Final answer:
Nitroprusside (Nipride) is the vasoactive drug that reduces preload and afterload, reducing heart oxygen demand by acting as a vasodilator. Nitric oxide is a paracrine chemical causing vasodilation, while epinephrine is used to treat anaphylactic shock by counteracting vasodilation.
Step-by-step explanation:
Among the vasoactive drugs mentioned, Nitroprusside (Nipride) results in reduced preload and afterload, which in turn reduces the oxygen demand of the heart. This drug acts as a vasodilator, meaning it relaxes the smooth muscles of the blood vessels, allowing them to widen and thus decreasing the resistance the heart has to overcome to eject blood during systole (afterload) as well as reducing the volume of blood returning to the heart during diastole (preload). In contrast, Epinephrine (Adrenaline) and Dopamine (Intropin) typically act as inotropic and pressor agents which can increase cardiac output but also potentially increase the heart’s oxygen demand, while Methoxamine (Vasoxyl) is primarily a vasoconstrictor, which could raise afterload.
In the context of paracrine chemicals, nitric oxide is a substance that causes vasodilation, which contributes to reducing both preload and afterload when used therapeutically.
For treating anaphylactic shock, the drug of choice is Epinephrine, as it can counteract the widespread vasodilation and subsequent drop in blood pressure caused by the severe allergic response.