Inhibitory effects of beta adrenoceptor antagonist, atenolol, on the thromboxane system in the kidney of spontaneously hypertensive rats

We attempted to investigate the alterations in the vasoconstrictor thromboxane (TXA2) system in the kidney when spontaneously hypertensive rats (SHR) were treated subchronically with atenolol, a beta 1-adrenoceptor antagonist. Atenolol treatment (30 mg/kg body weight per day for 2 weeks) reduced systolic blood pressure by 11%, being accompanied by a decrease in heart rate. This treatment strikingly decreased thromboxane content in the renal cortex by 48% (p less than 0.05), whereas the tissue content was unaltered for prostaglandin E2 (PGE2) or slightly decreased for prostacyclin (PGI2). These alterations in the eicosanoid system led to an increase in the ratio of PGE2/TXA2 and of PGI2/TXA2. Similarly, thromboxane content in the renal papilla was lowered significantly with atenolol treatment, which raised the ratio of PGE2 to TXA2. Thromboxane reduction was not observed in the aortic walls and heart. However, in the vascular walls, PGI2 synthesis was markedly stimulated with atenolol treatment, resulting in an increase in the ratio of PGI2 to TXA2. Thus, these data indicate that subchronic atenolol-treatment inhibits the thromboxane system in the kidney, thereby shifting the eicosanoid system towards a vasodilator state. These alterations contribute, in part, to the anti-hypertensive properties of atenolol in genetic hypertension.     

Effect of eicosanoids on the accumulation of cholesterol and the proliferation of subendothelial cells in the human aorta

The effect of prostacyclin and stable thromboxane analog A2 on endothelial culture of human aorta was studied. It was shown that prostacyclin inhibited accumulation of cholesterol in the cells and their proliferation, while thromboxane exhibited an opposite effect. Calcium antagonists potentiated effects of prostacyclin and inhibited them in respect to thromboxane. Screening of a number of synthetic agents affecting arachidonic acid metabolism was carried out. It was found that lipoxygenase inhibitors suppress cholesterol accumulation and proliferation in cells presumably due to enhancement of prostacyclin synthesis and inhibition of leukotriene formation. The balance between various eicosanoids is supposed to be an important factor of atherogenesis regulation, while antiatherogenic effect of calcium antagonists is somehow associated with the impact of eicosanoids on atherogenesis regulation.     

Pharmacological modulation of prostacyclin and thromboxane production of rat and cat venous tissue slices.

To reveal a potential modulating effect of vasoactive pharmacological agents on the prostanoid production of the venous wall, prostacyclin and thromboxane release from venous tissue slices was studied. Aortic and caval vein samples from 20 rats as well as from 21 cats were studied. Prostacyclin and thromboxane productions were determined by radioimmunoassay as 6-keto-PGF1 alpha and TxB2 released into the incubation medium. Venous tissue produced significantly less prostacyclin per unit weight than arterial tissue in rats (30.7 +/- 4.6 vs. 52.1 +/- 8.2 pg/mg/min), while in cats an opposite situation was found (16.6 +/- 3.2 vs. 7.06 +/- 1.9 pg/mg/min). Thromboxane production of venous tissue was consequently higher than corresponding values for aortic tissue (3.72 +/- 0.46 vs. 1.54 +/- 0.14 in rats and 3.4 +/- 0.6 vs. 1.33 +/- 0.19 in cats, all values in pg/mg/min). Norepinephrine and dopamine significantly increased both the prostacyclin and the thromboxane release from venous tissue, while isoproterenol had no effect. Vasopressin significantly increased thromboxane release and decreased the ratio of prostacyclin vs. thromboxane production (from 10.4 +/- 1.6 to 7.5 +/- 1.6, in acetylsalicylic acid pretreated cats). Angiotensin and thrombin had no significant effects. Bradykinin (0.5 microgram/ml) significantly augmented prostacyclin release from venous tissue (14.4 +/- 2.6 from 10.9 +/- 2.4 pg/mg/min) and decreased thromboxane release (0.65 +/- 0.18 from 1.35 +/- 0.22 pg/mg/min). Methionine-enkephalin (5 micrograms/ml) significantly reduced the thromboxane release from venous tissue slices. The presented material demonstrates that several vasoactive agents modulate the vasoactive prostanoid release of the venous wall. In some cases, the prostacyclin and the thromboxane productions are influenced separately, which in turn will have its impact on smooth muscle activity and thrombocyte aggregation.     

