In vivo measurement of thromboxane B2 and 6-keto-prostaglandin F1 alpha in humans in response to a standardized vascular injury and the influence of aspirin

Prostanoids in the pathophysiology of human coronary artery

Coronary artery disease is one of the leading causes of death in wordwide. There is growing evidence that prostanoids are involved in the physiology and pathophysiology of the human coronary artery by controlling vascular tone, remodelling of the vascular wall or angiogenesis. In this review, the production of prostanoids and the expression of prostanoid receptors in human coronary artery in health or disease are described. In addition, the interactions between sex hormones and prostanoids, their participations in the development of coronary artery diseases have been addressed. Globally, most of the studies performed in human coronary artery preparations have shown that prostacyclin (PGI₂) has beneficial effects by inducing vasodilatation and promoting angiogenesis while reverse effects are confirmed by thromboxane A₂ (TxA₂). More studies are needed to determine the roles of the other prostanoids (PGE₂, PGD₂ and PGF_2α) in vascular functions of the human coronary artery. Finally, in addition to the in vitro data about the human coronary artery, myocardial infarction induced by cyclooxygenase-2 (COX-2) inhibitor and the protective effects of aspirin after coronary artery bypass surgery suggest that prostanoids are key mediators in coronary homeostasis.

Systemic prostacyclin and thromboxane production in obstructive sleep apnea

PURPOSE

Obstructive sleep apnea increases the risk of cardiovascular diseases. Alternations in prostacyclin and thromboxane concentrations and balance could constitute one of mechanisms linking sleep apnea and cardiovascular events. Thus we aimed to assess the concentrations of 6-keto-prostaglandin F1α (6-keto-PGF1α) (metabolite of prostacyclin) and thromboxane B2 (TXB2) (metabolite of thromboxane A2) in urine and blood of obstructive sleep apnea patients and controls (snoring subjects with otherwise normal polysomnogram).

MATERIAL AND METHODS

Overnight urine and morning blood samples were taken from subjects and controls at baseline and in sleep apnea group during continuous positive airway pressure (CPAP) treatment. Samples were analyzed using mass chromatography/gas spectrometry.

RESULTS

We analyzed data from 26 obstructive sleep apnea subjects (mean apnea-hypopnea index 45.4±17.3) and 22 well-matched controls. At baseline sleep apnea patients, when compared to controls, have higher 6-keto-PGF1α in urine (0.89±0.15 vs 0.34±0.06, p=0.01) and blood (24.49±1.54 vs 19.70±1.77, p=0.04). TXB2 levels in urine and blood were not different across groups. CPAP treatment significantly decreased 6-keto-PGF1α in urine (0.92±0.17 vs 0.22±0.10, p=0.04), but not in blood. TXB2 levels during CPAP treatment did not change significantly.

CONCLUSIONS

These results suggest augmented systemic prostacyclin production in obstructive sleep apnea patients, which potentially could constitute a protective mechanism against detrimental effects of sleep apnea.

Anti-platelet therapy: cyclo-oxygenase inhibition and the use of aspirin with particular regard to dual anti-platelet therapy

Aspirin and P2Y(12) antagonists are commonly used anti-platelet agents. Aspirin produces its effects through inhibition of thromboxane A(2) (TXA(2)) production, while P2Y(12) antagonists attenuate the secondary responses to ADP released by activated platelets. The anti-platelet effects of aspirin and a P2Y(12) antagonist are often considered to be separately additive. However, there is evidence of an overlap in effects, in that a high level of P2Y(12) receptor inhibition can blunt TXA(2) receptor signalling in platelets and reduce platelet production of TXA(2). Against this background, the addition of aspirin, particularly at higher doses, could cause significant reductions in the production of prostanoids in other tissues, e.g. prostaglandin I(2) from the blood vessel wall. This review summarizes the data from clinical studies in which dose-dependent effects of aspirin on prostanoid production have been evaluated by both plasma and urinary measures. It also addresses the biology underlying the cardiovascular effects of aspirin and its influences upon prostanoid production throughout the body. The review then considers whether, in the presence of newer, more refined P2Y(12) receptor antagonists, aspirin may offer less benefit than might have been predicted from earlier clinical trials using more variable P2Y(12) antagonists. The possibility is reflected upon, that when combined with a high level of P2Y(12) blockade the net effect of higher doses of aspirin could be removal of anti-thrombotic and vasodilating prostanoids and so a lessening of the anti-thrombotic effectiveness of the treatment.

