Time course of platelet alpha granule release in acute myocardial infarction treated with streptokinase

Isosorbide dinitrate inhibits platelet adhesion and aggregation in nonthrombolyzed patients with acute myocardial infarction

BACKGROUND

Apart from their vasodilatatory properties, nitrates have been shown to inhibit platelet aggregation. The effects of nitrates on platelet adhesion have not been studied. Nonselected patients with acute myocardial infarction (AMI) have been suggested to gain no benefit from administration of nitrates. However, the importance of nitrates may be greater in a subgroup of nonthrombolyzed patients with AMI.

HYPOTHESIS

Isosorbide dinitrate (ISDN) decreases platelet adhesion and aggregation in nonthrombolyzed patients with AMI.

METHODS

Consecutive 48 men with AMI, not eligible for thrombolytic therapy because of late presentation (> 12 h), were prospectively randomized 2:1 to double-blind ISDN (mean dose 2.4 +/- 0.9 mg/h) (n = 33) or placebo (0.9% sodium chloride) (n = 15) infusion. All patients received aspirin. Blood samples were taken at baseline (no study medication) and 3 h into ISDN or placebo infusion. Platelet adhesion to collagen was measured in the ethylene diamine tetraacetic acid (EDTA)-platelet rich plasma by recording changes in light transmission with an optical aggregometer. Platelet aggregation was measured using the Born's method.

RESULTS

Isosorbide dinitrate significantly decreased both platelet adhesion and aggregation. No effect was seen in the placebo group.

CONCLUSIONS

In patients with AMI who do not receive thrombolytic therapy, ISDN effectively inhibits platelet adhesion and aggregation. These effects of nitrates may be of therapeutic and prognostic significance in this group of patients.

High levels of platelet inhibition with abciximab despite heightened platelet activation and aggregation during thrombolysis for acute myocardial infarction: results from TIMI (thrombolysis in myocardial infarction) 14

BACKGROUND

We evaluated platelet activation and aggregation in patients with acute myocardial infarction (AMI) treated with thrombolytic therapy alone or with reduced-dose thrombolysis and concomitant abciximab.

METHODS AND RESULTS

The study was performed in 20 control subjects and 51 patients with AMI before and after reperfusion with either alteplase or reteplase or reduced doses of these agents with concomitant abciximab. Platelet activation was assayed by platelet surface expression of P-selectin. Turbidometric platelet aggregation in response to ADP was measured in patients before thrombolytic therapy and 90 minutes and 24 hours after the beginning of thrombolytic therapy. P-selectin expression was greater at baseline in patients than normal control subjects (30.4% versus 9. 8%, P<0.0001) but was identical between the 2 groups after stimulation with ADP (64.4% versus 69.3%, P=0.37). However, at 24 hours, basal P-selectin expression declined in patients (P=0.0025 versus baseline), whereas ADP-stimulated P-selectin expression was lower in patients than in control subjects (48% versus 69%, P=0. 0004). When combined with reduced doses of either alteplase or reteplase, abciximab achieved 91% and 83% inhibition of 5 and 20 micromol/L ADP-induced platelet aggregation, which decreased to 46% and 40%, respectively, at 24 hours. No appreciable difference in the platelet inhibition profile of abciximab was observed between the 2 thrombolytics.

CONCLUSIONS

Platelet activation and aggregation are heightened in the setting of thrombolysis for AMI. Despite this enhanced level of platelet activation, abciximab, combined with a reduced-dose thrombolytic, inhibited platelet aggregation similarly to the level reported in elective settings.

Plasma thromboxane and prostacyclin are linear related and increased in patients presenting with acute myocardial infarction

The role of prostanoids in patients with ischemic heart disease including acute myocardial infarction (AMI) has been recognized. However, there is very limited knowledge of the baseline TXB2 and 6-keto-PGF1a plasma levels in patients with AMI before therapy has been administered. We compared plasma levels of TXB2 and 6-keto-PGF1a by enzyme immunoassay in 18 AMI patients before thrombolysis, with those of 13 healthy controls. Plasma levels of TXB2 (319.78+/-16.50 pg/ml) and 6-keto-PGF1a (536.72+/-56.71 pg/ml) were heterogeneous, but significantly higher in the AMI patients than in controls (175.92+/-17.29 pg/ml and 192.08+/-26.11 pg/ml, respectively). In some patients, long-term aspirin therapy mildly inhibits baseline prostanoid levels, however, limited data prevents us from further speculations on this issue. Although, the contributions by prostanoids to the pathogenesis of AMI have been well proposed, their plasma concentrations are not uniformly elevated, and it is still unclear whether the resultant changes are indicative of clinically meaningful effects.

