Aspirin: A paradoxical effect on bleeding-time

Benefit-Risk Assessment of Fish Oil in Preventing Cardiovascular Disease

Cardiovascular disease (CVD) is a preventable disease, which combines two general processes: chronic vascular inflammation and acute thrombosis. Both are amplified with positive feedback signals by n-6 eicosanoids derived from food-based n-6 highly unsaturated fatty acids (n-6 HUFA). This amplification is lessened by competing actions of n-3 HUFA. Death results from fatal interactions of the vascular wall with platelets and clotting proteins. The benefits of fish oil interventions are confounded by complex details in pharmacokinetics, pharmacodynamics, adverse events, timescale factors, topology, financial incentives and people's sense of cause and effect. Two basic aspects of n-3 HUFA that are overlooked in CVD dynamics are saturable, hyperbolic responses of the enzymes continually supplying n-6 HUFA and hard-to-control positive feedback receptor signals by excessive n-6 HUFA-based mediators. Multiple feedback loops in inflammation and thrombosis have diverse mediators, and reducing one mediator that occurs above its rate-limiting levels may not reduce the pathophysiology. Clinicians have developed some successful interventions that decrease CVD deaths in the form of secondary prevention. However, the current high CVD prevalence in the USA remains unchanged, and successful primary prevention of CVD remains uncertain. This review weighs the available evidence to help clinicians, the biomedical community and the public put the use of fish oil supplements into a balanced perspective.

Interrelationships between prostacyclin and thromboxane A2

Prostacyclin is a product of arachidonic acid metabolism generated by the vessel wall of all mammalian species studied including man. Prostacyclin is a potent vasodilator and the most potent inhibitor of platelet aggregation so far described. It inhibits platelet aggregation through stimulation of adenylate cyclase leading to an increase in cyclic AMP in the platelets. The enzyme which synthesizes prostacyclin is mainly localized in the endothelial layer of the vascular wall. Prostacyclin can also be a circulating hormone constantly released by the pulmonary circulation. On the basis of these observations we proposed that platelet aggregability in vivo is controlled via a prostacyclin mechanism. In contrast to the vessel wall, in blood platelets arachidonic acid is converted by the enzyme thromboxane synthetase to a potent vasoconstrictor and proaggregating substance, thromboxane A2. Therefore arachidonic acid is metabolized in the vessel wall and the platelets to potent substances with opposing biological activities. The balance between the activities of these substances is important in the homeostatic interaction of the platelets and the vessel wall. The different ways of interfering with this balance and its impact in the development of thrombosis and atherosclerosis are discussed. The balance between thromboxane A2 and prostacyclin might be important in the control of the pulmonary circulation. This possibility is discussed in the light of the present evidence.

Adventures in vascular biology: a tale of two mediators

I would like to thank the Royal Society for inviting me to deliver the Croonian Lecture. In so doing, the Society is adding my name to a list of very distinguished scientists who, since 1738, have preceded me in this task. This is, indeed, a great honour. For most of my research career my main interest has been the understanding of the normal functioning of the blood vessel wall and the way this is affected in pathology. During this time, our knowledge of these subjects has grown to such an extent that many people now believe that the conquering of vascular disease is a real possibility in the foreseeable future. My lecture concerns the discovery of two substances, prostacyclin and nitric oxide. I would like to describe the moments of insight and some of the critical experiments that contributed significantly to the uncovering of their roles in vascular biology. The process was often adventurous, hence the title of this lecture. It is the excitement of the adventure that I would like to convey in the text that follows.

Increased platelet sensitivity to collagen in individuals resistant to low-dose aspirin

BACKGROUND AND PURPOSE

The purpose of this study was to assess individual differences in the pharmacological effects of acetylsalicylic acid (ASA) on bleeding time as measured by in vitro platelet aggregation and to examine the consistency of responses over time.

METHODS

We measured template IIR bleeding time and platelet aggregation in 8 healthy male volunteers before and 2 hours after ingestion of 324 mg of ASA. An individual was considered a nonresponder if his post-ASA bleeding time was not 2 SDs above his baseline bleeding time, where SD was estimated from the baseline bleeding times of the 8 volunteers. The same experiment was done after a 30-month interval.

RESULTS

Five volunteers were identified as ASA responders, and 3 were identified as nonresponders. Bleeding time before and after ingestion of ASA was 408+/-121 seconds (mean+/-SD) and 720+/-225 seconds, respectively, in ASA responders and 330+/-30 seconds and 330+/-52 seconds, respectively, in ASA nonresponders. The mean ED(50) for collagen-induced platelet aggregation, that is, the mean concentration of collagen that caused a response at 50% of maximum, was 0.91 microg/mL (95% CI, 0.73 to 1. 14) in ASA responders and 0.48 microg/mL (95% CI, 0.38 to 0.60) in nonresponders. When optimum concentrations of collagen, ie, concentrations that yielded 90% maximum aggregation, were used as stimuli, the mean IC(50) for ASA, that is, the mean concentration that yielded 50% inhibition, was 322.5 micromol/L (95% CI, 264.8 to 392.6) in ASA responders and 336.1 micromol/L (95% CI, 261.0 to 432. 8) in nonresponders. The variability in individual responsiveness in the second experiment remained consistent with that in the first experiment.

