Karyometric investigation on circadian rhythmic changes in the periportal and perivenous zones of the acinus of the rat liver.

In untreated adult male albino rats changes in nuclear volume within the periportal and the perivenous zones of the liver acinus were measured during a full day and night cycle. Only the perivenous zone displayed circadian rhythmic changes as expressed in the sinus-like course of the nuclear volume-distribution graph (polynomial) with a maximum between 16.00 h and 18.00 h and a minimum at 8.00 h. In all groups studied zonal heterogeneity of the means of nuclear volume and the percent-distribution graphs of nuclear volume classes were retained during the full cycle. Within each zone, however, distribution curves of nuclear volume classes were homogeneous indicating an equally directed trend in time-dependent changes in nuclear volume.