Role of endothelium, oxygen and ionic milieu in the prostacyclin and thromboxane production of rat aortic tissue slices.

The present study was executed in order to get further data on the role of vessel wall constituents in prostanoid synthesis and on the effect of anorganic constituents on it. Prostacyclin and tromboxane production of rat aortic tissue slices with intact endothelium and after mechanical as well as chemical endothelium removal were studied. The effects of hypoxia and changes in the ionic milieu on the release of these prostanoids were also examined. The tissue slices were incubated in normal or in modified Krebs-Ringer solution, bubbled with 95% O2 and 5% CO2 (with the exception of the studies in hypoxic conditions). Prostacyclin and thromboxane release was determined by specific radioimmunoassay of the stable metabolites, 6-keto-PGF1 alpha and TxB2, from the incubation medium. 174 tissue samples obtained from 164 rats were studied. Mechanical removal of the endothelium increased prostacyclin production of the aortic segments about fivefolds from a basal rate of 52.9 +/- 19.4 ng/gr/min, while it had no significant effect on thromboxane release (basal rate 0.83 +/- 0.13 ng/gr/min). Treating the endothelium with 1.0 M HCl almost totally suppressed prostacyclin release. Lowering the partial oxygen tension of the incubation medium significantly decreased the production of prostacyclin, while release of TxB2 somewhat increased. Increasing the Ca2+ concentration of the medium between 0-5 mM the release of prostacyclin was augmented and the release of thromboxane was diminished. Potassium free medium caused a very large increase in prostacyclin release of the tissue slices. The results show that release of vasoactive prostanoids from isolated rat aortic wall is dependent not exclusively on the endothelium and that various methods of endothelium removal may have distinct influences on prostacyclin and thromboxane productions. The changes in anorganic constituents of the surrounding medium could massively affect prostacyclin and thromboxane production of rat aortic tissue. The alternative effects of the above listed treatments on the release of prostacyclin and thromboxane from the rat aortic wall suggest the existence of different mechanisms in the control of the production of the two major prostanoids possessing opposite physiological effects.     

Differential salicylate-aspirin interaction on vascular prostacyclin and platelet thromboxane synthesis in patients undergoing saphenectomy

We studied the ability of salicylate to counteract the effect of aspirin on platelet thromboxane synthesis and prostacyclin formation in venous tissue in patients undergoing saphenectomy. A single intravenous dose of 40 mg aspirin completely blocked thromboxane formation and reduced prostacyclin to about 43% of the control values. When salicylate (1000 mg po) corresponding in anesthetized subjects to blood levels of 25.9 +/- 5 micrograms/ml was administered before aspirin, vascular prostacyclin was no longer inhibited, whereas platelet thromboxane was still significantly blocked. These results suggest that the combination of salicylate with aspirin at an appropriate dose ratio may result in almost complete dissociation of the drug's effect on platelets and vessels in man.     

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

The levels of the stable degradation products of prostacyclin (PGI2) and thromboxane A2 (TXA2): 6-oxo-prostaglandin E1 alpha (6-oxo-PGE1 alpha) 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 in vivo compared with platelets in vitro.     

Analysis of urinary prostacyclin and thromboxane/prostacyclin ratio in patients with rheumatoid arthritis using gas chromatography/selected ion monitoring.

We investigated production of prostacyclin and the urinary ratio of thromboxane and prostacyclin in patients with rheumatoid arthritis. The prostacyclin production level was assessed according to the level of urinary 2,3-dinor-6-keto-prostaglandin F(1 alpha)measuring by gas chromatography/selected ion monitoring. In patients receiving medication, the prostacyclin level was lower and the thromboxane/prostacyclin ratio was greater compare with that of healthy volunteers. The prostacyclin level in patients without medication was approximately 4-fold higher than that of healthy volunteers and 8-fold higher than those of medicated groups. Although the ratio of the group without medication was similar to that of healthy volunteers, the urinary levels of each prostanoid were higher than those of other groups. Then, the ratios of groups receiving steroids were higher than that of other groups owing to high TX level. The present findings demonstrated that endogenous prostacyclin and thromboxane production increased in patients without medication, and prostacyclin production decreased with medication.     

