Effect of cholesterol feeding on circadian rhythm of hepatic and intestinal cholesterol biosynthesis in hamsters.

Forty-eight adult hamsters were divided equally into two groups fed a control diet and a 2% cholesterol diet, respectively, under a rigid lighting (6 PM-6 AM) and feeding (6 PM-8 AM) schedule for three weeks. The cholesterol synthetic activity of the liver, stomach, small intestine, cecum, colon and kidney was measured by in vivo conversion of acetate-1-14C to cholesterol in four animals each time at 4 hour intervals. A remarkable circadian rhythm with the peak at midnight and the nadir at noon was found in the liver of the control hamsters, but was completely abolished in the cholesterol-fed animals since the activity was nearly totally suppressed at all times. The small intestine exhibited a similar rhythm with the peak at midnight but maintained a high baseline activity from 8 AM to 6 PM. Cholesterol feeding did not alter the baseline activity but reduced 17% of the peak activity. Other organs failed to show such a circadian rhythm.     

Entrainment of circadian rhythms of cholesterol‐LDL,corticosterone and motor activity by feeding schedules in rats

Abstract

The daily variations of locomotor activity, plasma and adrenal corticosterone levels and cholesterol‐LDL were studied in male Wistar rats with food ad libitum and feeding restricted to the first 4 hours of the light phase in LD 12:12..

Under LD 12:12 (light on from 9:00 to 21:00h) rats with food ad libitum were eating and moving during the dark period and the locomotor activity clearly showed a biphasic pattern with three harmonic components. Plasma and adrenal corticosterone levels increased during the light period and reached a maximum value just before the dark period whereas the acrophase of cholesterol‐LDL is found at the beginning of the light phase.

The acrophases of activity, plasma and adrenal corticosterone levels in the restricted feeding schedule rats occurred in the first three hours of lighting and the cholesterol‐LDL acrophase at the beginning of the dark phase.

These results confirm a previous report that the shift of feeding to the light phase seems to cause a concomitant phase‐shift in all the variables measured.     

Effects of bovine growth hormone on plasma FFA concentrations and liver, muscle and carcass lipid content in rainbow trout, Salmo gairdneri Richardson

Bovine growth hormone (GH) given daily to rainbow trout, Sulmo gairdneri for 4 or 7 days at either 10.00 or 14.00 hours, significantly increased plasma free fatty acid (FFA) levels but had not effect on plasma cholesterol levels. Liver lipid content of the GH-injected trout after seven injections was significantly lower than comparable controls in groups injected at both 10.00 and 14.00 hours. There were no apparent effects of GH on carcass or muscle lipid content although in fish injected and sampled at 14.00 hours there was a significant correlation between the number of injections and carcass lipid content.
Changes in hepatosomatic index (HSI), liver, muscle and carcass lipid content, plasma FFA and cholesterol concentrations and somatotrop activity during food-deprivation for up to 60 days are described. Despite significant decreases in liver and muscle lipid content and increases in plasma FFA levels in food-deprived fish, there was no concomitant change in apparent somatotrop activity.
The data are interpreted to indicate that although exogenous GH, in the doses used here, appears to stimulate mobilization of lipid reserves, particularly from the liver, there is no evidence that enforced changes in lipid reserves elicits a response of the endogenous somatotrop cells.     

Changes in rhythmicity of ambulatory and drinking activities produced by presentation of short time lightings during dark period in rats]

It is well known that the lighting conditions affect many physiological phenomenon of laboratory animals. However, lighting conditions are frequently disturbed by investigators themselves. In this study, behavioral (ambulation and drinking) rhythmicities of rats were investigated after irregular lighting; i. e. presentation of short time lighting at 21:00, 24:00 and 3:00 for 12 min during dark period (18:00-6:00). Vaginal smear was taken and sexual cycle was observed everyday. Ambulatory and drinking activities were measured by Gundai type Ambulo-drinkometer. The irregular lighting produced the following changes in the rhythmicities: 1) increase in the ambulatory activity during 15:00-18:00 immediately before dark period 2) decrease in ambulatory activity before ovulation 3) disappearance of inhibitory phenomenon of drinking activity which was usually observed before ovulation 4) increase in the drinking activity during 6:00-9:00 immediately after dark period 5) the changes in rhythmicities of the behavioral activities lasted for more than 1 month after replacement to the regular lighting condition.     

Relative value of light and food as synchronizers of liver phosphorylase circadian rhythm.

