Cumulative inhibitory effect of low-dose aspirin on vascular prostacyclin and platelet thromboxane production in patients with atherosclerosis

Differential effects of cyclo-oxygenase 1 and 2 inhibition on angiogenesis inhibitor-induced hypertension and kidney damage

Vascular endothelial growth factor antagonism with angiogenesis inhibitors in cancer patients induces a ‘preeclampsia-like’ syndrome including hypertension, proteinuria and elevated endothelin (ET)-1. Cyclo-oxygenase (COX) inhibition with aspirin is known to prevent the onset of preeclampsia in high-risk patients. In the present study, we hypothesised that treatment with aspirin would prevent the development of angiogenesis inhibitor-induced hypertension and kidney damage. Our aims were to compare the effects of low-dose (COX-1 inhibition) and high-dose (dual COX-1 and COX-2 inhibition) aspirin on blood pressure, vascular function, oxidative stress, ET-1 and prostanoid levels and kidney damage during angiogenesis-inhibitor therapy in rodents. To this end, Wistar Kyoto rats were treated with vehicle, angiogenesis inhibitor (sunitinib) alone or in combination with low- or high-dose aspirin for 8 days (n=5–7/group). Our results demonstrated that prostacyclin (PGI₂) and ET-1 were increased during angiogenesis-inhibitor therapy, while thromboxane (TXA₂) was unchanged. Both low- and high-dose aspirin blunted angiogenesis inhibitor-induced hypertension and vascular superoxide production to a similar extent, whereas only high-dose aspirin prevented albuminuria. While circulating TXA₂ and prostaglandin F_2α levels were reduced by both low- and high-dose aspirin, circulating and urinary levels PGI₂ were only reduced by high-dose aspirin. Lastly, treatment with aspirin did not significantly affect ET-1 or vascular function. Collectively our findings suggest that prostanoids contribute to the development of angiogenesis inhibitor-induced hypertension and renal damage and that targeting the prostanoid pathway could be an effective strategy to mitigate the unwanted cardiovascular and renal toxicities associated with angiogenesis inhibitors.

Effect of Different Doses of Acetylsalicylic Acid on the Antithrombotic Activity of Clopidogrel in a Mouse Arterial Thrombosis Model

Objective- Dual-antiplatelet therapy with acetylsalicylic acid and a P2Y₁₂ antagonist, such as clopidogrel, is the standard of care for acute coronary syndromes. However, the drugs have divergent effects on the formation of cAMP, an inhibitory second messenger. Thus, by inhibiting the synthesis of prostacyclin, acetylsalicylic acid reduces cAMP formation, whereas clopidogrel potentiates it. Therefore, with higher doses of acetylsalicylic acid, the potentiation of cAMP production by clopidogrel may be attenuated, which could limit the antithrombotic potential of the drug combination. The purpose of this study was to examine this possibility in vivo. Approach and Results- Mice were given oral acetylsalicylic acid at varying doses, oral clopidogrel (5 mg/kg body weight), or both. At doses of 0.15 and 0.6 mg/kg, acetylsalicylic acid inhibited arachidonic acid-induced platelet aggregation, but only 0.6 mg/kg acetylsalicylic acid, or higher, decreased the plasma levels of 6-keto-prostaglandin-F_1α, the stable metabolite of prostacyclin. When given with clopidogrel, laser injury-induced arterial thrombi were significantly larger with the 0.6 mg/kg dose of acetylsalicylic acid than with the 0.15 mg/kg dose. Thrombi in mice treated with clopidogrel and the 0.15 mg/kg dose of acetylsalicylic acid were smaller than in mice treated with clopidogrel alone, suggesting that acetylsalicylic acid can add to the antithrombotic effect of clopidogrel but that higher doses of acetylsalicylic acid blunt the antithrombotic effect of clopidogrel. Conclusions- These findings support the use of lower, prostacyclin-preserving, doses of acetylsalicylic acid in conjunction with clopidogrel.

Cytochrome P450 is Responsible for Nitric Oxide Generation from NO-Aspirin and Other Organic Nitrates

Nitric oxide (NO) biotransformation from NO-aspirin (NCX-4016) is not clearly understood. We have previously reported that cytochrome P450 (P450) plays important role in NO generation from other organic nitrates such as nitroglycerin (NTG) and isosorbide dinitrate (ISDN). The present study was designed to elucidate the role of human cytochrome P450 isoforms in NO formation from NCX-4016, using lymphoblast microsomes transfected with cDNA of human P450 or yeast-expressed, purified P450 isoforms. CYP1A2 and CYP2J2, among other isoforms, were strongly related to NO production from NCX-4016. In fact, these isoforms were detected in human coronary endothelial cells. These results suggest that NADPH-cytochrome P450 reductase and the P450 system participate in NO formation from NCX-4016, as well as other organic nitrates.

[Administration-time dependent effects of acetyl-salicylic acid on blood pressure in patients with mild essential hypertension]

BACKGROUND AND OBJECTIVES

Previous studies on the potential influence of aspirin (AAS) on blood pressure have not taken in consideration the chronopharmacologic effects of non-steroidal antiinflammatory drugs. This pilot study investigated the effects of AAS on blood pressure in hypertensive patients under no antihypertensive treatment who received AAS at different day times according to their rest-activity cycle.

PATIENTS AND METHOD

We studied 64 untreated patients with mild hypertension (24 men), 43.5 (12.0) (mean [SD]) years of age, randomly divided in 3 groups: group 1, non-pharmacological hygienic-dietetic recommendations; group 2, the same recommendations plus AAS (100 mg/day) on awakening, and group 3, the same recommendations plus AAS (100 mg/day) before bedtime. Blood pressure was measured every 20 min during the day and every 30 min at night for 48 consecutive hours before and after 3 months of intervention. The circadian pattern of blood pressure in each group was established by population multiple-component analysis. Circadian parameters obtained for each group of patients before and after the intervention were compared with a nonparametric paired test.

RESULTS

After 3 months of non-pharmacological intervention, there was a small and non-significant reduction of blood pressure (< 1.5 mmHg; p = 0.28). There was no change in blood pressure when AAS was given on awakening (p = 0.21). A highly significant blood pressure reduction was, however, observed in patients who received AAS before bedtime (decrease of 7 and 5 mmHg in systolic and diastolic blood pressure, respectively; p = 0.006).

CONCLUSIONS

Our results indicate a statistically significant time-dependent administration effect of low-dose AAS on blood pressure in untreated patients with mild hypertension. This effect reinforces the need to quantify and control AAS effects in patients using this agent in combination with antihypertensive agents.

