Endocrine Pharmacology — MCQs

Endocrine Pharmacology Indian Medical PG Practice Questions and MCQs

Question 261: Which of the following is an oxytocin antagonist?

A. Nitrates
B. Sultraban
C. Atosiban (Correct Answer)
D. Rimonabant

Explanation: **Explanation:** **Correct Answer: C. Atosiban** Atosiban is a competitive **oxytocin receptor antagonist**. It works by blocking oxytocin receptors in the myometrium, thereby inhibiting uterine contractions. Clinically, it is used as a **tocolytic agent** to delay imminent preterm birth in pregnant women. By decreasing the frequency of contractions and uterine tone, it provides a window to administer corticosteroids (for fetal lung maturity) or arrange transport to a tertiary care center. **Analysis of Incorrect Options:** * **A. Nitrates:** These are nitric oxide donors that cause vasodilation and smooth muscle relaxation via the cGMP pathway. While Nitroglycerin is occasionally used off-label as a rapid-acting tocolytic for uterine relaxation (e.g., during breech extraction), it is not a specific oxytocin antagonist. * **B. Sulprostone (Sultraban):** This is a **Prostaglandin E2 (PGE2) analogue**. It is used to induce labor or manage postpartum hemorrhage (PPH) because it stimulates uterine contractions, making it an agonist-like drug rather than an antagonist. * **D. Rimonabant:** This is a selective **Cannabinoid receptor-1 (CB1) antagonist**. It was previously used as an anti-obesity drug but was withdrawn globally due to serious psychiatric side effects, including depression and suicidal ideation. **High-Yield NEET-PG Pearls:** * **Atosiban** is unique because it also has antagonist activity at **Vasopressin (V1a) receptors**. * Other common tocolytics include **Nifedipine** (Calcium channel blocker - often first-line due to oral ease), **Terbutaline** (Beta-2 agonist), and **Magnesium Sulfate** (also provides neuroprotection to the fetus). * **Oxytocin (Pitocin)** is the drug of choice for **Induction of Labor** and prevention/treatment of **Postpartum Hemorrhage (PPH)**.

Question 262: Which of the following is NOT true regarding GnRH analogues?

A. Drug of choice for precocious puberty
B. Side effect is osteoporosis
C. Can be used for controlled ovarian hyperstimulation for IVF
D. First-line management of menorrhagia (Correct Answer)

Explanation: The correct answer is **D (First-line management of menorrhagia)**. While GnRH analogues (e.g., Leuprolide, Goserelin, Nafarelin) are effective in reducing menstrual blood flow by inducing a hypoestrogenic state, they are **not** first-line treatments. First-line management for menorrhagia typically includes NSAIDs, Tranexamic acid, or hormonal contraceptives (OCPs/LNG-IUS). GnRH analogues are reserved for short-term use (usually <6 months) or as a bridge to surgery due to their significant side-effect profile [2]. **Analysis of other options:** * **A. Precocious Puberty:** Continuous administration of GnRH analogues desensitizes the pituitary GnRH receptors (downregulation), suppressing the pituitary-gonadal axis [1], [2]. This makes them the **gold standard** for treating central precocious puberty. * **B. Osteoporosis:** Chronic use leads to a "pseudomenopause" state. Low estrogen levels increase osteoclast activity, leading to decreased bone mineral density and osteoporosis. This is why "add-back therapy" (low-dose estrogen/progestin) is often used. * **C. IVF:** In controlled ovarian hyperstimulation, GnRH analogues are used to suppress the endogenous LH surge, preventing premature ovulation before oocyte retrieval. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Pulsatile GnRH stimulates FSH/LH; **Continuous** GnRH inhibits FSH/LH (Downregulation) [1], [2]. * **Flare Phenomenon:** Initial administration causes a transient rise in gonadotropins [2]. In prostate cancer patients, this can cause a "bone pain flare," often prevented by co-administering Flutamide. * **Other Indications:** Endometriosis, uterine fibroids (to shrink size pre-operatively), and advanced prostate cancer [2].

Question 263: What is the primary mechanism of action of metformin?

