Source / episode info
- **Episode:**279
- **Title:**Divine Intervention Episode 279 – The NBME and Prostaglandins.
- **Published:**2020-12-14
- Source:Episode page
One-liner
This episode provides a comprehensive review of eicosanoid synthesis pathways, detailing how arachidonic acid is converted into prostaglandins and leukotrienes via COX and LOX enzymes, covering clinical applications from antiplatelet therapy (Aspirin) to labor induction and managing congenital heart defects like the Patent Ductus Arteriosus.
High-yield summary
- Arachidonic Acid Source: Membrane phospholipids are cleaved by {PLA}_2 to release Arachidonic Acid ({AA}). This step is inhibited by cortical steroids (e.g., glucocorticoids).
- COX vs LOX Pathways: COX converts AA into prostaglandins and thromboxanes; LOX converts AA into leukotrienes. Both pathways are critical mediators of inflammation, bronchoconstriction, and vascular changes.
- Antiplatelet Mechanism: Aspirin irreversibly inhibits {COX}-1, preventing the synthesis of Thromboxane {A}_2 ({TXA}_2) in platelets, thus exerting its antiplatelet effect.
- Fetal Circulation & PDA: The Patent Ductus Arteriosus (PDA) allows mixing of oxygenated and deoxygenated blood. Neonatal management requires keeping the ductus open; therefore, high levels of supplemental {O}_2 or hyperoxia should be avoided as they cause vasoconstriction and premature closure.
- Prostaglandin Analogs: Synthetic analogs are used clinically: PGE_1 analog (e.g., Prostadil) is first-line for PDA patency; {PGE}_2 analog (e.g., Dinoprostone) can be used for labor induction or cervical ripening.
- Gastroprotection: {NSAIDs} increase risk of gastric ulcers; prophylactic use of a {PGE}_1 analog like Misoprostol reduces gastric acid secretion and provides mucosoprotection.
Learning objectives
- Describe the biochemical pathways (COX and LOX) responsible for eicosanoid synthesis from arachidonic acid.
- Differentiate the clinical uses of specific prostaglandin analogs (\text{PGE}_1 vs \text{PGE}_2) in obstetrics and neonatology.
- Explain the mechanism by which aspirin exerts its antiplatelet effect via irreversible inhibition of COX-1.
- Identify the risk factors associated with eicosanoid pathway dysregulation, such as Aspirin Exacerbated Respiratory Disease (AERD).
- Understand the physiological basis for PDA patency and the dangers of hyperoxia in neonates.