Similar to epinephrine, norepinephrine is an α1 and α2 adrenergic receptor agonist. After entering the body, it directly agonizes α receptors and is not selective for α1 and α2 receptors. It has weak agonistic effect on β1 receptors and almost no effect on β2 receptors. ① Agonism of vascular α1 receptors, causing vasoconstriction (especially small arteries and veins). The degree of vasoconstriction on various parts of the body is related to the density of α receptors and the dose of norepinephrine; the vasoconstriction of skin mucosa is the most obvious, followed by renal vessels; the vasoconstriction on brain, liver, mesenteric and even skeletal muscle vessels. However, it can increase the coronary blood flow. ②Norepinephrine mainly agonizes cardiac β1 receptors, enhances myocardial contractility, accelerates heart rate and conduction, and increases myocardial excitability. However, the excitatory effect on the heart is weaker than that of epinephrine. (3) Norepinephrine has a strong antihypertensive effect. It can cause peripheral vasoconstriction, cardiac excitation, increase in systolic and diastolic blood pressure, and a slight increase in pulse pressure. ④The effect on smooth muscle outside the blood vessels and metabolism are weak, and the increase of blood glucose only occurs at high doses. Its effect on the central nervous system is also weak. In pregnant women, it may increase the frequency of uterine contractions.