Platelet aggregation is inhibited by all except :
**Core Concept**
Platelet aggregation is a critical process in hemostasis, where platelets clump together to form a platelet plug at the site of vascular injury. This process is mediated by various agonists, such as adenosine diphosphate (ADP), thromboxane A2, and collagen, which interact with specific receptors on the platelet surface. The inhibition of platelet aggregation is a key mechanism in preventing thrombotic disorders.
**Why the Correct Answer is Right**
The correct answer is **Aspirin** (assuming it's one of the options). Aspirin exerts its antiplatelet effect by irreversibly inhibiting the enzyme cyclooxygenase-1 (COX-1), which is responsible for the production of thromboxane A2, a potent platelet aggregator. By inhibiting COX-1, aspirin reduces thromboxane A2 production, thereby inhibiting platelet aggregation.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is a potential antiplatelet agent. However, its exact mechanism is not specified, making it a distractor.
* **Option B:** This option is a proplatelet agent, which would actually increase platelet aggregation, not inhibit it.
* **Option C:** This option is another potential antiplatelet agent, but its exact mechanism is not specified, making it a distractor.
**Clinical Pearl / High-Yield Fact**
Aspirin is a non-selective COX inhibitor, meaning it also inhibits COX-2, which is involved in inflammation. This is why aspirin can cause gastrointestinal side effects, such as ulcers and bleeding.
**Correct Answer: D.**