Nonsurgical bleeding diathesis in anemic thrombocytopenic patients: role of temperature, red blood cells, platelets, and plasma-clotting proteins

Research at the Naval Blood Research Laboratory (Boston, MA) for the past four decades has focused on the preservation of red blood cells (RBCs), platelets (PLTs), and plasma-clotting proteins to treat wounded servicemen suffering blood loss. We have studied the survival and function of fresh and preserved RBCs and PLTs and the function of fresh and frozen plasma-clotting proteins. This report summarizes our peer-reviewed publications on the effects of temperature, RBCs, PLTs, and plasma-clotting proteins on the bleeding time (BT) and nonsurgical blood loss. The term nonsurgical blood loss refers to generalized, systemic bleeding that is not corrected by surgical interventions. We observed that the BT correlated with the volume of shed blood collected at the BT site and to the nonsurgical blood loss in anemic thrombocytopenic patients after cardiopulmonary bypass surgery. Many factors influence the BT, including temperature; hematocrit (Hct); PLT count; PLT size; PLT function; and the plasma-clotting proteins factor (F)VIII, von Willebrand factor, and fibrinogen level. Our laboratory has studied temperature, Hct, PLT count, PLT size, and PLT function in studies performed in non-aspirin-treated and aspirin-treated volunteers, in aspirin-treated baboons, and in anemic thrombocytopenic patients. This monograph discusses the role of RBCs and PLTs in the restoration of hemostasis, in the hope that a better understanding of the hemostatic mechanism might improve the treatment of anemic thrombocytopenic patients. Data from our studies have demonstrated that it is important to transfuse anemic thrombocytopenic patients with RBCs that have satisfactory viability and function to achieve a Hct level of 35 vol percent before transfusing viable and functional PLTs. The Biomedical Excellence for Safer Transfusion (BEST) Collaborative recommends that preserved PLTs have an in vivo recovery of 66 percent of that of fresh PLTs and a life span that is at least 50 percent that of fresh PLTs. Their recommendation does not include any indication that preserved PLTs must be able to function to reduce the BT and reduce or prevent nonsurgical blood loss. One of the hemostatic effects of RBC is to scavenge endothelial cell nitric oxide, a vasodilating agent that inhibits PLT function. In addition, endothelin may be released from endothelial cells, a potent vasoconstrictor substance,to reduce blood flow at the BT site. RBCs, like PLTs at the BT site, may provide arachidonic acid and adenosine diphosphate to stimulate the PLTs to make thromboxane, another potent vasoconstrictor substance and a PLT-aggregating substance. At the BT site, the PLTs and RBCs are activated and phosphatidyl serine is exposed on both the PLTs and the RBCs. FVa and FXa, which generate prothrombinase activity to produce thrombin, accumulate on the PLTs and RBCs. A Hct level of 35 vol percent at the BT site minimizes shear stress and reduces nitric oxide produced by endothelial cells. The transfusion trigger for prophylactic PLT transfusion should consider both the Hct and the PLT count. The transfusion of RBCs that are both viable and functional to anemic thrombocytopenic patients may reduce the need for prophylactic leukoreduced PLTs, the alloimmunization of the patients, and the associated adverse events related to transfusion-related acute lung injury. The cost for RBC transfusions will be significantly less than the cost for the prophylactic PLT transfusions.

Correlation between in vitro aggregation and thromboxane A2 production in fresh, liquid-preserved, and cryopreserved human platelets: effect of agonists, pH, and plasma and saline resuspension

BACKGROUND

Some of the tests used to assess the quality of fresh and preserved platelets (PLTs) include PLT number, PLT morphology, pH of the PLT medium, PLT response to hypotonic stress, and PLT aggregation to agonists. This study was performed to assess the function of fresh and preserved PLTs by their response to aggregation and their production of thromboxane A2 after in vitro stimulation with agonists.

STUDY DESIGN AND METHODS

PLTs isolated by apheresis procedures were stored at 22 degrees C for as long as 5 days and then frozen with 6 percent dimethyl sulfoxide, stored at -80 degrees C, thawed, washed, and resuspended in medium. The effects of agonists and the pH and composition of the medium on PLT aggregation and PLT production of thromboxane A2 after stimulation were measured.

RESULTS

The agonists and the pH and composition of the medium affected both the aggregation response and the production of thromboxane A2 by the fresh and preserved PLTs. PLT aggregation response to arachidonic acid (AA) and adenosine diphosphate (ADP) was significantly lower in the cryopreserved PLTs than in the fresh and preserved PLTs. After stimulation with AA and ADP, the cryopreserved PLTs produced more thromboxane than did the fresh and liquid-preserved PLTs.

CONCLUSIONS

The agonists and the pH and composition of the medium affected the response to aggregate and produce thromboxane in vitro in both the fresh and the liquid-preserved PLTs. PLT thromboxane A2 production may be a better in vitro test than PLT aggregation to assess PLT function in vivo.

Predictors of stent thrombosis after primary stenting for acute myocardial infarction

The aim of the study was to determine if a hypercoagulable state that may persist for several months after an acute myocardial infarction may contribute to an increased incidence of stent thrombosis. Primary stenting was performed in 104 consecutive patients with acute myocardial infarction using 147 coronary stents. Twenty-eight patients (27%) were diabetic and 55 patients (53%) were smokers. A single stent was placed in 63%, two stents in 33%, and more than two stents in 4% of the patients. Procedural success was obtained in 97% of the patients. All stents were deployed using high-pressure balloon inflation. The reference vessel diameter and minimal lumen diameter after stent deployment were 3.30 +/- 0.42 and 3.23 +/- 0.42 mm, respectively. Six patients (5.7%) developed stent thrombosis within 1 month after the procedure complicated by reinfarction in five of the six patients. At 1-month follow-up, all patients remained alive. On multivariate analysis, independent predictors of stent thrombosis were diabetes mellitus (relative risk [RR] 5.2; 95% confidence interval [CI] 1.8, 25.1), tobacco use (RR 4.5; 95% CI 1.3, 24.5), number of stents: 1 vs. > 1 (RR 3.7; 95% CI 1.1, 15.9), minimal lumen diameter poststent placement (RR 0.03; 95% CI 0.0002, 0.74), and duration of chest pain before intervention (RR 1.1; 95% CI 1.01, 1.25). Stent thrombosis had not been associated with diabetes mellitus and tobacco use previously but is in agreement with the enhanced platelet aggregability, coagulation factor abnormalities, and impaired fibrinolysis characteristic of these patients.

