The mechanism of methylxanthines action is:

Correct Answer: A

Rationale: The correct answer is A: Inhibition of the enzyme phosphodiesterase. Methylxanthines like theophylline and caffeine work by inhibiting phosphodiesterase enzymes, leading to increased levels of intracellular cyclic AMP. This results in smooth muscle relaxation, bronchodilation, and increased heart rate. Choice B is incorrect as methylxanthines do not directly stimulate beta2-adrenoreceptors. Choice C is incorrect as they do not inhibit the production of inflammatory cytokines. Choice D is incorrect as they do not inhibit M-cholinoreceptors.

Correct Answer: A

Rationale: Verapamil is a calcium channel blocker that can worsen heart failure symptoms by reducing heart contractility. Digoxin, dobutamine, and dopamine are commonly used to treat severe congestive heart failure by improving heart function. Verapamil is not recommended for heart failure management due to its negative inotropic effects.

Correct Answer: A

Rationale: Rationale: A: Incorrect. Bradycardic agents like Falipamil and Alinidine primarily act on cardiac tissue to decrease heart rate. They do not directly stimulate nerve endings to cause reflex and vascular dilative actions. B: Correct. The main effect of bradycardic drugs is to decrease heart rate without significant changes in arterial pressure. C: Correct. Bradycardic agents reduce oxygen demand on the heart which can be protective, especially in conditions like angina pectoris. D: Correct. Specific bradycardic agents are indeed used in the management of cardiovascular disorders like sinus tachyarrhythmias and angina pectoris.

Correct Answer: A

Rationale: Rationale: 1. Aminalon and Picamilon are GABA derivatives known to influence blood flow in the brain by enhancing cerebral circulation. 2. GABA derivatives like Aminalon and Picamilon act as vasodilators, improving blood flow without affecting blood pressure. 3. Nimodipine and Cinnarizine are calcium channel blockers that mainly act on vascular smooth muscle, not directly related to GABA. 4. Heparin and Warfarin are anticoagulants used to prevent blood clots, not directly affecting blood flow in the brain. 5. Vinpocetine and Nicergoline are vasodilators that enhance cerebral blood flow, but they are not derivatives of GABA.

Correct Answer: B

Rationale: The correct answer is B: FALSE. Bovine insulin is actually more antigenic than porcine insulin due to differences in amino acid sequences between bovines and humans, leading to a higher likelihood of immune response. Choice A is incorrect as it states that bovine insulin is less antigenic, which is false. Choices C and D do not apply since the correct answer is B.