l-Norepinephrine

**Semantic type:** Hormone

**Definition:** 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.

**Synonyms:** - (-)-alpha-(aminomethyl)-3,4-dihydroxybenzyl Alcohol - (R)-4-(2-Amino-1-hydroxyethyl)-1,2-benzenediol - NOREPHINEPHRINE - l-3,4-Dihydroxyphenylethanolamine - l-Arterenol - l-Noradrenaline