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Abstract
The impact of L-serine on the daily rhythms of growth hormone (GH) and corticosterone remains unknown. We explored whether the daily rhythms of these hormones were affected by L-serine supplementation as well as the supplementation time. The results showed that plasma GH concentration at Zeitgeber time (ZT)4 and 8 were significantly increased by L-serine supplementation at ZT22, while the diurnal rhythms peaks of plasma corticosterone at ZT12 were suppressed by L-serine supplementation at ZT10. After the supplementation was stopped, the effects of L-serine on the diurnal rhythms of plasma GH and corticosterone lasted for 2 days then they were fading on day 4. L-serine concentrations in plasma and hypothalamus after supplementation at ZT22 was lower than those after supplementation at ZT10. In conclusion, L-serine modulates the daily rhythms of GH and corticosterone depending on its supplementation time. The modulation effect might be association with the daily rhythms of L-serine metabolism.