Circadian fluctuations in serum serotonin concentrations of normal, healthy men

Abstract

The biogenic amine, serotonin (5-HT), is synthesized from tryptophan (an essential amino acid) and acts multipotent as neurotransmitter/neuromodulator/hormone/precursor for methoxy-indole compounds such as N-acetyl-5-methoxytryptamine (melatonin). The circadian secretion pattern of melatonin is well known. Circadian fluctuations in pineal gland (“central”) concentrations of 5-HT have already been reported in literature. Since information with regard to possible circadian fluctuations in “peripheral" (plasma/serum) serotonin concentrations is scanty, the main objective of this study was to ascertain whether such fluctuations do in fact occur. Serum serotonin concentrations were determined in blood samples obtained hourly from twelve healthy male subjects during a period of 24 hours. The results clearly suggest a triphasic secretion pattern for serum serotonin. (The said circadian secretion tendency does not correspond with that of any determinable 5-HT metabolite).