A. Increased peripheral glucose uptake (Correct Answer)
B. Stimulate insulin release
C. Decrease glucose resorption in the intestine
D. None of the above

Explanation: **Explanation:** Metformin, a biguanide, is the first-line oral hypoglycemic agent for Type 2 Diabetes Mellitus. Its primary mechanism involves the activation of **AMP-activated protein kinase (AMPK)**. 1. **Why Option A is correct:** Metformin increases the translocation of glucose transporters (**GLUT-4**) to the cell membrane in skeletal muscles and adipose tissue. This significantly **increases peripheral glucose uptake** and utilization. Simultaneously, it inhibits hepatic gluconeogenesis, reducing the liver's glucose output. Unlike sulfonylureas, metformin is an "euglycemic" agent; it lowers blood glucose without causing hypoglycemia. 2. **Why other options are incorrect:** * **Option B:** Stimulating insulin release is the mechanism of **Sulfonylureas** (e.g., Glipizide) and **Meglitinides** (e.g., Repaglinide). Metformin does not affect pancreatic beta cells and is insulin-sparing. * **Option C:** While metformin may slightly delay intestinal glucose absorption, this is a minor secondary effect. The primary drug class acting via this mechanism (inhibiting alpha-glucosidase) is **Acarbose/Voglibose**. **High-Yield Clinical Pearls for NEET-PG:** * **Weight Neutral/Loss:** Metformin is preferred in obese patients as it does not cause weight gain. * **Adverse Effects:** The most common side effects are GI-related (diarrhea, abdominal pain). The most serious, though rare, is **Lactic Acidosis**. * **Contraindications:** Avoid in patients with renal impairment (eGFR <30 mL/min) due to the risk of lactate accumulation. * **Vitamin B12 Deficiency:** Long-term use can lead to malabsorption of Vitamin B12. * **PCOS:** It is also used to improve ovulation and menstrual regularity in Polycystic Ovary Syndrome.

Question 264: What drug is used to stop the growth of the prostate in a 70-year-old male with benign prostatic hyperplasia?

A. Spironolactone
B. Ketoconazole
C. Finasteride (Correct Answer)
D. Flutamide

Explanation: The correct answer is **Finasteride**. **1. Why Finasteride is correct:** Benign Prostatic Hyperplasia (BPH) is driven by **Dihydrotestosterone (DHT)**, a potent androgen synthesized from testosterone by the enzyme **5-alpha-reductase** [1]. Finasteride is a competitive inhibitor of Type II 5-alpha-reductase. By decreasing the intraprostatic levels of DHT, it reduces the size of the prostate gland (mechanical obstruction), improves urinary flow, and prevents further growth. Unlike alpha-blockers (e.g., Tamsulosin) which only provide symptomatic relief by relaxing smooth muscle [3], [4], 5-alpha-reductase inhibitors actually modify the disease progression. **2. Why the other options are incorrect:** * **Spironolactone (A):** A potassium-sparing diuretic that also acts as an aldosterone antagonist and a weak androgen receptor blocker [2]. It is not used for BPH; its anti-androgenic side effects (like gynecomastia) are usually considered adverse effects [2]. * **Ketoconazole (B):** An antifungal that inhibits steroid synthesis (CYP450 enzymes) at high doses [1]. While it lowers testosterone, it is too toxic for long-term BPH management and is reserved for refractory prostate cancer or Cushing’s syndrome. * **Flutamide (D):** A pure non-steroidal androgen receptor antagonist. It is primarily used in the treatment of **Prostate Cancer**, not BPH, due to its side effect profile and the risk of hepatotoxicity. **Clinical Pearls for NEET-PG:** * **Dutasteride** is a similar drug but inhibits both Type I and Type II 5-alpha-reductase. * **Timeframe:** Finasteride takes **6–12 months** to significantly reduce prostate size. * **PSA Levels:** Finasteride can decrease Serum PSA levels by approximately 50%; this must be accounted for when screening for prostate cancer. * **Other Use:** Finasteride (1mg) is also FDA-approved for **Male Pattern Baldness (Androgenetic Alopecia)**.