Comparison of the effects of transfusions of cryopreserved and liquid-preserved platelets on hemostasis and blood loss after cardiopulmonary bypass

OBJECTIVE

The aim of the study was to compare the clinical effects and hemostatic efficiency of transfusions of platelets preserved in the frozen state for as long as 2 years with transfusions of platelets preserved in the conventional manner for as long as 5 days in patients undergoing cardiopulmonary bypass.

METHODS

Seventy-three patients were prospectively randomly assigned to receive transfusions of cryopreserved or liquid-preserved platelets. Nonsurgical blood loss was measured during and after the operation. Bleeding time, hematologic variables, and the bleeding time site shed blood were assayed before cardiopulmonary bypass and at 30 minutes and 2, 4, and 24 hours after transfusion. In vitro platelet function tests were conducted on platelets obtained from healthy volunteers.

RESULTS

No adverse sequelae of the transfusions were observed. Blood loss and the need for postoperative blood product transfusions were lower in the group receiving cryopreserved platelets. Lower posttransfusion platelet increments and a tendency toward decreased platelet survival were observed in patients receiving cryopreserved platelets. Hematocrit and plasma fibrinogen were significantly higher in this group, and the duration of intubation was shorter. In vitro, cryopreserved platelets demonstrated less aggregation, lower pH, and decreased response to hypotonic stress but generated more procoagulant activity and thromboxane.

CONCLUSIONS

(1) Cryopreserved platelet transfusions are superior to liquid-preserved platelets in reducing blood loss and the need for blood product transfusions after cardiopulmonary bypass. (2) The reduction in blood loss in the patients receiving cryopreserved platelet transfusions after cardiopulmonary bypass probably reflects improved in vivo hemostatic function of cryopreserved platelets. (3) Some in vitro measures of platelet quality (aggregation, pH, hypotonic stress) may not reflect in vivo quality of platelet transfusions after cardiopulmonary bypass, whereas other in vitro measures (platelet procoagulant activity and thromboxane) do.

Effects of the mitogen-activated protein (MAP) kinase kinase inhibitor 2-(2'-amino-3'-methoxyphenyl)-oxanaphthalen-4-one (PD98059) on human platelet activation

The role of mitogen-activated protein (MAP) kinase cascades in platelet function remains to be determined. Several studies have suggested a role in the activation of phospholipase A2; however, other functions seem likely. The object of the present study was to determine the role of the MAP kinase cascade in platelet function. An inhibitor of the mitogen-activated protein kinase kinase MEK1, 2-(2'-amino-3'-methoxyphenyl)-oxanaphthalen-4-one (PD98059), was used, at concentrations consistent with those reported to inhibit MEK1, to examine the role that this enzyme plays in platelet function. PD98059 inhibited aggregation in response to low-dose collagen and arachidonic acid, but not that in response to high-dose collagen, thrombin, thrombin receptor-activating peptide (TRAP), 9,11-dideoxy-11alpha, 9alpha-epoxymethano-prostaglandin F2alpha (U46619), or phorbol ester. Thrombin, thrombin receptor-activating peptide, U46619, collagen, and arachidonic acid each caused the release of [3H]serotonin from dense granules, but only that elicited by low-dose collagen and arachidonic acid was inhibited by PD98059. The release of [3H]arachidonic acid in response to thrombin or collagen was unaffected by PD98059 pretreatment. In contrast, collagen- and arachidonic acid-induced thromboxane formation was inhibited by PD98059. These data suggest that MEK1 is not involved in the platelet response to thrombin or U46619. Furthermore, the inhibitory effects of PD98059 on collagen- and arachidonic acid-induced responses suggest that PD98059 may inhibit the conversion of arachidonic acid to thromboxane, in addition to its reported effects on MEK1.

Effect of aspirin dosage and enteric coating on platelet reactivity

Although aspirin is effective in the prevention and treatment of cardiovascular diseases, the optimal dose remains uncertain. The purpose of this study was to compare the platelet inhibitory and prostacyclin-sparing effects of 2 doses (81 and 325 mg) and forms (enteric-coated and regular) of aspirin. Since platelet reactivity has been reported to increase after strenuous exercise, a known trigger of myocardial infarction, subjects were studied following maximal treadmill exercise as well as at rest. Forty male healthy subjects were evaluated using a randomized, double-blind, parallel study design. Blood samples were obtained before and after maximal treadmill exercise at baseline and after 7 days on aspirin therapy. Both enteric and regular aspirin in 81- and 325-mg dosages markedly inhibited adenosine diphosphate and epinephrine-induced aggregation at rest and after exercise. Aspirin also inhibited the platelet response to collagen as assessed by a longer lag time to aggregation. The prolongation of lag time was greater for 325 mg than for 81 mg (100 +/- 7 vs 91 +/- 7; p = 0.04, after exercise). There were no significant dose-related differences in plasma 6-keto-prostaglandin F1alpha level; however, enteric-coated aspirin inhibited the exercise-induced increase in 6-keto-prostaglandin F1alpha to a lesser extent than regular aspirin. Although both doses (81 and 325 mg) and types (regular and enteric-coated) of aspirin inhibited adenosine diphosphate and epinephrine-induced aggregation equally, the 325-mg dose inhibited collagen-induced aggregation to a greater extent than 81 mg. The greater platelet inhibition observed with 325 mg may be clinically relevant in acute coronary syndromes characterized by plaque rupture with extensive collagen exposure and platelet activation.

