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Questions and Answers
What is the primary use of Misoprostol?
Which of the following is a function of PGF2α?
What medical condition is Carboprost tromethamine primarily used to treat?
Dinoprostone is primarily used for which purpose?
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What function do eicosanoids serve in the body?
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How does Enprostil function in the treatment of gastric ulcers?
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What effect do PGE2 and PGF2α have when inducing labor?
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Which prostaglandin is known to relax vascular and other smooth muscle?
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What condition is Latanoprost primarily used to treat?
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What role does PGE2 play during fetal development?
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What effect do NSAIDs have on prostaglandin production?
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What is the primary role of Prostacyclin (PGI2) in the body?
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Which prostaglandin is associated with dysmenorrhea due to its role in uterine contractions?
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What is a key physiological role of PGE1?
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What is the primary mode of eicosanoid metabolism in the body?
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Which eicosanoid is particularly known for reducing intraocular pressure?
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What are eicosanoids primarily derived from?
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Which eicosanoid precursor is most abundant in humans?
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Which enzyme is involved in the conversion of arachidonic acid to prostaglandin endoperoxides?
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What distinguishes COX-1 from COX-2?
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What is produced by both COX-1 and COX-2 during the cyclization of arachidonic acid?
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Which pathway is involved in eicosanoid synthesis after arachidonic acid is mobilized?
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What are PGH2 and its derivative prostaglandins collectively known as?
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In what two ways do prostaglandins differ from one another?
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Study Notes
Eicosanoids
- Eicosanoids are fatty acid derivatives.
- Derived from the Greek word "eikosi" (twenty).
- Include:
- Straight-chain derivatives (Leukotrienes)
- Cyclic derivatives (prostacyclin, prostaglandins, and thromboxane)
Precursors
- Precursors are essential fatty acids with 20 carbons.
- Examples:
- Eicosatrienoic acid (dihomo-y-linolenic acid)
- Eicosatetraenoic acid (arachidonic acid (AA))
- Eicosapentaenoic acid (EPA)
- Arachidonic acid (AA) is the most common precursor in humans.
- AA is released from membrane phospholipids by lipases from the phospholipase A2 (PLA2) type.
- Mobilized AA is oxygenated by different routes:
- Cyclooxygenase (COX)
- Lipoxygenase
- P450 epoxygenase
- Isoeicosanoid pathways
Synthesis of Prostaglandin Endoperoxide Synthases (Cyclooxygenases)
- Two COX isozymes convert AA into prostaglandin endoperoxides.
- COX-1 is expressed constitutively in most cells.
- COX-2 is inducible and its expression is stimulus-dependent.
- COX-2 is up-regulated by shear stress, growth factors, tumor promoters, & cytokines.
- COX-1 is responsible for prostanoids in physiological processes.
- COX-2 is the major source of prostanoids in inflammation and cancer.
- Both COX-1 and COX-2 promote the uptake of two oxygen molecules to form PGG2.
- PGG2 is modified by the peroxidase moiety of the COX enzyme to form PGH2.
- PGH1 and PGH3 are derived from homo-y-linolenic acid & eicosapentaenoic acid respectively.
- Prostaglandins, thromboxane, & prostacyclin are collectively termed prostanoids, generated from PGH2.
Pharmacological Effects of Eicosanoids
- Eicosanoids act locally (autocrine & paracrine).
- Eicosanoids bind to receptors on the cell surface.
- All Eicosanoid receptors are G protein-coupled.
Effects of Prostaglandins
- PGE2 & prostacyclin (PGI2) are vasodilators.
- PGE1 and its derivatives protect the gastric mucosa.
- PGE1 and PGE2 relax vascular and other smooth muscle.
- PGE2 is a key vasodilator in fetal development.
- PGs modulate glomerular filtration, affecting arterioles and mesangial cells.
- PGE2 and PGF2α are released during menstruation.
- PGE2 helps in cervical ripening.
- Dysmenorrhea is linked to PGF2α-induced uterine contractions.
- Platelet aggregation is strongly activated by thromboxane.
- PGF2a reduces intraocular pressure.
Biotransformation
- Eicosanoids have short half-lives and undergo rapid metabolism.
- Metabolism can be by:
- Hydration (for PGI2 & TXA2)
- Oxidation of the 15-hydroxyl group by PG 15-OH dehydrogenase
- Further metabolism is by reduction & oxidation.
Clinical Uses of Prostaglandins
-
Alprostadil (PGE₁) is used for its smooth muscle relaxing effects:
- To maintain the patency of the ductus arteriosus in neonates.
- In the treatment of erectile dysfunction (impotence).
-
Misoprostol, a PGE₁ derivative, is used:
- As a cytoprotective PG to prevent peptic ulcers.
- For labor induction.
- For terminating early pregnancies.
-
PGE2 & PGF2α induce uterine contraction:
- Carboprost tromethamine, a PGF2α analog, is used for second-trimester abortion and postpartum hemorrhage.
- Dinoprostone (PGE2) is used to dilate the cervix during induction of labor.
- Enprostil, a synthetic analogue of PGE2, is used for duodenal or gastric ulcers.
-
Latanoprost, Bimatoprost, travoprost, & unoprostone are topically active PGF2a derivatives:
- Used to treat open-angle glaucoma or ocular hypertension.
- Increase aqueous humor outflow to reduce intraocular pressure.
-
Bimatoprost is approved for the treatment of eyelash hypotrichosis.
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Prostacyclin (PGI2) is produced by the vascular endothelium.
- It is a powerful vasodilator and inhibitor of platelet aggregation.
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Description
Explore the fascinating world of eicosanoids, essential fatty acid derivatives that play crucial roles in various physiological processes. This quiz covers their types, precursors like arachidonic acid, and the synthesis pathways involving cyclooxygenases. Test your knowledge on the chemistry and biology behind these important biomolecules!