CONCLUSIONS

ASA resistance may be caused by an increased sensitivity of platelets to collagen. A platelet aggregation study specific for collagen dose response may be useful for strict selection of ASA responders for low-dose ASA therapy and for identifying ASA nonresponders for high-dose ASA therapy.

Eleven myths of dentoalveolar surgery

Through the years, dentists who perform dentoalveolar surgery have perpetuated many myths and other unproven beliefs from one generation to another. Sometimes, these beliefs originated in older textbooks, while others were given birth by mentors sharing anecdotal experiences with their students. Even today, many of these scientifically unsupported statements are perpetuated in surgical textbooks and in continuing education forums and are passed on to students in dental schools. In today's evolving environment of evidence-based medicine and dentistry, these anecdotal observations do not withstand scrutiny. The purpose of this article is to review the more common surgical myths and to test their validity against scientific evidence.

Aspirin effects on colonic mucosal bleeding: implications for colonic biopsy and polypectomy

BACKGROUND

Many patients who require endoscopic treatments such as biopsy and polypectomy are given antiplatelet agents reluctantly. We have studied the effects of aspirin on colonic mucosal hemostasis.

METHODS AND PATIENTS

We developed a new endoscopic device to make a standard incision (7-mm length) on the colonic mucosa to study colon bleeding time. We measured the colon bleeding time of normal colonic mucosa in 47 cases. The colon bleeding time and skin bleeding time (Simplate method) were measured before and one hour after aspirin ingestion (990 mg) in ten healthy subjects.

RESULTS

The bleeding time of normal colonic mucosa was 156 +/- 71 (mean +/- standard deviation) seconds. Significant prolongation was noted in both skin bleeding time (357 +/- 192 vs. 477 +/- 183 seconds; P < 0.05) and colon bleeding time (155 +/- 47 vs. 244 +/- 169 seconds; P < 0.05) after aspirin ingestion.

CONCLUSIONS

Bleeding time was measured safely under direct colonoscopic visualization. Aspirin prolonged the colon bleeding time. Therefore, endoscopists should be aware of a risk of abnormal bleeding after endoscopic biopsy and polypectomy in patients with aspirin use. Two days were necessary for colon bleeding time to become normalized in patients with aspirin use.

Blood loss in long-term aspirin users undergoing transurethral prostatectomy

As aspirin is now widely used for preventing recurrence of cardiovascular and cerebrovascular disorders, many men selected for transurethral resection of the prostate (TURP) are aspirin users. The previous indication for aspirin as a preoperatively administered antithrombotic agent is no longer common. In this study we investigated the blood loss in long-term aspirin users (250 mg/day) undergoing TURP. The mean blood loss in the 40 aspirin users was 358 (range 50-1550) ml, and in a control group of 42 men it was 478 (40-2400) ml. When mean blood loss was correlated to operating time and prostatic weight, the intergroup difference was not significant. In the late postoperative period two aspirin-treated men had bleeding with tamponade of the urinary bladder requiring emptying in the operating room. As blood loss was not enhanced by aspirin use, avoidance of aspirin before TURP appears to be unnecessary.

Reversible prolonged skin bleeding time in acute gastrointestinal bleeding presumed due to NSAIDs

The purpose of this research was to look for a possible mechanism whereby NSAIDs, and particularly ASA, might cause gastrointestinal bleeding. A total of 34 hospitalized GI bleeders and 29 age- and sex-matched controls were studied. Skin bleeding time (SBT) was measured within 6 h of coming to hospital and before any blood products were given. All patients and controls were questioned regarding current NSAID use. This history was supplemented by estimation of serum salicylate and of platelet cyclooxygenase activity to detect unreported current aspirin (ASA) use. Various aspects of platelet function were also tested by lumiaggregation in 28 controls and, after recovery, in 27 of the bleeders. Of 34 bleeders, 26 bled from the upper GI tract, (13 from peptic ulcer) and eight from the lower GI tract, 30 (88%) had a current intake of NSAIDs and of these 22 (73%) used ASA, some in combination with other NSAIDs, whereas 12 of 29 controls were using NSAID's, 11 of which were ASA. SBT in the bleeders was 9.0 +/- 1.02 min versus 4.8 +/- 0.42 min in the controls (p < 0.001). SBT measured 6.6 days later in 28 bleeders was 4.7 +/- 0.22 min (p < 0.0006), and of those tested after recovery all but one had fallen to 6.5 min or less. None had any residual constitutional platelet abnormalities as tested by lumiaggregation. By logistic regression, NSAID intake was strongly associated with prolonged SBT to > 6 min (odds ratio [OR], 16.7; p < 0.0002), whereas NSAID intake (OR 14.6; p < 0.0003) and SBT > 6 min (OR 1.8; p < 0.005) contributed to a bleeding outcome. Almost 90% of GI bleeders had recently consumed NSAIDs, mostly ASA, on an average 15 h before onset of bleeding. Although most of the nonbleeders who had used NSAIDs did not have a prolonged SBT, most of the bleeders who used NSAIDs had an abnormal elevation of SBT, suggesting a possible mechanism for GI bleeding. Retesting approximately 7 days after recovery from bleeding showed normalization of the SBT, indicating that the defect was transient and spontaneously reversible.