Time related neutralization of two doses acetyl salicylic acid

Aspirin has a well established role in the prevention of arterial thrombosis. Discussion on the efficacy and safety of aspirin in the treatment and prophylaxis of thrombosis has become an important issue. In fact, hemorrhage complications are often associated with its use. On the other hand, previous studies showed unexpected thrombotic potencies associated with the presence of this drug at ultra low doses (ULD) in the circulation. In this study, we aimed to evaluate the effect of aspirin at ULD, injected 1, 2, or 3 hours after the administration of aspirin at 100 mg/kg, on hemostasis and bleeding in rats. We used an experimental model of thrombosis induced by laser beams to evaluate these effects. Platelet aggregation was determined by Cardinal and Flower method. Results from this investigation demonstrate that the neutralizing effect of aspirin at ULD did not operate significantly 1 hour after the injection of aspirin at 100 mg/kg. This effect was observed 2 and 3 hours after. The use of aspirin at ULD to neutralize the side effects of aspirin at high doses will reduce the hemorrhagic risk during extra corporeal circulation. The therapeutic benefit and safety of aspirin therapy in the treatment of cardiovascular diseases can be obtained.

Effects of acetyl salicylic acid therapy on an experimental thrombosis induced by laser beam

Aspirin inhibits the synthesis of both platelet and vascular arachidonic acid metabolism which have opposite effects on platelet functions. The rationale for its clinical use as an antithrombotic drug has therefore been questioned. Therefore, we investigated the effects of acetylsalicylic acid (ASA) at 100 mg/kg on an experimental thrombosis induced by laser beams using different groups of rats that were previously treated with the same dose (100 mg/kg), according to the delay between the first and second injections. A partial occlusion was induced by laser beams in the rat mesenteric microvessels (15-25 m). The thrombus formed within seconds after the laser lesion; both it and the embolization which began within minutes after, were continuously accounted. Experiments were done on 11 groups of 5 animals each: 45 rats received a first injection of ASA at j(0) and a second injection 30 minutes before thrombosis induction at j(0)+x (x=2, 4, 6, 8, 9, 10, 12, 14 and 16 days). Different groups are defined according to the x value. The rats receiving NaCl 0.9% or a single injection of ASA at 100 mg/kg 30 minutes before thrombosis induction were used as control (Group I) and reference group (Group II) respectively. In this study, ASA treatment showed two types of results. The administration of ASA (100 mg/kg) 30 minutes before laser-induced thrombosis prevented thrombus formation. In the same way, ASA injected to rats already treated with the same dose 2 or 4 day later also demonstrated a potent antithrombotic effect. The same trends were observed with animals receiving the second injection (100 mg ASA) at j(0+8), j(0+12), j(0+14), and j(0+16). However, when injected to rats at j(0+6) and at j(0+10), ASA did not shown any effects on thrombus formation compared to the control (p>/=0.05). The same phases of ASA action were observed on the induced hemorrhagic time. The antithrombotic effects of the later second injection of ASA (100 mg/kg) were neutralized in rats previously receiving the same dose of this drug. This phenomenon seems to be periodic and is of great importance for the observance of ASA treatment.

Production of prostanoids and nitric oxide by infarcted heart in situ and the effect of aspirin

The production of prostacyclin (PGI2) and thromboxane A2 (TXA2) in infarcted and noninfarcted portions of the rabbit heart was studied prior to and following administration of acetylsalicylic acid (aspirin). Aspirin was administered intravenously (iv) as water-soluble Aspisol, d-lysinmono (acetylsalicylate) (Bayer, Leverkusen, Germany) into an ear vein. A branch of the left circumflex coronary artery was ligated. The animals were divided into three groups. The first group received 150 mg/kg/day of aspirin (75 mg/kg of aspirin every 12 h, n = 10). The first administration of aspirin was 1 h after ligation of the coronary artery and the last injection was 1 h before euthanasia. The second group received 5 mg/kg/day of aspirin (every 24 h, n = 10). A separate group of rabbits not receiving aspirin served as controls (n = 12). Two days following onset of ischemia, inducible form of nitric oxide synthase (iNOS) was measured in heart muscle and the oxidation products of nitric oxide (nitrite, NO-2 plus nitrate, NO-3: their sum referred to as NOx) were determined in arterial and coronary venous blood. Concentrations of both PGI2 and TXA2 were elevated in the infarcted portions of the heart compared to the noninfarcted regions. Formation of prostanoids was accompanied by increased activation of iNOS. Both doses of aspirin diminished the concentrations of PGI2 and TXA2 in infarcted heart muscle; in contrast, small doses of aspirin failed to influence myocardial iNOS activity. Apparently small doses of aspirin changed the relationship of iNOS to cyclooxygenase (COX). Coronary arterial-venous difference of NOx and myocardial iNOS activity showed parallel increases. Diminution of prostacyclin by aspirin can damage gastric mucosa and interfere with vasodilatation. Since NO counters these deficiencies, a combination of aspirin with a nitric oxide donor may be advantageous.

Aprotinin counterbalances an increased risk of peri-operative hemorrhage in CABG patients pre-treated with Aspirin

OBJECTIVE

As Aspirin (ASA) has proven efficacy in preventing patients with CAD from complications related to cardiovascular diseases, most patients scheduled for CABG are treated with ASA therapy. Consequently, impaired hemostasis is a problem in the management of CABG patients. Clinical studies have shown that Aprotinin can reduce bleeding and the use of blood products by 50% in patients both with and without pre-operative ASA therapy. Concerning the combined effect of peri-operative low-dose ASA therapy and intra-operative high-dose Aprotinin therapy, the gathering of additional and prospective data seemed to be necessary.

METHODS

We conducted a double-blind two-centre randomised three-arm study in patients with elective primary CABG surgery. Three groups have been tested, comprising 119 patients in total (group A: ASA + Aprotinin, group B: placebo + Aprotinin, group C: placebo + placebo) to investigate a possible reduction of bleeding in Aprotinin treated patients. For all patients, thromboxane levels were used to identify ASA or placebo treatment.