Question 265: Danazol is a :

A. Androgen derivative (Correct Answer)
B. Oestrogen
C. Progesterone
D. FSH derivative

Explanation: **Explanation:** **Danazol** is a synthetic ethisterone derivative with weak androgenic properties. It is chemically classified as an **isoxazole derivative of 17-α-ethinyl testosterone**, making it an **androgen derivative (Option A)**. ### Why the correct answer is right: Danazol exerts its effect through a multi-pronged mechanism: 1. **Gonadotropin Inhibition:** It suppresses the mid-cycle surge of LH and FSH (pituitary inhibition). 2. **Enzyme Inhibition:** It inhibits several enzymes involved in steroidogenesis (e.g., 3β-HSD, p450c17). 3. **Direct Binding:** It binds to androgen, progesterone, and glucocorticoid receptors, though it primarily acts as a weak androgen. By creating a "hypoestrogenic and hyperandrogenic" environment, it causes atrophy of ectopic endometrial tissue. ### Why incorrect options are wrong: * **Option B & C:** While Danazol has some affinity for progesterone receptors, it is not an estrogen or progesterone derivative. In fact, it antagonizes the effects of estrogen on target tissues. * **Option D:** Danazol is not a derivative of FSH; instead, it acts to suppress the secretion of gonadotropins (FSH/LH) from the anterior pituitary. ### High-Yield Clinical Pearls for NEET-PG: * **Primary Indications:** Endometriosis (historically the drug of choice, though now second-line), Hereditary Angioedema (increases synthesis of C1 esterase inhibitor), and Fibrocystic breast disease. * **Side Effects:** Significant androgenic side effects including weight gain, acne, hirsutism, deepening of voice (may be irreversible), and decreased breast size. * **Contraindications:** It is contraindicated in pregnancy due to the risk of **pseudohermaphroditism** (virilization) of the female fetus. * **Metabolic Effect:** It can cause a decrease in HDL levels and an increase in LDL levels.

Question 266: Insulin acts on which type of receptor?

A. Gs receptor
B. Nuclear receptor
C. Tyrosine kinase receptor (Correct Answer)
D. Ligand gated receptor

Explanation: **Explanation:** **1. Why Tyrosine Kinase Receptor is Correct:** Insulin acts via a specific type of **Enzyme-linked receptor** known as the **Receptor Tyrosine Kinase (RTK)**. The insulin receptor is a heterotetramer consisting of two extracellular alpha subunits (binding site) and two transmembrane beta subunits. Upon insulin binding, the beta subunits undergo **autophosphorylation**, which activates the intrinsic tyrosine kinase activity. This triggers a signaling cascade involving **Insulin Receptor Substrates (IRS 1-4)** and the **PI3K/Akt pathway**, leading to the translocation of **GLUT-4** transporters to the cell membrane, facilitating glucose uptake. **2. Why Other Options are Incorrect:** * **Gs receptor (G-protein coupled):** These act via the Adenylyl Cyclase-cAMP pathway. Examples include Glucagon and Beta-adrenergic receptors. Insulin does not use G-proteins. * **Nuclear receptor:** These are intracellular receptors for lipid-soluble hormones like Steroids, Thyroid hormones, and Vitamin D. Insulin is a peptide hormone and cannot cross the lipid bilayer; it must act on surface receptors. * **Ligand-gated receptor:** These are ion channels that open in response to a neurotransmitter (e.g., Nicotinic ACh receptors). Insulin signaling involves enzymatic phosphorylation, not direct ion flux. **Clinical Pearls for NEET-PG:** * **GLUT-4** is the only insulin-dependent glucose transporter, found primarily in **skeletal muscle and adipose tissue**. * The **MAP Kinase pathway** is the other major pathway activated by insulin, responsible for its **growth-promoting and mitogenic effects**. * **Downregulation** of these receptors or defects in the IRS signaling leads to **Insulin Resistance** (Type 2 Diabetes). * Other hormones using Tyrosine Kinase: **IGF-1, EGF, and PDGF.**

Question 267: Ergometrine is not used for the initiation of labour because:

A. It has a slow onset of action.
B. It causes fetal hypoxia. (Correct Answer)
C. It increases blood pressure.
D. It acts on D2 receptors to cause vomiting.