Evidence for coordinate, selective regulation of eicosanoid synthesis in platelet-derived growth factor-stimulated 3T3 fibroblasts and in HL-60 cells induced to differentiate into macrophages or neutrophils

We used Swiss 3T3 fibroblasts stimulated with platelet-derived growth factor and HL-60 cells induced to differentiate into macrophages or neutrophils to study the regulation of prostaglandin and leukotriene synthesis. Addition of platelet-derived growth factor to quiescent 3T3 fibroblasts led within 4 h to a dramatic and preferential increase in prostacyclin synthesis from endoperoxide prostaglandin H2, and microsomal assays showed a strong platelet-derived growth factor-dependent increase in the maximal velocities (Vmax) of both prostaglandin H synthase and prostacyclin synthase. In contrast, addition of phorbol ester to HL-60 cells to induce differentiation into macrophages led within 4 h to a strong and preferential increase in thromboxane synthesis from prostaglandin H2, and microsomal assays disclosed a major rise in Vmax for both prostaglandin H synthase and thromboxane synthase. No comparable changes occurred in HL-60 cells that were differentiating into neutrophils, though upregulation of 5-lipoxygenase pathway enzymes occurred in both differentiation systems. Actinomycin D and cycloheximide prevented the appearance of all of these enzymes of eicosanoid synthesis in all three model systems. Thus, the distinctive patterns of eicosanoid synthesis that are seen in replicating fibroblasts and in differentiating macrophages and neutrophils appear to depend on a coordinate, selective upregulation of several enzymes of eicosanoid biosynthesis that is specific for each cell system.     

Prostacyclin and thromboxane A2 production in nitric oxide-deficient hypertension in vivo. Effects of high calcium diet and angiotensin receptor blockade

The effects of chronic nitric oxide deficiency on prostacyclin and thromboxane A(2) production in vivo are unknown. Therefore, we treated rats with N(G)-nitro-L-arginine methyl ester (L-NAME), and used losartan and high calcium diet as antihypertensive treatments. Forty eight Wistar rats were divided into six groups: control; losartan (20mgkg(-1)day(-1)); high calcium diet (dietary calcium elevated from 1.1% to 3%); L-NAME (20mgkg(-1)day(-1)); losartan+L-NAME and high calcium diet+L-NAME. Prostacyclin and thromboxane A(2) production were measured after eight weeks as urinary 2,3-dinor-6-keto-PGF(1alpha) and 11-dehydro-TXB(2), respectively. Both the high calcium diet and losartan reduced blood pressure in L-NAME hypertension. Chronic nitric oxide deficiency did not modulate prostacyclin production but it nearly doubled thromboxane A(2) production in vivo. This effect was not influenced by lowering of blood pressure by blockade of angiotensin II type 1 receptors. Independent of the level of blood pressure and blockade of nitric oxide synthesis the high calcium diet decreased prostacyclin production by one third and increased thromboxane A(2) production almost two-fold in vivo.     

Eicosanoids in preeclampsia

Preeclampsia is characterized by an imbalance between two cyclooxygenase metabolites of arachidonic acid, thromboxane and prostacyclin, that favors thromboxane. Because of the biologic actions of these two eicosanoids, this imbalance might explain major clinical symptoms of preeclampsia, such as hypertension, platelet aggregation and reduced uteroplacental blood flow. In the maternal circulation, this imbalance is primarily manifested by decreased production of prostacyclin by endothelial cells. Platelet thromboxane synthesis is only increased in severe preeclampsia. In the placenta and in leukocytes, the imbalance is exacerbated by increased production of thromboxane coupled with decreased production of prostacyclin in both mild and severe preeclampsia. Longitudinal measurements of urinary metabolites of thromboxane and prostacyclin reveal that the thromboxane/prostacyclin imbalance predates the onset of clinical symptoms of preeclampsia. The imbalance between thromboxane and prostacyclin is most likely caused by oxidative stress, which is manifest in preeclampsia by increased lipid peroxidation and decreased antioxidant protection. Oxidative stress may drive this imbalance because lipid peroxides activate the cyclooxygenase enzyme to increase thromboxane synthesis, but at the same time they inhibit prostacyclin synthase to decrease prostacyclin synthesis. Low-dose aspirin therapy (50-150 mg/day) has been considered for the prevention of preeclampsia because it selectively inhibits thromboxane synthesis. Several studies reported dramatic decreases in the incidence of preeclampsia with low-dose aspirin therapy. However, two large multicenter studies reported only modest decreases, which dampened enthusiasm. The two large studies were "intent to treat" studies which included patients who were noncompliant and who discontinued the use of aspirin. In one of the studies for which compliance statistics were available only 53% of the aspirin group had a compliance rate greater than 75%, which raises a question as to whether the effectiveness of aspirin was being tested. Low-dose aspirin therapy should not yet be dismissed for the prevention of preeclampsia, but be reconsidered with emphasis on compliance using doses of aspirin in the range of 100-150 mg/day combined with antioxidants.     