Aspirin, a silent risk factor in urology

Aspirin is a widely used drug for its analgetic, antiinflamatory and antipyretic effects as well as for prophylactic effect in cardiovascular diseases. However, an increased number of operative hemorrhagic complications in patients on daily aspirin have been reported, an adverse effect highly relevant in urology. In this review the normal hemostatic mechanism and the chief pharmacological effect of aspirin on hemostasis is described. The literature is reviewed for hemorrhagic complications to aspirin in urology. Few reports indicate that aspirin increases bleeding and need for transfusion following prostatectomy, but no placebo-controlled clinical trials with large patient groups have been carried out. Following prostate biopsy and extracorporeal shock wave lithotripsy aspirin-induced hemorrhagic complications have been reported. Cessation of aspirin ingestion one week prior to invasive urologic procedures and correction of bleeding complications with desmopressin, platelet concentration or fresh whole blood is described.

Aspirin therapy: optimized platelet inhibition with different loading and maintenance doses

Inhibition of cyclooxygenase by aspirin has been shown to be beneficial in clinical situations such as acute myocardial infarction or unstable angina. The precise effect of various doses of aspirin on acute and long-term inhibition of platelet aggregation and thromboxane synthesis remains unclear. In this study we evaluated the effect of oral aspirin (0, 40, 100, 300, or 500 mg) as the initial loading dose in combination with different maintenance doses of aspirin (0, 40, or 100 mg/day) for 14 days on platelet function in healthy men. Bleeding time 2 or 24 hours after the first aspirin administration was significantly increased for 300 and 500 mg aspirin (p < 0.01). Two hours after the first administration of 100, 300, and 500 mg aspirin, a significant inhibition of collagen-induced platelet aggregation (ED50 collagen: from 3 +/- 1 to 17 +/- 2, 24 +/- 3, 22 +/- 3 micrograms/ml, respectively) was seen. At the same time serum thromboxane B2 synthesis was inhibited by more than 99% with 300 and 500 mg aspirin. At the end of the 14-day observation period, bleeding time was significantly prolonged for the different combinations of aspirin doses compared with initial values (p < 0.01). Collagen-induced platelet aggregation and serum thromboxane B2 synthesis were significantly inhibited for all aspirin combinations tested at 14 days (p < 0.05). The 40/40 mg aspirin combination was less effective, because it reached its maximal effect very late at day 7 of the observation period compared with the other combinations.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of nonsteroidal antiinflammatory drugs on platelet function and systemic hemostasis

Aspirin and nonaspirin nonsteroidal antiinflammatory drugs (NSAIDs) inhibit platelet cyclooxygenase, thereby blocking the formation of thromboxane A2. These drugs produce a systemic bleeding tendency by impairing thromboxane-dependent platelet aggregation and consequently prolonging the bleeding time. Aspirin exerts these effects by irreversibly blocking cyclooxygenase and, therefore, its actions persist for the circulating lifetime of the platelet. Nonaspirin NSAIDs inhibit cyclooxygenase reversibly and, therefore, the duration of their action depends on specific drug dose, serum level, and half-life. The clinical risks of bleeding with aspirin or nonaspirin NSAIDs are enhanced by the concomitant use of alcohol or anticoagulants and by associated conditions, including advanced age, liver disease, and other coexisting coagulopathies.

Low-dose preoperative aspirin therapy, postoperative blood loss, and transfusion requirements

The effects of three low-dose regimens of preoperative aspirin therapy on postoperative blood loss, transfusion requirements, and length of hospital stay were recorded in a prospective cohort study of 202 patients undergoing elective coronary artery bypass grafting. One hundred one patients had been prescribed daily aspirin by the referring cardiologist (44 at 75 mg, 28 at 150 mg, and 29 at 300 mg); the remaining 101 patients who had not been prescribed aspirin acted as a control group. A median postoperative blood loss of 870 mL in the control group was increased by 280 mL in the 75-mg aspirin group (p less than 0.001), by 490 mL in the 150-mg aspirin group (p less than 0.001), and by 230 mL in the 300-mg aspirin group (p = 0.03). The median requirement for blood transfusion of 2 U red blood cell concentrates in the control group was increased by 2 U in the 75-mg aspirin group (p less than 0.001), 2 U in the 150-mg aspirin group (p less than 0.001), and 1 U in the 300-mg aspirin group (p = 0.05). Hemostatic "packs" (fresh frozen plasma, platelets, and cryoprecipitate) were required in 20 patients in the aspirin groups as compared with 5 in the control group (p less than 0.01 by chi 2 test). The mean postoperative hospital stay was 8 days for all groups. Regular daily low-dose aspirin therapy produces significant increases in postoperative blood loss, resulting in a substantial increase in blood transfusion and hemostatic pack requirements, but does not prolong postoperative hospital stay.

