ICAR AIEEA PG 2024 - Veterinary Science

Monensin sodium (produced by Streptomyces cinnamonensis) is a classic carboxylic polyether ionophore antibiotic widely used in poultry feeds as an effective anticoccidial agent and in cattle feeds as a ruminal fermentation modifier / growth promoter. Halofuginone is a quinazolinone, arprinocid is a purine derivative, and robenidine is a guanidine derivative.

Antiparasitic drug therapeutics match as follows:
Schistosoma sp. -> Praziquantel is the drug of choice for blood flukes (II)
Fasciola gigantica -> Triclabendazole is the gold standard flukicide effective against both immature and adult liver flukes (IV)
Poultry cestodes (e.g., Raillietina, Choanotaenia) -> Butynorate (dibutyltin dilaurate) historically formulated in feed for avian tapeworms (I)
Dictyocaulus filaria (lungworm) -> Ivermectin macrocyclic lactones achieve high efficacy against lung nematodes (III).

Cardiac glycosides (digitalis, digoxin) bind specifically to and inhibit the sarcolemmal $Na^+/K^+$-ATPase pump. This increases intracellular $[Na^+]_i$, which dissipates the inward sodium electrochemical gradient required to drive the forward mode of the $Na^+/Ca^{2+}$ exchanger ($NCX$, which normally extrudes $1\text{ Ca}^{2+}$ in exchange for $3\text{ Na}^+$ influx). Consequently, $NCX$ forward activity decreases (diminished $Na^+$ influx and diminished $Ca^{2+}$ efflux), leaving more $Ca^{2+}$ in the cytosol to be sequestered into the sarcoplasmic reticulum by SERCA2a, yielding greater $Ca^{2+}$ release and enhanced myocardial contractility during subsequent systoles.

Aldosterone antagonists (e.g., spironolactone, eplerenone) are competitive antagonists that act intracellularly on cytosolic mineralocorticoid receptors within principal cells of the collecting duct. Because they enter tubular epithelial cells from the systemic capillary blood across the basolateral membrane and bind intracellular nuclear receptors, they do not need to be filtered or secreted into the tubular lumen to exert their diuretic action. In contrast, loop diuretics (NKCC2), thiazides (NCC), and carbonic anhydrase inhibitors must be present in the luminal fluid to inhibit apical transporters/enzymes.

Rosiglitazone is a thiazolidinedione (TZD / glitazone) that functions as a selective agonist for the nuclear peroxisome proliferator-activated receptor-gamma ($PPAR\text{-}\gamma$), acting as an insulin sensitizer in adipose tissue, liver, and skeletal muscle rather than promoting insulin secretion. In contrast, Exenatide (GLP-1 receptor agonist), Sitagliptin (DPP-4 inhibitor), and Repaglinide (meglitinide $K_{ATP}$ channel blocker) all directly stimulate insulin secretion from pancreatic beta cells.