Okay, let's tackle this question about the genetic expression of Na-K-ATPase being inducible by which factor. First, I need to recall what the Na-K-ATPase is and what regulates its expression. The Na-K-ATPase is an enzyme that pumps sodium out and potassium into the cell, maintaining the electrochemical gradient. Its activity is crucial for various cellular processes.

The question is about genetic expression being inducible. So, what factors influence the gene expression of this enzyme? I remember that hormones like aldosterone play a role in upregulating Na-K-ATPase. Aldosterone is involved in regulating electrolyte balance, acting on the kidneys. It increases sodium reabsorption and potassium excretion, which would require more Na-K-ATPase in the cell membrane to maintain the gradient.

Let me think about the other options. If the options included cortisol, that's a glucocorticoid, not mineralocorticoid. Aldosterone is a mineralocorticoid. Cortisol might have some effects but isn't the primary inducer. Thyroid hormones can influence metabolism and might affect Na-K-ATPase indirectly, but the direct inducer is aldosterone. Insulin also affects the enzyme's activity but not necessarily its expression.

So the correct answer should be aldosterone. The other options are incorrect because they either don't regulate this enzyme's expression or have different primary functions. The clinical pearl here is that aldosterone's role in sodium retention and potassium excretion is mediated through upregulating Na-K-ATPase in the distal tubules and collecting ducts of the kidneys. That's a key point for exams like NEET or USMLE.

**Core Concept**
The Na⁺-K⁺-ATPase is a transmembrane enzyme critical for maintaining ion gradients. Its gene expression is regulated by hormonal signals, particularly **aldosterone**, which enhances sodium reabsorption and potassium excretion in renal tubules.

**Why the Correct Answer is Right**
Aldosterone, a mineralocorticoid hormone secreted by the adrenal cortex, binds to intracellular receptors in distal tubules and collecting ducts. This activates transcription of the *ATP1A1* gene (encoding Na⁺-K⁺-ATPase α-subunit) via genomic pathways. Increased enzyme expression boosts sodium reabsorption and potassium excretion, aligning with aldosterone’s role in volume and electrolyte homeostasis.

**Why Each Wrong Option is Incorrect**
**Option A:** Cortisol (glucocorticoid) primarily regulates glucose metabolism and has minimal direct effect on Na⁺-K⁺-ATPase expression.
**Option B:** Thyroid hormones increase basal metabolic rate but do not directly induce Na⁺-K+-ATPase gene transcription.
**Option D:** Insulin modulates Na⁺-K+-ATPase activity via phosphorylation but does not upregulate its genetic expression.

**Clinical Pearl**
Aldosterone’s genomic effects on Na⁺-K+-ATPase are central to conditions like **hyperaldosteronism** (e.g., Conn’s syndrome), causing hypokalemia and hypertension. Remember: "Aldo for salt, and K+ goes out—ATPase pumps hard when aldosterone’s about!"

**Correct Answer: C. Aldosterone

✓ Correct Answer: A. Aldosterone