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Platelet-mediated cardiac ischemia
Insights
Platelet activation in coronary arteries can cause cardiac ischemia. Aspirin effectively prevents this, suggesting a key role for arachidonate metabolism products in platelet-induced heart damage.
Area of Science:
- Cardiovascular Biology
- Hematology
- Ischemic Heart Disease
Background:
- Platelets are linked to heart conditions like angina and myocardial infarction.
- The precise role of platelets in causing and worsening cardiac ischemia is not fully understood.
Purpose of the Study:
- To investigate the impact of platelet activation within the coronary circulation on cardiac ischemia.
- To test if inhibiting platelet function can prevent platelet-induced cardiac ischemia.
Main Methods:
- Human platelets were isolated and introduced into a Langendorff rabbit heart model.
- Cardiac ischemia was monitored using NADH fluorescent photography.
- Platelet function was inhibited using prostaglandin E1 (PGE1) or aspirin.
Main Results:
- Platelet activation with thrombin induced immediate and irreversible global cardiac ischemia.
- Low-dose PGE1 did not prevent ischemia, but higher doses did.
- Aspirin completely prevented platelet-induced myocardial ischemia, even without blocking aggregation.
Conclusions:
- Platelet activation in the coronary circulation is sufficient to cause irreversible cardiac ischemia.
- Aspirin's effectiveness points to a critical role for arachidonate metabolism products, like thromboxanes, in platelet-mediated myocardial ischemia.
Abstract:
Although platelets have been associated with angina pectoris, myocardial infarction, and sudden death, the platelet's capacity for induction and propagation of cardiac ischemia remains incompletely defined. We therefore evaluated the effects of platelet activation occurring within the coronary circulation and tested the hypothesis that inhibition of platelet function would prevent platelet-induced cardiac ischemia. Human platelets were isolated from blood obtained from normal donors by Sepharose 2B column chromatography, resuspended in Hepes buffer, and added to the perfusate of a Langendorff rabbit heart (platelet counts greater than 10,000/microliters). Without, and with low dose (10 microM) prostaglandin E1 (PGE1), a reversible inhibitor of platelet function, immediate and irreversible global cardiac ischemia, as monitored by NADH fluorescent photography, ensued (N = 4) following platelet activation with thrombin (0.1 to 1 U/ml). Higher concentrations of PGE1 (0.1 to 1 mM, N = 2) or aspirin ingestion (1000 mg taken approximately 12, 4, and 1 hr prior to experiment, N = 2) completely prevented this platelet-induced myocardial ischemia. Aspirin, unlike PGE1, was effective despite its inability to block thrombin-induced platelet aggregation in our in vitro gel-filtered system. We conclude that activation of platelets within the coronary circulation is sufficient for induction of irreversible cardiac ischemia. The efficacy of aspirin, a cyclooxygenase inhibitor, further suggests that the products of arachidonate metabolism (e.g., thromboxanes) have a fundamental role in the genesis of platelet-mediated myocardial ischemia.