Which of the following is an example of a vasopressor?

Norepinephrine is classified as a vasopressor because it primarily acts to constrict blood vessels, thereby increasing blood pressure. This mechanism is particularly important in critical care settings where patients may experience significant hypotension, often due to conditions like septic shock or cardiogenic shock. Norepinephrine works by stimulating alpha-adrenergic receptors, leading to vasoconstriction, and also has some beta-adrenergic activity, which can increase cardiac output.

The use of vasopressors like norepinephrine is essential in managing acute cases of heart failure or other conditions where maintaining adequate blood pressure is crucial for ensuring adequate perfusion to vital organs. In contrast, the other options listed do not share this primary function; for instance, furosemide is a diuretic used to manage fluid overload, insulin regulates blood glucose levels, and atropine is primarily an anticholinergic agent used in bradycardia or to reduce secretions.