Differential effects of ibuprofen,indomethacin, and meclofenamate on prostaglandin endoperoxide H2 metabolism

Summary Previous studies have suggested the possibility that the non-steroidal antiflammatory drug (NSAID), ibuprofen, may inhibit thromboxane (TX) A₂ synthase activity in addition to inhibiting cyclooxygenae activity. Microsomal fractions isolated from the cat lung contain cyclooxygenase as well as prostacyclin (PGI₂) synthase, TX synthase, and a GSH-dependent prostaglandin (PG) E₂ isomerase activities. When [1-¹⁴C] PG endoperoxide H₂ (PGH₂) was used as substrate, ibuprofen, indomethacin, and meclofenamate exhibited differential effects on terminal enzyme activities. Ibuprofen, at concentrations up to 1 mM, had no effect on the activities of PGI₂ synthase, TXA₂ synthase of GSH-dependent PGE₂ isomerase, whereas indomethacin selectively inhibited PGI₂ synthase activity at 5 x 10^–4 M and 10^–3 M. Meclofenamate selectively inhibited TXA₂ synthase activity at 5 x 10^–4 M and 10^–3 M. At concentrations of 5 x 10^–3 M, this selectivity was not oberved, and indomethacin and meclofenamate decreased the formation of both 6-keto-PGF₁ and TXB₂. These data indicate that the choice of NSAID and the concentration employed may specifically alter PGH₂ metabolism. This action may affect the physiologic consequences of the exchange of PGH₂ between cells. The data further indicate that indomethacin has the potential for use as a tool to specifically attenuate PGI₂ synthase activity in vitro.     

Inhibition of GSH-dependent PGH2 isomerase in mammary adenocarcinoma cells by allicin.

We have reported tha allicin, a constituent of garlic oil, has no effect on the activities of platelet cyclooxygenase or thromboxane synthase, or vascular PGI₂ synthase. The effect of allicin on glutathione (GSH) dependent PGH₂ to PGE₂ isomerase is unknown. We therefore studied the effect of allicin on PGE₂ biosynthesis in a murine mammary adenocarcinoma cell line (No 4526). Intact or sonicated cells were incubated with either ¹⁴C-arachidonic acid (AA) or ¹⁴C-PHG₂, respectively. Following metabolism, products were extracted, separated by TLC and analyzed by radiochromatographic scan. PGE₂ was predominantly formed with minimal amounts of PGF_2α and PGD₂. Formation of 6-keto-PGF_1α or TXB₂ was not detected indicating the absence of TXA₂ and PGI₂ synthase activity. Indomethacin and ibuprofen inhibited the PGE₂ formation (p < 0.05). The enzymatic PGE₂ formation in sonicates was blocked by depletion of the cellular non-protein thiols by buthionine sulfoximine and was shown to be dependent on GSH. Allicin, over the range of 10–1000 μM, inhibited the formation of PGE₂ in cells exposed to 2.0 μM ¹⁴C-AA for 20 min. and in sonicated cells incubated with 20.0 μM ¹⁴C-PGH₂ for 2 min (p < 0.05). Allicin did not alter cyclooexygenase-mediated oxygen utilization in ram seminal vessicle microsomes, suggesting that allicin selectively inhibits the GSH-dependent PGH₂ to PGE₂ isomerase in this adenocarcinoma cell line.     

Concentration-activity profile of the modulation of cyclooxygenase product formation by reduced glutathione in microsomal fractions from the goat lung