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.

Diminished platelet residence time on active human atherosclerotic lesions in-vivo--evidence for an optimal dose of aspirin?

Although aspirin is an old drug, its optimal dose for the treatment of human atherosclerosis has not been finally proven. Various in-vitro and ex-vivo platelet function tests revealed a dose range from 1 to 3000 mg as being optimal. It was thus the goal to examine its in-vivo efficacy in human suffering from peripheral vascular disease in 7 different doses ranging from 1 mg to 1000 mg a day. All these patients have been treated for 3 months. Platelet half-life and platelet uptake ratio show an in part significant improvement being most pronounced at the daily doses of 20 and 1000 mg respectively. No change occurs in the placebo treated controls. These findings indicate, that 20 or 1000 mg aspirin taken daily per os, are superior to the other doses examined concerning the in-vivo platelet function (as measured by platelet half-life) and rendering the arterial surface less thrombogenic (as reflected by platelet uptake ratio-measurements).

Effects of paracetamol and acetylsalicylic acid on the post-operative course after experimental orthopaedic surgery in dogs

In placebo-controlled cross-over trials in dogs, two 'identical' operations were performed on the forelimbs of each animal with an interval of 28 days, to evaluate how daily doses of 1.5 g paracetamol, 1.5 g acetylsalicylic acid (ASA) and 0.5 g ASA might modulate an acute post-operative inflammatory reaction. On the third post-operative day the reductions in swelling compared with placebo averaged 33% with 1.5 g paracetamol (P = 0.02), 24% with 1.5 g ASA (P = 0.03) and 15% with 0.5 g ASA (P = 0.18); while the reductions in pain estimates averaged 47% with 1.5 g paracetamol (P = 0.01), 32% with 1.5 g ASA (P = 0.07) and 28% with 0.5 g ASA (P = 0.21). There were no clinical signs of adverse drug effects, such as vomiting, haematochezia, cyanosis or depression. The results disagree with the traditional view that paracetamol has little or no anti-inflammatory effect, and demonstrate that paracetamol may reduce an acute inflammatory reaction, at least as efficiently as ASA. The potential pro-inflammatory effect of ASA in low doses is discussed. It is concluded that paracetamol appears to be a valuable drug against post-operative or post-traumatic sequelae in the veterinary as well as in the human clinic.

A study of bleeding time in 120 long-term aspirin trial patients

The bleeding time was measured in 120 patients participating in a longterm randomised double-blind trial of aspirin in thromboembolic prophylaxis (UK-TIA aspirin Study). In 70 patients taking aspirin 300 mg or 1,200 mg daily for a mean duration of 35 months the bleeding time averaged 228 seconds. In comparison with 30 patients randomised to placebo and not taking aspirin whose bleeding time averaged 217 seconds, there was no significant difference. Stratification of bleeding time estimation by duration of treatment suggested no significant trend in either placebo or aspirin groups over several years. These results suggest that the longterm trials of aspirin should be looked at again from the point of view of efficacy of treatment by time from randomisation.

Improving micrograft patency

To help clarify many of the controversial issues affecting early microvascular graft patency, a series of experiments was performed comparing the relative importance of graft material used alone and in conjunction with antiplatelet agents. Using a rat carotid model employing 1 cm micrografts with 1 mm luminal diameter, this study demonstrated that 1) untreated 1 mm polytetrafluoroethylene (PTFE) and human umbilical vein (HUV) micrografts have unacceptably low patency rates; 2) treatment with the antiplatelet agents indomethacin, ibuprofen, and aspirin significantly improved micrograft patency; 3) differences in patency among the three agents were not significant; and 4) PTFE had higher patency rates than HUV, although this difference did not achieve significance.

Platelet deposition on human atherosclerotic lesions is decreased by low-dose aspirin in combination with dipyridamole

Eighteen patients with ischaemic peripheral vascular disease were treated for a 5-week period with either 20 mg aspirin daily, 75 mg dipyridamole three times daily or a combination of these two treatments. Before and after 4 weeks' treatment autologous platelet labelling with 111In was carried out and sites of active vascular platelet uptake monitored, and platelet half-life measured. Neither aspirin nor dipyridamole alone had any effect on platelet uptake or on platelet half-life. The combination of aspirin and dipyridamole resulted in a significant decrease in platelet uptake and a nonsignificant trend towards prolongation of platelet half-life. These findings suggest that this combined therapy may be of benefit in the treatment of atherosclerosis in man.

