Which pair of arachidonic acid metabolites exerts directly opposite effects on platelet aggregation within vessels?

• A PGE2 and PGD2
• B Thromboxane A2 and prostacyclin (PGI2) ✓
• C LTC4 and LTD4
• D Lipoxin A4 and resolvin D1

Explanation

Thromboxane A2, produced by platelets via COX-1, promotes vasoconstriction and platelet aggregation, while prostacyclin PGI2, produced by endothelial cells, inhibits aggregation and causes vasodilation. This balance underlies aspirin's antiplatelet effect through irreversible COX-1 inhibition. LTC4 and LTD4 are bronchoconstrictor cysteinyl leukotrienes, and lipoxin with resolvin are pro-resolving mediators, none of which regulate platelet aggregation oppositely.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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