Age-related changes in pulmonary formation of arachidonic acid (AA) metabolites are thought to play an important role in regulating cardiopulmonary function. This study addresses the potential role of reduced glutathione (GSH) in modulating cyclooxygenase product formation in the developing lung. Prostaglandin H2 (PGH2) metabolism was studied in microsomal fractions isolated from the lungs of unventilated fetal, neonatal and adult goats. GSH-dependent PGH2 to PGE2 isomerase activity in microsomal fractions from the perinatal (fetal and neonatal) goat lung was not saturable with respect to GSH and can respond to changes in GSH concentration over the range of 0.01 to 30 mM, which encompasses the full range the intracellular GSH levels reported in the literature. However, in fractions from the adult, a lower rate of PGE2 formation is observed at higher GSH concentrations. In addition, the tissue levels of GSH exhibited developmental stage-related differences with fetal being higher than neonatal or adult. The present observations may have physiologic relevance, in that decreases in pulmonary GSH levels after birth may contribute to decreases in plasma PGE2 levels by decreasing pulmonary PGE2 synthesis, thereby contributing to closure of the ductus arteriosus; conversely, increased GSH levels associated with hyperoxia may contribute to persistence of ductal patency. Formation of 6-keto-PGF1 alpha and of TXB2 (the stable metabolites of prostacyclin and TXA2) was decreased when PGE2 formation was increased by GSH activation of PGE2 isomerase in fractions isolated from all three developmental stages. A similar pattern of product formation was observed when AA was employed as substrate. These data suggest the possibility that changes in GSH concentration may modulate eicosanoid formation in cells that contain GSH-dependent PGE2 isomerase, as well as either or both prostacyclin or thromboxane synthase(s).     

Atherosclerosis decreased prostacyclin formation in rabbit lungs and kidneys

Metabolism of arachidonic acid (AA) was studied in perfused lungs and kidneys of normal and atherosclerotic rabbits by determination of PGE₂, PGF_2α and the stable metabolites of PGI₂ (6-keto-PGF_1α) and TXA₂ (TXB₂). PGI₂ was the main AA metabolite formed by normal lungs and kidneys. Atherosclerosis reduced the formation of PGI₂ by about 50 % in both organs. TXA₂ formation was similarily decreased in lungs. In kidneys, the decrease in PGI₂ formation was accompanied by an increase in PGE₂ formation.     

Influence of chronic antigen exposure on the metabolism of PGH2 by microsomal preparations of airway and parenchymal tissues in the sheep

The effects of repeated antigen exposure on the synthesis of mediators by lung tissues are not well understood. To investigate the influence of antigen challenge on the synthesis of prostaglandins by central airway and peripheral lung tissues, fourteen sensitive sheep underwent biweekly exposure to aerosolized $\text{Ascaris suu}$ antigen (7) or saline (7). Following the fifth exposure, microsomal and high speed supernatant fractions were prepared from trachealis muscle and lung parenchyma. Synthesis of thromboxane (TX) A₂, prostaglandin (PG) D₂ and PGI₂ from the PG endoperoxide intermediate, PGH₂, was assayed over a range of substrate concentrations from 3–200 uM. Synthesis of PGI₂ by trachealis microsomes was approximately 5-fold greater than that of TXA₂. PGI₂ and TXA₂ production was identical in tracheal preparations from Ascaris- and saline-exposed animals. In parenchymal tissues, where TXA₂ production predominated over PGI₂ by 9-fold, preparations from Ascaris- exposed animals synthesized 50% more TXA₂ than controls at PGH₂ concentrations of 25 uM and above, whereas synthesis of PGI₂ and PGD₂ were similar in preparations from both groups of animals. The density of pulmonary mast cells was decreased by 21% in the Ascaris group, whereas polymorphonuclear leukocyte density was unchanged. These results demonstrate the differential synthesis of TXA₂ and PGI₂ in central airways and peripheral lung regions of the sheep. They further indicate that repeated exposure of the airways to antigen selectively enhances TXA₂ synthesis in the lung periphery of sensitized animals. The site of this increased enzymatic activity, whether in resident cells or newly-infiltrated cells, has not been determined.     

PGD2 formation in the vasculature: Characteristics of rat tail vein prostaglandin endorperoxide-D isomerase

Rat tail vein homogenates, microsome and high speed supernatant fractions were incubated with [1-¹⁴C]prostaglandin endoperoxide (PGH₂) and products separated and identified by radio-thinlayer chromatography. PGI₂ synthase was localized to the microsomal fraction, but exhibited low activity compared to rat tail arteries prepared in the same manner. PGH-D isomerase was maximally active in the presence of reduced glutathione at pH 7.5–8.0, exhibited a K_m for PGH₂ of 33 μM, and was inhibited sulfhydryl-directed reagents. The similarities of this enzyme to PGD synthase of the rat cerebral microvasculature are discussed.     

