Illustration of Photographyrepinephrine (Photographyradrenaline, stick and ball models) molecules in a blood vessel. Photographyrepinephrine acts as a stress hormone and neurotransmitter. As a hormone, Photographyradrenaline is formed in the adrenal gland (adrenal medulla) and increases heart rate and blood pressure by constricting blood vessels. As a neurotransmitter, it is produced in the locus caeruleus of the brain and plays a role in increasing alertness, wakefulness, and concentration, among other functions. Atoms are represented by spheres and are colour coded: carbon (grey), hydrogen (white), nitrogen (blue) and oxygen (red).