parturition. PGE2 is probably more important for labor onset, while PGF2α may play a more important role in labor accomplishment, which may be attributed to the differential effects of PGE2 and PGF2α in gestational tissues. PGE2 is more powerful than PGF2α in the induction of cervical ripening. In terms of myometrial contraction, PGE2 produces a biphasic effect with an initial contraction and a following relaxation, while PGF2α consistently stimulates myometrial contraction. In the fetal membranes, both PGE2 and PGF2α appear to be involved in the process of membrane rupture. In addition, PGE2 and PGF2α may also participate in the inflammatory process of intrauterine tissues at parturition by stimulating not only neutrophil influx and cytokine production but also cyclooxygenase-2 expression thereby intensifying their own production. This review summarizes the differential roles of PGE2 and PGF2α in parturition with respect to their production and expression of receptor subtypes in gestational tissues. Dissecting the specific mechanisms underlying the effects of PGE2 and PGF2α in parturition may assist in developing specific therapeutic targets for preterm and post-term birth.

Monocarboxylate Transporter 6-Mediated Interactions with Prostaglandin F2α: In Vitro and In Vivo Evidence Utilizing a Knockout Mouse Model

Monocarboxylate transporter 6 (MCT6; SLC16A5) is a recently studied drug transporter that currently has no annotated endogenous function. Currently, only a handful of compounds have been characterized as substrates for MCT6 (e.g., bumetanide, nateglinide, probenecid, and prostaglandin F_2α (PGF2α)). The objective of our research was to characterize the MCT6-specific transporter kinetic parameters and MCT6-specific in vitro and in vivo interactions of PGF2α. Murine and human MCT6-mediated transport of PGF2α was assessed in MCT6-transfected oocytes. Additionally, endogenous PGF2α and a primary PGF2α metabolite (PGFM) were measured in plasma and urine in Mct6 knockout (Mct6^−/−) and wild-type (Mct6^+/+) mice. Results demonstrated that the affinity was approximately 40.1 and 246 µM respectively, for mouse and human, at pH 7.4. In vivo, plasma PGF2α concentrations in Mct6^−/− mice were significantly decreased, compared to Mct6^+/+ mice (3.3-fold). Mct6^-/- mice demonstrated a significant increase in urinary PGF2α concentrations (1.7-fold). A similar trend was observed with plasma PGFM concentrations. However, overnight fasting resulted in significantly increased plasma PGF2α concentrations, suggesting a diet-dependent role of Mct6 regulation on the homeostasis of systemic PGF2α. Overall, these results are the first to suggest the potential regulatory role of MCT6 in PGF2α homeostasis, and potentially other PGs, in distribution and metabolism.

Effect of azelastine on airway hyperresponsiveness mediated by stimulated macrophages

The effect of the anti-allergic drug azelastine, 4-(p-chlorobenzyl)-2-(hexahydro-1-methyl-1H-azepine-4-yl)-1-(2H)-phth alazione), on airway hyperresponsiveness induced by immunologically stimulated pulmonary alveolar macrophages was investigated in canine bronchial segments under isometric conditions in vitro. Macrophages stimulated with anti-dinitrophenyl immunoglobulin E (IgE) antibody and dinitrophenyl-human serum albumin potentiated the contractile responses to electrical field stimulation at all frequencies, an effect that was abolished by azelastine (3 x 10(-5) M). In contrast, azelastine had no effect on the potentiation of the contractile responses to electrical stimulation by U46619, a thromboxane A2 mimetic. The IgE-mediated release of thromboxane A2 from macrophages was inhibited by azelastine in a concentration-dependent fashion, the maximal decrease and the concentration required to produce a half-maximal effect being 84 +/- 6% (P < 0.001) and 16 microM, respectively. These results suggest that azelastine may attenuate macrophage-induced parasympathetic airway hyperresponsiveness through an inhibition of the release of thromboxane A2.

Influence of endothelium and surgical preparation on responses of human saphenous vein and internal thoracic artery to angiotensin II

1. The saphenous vein (SV) and internal thoracic artery (ITA) are the most commonly used conduits for coronary artery bypass surgery (CABS). The ITA shows better long term patency than the SV, at least in part due to their different responses to agonists, as well as physical differences between the ITA and SV at the time of grafting. 2. Angiotensin II (A II), a potent endogenous vasoconstrictor circulates at augmented levels during and after CABS, but little is known about the effects of A II on the SV and ITA. 3. We studied the contractile effects of A II on SV and ITA as intact rings from a heterogeneous group of patients undergoing CABS. Two groups of SV samples were studied; freshly excised SV (FSV) with no further manipulation and SV that had been surgically prepared for use as a bypass conduit (PSV). We also assessed the function of the endothelium in FSV, PSV and ITA, by measuring the relaxation of preconstricted rings to bradykinin. In some tissues endothelial presence was examined histologically. 4. Surgical preparation of SV affected the contractile ability of the smooth muscle, as PSV contracted less than FSV to potassium chloride (KCl, 90 mM) (P < 0.0001). Loss of endothelial function was seen in 25% of FSV, 50% of PSV and 33% of ITA. 5. A II caused concentration dependent contractions in all rings, over the same concentration range (1 nM-100 nM). In rings of FSV the presence of functional endothelium attenuated the response, median values with endothelium being less than half that without endothelium (P < 0.0007, at 100 nM).(ABSTRACT TRUNCATED AT 250 WORDS)

