Dopamine at low doses influences mainly:

Correct Answer: B

Rationale: The correct answer is B because at low doses, dopamine primarily acts on dopamine receptors, leading to vasodilation of renal and mesenteric vessels. This is known as the renal dose of dopamine. Choices A and C are incorrect because low doses of dopamine do not significantly impact alpha-adrenoreceptors for peripheral vasoconstriction or beta-1 adrenoreceptors for enhancing cardiac output. Choice D is incorrect as dopamine at low doses does not affect all the mentioned receptors simultaneously.

Correct Answer: D

Rationale: The correct answer is D because mifepristone (RU-486) acts in multiple ways to terminate pregnancy. It inhibits ovulation by blocking progesterone receptors, suppresses midcycle gonadotropin release, inhibits progesterone action on the uterus during the luteal phase, induces prostaglandin release from the endometrium, facilitates luteolysis, induces menstruation, increases uterine motility, softens the cervix, and causes detachment of the embryo. Therefore, all the actions described in options A, B, and C are correct, making option D the correct choice. Options A, B, and C are incorrect because they each only describe a single aspect of mifepristone's mechanism of action, whereas option D encompasses all the actions of mifepristone.

Correct Answer: B

Rationale: Delayed allergy reaction (type IV allergic reaction) is characterized by a delayed onset, typically appearing hours after exposure. This differs from immediate allergic reactions (type I) that occur within minutes. Choice A refers to an immediate allergic response. Choice C describes type III allergic reactions involving antigen-antibody complexes, not type IV. Choice D is related to tissue damage caused by elevated antigen-antibody complexes, which is not specific to delayed allergy reactions. Thus, choice B is correct as it aligns with the delayed nature of type IV allergic reactions.

Correct Answer: D

Rationale: The correct answer is D because coenzymes are nonprotein organic substances that combine with specific apoenzymes to form active enzyme systems. This is essential for catalyzing biochemical reactions. Choice A describes vitamins, not coenzymes. Choice B describes anti-nutrients, not coenzymes. Choice C describes enzymes, not coenzymes. Thus, the correct answer is D.

Correct Answer: B

Rationale: The correct answer is B, Allopurinol. Allopurinol is a xanthine oxidase inhibitor, which helps reduce uric acid levels in conditions like gout. Xanthine oxidase is an enzyme involved in the production of uric acid. Physostigmine (A) is a cholinesterase inhibitor used in conditions like myasthenia gravis. Aminocaproic acid (C) is an antifibrinolytic agent. Acetazolamide (D) is a carbonic anhydrase inhibitor used in conditions like glaucoma and altitude sickness. Therefore, Allopurinol is the correct choice as a xanthine oxidase inhibitor.