Massarelli_1977_Neurosci.Lett_5_95

The present study reports on the diurnal variation of choline acetyltransferase (ChAT; EC 2.3.1.6.) activity observed in human blood. The product of the enzymatic reaction, acetylcholine, was identified by thin-layer chromatography. The oscillation, first found in the blood of a male volunteer, was confirmed in the blood of a man and a woman volunteers during several days. The maximum enzyme activity appeared to be localized in the afternoon hours and the minimum in the morning hours. Similar results were found on several volunteers of both sexes who showed a statistically significant difference in ChAT activity between 11:30 and 18:30 h. No statistically significant sexual differences was observed. The results are related to the diurnal oscillation of the cholinergic system in rat brain and would indicate a cellular localization of the rhythm.