Thromboxane--co-factor of pulmonary disturbances in intramedullary nailing

Pulmonary complications during and after intramedullary nailing particularly in trauma patients have directed clinical interest to thromboembolic events and metabolic alterations, as found in different methods of fracture stabilisation. In 30 patients (mean age 34 years) isolated, closed or 1 degree open fractures of the tibia were operated on in three groups with reamed nailing (RN; n = 11), unreamed nailing (UN; n = 11) and external fixation (EF; n = 8) respectively. In blood samples of the femoral vein of the fractured limb, a 5-7 fold increase of the thromboxane (TXB2) concentration was found in all patients. However, differences of TXB2 concentrations in the arterial blood after passage of the lungs were conspicuous. The highest arterial TXB2 concentrations were found in connection with RN, followed by UN and finally EF. The transpulmonary TXB2-clearance displayed the following relationship: EF > UN > RN (5.7:4,4:2.2). A similar correlation was found for PGF2 alpha while other arachidonic acid metabolites showed no significant behaviour. TXB2 and PGF2 alpha cause bronchoconstriction, pulmonary vasoconstriction and aggregation of thrombocytes. These pulmonary disturbances may results in ARDS, a feared complication after intramedullary nailing.

CONCLUSION

Early fracture stabilisation particularly in severely injured patients is an established procedure. To prevent pulmonary disturbances the external fixator is preferrable to the UN and finally the RN. Our data suggest that for the prevention of pulmonary disturbances EF is superior to UN and RN.

Vasoactive intestinal peptide and helodermin inhibit the release of cyclo-oxygenase products induced by leukotriene D4 and bradykinin from guinea-pig perfused lung

Vasoactive intestinal peptide (VIP, 10 nM) inhibited the release of cyclo-oxygenase products, detected by both bioassay and radioimmunoassay, induced by leukotriene (LT) D4 (3-30 pmol) and bradykinin (BK, 3-30 nmol) from guinea-pig isolated perfused lung. Helodermin (10 nM), a peptide that is structurally related to VIP, and salbutamol (10 nM), a beta 2-adrenoceptor agonist, evoked a similar inhibitory effect on LTD4-induced release of cyclo-oxygenase products. The generation of TxB2 and 6-keto-PGF1 alpha following stimulation with exogenously administered arachidonic acid (30-300 nmol) was not significantly attenuated in the presence of either VIP, helodermin or salbutamol. These results show that VIP, helodermin and salbutamol are potent inhibitors of the release of cyclo-oxygenase products induced by agonists known to activate endogenous arachidonic acid metabolism in guinea-pig lung. Since the metabolism of exogenously administered arachidonic acid was not inhibited these results suggest that the inhibitory effect may be exerted on events preceding the mobilisation of arachidonic acid and may involve cyclic AMP.

Effect of K+ channel-modulating drugs on the vasoconstrictor responses of leukotrienes C4, D4 and angiotensin II in the guinea-pig isolated perfused heart

1. The vascular actions of leukotrienes C4 (LTC4) and LTD4 in the guinea-pig isolated perfused heart were studied in the presence of potassium (K+) channel modulatory compounds. 2. Cromakalim (0.35-10 microM), a K+ channel activator, inhibited the vasoconstrictor responses of LTC4 (30 pmol), LTD4 (30 pmol) and angiotensin II (AII) (100 pmol) in a concentration-dependent manner. 3. Glyceryl trinitrate (10 mgl-1) and vasoactive intestinal peptide (10 nM) induced a similar vasodilator action to cromakalim in the isolated heart but had no effect on responses to LTC4 and LTD4. 4. The inhibitory action by cromakalim (10 microM) on the LTC4 (30 pmol) response could be reversed in the presence of an equimolar concentration of glibenclamide. However, glibenclamide (10 microM) only partially restored the LTD4 (30 pmol) actions. 5. Galanin (10 nM) and charybdotoxin (60 nM) had no effect on the vascular responses to LTC4 and LTD4 (30 pmol). 6. Inhibition by cromakalim of coronary vasospasm induced by vascular LTC4, LTD4 and AII appears to be separate from its vasodilator action and it is postulated that a cromakalim-sensitive mechanism in the coronary vasculature is important in the vasoconstrictor responses to LTC4, LTD4 and AII.

Effects of vasoactive intestinal peptide, helodermin and galanin on responses of guinea-pig lung parenchyma to histamine, acetylcholine and leukotriene D4

1. The effect of vasoactive intestinal peptide (VIP) was studied on the contractile response of guinea-pig lung parenchymal strips (GPP) induced by bronchoconstrictor agonists, such as leukotriene D4 (LTD4), histamine and acetylcholine (ACh). This effect of VIP was compared with helodermin, a peptide that is structurally related to VIP, and galanin, another neuropeptide that is thought to co-exist with VIP. 2. VIP (10 nM) induced a potent and reversible inhibition of the contractions of GPP induced by LTD4 (1-30 pmol) but did not affect those due to ACh (1-100 nmol) or histamine (1-30 nmol). A ten fold higher concentration of VIP (100 nM) did not further inhibit LTD4-induced responses or reduce those induced by histamine or ACh. 3. Helodermin (10 nM) had a similar inhibitory effect on contractions of GPP induced by LTD4 (3-30 pmol) but did not affect contractions induced by histamine (1-10 nmol). 4. Indomethacin (2.8 microM) and salbutamol (10 nM) significantly reduced responses elicited by LTD4 and histamine but not those due to ACh. A ten fold higher concentration of salbutamol (100 nM) further inhibited the contractions due to LTD4 and histamine and at this concentration responses induced by ACh were inhibited. 5. VIP (10 nM) and helodermin (10 nM) significantly reduced the LTD4-induced release of thromboxane A2 (TXA2), measured as TxB2 by radioimmunoassay, from GPP. The smaller release of TxA2 induced by histamine was not significantly reduced in the presence of VIP. 6. In comparative studies, galanin (10-100 nM) did not affect contractions of GPP induced by either LTD4, histamine or ACh. In contrast to VIP and helodermin, both at 0.1-3 nmol, which induced doserelated relaxations of guinea-pig trachea, galanin was inactive on this preparation in doses of up to 3 nmol.7. In conclusion, our results show that contractions of GPP induced by LTD4 are more sensitive to inhibition by VIP and helodermin than are contractions due to histamine or ACh. This inhibition appears to be associated with the different contribution of released TxA2 to contractions evoked by the agonists. VIP and helodermin inhibit the cyclo-oxygenase-dependent component of the LTD4-induced response, as in the case of indomethacin.

