Norepinephrine is a sympathomimetic that is regularly found to be the primary neurotransmitter in postganglionic neurons. When taken pharmacologically it acts on the sympathetic nervous system in the heart and the blood vessels. It is mainly used pharmacologically for hypotension and vasodilatory shock states. It acts on all adrenergic receptors, but the main mechanism of action is on the alpha 1A receptor in blood vessel smooth muscles, and the beta 1 receptor in heart muscles. In the heart Norepinephrine activates beta adrenergic receptors, either 1, 2, or 3 although the most common in the heart is beta-1 adrenergic receptor. This receptor activates the G-coupled receptor cascase which activates cAMP-dependent protein kinase which activates voltage-gated calcium channels. The voltage-gated calcium channels allow calcium to enter the cell. The calcium activates the ryanodine receptor on the sarcoplasmic reticulum in order to release more calcium into the cytosol. This calcium binds with troponin to activate tropomyosin which leads to contraction of the heart. Myosin, with an ADP and phosphate attached, binds to actin to form a cross bridge. Myosin performs a powerstroke, drawing the actin filaments together. Many actin filaments pulled together at the same time leads to muscle contraction.

Norepinephrine Beta-1 Adrenergic Cardiac Pathway References