Plasma drug and antiplatelet profiles of the original acetylsalicylic acid preparations used in the AMIS, PARIS and German-Austrian trials for secondary prevention of myocardial infarction

In a cross-over study 6 healthy male subjects were given for 9 days the acetylsalicylic acid (ASA) preparations used in the Aspirin Myocardial Infarction Study (AMIS), Persantine-Aspirin Reinfarction Study (PARIS) and German-Austrian secondary heart attack prevention trials, exactly according to the original study protocols. Plasma concentrations of ASA and its main metabolites salicylic acid (SA) and salicyluric acid (SUA), as well as platelet function (collagen-induced platelet aggregation; tissue extract-induced change in platelet shape) were studied repeatedly on the first day of each medication period and were again examined on the sixth and ninth days. Differences in the plasma concentrations of ASA and its metabolites were found only on the first day, probably as a result of different absorption rates. Collagen-induced platelet aggregation was more rapidly inhibited the faster the preparation was absorbed. Each ASA preparation inhibited tissue extract-induced platelet shape change from the first dose, although statistically significant inhibition was seen only with the AMIS preparation. It is concluded that differences in the antithrombotic efficiency of ASA cannot be explained by differences in the pharmacokinetic and antiplatelet profiles of the various ASA preparations tested.

The effect of acetylsalicylic acid on menstrual blood loss in women with IUDs

Fifty-three volunteer women using Copper T 220C IUDs, complaining of increased menstrual bleeding, received per os 1 g, three times a day, of acetylsalicylic acid, for 5 days, during their menstrual periods. Menstrual bleeding for each patient was measured at least once before treatment. Bleeding estimates were also performed from the second to the fifth treatment cycle. From the 53 women admitted to the study, only 13 subjects (24.7%) had pre-treatment menstrual bleeding of more than 80 ml; 40 subjects had less than 80 ml. The group with hypermenorrhea had slightly decreased (not significant) the amount of menstrual blood loss with acetylsalicylic acid intake. On the other hand, 67.1% of women with bleeding less than 80 ml observed a significant increase in menstrual blood loss.

Aspirin prolongs bleeding time in uremia by a mechanism distinct from platelet cyclooxygenase inhibition

We reported that aspirin (ASA) abnormally prolongs bleeding time (BT) in uremia. The present study was designed to investigate whether the abnormally prolonged post-ASA BT in uremia is due to different ASA pharmacokinetics and bioavailability that might be a consequence of uremic condition, platelet cyclooxygenase is peculiarly sensitive to ASA in uremia, and ASA affects primary hemostasis in uremia by a mechanism independent of cyclooxygenase inhibition. Our results showed that in patients with uremia, but not in normal subjects, ASA markedly prolongs the BT. This effect is transient and depends on the presence of ASA in the blood. The observed differences in ASA kinetic parameters are not an explanation of the exaggerated effect of ASA on primary hemostasis in uremia. The sensitivity of platelet cyclooxygenase to ASA inhibition is comparable in uremics and in normal subjects. The temporal dissociation between ASA-induced prolongation of BT and the effect on platelet thromboxane A2 generation suggests that ASA inhibits platelet function in uremia by a mechanism distinct from cyclooxygenase blocking. This possibility is strengthened by the observation that ibuprofen at a dose that fully inhibits platelet cyclooxygenase activity does not significantly prolong BT.

Aspirin and other antiplatelet drugs in the prophylaxis of thrombosis

Aspirin is of proven value as an antithrombotic drug. In unstable angina it reduces the risk of death and myocardial infarction by half. After a myocardial infarction it reduces the risk of death by about 10% and of coronary incidence (coronary death or definite myocardial infarction) by about 25%. These effects appear to be additive with those of beta-blocking drugs. Aspirin also reduces the risk of occlusion of aortocoronary saphenous vein grafts by about half. In transient cerebral ischaemia, aspirin may reduce the risk of stroke and death by 50%. In most clinical trials to date the daily dose of aspirin ranges from 325 mg to 1400 mg. Interest in very low doses of aspirin (less than 60 mg daily) is considerable but has yet to be translated into proven clinical benefit. Dipyridamole has not been shown to be effective as an antithrombotic when used alone. Its antiplatelet action ex vivo may be enhanced by combination with aspirin but clinical trials have shown relatively little advantage of the combination over aspirin alone. Sulphinpyrazone has not become established as a first line antithrombotic drug. Epoprostenol is useful in extracorporeal circulations to prevent platelet consumption and possibly in severe inoperable peripheral vascular disease.