RESULTS

The post-operative blood loss is significantly reduced by 21% after Trasylol administration (B vs. C; P = 0.009). The unexpected result of this study has been that the pre-treatment with ASA led to a further reduction of 18% (A vs. C; P < 0.0001). The difference between the two Aprotinin groups (A and B) is significant (P = 0. 01) in favour of ASA pre-treatment. Myocardial infarction (MI) had been diagnosed at levels of 1.8% in total (2/113), 2.6% (1/38) in group B and 3.2% (1/31 ) in group C. An additional blinded evaluation of ECG, enzyme levels and clinical status revealed 'definite, probable and possible' MIs of 5% in group A, compared to 16% in group B and 13% in group C, thus providing no evidence for a higher risk of infarction by Aprotinin treatment. When comparing the ASA group to non-ASA pre-treatment, a strong trend towards a reduction in MI rate becomes obvious, from 15% to 5% in favour of the ASA pre-treatment (P = 0.08). Concerning other peri-operative complications, no statistical difference between the groups could be detected.

CONCLUSIONS

A reduction in post-operative blood loss in primary elective CABG surgery with intra-operative Aprotinin treatment could be confirmed. A low-dose ASA treatment combined with a high-dose aprotinin administration during surgery not only neutralized a potentially higher risk of bleeding, but did in fact reduce the post-operative blood loss. The protective effect of ASA on peri-operative MI has been evident through a reduction of MI rate in ASA treated patients.

Thromboembolic complications several days after a single-dose administration of aspirin

The antithrombotic properties of acetyl salicylic acid (ASA) used at current doses are largely demonstrated. However, our previous study showed unexpected thrombotic potencies associated with the use of this drug. In this study we investigate the effect of aspirin on an experimental thrombosis induced by laser beams, according to its in vivo plasma concentration. Experiments were done on nine groups of seven Wistar male rats. The groups are defined by the delay between aspirin administration time and the laser-induced thrombosis time. Results from this study showed an enhancement of thromboembolic complications when thrombosis was induced 8 or 10 days after aspirin administration; the number of emboli and the duration of embolization are increased, compared to the control group. The prothrombotic properties of ASA demonstrated in this study, might limit its therapeutic benefit and might explain thromboembolic complications observed in some ASA-treated patients. These results also suggest a biological monitoring several days after aspirin administration to patients.

Influence of aspirin usage on blood pressure: dose and administration-time dependencies

This study investigates the possible effects of acetylsalicylic acid (ASA; aspirin) on systolic (S) and diastolic (D) blood pressure (BP) in healthy and mildly hypertensive subjects receiving ASA at different times according to their rest-activity cycle. A double-blind, randomized, controlled trial was conducted in 73 healthy young adult volunteers and 18 previously untreated subjects with mild hypertension. The BP of each subject was automatically monitored every 30 minutes for 48h before the trial and at the end of a one-week course of placebo and a one-week course of ASA. Healthy volunteers were randomly assigned to one of six groups, defined according to the dose of ASA (either 500 mg/day, the usual commercial dose; or 100 mg/day) and timing of ASA and placebo (within 2h after awakening, Time 1; 7h to 9h after awakening, Time 2; or within 2h of bedtime, Time 3). Subjects with mild hypertension received the low dose of 100 mg/day ASA, as well as one week of placebo, and were randomly assigned to one of the same three groups defined above according to the time of treatment. A small (approximately 2 mmHg in the 24h mean of SBP), but statistically significant, BP reduction was found when 500 mg/day ASA was given to healthy volunteers at Time 2. With 100 mg/day, the effect of ASA in healthy subjects was comparable to the BP reduction found with the higher dose for Time 2; there was again no effect on BP at Time 1, but we found a statistically significant effect at Time 3 (2.3 mmHg reduction in the 24h mean of SBP), larger than for Time 2. For hypertensive patients, the BP reduction was again statistically significant for Time 2 and, to a greater extent, for Time 3 (approximately 4.5 mmHg for both SBP and DBP); all patients in these two groups showed a BP reduction after one week of ASA. The effect was about three times as large as the BP reduction obtained in healthy subjects treated with 100 mg/day ASA. Results indicate a statistically significant time- and dose-dependent effect of ASA on BP. In any meta-analysis of ASA effects, inquiries about the time when subjects took the drug are indicated and may account for discrepancies in the literature. Moreover, the influence of ASA on BP demonstrated here indicates the need to identify and control for ASA effects in patients using ASA before and during their participation in antihypertension medication trials.

Prostacyclin and thromboxane production of rat and cat arterial tissue is altered independently by several vasoactive substances

The modulation of the production of prostacyclin and thromboxane from cat and cat aortic tissue slices by different vasoactive agents has been studied in order to reveal whether the release of these main two vasoactive prostanoids goes in parallel or may be controlled independently. Norepinephrine, isoproterenol, phentolamine, propranolol, angiotensin II, vasopressin, bradykinin, thrombin, verapamil, gallopamil, dopamine or methionin enkephalin were added to the incubation medium and 6-keto-PGF1 alpha (the stable metabolite of prostacyclin) and TxB2 (the stable metabolite of thromboxane) were determined in the supernatant by radioimmunoassay. The ratio of the release of prostacyclin and thromboxane was computed. Norepinephrine increased both prostacyclin and thromboxane release. Isoproterenol increased the ratio of prostacyclin and thromboxane released in cat aortic tissue slices. Phentolamine and propranolol had no effects. Angiotensin II induced a slight but statistically insignificant increase in the ratio of the two prostanoids released. Vasopressin increased thromboxane release only. Bradykinin stimulated the prostacyclin while thrombin stimulated the thromboxane release. Verapamil decreased both prostacyclin and thromboxane production. Gallopamil decreased prostacyclin release and increased thromboxane release from vessel wall slices in a certain concentration range causing a characteristic dose dependent minimum in the ratio of prostacyclin and thromboxane release. Dopamine separately increased prostacyclin release while enkephalin had no significant effect. The data obtained show that in vascular tissue some unidentified yet cytophysiological mechanisms might exist which specifically control the activities of the prostacyclin synthase and thromboxane synthase enzymes.