Inhibition of collagen-induced platelet activation by arachidonyl trifluoromethyl ketone

Collagen-induced platelet activation is associated with, and markedly potentiated by, the release of arachidonic acid and its subsequent conversion to thromboxane A2. The precise mechanism of arachidonic acid release is unknown. An inhibitor of isolated cytosolic phospholipase A2 (cPLA2), arachidonyl trifluoromethyl ketone (AACOCF3), was used to examine the role that cPLA2 plays in this process. AACOCF3 inhibited platelet aggregation in response to collagen and arachidonic acid but not to thrombin, calcium ionophore, phorbol ester, or a thromboxane mimetic. Thromboxane formation stimulated by thrombin or collagen was inhibited by AACOCF3. However, AACOCF3 did not inhibit collagen-induced [14C]arachidonic acid release. These data are consistent with the inhibitory effects of AACOCF3 on collagen-induced aggregation involving an action on the conversion of arachidonic acid to thromboxane.

Heparin causes platelet dysfunction and induces fibrinolysis before cardiopulmonary bypass

BACKGROUND

Platelet dysfunction and increased fibrinolysis are the most important etiologic factors in the hemostatic defect observed following the institution of cardiopulmonary bypass. This study examined the effects of heparin per se, administered before the institution of cardiopulmonary bypass, on platelet function and fibrinolysis.

METHODS

Sampling was performed in 55 patients undergoing cardiac operations before and 5 minutes after the routine administration of heparin, before the institution of cardiopulmonary bypass.

RESULTS

Heparin administration resulted in a significant prolongation of the bleeding time (from 6.3 +/- 2.1 to 12.6 +/- 4.9 minutes; p < 0.00001), a significant reduction in the level of shed blood thromboxane B2 (from 1,152 +/- 669 to 538 +/- 187 pg/0.1 mL; p = 0.00002), and an increase in the plasma levels of plasmin (from 11.8 +/- 9.7 to 125.4 +/- 34.8 U/L; p < 0.0001) and D-dimer (from 571.3 +/- 297.1 to 698.5 +/- 358.6 micrograms/mL; p = 0.05). There were no significant differences before and after heparin administration in the plasma levels of fibrinogen, plasminogen, tissue plasminogen activator, antiplasmin, antithrombin III, and von Willebrand factor.

CONCLUSIONS

Heparin, independent of cardiopulmonary bypass, causes both platelet dysfunction and increased fibrinolysis. The use of an alternative anticoagulant or a lower dose of heparin in conjunction with heparin-coated surfaces might improve the hemostatic balance during open heart operations.

Low-dose aspirin to pregnant women: single dose pharmacokinetics and influence of short term treatment on bleeding time

Single dose pharmacokinetics of 75 mg aspirin was investigated in two groups of ten women with clinically normal pregnancies. Eleven non-pregnant subjects in the same age were controls. In group A, gestational age was 27-30 completed weeks, and in group B, 36-39 weeks. Venous blood samples were taken before and up to 240 minutes after the intake of the aspirin. Liquid chromatographic assays for acetylsalicylic acid (ASA) and its metabolite, salicylic acid (SA), was performed. The pharmacokinetics of ASA and SA were similar in group A and B but pregnant subjects had a slower uptake and a lower peak level than controls. The late elimination phase for their compound did not differ between the groups. Nine pregnant women with normal pregnancies had their bleeding time measured by a modified Ivy technique using a Simplate II device before, at the end of, and two weeks after daily administration of 75 mg ASA for two weeks. All had a normal bleeding time before and two weeks after the end of the medication. Eight of the nine subjects had an increased bleeding time by Ivy tests, (p < 0.01) whereas the bleeding time assessed by Duke's method was within normal limits. These studies suggest that during pregnancy changes of the uptake rate and distribution volume modulate the pharmacokinetics of ASA and that this drug given in low dosage to gravidae marginally alters their platelet function.

Nicotine effects on eicosanoid formation and hemostatic function: comparison of transdermal nicotine and cigarette smoking

OBJECTIVES

The purpose of this study was to examine the possible role of nicotine in enhancing coagulation and to assess the potential cardiovascular toxicity of transdermal nicotine therapy for smoking cessation.

BACKGROUND

Cigarette smoking increases the risks of acute coronary events. A likely contributing mechanism is activation of coagulation. The role of nicotine in enhancing coagulability has not been resolved.

METHODS

We compared in a crossover study the effects of cigarette smoking, transdermal nicotine and placebo transdermal nicotine, each for 5 days, in 12 healthy smokers.

