Pharmacology of catecholamines and of serotonin
The catecholamines (named for the catechol moiety that is part of their structure, Figure 10.1) are important in both the peripheral autonomic system and the central nervous system. Key functions in the periphery are regulation of heart rate and blood pressure. In the brain, they are in-volved in the regulation of posture and movement, and of psychical functions such as mood and alertness.
Although all three mediators occur both peripherally and centrally, dopamine and norepinephrine are the main ones found as transmitters in the brain, whereas norepinephrine and epinephrine are more important than dopamine in the periphery. Norepinephrine occurs in both synapses and in the adrenal gland, whereas epinephrine is mainly found in the adrenal gland and thus really is a hormone more than a transmitter.
Serotonin is a mediator similar to the catecholamines that is derived from tryptophan rather than tyrosine (Figure 10.2b). It also occurs as a mediator in the periphery, but its major interest in clinical pharmacology is due to its role in the central nervous system, where it shares with the cate-cholamines in the regulation of mood. The functional orga-nization of synapses for both catecholamines and serotonin is closely similar, so that it is useful to discuss them side-by-side.