Effect of IgE-stimulated alveolar macrophages on tracheal epithelial bioelectric properties in dogs

To investigate a possible interaction between pulmonary alveolar macrophages (AMs) and airway epithelial cells in patients with allergic conditions, we studied the effect of AMs on bioelectric properties of canine tracheal epithelium under short-circuited conditions in vitro. Mucosal addition of the supernatants from AMs stimulated with monoclonal antidinitrophenyl (DNP) IgE antibody and DNP-human serum albumin (DNP-HSA) increased short-circuit current (Isc) of cultured epithelium in a dose-dependent manner. The maximal increase from the baseline value and the EC50 were 10.2 +/- 2.0 microA/cm2 (mean +/- SE, p less than 0.01) and 3 x 10(5) AMs/ml, respectively. This effect was accompanied by the release of prostaglandin E2 and F2 alpha from AMs. In contrast, AMs incubated with anti-DNP IgE antibody alone or DNP-HSA alone had no effect. The AM-induced increase in Isc was attenuated by diphenylamine-2-carboxylate and Cl-free medium but not by amiloride. Pretreatment of AMs with indomethacin or piroxicam inhibited the effect of AMs on epithelial Isc. These results suggest that AMs may stimulate Cl secretion across the airway mucosa through an IgE-dependent release of prostaglandins.

Stimulation of airway ciliary motility by immunologically activated canine pulmonary macrophages: role of leukotrienes

To elucidate a possible interaction between alveolar macrophages and airway epithelial cells in allergic conditions, we studied the effect of immunologically stimulated macrophages on ciliary beat frequency (CBF) of cultured canine tracheal epithelium by a photoelectric method. Administration of supernatants from macrophages incubated with anti-dinitrophenyl (DNP) IgE antibody and anti-dinitrophenyl-human serum albumin dose-dependently increased ciliary beat frequency, the maximal increase from the baseline being 30.4 +/- 5.0% (mean +/- SE, P less than 0.01), an effect that was accompanied by the release of leukotriene (LT) C4 and leukotriene D4. This ciliostimulation was not affected by pretreatment of macrophages with indomethacin but was inhibited by that with nordihydroguaiaretic acid. Addition of FPL 55712 abolished the response of ciliary beat frequency to the stimulated macrophages, and exogenously administered leukotriene C4 and leukotriene D4 dose-dependently increased ciliary beat frequency. These results suggest that macrophages increase respiratory ciliary motility through the IgE-mediated release of leukotrienes and may modulate mucociliary transport function in the airway.

Primary pulmonary hypertension: diagnosis, medical and surgical treatment

Primary pulmonary hypertension continues to present both diagnostic and therapeutic challenges to the physician, reflecting the lack of understanding about the basic mechanism of the disease. The natural history of the condition has been described only recently, and this has allowed a reasonably accurate prognosis for the individual patient to be determined. New treatments have been found effective, including heart-lung transplantation, which can now offer improved survival. Long-term intravenous infusion of prostacyclin has a place in the treatment of severely affected patients awaiting heart-lung transplantation. However, the major impact of prostacyclin has been, perhaps, to concentrate research upon the role of the endothelial cell in the development of this disorder, in particular the potential role of an impairment of release of the recently described endothelium-derived relaxing factor in certain forms of pulmonary hypertension. We have attempted in this review to focus on the problems of diagnosis and treatment together with current developments in the understanding of primary pulmonary hypertension.

The role of the epithelium in modulating the responses of guinea-pig trachea induced by bradykinin in vitro

1. The effect of removing the epithelium on the responses of the guinea-pig isolated trachea (GPT) to bradykinin (BK) and prostaglandin E2 (PGE2) was investigated. 2. BK (3 pmol-10 nmol) induced dose-related relaxations of the intact (with epithelium), and contracted the rubbed (without epithelium) preparation of GPT. Similar responses were also obtained with PGE2 (0.3-3.0 nmol). 3. Indomethacin (1.4 microM) modified the BK-induced response of intact GPT, from a relaxation to a contraction, but inhibited the BK-induced contraction of the rubbed GPT. 4. There was a significant increase in PGE2 release from the intact GPT following stimulation with BK. 5. Removal of the epithelium from the GPT significantly reduced both basal and BK-induced generation of PGE2. 6. The induction of tone in the rubbed GPT by addition of acetylcholine (ACh) caused BK and PGE2 (0.3 nmol-3 nmol) to produce relaxations of the tissue. 7. Salbutamol (10(-8) M-10(-6) M) reduced the relaxations induced by BK on intact GPT, in a concentration-dependent manner. 8. These results suggest that both tone and an epithelial-dependent cyclo-oxygenase mechanism are important in modulating BK-induced responses of GPT.