RESULTS

Cigarette smoking increased the urinary excretion of 11-dehydro-thromboxane B2 (reflecting thromboxane A2 generation) and increased plasma concentration of the platelet alpha-granule constituents, platelet factor 4 and beta-thromboglobulin, compared with placebo treatment, indicating in vivo platelet activation. Cigarette smoking was also associated with higher levels of fibrinogen in plasma. Transdermal nicotine produced plasma levels of nicotine in the same range as those during smoking but had no effect on thromboxane A2 metabolite excretion, platelet alpha-granule release or plasma fibrinogen, compared with placebo. Excretion of 2,3-dinor-6-keto-PGF1 alpha (reflecting prostacyclin generation) was not significantly influenced by any treatment. These results suggest that nicotine as such is not responsible for the platelet activation or elevation of plasma fibrinogen seen in smokers. However, we cannot exclude the possibility that intermittent bolus-like dosing of nicotine from cigarettes could have different effects from those produced by continually released transdermal nicotine. Other findings were that cigarette smoking and transdermal nicotine treatment were both associated with a higher white blood cell count compared with the placebo patch condition, suggesting a direct effect of nicotine to increase circulating white cells. Factor VII coagulant activity (VIIc) was significantly lower during cigarette smoking, than during either nicotine or placebo patch conditions.

CONCLUSIONS

Transdermal nicotine has less effect on platelet activation and catecholamine release than does cigarette smoking, and its use in smoking cessation treatment of patients with coronary heart disease is likely to be safer than cigarette smoking.

Effect of dietary alpha-linolenic acid and its ratio to linoleic acid on platelet and plasma fatty acids and thrombogenesis

The effect of dietary alpha-linolenic acid (18:3n-3) and its ratio to linoleic acid (18:2n-6) on platelet and plasma phospholipid (PL) fatty acid patterns and prostanoid production were studied in normolipidemic men. The study consisted of two 42-d phases. Each was divided into a 6-d pre-experimental period, during which a mixed fat diet was fed, and two-18 d experimental periods, during which a mixture of sunflower and olive oil [low 18:3n-3 content, high 18:2/18:3 ratio (LO-HI diet)], soybean oil (intermediate 18:3n-3 content, intermediate 18:2/18:3 ratio), canola oil (intermediate 18:3n-3 content, low 18:2/18:3 ratio) and a mixture of sunflower, olive and flax oil [high 18:3n-3 content, low 18:2/18:3 ratio (HI-LO diet)] provided 77% of the fat (26% of the energy) in the diet. The 18:3n-3 content and the 18:2/18:3 ratio of the experimental diets were: 0.8%, 27.4; 6.5%, 6.9; 6.6%, 3.0; and 13.4%, 2.7, respectively. There were appreciable differences in the fatty acid composition of platelet and plasma PLs. Nevertheless, 18:1n-9, 18:2n-6 and 18:3n-3 levels in PL reflected the fatty acid composition of the diets, although very little 18:3n-3 was incorporated into PL. Both the level of 18:3n-3 in the diet and the 18:2/18:3 ratio were important in influencing the levels of longer chain n-3 fatty acid, especially 20:5n-3, in platelet and plasma PL. Production of 6-keto-PGF1 alpha was significantly (P < 0.05) higher following the HI-LO diet than the LO-HI diet although dietary fat source had no effect on bleeding time or thromboxane B2 production.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of regular and enteric-coated aspirin on bleeding time, thromboxane, and prostacyclin

We compared the effect of different aspirin schedules, dosages, and formulations on various bleeding time parameters including bleeding time, plasma and total blood volume, and levels of the stable metabolites of thromboxane A2 (TXA2) and prostacyclin (PGI2) (respectively, TXB2 and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha)) to determine the optimal dosage and formulation of aspirin to inhibit TXA2 production while sparing PGI2. In a randomized, parallel study, 52 healthy male volunteers (62 independent observations) with no history of bleeding disorders were given 80 mg or 325 mg of regular aspirin, or 325 mg of enteric-coated aspirin to ingest daily (14 pills) or every other day (7 pills) for a continuous 14 day period. Bleeding times were performed on day 1 before aspirin, 6 h after aspirin on day 1, and before aspirin on day 14. Bleeding times, plasma volume, and total volume increased significantly from before aspirin to after 6 h and 14 days (p < 0.0001 for all parameters) for all aspirin formulations. For day 1 before aspirin ingestion to 6 h later, both TX and PGI2 (p < 0.008) decreased significantly. 6 h after ingestion of aspirin on day 1 to day 14, both TX and PGI2 levels also significantly decreased (p < 0.0001). There was a highly significant decrease in PGI2 production on every other day aspirin schedules (p = 0.0001) particularly with 80 mg of aspirin, while the decrease in PGI2 production on daily aspirin was not significant (p = 0.10). The most favourable ratio of 6-keto-PGF1 alpha to TXB2 occurred with 80 mg daily.(ABSTRACT TRUNCATED AT 250 WORDS)

Type A behavior and alcohol consumption: effects on resting and post-exercise bleeding time thromboxane and prostacyclin metabolites

