Circadian synchronization of hepatocyte proliferation in young XXXX : the role played by adrenal hormones.

@entity35 @entity1442 @entity2819 @entity3812
The circadian rhythm of hepatic cell proliferation in @entity35 appears on the 20th day of life, when the hypothalamo-adrenal axis is mature enough for circadian activity to occur. From the 20th day to the 30th day of life, the mitotic rhythm is progressively induced by a reduction in nocturnal values, while diurnal @entity1442 remain unchanged. Mitotic peaks emerge at 10.00 hours. A labelling index wave occurs 8 hr before the corresponding mitotic wave, with a peak at 02.00 hours and a minimum in the evening, coincidental with the acrophase of plasma @entity2819 level (activity phase). Labelled mitoses curves and metaphase accumulation after @entity3812 injection show that the duration of the S, G2 and M phases remain approximately constant and that the circadian variation is due to a variation in the rate of cells that enter these successive phases. During the synchronization period (from day 20 to 30), the growth fraction decreases progressively. Adrenalectomy at this time is followed by a higher cell proliferation and all @entity1442 disappear after 2 days. @entity2819 injected before the triggering of the rhythmic activity in 17-day-old @entity35 immediately reduces the labelling index, while the mitotic index is decreased 10 hr later; this delay is equal to the S + G2 duration. The results are discussed. They favour the hypothesis that the circadian variation of @entity2819 is responsible for the induction of a circadian variation in developmental cell proliferation by inhibition of the G1-S transition when it is higher in the evening.