Explanation: **Explanation:** The primary goal during the initiation of labor is to mimic natural uterine contractions, which are rhythmic and followed by periods of relaxation. These relaxation phases are crucial for maintaining uteroplacental blood flow and fetal oxygenation. **Why Option B is Correct:** Ergometrine (an ergot alkaloid) induces **tetanic or sustained uterine contractions** with high basal tone. Unlike oxytocin, it does not allow for adequate uterine relaxation between contractions. This continuous compression of the intramyometrial blood vessels severely compromises blood flow to the placenta, leading to **fetal hypoxia and distress**. Therefore, its use is strictly contraindicated before the delivery of the fetus. **Analysis of Incorrect Options:** * **Option A:** Ergometrine actually has a rapid onset of action (1–5 minutes depending on the route), making it effective for emergency management of postpartum hemorrhage (PPH). * **Option C:** While ergometrine can cause vasoconstriction and increase blood pressure (making it contraindicated in pre-eclampsia/eclampsia), this is a maternal side effect and not the primary reason it is avoided for labor induction. * **Option D:** Ergometrine does have partial agonist activity at D2 receptors in the CTZ, causing nausea and vomiting, but this is a manageable side effect and not a contraindication for labor initiation. **High-Yield NEET-PG Pearls:** * **Drug of Choice (DOC) for Induction of Labor:** Oxytocin (due to its physiological, rhythmic contractions). * **DOC for Postpartum Hemorrhage (PPH):** Oxytocin (prophylaxis); Ergometrine or Carboprost (treatment). * **Contraindications for Ergometrine:** Pregnancy (before delivery), Hypertension, Preeclampsia, and Peripheral Vascular Disease. * **Mechanism:** Acts on 5-HT2 and alpha-adrenergic receptors in the myometrium.

Question 268: What is the mechanism of action of finasteride?

A. Androgen receptor antagonist
B. 5-alpha reductase inhibitor (Correct Answer)
C. 17-alpha hydroxylase inhibitor
D. Aromatase inhibitor

Explanation: ### Explanation **Correct Answer: B. 5-alpha reductase inhibitor** **Mechanism of Action:** Finasteride is a selective inhibitor of the **Type II 5-alpha reductase** enzyme. This enzyme is responsible for converting Testosterone into its more potent metabolite, **Dihydrotestosterone (DHT)**, primarily within the prostate gland and hair follicles. By inhibiting this conversion, finasteride significantly lowers serum and tissue DHT levels without suppressing testosterone itself. This leads to a reduction in prostate volume and prevents the miniaturization of hair follicles. **Analysis of Incorrect Options:** * **A. Androgen receptor antagonist:** These drugs (e.g., **Flutamide, Bicalutamide, Spironolactone**) block the binding of androgens to their receptors. Unlike finasteride, they do not inhibit the synthesis of DHT. * **C. 17-alpha hydroxylase inhibitor:** This describes **Abiraterone**, which inhibits the synthesis of cortisol and androgens in the adrenal glands and testes. It is used in metastatic castration-resistant prostate cancer. * **D. Aromatase inhibitor:** These drugs (e.g., **Anastrozole, Letrozole**) block the conversion of androgens to estrogens. They are primarily used in the treatment of ER-positive breast cancer. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Uses:** Finasteride is FDA-approved for **Benign Prostatic Hyperplasia (BPH)** to reduce prostate size and **Androgenetic Alopecia (Male pattern baldness)**. * **Dutasteride vs. Finasteride:** Dutasteride is a non-selective inhibitor of both Type I and Type II 5-alpha reductase, whereas Finasteride is selective for Type II. * **Side Effects:** Decreased libido, erectile dysfunction, and gynecomastia. * **Contraindication:** It is highly **teratogenic** (Category X). Pregnant women should not even handle crushed tablets due to the risk of hypospadias in a male fetus.

Question 269: Monotherapy with which of the following antidiabetic drugs can cause hypoglycemia?

