Illustration of norepinephrine (noradrenaline). Norepinephrine acts as a stress hormone and neurotransmitter. As a hormone, noradrenaline is formed inside the adrenal gland (adrenal medulla), and as a neurotransmitter it is produced in the brain. As a hormone, norepinephrine increases heart rate and blood pressure by constricting blood vessels. As a neurotransmitter, norepinephrine is produced in the locus caeruleus of the brain and plays a role in increasing alertness, wakefulness, and concentration, among other functions.