[Circadian variation of the mitotic activity of the adrenal cortex in male rats].

The mitotic activity in the adrenal cortex has been studied during a 24 hours-cycle in male rats that have been sacrificed by perfusion of fixative. A method of calculation of the thickness of the zona germinativa is proposed : it permits to compute mitotic densities in relation to surface, and mitotic index. Mitotic activity seems to be the combination of a relatively low and constant activity occurring from 7 a.m. (local time) to 11 p.m., and an hyperactivity from 0 to 6 a.m. Two maxima are demonstrated : one at 0 h, and another one, more important, at 5 a.m. (local time). Results are analyzed, discussed and compared with others obtained on different organs : each tissue seems to have its own characteristics according to horary and intensity in mitotic activity.