Transpulmonary prostaglandin F2 alpha metabolism in sheep: an in vivo model

We investigated transpulmonary enzymatic conversion of prostaglandin F2 alpha (PGF) to the 13,14-dihydro-15-keto metabolite (PGFM) in normal and acutely lung injured sheep. PGF was infused directly into the right ventricle. Sequential, simultaneous blood samples were drawn from the pulmonary artery (PA) and aorta (A). PGF and PGFM plasma concentrations were quantitated by double antibody radioimmunoassay (RIA). The pulmonary conversion rate of PGF in normal lung was established over a wide range of concentrations in intubated, normoxic, and hemodynamically stable sheep. Both zero and first order kinetics were present. PGF had no physiological effects on either pulmonary or systemic hemodynamics at any infusion rate studied. Acute lung injury was produced by intravenous injections of oleic acid into the PA until the resting mean pulmonary artery pressure doubled. Infusions were then repeated and fractional metabolism of PGF across the lung was assessed. PGF, at infusion rates of 2 micrograms/kg/min and 8 micrograms/kg/min, was metabolized greater than 70% respectively. Thus, there was no difference between control or experimental groups in PGF conversion. We conclude that the in vivo sheep lung has an extensive substrate-dependent capacity to metabolize PGF and this mechanism is resistant to severe acute oleic acid lung injury.

Prostanoid production by rat aortic endothelial cells by bradykinin and histamine

The present studies demonstrate that rat aortic endothelial cells, when stimulated with either bradykinin or histamine, caused the release of both PGI2 and PGE2. The method has also been used to characterize the histamine receptor involved which is H1-subtype. The findings suggest that prostanoid production by bradykinin and histamine constitutes an alternative mechanism to endothelium-derived relaxing factor in mediating vasodilatation.

Sequential patterns of eicosanoid, platelet, and neutrophil interactions in the evolution of the fulminant post-traumatic adult respiratory distress syndrome

Thirty multiply injured blunt-trauma patients at high risk for development of ARDS (multisystem trauma including more than one organ or extremity, Injury Severity Score of 26 or more, hypotension and need for 1500 mL or more blood within the first hour after admission, and PaO2 less than or equal to 70 torr) were studied sequentially with blood and physiologic evaluations beginning immediately after injury and every eight hours for eight days, or until death, to study the evolution of the ARDS process. Mixed venous blood samples were obtained for eicosanoids PGE2, PGF2 alpha, thromboxane B2, PGI2 (6-KetoPGF1 alpha) and leukotriene B4 (LTB4). Platelet (PLAT), and neutrophil (WBC) counts were also done and plasma elastase was measured. At 7:00 AM each day patient neutrophils were obtained for a study of zymosan-activated superoxide production using a chemiluminescence assay. These data were correlated with physiologic measurements of the Respiratory Index (RI), per cent pulmonary shunt (QS/QT), and respiratory compliance measures. Seven patients developed a fulminant post-traumatic ARDS syndrome within 96 hours after injury. Twelve patients without ARDS developed sepsis (TS) four or more days after injury, and 11 had uncomplicated postinjury courses (TR). Compared to both TR and TS, ARDS had a significant (p less than 0.01) rise in neutrophil superoxide production beginning on day 2 through day 4 after injury. This was preceded by rises in PGE2 and LTB4, which were significantly correlated with subsequent falls in PLAT and WBC and rises in TXB2, PGF1, and superoxide production and followed by increases in RI, QS/QT, and a fall in compliance. The significant difference in the pattern and sequence of events in ARDS compared to TR and TS patients suggests that in ARDS the earliest event may be related to peripheral release of PGE2 and LTB4 due to platelet activation and lung sequestration with release of PGF2 alpha, and by aggregation and leukocyte adherence with release of elastase. However, fulminant ARDS mortality appears to be related to the subsequent amplification of the LTB4 leukocyte activation with superoxide production that does not achieve significance before the second day after injury and rises to a maximum by day 4 after injury. These data suggest that post-trauma ARDS follows a different evolutionary pattern than that reported in animal models and is also different from that seen in human TS or TR patients.(ABSTRACT TRUNCATED AT 400 WORDS)

Inhibition of leukotriene release in anaphylactic guinea-pig hearts by a 5-lipoxygenase inhibitor, CGS 8515

1. Ovalbumen (100 micrograms)-induced coronary vasoconstriction and decrease in cardiac developed tension were studied in isolated perfused hearts from sensitized guinea-pigs. Leukotriene-like material released in the cardiac effluent was assayed against synthetic leukotriene C4 (LTC4). 2. LTC4 was released in a time-dependent fashion, and release was enhanced when hearts were challenged in the presence of indomethacin (2.8 microM). The release was maximal at 2-3 min and detectable for as long as 10 min following ovalbumen challenge. Immunoreactive (ir) thromboxane-B2 (TxB2) was also detected in cardiac effluent which had been partially purified using C18 Sep-Paks. 3. CGS 8515 (0.03-1.0 microM), an inhibitor of 5-lipoxygenase, dose-dependently inhibited ovalbumen-induced coronary vasoconstriction and leukotriene-C4 release. CGS 8515 inhibited ovalbumen-induced decreases in cardiac developed tension at 0.3 and 1.0 microM, but did not antagonize coronary vasoconstriction induced by synthetic LTC4. 4. The release of cyclo-oxygenase products following ovalbumen challenge was not inhibited by CGS 8515, but was markedly inhibited by indomethacin (2.8 microM) pretreatment. 5. We conclude that leukotrienes have a major role in guinea-pig cardiac anaphylaxis, and that CGS 8515 has a cardio-protective action. The results obtained in these experiments in vitro show that CGS 8515 is a potent and selective 5-lipoxygenase inhibitor.

