The effect of salicylates on the hemostatic properties of platelets in man

Aspirin treatment reduces platelet resistance to deformation

The present investigation has evaluated the influence of aspirin, its constituents, and other nonsteroidal anti-inflammatory agents on the resistance of human platelets to aspiration into micropipettes. Aspirin increased the length of platelet extensions into the micropipette over the entire negative tension range of 0.04 to 0.40 dynes/cm after exposure to the drug in vitro or after ingestion of the agent. Other cyclooxygenase inhibitors, ibuprofen and indomethacin, did not increase platelet deformability. The influence of aspirin was mimicked to some degree by high concentrations of salicylic acid, but acetylation of platelets with acetic anhydride had little influence on platelet deformability. Incubation of platelets with both salicylic acid and acetic anhydride had no more effect than salicylic acid alone. Benzoic acid, chemically similar to salicylic acid, had a minimal effect. The studies demonstrate that aspirin makes platelets more deformable, while components of the drug or other nonsteroidal antiinflammatory agents and cyclooxygenase inhibitors do not have the same influence on resistance to deformation.

Platelet aggregation and thromboxane release induced by arachidonic acid, collagen, ADP and platelet-activating factor following low dose acetylsalicylic acid in man

The present study was undertaken in order to characterize the dose-dependent nature of acetylsalicylic acid (ASA) on platelet aggregation and plasma thromboxane B2 (TXB2) release in healthy volunteers. Volunteers received either 25, 50, 100 or 500 mg daily for five consecutive days. At the end of the five day period, all dosages of ASA were capable of completely suppressing TXB2 production and arachidonic acid-induced platelet aggregation. At that time, the second phase of ADP-induced aggregation was also blocked. However, while the inhibition following 500 mg ASA was complete after 24 hours, total inhibition with 100, 50 and 25 mg was attained only after two, three and four days, respectively, indicating the cumulative effect of ASA on platelets. Aggregation induced by collagen was also inhibited dose-dependently- yet slower and at no time complete. ASA had no inhibitory effect on aggregation by platelet-activating factor (PAF). It is concluded that a daily dose of 50 mg ASA would suffice in blocking platelet TXA2 production and aggregation induced by most physiological agents.

Reduction of paracetamol and aspirin metabolism during viral hepatitis

The single-dose pharmacokinetics of two analgesic drugs, paracetamol (acetaminophen) and aspirin, were studied in healthy volunteers and in patients with viral hepatitis during the acute and the convalescent phase. Impaired elimination of paracetamol and aspirin was found in hepatitis patients, while plasma peak concentrations were unaffected. Recovered patients were not different from healthy controls in the rate of drug elimination. The data suggest normal single dosage for these drugs in acute viral hepatitis, and dosage modification only in severe cases.

In vivo indexes of platelet and vascular function during fish-oil administration in patients with atherosclerosis

Populations that consume a diet rich in marine lipids may have a lower risk of atherosclerotic disease. Fish oil contains the N-3 polyunsaturated fatty acid eicosapentaenoate, and the biosynthesis of thromboxanes and prostacyclins from eicosapentaenoate (thromboxane A3 and prostaglandin I3), rather than from the usual precursor arachidonate (thromboxane A2 and prostaglandin I2), may help to reduce the risk. To examine this hypothesis, we studied the effect of eicosapentaenoate supplementation (10 g per day) for one month on the synthesis of thromboxanes and prostacyclins, as assessed by urinary metabolite excretion, in six patients with peripheral vascular disease and seven normal controls. Supplementation markedly increased the eicosapentaenoate content of phospholipids from red cells and platelets. Synthesis of the platelet agonist thromboxane A2, which was elevated in the patients at base line, declined by 58 percent during supplementation but did not reach normal values. The decline in thromboxane A2, which is synthesized from arachidonate, coincided with the formation of the inactive thromboxane A3, which is synthesized from eicosapentaenoate. A lower dose of eicosapentaenoate (1 g per day) was not sufficient to maintain the changes in thromboxane A2 synthesis. Platelet function was only moderately inhibited during eicosapentaenoate supplementation, consistent with incomplete suppression of thromboxane A2 synthesis. These studies show that a high dose of eicosapentaenoate alters the pattern of synthesis of thromboxanes and prostacyclins. However, effects comparable to those of aspirin require long-term administration in high doses. Whether other properties of fish oil might render it a more attractive antithrombotic therapy remains to be determined.

Effects of salicylic and acetylsalicylic acid alone and in combination on platelet aggregation and prostanoid synthesis in man

