H1 histamine receptor subtype is distributed in:

Correct Answer: A

Rationale: The correct answer is A because H1 histamine receptors are primarily found in smooth muscle, endothelium, and the brain. Smooth muscle and endothelium are major sites of action for H1 receptors, regulating functions like vasodilation and bronchoconstriction. The presence of H1 receptors in the brain also plays a role in neurotransmission. Choice B is incorrect because gastric mucosa, cardiac muscle, and mast cells are associated with H2 histamine receptors, not H1. Choice C is incorrect because presynaptic H3 receptors are found in the brain, whereas H1 receptors are primarily postsynaptic. Choice D is incorrect because not all locations listed in the other choices are where H1 receptors are predominantly found.

Correct Answer: B

Rationale: The correct answer is B: Urokinase. Urokinase is an enzyme that plays a key role in the fibrinolytic system by converting plasminogen to plasmin, which degrades fibrin blood clots. Pepsin (A) is a digestive enzyme, L-asparaginase (C) is used in cancer treatment, and Lydaze (D) is not a known enzyme. Therefore, only urokinase (B) is directly involved in fibrinolysis, making it the correct choice.

Correct Answer: B

Rationale: The correct answer is B, Nicotinic acid (niacin). Niacin commonly causes flushing as a side effect due to prostaglandin release. Taking it after meals can slow down absorption and reduce flushing. Pretreatment with aspirin also helps by inhibiting prostaglandin synthesis. Lovastatin (A), Gemfibrozil (C), and Probucol (D) do not cause flushing as a side effect, so the strategies of taking after meals or pretreatment with aspirin would not be effective for reducing flushing caused by these drugs.

Correct Answer: A

Rationale: Rationale for correct answer (A): Alendronate is a bisphosphonate used to treat osteoporosis and Paget's disease by inhibiting bone resorption. It is not indicated for hypoparathyroidism, which involves low levels of calcium due to parathyroid hormone deficiency. Alendronate does not address the underlying cause of hypoparathyroidism. Summary of incorrect choices: B: Alendronate is used for glucocorticoid-induced osteoporosis. C: Alendronate is indicated for Paget's disease. D: Alendronate is effective for syndromes of ectopic calcification.

Correct Answer: B

Rationale: The correct answer is B: Furosemide (Lasix). Furosemide is a loop diuretic that inhibits sodium and chloride transport in the cortical thick ascending limb. This leads to increased excretion of these ions and water. Acetazolamide (A) inhibits carbonic anhydrase in the proximal tubule, Hydrochlorothiazide (C) acts on the distal convoluted tubule, and Amiloride (D) inhibits sodium reabsorption in the collecting duct. Therefore, only Furosemide affects sodium and chloride transport in the cortical thick ascending limb.