The role played by light and feeding schedules on the circadian rhythm of glycogen content and phosphorylase activity of the liver has been studied. In one experiment, mice were subjected to a regimem of constant darkness during 21 days and compared with mice kept in 12 hrs of light alternating with 12 hrs of darkness. Both groups received food and water ad libitum. Liver glycogen content as well as phosphorylase activity showed, with slight differences, similar circadian variations. In a second experiment, mice under similar lighting conditions (LD 12:12), with water access ad libitum, were divided into two groups; one was offered food ad libitum while the other group recieved food from 0700 to 1800 only. This experiment allowed up to compare two different schedules of food intake; ad libitum, normal schedule (from 1800 to 0600) and reversed schedule (from 0700 to 1800). A complete reversal of the circadian rhythm was observed after 21 days in the group with the reverted feeding schedule. We conclude that food can function as the primary synchronizer in spite of the lighting regimen.     

Circadian Rhythm of Liver Parameters (Cellular Structures, Mitotic Activity, Glycogen and Lipids in Liver and Serum) During Three Consecutive Cycles in Phenobarbital-Treated Rats

The circadian rhythm of gastric content, serum alkaline phosphatase (alk.P.), serum lipids, body weight (wt), relative (rel.) liver wt, cellular structures (by light- and electron-microscopy), mitotic activity of hepatocytes, glycogen content, protein and lipids in liver was studied in 180 male Sprague-Dawley rats orally treated at 0830-1030 with 50 mg/kg phenobarbital (PB) for 7 days. Thereafter, five PB-treated males and five controls each were studied at 4-hr intervals at 0600, 1000, 1400, 1800, 2200 and 0200 on 3 consecutive days. The lighting schedule in the colony was 12:12 = light/dark (light from 0600 to 1800). Following the rhythm of gastric emptying, the rel. liver wt showed a clear circadian rhythm with a peak at 0800. The rel. liver wt was raised in PB-treated rats at all times of the day. The circadian rhythm of cellular structures was closely related to the hepatic glycogen content which exhibited a clear rhythm with the peak also at 0800, but lowered values were found in PB-treated rats. The mitotic activity of hepatocytes was significantly increased in PB-treated rats but displayed the same circadian rhythm as controls with peaks at noon and troughs at midnight. The well-known hypertrophy of the smooth endoplasmic reticulum in PB-treated rats was not found at 0600, but was fully developed at 1400 and 2200. PB-treatment increased significantly the liver content of cholesterol, triglycerides and phospholipids. Liver cholesterol showed a clear circadian rhythm with peaks at 1800. No rhythm of liver protein, triglycerides and phospholipids was observed. In serum, levels of cholesterol were significantly elevated, those of triglycerides and alk.P. significantly lowered, while those of phospholipids were not affected by the treatment. The three serum lipids, alk.P. and beta-lipoprotein exhibited a clear circadian rhythm, while serum glucose and non-esterified fatty acids did not.     

Circadian Rhythm of Liver Parameters (Cellular Structures,Mitotic Activity,Glycogen and Lipids in Liver and Serum) During Three Consecutive Cycles in Phenobarbital-Treated Rats

The circadian rhythm of gastric content, serum alkaline phosphatase (alk.P.), serum lipids, body weight (wt), relative (rel.) liver wt, cellular structures (by light- and electron-microscopy), mitotic activity of hepatocytes, glycogen content, protein and lipids in liver was studied in 180 male Sprague-Dawley rats orally treated at 0830-1030 with 50 mg/kg phenobarbital (PB) for 7 days. Thereafter, five PB-treated males and five controls each were studied at 4-hr intervals at 0600, 1000, 1400, 1800, 2200 and 0200 on 3 consecutive days. The lighting schedule in the colony was 12:12 = light/dark (light from 0600 to 1800). Following the rhythm of gastric emptying, the rel. liver wt showed a clear circadian rhythm with a peak at 0800. The rel. liver wt was raised in PB-treated rats at all times of the day. The circadian rhythm of cellular structures was closely related to the hepatic glycogen content which exhibited a clear rhythm with the peak also at 0800, but lowered values were found in PB-treated rats. The mitotic activity of hepatocytes was significantly increased in PB-treated rats but displayed the same circadian rhythm as controls with peaks at noon and troughs at midnight. The well-known hypertrophy of the smooth endoplasmic reticulum in PB-treated rats was not found at 0600, but was fully developed at 1400 and 2200. PB-treatment increased significantly the liver content of cholesterol, triglycerides and phospholipids. Liver cholesterol showed a clear circadian rhythm with peaks at 1800. No rhythm of liver protein, triglycerides and phospholipids was observed. In serum, levels of cholesterol were significantly elevated, those of triglycerides and alk.P. significantly lowered, while those of phospholipids were not affected by the treatment. The three serum lipids, alk.P. and beta-lipoprotein exhibited a clear circadian rhythm, while serum glucose and non-esterified fatty acids did not.     