The present study was designed to investigate the effects of salicylate on the antiplatelet action of acetylsalicylic acid as well as on in vivo prostanoid formation and platelet function in healthy volunteers. In the first study six female volunteers received 350 mg acetylsalicylic acid intravenously, with and without previous oral administration of sodium salicylate (1200 mg daily for 3 days). Urinary prostanoid excretion as well as platelet aggregation and thromboxane formation were measured before and during salicylate and after acetylsalicylic acid. In the second study seven female volunteers received sodium salicylate (52.6 mg kg-1) or acetylsalicylic acid (60.7 mg kg-1) for 8 days in a randomized cross-over protocol. Urinary prostanoid excretion, platelet aggregation and thromboxane formation as well as salicylate plasma concentrations were determined before, during and after administration of each drug. Sodium salicylate did not impair the complete suppression of arachidonic acid-induced platelet thromboxane formation and aggregation obtained by the single intravenous dose of acetylsalicylic acid in the first study. Sodium salicylate in the second study did not affect urinary excretion of prostaglandin E2, its major urinary metabolite (7 alpha-hydroxy-5,11-diketo-tetranor-prostane-1,16-dioic acid), and 2,3-dinor-6-keto-prostaglandin F1 alpha, the main urinary metabolite of epoprostenol (prostacyclin, PGI2). In contrast, acetylsalicylic acid significantly decreased excretion rates of these prostanoids by 64, 59 and 61%, respectively. In both studies platelet aggregation and thromboxane formation induced by collagen, thrombin or arachidonic acid were not significantly affected by salicylate administration, whereas acetylsalicylic acid inhibited platelet aggregation induced by all three agents as well as thrombin- and arachidonic acid induced thromboxane formation.(ABSTRACT TRUNCATED AT 250 WORDS)

Gastrointestinal intolerance and bleeding with non-narcotic analgesics

Aspirin and paracetamol (acetaminophen) are the most commonly used minor analgesics, but their effects on the gastrointestinal tract differ widely. The effects of other nonsteroidal anti-inflammatory drugs (NSAIDs), including phenylbutazone, are intermediate. Aspirin is significantly associated with major upper gastrointestinal haemorrhage, whereas paracetamol is not. Short term use of aspirin produces erythema, erosions and occasionally ulcers; paracetamol does not, while other NSAIDs do so to varying degrees. Chronic gastric ulcer is linked to aspirin intake in patients with rheumatic disease, and epidemiologically in all heavy aspirin users. In only one epidemiological study was a paradoxical significant association reported between paracetamol intake and chronic gastric ulcer. Faecal occult blood loss is increased in most regular aspirin users but not in those taking paracetamol. Although formal studies in children have apparently not been made, in isolated small clinical series it has been reported that gastrointestinal bleeding and anaemia do occur in the paediatric age group after the use of aspirin. Pathophysiologically, aspirin alters the gastric mucosal barrier to hydrogen ions and lowers gastric potential difference; paracetamol has no effect on these parameters. Such changes correlate ultrastructurally with damage in surface epithelial cells and microerosions after the use of aspirin, but not after the use of paracetamol. Aspirin and other NSAIDs cause a dramatic reduction in the ability of gastric mucosa to generate protective prostaglandins; however, paracetamol also reduces prostaglandins. Other postulated mechanisms of aspirin damage include reduction in gastric mucosal secretion, reduction in bicarbonate output, and alteration of cell turnover. Because damage to gastric mucosa by aspirin and NSAIDs is often 'silent', the clinician needs a high level of suspicion and awareness regarding this problem. In patients prone to gastric damage, or in those with a past history of aspirin-induced gastric damage, paracetamol is the drug of choice when a minor, non-inflammatory problem requires an analgesic.

Pharmacology of platelet inhibition in humans: implications of the salicylate-aspirin interaction

The current dispute over the effects of "low" vs "high" doses of aspirin should take into consideration the pharmacokinetics of this drug. In fact, different pharmaceutical formulations of aspirin may deliver little or no aspirin to the systemic blood. This was the case, for instance, in healthy volunteers taking 320 mg of compressed aspirin or 800 mg of enteric-coated aspirin. In all instances thromboxane B2 generation in serum was fully inhibited. Platelet cyclooxygenase might therefore be effectively acetylated by exposure to aspirin in the portal circulation, whereas vascular cyclooxygenase could be spared. Thus aspirin formulations ensuring complete first-pass deacetylation should be sought rather than "low" or "high" doses of unspecified aspirin formulations. Regardless of the type and dose of aspirin administered, salicylate is formed and accumulates in the circulation. It may antagonize the effects of aspirin on cyclooxygenase, at least in acute conditions. As an example, after administration of 1 g of salicylate to healthy volunteers, when plasma levels of the drug were about 75 micrograms/ml, the effect of 40 mg iv aspirin (given 40 min later) on platelet cyclooxygenase and aggregation was significantly diminished. In contrast, in patients undergoing saphenectomy, the same dose of salicylate (1 g) gave plasma drug levels of about 25 micrograms/ml; salicylate was unable to prevent the inhibitory effect on platelets of 40 mg iv aspirin (given 1 hr later) but did act on vascular prostacyclin. Thus the combination of salicylate with aspirin at an appropriate dose and blood level ratio may result in almost complete dissociation of the drug's effect on platelets and vessels in man.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of oral phenylbutazone on whole blood platelet aggregation in the dog

Platelet aggregation to collagen, arachidonic acid and adenosine diphosphate was evaluated in six dogs using a whole blood electronic aggregometer. The six dogs were then given phenylbutazone orally according to four different dosage levels and durations of treatment. Aggregation responses were measured at established intervals of time following phenylbutazone administration. Data on untreated dogs indicated that arachidonic acid, at a final concentration of 50 micrograms/mL and collagen, at a final concentration of 5 micrograms/mL, were useful agents for studying whole blood platelet aggregation in the dog, but adenosine diphosphate, at a final concentration of 30 microM was not. The high single dose (900 mg) of phenylbutazone significantly inhibited platelet aggregation to arachidonic acid at 1.5,4,7 and 12 hours following administration. The results indicated that the whole blood electronic aggregometer was of limited value in detecting subtle changes in platelet aggregation. It was concluded, however, that the instrument is potentially useful as a rapid screening aid for detecting canine patients at high risk of platelet-related bleeding problems.