Hemostatic mechanisms, independent of platelet aggregation, arrest gastric mucosal bleeding

Platelet adhesion, aggregation, and subsequent plug formation play a major role in the control of cutaneous and vascular hemostasis. Little is known, however, about the hemostatic processes in gastric mucosal tissue. A method for evaluating bleeding from a standard incision in the gastric mucosa of the rat, rabbit, and dog has therefore been developed. By using pharmacological agents that interfere with platelet aggregation and blood coagulation, the mechanism of gastric hemostasis has been compared to that in the vasculature, using the rat mesenteric artery. Intravenous infusion of prostacyclin (0.5 micrograms X kg-1 X min-1), which inhibits platelet aggregation directly, or administration of the thromboxane synthase inhibitor 1-benzylimidazole (50 mg X kg-1) significantly prolonged bleeding in the mesenteric artery yet failed to alter gastric mucosal bleeding. In contrast, a low dose of heparin (100 units X kg-1), which interferes with the clotting process, had no effect on mesenteric bleeding but substantially prolonged bleeding from the gastric mucosa. These findings suggest that, unlike in the skin or vasculature, platelet aggregation plays a minimal role in the initial hemostatic events in the gastric mucosa and that the arrest of gastric hemorrhage is brought about largely by processes primarily involving the coagulation system.

The effects of different doses of some acetylsalicylic acid formulations on platelet function and bleeding times in healthy subjects

In an attempt to find the most appropriate dose and formulation(s) of acetylsalicylic acid (ASA) for thrombosis prophylaxis, healthy volunteers were given doses of ASA for 1 wk daily ranging from 50 to 3900 mg as either Aspro-Clear (soluble), Astrix (enteric coated pellets) or Ecotrin (enteric coated tablets). Platelet function and bleeding times were monitored. All doses of ASA significantly inhibited platelet function (p less than 0.05) and increased bleeding times (p less than 0.05) relative to control values. Irrespective of the formulation, maximum increases in bleeding time and platelet dysfunction were obtained with daily doses of about 100 mg, and no further changes were observed with higher doses.

[Importance of prostaglandins for the in vitro adhesiveness and in vivo margination of neutrophilic granulocytes]

The (patho-)physiological role of prostaglandins and thromboxanes on granulocyte function remains controversial. In a combined in vitro and in vivo study, we analyzed the influence of these arachidonic acid metabolites on granulocyte adhesion and margination. A dichotomous dose-dependent effect on epinephrine-induced granulocyte demargination parallels the paradoxical effect of low (0.5 g)- and high (4 g)-dose aspirin on bleeding time. These observations suggest that prostacyclin acts as a modulator for low-affinity adhesion and margination of granulocytes. With respect to the induction of high-affinity adhesion, which is reflected in a state of hypermargination in vivo and accompanied by potentially cytotoxic cell activation, prostaglandins in general and prostacyclin in particular are without effect when such activation is induced, either by endotoxin, by formylated chemotactic peptide, or by activated complement.

Platelets, carotids, and coronaries. Critique on antithrombotic role of antiplatelet agents, exercise, and certain diets

"Antiplatelet" drugs and certain life styles seem to have an "antithrombotic" effect that may help protect against stroke and heart attack. This review of the experience with aspirin, dipyridamole, and sulfinpyrazone offers new interpretations of some of the major clinical trials, suggests guidelines for use of antiplatelet drugs, and integrates novel observations on diet and exercise into the "thromboxane-prostacyclin balance" hypothesis. It is argued that the Canadian stroke study showed that aspirin protects men with transient ischemic attacks from coronary death as well as from stroke, that type II errors may have been made in some clinical trials, that aspirin protects women as well as men, that aspirin benefits patients who have had a heart attack, that the effect of aspirin in angina varies with the type of angina, that the dose of aspirin used may not be critical, that guidelines for use of dipyridamole and sulfinpyrazone are still inconclusive, and that exercise and fish oil supplements may be "antithrombotic."

Improved aortocoronary bypass patency by low-dose aspirin (100 mg daily). Effects on platelet aggregation and thromboxane formation

Prevention of aortocoronary bypass occlusion by aspirin (ASA, 1 X 100 mg per day) was studied in a prospective double-blind trial of 83 patients. 60 (72%) were randomly allocated to ASA or placebo starting 24 h after operation. 90% of grafts in the ASA group and 68% in the placebo group were patent at four months. At least one anastomosis was occluded in 62% of the patients on placebo and in 27% of those on aspirin. Ventricular arrhythmias increased after surgery in more patients on placebo (12/18) than in patients on ASA (5/17). Platelet thromboxane formation on collagen tested before operation was significantly higher in patients in whom bypass occlusion developed (occlusion: 40 +/- 19, no occlusion: 25 +/- 13 ng/ml). A 100 mg dose of ASA per day effectively blocked platelet thromboxane formation and thromboxane-supported aggregation on collagen and was safe in the postoperative phase. No side effects were reported throughout the trial. The reduced toxicity with full efficacy favours a low and infrequent dosage of aspirin.