Prostacyclin and thromboxane formation in human umbilical arteries following stimulation with vasoactive autacoids

The formation of prostacyclin (PGI₂) and thromboxane A₂ (TXA₂) (measured as the stable metabolites 6-keto-PGF_1α and TXB₂) during stimulation with vasoactive autocoids was registered in human umbilical arteries perfused . Responses were registered within 3–4 minutes after addition of the subtances. Both angiostensin I and II were found to increase the formation of PGI₂ while depressing that of TXA₂. Serotonin increased the formation of TXA₂ but not that of PGI₂. Both PGE₂ and PGF_2α stimulated the PGI₂ formation. The TXA₂ mimetic U46619, increased PGI₂ production, whereas PGI₂ slighlty increased the formation of TXA₂. All responses were found to be completely inhibited by indomethacin.     

Prostaglandin production in cultured gastric mucosal cells: Role of cAMP on its modulation

The effect of cAMP on prostaglandin production may depend on cell types. To clarify the relationship between PG and cAMP, we examined arachidonate's effects on PG synthesis and intracellular cAMP accumulation in monolayers of rat gastric mucosal cells. These cells produced PGE₂, PGI₂ and thromboxaneA₂ (TXA₂) in amounts of 316±18, 100±7 and 30±5 pg per 10⁵ cells in 10 min, respectively, in response to 10μM arachidonic acid (AA). The production of these PG, however, leveled off subsequently. Cells initially exposed to AA responded poorly to a subsequent stimulation by AA. AA simultaneously stimulated intracellular cAMP accumulation; this stimulatory effect on cAMP production was abolished by the pretreatment with indomethacin. Nevertheless, the pretreatments with dibutyryl cAMP (0.1–5mM) did not alter the amount of subsequent AA-induced PGE₂ production. Furthermore, the preincubation with 1mM isobutyl methyl xanthine also failed to affect PGE₂ synthesis, while it increased intracellular cAMP accumulation. Our studies suggest (1) AA stimulates intracellular cAMP formation in cultured gastric mucosal cells, linked with conversion of AA to cyclooxygenase metabolites, (2) AA-induced PG production is limited in these cells, and (3) it seems, however, unlikely that intracellular cAMP modulates AA metabolism to PG.     

Effects of nitrogen dioxide exposure on prostacyclin synthesis in lung and thromboxane A2 synthesis in platelets in rats

Effects of nitrogen dioxide (NO₂) exposure on prostacyclin (PGIP₂) synthesis in the rat lung and thromboxane A₂ (TXA₂) synthesis in the platelets were studied. Male Wistar rats were exposed to 10 ppm NO₂ for 1, 3, 5, 7 and 14 days. PGI₂ synthesizing activity of homogenized lung decreased. The damage of PGI₂ synthesizing activity reaches its maximum at 3 days. At 14 days, PGI₂ synthesizing activity returned to the normal level. The activity of PGI₂ synthetase decreased significantly. The formation of lipid peroxides due to NO₂ exposure may cause the depression of PGI₂ synthesizing activity of lung. On the other hand, platelet TXA₂ synthesizing activity increased. This increased TXA₂ synthesizing activity lasted at least till 3 days. Then, it returned to the normal level. The counts of platelet were decreased significantly by 1, 3, 5 and 7 days NO₂ exposure. Then the decreased counts of platelet returned to the normal level at 14 days NO₂ exposure. These results indicate that the depression of PGI₂ synthesizing activity lung by NO₂ exposure cause an increase in TXA₂ synthesizing activity of platelets. It may contribute to induce platelet aggregation and to the observed decrease in the number of platelets during NO₂ exposure.     