Interactions between sodium salicylate and acetyl salicylic acid evaluated using ADP induced platelet aggregation and bleeding time

1 g acetyl salicylic acid orally significantly enhanced the initial rate of platelet aggregation induced by 1 mumol/l and 2.5 mumol/l ADP. Sodium salicylate was without effects on the platelet aggregation and specifically it did not prevent acetylsalicylic acid from inhibiting the secondary aggregation. Sodium salicylate was without effect on the bleeding time and did not inhibit the prolongation induced by acetyl salicylic acid. Our study does not lend support to the concept of an important interaction in vivo between acetyl salicylic acid and its first metabolite salicylate in man.

The combined effects of sodium salicylate, aspirin and indomethacin on the metabolism of arachidonic acid in human platelets

The effects of acetylsalicylic acid (ASA, aspirin), indomethacin and sodium salicylate on the metabolism of exogenous 14C-arachidonic acid (AA) were studied in intact human platelets in vitro. ASA (100 microM) and indomethacin (1 and 10 microM) suppressed the metabolism of AA via the cyclo-oxygenase but had no effect on the lipoxygenase pathway. Sodium salicylate at 1 mM was ineffective whereas 2 mM salicylate significantly decreased the formation of TXB2 and HHT and increased that of other cyclo-oxygenase products without clearly affecting total cyclo-oxygenase activity. The formation of 12-HETE, the main metabolite of AA in human platelets, was decreased by 2 mM sodium salicylate as well as by the combination of 1 mM salicylate plus ASA or indomethacin. Pretreatment of platelets with sodium salicylate (1 or 2 mM) effectively prevented the inhibition of the cyclo-oxygenase by ASA (100 microM) but had no effect on the inhibition produced by indomethacin (1 or 10 microM). When sodium salicylate was added to the platelet-containing buffer after ASA or indomethacin it did not reverse the effects of these drugs on the cyclo-oxygenase. The present study suggests that sodium salicylate effectively prevents the inhibitory effect of ASA but not that of indomethacin on human platelet cyclo-oxygenase at the concentrations used. In addition, a high concentration of sodium salicylate (2 mM) may selectively inhibit the formation of TXB2 without clearly affecting total cyclo-oxygenase activity.

The effects of aspirin-containing serum in the continuous culture of Plasmodium falciparum

In vitro culture of Plasmodium falciparum-infected human erythrocytes (RBC) has permitted systematic study of human host-parasite relations. In this study the effect of aspirin in the culture system was examined by using serum from blood of fasting, healthy male volunteers, before and after the ingestion of aspirin. The addition of aspirin-containing serum disturbed parasite growth and development: 0-1/2 dilutions of treated/control sera inhibited parasite development, with nuclear pyknosis, pyknotic extracellular parasites (trophozoites) in the media, decreased numbers and sizes of "rings" (early trophozoites), and an increased number of later trophozoites and schizonts. Paradoxically, while the incorporation of [3H]isoleucine into protein was not affected by the aspirin-containing sera, the incorporation [3H]hypoxanthine was significantly changed and did not correlate with morphological evidence of cytotoxicity. Thus, the so-called "incorporation" of a radioactive tracer is not a fully reliable index of parasite growth in the presence of certain compounds. The findings underscore the importance, in this culture system which employs human serum, of avoiding serum from donors who have recently ingested aspirin.

Effect on platelet aggregation of oral administration of 10 non-steroidal analgesics to humans

Platelet aggregation was investigated in platelet-rich plasma from normal volunteers before and at various times after intake of 10 analgesic drugs. The drugs used were aspirin, piroxicam, naproxen, indomethacin, diclofenac, ibuprofen, diflunisal, paracetamol and oxyphenbutazone. Aggregation of the platelets was induced by adrenaline or ADP and the first and second waves of aggregation were evaluated. It was found that no drug exerted any effect on the first wave of aggregation. The second wave of aggregation was abolished by aspirin that produced a long-lasting effect for 5-8 d. Piroxicam also abolished the second wave of aggregation and this effect persisted on the 2 following d. Naproxen was normalized in half of the volunteers on the 2nd d. The inhibition caused by indomethacin and diclofenac was corrected on the 2nd d. Ibuprofen and diflunisal produced a definite but short-term effect. The effect of salicylic acid was weak. Paracematol and oxyphenbutazone did not affect platelet aggregation.

