Diurnal Fluctuations in Plasma Hydrogen Sulfide of the Mice

Circadian rhythms are essential in a myriad of physiological processes to maintain homeostasis, especially the redox homeostasis. However, little is known about whether plasma H(2)S exhibits the physiological diurnal variation. The present study was performed to investigate the diurnal fluctuations of plasma H(2)S and explore the potential mechanisms. We found that the plasma H(2)S of the C57BL/6J mice was significantly higher at 19 o’clock than those at 7 o’clock which was not affected by the blood-collecting sequence and the concentrations of plasma cysteine (a precursor of H(2)S). No significant differences in mRNA or protein expression of the CSE, CBS, or MPST were observed between 7: 00 and 19: 00. There were also no significant differences in the CSE and CBS activities, while the activities of MPST in tissues were significantly higher at 19 o’clock. After treatment with AOAA (a CBS inhibitor) or PPG (a CSE inhibitor) for 14 days, plasma H(2)S concentrations at 19 o’clock were still significantly higher than those at 7 o’clock, although they were both significantly decreased as compared with controls. Identical findings were also observed in CSE KO mice. We also found the plasma H(2)O(2) concentrations were significantly higher at 19 o’clock than those at 7 o’clock. However, H(2)O(2) concentrations were significantly decreased at 19 o’clock than those at 7 o’clock when mice were exposed to continuous light for 24 h. Meanwhile, the diurnal fluctuations of plasma H(2)S levels and MPST activities in tissues were disappeared. After treatment with DTT for 14 days, there was no significant difference in plasma H(2)O(2) concentrations between 7 o’clock and 19 o’clock. Meanwhile, the diurnal fluctuations of plasma H(2)S levels and MPST activities in tissues were disappeared. Identical findings were also observed in SOD(2+/-) mice. When heart tissues were incubated with increasing concentrations of H(2)O(2) in vitro, H(2)O(2) could dose-dependently increase the activity of MPST within a certain concentration range. In conclusion, our studies revealed that plasma H(2)S concentration and tissue MPST activity exhibited diurnal fluctuations. Modulated by plasma H(2)O(2) concentration, changes of MPST activity probably led to the diurnal fluctuations of plasma H(2)S.