Variations of mitotic activity in the adenohypophysis of male rats during a 24-hour cycle.

The mitotic activity in the adenohypophysis of male rats during a 24 hours' cycle has been studied at the time of the spring equinox. The animals were killed by perfusion of fixative. The mitotic activity seems to be the combination of two elements: a relatively low and nearly constant activity with two peaks of high activity. The first one takes place at 6 o'clock (local time) with an index reaching 4.25; the second one occurs at 11 o'clock (local time) and its index is 2.09. The afternoon activity is weak with an average index of 0.56 between 1 p.m. and 9 p.m. The results are analyzed, discussed and compared with other results observed in different organs.