A platelet release defect induced by aspirin or penicillin G does not increase gastrointestinal blood loss in thrombocytopenic rabbits

Gastrointestinal blood loss was compared in groups of normal and thrombocytopenic animals treated with medications known to induce qualitative platelet dysfunction. Thrombocytopenia was induced in rabbits by the intraperitoneal injection of busulphan dissolved in polyethylene glycol (PEG) at a dose of 60 mg/kg. Control animals received PEG alone; each group subsequently received daily intravenous injections of penicillin G, aspirin, sodium salicylate or isotonic saline. Mean daily gastrointestinal blood loss was determined by monitoring the appearance of 51Cr radioactivity in the faeces following the administration of 51Cr-labelled erythrocytes prior to the administration of the test and control therapies. The administration of penicillin G was not associated with increased gastrointestinal blood loss in the thrombocytopenic animals as compared with the saline treated thrombocytopenic controls. Platelet aggregation studies confirmed the presence of a mild but significant defect in platelet aggregation. Aspirin produced a more pronounced defect in platelet aggregation but did not induce increased bleeding in the normal animals as compared with the controls, nor did it exacerbate the bleeding in thrombocytopenic animals. Sodium salicylate did not produce an aggregation defect and did not significantly modify gastrointestinal blood loss. It was concluded that drug-induced qualitative platelet dysfunction does not necessarily increase bleeding through intact vessels despite previous evidence of a significant effect on platelet plug formation as monitored by the bleeding time.

Long-term results of cardiac valve replacement with the Delrin-disc model of the Björk-Shiley valve prosthesis

One hundred two Björk-Shiley valve prostheses with the Delrin-disc occluder were implanted in 83 patients between January, 1971, and July, 1972. Fifty-eight were in the mitral position, 42 in the aortic, and 2 in the tricuspid. Complete follow-up until 1981 was obtained in 93% of the patients (mean follow-up, 66.8 months). Hospital mortality was 18% and late mortality, 19%. Survival according to actuarial methods was 84.8% at 5 years and 78.1% at 9 years after operation. Thromboembolism was detected in 8.8% of patients but caused no deaths. The incidence was 1.2% and 1.5% per year in those patients treated with Coumadin and antiplatelet agents, respectively. Reoperation was necessary in 13% of the patients. Most survivors (72%) are in New York Heart Association Functional Class I, despite a preoperative status of Class III or IV in 57% of the patients. Hospital mortality may be due to poorer understanding of patient management and less refined techniques of myocardial protection. Long-term survival with this prosthesis is similar to that in more recent studies, and rates of thromboembolism and malfunction compare favorably with other prosthetic valves.

Enteric-coated aspirin, platelet cyclooxygenase activity and function

Recent studies evaluating the effect of slow releasing enteric-coated aspirin formulations have reported contradictory findings regarding the bioavailability of the active molecule in the circulating blood and the length of duration of the inhibitory effect on platelet function. In the present study, we have evaluated the effect of a single dose of two commercially available enteric-coated aspirins on platelet arachidonic acid metabolism and function. A single dose of slow releasing aspirin was as effective as fast acting regular aspirin in its effect on cyclooxygenase activity and platelet function in both human and canine platelets. However, in view of its slow releasing property, the onset of inhibition was considerably delayed compared to the action of fast acting aspirin in those subjects who ingested enteric-coated aspirins.

[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.

Study of platelet activation in migraine: control by low doses of aspirin

Although platelet activation is known to occur during migraine attacks, the cause-effect relationship remains to be determined. This problem was approached by studying the possible occurrence of platelet activation in vivo in headache-free periods of subjects affected by common or classic migraine and, subsequently, by verifying the possibility of its pharmacological control through administration of a classic anti-aggregation drug such as aspirin (ASA). The plasma levels of beta-thromboglobulin (beta-TG) and platelet factor 4 (PF4), indices of the occurrence of platelet activation in vivo, were therefore first assayed in both groups of migraine sufferers in the absence of therapy and then during the administration of aspirin (50 mg/daily). In the group of 15 patients affected by classic migraine, basal plasma levels of beta-TG and PF4 were significantly higher than control subjects. On the other hand, only beta-TG plasma levels were significantly higher in the group of 18 patients affected by common migraine. Patients suffering from classic migraine showed a high incidence of platelet activation (greater than 90%) in comparison with common migraine patients (approximately 33%). This suggests that platelet activation occurs in vivo in migrainous patients also during headache-free periods. Administration of aspirin to the patients affected by common and classic migraine caused a decrease in plasma beta-TG and PF4 concentration. Consequently, pharmacological treatment with aspirin in adequate dose may prove to be helpful in diminishing the vascular side-effects known to occur in migraine sufferers.

A comparative study of the effects of aspirin and paracetamol (acetaminophen) on platelet aggregation and bleeding time

In a double blind, randomised trial, the effects of 1 g aspirin and 1 g paracetamol were compared on bleeding time and platelet aggregation in 40 volunteers (20 females). Also investigated was the relationship between plasma aspirin esterase activity and both bleeding time and platelet aggregation after aspirin. Following 1 g aspirin there was a significant increase in bleeding time at 24 h (p less than 0.01). A significant reduction (P less than 0.01) in platelet aggregation with collagen was observed at 1, 6 and 24 h after aspirin, but no significant reduction (P greater than 0.05) was observed with ADP. Paracetamol had no effect on bleeding time or platelet aggregation. Plasma aspirin esterase activity ranged from 0.26-0.6 mumol/ml/min. A significant negative correlation (R = -0.55, P less than 0.001) was observed between percentage increase in bleeding time (24 h) and plasma aspirin esterase activity. Further significant correlations were observed between plasma aspirin esterase activity and change in platelet aggregation with collagen at 1 h (R = 0.68, P less than 0.001), 6 h (R = -0.73, P less than 0.001) and 24 h (R = -0.67, P less than 0.001). These results suggest that it might be possible to predict an individual's haemostatic response to aspirin from knowledge of their plasma aspirin esterase activity.