Heterogeneity of platelet aggregation and major surface receptor expression in patients with acute myocardial infarction

BACKGROUND

Platelets play an important role in the natural history of acute myocardial infarction (AMI).

METHODS AND RESULTS

Platelet aggregation and receptor expression were studied in 23 patients with AMI before reperfusion therapy and compared with 10 healthy control subjects. Platelet aggregation was induced with 5 micromol/L adenosine 5'-diphosphate, 10 micromol/L ADP, 1 microg/mL collagen, 1 mg/mL thrombin, and 1.25 mg/mL ristocetin. Receptor expression was measured by flow cytometry with monoclonal antibodies to p24 (CD9), Ib (CD42b), IIb (CD41b), IIIa (CD61), IIb/IIIa (CD41b/CD61), very late antigen-2 (CD49b), P-selectin (CD62p), platelet/endothelial cell adhesion molecule-1 (CD31); and vitronectin (CD51/CD61). The percentage of platelet aggregation was higher in patients with AMI when induced by 5 micromol/L ADP (64.1+/-12.7 vs 52.0+/-6.7; P=.04), by 10 micromol/L ADP (71.7+/-13.0 vs 59.2+/-7.2, P=.003), by thrombin (75.8+/-10.9 vs 60.5+/-6.9, P=.01), and by ristocetin (92.5+/-7.8 vs 71.3+/-7.4, P=.0001). Collagen-induced platelet aggregation did not differ between groups. Expression of P-selectin (log amplification of fluorescence intensity) (31.5+/-5.0 vs 25.1+/-2.6, P=.003) and platelet/endothelial cell adhesion molecule-1 (56.8+/-17.7 vs 44.5+/-3.7, P=.04) were significantly increased in patients with AMI. The expression of IIb (28.4+/-2.5 vs 37.2+/-1.7, P=.0001) and Ib (103.6+/-29.9 vs 133.8+/-8.0, P=.007) were reduced in patients with AMI.

CONCLUSIONS

Platelets are not necessarily systemically activated during the prereperfusion phase of AMI. For each agonist used and surface antigen measured, there was a cohort of patients with AMI within the normal or even below normal range of platelet status.

Effects of reteplase and alteplase on platelet aggregation and major receptor expression during the first 24 hours of acute myocardial infarction treatment. GUSTO-III Investigators. Global Use of Strategies to Open Occluded Coronary Arteries

OBJECTIVES

We sought to compare platelet characteristics after reteplase and alteplase therapy in the setting of the Global Use of Strategies to Open Occluded Coronary Arteries (GUSTO)-III trial.

BACKGROUND

Platelet function may be impaired during thrombolysis in patients with an acute myocardial infarction. The effects of reteplase and alteplase on platelet aggregation and major surface antigen expression during the first 24 h of infarction therapy are unknown.

METHODS

Platelet aggregation and receptor expression by flow cytometry were determined in 23 patients before thrombolysis and thereafter at 3, 6, 12 and 24 h.

RESULTS

Aggregation was higher after reteplase at 24 h when induced by 5 micromol/liter adenosine diphosphate (ADP) (p = 0.007), 10 micromol/liter ADP (p = 0.02), collagen (p = 0.003) and thrombin (p = 0.009) than after alteplase. Reteplase therapy exhibited greater glycoprotein (GP) IIb/IIIa (p = 0.04), very late antigen-2 (p = 0.04) and platelet/endothelial cell adhesion molecule-I (p = 0.002) expression at 24 h. Trends toward decreased receptor expression early (3 to 6 h), followed by a progressive increase at 12 h and especially at 24 h occurred after both agents.

CONCLUSIONS

In this prospective clinical ex vivo platelet study, similar patterns of platelet aggregation and surface receptor expression occurred during the first 24 h of coronary thrombolysis with reteplase and alteplase. However, after reteplase, indicators of platelet activity were higher at 24 h after thrombolysis than after alteplase. These data suggest that GP IIb/IIIa inhibitors or other antiplatelet strategies may be particularly advantageous when used 12 to 24 h after thrombolysis, especially after reteplase therapy. It is at this time point during the first day of coronary thrombolysis that GP IIb/IIIa is markedly expressed and platelets are most active.