Effect of photoperiod reversal on twenty-four hour patterns for dopamine levels in the corpus striatum and upper and lower brainstem of the rat.

Dopamine levels were measured in the corpus striatum, upper and lower brainstem at 6 hour intervals for a period of 24 hours in rats adapted for 3 weeks to either of two concomitantly-conducted lighting programs. On the normal cycle the animals were illuminated from 08(00)--20(00); on the reverse cycle, from 20(00)--08(00). In the corpus striatum dopamine levels peaked during the dark phase of both illumination cycles indicating that 24 hour rhythm is exogenous. On the other hand, in the upper and lower brainstem, dopamine peaks occurred in both light cycles at 00(00) or 06(00) indicating that these 24 hour rhythms are endogenous in nature. Photoperiod reversal resulted in significantly elevated dopamine levels in the corpus striatum and lower brainstem. The existence of a stress as well as a seasonal factor which affects striatal dopamine is suggested.     

Ontogeny of DNA synthetic rhythms in chick (Gallus domesticus) liver.

1. The diurnal pattern of DNA synthesis and mitotic activity in neonatal (1-4-day-old) chick liver were investigated under various feeding and lighting regimens. 2. In the meal-fed chicks under the condition of light-dark cycle, DNA synthesis exhibited a 12 hr cycle; the peaks occurring at 9:00 and 21:00. 3. Fasting caused a gradual decrease in the 21:00 peaks. 4. The changes in the lighting regimen to 24 hr continuous lighting also caused a profound change in the DNA-synthetic pattern, suggesting a complex interplay of feeding and lighting regimens in the manifestation of the DNA-synthetic rhythm in neonatal chick liver.     

Dietary protein level and circadian variation of enzyme activities for glucose metabolism and lipogenesis in male rats (author's transl)]

One hundred and seven Wistar rats, 8 weeks old and weighing 180-200 g, were housed under conditions of controlled temperature (22 plus or minus 2 degrees) and lighting (light on from 07:00 to 19:00). They were divided into 2 groups and fed diets containing either 15 per cent cas-protein for 23 days. Food consumption was recorded every 2 hours for each animal during 48 hours. Four or five rats from each group were killed every 2 hours for 24 hours and the hepatic activities of PK (EC.2.7.1.40),G6P-DH (EC1.1.1.49), ME (EC1.1.1.40), Acetyl-CoA-carbox (EC.6.4.1.2.),PC(EC.6.4.1.1.), PEP-CK(EC.4.1.1.32), G6Pase (EC.3.1.3.9) and GPT (EC.2.6.1.2.) were measured...     

Circadian rhythm of serum testosterone levels in male beagle dogs--effects of lighting time zone

In a previous study, the author found that serum testosterone (T) levels in male beagle dogs showed a circadian rhythm which was lowest at 12:00, and increased to a peak at 18:00-6:00, thereafter decreasing until 12:00. The reason was thought to be that dogs were breeding under rigid controlled conditions. The present study was performed to investigate the effects of lighting on the circadian rhythm of T level by means of a reversal of the lighting time zone, because lighting is considered an important factor in modulating T levels. Six male beagle dogs of 2 years were used in this study. The routine lighting time (8:00-20:00) and dark time (20:00-8:00) zone in the breeding room was reversed completely and T levels were measured at intervals of 1-5 weeks for up to 54 weeks. Blood samples were collected at 6:00, 12:00, 18:00 and 24:00. The results showed that the circadian rhythm of the T level and the T level at each blood sampling time did not change significantly within 54 weeks. As a result, it was recognized that the circadian rhythm of the T level in male dogs may not be affected by changes in the lighting time zone.     