Beneficial effect of CV-4151 (Isbogrel), a thromboxane A2 synthase inhibitor, in a rat middle cerebral artery thrombosis model

Effects of thromboxane A2 (TXA2) synthase inhibitors (CV-4151 and ozagrel) on cerebral thrombosis and cerebral damage were examined in a rat middle cerebral artery (MCA) thrombosis model and their potencies were compared with the conventional antithrombotic agents, aspirin and ticlopidine. CV-4151 significantly inhibited photochemically induced MCA thrombosis by oral (1 and 10 mg/kg) and intravenous (1 mg/kg) administration. Ozagrel (10 mg/kg, p.o.) also inhibited it. The potency of CV-4151 was about 10 times stronger than that of ozagrel, being comparable with the inhibition of blood TXA2 generation. Aspirin (100 mg/kg, p.o.) and ticlopidine (300 mg/kg, p.o.) showed an inhibitory tendency on MCA thrombosis. Twenty-four h after photochemical stimulation, cerebral edema and cerebral infarction were observed, and the lactate content in the brain increased. CV-4151 and ozagrel prevented this edema, and the antiedema effects of the drugs were correlated with the antithrombotic effect on thrombotic MCA occlusion. CV-4151 (10 mg/kg, p.o.), furthermore, significantly reduced the infarct size and inhibited the increase in lactate content. These results indicate that TXA2 synthase inhibitors inhibit cerebral damage by inhibition of MCA occlusion with thrombosis, probably resulting from the inhibition of TXA2 generation, and their effects are superior to those of aspirin and ticlopidine. TXA2 might play an important role in cerebral damage in the MCA thrombosis model. CV-4151 might be a useful drug for the treatment of cerebral thrombosis and for the prevention of cerebral infarction.

Effect of n-3 fatty acid ethyl ester supplementation on fatty acid composition of the single platelet phospholipids and on platelet functions

Twenty healthy male volunteers were randomly assigned to receive either four 1-g capsules of n-3 polyunsaturated fatty acids (PUFA) ethyl esters or four 1-g capsules of olive oil (as placebo) for a period of 4 months, followed by a 3-month wash-out period. Fatty acids of platelet phospholipid fractions, platelet aggregation, and thromboxane B2 (TXB2) formation were analyzed at 0, 2, and 4 months of treatment and at 1, 2, and 3 months of wash-out. During n-3 PUFA supplementation, accumulations of eicosapentaenoic (EPA), docosapentaenoic (DPA), and docosahexaenoic (DHA) acids were markedly increased after 2 months, with slight differences in further accumulation up to 4 months among the various phospholipid fractions. Significant decreases in platelet sensitivity to collagen, serum TXB2 levels, and urinary TXB2 metabolites were also observed following n-3 PUFA treatment. During the first and second month of wash-out, slight differences were observed in changes of various fatty acids among different phospholipid fractions, but after 3 months of wash-out, alterations were no longer detectable with respect to pretreatment values. After 3 months of wash-out, platelet function parameters also were returned to baseline. Thus, both platelet lipids and function are influenced by n-3 PUFA ethyl ester supplementation, and significant alterations are still detectable after 2 months of wash-out.

Control of vascular resistance in the maternal and feto-placental arterial beds

This review aims to provide a comprehensive summary of the mechanisms involved in the physiological adaptation of the vasculature to pregnancy. Profound changes occur both systemically and in discrete circulations in the mother, but it is debatable which factors are responsible. Similarly, whilst the feto-placental circulation must be substantially controlled by humoral mechanisms, the exact role of each potential contributor is not known. In view of the hitherto unappreciated and very important role of the endothelium-derived vasodilator, nitric oxide, in the control of peripheral vascular resistance, considerable emphasis will be placed on the many recent investigations in this area.

Effects of a thromboxane A2-receptor antagonist, a thromboxane synthetase inhibitor and aspirin on prostaglandin I2 production in endothelium-intact and -injured aorta of guinea pigs

We examined the effects of KW-3635, a thromboxane (TX) A2-receptor antagonist, and OKY-046, a TX synthetase inhibitor, on the prostaglandin (PG) I2 production in endothelium-intact and -injured guinea pig aorta and compared them with those of aspirin. In the endothelium-intact aorta, both the low (3 mg/kg) and the high (100 mg/kg) dose of aspirin similarly reduced the PGI2 production, as measured ex vivo 1 hr after the injury. In contrast, neither KW-3635 (10 mg/kg) nor OKY-046 (30 mg/kg) inhibited the PGI2 production. The endothelial injury, induced by balloon catheterization, caused a reduction of PGI2 production in the aorta and decline of plasma PGI2/TXA2 ratio. In the endothelium-injured animals, the high dose of aspirin further reduced the PGI2 production in the aorta, whereas KW-3635 and OKY-046 did not affect it. KW-3635 and OKY-046 also ameliorated the reduced ratio of PGI2/TXA2 in the plasma. The present results demonstrate that aspirin, but not KW-3635 or OKY-046, reduces the PGI2 production in the aorta either in the endothelium-intact or -injured state. It is thus suggested that the TXA2-receptor antagonist and the TX synthetase inhibitor have some advantages over aspirin when used for the prevention of acute thrombosis after percutaneous transluminal angioplasty.

Clinical and experimental study on the long-term effect of dietary gamma-linolenic acid on plasma lipids, platelet aggregation, thromboxane formation, and prostacyclin production

Effects of a dietary intake of the polyunsaturated omega-6 essential fatty acids (EFAs) linoleic and gamma-linolenic acids (GLA) on blood lipids, platelet function, and vascular prostacyclin production were studied 12 hyperlipidemic patients (doses of 3 g/day) and 12 male Wistar rats (doses of 3 mg/kg/day) for 4 months. In humans, GLA supplementation decreased plasma triglyceride (TG) levels by 48% (p < 0.001) and increased HDL-cholesterol concentration by 22% (p < 0.01). Total cholesterol and LDL-cholesterol levels were significantly decreased by omega-6 EFAs. Platelet aggregation induced by low concentrations of adenosine diphosphate (ADP) and epinephrine, and serum thromboxane B2 decreased by 45% both in humans and animals after GLA supplementation. Bleeding time increased 40% (p , 0.01). In rats, vascular prostacyclin production measured by radioimmunoassay of 6-keto-PGF1 alpha was enhanced by GLA intake. These effects of omega-6 EFAs may contribute to cardiovascular protection and prevention of the atherosclerotic disease.

Low dose acetylsalicylic acid in the antithrombotic treatment of patients with stable angina pectoris and acute coronary syndromes (unstable angina pectoris and acute myocardial infarction)

Acetylsalicylic acid has an antithrombotic effect by inhibition of thromboxane A2 synthesis in platelets. Thromboxane A2 is a potent stimulator of platelet aggregation and vasoconstriction and synthesis may be completely inhibited by a single oral dose of 150 mg acetylsalicylic acid or an intravenous dose of 100 mg. A daily maintenance dose of 75 mg acetylsalicylic acid is sufficient to effectively inhibit thromboxane A2 synthesis in long-term treatment. Acetylsalicylic acid therapy reduces acute myocardial infarction and sudden death in patients with stable angina pectoris and the drug is equally effective in patients with symptomatic and 'silent' angina pectoris. Early intervention with acetylsalicylic acid in patients with unstable angina pectoris reduces the risk of acute myocardial infarction and death. In patients with acute myocardial infarction, acute therapy with acetylsalicylic acid significantly reduces mortality both in monotherapy and in combination with thrombolytics. In the secondary prophylaxis following acute myocardial infarction, acetylsalicylic acid reduces the incidence of reinfarction and coronary death. Treatment of 100 patients with acute coronary syndrome (unstable angina pectoris or acute myocardial infarction) for 2 years may hinder the development of 3-4 fatal and 4 non-fatal vascular events. The risk of gastrointestinal side-effects and bleeding during acetylsalicylic acid therapy is dose-dependent and the incidence is low with a daily dose of 75-150 mg.