A. Metformin
B. Gliclazide (Correct Answer)
C. Pioglitazone
D. All of the above

Explanation: **Explanation:** The risk of hypoglycemia with antidiabetic monotherapy depends on whether the drug’s mechanism is **insulin-independent** (euglycemic) or **insulin-secretagogue** (insulin-releasing). **1. Why Gliclazide is Correct:** Gliclazide is a **Second-Generation Sulfonylurea**. It works by binding to the SUR1 subunit of the ATP-sensitive K⁺ channels in pancreatic beta cells. This causes channel closure, depolarization, and a subsequent influx of calcium, leading to the **exocytosis of insulin regardless of blood glucose levels**. Because it forces insulin release even when blood sugar is normal, it can cause significant hypoglycemia. **2. Why Other Options are Incorrect:** * **Metformin (Biguanide):** It is an "insulin sensitizer." It primarily decreases hepatic gluconeogenesis and improves peripheral glucose uptake. It does not stimulate insulin secretion; hence, it is considered a **euglycemic** agent and does not cause hypoglycemia when used alone. * **Pioglitazone (Thiazolidinedione):** It acts as a PPAR-γ agonist, increasing insulin sensitivity in adipose and muscle tissue. Like Metformin, it does not increase insulin secretion from the pancreas, making the risk of monotherapy-induced hypoglycemia negligible. **High-Yield Clinical Pearls for NEET-PG:** * **Highest Risk:** Among sulfonylureas, **Glibenclamide** (long-acting) has the highest risk of hypoglycemia, while **Gliclazide** has a relatively lower risk due to its shorter half-life and reversible binding. * **Weight Gain:** Drugs that cause hypoglycemia (Sulfonylureas, Meglitinides, Insulin) typically also cause weight gain. * **Safe in Renal Failure:** Among sulfonylureas, **Gliquidone** is primarily excreted in bile, making it safer in renal impairment. * **Other Hypoglycemic Classes:** **Meglitinides** (Repaglinide) also act as secretagogues and can cause hypoglycemia.

Question 270: Which of the following is NOT a side effect of steroids?

A. Hypoglycemia (Correct Answer)
B. Hypertension
C. Psychosis
D. Growth retardation

Explanation: ### Explanation **Correct Answer: A. Hypoglycemia** **Why Hypoglycemia is the correct answer:** Glucocorticoids are **counter-regulatory hormones** that antagonize the actions of insulin. They promote **hyperglycemia** (not hypoglycemia) through several mechanisms: 1. **Increased Gluconeogenesis:** Stimulating the liver to produce glucose from non-carbohydrate sources. 2. **Decreased Peripheral Glucose Uptake:** Reducing glucose utilization by muscle and adipose tissue (insulin resistance). 3. **Permissive Action:** Enhancing the effects of glucagon and catecholamines. Therefore, steroid therapy typically leads to "Steroid-induced Diabetes" or worsening of glycemic control in known diabetics. **Analysis of Incorrect Options:** * **B. Hypertension:** Steroids cause sodium and water retention (mineralocorticoid effect) and increase vascular sensitivity to catecholamines, leading to elevated blood pressure. * **C. Psychosis:** Glucocorticoids cross the blood-brain barrier and can cause a spectrum of neuropsychiatric effects, ranging from mild euphoria and insomnia to severe "steroid psychosis" and depression. * **D. Growth Retardation:** In children, chronic steroid use inhibits linear bone growth by suppressing growth hormone secretion and exerting direct inhibitory effects on chondrocytes and osteoblasts at the epiphyseal plates. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Steroid Side Effects (CUSHINGOID):** **C**ataracts, **U**lcers, **S**kin thinning/Striae, **H**ypertension/Hirsutism, **I**mmunosuppression, **N**ecrosis (Avascular necrosis of femoral head), **G**lucose elevation, **O**steoporosis, **I**mpaired wound healing, **D**epression/Psychosis. * **Ocular side effects:** Steroids are notorious for causing **Posterior Subcapsular Cataracts** and **Open-angle Glaucoma**. * **Withdrawal:** Abrupt cessation after chronic use can lead to **Acute Adrenal Insufficiency** (Addisonian Crisis) due to prolonged HPA-axis suppression.

Practice by Chapter

Hypothalamic and Pituitary Hormones

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Thyroid Drugs and Antithyroid Agents

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Insulin and Oral Hypoglycemic Agents

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Adrenocorticosteroids

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Sex Hormones: Estrogens and Progestins

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Androgens and Anabolic Steroids

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Hormonal Contraceptives

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Drugs Affecting Calcium Metabolism

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Drugs for Osteoporosis

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Pharmacological Management of Obesity

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