Aspirin and recurrent hyphema after blunt ocular trauma

Recurrent hyphema after traumatic blunt injury to the eye is associated with a more serious prognosis than that occurring from the initial trauma, resulting in a higher risk of glaucoma, corneal staining, surgical intervention, poor visual acuity, and enucleation. Risk factors associated with the development of recurrent bleeding are not well defined, but recent evidence suggests a high association with concurrent aspirin ingestion. Of 25 consecutive patients with hyphemas (20 males and five females, ranging in age from 2 to 53 years), 12 took aspirin after the initial trauma and seven had recurrent hyphemas. Platelet aggregation determinations in these seven patients showed defects associated with aspirin. Only one of 13 patients without aspirin intake had recurrent bleeding.

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.

Studies on the mechanism of antiaggregatory effect of Moutan Cortex

The effects of Moutan Cortex and one of its major components, paeonol, on platelet aggregation and arachidonic acid (AA) metabolism in human platelets were studied. One week oral administration of water extract of Moutan Cortex [Moutan Cortex (w), 3 g/day] significantly reduced platelet aggregation and thromboxane B2 (TXB2) formation induced by collagen, epinephrine and ADP. Paeonol dose-dependently inhibited ADP and collagen induced platelet aggregation in vitro. Moutan Cortex (w) and paeonol dose-dependently inhibited the conversion of exogenous [14C]AA to [14C]heptadecatetraenoic acid [( 14C]HHT) and [14C]TXB2 by washed human platelets, while both of them increased its conversion to [14C]12-hydroxy eicosatetraenoic acid [( 14C]12-HETE). High dose of Moutan Cortex (w) inhibited the release of [14C]AA from prelabeled platelets in vitro, while paeonol did not. These results suggest that a reduction in platelet aggregation by the oral administration of Moutan Cortex might be ascribed to a decrease in thromboxane synthesis and that paeonol might play an important role in the antiaggregatory effect of Moutan Cortex because of its potent inhibitory effect on platelet aggregation and thromboxane formation.

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.

Aspirin for prevention of stroke: a review

Most neurologists concede that thromboembolism is the principal pathogenetic mechanism for ischemic cerebrovascular disease, including both transient ischemic attacks and cerebral infarction. Surgical removal of atherosclerotic lesions may eradicate the site of origin of emboli, but a safer and more rational approach may be found in using antithrombotic drugs. Aspirin has been shown in clinical trials to be an effective agent in treating transient ischemic attacks and preventing infarction. An apparent difference in response between men and women patients was found in the results of one large study but not substantiated by others. It has been suggested that a lower dose of aspirin than that used in these trials may be equally or more effective. This proposition still needs to be tested in a clinical trial.

Influence of aspirin on platelets and the bleeding time

Aspirin influences the bleeding time, presumably through the inhibition of prostaglandin biosynthesis and the resultant platelet secretion reaction. This can be measured by prolongation of the bleeding time and changes in platelet function results. Despite these changes, bleeding is rarely a problem in patients who have normal hemostatic mechanisms. To investigate this, we have studied the technical variables associated with the determination of the bleeding time. Both venostasis and direction of the incision play a major role in the bleeding time prolongation induced by aspirin. When a bleeding time determination is performed with vertical incision without venostasis, there is almost no detectable prolongation of the bleeding time. These studies support our previous observations that aspirin has a mild influence on primary hemostasis.

Effects of oxaprozin alone or in combination with aspirin on hemostasis and plasma protein binding

Oxaprozin, a new nonsteroidal antiinflammatory agent, was studied alone and in combination with aspirin for its effects on hemostasis and protein binding in 10 healthy adults. When both oxaprozin and aspirin were given separately for seven days and in combination for five days, both drugs prolonged bleeding time and inhibited collagen- and epinephrine-induced platelet aggregation to a similar degree. The effects of the combination of oxaprozin and aspirin were not additive. The data from the protein binding study showed that oxaprozin was more than 99 per cent bound to plasma proteins. Aspirin displaced oxaprozin from its binding sites. As a result, the rate of plasma clearance of oxaprozin significantly increased from 20 to 26 ml/min/kg (P less than 0.05), and the plasma half-life decreased from 45 to 40 hours. Platelet count and the humoral clotting mechanism were not affected by either drug alone or in combination. There was no clinical evidence of bleeding. One subject who received oxaprozin for 12 days and, in addition, aspirin for the last five days developed a rash that subsided after both drugs were discontinued; one subject treated with aspirin experienced tinnitus. These data suggest that oxaprozin, like aspirin and other nonsteroidal antiinflammatory drugs, should be used with caution when administered to patients who have suffered trauma, who undergo surgery, or who have known defects in hemostasis.

