Die Ultrastruktur der physiologischen Tagesschwankungen in Leberzellen Von Ratten

Rhythms in morphology and function of hepatocytes

In standard textbooks of histology, hepatocyte structure is described as being, for the most part, static. However, more than 50 years ago, it was reported that the glycogen content of rabbit hepatocytes varies significantly over 24 h. Since then, numerous investigators have confirmed this phenomenon in a variety of animals by use of morphological, histochemical and biochemical techniques, and it has been shown that the variation in glycogen content of hepatocytes corresponds with variations in enzymes related to glycogen metabolism. Moreover, there are also variations in most subcellular organelles and in many other proteins over 24 h. It is clear that circadian rhythms need to be taken into account in studies of morphology and function of hepatocytes.

Circadian rhythm of the liver of male rats dosed with phenobarbital--I. Organ weight, cellular structures, glycogen contents and mitotic activity

The circadian rhythm of the liver, namely organ weight, cellular structures (by light-microscopy), glycogen content (by periodic acid-Schiff (PAS) reaction) and mitotic activity, was studied in 166 male Sprague-Dawley rats orally treated daily at 0800-0900 with 70 (study 1) or 50 (study 2) mg/kg phenobarbital (PB) for 7 days. Thereafter, eight (study 1) or five (study 2) rats each were studied at 4-hr intervals at 1000, 1400, 1800, 2200, 0200, 0600 and 1000 through till the following day. The lighting schedule in the colony was 12:12, light:dark (light from 0600 to 1800). The liver weight was raised in PB-treated rats at all times of the day compared to controls and showed a distinct circadian rhythm with a peak at 1000 and a minimum at 2200 in PB-treated rats and the controls. The circadian rhythm of cellular structures was closely related to the hepatic glycogen content which was in good agreement with the controls, but at 1400 and 1800 the glycogen particles were more distinctly diminished in the enlarged centrilobular hepatocytes of PB-treated rats. The mitotic activity of hepatocytes was markedly increased in rats treated with PB but showed the same circadian rhythm as controls with a peak at 1000.

Circadian rhythm of the liver of male rats pre-treated with phenobarbital--II. Hexobarbital sleeping time and lipids content in liver and serum

The circadian rhythm of hexobarbital sleeping time and lipids content in liver and serum were studied in 226 male Sprague-Dawley rats pretreated daily at 0800-0900 with 70 mg/kg (study 1 or 3) or 50 mg/kg (study 2) phenobarbital (PB) orally for 7 days. Thereafter, eight (study 1) or five (study 2 and 3) rats each were studied at 4-hr intervals at 1000, 1400, 1800, 2200, 0200, 0600 and 1000 through the following day. The lighting schedule in the colony was 12:12 +/- light:dark (light from 0600 to 1800). The hexobarbital sleeping times of PB-pretreated rats were generally shortened compared to the controls and no circadian rhythm was observed. PB-treatment increased slightly the liver content of cholesterol, and significantly that of triglycerides and phospholipids. Liver cholesterol and phospholipids showed circadian rhythms with peaks during the dark phase. No circadian rhythm of liver triglycerides existed. In serum, levels of triglycerides and phospholipids were slightly lowered by PB-treatment, while levels of cholesterol and beta-lipoprotein were not influenced. Serum values did not exhibit circadian rhythms.

Circadian rhythm of hepatocellular structures in rats dosed phenobarbital

The circadian rhythm of liver weight and hepatic structures was studied in rats given a maximum tolerated dose of 70 or 80 mg/kg/day Phenobarbital during 7 days and killed at four different hours of the following day. The drug-induced increase in liver weight in % of body weight of rats was about 1% in the morning and in the afternoon in comparison with controls. At 6.00--7.00 during the glycogen maximum, the fine structure of hepatocytes was normal except enlargement and glycogen depletion of cells in the near neighbourhood of central veins. From 9.00--10.00 the mitotic activity was markidly increased and parallel to the progressive disappearance of glycogen the smooth endoplasmic reticulum (SER) became prominent. Hypertrophy of SER was fully developed at 15.00--16.00 and 17.00--18.00.

Time -- a key in experimental and practical medicine

This paper gives an overview on circadian rhythms which governs visibly all biological features. By illustrative examples of circadian rhythms of man and experimental animals it is shown that: 1. The components of all tissues, organs, and blood undergo circadian changes, manifested in drmatic morphologic and chemical differences. These circadian changes simply do not represent minute "physiologic" variations around a 24-h means. 2. The endogenous nature and the influences of the environmental factors such as food, light, laboratory stress, and seasons acting on circadian rhythms are demonstrated. 3. The different circadian phases determine significantly the in vivo and in vitro results in response to hormones, drugs and poisons. The neccessity to consider circadian rhythms is shown by chronotoxicologic experiments: mortality rates between 0 and 100% may occur after application of identical doses of a given drug at different day times.