Low-dose acetylsalicylic acid (100 mg/day) after aortocoronary bypass surgery: a placebo-controlled trial

The effect of low-dose acetylsalicylic acid (100 mg/day) upon bypass patency-rate and clinical course after aortocoronary bypass surgery was investigated in a randomized, placebo-controlled clinical trial. Sixty patients with 143 distal anastomoses of bypasses were randomized, 46 underwent repeat angiography after 4 months. Using the intention to treat-strategy, treatment was superior to placebo as judged by bypass patency rate and occurrence of cardiovascular complications or death. Counting the six drop-outs as failures, only nine of the 31 patients of the placebo group, but 16 of the 29 patients of the treatment group were considered successes (P less than 0.04). Eighteen patients in the placebo group and eight patients of the treatment group received beta-adrenoceptor blockers postoperatively, suggesting again a favourable effect of the treatment. Adverse drug reactions were very rare and minor. Supported by pathophysiological insights and positive trends in similar trials, the positive result justifies the recommendation of prescribing 100 mg of acetylsalicylic acid once daily to all patients without contraindications after aortocoronary bypass surgery. The positive result of this trial warrants further clinical trials of low-dose acetylsalicylic acid for other indications in arterial diseases.

The effects of acetylsalicylic acid on swelling, pain and other events after surgery

In a double-blind crossover study acetylsalicylic acid (ASA) in low (2 g daily) or high (4 g daily) dosage was tested against placebo in two groups of 20 patients who each underwent identical oral surgical procedures on two separate occasions. Medication started 3 h post-operatively and continued for 3 days. ASA in low dosage tended to increase the postoperative swelling, which on day 3 and 6 averaged 109 and 133% respectively of that with placebo (P greater than 0.05). In contrast, ASA in high dosage tended to reduce the swelling, which on day 3 and 6 averaged 85 and 90% respectively of that with placebo (P greater than 0.05). Comparison of the two groups receiving ASA in low or high dosage revealed a significant difference in their effect on swelling; day 3, P = 0.05. Pain was significantly reduced with ASA, but there appeared to be no greater analgesic effect with 4 g ASA daily than with 2 g ASA daily. There was, however, a substantial increase in the number of patients who reported tinnitus after taking 4 g ASA daily. Subjective postoperative bleeding scores were significantly increased with 2 g ASA daily, but not with 4 g ASA daily. None of the dosages of ASA appeared to reduce the swelling as efficiently, give better pain relief, or as high preference scores as previously obtained in studies when paracetamol and short term glucocorticoid administration were tested against placebo in this model.

Prolongation of bleeding time and inhibition of platelet aggregation by low-dose acetylsalicylic acid in patients with cerebrovascular disease

Platelet aggregation and bleeding time was measured in 43 cerebrovascular patients participating in a controlled double-blind study of low-dose acetylsalicylic acid. In 19 patients with satisfactory inhibition of the platelet aggregation obtained by 50 to 70 mg acetylsalicylic acid per day the bleeding time averaged 11.2 minutes in contrast to 7.0 minutes in the placebo group, p less than 0.001. This study confirms our previous findings of platelet inhibition by low-dose acetylsalicylic acid in patients with cerebrovascular disease. The prolongation of the bleeding time demonstrates that we are dealing not merely with an in vitro phenomenon but with a significant in vivo effect. The study provides the rationale for clinical evaluations of low-dose acetylsalicylic acid in stroke prophylaxis.

[Effects of acetylsalicylic acid on partial functions of human thrombocytes are not inhibited in vivo by salicylic acid]

Acetylsalicylic acid inhibits platelet function. In plasma acetylsalicylic acid is rapidly deacetylated to salicylic acid which is slowly eliminated and has no direct inhibitory effects on platelet function. However, salicylic acid prevents the inhibition by acetylsalicylic acid of collagen-induced aggregation of human thrombocytes in vitro. It was suggested that salicylic acid might inhibit the antiplatelet effects of acetylsalicylic acid in vivo and therefore low-dose acetylsalicylic acid would be more effective for antithrombotic therapy. A 500-mg tablet of acetylsalicylic acid applied 90 min after oral administration of 500 mg salicylic acid to six healthy male volunteers led to the same inhibition of collagen-induced platelet aggregation and tissue-extract-induced platelet stimulation as 500 mg acetylsalicylic acid alone. These results cannot give additional support to the recommendation of low-dose acetylsalicylic acid in the prevention of thromboembolic disease.

Sodium salicylate interferes with the inhibitory effects of aspirin and indomethacin on human platelets

The interference of sodium salicylate with the effects of acetylsalicylic acid (ASA, aspirin) and indomethacin on arachidonic acid-induced platelet aggregation and thromboxane formation was studied in human platelet rich plasma. ASA and indomethacin suppressed both aggregation and the concomitant formation of thromboxane B2 whereas sodium salicylate alone had no significant effect on these parameters of platelet function. It did, however, partially prevent the inhibitory effects of ASA and indomethacin on platelet aggregation when it was added to platelet rich plasma before ASA or indomethacin. The inhibition of thromboxane formation by indomethacin was also prevented by sodium salicylate. When sodium salicylate was added to platelet rich plasma after ASA or indomethacin it did not modify the effects of these drugs. The present study indicates that sodium salicylate interferes with the effects of ASA and indomethacin on human platelet cyclo-oxygenase in vitro.