Mechanisms of action: aspirin

Aspirin, one of the oldest antiplatelet agents used for antithrombotic therapy, has been demonstrated to cause acetylation of the cyclo-oxygenase and irreversible inhibition of thromboxane synthesis for the life of the platelet. Aspirin has a similar effect upon the endothelial cyclo-oxygenase, but in contrast to that of the platelet, it is less sensitive and has the capacity to generate new cyclo-oxygenase activity if aspirin is removed from the system. Other non-steroidal anti-inflammatory agents such as ibuprofen react in a reversible manner with either the platelet or the endothelium and may actually "protect" the cyclo-oxygenase against aspirin or other agents which interact with the cyclo-oxygenase. Aspirin may act in other ways to exert an antithrombotic effect, but cause and effect relationships have not yet been demonstrated.

Human platelet response to three salicylate dosage forms

Acetylsalicylic acid (ASA) inhibition of platelet aggregation as evaluated by collagen-induced 14C-serotonin release, has been measured in 12 healthy male subjects. Each subject received a single oral dose (650 mg) of enteric-coated ASA (ecASA) and compressed ASA tablets (cASA), or ecASA and sodium salicylate (578 mg) separated by a minimum of 5 weeks. The platelet response was related to plasma ASA and salicyclic acid determined by high-pressure liquid chromatography. Both ecASA and cASA inhibited 14C-serotonin release; no significant difference was observed in the maximum effect between these two products (p less than 0.05). No relationship was found between the maximum observed plasma ASA level and the maximum effect. Further, no correlation was found between the maximum inhibition of 14C-serotonin release in vivo and the release predicted from in vitro experiments wherein the effect was measured after incubating plasma containing specified ASA concentrations.

Aspirin: plasma concentration and effects

The antithrombotic effect of acetylsalicylic acid is intimately linked to its reactivity. The labile acetyl moiety irreversibly acetylates not only cyclo-oxygenase, but other biological components. The presence off ubiquitous esterases leads to the rapid disappearance of ASA from the body. The pharmacokinetics of ASA is affected by the dosage form used and the presence of food. Despite the absence of a definable relationship between plasma ASA levels and response, recent data would suggest a dose of about 0.5 mg/kg/day adequately suppresses platelet aggregation without affecting prostacyclin formation.

Human blood platelet behaviour after inhibition of thromboxane synthetase

1 We have determined the extent to which sodium arachidonate (NaAA) induces a release reaction in platelet-rich plasma (PRP) from different individuals and have studied the ability of the thromboxane synthetase inhibitor UK 34787 to modify this release. We have also determined the extent of the platelet release reaction induced in PRP from different individuals by preparations of platelet-derived thromboxane A2 (TXA2). 2 The release of [14C]-serotonin induced by NaAA is more extensive in PRP from some individuals than from others. 3 There is a direct relation between the extent of the release reaction induced in different PRPs by NaAA and TXA2. 4 UK 34787 prevents the NaAA-induced release reaction in PRP from some individuals ("responders") but not in PRP from others ("non-responders"). 5 The mean extent of the NaAA-induced release reaction for the "non-responders" was significantly higher than that for the "responders" even in the absence of UK 34787, but there was some overlap between the individual results. 6 Platelets from "responders" and "non-responders" did not differ in the amount of malondialdehyde (MDA) produced or in the effectiveness with which UK 34787 inhibited MDA production. 7 Platelet-derived TXA2 from "responders" and "non-responders" did not have markedly different effects when tested in a single preparation of PRP.

Effects of dazoxiben and low-dose aspirin on platelet behaviour in man

1 We have studied the effects on platelet behaviour of ingestion of the thromboxane synthetase inhibitor dazoxiben (UK 37248), by healthy subjects, and compared the results with the effects of a low dose of aspirin (a cyclo-oxygenase inhibitor), and of a combination of dazoxiben and a low dose of aspirin. 2 Dazoxiben ingestion prevented the release reaction induced by sodium arachidonate (NaAA) in platelet-rich plasma (PRP) from some individuals ("responders") but not in PRP from others ("non-responders"). In vitro testing of PRP from the same subjects, incubated with 10(-4)M dazoxiben, correlated with the effect of dazoxiben ingestion on NaAA-induced release. Platelets from "non-responders" tended to undergo a more extensive release reaction than platelets from "responders" even in the absence of any drug although there was some overlap between the results in the two groups. Platelets from "non-responders" required significantly lower concentrations of NaAA to induce release reaction than platelets from "responders". Platelets from "responders" and "non-responders" did not differ in the amount of malondialdehyde (MDA) produced or in the effectiveness with which dazoxiben ingestion inhibited MDA production. 3 Low dose aspirin had comparable effects on NaAA-induced release to dazoxiben, but in contrast to dazoxiben, the effectiveness of low-dose aspirin in inhibiting NaAA induced release reaction was related to its effectiveness in inhibiting MDA generation. 4 Neither dazoxiben nor low-dose aspirin significantly affected the release reaction induced by adenosine diphosphate (ADP), although both drugs significantly inhibited adrenaline-induced release. 5 A combination of dazoxiben and low dose aspirin had a greater effect on platelet behaviour in response to NaAA, ADP, and adrenaline than either drug alone.