The detection of 5-lipoxygenase and cyclo-oxygenase products in sputum of patients with chronic bronchitis and bronchiectasis

Leukotrienes (LTs) and prostanoids (Ps) were detected in sputum of patients with chronic bronchitis and/or bronchiectasis (CB/B) using selective superfusion bioassay and radioimmunoassay (RIA) techniques. Analysis of sputum extracts showed a 4-fold increase in the level of LTB4 compared to the cysteinyl-containing LTs (LTC4/LTD4). The measurement of cyclo-oxygenase products (COPs) indicated relatively greater amounts of the vasodilator prostaglandin E2 (PGE2) and prostacyclin (PGI2) compared to the vasoconstrictor prostaglandin F2 alpha (PGF2 alpha) and thromboxane A2 (TxA2) agents (70:30% of total COPs respectively). The presence of eicosanoids (LTs and Ps) in sputum of patients with CB/B suggest that these biologically active substances may act as mediators of bronchoconstriction and inflammation in these diseases.

Measurement of endothelial metabolic functions in vivo

Lung metabolic functions include the interaction of microvascular endothelium with blood-borne substances such as physiologically important amine, eicosanoid, and peptide hormones and drugs. This activity is mediated by endothelial transport systems and enzymes which either synthesize or degrade these substances. Because they can alter the hormone content of aortic blood, these functions play a role in homeostasis, and their disturbance has been implicated in the pathogenesis of several forms of lung injury and disease. Both steady-state infusion and single injection, multiple indicator dilution techniques have been applied to measure endothelial metabolic functions in the intact lung. Considerable progress has been made in development of mathematical models for the processes, and their application has been tested both under normal conditions and also when the lung is perturbed experimentally. Unique experimental challenges are presented by measurement of metabolic functions in vivo, when steady-state infusion techniques cannot be used because systemic toxicity could result. In this case, the bolus injection approach has been used, with some success, both in laboratory animals and man. Although major challenges remain, their solution is essential if we are to apply knowledge of endothelial cell function in vitro to understanding lung microvascular physiology and pathophysiology in the intact animal.

The clinical significance of prostaglandins and thromboxane as mediators of septic shock

An evaluation was made of 106 surgical patients with Gram-negative septic shock, both for clinical criteria as well as the biochemical mediators endotoxin, prostaglandin F2 alpha, prostaglandin I2 (prostacyclin), and thromboxane. These data were correlated to various defined shock phases, functional data of vital organs, and clinical outcome. Patients underwent invasive organ function monitoring and the usual laboratory tests of intensive care. Prostaglandins and thromboxane were measured radioimmunologically, endotoxin by the limulus amebocyte lysate test. Endotoxin proved to be a more accurate predictor of severe sepsis than did positive blood cultures. Endotoxin as well as prostaglandins and thromboxane are predominantly released in early shock phases, appearing in plasma concentrations, which correlate with the severity of organ failure. Sepsis-induced respiratory failure coincides with a deterioration of pulmonary prostaglandin inactivation, which contributes to the release mechanism. High systemic prostacyclin activity benefits the patients' organ functions and clinical outcomes, while a predominance of thromboxane seems to effect the opposite. Transpulmonary-thromboxane gradients correlate significantly with pulmonary hypertension in the early phases of septic shock.

Detection of sputum eicosanoids in cystic fibrosis and in normal saliva by bioassay and radioimmunoassay

We have measured arachidonic acid (AA) metabolites, leukotrienes (LTs) and prostanoids (Ps), in sputum of patients with cystic fibrosis (CF) and in normal saliva using bioassay and radioimmunoassay (RIA). Almost three times as much LTB4 is present in CF extracts compared with slow reacting substances (SRSs). Leukotrienes were not detected in normal saliva. In CF sputum there is a three-fold increase in the level of the vasodilator prostanoid prostaglandin E2 (PGE2) and the stable metabolite of prostacyclin, 6-oxo PGF1 alpha compared with the vasoconstrictor prostaglandin F2 alpha (PGF2 alpha) and thromboxane B2 (TxB2), a hydrolysis product of thromboxane A2. Experiments with BW755c (25 micrograms ml-1, n = 3) indicated that the majority of this activity was not produced during the extraction procedure. The detection of LTs and Ps in sputum of CF patients shows that these substances are present at biologically active concentrations and may contribute to the pathophysiology of this disease.