Effects of acetylsalicylic acid and dietary intervention on primary hemostasis

There is evidence that pathological aggregation of platelets in atherosclerotic arteries is initiated by hemorrhage through fissures in atheromatous plaques. Bleeding time determination reflects in vivo the physiologic function of platelets in their aggregation in injured vessels and can be used as a relevant model for primary hemostasis in investigations with antithrombotic aims. Acetylsalicylic acid is known to cause prolongation of bleeding time by inhibiting prostaglandin biosynthesis. Recent experiments have shown that dietary supplementation with omega-3 polyunsaturated fatty acids results in prolongation of bleeding time and decreased platelet aggregability. This paper is mainly concerned with the effect of different doses of aspirin (3.5 mg/kg, 5 mg/kg, and 10 mg/kg), and fish diets rich in omega-3 polyunsaturated fatty acids, on bleeding time and platelet aggregation. The effects of aspirin separately, as well as aspirin administration during dietary intervention, will be described. Administration of all three dose levels of aspirin prolonged bleeding time significantly (p less than 0.001). The effect of aspirin on bleeding time was dose-dependent and an optimum interval was found. A fish diet, rich in omega-3 polyunsaturated fatty acids, causes bleeding time prolongation and decreased platelet aggregability similar to those caused by aspirin. Aspirin taken during this diet prolonged bleeding time by more than the sum of the increases in bleeding time caused by aspirin and the diet with omega-3 polyunsaturated fatty acids, separately, but the synergism was not significantly more than additive. These observations suggest that fish diets affect primary hemostasis by mechanisms different from those of aspirin. Dietary intervention may therefore enhance the antithrombotic effects of aspirin.

The antithrombotic effect of aspirin and dipyridamole in relation to prostaglandin synthesis

The antithrombotic effect of aspirin (ASA) and dipyridamole (DIP) was evaluated in rabbits in which platelet thromboxane A2 (TXA2) and arterial prostacyclin (PGI2) were measured. An intracarotid cannula thrombosis model previously shown to be sensitive to antiplatelet agents was used. Prostaglandins were determined by radioimmunoassays for thromboxane B2 (TXB2) and 6-keto-prostaglandin PGF1 alpha, the stable metabolites of TXA2 and PGI2. In the aspirin-treated animals, reduction in thrombosis was seen only in rabbits which received a low-dose (1-2 mg/kg), and was related to a selective suppression of platelet TXA2. In contrast, higher doses of ASA (10 or 100 mg/kg), which suppressed both TXA2 and PGI2, were not associated with thrombus inhibition. DIP alone had a lesser antithrombotic effect which was augmented by low-dose ASA but not by high-dose ASA. It is concluded that 1) the antithrombotic effect of ASA in this animal model is dependent on selective TXA2 suppression; 2) ASA has no antithrombotic properties beyond its inhibition of prostaglandin synthesis by platelets; 3) selective suppression of TXA2 in vivo can be achieved in rabbits by a single dose of ASA but only over a narrow dose-range; 4) DIP may have an antithrombotic effect additive to that of low-dose ASA; 5) measurement of serum TXB2 may be used to determine the minimal ASA dose necessary to suppress TXA2 and therefore be most likely to spare PGI2.

Plasma levels of acetylsalicylic acid and salicylic acid after oral ingestion of plain and buffered acetylsalicylic acid in relation to bleeding time and thrombocyte function

Buffered acetylsalicylic acid (Alka Seltzer, B-ASA) and plain aspirin (P-ASA) tablets were compared as to their effects on bleeding time and platelet function in eight healthy male volunteers. Two doses (500 and 1000 mg) of each preparation were investigated in a cross-over design, each volunteer being his own control in each dose group (n=4). Both preparations disturbed platelet aggregation to the same extent. Bleeding time increased after both preparations, though significantly more after the buffered preparation than after plain acetylsalicylic acid, irrespective of the dosage. The 1000 mg dose prolonged bleeding time significantly more than the 500 mg dose, irrespective of the preparation. Kinetic analysis showed that B-ASA gave higher peak plasma levels of acetylsalicylic acid (ASA) and accordingly salicylic acid peak levels were also higher after the buffered preparation. It is concluded that B-ASA in equi-analgesic doses prolongs bleeding time more than the plain preparation. Since it is less agressive on the gastro-intestinal mucosa, its use may be advantageous in situations where acetylsalicylic acid induced loss of platelet aggregation is desired. However, the risk of prolonged bleeding--e.g. after tooth extractions--is probably higher after the buffered preparation.