The vasoactive eicosanoids, prostacyclin and thromboxane, are thought to play an important role in the genesis of cardiovascular disease. Since an altered basal production of these eicosanoids among individuals exhibiting the Type A behavior pattern had previously been observed by the authors, the present study evaluated the extent to which the TABP-eicosanoid relationship would be altered by two lifestyle variables known to affect platelet activity: alcohol consumption and stressful physical activity. 55 male participants aged 18-25 years, participated in the study. They were classified as either Type A or Type B on the basis of the Structured Interview and as either moderate, heavy, or abstinent alcohol drinkers. Bleeding times were performed and bleeding time thromboxane and prostacyclin metabolites were measured in all subjects both before and following treadmill exercise. The results indicated that following exercise, Type A participants, who reported moderate alcohol intake, had decreased levels of thromboxane B2 formation relative to Type As reporting heavy consumption. Further, prostacyclin production, measured as the primary metabolite, 6-keto-prostaglandin F1 alpha, was significantly suppressed following exercise among drinkers as compared with participants reporting abstinence. These results were discussed in relation to the proposition that moderate alcohol consumption reduces coronary heart disease risk.

Aspirin effect on early and late changes in acute lung injury in sheep

OBJECTIVE

There have been several studies that have already explored the potential beneficial role of cyclo-oxygenase (CO) inhibitors on oleic acid (OA)-induced lung injury in different species. These studies report no significant effect of CO inhibition, though thromboxane B2 (TxB2) was effectively blocked. However, recent studies indicate that pre-treatment with aspirin (ASA) preserve gas exchange in OA lung injury in dogs. Aim of our study has been to evaluate the potential beneficial effects of the pre-treatment with low doses of ASA on gas exchange, hemodynamics, respiratory mechanics, prostanoids and lung histology in OA-induced lung injury in sheep.

DESIGN

0.09 ml/kg of OA was administered into the right atrium of 14 anaesthetized sheep. Six received a bolus of ASA (10 mg/kg i.v.) 30 min before OA, the others saline as placebo.

MEASUREMENTS AND RESULTS

Pulmonary and tissue gas exchange, pulmonary and systematic hemodynamics, respiratory system mechanics, TxB2 and 6-keto-PGF1 alpha, leukocytes and platelets concentrations were measured throughout the subsequent 3 h and lung histology was effected at end-experiment. The principal findings of our study are: 1) ASA reduces OA-induced early pulmonary vasoconstriction and bronchoconstriction, parallelled by a suppression of TxB2 generation; 2) the late increase in pulmonary artery pressure and airway resistance due to OA is not inhibited by ASA; 3) the early disturbance in pulmonary gas exchange is reduced by ASA, whereas the late severe deterioration is exaggerated by ASA; 4) the stability of tissue exchange ratio (R) at approximately 1 in ASA-group compared to its fall to approximately 0.7 in controls.

CONCLUSION

Our findings suggest that ASA: 1) is only effective to treat the very transient TxB2-induced pulmonary vasoconstriction resulting in hydrostatic edema, and it is ineffective, even accentuates, the subsequent major pulmonary endothelial cell injury leading to alveolar flooding that is unrelated to TxB2; 2) has a transient protective effect on the TxB2-induced early bronchospasm; 3) has a biphasic behaviour on gas exchange, with a benefit which lasts only one hour and then results in a worse gas exchange; 4) has an immediate, stabilizing, persisting effect on R, contrasting with its transient effect on pulmonary hemodynamics and PaO2.

Urinary excretion of thromboxane and prostacyclin metabolites during chronic low-dose aspirin: evidence for an extrarenal origin of urinary thromboxane B2 and 6-keto-prostaglandin F1 alpha in healthy subjects

In vivo biosynthesis of thromboxane and prostacyclin is currently evaluated by measuring urinary excretion of selected metabolites. Urinary thromboxane B2 (TXB2) and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) (non-enzymatic hydrolysis products of thromboxane and prostacyclin) are thought to derive from renal biosynthesis of the parent compounds, while enzymatic metabolites such as 2,3-dinor-TXB2 and 2,3-dinor-6-keto-PGF1 alpha appear to be mainly derived from systemic (platelet) thromboxane and (vascular) prostacyclin, respectively. Using immunoaffinity extraction and high-resolution gas chromatography-negative ion chemical ionization mass spectrometry (HRGC-NICIMS), we measured the paired excretion of non-enzymatic and enzymatic metabolites of thromboxane and prostacyclin in healthy subjects before, during and after an eight-day schedule of oral low-dose aspirin (30 mg/day), a treatment known to inhibit platelet and perhaps vascular but not renal cyclooxygenase. Low-dose aspirin cumulatively reduced urinary excretion of TXB2 and 2,3-dinor-TXB2 (about 80% inhibition on day 8 of aspirin treatment, P less than 0.01), as well as 6-keto-PGF1 alpha and 2,3-dinor-6-keto-PGF1 alpha (about 45% inhibition on day 8 of aspirin treatment, P less than 0.01). Excretion of all metabolites recovered slowly after aspirin withdrawal. Urinary PGE2, taken as an index of renal cyclooxygenase activity, was not inhibited by aspirin. A highly significant correlation was found between paired excretion values of non-enzymatic vs. enzymatic metabolites of thromboxane and prostacyclin in all individuals studied (TXB2 vs. 2,3-dinor-TXB2 (r = 0.91 +/- 0.03); 6-keto-PGF1 alpha vs. 2,3-dinor-6-keto-PGF1 alpha (r = 0.92 +/- 0.06], irrespective of aspirin treatment. TXB2/2,3-dinor-TXB2 and 6-keto-PGF1 alpha/2,3-dinor-6-keto-PGF1 alpha mean ratios remained unchanged throughout the experiment. These data do not support the view that urinary TXB2 and 6-keto-PGF1 alpha derive mainly from renal biosynthesis in healthy subjects, but rather suggest that they may represent a fraction of systemic (platelet) thromboxane and (vascular) prostacyclin escaping metabolism. These data also suggest that chronic low-dose aspirin may partly inhibit vascular prostacyclin in addition to platelet thromboxane biosynthesis.

