ABSTRACT
The adrenergic transmitter system involves adrenergic receptors (ARs) that are activated via catecholamines (CAs) including dopamine, epinephrine, and norepinephrine (NE). There are two major groups of ARs, including α and β; each of them contains multiple subtypes. Tyrosine hydroxylase is considered to be the rate-limiting enzyme in CA biosynthesis, which converts l-tyrosine to l-DOPA in the biosynthetic pathway. Three major groups are differentiated by their separate signal transduction pathways and pharmacology. α1-ARs are associated with the activation of mitogen-activated protein kinases and phospholipase D, while α2-ARs are coupled to Gi/Go proteins that result in the stimulation of phospholipase A2 and inhibition of adenylyl cyclase activity. Reuptake of NE into sympathetic nerve endings is the main process that results in termination of the activity of NE on postsynaptic cells. It is known that α1-ARs are postsynaptic in nature and expressed on various effector tissues. In this chapter, we have summarized adrenergic neurotransmission; mechanisms associated with synthesis, storage, release, and termination of action of CAs; and signal transduction pathways associated with ARs. In addition, we have focused on the effects mediated by ARs in various effector organs and possible roles of CAs in various diseases.
