Biotransformation of a medicinal substance results in:

Correct Answer: A

Rationale: The correct answer is A: Faster urinary excretion. Biotransformation involves converting a drug into metabolites that are more easily excreted by the body, primarily through urine. This process increases the water solubility of the drug, allowing it to be eliminated more efficiently. Option B is incorrect because biotransformation typically leads to faster, not slower, urinary excretion. Option C is incorrect as biotransformation does not affect distribution within the organism. Option D is incorrect because biotransformation does not directly impact the binding of the drug to membranes.

Correct Answer: A

Rationale: The correct answer is A: Heart. M2 cholinoreceptors are primarily located in the heart. These receptors are involved in regulating heart rate and contractility by inhibiting adenylate cyclase activity. This leads to decreased cAMP levels, resulting in a decrease in heart rate and contractility. The other choices (B: Glands, C: Smooth muscle, D: Endothelium) are incorrect as M2 receptors are not typically found in these locations. In glands, M3 receptors are more common, in smooth muscle M3 receptors predominate, and in the endothelium, muscarinic receptors are not the primary receptors involved in regulation.

Correct Answer: C

Rationale: The correct answer is C: Atropine. Atropine is useful in the treatment of uterine spasms because it acts as an antispasmodic agent by blocking the action of acetylcholine on smooth muscle, including the uterus. Carbachol (A) is a cholinergic agonist that would exacerbate spasms. Vecuronium (B) is a neuromuscular blocking agent used for muscle relaxation during surgery. Edrophonium (D) is a cholinesterase inhibitor used for diagnosing myasthenia gravis. In summary, Atropine is the correct choice due to its antispasmodic properties, while the other options would not be effective or appropriate for treating uterine spasms.

Correct Answer: A

Rationale: The correct answer is A: Heart. Alpha adrenoreceptor subtypes are mainly associated with smooth muscle tissues, not cardiac muscle like the heart. Alpha-1 receptors are present in blood vessels, prostate, and pupillary dilator muscle, helping in vasoconstriction, ejaculation, and pupil dilation respectively. Alpha-2 receptors are also found in these tissues, modulating neurotransmitter release and smooth muscle contraction. The heart primarily contains beta adrenoreceptor subtypes, which regulate heart rate and contractility. Therefore, the distribution of alpha adrenoreceptor subtypes is not associated with the heart.

Correct Answer: C

Rationale: Rationale: 1. Prazosin is an alpha1-selective antagonist used to treat hypertension by blocking alpha1 receptors in blood vessels. 2. Phentolamine (A) is a non-selective alpha-blocker. 3. Dihydroergotamine (B) is a 5-HT1 receptor agonist used for migraine. 4. Labetalol (D) is a non-selective alpha and beta blocker. Therefore, C (Prazosin) is the correct answer as it is a selective alpha1 blocker.