Kinetics of the generation and action of chemical mediators in zymosan-induced inflammation of the rabbit peritoneal cavity

Acute inflammation was induced by intraperitoneal injection of zymosan (yeast cell walls) in the rabbit. Peritoneal inflammation was monitored by the local accumulation of intravenously-injected Evans blue dye (which binds to plasma albumin) and of polymorphonuclear leukocytes (PMNLs). The zymosan-induced exudate fluid contained a microvascular permeability-increasing factor or factors which, unlike histamine and bradykinin, had a long duration of action when tested in rabbit skin and was dependent on circulating PMNLs. Using radioimmunoassay, high levels of rabbit C5a, or C5a des Arg, were detected in the exudate fluid and accounted for much of the permeability-increasing activity, as judged by skin bioassay after separation on Sephadex G-100. The vasodilator prostaglandin, prostaglandin I2 (PGI2), was generated in the inflammatory reaction, as judged by the presence of high levels of 6-oxo-PGF1 alpha detected in the exudate by radioimmunoassay. However, in contrast to observations in rabbit skin, inhibition of prostaglandin generation had a relatively small effect on peritoneal oedema formation. C5a and C5a des Arg increase microvascular permeability by a PMNL-dependent mechanism in the rabbit. However, in response to zymosan, protein leakage was detected considerably earlier than PMNL accumulation. A hypothesis to account for this difference is proposed.

Coronary vasoconstriction in the rat, isolated perfused heart induced by platelet-activating factor is mediated by leukotriene C4

Platelet-activating factor (Paf, 0.04-4.50 nmol) dose-dependently induced coronary vasoconstriction and decreased cardiac contractility in rat, isolated perfused hearts and concomitantly released leukotriene-like bioactivity into the cardiac effluent. Platelet-activating factor (0.9 nmol) induced an increase in 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha), PGF2 alpha, PGE2 and thromboxane B2 (TXB2) measured by radioimmunoassay (RIA) of cardiac effluents following partial purification using C18 Sep-Paks. The leukotriene-like bioactivity released by Paf was identified as leukotriene C4 (LTC4) using a combination of isolation on reverse phase-h.p.l.c. (r.p.h.p.l.c.) and quantitation by RIA. In addition, LTB4 was also identified by r.p.h.p.l.c. and the levels, determined by RIA, were within the range having biological activity. The release of cyclo-oxygenase products by Paf was prevented by indomethacin (2.8 microM), markedly attenuated by diethylcarbamazine (7.7 mM) but unaffected by FPL 55712 (1.9 microM)-pretreatment. Furthermore, LTC4 (50 pmol) did not increase the release of the cyclo-oxygenase products measured. The release of LTB4 and LTC4 appeared to be unaffected by indomethacin pretreatment whereas diethylcarbamazine-pretreatment markedly inhibited release. The coronary vasoconstriction induced by Paf (0.9 nmol) was attenuated by pretreatment with indomethacin or diethylcarbamazine, whereas FPL 55712 caused a marked inhibition of the response. In contrast, the decrease in cardiac contractility was prevented by indomethacin or diethylcarbamazine and unaffected by FPL 55712 pretreatment. It is concluded that LTC4 may be largely responsible for the coronary vasoconstriction induced by Paf with cyclo-oxygenase products having a possible modulatory role whereas the latter appear to be involved in the Paf-induced decrease in cardiac contractility.

Generation of C5a and prostacyclin (PGI2) in an inflammatory response to zymosan and a reversed passive Arthus-type reaction in the peritoneal cavity of the rabbit

Exudate fluids were removed from the rabbit peritoneal cavity 2 h after the injection of zymosan or the initiation of a reversed passive Arthus-type reaction. Inflammatory oedema was measured using Evans blue dye extravasation and the concentrations of C5a and the PGI2 metabolite, 6-oxo-PGF1 alpha, were measured by radioimmunoassay. High levels of C5a were found in these inflammatory exudates and we suggest that the extravascular generation of C5a is important in the induction of increased microvascular permeability. The presence of PGI2 may have an enhancing effect on plasma protein leakage.

Effect of cyclosporin A and inhibitors of arachidonic acid metabolism on blood flow and cyclo-oxygenase products in rat skin allografts

Using skin blood flow as a measurement of skin graft rejection in rats, it has been shown that in both isografts and allografts the blood flow at first increases above the normal, after which the flow in isografts returns to normal while that in allografts ceases at the onset of rejection. Cyclosporin A (CSA) 5-40 mg kg-1 intramuscularly produced a dose-related inhibition of graft rejection and the pattern of blood flow in the treated allografts became similar to that in isografts in that it remained about 20% above normal throughout the period of treatment. Indomethacin (Indo), inhibitor of cyclo-oxygenase and benoxaprofen (Ben), inhibitor of cyclo-oxygenase and lipoxygenase, caused an enhancement of the onset of rejection and an early cessation of blood flow in allografts. The total content of 4 cyclo-oxygenase products (COP), (prostaglandin E2 (PGE2), PGF2 alpha, 6-oxo-PGF1 alpha and thromboxane B2 (TxB2] increased both in isografts and allografts, but when individual COP were expressed as a percentage of the total, only 6-oxo-PGF1 alpha (the stable metabolite of prostacyclin) increased in allografts. This increased proportion was reduced to normal by a dose of CSA which prolonged graft survival. Indo and Ben partially inhibited COP formation and in particular that of 6-oxo-PGF1 alpha. In addition, CSA caused a dose-related inhibition of the prostacyclin produced by zymosan-activated macrophages. These findings in the rat suggest that prostacyclin is partly responsible for the increase in blood flow in allografts prior to rejection; that CSA inhibits both the recruitment of prostacyclin-producing macrophages and prostacyclin formation directly; and that inhibitors of cyclo-oxygenase enhance skin graft rejection by abrogating the immunoregulatory activity of prostacyclin.