Two different mechanisms for modulation of bronchoconstriction in guinea-pigs by cyclooxygenase metabolites

Leukotriene D₄ (LTD₄)-induced bronchoconstriction in guinea-pig airways has a cyclooxygenase (COX)-dependent component. The main objective of this study was to establish if prostaglandin (PG) D₂-induced bronchoconstriction also was modulated by COX products. The effects of non-selective and selective COX-1 and COX-2 inhibitors on bronchoconstriction induced by LTD₄ and PGD₂ were investigated in the perfused and ventilated guinea-pig lung (IPL). Both LTD₄-induced bronchoconstriction and thromboxane (TX) A₂ release was suppressed by COX inhibitors or by TX synthesis inhibition. The release of additional COX products following CysLT₁ receptor activation by LTD₄ was established by measurements of immunoreactive 6-keto PGF_1α (a stable metabolite of PGI₂) and PGE₂. In contrast, TP receptor-mediated bronchoconstriction by PGD₂ was somewhat enhanced by COX inhibitors, and there was no measurable release of COX products after TP receptor activation with U-46619. PGE₂ was bronchoprotective in IPL as it inhibited the histamine-induced bronchoconstriction. In the isolated guinea-pig trachea, neither PGD₂ nor U-46619 actively released PGE₂, but continuous production of PGE₂ and PGI₂ was established, and the response to PGD₂ was enhanced also in the trachea by COX inhibition. The study documented that bronchoconstriction induced by LTD₄ and PGD₂ in IPL was modulated differently by COX products. Whereas bronchoconstriction induced by LTD₄ was amplified predominantly by secondarily released TXA₂, that induced by PGD₂ was attenuated by bronchoprotective PGE₂ and PGI₂, presumably tonically produced in the airways.     

A novel single‐chain enzyme complex with chain reaction properties rapidly producing thromboxane A2 and exhibiting powerful anti‐bleeding functions

Uncontrollable bleeding is still a worldwide killer. In this study, we aimed to investigate a novel approach to exhibit effective haemostatic properties, which could possibly save lives in various bleeding emergencies. According to the structure‐based enzymatic design, we have engineered a novel single‐chain hybrid enzyme complex (SCHEC), COX‐1‐10aa‐TXAS. We linked the C‐terminus of cyclooxygenase‐1 (COX‐1) to the N‐terminus of the thromboxane A₂ (TXA₂) synthase (TXAS), through a 10‐amino acid residue linker. This recombinant COX‐1‐10aa‐TXAS can effectively pass COX‐1–derived intermediate prostaglandin (PG) H₂ (PGH₂) to the active site of TXAS, resulting in an effective chain reaction property to produce the haemostatic prostanoid, TXA₂, rapidly. Advantageously, COX‐1‐10aa‐TXAS constrains the production of other pro‐bleeding prostanoids, such as prostacyclin (PGI₂) and prostaglandin E₂ (PGE₂), through reducing the common substrate, PGH₂ being passed to synthases which produce aforementioned prostanoids. Therefore, based on these multiple properties, this novel COX‐1‐10aa‐TXAS indicated a powerful anti‐bleeding ability, which could be used to treat a variety of bleeding situations and could even be useful for bleeding prone situations, including nonsteroidal anti‐inflammatory drugs (NSAIDs)‐resulted TXA₂‐deficient and PGI₂‐mediated bleeding disorders. This novel SCHEC has a great potential to be developed into a biological haemostatic agent to treat severe haemorrhage emergencies, which will prevent the complications of blood loss and save lives.     