Platelet aggregation inhibitors in neurology

This literature review reports on secondary prevention of ischaemic stroke. The aim of secondary prevention is to protect patients who belong to a risk group from the occurrence of brain infarction. Symptomatic patients with a demonstrated carotid artery stenosis of 70% and more will most probably benefit from carotid endarterectomy if performed by a skilled surgeon in the absence of contraindications. Oral anticoagulant drugs play a minor role in the medical prevention of brain infarction. Antiplatelet drugs, however, have been in use for almost two decades and (meta-)analysis of clinical trials points to acetylsalicylic acid as a drug with a modest but certain contribution of about 15% in the endpoint reduction, even at lower dosages. The addition of dipyridamole to classic acetylsalicylic acid dose appears to increase the endpoint reduction to 30%. Neither dipyridamole nor sulfinpyrazone as monotherapy have been demonstrated to be efficacious in the secondary prevention of ischaemic stroke. Ticlopidine seems a promising alternative for acetylsalicylic acid in those patients who suffer adverse effects from acetylsalicylic acid. Ticlopidine itself, however, has a number of side-effects that limit its application. New clinical trials are under way in order to improve the efficacy of drug treatment in the secondary prevention of brain infarction.

Interruption of thrombosis and hemostasis by anti-platelet agents

Blood platelets play a fundamental role in hemostasis and thrombosis. The physiological role of platelets is to preserve the integrity of the cardiovascular system such that upon injury platelets are activated and serve to interrupt a potentially deleterious situation (i.e., hemorrhage). However, platelets are also involved in the pathophysiology of thrombosis in which the normal repair process is grossly exacerbated, resulting in interruption of blood flow to vital tissues. Thus, a critical balance exists between the normal function of blood platelets to preserve tissue function and a pathophysiological function in which tissue is damaged due to thrombosis and subsequent ischemia. Numerous anti-platelet agents have been developed in an attempt to interrupt the thrombotic process without severely compromising the hemostatic state of patients. This article will be devoted to a discussion of a commonly utilized anti-thrombotic agent, aspirin, as well as a class of newer, possibly more effective anti-thrombotic agents referred to collectively as fibrinogen receptor antagonists.

Low-dose aspirin in the prevention of preeclampsia and fetal growth retardation: rationale, mechanisms, and clinical trials

Preeclampsia is characterized by a functional imbalance between vascular prostacyclin and thromboxane A2 production. On the basis of the hypothesis that preeclampsia is at least partially caused by an increase in thromboxane A2, some studies attempted to correct this pathologic condition by pharmacologic manipulation with low-dose aspirin. The current literature suggests that the use of low-dose aspirin during pregnancy is safe with regard to congenital anomalies and fetal, neonatal, and maternal cardiovascular physiologic state and hemostasis. Aspirin at least partially corrects the pathologic increase in angiotensin II sensitivity that precedes the clinical development of preeclampsia. In addition, some clinical trials have demonstrated that low-dose aspirin is effective in reducing the incidence of preeclampsia and/or fetal growth retardation in selected high-risk women. Currently, large clinical trials are in progress to evaluate the effectiveness and side effects of the use of low-dose aspirin in preventing preeclampsia and/or fetal growth retardation. Until these studies have been completed, it will remain unclear whether antiplatelet therapy, such as low-dose aspirin, should be adopted for the prevention of either preeclampsia or fetal growth retardation.

Principles underlying the use of conjunctive agents with plasminogen activators

Pharmacological thrombolysis is a dynamic situation in which fibrin degradation occurs concomitant to procoagulant activity. The consequences of enhanced procoagulant and platelet activity may delay or prevent thrombolysis or lead to reocclusive events following successful recanalization. Although heparin and aspirin may attenuate ongoing thrombin and thromboxane generation, respectively, a relatively high percentage (10-20%) of patients treated with heparin and aspirin still have complications associated with thrombolysis. This suggests that heparin and aspirin are not universally effective as the heparin-antithrombin III complex may be inaccessible to fibrin-bound thrombin in the microenvironment of the thrombus and aspirin eliminates only thromboxane-dependent platelet aggregation. Therefore, careful consideration must be given to small molecule, active-site thrombin inhibitors which may prove to be more effective than heparin and to fibrinogen receptor antagonists which block aggregation to all known platelet agonists and have a much broader spectrum of activity than aspirin. Hopefully, well-designed clinical trials will be conducted with safe and effective thrombin inhibitors and/or fibrinogen receptor antagonists in thrombolysis and compared to heparin and aspirin such that potentially the overall efficiency of thrombolysis can be improved upon.

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.

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.

Aspirin-induced decline in prostacyclin production in patients with coronary artery disease is due to decreased endoperoxide shift. Analysis of the effects of a combination of aspirin and n-3 fatty acids on the eicosanoid profile

BACKGROUND

It was the purpose of this study to determine the effects of the combination of aspirin (ASA) and fish oil, which is rich in n-3 polyunsaturated fatty acids, on the eicosanoid profile of patients with coronary artery disease. Specifically, we wanted to determine whether the ASA-induced reduction in prostacyclin production is due to inhibition of endothelial cell cyclooxygenase or to reduced endoperoxide shift from platelets and whether ASA negates the potentially beneficial effects of fish oil on the eicosanoid profile.