A regimen for low-dose aspirin?

The effects of different regimens of 40 mg aspirin on platelet thromboxane A2 synthesis and vascular prostacyclin synthesis were determined in patients who were undergoing elective surgery for removal of varicose veins. Aspirin 40 mg taken at intervals of 48 hours consistently reduced platelet thromboxane A2 synthesis to a level at which it failed to support platelet aggregation and the associated release reaction. This effect lasted for at least 36 hours. In contrast, aspirin 40 mg every 72 hours did not have the same consistent effect. Both dose regimens led to a reduction in vascular prostacyclin synthesis 12 hours after the last dose, but 36 or 72 hours after the last dose prostacyclin synthesis was not reduced; thus the inhibition of prostacyclin synthesis was short lived. If the balance between platelet thromboxane A2 and vascular prostacyclin synthesis is important in thrombosis 40 mg aspirin every 48 hours may have the maximum antithrombotic effect.     

In vivo biosynthesis of thromboxane and prostacyclin during exposure to physiological levels of epinephrine

The effects of 20-min epinephrine infusion (0.025 and 0.3 nmol/kg/min) on the in vivo synthesis of thromboxane A2 and prostacyclin were studied in ten healthy male volunteers. We assessed the in vivo biosynthesis of thromboxane A2 and prostacyclin by measurement of the urinary metabolites 2,3-dinor-TxB2 and 2,3-dinor-6-keto-PGF1 alpha, respectively. Epinephrine infusion did not cause any significant changes in the urinary excretion of the two metabolites. Thus, we conclude that physiological levels of epinephrine do not affect the in vivo biosynthesis of thromboxane A2 and prostacyclin.     

The effect of aspirin and two nitric oxide donors on the infarcted heart in situ

Nitric oxide (NO) donors are heterogeneous substances which release NO, a biologically active compound. NO released by nitric oxide donors has important effects on the circulation by causing vasodilation, diminishing myocardial contractile force, inhibiting platelet aggregation, and counteracting the effects of thromboxane A2. In the infarcted heart, activation of the inducible form of nitric oxide synthase (iNOS) and the formation of prostacyclin and thromboxane A2 by cyclooxygenase (COX) were increased. Myocardial infarction also resulted in increased myocardial NO production. Aspirin (acetylsalicylic acid. ASA) at low concentration (35 mg/kg/day) fails to change iNOS production, in contrast to higher dose (150 mg/kg/day) which, as previously shown, inhibits iNOS activity. ASA at all doses also suppresses myocardial prostanoid formation because of inhibition of COX. Recently, two NO donors have been synthesized: NCX 4016 and Diethylenetriamine/NO (DETA/NO). NCX 4016 combines an NO-releasing moiety with a carboxylic residue via an esteric bond. We describe here that NCX 4016 (65 mg/kg/day) increased prostacyclin and thromboxane A2 production in the infarcted heart muscle, overcoming the inhibitory effects of ASA. As a result of nitric oxide release, oxidation products of NO (NO2- and NO3-; NOx) in arterial blood rose following administration of NCX 4016. On oral administration, NCX 4016 did not change systemic arterial pressure. The effects of a single NO donor, DETA/NO (1.0 mg/kg/day) on the infarcted heart were also investigated On intravenous administration, the compound increased NO concentration in arterial blood slightly but to a lesser degree than NCX 4016. Like NCX 4016, it raised myocardial production of prostacyclin and thromboxane A2 in the infarcted heart. However, it caused a severe fall in blood pressure. These findings demonstrate that newly-synthesized NO donors release nitric oxide in situ and increase myocardial production of prostanoids. NCX 4016 has therapeutic potential because it can be orally administered, lacks hypotensive effects, increases blood levels of nitric oxide and myocardial prostacyclin production.     