Prostacyclin and thromboxane A2 release in isolated rat lungs

The influence of platelets and platelet membranes on the generation of prostacyclin (PGI₂) and thromboxane A₂(TXA₂) by isolated rat lung and porcine aortic endothelial cell, as measured by RIA of their stable end-producs, 6-oxo-PGF_1α and TXB₂ respectively, was studied. After introduction of either aspirin-treated platelets or membranes from aspirin-treated platelets to the perfusate, 1 5-fold increase in the amount of 6-oxo-PGF_1α and TXB₂ in the perfusate was observed. Treatment of the lung with aspirin produced a 50% reduction in the platelet-stimulated release of PGI₂ and TXA₂. Treatment of the lung with the phospholipase inhibitor, mepacrine, significantly reduced the platelet-stimulated release of PGI₂ and TXA₂. Incubation of endothelial cells with untreated platelet membranes did not alter the generation of PGI₂. These results suggest that platelet-stimulated release of PGI₂ and TXA₂ occurs via mechanical stimulation of phospholipase A₂, liberating arachidonic acid.     

Arachidonic acid stimulates interleukin-6 release from rat peritoneal macrophages in vitro: Evidence for a prostacyclin-dependent mechanism

Interleukin-6 (IL-6) is a cytokine involved in the differentiation of B-cells to antibody secreting plasma cells, the activation of T-cells, and the stimulation of hepatocyte production of acute phase proteins. Because of the pro-inflammatory effects of this cytokine, we investigated the ability of the fatty acid arachidonic acid (AA) to regulate the release of IL-6 from rat resident peritoneal macrophages (Mø) in vitro. AA (0.5–16 μM) stimulated IL-6 release during a 4 h incubation period in a biphasic manner, with 4 μM AA generating a peak of IL-6 release (3-5-fold). AA (0.5–16 μM) also induced an increasing release of the AA metabolite thromboxane B₂ (TXB₂). The AA-induced release of IL-6 occurred within 1–2 h of incubation, whereas TXB₂ concentrations were elevated within 5 min of AA treatment. The TX synthetase inhibitor CGS 12970 (4.0 μM and 40.0 μM) effectively blocked the generation of TXB₂, but increased prostacyclin (PGI₂) generation and potentiated the release of IL-6. In addition, PGI₂, as well as the PGI₂ agonists iloprost and cicaprost, stimulated IL-6 release from Mø by greater than 5-fold over vehicle-treated basal levels. These data suggest that PGI₂ (but not TXA₂) is involved in AA-induced IL-6 release from peritoneal Mø.     

Prostaglandin F2α antagonizes thromboxane A2-induced human platelet aggregation

The effects of prostaglandin F_2α on human blood platelet function were investigated. PGF_2α at 15 μM completely blocked platelet aggregation induced by 500 μM arachidonic acid or 3 μM U46619 but had no effect on aggregatin induced by 7.5 μM ADP. A similar specificity of action was not obtained with either PGI₂ or PGE₂. Thus concentrations of PGI₂ (3 nM) or PGE₂ (20 μ M) which inhibited U46619-induced aggregation by 100% also blocked ADP-stimulated aggregation.The inhibitory properties of PGF_2α were not related to increases in platelet cAMP, since direct measurement of intracellular cAMP revealed that 15 μ M PGF_2α produced no substantial change in cAMP levels. This finding was in direct contrast to results obtained using either PGI₂ or PGE₂. Both PGI₂ (3 nM) and PGE₂ (20 μ M) induced significant increases in platelet cAMP levels.The possibility that PGF_2α directly interacts at the platelet TXA₂/PGH₂ receptor was investigated by measuring [³H]PGF_2α binding to isolated platelet membranes. It was found that [³H] PGF_2α binding reached equilibrium within 30 min at room temperature and could be 90% displaced by addition of 1000 fold excess of unlabelled PGF_2α. Furthermore, when 1000 fold excess of either the TXA₂/PGH₂ “mimetic” U46619 or the TXA₂/PGH₂ antagonist 13-azaprostanoic acid was added, specific [³H] PGF_2α binding was displaced by 95% and 85% respectively. In contrast, the same molar excess of 6-keto-PGF_1α, azo analog 1, or TXB₂, caused displacement of only 15%, 20% or 25% of the [³H] PGF_2α binding. Scatchard analysis indicated that [³H] PGF_2α has two binding sites; i.e., a high affinity binding site with an apparent Kd of 50 nM and a low affinity binding site with apparent Kd of 320 nM. These results suggest that the selective inhibition by PGF_2α of AA or U46619-induced aggregation may be mediated through interaction at the platelet TXA₂/PGH₂ receptor.     