METHODS AND RESULTS

Fourteen patients with clinically stable but advanced coronary artery disease received 12 g (n = 8) or 16 g (n = 6) of fish oil concentrate containing 6 or 8 g of n-3 fatty acids for 6 weeks. In addition to the fish oil, patients received increasing daily doses of ASA (50 mg, 100 mg, 325 mg, and 1,300 mg; the latter in four divided doses). Each dose was taken for 2 weeks. With fish oil supplementation, red blood cell phospholipid fatty acid content of arachidonic acid (AA) decreased and of eicosapentaenoic acid (EPA) increased so that EPA as a percent of AA increased from 2% to 26%. Serum thromboxane B2, which represents the production of TXA2 by maximally stimulated platelets, was suppressed by 38% on fish oil alone and by 97% or greater on all doses of ASA. Excretion of PGI2-M, the main urinary metabolite of PGI2 (derived from AA), fell from 50 +/- 4 ng/g of creatinine to 42 +/- 2 ng/g on fish oil alone (p = 0.02). On 50 mg of ASA per day, PGI2-M excretion was 26 +/- 2 ng/g of creatinine (p less than 0.001 versus fish oil alone). On 100 mg and 325 mg of ASA per day, PGI2-M was 24 +/- 3 ng/g and 27 +/- 3 ng/g, respectively (p V NS versus value on 50 mg per day). PGI3-M, the main urinary metabolite of PGI3 (derived from EPA), increased from 0.2 +/- 0.1 ng/g of creatinine to 4.9 +/- 0.7 ng/g on fish oil alone (p less than 0.001). In contrast with the marked ASA-induced decline in PGI2-M, PGI3-M excretion was not affected by the addition of ASA, even at the higher doses (4.6 +/- 0.7 ng/g and 4.9 +/- 0.5 ng/g on 325 mg per day and 325 mg four times daily, respectively).

CONCLUSIONS

Moderate-dose (325 mg per day or less) ASA taken once daily has no effect on PGI3 production despite significantly reducing PGI2 production. This suggests that endothelial cell cyclooxygenase is minimally inhibited by such doses of ASA and that a large percent of the PGI2 produced in patients with advanced coronary artery disease derives from the transfer of prostaglandin endoperoxides from activated platelets to endothelial cells. The loss of these substrates accounts for the decrease in PGI2 with moderate-dose ASA. Thus, the ASA-induced decrease in PGI2 may in large part be an unavoidable consequence of ASA-induced platelet cyclooxygenase inhibition. ASA does not negate the potentially beneficial effects of n-3 fatty acids on the eicosanoid profile.

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.

Bioinequivalence of four 100 mg oral aspirin formulations in healthy volunteers

The single dose pharmacokinetics of 4 commercially available 100 mg oral aspirin formulations were studied in 6 healthy men and 6 healthy women. Two of the formulations were rapid release ('Cardiprin' 100, 'Platelin') and the other 2 were enteric coated formulations ('Astrix' 100, 'Cartia'). There were marked differences in the plasma concentration-time profiles between the rapid release and the enteric coated formulations. There were no significant differences (p greater than 0.05) in the mean time to achieve maximum aspirin concentrations between 'Cardiprin' 100 (0.48 h) and 'Platelin' (0.35 h), but this was significantly prolonged (p less than 0.001) for 'Astrix' 100 (3.73 h) and even more prolonged for 'Cartia' (6.84 h). Similar between-formulation differences were seen in the areas under the plasma concentration-time curves, for which the rank order was 'Cardiprin' 100 (1.60 mg/L.h) = 'Platelin' (1.54 mg/L.h) greater than 'Astrix' 100 (0.73 mg/L.h) greater than 'Cartia' (0.56 mg/L.h). For 'Cardiprin' 100, 'Platelin' and 'Astrix' 100 plasma aspirin concentrations were below 5 micrograms/L by 7 h after ingestion, whereas for 'Cartia' aspirin was detectable for up to 16 h, giving the appearance of sustained release. The enteric coated formulations produced the greatest variability in the plasma aspirin concentration vs time profiles. The urinary recovery of salicylate was greater than 80% of the administered dose for all 4 formulations. The clinical significance of the marked pharmacokinetic differences observed with these 4 low-dose aspirin formulations is not known.

Inhibition of human endothelial prostacyclin synthesis by different aspirin formulations

The availability of different formulations of low-dose aspirin for use as anti-thrombotic agents merits a comparison of their effects on vessel wall biochemistry. We compared the effect of ingestion of an enteric-coated slow-release aspirin (Astrix) with that of soluble aspirin (Cardiprin) on human endothelial prostacyclin synthesis. Patients undergoing varicose vein surgery (10 per group) ingested 100 mg aspirin per day as Astrix or Cardiprin for 7 days prior to surgery. A control group ingested no aspirin. Prostacyclin synthesis by the endothelial surface of the great saphenous vein was determined in vitro. Both aspirin formulations caused significant inhibition of endothelial prostacyclin synthesis compared with the control group. Using the median values, the enteric-coated slow-release aspirin caused 76% inhibition, whereas the soluble formulation caused significantly greater inhibition (95%). If differential inhibition of platelet thromboxane synthesis with 'sparing' of endothelial prostacyclin synthesis is necessary for an optimum anti-thrombotic effect of aspirin, the results suggest that a lower dose of soluble aspirin than enteric-coated slow-release aspirin may be preferred.

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.

Effect of the antiinflammatory prodrug, nabumetone and its principal active metabolite on rat gastric mucosal, aortic and platelet eicosanoid synthesis, in vitro and ex vivo

Nabumetone is a novel non-steroidal antiinflammatory drug which although a weak cyclooxygenase inhibitor is converted by the liver to metabolites that are more potent inhibitors of cyclooxygenase. Nabumetone may thus avoid the occurrence of prostanoid-mediated gastropathy while maintaining its efficacy as an antiinflammatory agent. We compared the effect of nabumetone and 6-methoxy-2-naphthylacetic acid (6-MNA; the principal active metabolite of nabumetone) with that of naproxen and indomethacin on the synthesis of rat gastric prostaglandins I2 and E2, in vitro and ex vivo. Ex vivo platelet TXA2 and aortic PGI2 synthesis was also investigated in order to assess peripheral activity of nabumetone metabolites. In vitro, nabumetone was completely without effect on gastric mucosal prostanoid synthesis, whereas indomethacin, naproxen and 6-MNA (in this order of potency) inhibited prostanoid synthesis. Ex vivo, low dose naproxen and indomethacin (less than 5mg.kg-1) markedly inhibited gastric mucosal prostanoid synthesis at 30 min and 2 h post gavage, whereas nabumetone was without significant effect. Nabumetone administration also resulted in the inhibition of platelet TXA2 synthesis, whereas aortic PGI2 synthesis was unaltered. These data indicate that the administration of nabumetone may avoid NSAID gastropathy by leaving gastric mucosal prostanoid synthesis intact and also that the active metabolite(s) of nabumetone are effective inhibitors of cyclooxygenase in an NSAID-target tissue (platelet). The lack of effect of nabumetone administration on vascular PGI2 synthesis may confer an additional advantage over other NSAIDs, since the inhibition of peripheral PGI2 has been implicated in hypertensive and nephrotoxic side effects of NSAIDs.

