Which of the following is an example of a direct vasodilator?

Hydralazine is classified as a direct vasodilator because it works by relaxing the smooth muscles in the walls of blood vessels, thereby causing them to widen (dilate) and reducing vascular resistance. This mechanism directly lowers blood pressure by decreasing the peripheral resistance that the heart must work against, making it effective in the management of hypertension.

In contrast, nitroglycerin primarily serves as a venous dilator and is often used for angina, while atenolol is a beta-blocker that reduces heart rate and contractility rather than acting directly on the vessels. Furosemide is a loop diuretic that primarily promotes diuresis and reduces blood volume but does not primarily function as a vasodilator. Thus, hydralazine stands out as a drug specifically designed to directly relax vascular smooth muscle, making it a quintessential example of a direct vasodilator.