The acute effect of smoking on platelet and endothelial release reaction is suppressed in chronic smokers

Whilst increased plasma beta-thromboglobulin (beta TG), platelet factor 4 and thrombospondin levels are regarded as reflecting the release reaction of platelets, tissue-type plasminogen activator (t-PA) and plasminogen activator inhibitor-1 (PAI-1) levels represent endothelial release reaction and/or damage. In this study including 12 smokers and 9 nonsmokers, we investigated the acute and chronic effect of smoking on these parameters and antithrombin III, protein S and fibrinogen, as well. Nonsmokers were found to have somewhat higher plasma levels of beta TG, t-PA and PAI-1 than chronic smokers, and 30 minutes after smoking two cigarettes, these levels and protein S levels of nonsmokers showed more prominent increases than of chronic smokers. It is speculated that chronic exposure to cigarette smoke may cause "exhaustion" or "receptor down-regulation" of platelets and endothelial cells, resulting with diminished release reaction of platelets and endothelium in response to acute smoking.

Aerobic fitness level (VO2max) moderates the increased cardiovascular function and basal thromboxane formation of young healthy Type A males

The authors evaluated the interaction between physical fitness and Type A behavior on vascular production of prostacyclin and platelet thromboxane in response to a standard vessel injury. Ninety-seven male university students were classified as Type A or B on the basis of the Structured Interview of Rosenman. Reactivity, as measured by changes in systolic blood pressure (SBP), and heart rate (HR), measured before and after a stressful Stroop task 1 week later, showed that Type A individuals were more reactive to the stressor than Type Bs, providing independent confirmation of the behavioral interview assessment procedure. Fitness level was determined by a graded treadmill test and was not different for Type As and Type Bs. Basal thromboxane production, measured as the primary metabolite, thromboxane B2, in blood oozing from the bleeding-time site, was highest among unfit Type A subjects. Fit Type As and Type Bs showed significantly lower thromboxane production. No significant differences in prostacyclin production were seen. This study marks the first time that behavior pattern has been linked to an adverse aspect of a thrombosis-related parameter likely to be involved in the genesis of cardiovascular disease. The present results also indicate that physical fitness may, in some fashion, ameliorate the "toxic" effects of Type A behavior.

Two year Cottbus reinfarction study with 30 mg aspirin per day

All 701 heart infarction patients admitted to 15 hospitals in the district of Cottbus between 1981 and 1983 were randomly administered 30, 60 or 1000 mg aspirin daily according to the territorial affiliation of their local hospitals. The physical and drug therapy during the 2 years follow-up was highly standardized; deviations--as far as they occurred--were documented. Lower all-cause mortality was statistically demonstrated in patients over 60 and a lower fatal reinfarction rate in patients over 50 as well as in men. Deaths and fatal reinfarctions were significantly lower among patients with a history of angina pectoris, marked ST-depression, with an infarction location except for the posterior wall and among hypercholesterolemic patients. The preventive effect of 60 mg aspirin daily was less than that of 30 mg in comparison to the 1000 mg group. Side effects were seen in 4 and 8% (first and second year), respectively, of the patients administered 30 mg aspirin as opposed to 22 and 17% in patients allocated 1000 mg. We conclude that the optimum dose of aspirin for preventing reinfarctions could be as low as 30 mg daily.

Reevaluation of the Cottbus Reinfarction Study with 30 mg aspirin per day 4 years after the end of the study

Four to 6 years after the end of the Cottbus Reinfarction Study with 30, 60 and 1000 mg/day aspirin, the survivors (72% of the patients) were reevaluated under standardized conditions at the district hospital. Nearly all patients (82%) of the former 30 mg group took further on 30 mg aspirin daily whereas of the former 1000 mg group only 20% continued to take doses higher than 500 mg aspirin. Forty-five percent changed to very low doses. Whereas the death rate was nearly the same in all three former dosage groups the total reinfarction rate was higher (22.5%) in the previous 1000 mg group in comparison to the 30 mg group (17.4%, p less than 0.05). The non-fatal reinfarction rate was by 50% lower in the former 30 mg group compared with the previous 1000 mg group. In the age group 50-59 a 8.6% non-fatal reinfarction rate is contrasted to 1.7% reinfarctions in patients of the former 30 mg group (p less than 0.01). The risk factors were not significantly different in the three groups.