Prevention of lipid accumulation in experimental vein bypass grafts by antiplatelet therapy

The ameliorative effect of antiplatelet therapy on atherogenesis of vein grafts was assessed in autologous cephalic veins grafted into femoral arteries of 16 normolipemic and 11 hyperlipemic stump-tailed macaque monkeys. Before grafting, one half of each vein was distended at high pressure (700 mm Hg) and the other half at low pressure (350 mm Hg). Eight normolipemic monkeys were treated with aspirin, 80 mg/day, and dipyridamole, 50 mg/day, and eight were controls. When grafts were harvested at 12 weeks, tissue cholesterol and beta-apoprotein content in grafts from untreated monkeys were significantly higher than in ungrafted, uninjured veins. Antiplatelet therapy eliminated the increase in lipid content of vein segments distended at low pressure, and significantly lowered lipid content of segments distended at high pressure, though not to be control levels of ungrafted veins. Seven of the 11 hyperlipemic monkeys received antiplatelet drugs and four did not. The lipid content of all graft segments was significantly higher than in grafted or ungrafted veins from normolipemic monkeys. Antiplatelet therapy again significantly reduced the lipid content in vein segments distended at both levels of pressure, and also reduced the elevated cholesterol content in ungrafted veins. Although this animal preparation differs in many ways from human coronary bypass operations, these observations may be pertinent to the prevention of atherosclerosis in human vein bypass grafts.

Deficiency of platelet lipoxygenase activity in myeloproliferative disorders

The myeloproliferative disorders are characterized by frequent bleeding and thrombotic complications, which have been attributed to abnormal platelet function. In 24 of 60 patients studied, reduced activity of the platelet lipoxygenase pathway for oxygenation of arachidonic acid was revealed by a new direct assay. This assay measured arachidonic acid-induced oxygen consumption in platelets preincubated with aspirin to block cyclooxygenase activity. Patients with secondary polycythemia or thrombocytosis had normal lipoxygenase activity . In the cells of seven of eight patients with lipoxygenase deficiency arachidonic acid induced increased synthesis of thromboxane, the major cyclooxygenase product. Nevertheless, patients with deficient lipoxygenase activity tended to have episodes of hemorrhage rather than thrombosis. Bleeding complications occurred in 67 per cent of patients with lipoxygenase deficiency, but in only 19 per cent of those with normal lipoxygenase activity (P less than 0.001). In contrast, 13 per cent of lipoxygenase-deficient patients, but 31 per cent of patients with other myeloproliferative disorders, had thromboembolic complications. Measurement of platelet lipoxygenase activity may be of diagnostic value in distinguishing myeloproliferative disorders from secondary thrombocytosis or polycythemia. Lipoxygenase deficiency may prove to be a useful natural model for investigating the role of lipoxygenase products in hemostasis.

Effect of drug-induced platelet dysfunction on surgical bleeding

Two hundred patients scheduled to undergo a variety of surgical and gynecologic procedures were studied to determine whether increased surgical bleeding occurred in those who had drug-induced platelet dysfunction. Twelve of 55 patients (22 percent) who had a positive drug history and abnormal platelet aggregation were judged to have excessive bleeding at surgery or postoperatively, compared with 7 of 97 patients (7 percent) with a negative drug history and normal platelet aggregation (p less than 0.02). The data suggest that drug-induced qualitative platelet dysfunction predisposes to excessive surgical bleeding.

Plasma levels of aspirin following effervescent and enteric coated tablets, and their effect on platelet function

Single doses of effervescent tablets (1200 mg) and enteric coated (EC) tablets (1300 mg and 650 mg) of acetylsalicylic acid (aspirin, ASA) were given to healthy volunteers in random order. Plasma ASA and salicylic acid (SA) levels were measured and concurrent in vitro measurements of the volunteers' platelet aggregation were carried out. The effervescent preparation resulted in peak ASA concentrations of 17-40 mg/l, achieved 20 to 30 min after a 1200 mg dose, whereas peak ASA levels of 0.01-0.37 mg/l were observed 4-6 h after a 650 mg dose of the EC preparation. With all the aggregating agents that were added to the test system maximum inhibition of platelet aggregation (about 50% of pre dose levels) was seen 1.0 h after the effervescent ASA dose, and persisted to at least 24 h, but with the EC preparation not until 24 h, at which time the degree of inhibition was also about 50% of pre-dose levels. A 1.0 g dose of sodium salicylate had no effect on in vitro platelet function. It was concluded that mean plasma levels of ASA of less than 0.25 mg/l are sufficient to depress aggregation by approximately 50%. A low dose of ASA taken daily either as effervescent ASA or EC ASA, significantly inhibits platelet aggregation and so may reduce the risk of ischaemic episodes in susceptible patients.