Effect of dipyridamole of prostaglandin generation by human platelets and vessel walls

These experiments were conducted to determine the effects of dipyridemole on human platelet aggregation, platelet thromboxane A₂ (TXA₂) and human vessel wall prostacyclin (PGI₂) generation. Dipyridamole in varying concentrations (5 to 50 μg/ml) had no direct effect on ADP-induced platelet aggregation in vitro, but it potentiated PGI₂-induced platelet aggregation inhibition at these concentrations. Dipyridamole also inhibited arachidonic acid-induced platelet TXA₂ generation at these concentrations. In continuously perfused umbilical vein segments, dipyridamole treatment resulted in stimulation of PGI₂ release determined by bioassay and by measurement of its stable metabolite 6-keto-PGF_1α. Minimum concentration of dipyridamole causing PGI₂ release was 50 μg/ml. These in vitro studies suggest that anti-thrombotic effects of dipyridamole in man are mediated mainly by potentiation of PGI₂ activity and to some extent by TXA₂ suppression. Stimulation of PGI₂ release by human vessels may not be seen in usual therapeutic concentrations.     

Regulation of pancreatic β-cell function and mass dynamics by prostaglandin signaling

Prostaglandins (PGs) are signaling lipids derived from arachidonic acid (AA), which is metabolized by cyclooxygenase (COX)-1 or 2 and class-specific synthases to generate PGD₂, PGE₂, PGF_2α, PGI₂ (prostacyclin), and thromboxane A₂. PGs signal through G-protein coupled receptors (GPCRs) and are important modulators of an array of physiological functions, including systemic inflammation and insulin secretion from pancreatic islets. The role of PGs in β-cell function has been an active area of interest, beginning in the 1970s. Early studies demonstrated that PGE₂ inhibits glucose-stimulated insulin secretion (GSIS), although more recent studies have questioned this inhibitory action of PGE₂. The PGE₂ receptor EP3 and one of the G-proteins that couples to EP3, Gα_Z, have been identified as negative regulators of β-cell proliferation and survival. Conversely, PGI₂ and its receptor, IP, play a positive role in the β-cell by enhancing GSIS and preserving β-cell mass in response to the β-cell toxin streptozotocin (STZ). In comparison to PGE₂ and PGI₂, little is known about the function of the remaining PGs within islets. In this review, we discuss the roles of PGs, particularly PGE₂ and PGI₂, PG receptors, and downstream signaling events that alter β-cell function and regulation of β-cell mass.     

Regulation of microvascular prostacyclin and thromboxane with inhibitors or arachidonic acid metabolism

The levels of the stable degradation products of prostacyclin (PGI₂) and thromboxane A₂ (TXA₂): 6-oxo-prostaglandin F_1α(6-oxo-PGE_1α) and thromboxane B₂ (TXB₂) respectively were determined in the effluent of the rabbit epigastric skin flap after infusion of exogenous arachidonic acid. The blood to the flap passes through the microcirculation and thus the changes in eicosanoid biosynthesis in this part of the vasculature were recorded. The aim was to use inhibitors of arachidonic acid metabolism to increase the PGI₂/TXA₂ ratio. This may be potentially beneficial to ischaemic skin flaps by reducing platelet aggregation associated with damaged microvascular endothelium, overcoming vasospasm and increasing microvascular blood flow. Increased PGI₂/TXA₂ ratios (up to 5-fold) were best achieved using TXA₂ synthetase inhibitors such as dazoxiben hydrochloride. These were significantly more potent than the phosphodiesterase inhibitor dipyridamole, and the lipoxygenase inhibitor Bay g6575. No increase in blood flow was achieved. The cyclooxygenase inhibitor indomethacin did slow the blood flow at high concentrations (above 10⁻⁵ M), and inhibited both PGI₂ and TXA₂ synthesis. Approximately 2-fold higher concentrations of dazoxiben hydrochloride and dipyridamole were required to produce the same TXA₂ synthetase inhibition in the flap microvasculature compared with platelets .     

