[Circadian rhythm of ornithine decarboxylase activity in the rat epiphysis]

A distinct 24-hour rhythm of the ornithindecarboxylase (ODC) was revealed in the epiphyses of rats kept under controlled illumination regimen (14 hours illumination and 10 hours darkness). ODC was an enzyme playing, according to modern views, a significant role in the regulation of the rate of protein biosynthesis at the level of transcription and translation. The maximum ODC activity was observed during the darkness period, and the minimum--during illumination. The 24-hour rhythm of the enzyme activity was levelled in the animals kept under constant illumination and in blinded animals. This indicated that the ODC rhythm was not oxogenous, but endogenous, circadian, whereas the external stimulus (the illumination regimen) synchronized the circadian changes in the enzyme activity with the time of the 24-hour period. The data obtained open one of the possible ways of analysing the mechanism of the pineal rhythms formation.