The diseased lung and drugs

Among the numerous ways by which drug-lung relationships can be discussed we chose to examine three questions: Is the lung capable of directly modulating drug pharmacokinetics? Knowing that the pulmonary circulation can exert very selective and efficient clearance and catabolism of biogenic molecules such as serotonin (5-HT), norepinephrine (N.E.), prostaglandins PGE2 and PGF2 alpha, and bradykinin, as well as activation of angiotensin (A)I to AII, a similar behavior has been sought for drugs. Uptake of circulating drugs occurs clearance of biogenic amines, the significance of which remains to be fully evaluated, and iatrogenic phospholipidosis localization of which in the lung might result from the elevated drug concentration in the tissue. Lung cells contain enzymes, among them mixed function oxidases (MFO), which enables them to metabolize xenobiotics even in the intact organ. Although blood supply to the lung is higher than that to the liver, the comparatively low MFO content of the former organ predicts only a marginal pulmonary metabolic contribution in vivo. On the otherhand, enzymatic activity upon drugs can generate instable reactive metabolites which, even in minute amounts are toxic and can damage cells; furthermore, it is hypothesized that the relatively high bronchiolar Clara cell MFO content explains the striking susceptibility of the long to xenobiotics. Do lung diseases indirectly influence drug pharmacokinetics? Hindrance to blood flow is common in respiratory failure (R.F.), from both reduced area and hypoxic vasoconstriction, resulting in altered flow distribution to the liver and kidney.

First-pass elimination. Basic concepts and clinical consequences

First-pass elimination takes place when a drug is metabolised between its site of administration and the site of sampling for measurement of drug concentration. Clinically, first-pass metabolism is important when the fraction of the dose administered that escapes metabolism is small and variable. The liver is usually assumed to be the major site of first-pass metabolism of a drug administered orally, but other potential sites are the gastrointestinal tract, blood, vascular endothelium, lungs, and the arm from which venous samples are taken. Bioavailability, defined as the ratio of the areas under the blood concentration-time curves, after extra- and intravascular drug administration (corrected for dosage if necessary), is often used as a measure of the extent of first-pass metabolism. When several sites of first-pass metabolism are in series, the bioavailability is the product of the fractions of drug entering the tissue that escape loss at each site. The extent of first-pass metabolism in the liver and intestinal wall depends on a number of physiological factors. The major factors are enzyme activity, plasma protein and blood cell binding, and gastrointestinal motility. Models that describe the dependence of bioavailability on changes in these physiological variables have been developed for drugs subject to first-pass metabolism only in the liver. Two that have been applied widely are the 'well-stirred' and 'parallel tube' models. Discrimination between the 2 models may be performed under linear conditions in which all pharmacokinetic parameters are independent of concentration and time. The predictions of the models are similar when bioavailability is large but differ dramatically when bioavailability is small. The 'parallel tube' model always predicts a much greater change in bioavailability than the 'well-stirred' model for a given change in drug-metabolising enzyme activity, blood flow, or fraction of drug unbound. Many clinically important drugs undergo considerable first-pass metabolism after an oral dose. Drugs in this category include alprenolol, amitriptyline, dihydroergotamine, 5-fluorouracil, hydralazine, isoprenaline (isoproterenol), lignocaine (lidocaine), lorcainide, pethidine (meperidine), mercaptopurine, metoprolol, morphine, neostigmine, nifedipine, pentazocine and propranolol. One major therapeutic implication of extensive first-pass metabolism is that much larger oral doses than intravenous doses are required to achieve equivalent plasma concentrations. For some drugs, extensive first-pass metabolism precludes their use as oral agents (e. g. lignocaine, naloxone and glyceryl trinitrate).(ABSTRACT TRUNCATED AT 400 WORDS)

Evaluation of antiarrhythmic activity of prostaglandin F2 alpha in man

Since prostaglandin (PG) F2 alpha had been shown to act anti-arrhythmically in various animal models and also in preliminary investigations in man, further evaluation of this effect was made in 30 patients with cardiac extrasystoles and in 2 patients with tachycardias. PGF2 alpha was infused intravenously at individually adapted consecutive rates from 5 to 100 micrograms/min each for at least 5 min. In the incidence of extrasystoles a mean maximum decrease of 41% (P less than 0.001) was obtained. One patient showed repeated short interruptions of a ventricular tachycardia. A dose-dependent significant rise in blood pressure and no significant influences on heart rate, PQ interval and QRS interval of the ECG were found. It is concluded that PGF2 alpha has probably no practical importance for the therapy of cardiac arrhythmias.

Endogenous prostaglandin F2 alpha in the hyperdynamic state of severe sepsis in man

Nine surgical patients underwent haemodynamic and respiratory monitoring during the course of severe sepsis. Endogenous PGF2 alpha levels in mixed venous and arterial plasma were measured. Results indicate pulmonary net release of PGF2 alpha, since arterial levels (1252 +/- 119 pg/ml) are significantly higher than mixed venous ones (824 +/- 89 pg/ml) in full-pronounced hyperdynamic septic shock. By contrast, the inactive metabolite KH2PGF2 alpha was found in lowest concentrations during shock (368 +/- 72 pg/ml) which suggests impaired pulmonary degradation. It is concluded that circulating PGF2 alpha is a marker of stimulated prostaglandin production in severe human sepsis.