Some new prospects in the mechanism of control of arachidonate metabolism in human placenta and amnion

The conversion of (1-¹⁴C) PGH₂ was studied in human placental and fetal membrane cellular preparations (tissue fragments, homogenate, cytosol, microsomes). Placental and amnion homogenates convert labelled PGH₂ into PGE₂ through a very active PGE₂ isomerase. However isolated placental microsomes do not metabolise PGH₂ into PGE₂ but into T×A₂ (identified as T×B₂ by GC-MS) and presumably 12-HHT. This microsomal T×A₂ synthetase is not active in the whole tissue nor in the homogenate. Placental cytosol gives mainly PGD₂. No conversion into PGI₂ (identofied as 6 keto PGF_1α) nor PGF_2α was observed in any fraction.Some aspects of PG synthesis regulation by the placental cytosol were studied: the cytosol contains a heat-stable factor that inhibits T×A₂ synthesis and shifts PGH₂ placental microsome metabolism towards PGE₂. In addition the placental cytosol inhibits human platelet-aggregation through a heat-labile factor which is not PGI₂ nor PGD₂. A multiple step regulation of the various PG metabolites synthetised from arachidonic acid in the placenta can be outlined and its physiological implications are discussed.     

Consequences of long-term selenium-deficient diet on the prostacyclin and thromboxane release from rat aorta

It is known that peroxides, which are increased during Se deficiency because of reduced glutathione peroxidase (GSH-Px) activity, can influence the prostacyclin I₂/thromboxane A₂ (PGI₂/TXA₂) ratio. In this study we analyzed the PGI₂ and TXA₂ formation of aortas of long-term Se-deficient rats. Despite low GSH-Px activity in the Se-deficient group, the basal PGI₂ and TXA₂ formation was not different versus control animals (PGI₂: 2295 ± 1134 pg/mg vs 2940 ± 1134 pg/mg; TXA₂: 3.83 ± 1.06 pg/mg vs 5.67 ± 2.99 pg/mg). However, we checked the capacity of the aortas of Se-deficient rats to compensate for a suddenly increased peroxide concentration. After peroxide stimulation, the PGI₂ release was significantly lower in the Se-deficient group compared to the control group (PGI₂: 3507 ± 1829 pg/mg vs 7986 ± 2636 pg/mg). Again, the TXA₂ release did not show any differences. The release ratio of PGI₂/TXA₂ decreased under peroxide stress in Se-deficient animals. Although long-term Se deficiency showed a relatively well-balanced metabolism under resting conditions, sudden stress, accompanied by an excessive radical production, cannot be compensated.     

Antithrombotic effect of topically applied 3-Oxa-Methano-prostaglandin I1 in the microcirculation and antiplatelet functions of its active form

The antithrombotic effect of topical application of the 3-oxamethano-prostaglandin (PG) I₁ analog, SM-10902 in the microcirculation and in vitro antiplatelet functions of its active form SM-10906 were estimated in comparison with PGI₂ and PGE₁. In rat platelets, SM-10906 evoked accumulation of intracellular cyclic adenosine 3′,5′-monophosphate, and exhibited antiaggregatory and disaggregatory activities, which were all enhanced by the phosphodiesterase inhibitor theophylline. Additionally, SM-10906 was shown to inhibit platelet adhesion to collagen in human platelet-rich plasma. PGI₂ and PGE₁ also showed in vitro antiplatelet effects in the order of PGI₂ > SM-10906 ≥ PGE₁. SM-10902 exhibited a dose-dependent antithrombotic effect in the guinea pig mesenteric arteriole by a topical application, and this activity might be exerted by the antiplatelet functions of SM-10906. Although SM-10906, PGI₂ and PGE₁ also showed the antithrombotic effects, SM-10902 was the most potent. In conclusion, the present studies indicate that an external topical preparation of SM-10902 may be useful for the therapy of peripheral circulatory insufficiency.