Fluctuated changes in the rat hypothalamic content of corticotropin releasing factor around the peak of the circadian rhythm.

It is well known that hypothalamic corticotropin releasing factor (CRF) activity shows a marked circadian rhythm with the peak around 16 o'clock and the minimal level around 8 o'clock, followed by almost parallel changes of plasma corticosterone. But the circadian variations of CRF activity at short intervals (22 or 23 min) around 16 o'clock has not been obvious. In this experiment, we demonstrated fluctuated changes of CRF content in the non-stressed rat hypothalamus with 22 or 23 min intervals around the peak at a quarter past 16 o'clock.