Differences in sleep, light, and circadian phase in offshore 18:00-06:00 h and 19:00-07:00 h shift workers

Complaints concerning sleep are high among those who work night shifts; this is in part due to the disturbed relationship between circadian phase and the timing of the sleep-wake cycle. Shift schedule, light exposure, and age are all known to affect adaptation to the night shift. This study investigated circadian phase, sleep, and light exposure in subjects working 18:00-06:00 h and 19:00-07:00 h schedules during summer (May-August). Ten men, aged 46+/-10 yrs (mean+/-SD), worked the 19:00-07:00 h shift schedule for two or three weeks offshore (58 degrees N). Seven men, mean age 41+/-12 yrs, worked the 18:00-06:00 h shift schedule for two weeks offshore (61 degrees N). Circadian phase was assessed by calculating the peak (acrophase) of the 6-sulphatoxymelatonin rhythm measured by radioimmunoassay of sequential urine samples collected for 72 h at the end of the night shift. Objective sleep and light exposure were assessed by actigraphy and subjective sleep diaries. Subjects working 18:00-06:00 h had a 6-sulphatoxymelatonin acrophase of 11.7+/-0.77 h (mean+/-SEM, decimal hours), whereas it was significantly later, 14.6+/-0.55 h (p=0.01), for adapted subjects working 19:00-07:00 h. Two subjects did not adapt to the 19:00-07:00 h night shift (6-sulphatoxymelatonin acrophases being 4.3+/-0.22 and 5.3+/-0.29 h). Actigraphy analysis of sleep duration showed significant differences (p=0.03), with a mean sleep duration for those working 19:00-07:00 h of 5.71+/-0.31 h compared to those working 18:00-06:00 h whose mean sleep duration was 6.64+/-0.33 h. There was a trend to higher morning light exposure (p=0.07) in the 19:00-07:00 h group. Circadian phase was later (delayed on average by 3 h) and objective sleep was shorter with the 19:00-07:00 h than the 18:00-06:00 h shift schedule. In these offshore conditions in summer, the earlier shift start and end time appears to favor daytime sleep.     

Food restricted schedules promote differential lipoperoxidative activity in rat hepatic subcellular fractions

Restricted access to food (from 12:00 to 14:00 h) produces a behavioral activation known as food anticipatory activity (FAA), which is a manifestation of the food entrained oscillator (FEO). Peripheral oscillators, especially in the liver, are thought to be part of the FEO. A variety of metabolic adaptations have been detected in the liver during the expression of this oscillator, including activation of mitochondrial respiration and changes in the cytoplasmic and mitochondrial redox states. Biological clocks are regulated by redox-sensitive factors. The present study explored the lipoperoxidative activity (LP) in the liver during the activity of the FEO. Conjugated dienes (CD) and thiobarbituric acid reactive substances (TBARS), with and without Fe2+-supplementation, were quantified in six subcellular fractions: whole homogenate, plasma membrane, mitochondria, microsomes, nucleus, and cytosol. The experimental protocol involved control groups of ad libitum fed and 24-h fasted rats, and groups under the restricted food schedule (RFS) which were sampled before FAA (08:00 h), during FAA (11:00 h) and after feeding (14:00 h). Clear differences in pro-oxidant activity was observed between ad libitum fed and 24-h fasted rats in almost all the subcellular fractions studied. RFS rats presented: CD levels more similar to the fasted rats, even at 14:00 h, after food presentation, and basal and Fe2+-supplemented TBARS levels tended to be lower than both controls, suggesting an increased antioxidant capacity associated with food restriction. In addition, a microarray analysis showed that several isoforms of peroxiredoxins, a family of antioxidant and hydrogen peroxide-catabolizing enzymes, were consistently up-regulated in each and every condition in which RFS was applied. Together, these data indicate a rheostatic adaptation of the liver in the handling of pro-oxidant reactions during the activity of the FEO.     

A blood plasma inhibitor is responsible for circadian changes in rat renal Na,K-ATPase activity

Rhythmic changes in activity following a circadian schedule have been described for several enzymes. The possibility of circadian changes in Na,K-ATPase activity was studied in homogenates of rat kidney cortex cells. Male Sprague-Dawley rats were kept on a schedule of 12h light (06:00-18:00 h) and 12 h darkness (18:00-06:00 h) for 2 weeks. At the end of the conditioning period, one rat was killed every 2 h, until completion of a 24 h cycle. Outermost kidney cortex slices were prepared, homogenized and assayed for Na,K-ATPase activity. The whole procedure was repeated six times. Na,K-ATPase activity shows an important oscillation (2 cycles/24 h). Peak activities were detected at 09:00 and 21:00 h, whereas the lowest activities were detected at 15:00 and 01:00-03:00 h. The highest activity was 40+/-3 nmoles Pi mg protein(-1)min(-1) (09:00 h), and the lowest was 79+/-3 nmoles Pi mg protein(-1)min(-1) (15:00 h). The amount of the Na+-stimulated phosphorylated intermediate is the same for the 09:00 h and 15:00 h homogenates. Preincubation of 09:00 h kidney cortex homogenates with blood plasma drawn from rats at either 03:00 h or 15:00 h, significantly inhibited their Na,K-ATPase activity. This inhibition was not seen when the preincubation was carried out with either 09:00 h or 21:00 h blood plasma. The striking oscillation (2 cycles/24 h) of the Na,K-ATPase activity of rat kidney cortex cells is ascribed to the presence of an endogenous inhibitor in blood plasma.     

