Clinical Endocrinology. 2018;88:549–555. wileyonlinelibrary.com/journal/cen
© 2018 John Wiley & Sons Ltd
1 | INTRODUCTION
Serotonin is a neurotransmitter that modulates various neuropsycho-
logical processes, such as mood, perception, reward, anger, aggression,
appetite, memory, sexuality and attention.
However, more than 90%
of body serotonin is produced outside the central nervous system, par-
ticularly by duodenal enterochromaffin cells.
Most of the blood sero-
tonin is gut- derived and stored within platelets.
Conversely, a small
fraction of serotonin is also found in the serum or plasma. Given that
serotonin cannot cross the blood- brain barrier,
central and periph-
eral serotonergic systems are believed to be functionally separate.
Accumulated evidence suggests that serotonin regulates virtually
all aspects of peripheral organ physiology, including the regulation of
energy balance and bone metabolism, as well as gastrointestinal, car-
diovascular, genitourinary and pulmonary functions.
mediated regulation of insulin secretion,
autocrine and paracrine
mechanisms are thought to be important to the action of serotonin in
Interestingly, a recent study has shown that a lack
of gut- derived serotonin attenuates metabolic adaptation to fasting
in adipose tissue and liver in mice.
These results strongly suggest
Meal- related oscillations in the serum serotonin levels in
healthy young men
| Ji Hee Yu
| Eunheui Jeong
| Hyun Ju Yoo
| Min-Seon Kim
Medicine, Veterans Health Service Medical
This work was supported by grants from
(NRF) funded by the Ministry of Science
Context: Serotonin acts as a neurotransmitter in the central and enteric nervous
systems, modulating psychological, metabolic and gastrointestinal functions. Serotonin
is also found in the serum or plasma, indicating its potential role as a hormone.
Objective: We aimed to assess the 24- hour diurnal profile of serum serotonin in
relation to meal ingestion in healthy adult men.
Methods: Ten healthy (5 lean and 5 obese) male subjects were enrolled in this study.
Blood samples were drawn every 30- 60 minutes throughout a 24- hour period to
determine the serotonin levels. Three meals were provided on a fixed schedule. To con-
firm the effect of meal intake on serum serotonin levels, 4 subjects underwent fasting
until 1500 h and were then provided a meal without notice.
Results: Serum serotonin levels had distinct diurnal variations, with the highest levels
early in the morning and the lowest levels in the midafternoon and during sleep.
Notably, these diurnal oscillations were markedly reduced in obese subjects.
Fluctuations in serum serotonin levels were associated with meal intake, and the levels
peaked 30 minutes before meals and exhibited a trough during the postprandial pe-
riod. Fasting blunted the meal- related oscillations in serum serotonin levels. Moreover,
unexpected meal intake did not lead to a premeal increase in serum serotonin levels.
Conclusions: Serum serotonin levels displayed meal- related diurnal oscillations, which
were disrupted by fasting and obesity. These findings suggest the possibility that cir-
culating serotonin modulates metabolic function in humans.
circadian rhythm, meal, obesity, serotonin, serum