Diurnal variations in inducibility of rat liver tyrosine aminotransferase activity

Chronopharmacological study of KE-SI-TO in mice

Influence of dosing time on pharmacological effects and toxicity of KE-SI-TO (KST), analgesic and antipyretic drug, was investigated in ICR male mice under LD (12:12) cycle. Significant circadian rhythms were demonstrated for analgesic and hypothermal effects of KST (1 g/kg, i.p.) with higher values in the dark and lower ones in the light (p<0.01, respectively). The rhythmic patterns of KST-induced analgesia and hypothermia resembled overall the rhythms occuring in the nondrugged state. Injection of KST resulted in a parallel increasing in latency to hot plate and a parallel decreasing in rectal temperature. KST (6 g/kg, i.p.)-induced toxicity also showed a significant circadian rhythm with the highest mortality at 1700 and the lowest one at 0500 (p<0.05). The principles and concepts of biological rhythm should be included in the consideration of the actions of KST.

Chronopharmacokinetics of valproic acid following constant-rate administration in mice

This study was carried out to investigate the circadian rhythm in the pharmacokinetics of valproic acid (VPA). ICR male mice, housed under a light-dark (12 h:12 h) cycle, were used in these studies. In the constant-rate administration study (536.3 or 1,072.6 micrograms/h), osmotic minipumps were implanted subcutaneously in mice. There was a significant circadian rhythm in plasma VPA concentrations: higher values were obtained in the light phase and lower values were found during the dark phase. A significant circadian rhythm also was shown for clearance (CL) of the drug: lower values were obtained in the light phase and higher values were demonstrated in the dark phase. In the intravenous administration study, VPA (50 mg/kg) was injected into a tail vein of the mice. Mean plasma VPA concentrations were significantly higher in mice injected with the drug at 1700 h than at 0100 h. The CL was higher, the volume of distribution (V) was larger, and the area under the curve (AUC) was smaller (p less than 0.05, respectively) in mice injected with the drug at 0100 h than at 1700 h. As the values of CL and V increased similarly during the dark period, there was no effect on half-life (t 1/2) and obviously on the elimination rate constant (K). These findings indicate that the circadian rhythms of plasma VPA concentrations observed after constant-rate administration are due to those of CL and V. To keep drug concentrations constant, the drug release rate from the osmotic minipump should be controlled according to the rhythm of drug pharmacokinetics.

Circadian variation of epidermal growth factor receptor in mouse liver

The liver undergoes a biochemical and morphological circadian transformation. In this paper, we document circadian variation in the binding parameters of the hepatic epidermal growth factor receptor (EGFR). Liver membranes were prepared from ad libitum fed or fasted male CD2F1 mice killed at different circadian phases at 4 h intervals. Bmax (maximum binding) and Kd (dissociation constant) varied in a rhythmic fashion. The range of change for Bmax along the 24 h time scale was 423%. For Kd, it was 162%. Both peaked late in the dark span, and decreased late in the light span. Fasting and EGF treatment reduced Bmax and the amplitude of circadian variation.

Effect of selective parasympathetic denervation on the daily rhythm of tyrosine transaminase in the rat liver

The effect of section of the rostral hepatic nerve (RNH), branch of the left abdominal vagus, on the circadian rhythm of tyrosine transaminase (TAT) activity in rat liver has been investigated. It has been shown that the midnight peak of TAT activity is suppressed after section of the rostral hepatic nerve and by subdiaphragmatic vagotomy, but is unaffected by sham-operation and section of the ventral abdominal vagus caudal to the emergence of the rostral hepatic nerve. It is concluded that the rhythm of TAT activity is under neural control, either directly or reflexely.

Circadian variations in the activity of tyrosine hydroxylase, tyrosine aminotransferase, and tryptophan hydroxylase: relationship to catecholamine metabolism

Circadian variations in the activity of tyrosine hydroxylase, tyrosine aminotransferase, and tryptophan hydroxylase were observed in the rat brain stem. Tyrosine hydroxylase exhibited a bimodal pattern with peaks occurring during both the light and dark phases of the circadian cycle. Tyrosine aminotransferase had one daily peak of activity occurring late in the light phase, whereas tryptophan hydroxylase activity was maximal late in the dark phase. Circadian fluctuations in tyrosine hydroxylase activity did not correlate well with circadian variations in the turnover rates of norepinephrine or dopamine nor with levels of these catecholamines. This supports the idea that although tyrosine hydroxylase is the rate-limiting enzyme in the synthesis of catecholamines, other factors must also be involved in the in vivo regulation of this process. Administration of alpha-methyl-p-tyrosine (AMT) methyl ester HCl (100 mg/kg) had no effect on the activity of tryptophan hydroxylase, but effectively eliminated the peak of tyrosine hydroxylase activity that occurred during the light phase. AMT also lowered levels of tyrosine aminotransferase, but only at times near the daily light to dark transition. These chronotypic effects of AMT emphasize the importance of "time of day" as a factor that must be taken into account in evaluating the biochemical as well as the pharmacological and toxicological effects of drugs.

Diurnal variations in response of rat liver tyrosine aminotransferase activity to food intake

Effects of fasting and refeeding on the hepatic tyrosine aminotransferase activity were examined in rats that had been fed during the night. The tyrosine aminotransferase activity showed clear diurnal variations, with a maximal activity after the feeding time. The tyrosine aminotransferase rhythm persisted even under starvation, though the amplitude decreased remarkably. When the starved rats were refed at night, the tyrosine aminotransferase activity increased rapidly to a high level, but it increased slowly to a rather lower level when they were refed in daytime.

Scanning microdensitometry of glycogen zonation in the livers of rats adapted to a controlled feeding schedule and to 30, 60, or 90% casein diets

The effect of diet composition on diurnal changes in glycogen zonation patterns in rat liver was investigated in individually-caged male Sprague-Dawley rats adapted to the 2 + 22 controlled feeding and lighting schedule and to diets containing 30% casein/55% carbohydrates, 60% casein/25% carbohydrates, or 9.0% casein (30 rats/dietary group). Three rats from each dietary group were killed at the following times relative to the onset of feeding (0 min):--60, --30, 0, 15, 30, 45, 60, 90, 120, and 180 min. Glycogen in cryostat sections from the median and right lateral lobes of the liver was fixed and stained by standard techniques. The optical density of glycogen at points along the path between the central and portal veins of a given lobule was determined, and lobular glycogen gradients of replicate animals were integrated to form a composite lobular glycogen distribution profile. In the period from--60 to 0 min, liver glycogen levels were similar for rats on any of the diets, and the glycogen concentration was similar in periportal (P), midlobular (M), and centrilobular (C) hepatocytes. During the 0- to 45-min period, diet-related glycogen depletion occurred (90 > 60 > 30% casein) by asymmetrical glycogen loss (P > M > C hepatocytes) from the liver lobules. Similar food intake curves occurred for all diets. During the 45- to 180-min period, asymmetrical glycogen accumulation began in lobular parenchymal cells (P > M > C hepatocytes), and rate of accumulation was related to dietary to dietary composition (30 > 60 > 90% casein). The differential responses of parenchymal cells within liver lobules to physiological stimuli resulted in glycogen distribution changes that were rapid and of large magnitude. Our results are consistent with the hypothesis that periportal and midlobular hepatocytes are more metabolically responsive and active than centrilobular hepatocytes

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.