Several actions of growth hormone are exerted through the elaboration of:

Correct Answer: D

Rationale: The correct answer is D, Insulin like growth factor-1 (IGF-1). Growth hormone stimulates the production of IGF-1 in the liver, which mediates many of its growth-promoting effects. IGF-1 acts on target tissues to promote cell growth and division. A is incorrect because growth hormone does not directly act through cyclic AMP. B is incorrect as cyclic GMP is not a major mediator of growth hormone actions. C, somatostatin, is a hormone that inhibits growth hormone release and does not play a direct role in mediating growth hormone effects. In summary, the correct answer, D, is supported by the fact that IGF-1 is a key downstream mediator of growth hormone actions.

Correct Answer: C

Rationale: The correct answer is C: Bromocriptine. Gynaecomastia is often caused by hormonal imbalances, specifically increased estrogen levels relative to testosterone. Bromocriptine is a dopamine agonist that inhibits prolactin secretion, which can help restore hormonal balance and reduce gynaecomastia. Chlorpromazine (A) is an antipsychotic with no direct effect on hormonal levels. Cimetidine (B) is a histamine H2 receptor antagonist used for acid reflux and ulcers, not for gynaecomastia. Metoclopramide (D) is a dopamine receptor antagonist that can actually exacerbate gynaecomastia by increasing prolactin levels.

Correct Answer: D

Rationale: The correct answer is D because adrenocorticotropic hormone (ACTH) is primarily used for diagnosing pituitary-adrenal axis disorders. ACTH stimulates the adrenal glands to produce cortisol, so measuring cortisol levels after administering ACTH helps identify disorders like Cushing's syndrome or adrenal insufficiency. Choices A, B, and C are incorrect because ACTH is not used to treat Addison's disease, congenital adrenal hyperplasia, or autoimmune diseases. Instead, these conditions may require cortisol replacement therapy, specific enzyme inhibitors, or immunosuppressants, respectively.

Correct Answer: A

Rationale: The correct answer is A. Auricular fibrillation is not a complication of overtreatment with thyroxine. Thyroxine is a thyroid hormone that can increase heart rate and cardiac output, potentially leading to complications such as angina pectoris, congestive heart failure, and acceleration of atherosclerosis. However, auricular fibrillation, also known as atrial fibrillation, is not directly caused by thyroxine over-treatment. It is important to differentiate between the potential complications of thyroxine therapy to ensure proper management and avoid unnecessary risks to the patient's health.

Correct Answer: A

Rationale: Propyl thiouracil inhibits the enzyme 5'-deiodinase, which is responsible for converting thyroxine (T4) to triiodothyronine (T3) peripherally. Methimazole and carbimazole primarily inhibit thyroid hormone synthesis. Radioactive iodine destroys thyroid tissue. Therefore, choice A is correct as it specifically targets the peripheral conversion of T4 to T3.