Circadian rhythm of dry mass and weight-class-pattern of the rat hepatocytes--effects of light-dark and feeding regimens.

1. Dry weight has been determined of individual hepatocytes isolated from rats kept at natural or at reversed daily light-dark cycle, and from rats under time-restricted feeding. Behaviours of liver weight, mitotic activity and binuclearity frequency of the hepatocytes and serum corticosterone have been also investigated. 2. At natural light-dark cycle, liver weight, hepatocyte mitotic activity, and serum corticosterone were higher during the day than during the night. In accordance, dry weight and class number of the hepatocytes were both higher by day than by night. 3. By reversal of the light-dark cycle, circadian rhythms of liver weight, hepatocyte mitotic activity and serum corticosterone underwent a reversal. In accordance, circadian rhythm also reversed of both dry mass of the hepatocytes, which became heavier by night than by day, and pattern of the hepatocyte weight-classes, which became sharper, more discrete and more numerous by night, less defined and lower in number by day. 4. Feeding restriction to early morning or to late afternoon did not affect substantially the circadian rhythms of the parameters examined. 5. Binuclear cell frequency did never differ significantly at midnight with respect to midday, irrespectively to the experimental condition. 6. Regulation of the circadian rhythm of both weight-class pattern and dry mass of the hepatocytes appears to be mainly acted by the light-dark regimen likely via modulation of the plasma glucocorticoids (corticosterone) concentration, and increase/decrease of which causes a decrease/increase of the total solid content of hepatocytes, with redistribution of cells in the weight-classes. 7. Feeding rhythm and time elapsed from food intake mainly influence definition of the individual weight-classes and weight range of the hepatocytes.