Platelet thromboxane A2/prostaglandin H2 receptors in human volunteers on low doses of aspirin

Administration of aspirin (81 mg/day for 2-3 weeks) in nine healthy volunteers (out of an initial ten subjects, only nine qualified) resulted in a greater than 95% decrease of thromboxane B2 production by thrombin-stimulated platelets. At the same time, ligand binding studies with a thromboxane A2 antagonist, 125I-PTA-OH, measurements of shape change, and aggregation of platelets stimulated with U46619, a prostaglandin H2 analogue, indicated that administration of aspirin to normal human subjects does not result in the up-regulation of platelet thromboxane A2/prostaglandin H2 receptors.

Vascular prostacyclin is increased in patients ingesting omega-3 polyunsaturated fatty acids before coronary artery bypass graft surgery

Interest in the antithrombotic potential of diets enriched with fish oil-derived polyunsaturated fatty acids (omega-3 PUFAs) prompted us to examine how these fatty acids, when taken preoperatively, affect hemostasis, plasma lipid levels, and production of prostacyclin (PGI2) by vascular tissues in atherosclerotic patients undergoing coronary artery bypass graft surgery. Fifteen patients with angiographically proven coronary artery disease received 3 g/day eicosapentaenoic acid and 1.3 g/day docosahexaenoic acid as capsules of purified fish oil for 28 days before surgery. Platelet aggregation induced by low concentrations of ADP, collagen, and epinephrine decreased (p less than 0.05) and serum thromboxane B2 decreased 36% (p less than 0.01) from baseline values. Bleeding times increased 40% (p less than 0.01) from baseline. Serum triglycerides decreased 50% (p less than 0.05) without a change in total serum cholesterol. Spontaneous production of PGI2 measured as 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha), its stable hydrolytic product, by saphenous vein and aortic and atrial tissues obtained at surgery was greater in tissues from patients receiving omega-3 PUFA supplements than in tissues from matched controls (13.8 +/- 2.2 versus 8.6, 21.0 +/- 3.1 versus 11.5 +/- 2.1, and 166 +/- 13 versus 102 +/- 15 ng/g, respectively, all p less than 0.05). Arachidonate-stimulated production of PGI2, as indicated by increased levels of 6-keto-PGF1 alpha, was increased. Despite changes in platelet function, bleeding time, and vascular PGI2, the perioperative blood loss was not increased in subjects receiving fish oil supplements. Thus, omega-3 PUFAs at moderate dosages may exert antithrombotic effects by increasing prostacyclin production by vessel walls as well as by direct inhibition of platelet activity.

Effects on cyclo-oxygenase of low and high dose aspirin

The study was undertaken to develop clinically applicable methods to detect the influence of low dose treatment with acetylsalicylic acid (ASA) on the platelet function. The cyclooxygenase activity of the platelets was measured by determination of the metabolite 12-HHT after challenge with arachidonic acid. Two healthy subjects received 600 mg ASA in a single dose. Two hours after intake the salicylate concentration level in plasma was 600 nmol/ml, with a 90 per cent reduction after 24 hours. The platelet cyclooxygenase activity (12-HHT) was completely and irreversibly inhibited within two hours after ASA intake. Five subjects received 75 mg ASA for eight consecutive days. The salicylate concentrations two hours after the intake of the first and last tablet were within 65 and 71 nmol/ml plasma, indicating that no accumulation of salicylate occurred during the treatment period. The decrease in cyclooxygenase activity during low dose treatment varied in the different subjects between 60 and 90 per cent. The rate of recovery of cyclooxygenase activity after termination of the low dose ASA treatment was faster than after the large single dose.

Effect of aspirin and dipyridamole treatment on prostacyclin production by human veins

Patients admitted for surgical removal of varicose veins were treated in a blinded manner for 48 hours prior to surgery with either placebo, low-dose aspirin (25 mg twice daily), dipyridamole (150 mg twice daily) or both. Segments of vein excised at surgery were incubated with or without sodium arachidonate and subsequent prostacyclin (PGI2) production was measured without knowledge of treatment given. During the first 5 minute period of incubation in the presence of arachidonate, veins from dipyridamole-treated patients demonstrated increased (by 75%) arachidonate-stimulated PGI2 production compared to placebo-treated patients. By contrast, PGI2 production was reduced by 64% by aspirin treatment and 67% by aspirin plus dipyridamole compared to placebo-treated patients (p = less than 0.05). In unstimulated vein segments incubated in the absence of arachidonate, spontaneous PGI2 production during the first 5 minute incubation period was increased 32% following dipyridamole treatment but was unchanged following aspirin treatment. By contrast, unstimulated (spontaneous) PGI2 production in patients treated with aspirin plus dipyridamole was reduced by 57% (p = less than 0.05), compared to both placebo- and aspirin-treated patients, and by 71% (p = less than 0.05) compared to dipyridamole-treated patients. With repeated change of incubation medium, the ability of vein walls to produce PGI2 declined. This exhaustion was not prevented by drug treatment. However, drug effects between patient treatment groups were consistent over successive incubation periods. These results suggest that certain therapeutic benefits that might be achieved by enhancement of PGI2 production from vascular endothelium following dipyridamole treatment may be reduced by simultaneous aspirin treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Aspirin and dipyridamole and their limitations in the therapy of coronary artery disease

We have reviewed some of the voluminous literature on the effects of aspirin combined with dipyridamole on coronary thrombosis. There is clear evidence that aspirin is partially effective in preventing platelet aggregation and subsequent thrombosis in experimental constricted and damaged coronary arteries of dogs. Clinical studies show a clear reduction in myocardial infarction in male human subjects who are given aspirin as therapy for unstable angina, or as prophylaxis in asymptomatic individuals. In many studies aspirin and dipyridamole have been combined and are effective. We have not found dipyridamole to be effective in the dog with coronary artery constriction and find no substantial evidence that it is effective in preventing myocardial infarction in man. Until definitive studies show that combining dipyridamole with aspirin is more effective than aspirin alone, we do not recommend its use for prevention of coronary thrombosis.

Prevention of aortocoronary vein bypass graft occlusion: which antithrombotic treatment and for how long?