Platelet adherence to collagen: role of prostaglandin-thromboxane synthesis

The effect of aspirin and indomethacin on adherence of human platelets to collagen was assessed by affinity chromatography on collagen/Sepharose. Studies were done using platelets from normal subjects and subjects ingesting aspirin. Blood was anticoagulated with EDTA, EGTA or citrate, and platelets were suspended in plasma or buffer after separation by centrifugation or gel filtration. The adherence to collagen of platelets from subjects ingesting 1200 mg aspirin per day decreased significantly (P less than 0.05 or below). A significant reduction in adherence also occurred after exposure to aspirin and indomethacin in vitro. The reduction in adherence was associated with inhibition of malondialdehyde (MDA) production and was unaffected by the presence of CP/CPK. Exposure of platelets to aspirin at 24 degrees C caused no impairment of adherence. The addition of 1.0 mM Ca++, 0.5 or 1.0 mM Mg++, or 1 mM arachidonic acid significantly diminished the inhibition of adherence by aspirin. Imidiazole had an effect on adherence opposite to that of aspirin. Changes in release of 14C-serotonin in general paralleled changes in adherence. The data suggest that aspirin and indomethacin impair but do not fully inhibit platelet adherence to collagen. Factors affecting this inhibitory activity in our system are the presence of plasma and availability of divalent cation. Platelet-collagen adhesion appears partly dependent upon prostaglandin-thromboxane synthesis and may be promoted by a different pathway that is stimulated by divalent cations and unaffected by inhibition of prostaglandin synthesis.

Rapid return of cyclo-oxygenase active platelets in dogs after a single oral dose of aspirin

A single dose of oral aspirin in human subjects inhibits the aggregation response of platelets to arachidonate and other agents for approximately one week after ingestion. In the present study we have evaluated the rate at which cyclo-oxygenase active platelets return to the circulation in humans and dogs and compared the response curves obtained to improvements in cyclo-oxygenase activity produced by the aspirin platelets. After a single dose of aspirin, dog platelet function was compromised for several days. Normal responses to arachidonate and other aggregating agents were restored six days after aspirin, and the pattern of recovery was the same for dogs and human subjects. However, cyclo-oxygenase active platelets returned to the circulation in dogs more rapidly than in humans and chemical competence was restored in both species well before correction of the defective response to aggregating agents. The delay of 1-3 days before return of significant numbers of cyclo-oxygenase active platelets most likely reflects acetylation of bone marrow megakaryocytes by the drug. More rapid return of chemically competent cells in dogs than humans probably relates to the more rapid turnover and shorter life span of canine platelets. The basis for the discrepancy in return of chemical integrity compared to functional activity after aspirin in vivo compared to simultaneous correction of chemistry and function when 10% normal platelets are added to aspirin platelets in vitro remains unresolved.

Hermansky-Pudlak syndrome: albinism with lipofuscin storage

The Hermansky-Pudlak Syndrome, a "tyrosinase positive' form of oculocutaneous albinism, is a triad comprising albinism, a hemorrhagic diathesis and ceroid-lipofuscin storage. A pedigree is presented showing consanguinity with a pattern of pseudodominance. Electroretinography in two isolated Hermansky-Pudlak subjects was distinctly abnormal, showing decreased rod and cone responses (as well as abnormal flicker fusion responses) in one patient, and reduced photopic and scotopic responses in another. The decreased ERG responses are discussed with reference to the known retinal abnormalities in both generalized oculocutaneous albinism and Batten's disease, another ceroid-lipofuscin storage disorder.

Low dose aspirin, platelet function and prostaglandin synthesis: influence of epinephrine and alpha adrenergic blockade

The present investigation has evaluated the effects of low doses of oral aspirin on platelet prostaglandin synthesis and function. Whole (80 mg) or half (40 mg) tablets of baby aspirin given to adults had no effect on the response of their platelets to thrombin, ADP and epinephrine, but selectively inhibited aggregation induced by threshold concentrations of arachidonate 16-20 hours after ingestion. Larger amounts of arachidonate overcame the inhibition imposed by low dose aspirin, but not by adult aspirin tablets (600 mg). Epinephrine, in concentrations too low to cause aggregation, restored the sensitivity of aspirin-treated platelets to arachidonate. Studies with alpha-adrenergic agonists, antagonists and calcium channel blockers demonstrated that the corrective effect of epinephrine was mediated by an alpha-adrenergic receptor influence on calcium modulation of the platelet membrane.

Defective platelet aggregation and increased platelet turnover in patients with myelofibrosis and other myeloproliferative diseases

In 9 patients with myeloproliferative diseases (MPD) (6 with myelofibrosis, MF, 1 with Ph1 positive chronic granulocytic leukaemia, CGL, 1 with primary eosinophilia, PE, 1 with pre-leukaemia syndrome, preL) collagen, epinephrine, and ADP-induced aggregation, N-ethylmaleimide-induced malondialdehyde (MDA) production, beta-thromboglobulin (beta-TG) plasma levels, and platelet turnover were studied. Collagen-induced aggregation was found to be normal in 7 patients, absent in 1, and reduced in 1. In all but 3 patients, aggregation with ADP was markedly reduced. Epinephrine-induced aggregation was decreased in 7 patients. No difference was found between mean MDA production in MPD (3.21 +/- 0.50 nmol/10(9) PLTs) and in control group of 21 normal subjects (3.04 +/- 0.26 nmol/10(9) PLTs). Mean beta-TG levels were significantly higher (P less than 0.01) in MPD patients (165.00 +/- 28.29 ng/ml) than in healthy controls (81.76 +/- 14.63 ng/ml). Mean platelet production half-time was significantly shorter in MPD (2.48 +/- 0.24 d) than in the control group (3.43 +/- 0.17 d), after adjustment for age by covariance analysis (P less than 0.005). Our data do not indicate an abnormal prostaglandin synthesis and are consistent with the hypothesis that a disseminated intravascular platelet aggregation might take place in MPD patients.