Veterinary Pharmacology and Toxicology- ICAR JRF/SRF 2024

• Mechanism of Antiplatelet Action of Aspirin: Aspirin (acetylsalicylic acid) is a prototype antiplatelet drug that irreversibly inhibits platelet cyclooxygenase-1 (COX-1) via covalent acetylation of serine-529.
• Thromboxane Suppression: Platelets lack nuclei and cannot synthesize new enzyme; thus, aspirin permanently shuts down the synthesis of Thromboxane $A_2$ ($ ext{TXA}_2$), a potent platelet aggregator and vasoconstrictor, for the entire 7–10 day lifespan of circulating platelets.
• Other Options: While clopidogrel and ticlopidine are ADP-receptor blockers, aspirin remains the historical prototype antiplatelet agent.

Correct option: (1) Aspirin

• Osmotic Diuretics: Mannitol is the classic prototype osmotic diuretic.
• Mechanism: Mannitol is an inert six-carbon carbohydrate ($MW = 182\text{ Da}$) that is freely filtered at the glomerulus but undergoes negligible tubular reabsorption. It exerts high intraluminal osmotic pressure along the proximal convoluted tubule and thin descending loop of Henle, opposing water reabsorption and causing marked solute-driven diuresis.
• Contrasting Diuretics:
• Xipamide: Thiazide-like diuretic inhibiting the $\text{Na}^+/\text{Cl}^-$ cotransporter.
• Dichlorphenamide: Carbonic anhydrase inhibitor.
• Canrenone: Active aldosterone antagonist metabolite of spironolactone.

Correct option: (2) Mannitol

Matching the items of List I with List II for Venoms from snakes:

The correct combination is Option 1: (A) - (ill), (B) - (I), (C) - (IY), (B) - 0).

Correct option: (1) (A) - (ill), (B) - (I), (C) - (IY), (B) - 0)