ABSTRACT
Melatonin is a hormone secreted by the pineal gland located deep within the
brain. It is synthesised from the amino acid tryptophan by the enzymes
N-acetyltransferase and 5-hydroxyindole-O-methyltransferase (HIOMT). It is
itself a substrate for serotonin or 5-hydroxytryptamine, a neurotransmitter
engaged in regulating sleep (see Table 23.1).