The effects of 50 mg aspirin combined with 400 mg dipyridamole were compared with those of standard anticoagulant therapy, in the prevention of aortocoronary vein bypass graft occlusion. Early graft occlusion in 249 patients, with 749 distal vein graft anastomoses, were angiographically assessed 11.5 +/- 2 days after surgery and were almost equal in both treatment groups. In half of the patients in each group, active treatment was replaced by placebo after 3 months. Repeat angiography after 1 year (360 +/- 24 days) showed that more new late graft occlusions occurred in patients with only 3 months active medication (either regimen). The incidence of major complications was significantly higher in patients treated with anticoagulants, with minor side-effects more common in the antiplatelet group. Thus, this antiplatelet drug regimen was as effective as standard anticoagulant therapy in the prevention of early and late bypass graft occlusion, but carried a significantly lower risk of severe complications. In addition, as replacement of active treatment by placebo after 3 months resulted in significantly more graft occlusions, antithrombotic treatment should be continued for at least one year after coronary artery bypass graft surgery.

Pharmacology of UK-38485 (dazmegrel), a specific inhibitor of thromboxane A2 synthetase

Thromboxane A2 (TXA2) synthesis in rabbit and human platelet rich plasma (PRP) was inhibited in a dose-dependent manner by UK-38485 (dazmegrel) when the PRP was aggregated with collagen, arachidonic acid and ADP. The level of inhibition was time-dependent. That is, the dose-response curves shifted to lower concentrations with increasing incubation times with UK-38485 prior to addition of aggregation agents. Following bolus intravenous injections of UK-38485 in rabbits, the elimination from serum fitted a 3-exponential curve. The terminal elimination phase had a half-life of 69.8 +/- 3.8 min. Oral treatment of rabbits with UK-38485 for 2 weeks showed that animals with serum concentrations of 0.358 +/- 0.091 microgram/ml of the inhibitor had TXA2 synthesis inhibited in serum by 83.8 +/- 7.1%. This corresponded to animals which were treated with 20 mg/kg/day of the inhibitor.

Trial of low-dose aspirin plus dipyridamole versus anticoagulants for prevention of aortocoronary vein graft occlusion

In a prospective randomised trial, 249 patients who had aortocoronary vein bypass surgery were assigned either to a platelet inhibitory drug regimen or to standard anticoagulant therapy. Treatment was replaced by placebo in half of the patients in each group after 3 months. The platelet inhibitory drug regimen--very low-dose aspirin combined with dipyridamole--was as effective as standard anticoagulant therapy to prevent early and late graft occlusion. Death, myocardial infarction, and severe bleeding occurred significantly more often in patients receiving anticoagulants, whereas mild drug-related gastrointestinal and cerebral side-effects were more common in patients taking platelet inhibitory drugs. Antithrombotic treatment should be continued for at least 1 year after coronary artery bypass graft surgery.

Response of thromboxane B2, malondialdehyde and platelet sensitivity to 3 weeks low-dose aspirin (ASA) in healthy volunteers

To examine the effects of low-dose aspirin thromboxane B2 (TXB2), malondialdehyde (MDA) and platelet sensitivity to prostaglandin I2 (PGI2) have been measured in a total of 18 healthy volunteers. They were randomly assigned to 3 groups, 6 volunteers each, receiving either 1, 10 or 20 mg ASA orally a day for 3 weeks in a double-blind fashion. In order to assess the time course of ASA-induced changes, blood was drawn before, 1 hour and 2, 3, 5, 7, 9, 12, 14, 16 and 21 days after the first drug-intake. Serum-TXB2 was depressed time- and dose-dependently, after 1 mg daily to about 60%, after 10 mg to about 30%, after 20 mg to about 5% of controls. MDA-formation and conversion of exogenously added arachidonic acid (AA) to TXB2 also dropped significantly, (p less than 0.01), the extent depending on the ASA-dosage administered. The drop in MDA- and TXB2-values in the 3 groups correlated with r = 0.98, 0.94, 0.98, respectively. The platelet sensitivity during 20 and 10 mg ASA-administration did not change at all, whereas a significant increase (p less than 0.01) in platelet sensitivity during treatment with 1 mg ASA was observed.

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

The effects of smoking, aspirin ingestion, and sex differences on bleeding times and bleeding time thromboxane B2 and 6-keto-prostaglandin (PG)F1 alpha production were examined. Nonsmoking men produced more thromboxane B2 (3.99 +/- 0.76 ng/ml) than nonsmoking women (2.13 +/- 0.24 ng/ml). Female smokers produced more thromboxane B2 (5.01 +/- 0.97 ng/ml) than nonsmoking women. Twenty-four hours after a single dose of 600 mg aspirin, in vitro production of thromboxane B2 in response to collagen fell by 95%, whereas in vivo production of thromboxane B2 and 6-keto-PGF1 alpha in bleeding time blood fell by 87% and 66%, respectively. Subjects with the lowest absolute levels of thromboxane B2 24 hours after aspirin were also those with the longest postaspirin bleeding times. Recovery of 6-keto-PGF1 alpha production was faster than recovery of thromboxane B2 production, but 6-keto-PGF1 alpha production for most subjects was still below basal 72 hours after aspirin. The influence of two different doses of long-term aspirin (80 mg every other day and 325 mg daily) on the in vivo production of thromboxane B2 and 6-keto-PGF1 alpha was studied in normals and diabetics. After 14 days of 80 mg aspirin every other day, thromboxane B2 and 6-keto-PGF1 alpha production were both substantially inhibited (93% and 78%, respectively). After 14 days of 325 mg aspirin daily, thromboxane B2 production was similarly substantially inhibited (93%), whereas 6-keto-PGF1 alpha was significantly less affected (only 45% inhibition). Study of a second group of five normal subjects confirmed that 6-keto-PGF1 alpha production was significantly inhibited 24 hours after the first dose of 325 mg aspirin but was not significantly less than basal after 14 days of 325 mg aspirin. The results suggest that 325 mg aspirin daily is more antithrombotic compared with 80 mg every other day due to the superior preservation of prostacyclin production.

Aspirin and prevention of myocardial infarction

Determining the cardioprotective effects of aspirin (acetylsalicylic acid) remains a focus for both basic science and clinical investigation. Although other contributors are probably present, the favorable prostacyclin-to-thromboxane ratio induced by low-dose aspirin appears beneficial for reducing cardiovascular mortality associated with unstable angina and myocardial infarction. The precise dosage, frequency and timing of aspirin's administration to reduce the incidence of vaso-occlusive events remains to be determined. This article reviews aspirin's mechanism of action and use for the prevention of myocardial infarction.