Inducible nitric oxide synthase provides protection against injury-induced thrombosis in female mice

Nitric oxide (NO) is an important vasoactive molecule produced by three NO synthase (NOS) enzymes: neuronal (nNOS), inducible (iNOS), and endothelial NOS (eNOS). While eNOS contributes to blood vessel dilation that protects against the development of hypertension, iNOS has been primarily implicated as a disease-promoting isoform during atherogenesis. Despite this, iNOS may play a physiological role via the modulation of cyclooxygenase and thromboregulatory eicosanoid production. Herein, we examined the role of iNOS in a murine model of thrombosis. Blood flow was measured in carotid arteries of male and female wild-type (WT) and iNOS-deficient mice following ferric chloride-induced thrombosis. Female WT mice were more resistant to thrombotic occlusion than male counterparts but became more susceptible upon iNOS deletion. In contrast, male mice (with and without iNOS deletion) were equally susceptible to thrombosis. Deletion of iNOS was not associated with a change in the balance of thromboxane A(2) (TxA(2)) or antithrombotic prostacyclin (PGI(2)). Compared with male counterparts, female WT mice exhibited increased urinary nitrite and nitrate levels and enhanced ex vivo induction of iNOS in hearts and aortas. Our findings suggest that iNOS-derived NO in female WT mice may attenuate the effects of vascular injury. Thus, although iNOS is detrimental during atherogenesis, physiological iNOS levels may contribute to providing protection against thrombotic occlusion, a phenomenon that may be enhanced in female mice.     

Production of platelet thromboxane A2 and arterial prostacyclin I2 from hypercholesterolemic rats.

The plasma cholesterol, plasma malonaldehyde (MDA), platelet thromboxane A2 (TXA2) and vascular prostacyclin (PGI2) were measured in male Sprague-Dawley rats fed diets supplemented with cholesterol (1%) and cholic acid (0.5%). For comparisons, measurements were made in rats fed normal diets. The concentration of cholesterol in the plasma of rats had reached a maximum in 1 week of feeding experimental diets. TXA2 production from collagen and thrombin stimulated platelets was significantly decreased in animals fed experimental diets for 1 week. The production of MDA in the plasma of animals fed experimental diets for 8 weeks was significantly lower compared to the animals fed normal diets. There was a small but significant reduction in the formation of PGI2 in rats fed experimental diets for 8 weeks. These data suggest that feeding cholesterol rich diets to rats alters the platelet membrane properties differently from human and rabbit. Furthermore, cholesterol feeding to rats had some damaging effect on the arterial PGI2 synthesis.     

Preliminary studies on eicosanoid production by fish leucocytes, using GC-mass spectrometry

Culture supernatants from dogfish leucocytes, exposed to the Ca²⁺ ionophore A23187, were analyzed for eicosanoid production by gas chromatography-electron capture mass spectrometry. Consistently high levels of the prostaglandins (PG) D₂, F_2α and E₂ were produced, while thromboxane B₂ and leukotriene B₄ were found in smaller amounts. No 6-oxo PGF_1α, a degradation product of prostacyclin, or 13,14-dihydro-15-oxo-PGF_2α, a metabolite of PGE₂ and PGF_2α, were detected. The results are compared with similar experiments using mammalian leucocytes.     

Effects of Gramoxone-induced reactive oxygen radicals on eicosanoid synthesis of mouse lung

1. Studies were made to prove that a shift in the eicosanoid metabolism plays a role in the lung-damaging action of paraquat, the active ingredient of Gramoxone, in mice. 2. An attempt was made to inhibit the eicosanoid metabolism with acetylsalicylic acid (Aspisol). Among others, it was found that the metabolic effect impaired by paraquat is influenced in a favourable direction by Aspisol treatment, including the % of survival, the lipid peroxidation values and the superoxide dismutase activity in the lung. 3. At the same time, as a prostacyclin synthesis activator, paraquat participates in the efforts of the organism to eliminate the toxic material, but it later weakens the defence mechanisms by enhancing thromboxane A2 synthesis, and it initiates pulmonary fibrosis, which cannot then be averted with Aspisol.     