Effects of the oestrous cycle on the metabolism of arachidonic acid in rat isolated lung

1. The metabolism of exogenous arachidonic acid perfused through the pulmonary circulation was investigated in lungs taken from rats at different stages of the oestrous cycle. 2. Following perfusion with [14C]arachidonic acid there was more radioactivity associated with cyclo-oxygenase products in general at pro-oestrus than at any other stage of the cycle. 3. Production of 6-oxo-prostaglandin F1 alpha and hence of prostacyclin (PGI2) was also highest at pro-oestrus. 4. Production of thromboxane B2 was highest at pro-oestrus although it was never greater than PGI2 production at any stage. 5. Radioactivity retained in lung tissue was mostly present in phospholipid and free fatty acid fractions with the distribution at pro-oestrus being different from the other stages. 6. Following perfusion with [14C]oleic acid (which is not a substrate for cyclooxygenase), variations in the distribution of label in radioactivity in lung were also observed. However, these were not related to the stages of the oestrous cycle in the same way as those associated with arachidonic acid. 7. We conclude that both pathways of arachidonic acid metabolism in lung--oxidation via cyclo-oxygenase and incorporation into phospholipid - are affected by the progress of the oestrous cycle. 8. Altered arachidonate metabolism appeared to be associated chiefly with pro-oestrus and may be linked to those hormones involved in this stage of the oestrous cycle.

Bradykinin-stimulated prostaglandin E2 production by endothelial cells and its modulation by antiinflammatory compounds

Prostaglandin production was studied in cultures of pig aorta endothelial cells using radioimmunoassay, radiochromatography, and smooth muscle bioassay. PGE2 was produced in higher concentrations than other prostaglandins. Bradykinin produced a rapid dose-related stimulation of PGE2 production. These results provided the basis for establishment of a simplified test system for investigating new compounds which alter prostaglandin synthesis and might therefore affect inflammatory response. It was also observed that these endothelial cells do not metabolize prostaglandins via 15-hydroxyprostaglandin dehydrogenase.

The effects of aspirin and methysergide, singly and in combination, on systemic haemodynamic responses to pulmonary embolism

Pretreatment of anaesthetized rabbits with aspirin (A), 250 mg.kg-1, methysergide (M) 3 mg.kg-1 or a combination of both (A + M) was done before pulmonary embolism with a 1.0 ml autologous blood clot and compared with no pretreatment (C). Experiments were done until 10 survivors were present in each group. Mortality rate in controls (C) was 55 per cent (death in less than 30 minutes) compared to zero in (A) and (A + M) and nine per cent in (M). Arterial blood pressure fell to 60 per cent of pre-embolism values two minutes after embolism in (C) but had returned to 85 per cent of pre-embolism values after 60 minutes. This compares with a drop to 82 per cent at two minutes and 83 per cent at 60 minutes in (A), a drop to 70 per cent at two minutes and 90 per cent at 60 minutes in (M) and a very small drop to 92 per cent at two minutes which was unchanged at 60 minutes in (A + M). Right ventricular pressure increased by 75 per cent after two minutes compared to pre-embolism values in (C) and was still elevated by 37 per cent after 60 minutes. This compares with increases at two minutes and 60 minutes respectively of 58 and 23 per cent in (A), 65 and 35 per cent in (M) and 55 and 18 per cent in (A + M). Heart rate did not show any significant changes in any of the groups after embolism. These results show a dramatic reduction in mortality from pulmonary embolism with aspirin or methysergide pretreatment, which is associated with significant attenuation of the hypotensive response seen in controls. These agents may act by inhibiting the actions of a release of prostaglandins and serotonin. The additive effects of the combination used suggests that both mediators may play a role in the haemodynamic responses to pulmonary embolism.

Hypoventilation and elevation of end-expiratory pressure release a substance which relaxes isolated arteries and disaggregates platelets in the presence of cyclooxygenase inhibitors

A prostacyclin-like substance was detected by bioassay in the blood of dogs and cats during hypoventilation and increased end-expiratory pressure. This biologically active material, most likely originating from lungs, relaxed isolated vascular strips and disaggregated platelets. Its release was not prevented by indomethacin or aspirin. Biological activity was not abolished by 10 min incubation of blood at 38 degrees C. Although the identity of the substance has not been established the release of a biologically active prostacyclin-like material might play a role in circulatory adaptation to disturbed ventilatory function.

The effects of glucocorticoids on the distribution and mobilisation of arachidonic acid in fat cell ghosts

1 The prostaglandin synthesizing enzymes were found to be present in fat cell ghosts isolated from rabbit adipose tissue. 2 Prostaglandin E2 (PGE2) and PGF2, were synthesized by ghosts after stimulation with adrenocorticotrophic hormone (ACTH). 3 Indomethacin was found to inhibit this synthesis but not the synthesis of lipoxygenase products. 4 When fat cell ghosts were stimulated by ACTH, fatty acid release was observed from both neutral lipids and phospholipids. 5 The arachidonic acid (AA) pool within the ghosts and identified: approximately 90% was present in the phospholipid fraction, 8.5% in the neutral lipids and 1.5% unbound. 6 The glucocorticoids were found to stimulate incorporation of [14C]-AA into neutral lipids and inhibit its incorporation into phospholipids. 7 When fatty acid release was stimulated with ACTH, the glucocorticoids were found to inhibit the mobilisation of [14C]-AA from the phospholipids and enhance its release from the neutral lipids. 8 The glucocorticoids inhibit prostaglandin formation in fat cell ghosts.

Potential pitfalls in the conventional pharmacokinetic studies: effects of the initial mixing of drug in blood and the pulmonary first-pass elimination

The classical concept of assuming that an i.v. dose instantaneously distributes into the central or plasma compartment is reviewed, as is the potential for pulmonary first-pass effect. Based on available literature, the concept is shown to lead to serious errors in estimating pharmacokinetic parameters, particularly for drugs with high clearance.