Norepinephrine

Norepinephrine

l-Norepinephrine is a naturally occurring catecholamine hormone that functions as a neurotransmitter in the sympathetic nervous system. Norepinephrine directly stimulates adrenergic receptors. Stimulation of alpha-adrenergic receptors causes vasoconstriction of the radial smooth muscle of the iris, arteries, arterioles, veins, urinary bladder, and the sphincter of the gastrointestinal tract. Stimulation of beta-1 adrenergic receptors causes an increase in myocardial contractility, heart rate, automaticity, and atrioventricular (AV) conduction while stimulation of beta-2 adrenergic receptors causes bronchiolar and vascular smooth muscle dilatation.