The interactive effects of Type A behavior and hostility on bleeding time thromboxane and prostacyclin formation

Sixty-six male university students were classified as Type A or B on the basis of the Structured Interview of Rosenman and as hostile or non-hostile on the basis of the Cook-Medley scale. Vascular production of prostacyclin and platelet thromboxane in response to a standard vessel injury was evaluated. Basal thromboxane production, measured as the primary metabolite, thromboxane B2, in blood oozing from the bleeding-time site, was highest among hostile Type A subjects with significantly lower thromboxane production in hostile Type Bs and all non-hostile groups combined. Following an exercise treadmill test hostile subjects produced more thromboxane than non-hostile ones, and hostile Type As had significantly shorter bleeding times than hostile Type Bs. No significant differences on any measure were observed following a stressful color naming task. The observed interaction of hostility and Type A behavior on bleeding time thromboxane formation links behavior to an adverse aspect of a thrombosis-related parameter thought to be involved in the genesis of cardiovascular disease.

Studies in patients with bleeding disorders show that platelet-vessel interaction is important for thromboxane formation in bleeding time wounds

The production of thomboxane B2, the primary metabolite of thromboxane A2, and 6-keto prostaglandin F1 alpha, the primary metabolite of prostacyclin, were measured in response to a standardized vascular injury, the bleeding time, in patients with von Willebrand's disease and in patients with platelet function defects. Compared to controls, thromboxane B2 levels in bleeding time blood were significantly lower in subjects with von Willebrand's disease. In patients with platelet function defects associated with a deficient response to thromboxane A2, thromboxane B2 production in bleeding time blood was similar to controls. In subjects with other platelet function defects, thromboxane production was significantly lower than normal. 6-keto PGF1 alpha production in bleeding time blood was not significantly different in patients compared to controls. The results suggest that bleeding time thromboxane production is influenced by the extent of platelet-vessel interaction.

Low dose acetylsalicylic acid and thromboxane release at the site of plug formation in vivo in elderly patients with cardiovascular disease

Thromboxane B2 (TXB2) levels in bleeding time blood and in serum were measured in 13 elderly patients with cardiovascular disease, seven of whom were receiving continuous treatment with low dose acetylsalicylic acid (ASA, 125 mg every second day--250 mg daily) for prevention of stroke. Blood sampling was performed openly, but assays of TXB2 were performed by a blinded investigator. In patients treated with ASA, median serum TXB2-levels were 4% and TXB2-levels in bleeding-time blood were less than 16% of the corresponding levels in patients without ASA (P less than 0.01). The results show that in elderly atherosclerotic patients very low doses of ASA substantially suppress TXB2 formation, not only in serum but also at the site of local haemostasis. The extent of suppression is comparable to that previously reported from young healthy subjects.

The effect of exercise on bleeding time and local production of prostacyclin and thromboxane

Exercise at a heart rate corresponding to 30% VO2max for 15 min was associated with an increase in the volume of bleeding time blood from a mean of 133 microliters before exercise to a mean of 218 microliters during and immediately after the exercise. There was similarly an increase in thromboxane B2 production from 6.40 nmol.l-1 before to 11.50 nmol.l-1. Most subjects also showed an increase in the length of the bleeding time and in the production of bleeding time 6-keto-PGF1 alpha. The extent of increase in the bleeding time and in production of 6-keto-PGF1 alpha was quite variable, with subjects showing the largest increases in bleeding time also demonstrating the greatest increases in 6-keto-PGF1 alpha (r = 0.76, P = 0.004). The ingestion of aspirin before exercise markedly inhibited basal bleeding time thromboxane B2 production and blocked the exercise-associated increments in thromboxane B2 and 6-keto-PGF1 alpha production. While the aspirin itself increased the length of the bleeding time, there was not any further increase associated with exercise. In contrast to the effects of acute short-term exercise, long-distance running was associated with a significant decrease in bleeding time, but no change in bleeding time blood volume, bleeding time thromboxane B2, or bleeding time 6-keto-PGF1 alpha. The results show that acute low-level exercise can be associated with significant changes in the volume of blood oozing from a bleeding time incision and in the amount of thromboxane production stimulated at the incisional site. Following exhaustive exercise of long duration, the above changes are no longer seen.

Platelet thromboxane A2 receptors in habitual smokers

Cigarette smoking is a major risk factor for cardiovascular disease but its effect on platelet aggregability and particularly on TxA2 platelet metabolism is controversial. In present study TxA2 platelet receptors of 8 male clinically healthy habitual smokers (more than 20 cig./day) aged 30-55 (44 +/- 6 years) and of 9 age matched healthy controls were evaluated. Platelet TxA2 receptors were investigated by a radioligand binding method employing 125I-PTA-OH, a radio-iodinated hydroxy derivative of the 13-azapinane thromboxane antagonist (ONO 11120). Binding studies evidentiated a single class of specific high affinity receptors for the TxA2 analogue. In non smokers 990 + 220 receptors/platelet (rec/plt) with a dissociation constant (kd) of 22 +/- 11 nM were found. Smokers had a significantly larger number of TxA2 platelet receptors (1268 +/- 190 rec/plt p less than 0.01). No differences in the receptor affinity was found (23 +/- 6 nM, ns). Those changes could contribute to the high responsiveness of platelet from smokers to external aggregating stimuli.