Chronotype,gender, and time for sex

The study aimed at testing chronotype and gender differences in the time of day when humans feel the greatest need for sex and the time of day they actually undertake sexual activity. A Polish sample of 565 participants aged between 18 and 57 was tested. In females, regardless of chronotype, the greatest need for sex occurred between 18:00 and 24:00, but a secondary peak appeared only in morning types at 6:00–9:00. In males, the greatest need for sex occurred either in the morning or evening hours: in evening types at 9:00–12:00 and 18:00–3:00; in neither types at 6:00–9:00 and 18:00–24:00; in morning types at 6:00–12:00 and 18:00–24:00. Considering time of day when subjects were undertaking sexual activity most frequently, this appeared between 18:00 and 24:00 for all the participants, and prolonged until 3:00 at night in evening type males. Morningness preference was more strongly related to the timing of need for sex than to the timing of actual sexual activity (r?=??0.275 vs. r?=??0.174), while the timing of desire and the timing of sexual activity were positively, but moderately related (r?=?0.320).     

Effects of ultradian lighting and feeding schedules on the circadian rhythm of body temperature in monkeys

In estimating, by use of cosinor-test, the 12- and 24-h component parameters of body temperature circadian rhythm in monkeys under ultradian schedules of lighting and feeding (LD 6:6; DL 6:6) we have shown that an intensive 12-h component is registered in both cases. The presence of a 24-h component of circadian rhythm depends on the zeitgeber phase. This component is present in LD 6:6 (lighting hours 07:00-13:00 and 19:00-01:00) and is absent in DL 6:6 (01:00-07:00 and 13:00-19:00). We hold that the most satisfactory explanation of the phenomena observed is that 12-h component is the result of a masking effect induced by the 12-h schedule (exogenous component) whereas the 24-h component reflects the intrinsic pacemaker work (endogenous component). It should be noted that in our case the masking effect in body temperature rhythm is circadian phase-dependent.     

Differences in Sleep,Light, and Circadian Phase in Offshore 18:00–06:00 h and 19:00–07:00 h Shift Workers

Complaints concerning sleep are high among those who work night shifts; this is in part due to the disturbed relationship between circadian phase and the timing of the sleep‐wake cycle. Shift schedule, light exposure, and age are all known to affect adaptation to the night shift. This study investigated circadian phase, sleep, and light exposure in subjects working 18:00–06:00 h and 19:00–07:00 h schedules during summer (May–August). Ten men, aged 46±10 yrs (mean±SD), worked the 19:00–07:00 h shift schedule for two or three weeks offshore (58°N). Seven men, mean age 41±12 yrs, worked the 18:00–06:00 h shift schedule for two weeks offshore (61°N). Circadian phase was assessed by calculating the peak (acrophase) of the 6‐sulphatoxymelatonin rhythm measured by radioimmunoassay of sequential urine samples collected for 72 h at the end of the night shift. Objective sleep and light exposure were assessed by actigraphy and subjective sleep diaries. Subjects working 18:00–06:00 h had a 6‐sulphatoxymelatonin acrophase of 11.7±0.77 h (mean±SEM, decimal hours), whereas it was significantly later, 14.6±0.55 h (p=0.01), for adapted subjects working 19:00–07:00 h. Two subjects did not adapt to the 19:00–07:00 h night shift (6‐sulphatoxymelatonin acrophases being 4.3±0.22 and 5.3±0.29 h). Actigraphy analysis of sleep duration showed significant differences (p=0.03), with a mean sleep duration for those working 19:00–07:00 h of 5.71±0.31 h compared to those working 18:00–06:00 h whose mean sleep duration was 6.64±0.33 h. There was a trend to higher morning light exposure (p=0.07) in the 19:00–07:00 h group. Circadian phase was later (delayed on average by 3 h) and objective sleep was shorter with the 19:00–07:00 h than the 18:00–06:00 h shift schedule. In these offshore conditions in summer, the earlier shift start and end time appears to favor daytime sleep.     

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.