Abnormal response of urinary eicosanoid system to norepinephrine infusion in patients with essential hypertension.

To define the role of the renal eicosanoid system in sustaining renal homeostasis in hypertension, we investigated the alterations in urinary excretions of 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha), a stable metabolite of vasodepressor prostacyclin, and thromboxane B2 (TXB2), a stable metabolite of vasoconstrictor TXA2, when norepinephrine was continuously infused for 90 min in hypertensive (n = 13) and normotensive subjects (n = 14). There was no difference in plasma norepinephrine concentration after the infusion between the hypertensive and the normotensive subjects. Moreover, the percent changes in renal vascular resistance elicited by norepinephrine in the hypertensives were equal to those of the normotensive subjects. In the normotensive subjects, the norepinephrine infusion significantly increased urinary 6-keto-PGF1 alpha excretion and decreased urinary excretion of TX, both of which are beneficial for sustaining renal function. In fact, the greater the production of renal 6-keto-PGF1 alpha was, the less the reduction of renal blood flow and urinary sodium excretion was. In the hypertensive subjects, however, these normal responses of the renal eicosanoid system, seen in the normotensives, were abolished; urinary 6-keto-PGF1 alpha was unaltered and thromboxane generation was rather increased. Thus, the renal eicosanoid system dysfunctions in hypertensive subjects when the renal circulation is challenged by norepinephrine. These abnormal responses are likely to cause sodium retention and could contribute, in part, to the hypertensive mechanism in patients with essential hypertension.     

Acetylated low density lipoproteins promote the release and metabolism of arachidonic acid by murine macrophages

It has been postulated that the ratio of prostacyclin/thromboxane A2 in the blood is an important marker for atherosclerosis. We studied the role of the Acetylated Low Density Lipoprotein (Acetyl-LDL) on the arachidonic acid metabolism in macrophages, the progenitor of the foam-cells in atheroma. When stimulated by Acetyl-LDL, macrophage released and metabolized arachidonic acid. This effect was time- and dose-dependent. Only 50% of the Acetyl-LDL-induced arachidonic acid released was metabolized while more than 90% of zymosan or A23187 induced arachidonic acid released was metabolized. Furthermore, when the macrophages were stimulated by Acetyl-LDL, a decrease of prostaglandin E2 and an increase of the levels of prostacyclin and thromboxane were noted. The implications of these observations in the pathogenesis of atherosclerosis are discussed.     

Urinary thromboxane A2/prostacyclin balance reflects the pathological state of a diabetic

Levels of the stable urinary metabolites of thromboxane A2 and prostacyclin, 11-dehydro-thromboxane B2 (11-dehydro-TXB2) and 2,3-dinor-6-keto-prostaglandin F1alpha (2,3-dinor-6-keto-PGF1alpha) were measured in diabetics to elucidate the relation between the thromboxane A2/prostacyclin (TX/PGI) balance and pathological states of diabetes mellitus. 11-Dehydro-TXB2 and 2,3-dinor-6-keto-PGF1alpha were derivatized to methyl ester-propylamide-dimethylisopropylsilyl ether and methyl ester-methoxime-dimethylisopropylsilyl ether derivatives, respectively, and applied to a gas chromatography/selected ion monitoring. The TX/PGI ratios of diabetics were higher than those of healthy volunteers, suggesting the hypercoagulative states of this disease. The ratios showed positive correlations with the levels of blood glucose. The levels of hemoglobin A1c and triglyceride were correlated weakly with the ratio. Some of the patients who had relatively low levels of blood glucose also showed high TX/PGI ratios. Furthermore, the ratio increased in the order of the groups 1, 2, and 3; group 1 contained patients who did not take medicine for diabetes, group 2 contained those who took oral hypoglycemic agents, and group 3 contained those who received insulin therapy. These observations indicate that the TX/PGI ratio reflects the pathological conditions of diabetes and is a useful marker, having few different features from other markers that are presently used.