A 69-Year-Old Man Complains of Episodes of "Squeezing" Substernal Chest $\alpha$

A 69-year-old man complains of episodes of "squeezing" substernal chest pains that occur when he physically exerts himself. He sometimes feels the pain in his jaw, and it often radiates down his left arm. After thorough evaluation, he is diagnosed with chronic stable angina (exertional angina) and instructed to take nitroglycerin. The mechanism by which nitroglycerin exerts its beneficial effects in angina is by:

A) Blocking ( $\alpha$ ₁) -adrenergic receptors and reducing myocardial oxygen consumption by decreasing cardiac pre-load and afterload.
B) Blocking ( $\beta$ ₁) -adrenergic receptors and reducing myocardial oxygen consumption by preventing an increase in heart rate and contractility.
C) Blocking slow (Ca²⁺) channels and reducing myocardial oxygen consumption by decreasing cardiac contractility, heart rate, and arterial pressure.
D) Causing smooth muscle relaxation by stimulating the formation of nitric oxide, thereby causing an increase in the level of cyclic guanosine monophosphate ( cGMP ) .
E) Preventing platelet aggregation by inhibiting platelet cyclooxygenase activity.