In vivo demonstration of the circadian thythm of cholesterol biosynthesis in the liver and intestine of the rat

The existence of a circadian rhythm in the rate of hepatic cholesterol synthesis in the rat has been demonstrated in vivo by measuring the conversion of both [1-(14)C]acetate and (3)H(2)O to cholesterol. By both methods there was observed a similar increase in the rate of hepatic cholesterol synthesis between the nadir at noon and the peak at midnight. Circadian changes in the rate of hepatic cholesterol synthesis measured in vivo with [1-(14)C]acetate were very similar to changes in the activity of hepatic microsomal HMG CoA reductase. Cholesterol synthesis in the jejunum and in the distal ileum was also shown to exhibit the same circadian rhythm in vivo but with smaller amplitude (1.6- and 1.3-fold, respectively). Rats trained to eat during a 4-hr period (9 am-1 pm) while housed under normal illumination showed changes in the timing of the circadian rhythm of cholesterol synthesis; in the liver the maximum rate of cholesterol synthesis occurred at 6 pm, 9 hr after the presentation of food, while the two sections of the intestine investigated exhibited a maximum synthetic response between noon and 6 pm. Results obtained in this study support the hypothesis that the major portion of the rise in HMG CoA reductase activity and the increase in overall rate of cholesterol synthesis in liver and intestine during the circadian rhythm are due to the ingestion of food. Under the limited feeding schedule (food access 9 am-1 pm), the rates of hepatic and intestinal synthesis of fatty acids from the injected acetate also showed a circadian rhythm with a peak at about 3 hr after presentation of food.     

Deriving the reference value from the circadian motor active patterns in the “non-dementia” population,compared to the “dementia” population: What is the amount of physical activity conducive to the good circadian rhythm

Background: The circadian rhythm in older adults is commonly known to change with a decrease in physical activity. However, the association between circadian rhythm metrics and physical activity remains unclear. The objective of this study was to examine circadian activity patterns in older people with and without dementia and to determine the amount of physical activity conducive to a good circadian measurement. Method: Circadian parameters were collected from 117 older community-dwelling people (66 subjects without dementia and 52 subjects with dementia); the parameters were measured continuously using actigraphy for 7 days. A receiver operating characteristic (ROC) curve was applied to determine reference values for the circadian rhythm parameters, consisting of interdaily stability (IS), intradaily variability (IV), and relative amplitude (RA), in older subjects. Results: The ROC curve revealed reference values of 0.55 for IS, 1.10 for IV, and 0.82 for RA. In addition, as a result of the ROC curve in the moderate-to-vigorous physical Activity (MVPA) conducive to the reference value of the Non-parametric Circadian Rhythm Analysis per day, the optimal reference values were 51 minutes for IV and 55 minutes for RA. However, the IS had no classification accuracy. Conclusions: Our results demonstrated the reference values derived from the circadian parameters of older Japanese population with or without dementia. Also, we determined the MVPA conducive to a good circadian rest–active pattern. This reference value for physical activity conducive to a good circadian rhythm might be useful for developing a new index for health promotion in the older community-dwelling population.     

Reliability of the Circadian Rhythm of Water and Macronutrient-Rich Diets Intake in Dietary Choice

Rats with ad libitum water and the ability to self-select among three macronutrient-rich diets—carbohydrate (CHO), protein (PRO), and lipid (LIP)—show a circadian rhythmicity in their ingestion. The aim of the present study was to determine whether this circadian rhythmicity is reliable from day to day. Eight rats were offered ad libitum water and a choice of three isoenergetic diet rations providing carbohydrate, protein, and lipid. Water and food intake was recorded every 3 h for 7 days. The reliability of the circadian rhythm of water and food intake was assessed by the Intraclass Correlation Coefficient (ICC) and the test-retest reliability using the Pearson's Correlation Coefficient (r). The results showed that the circadian rhythm of water, CHO, and PRO intake are strongly reliable. However, the circadian rhythm of LIP intake is less reproducible. Among the three reliable parameters—water, CHO, and PRO, the circadian rhythm of water intake was the most reproducible over 7 days. This suggests that water intake may be used as a marker of circadian rhythmicity in ingestive behavior.     

Period lengthening of human circadian rhythms by lithium carbonate, a prophylactic for depressive disorders

The effect of lithium carbonate on the circadian system of man was studied. Four out of eight volunteers living without time cues in isolated huts in the arctic showed a lengthening of the periods of the body temperature rhythm, activity rhythm, and sleep/wakefulness rhythm by c. 1 h. Four of the participants did not show a change in the periods between the placebo and lithium ingestion phases. Two subjects who did not receive lithium salt showed internal desynchronization between the temperature rhythm and the sleep/wakefulness rhythm. Extreme isolation in bunkers is not necessary to allow free running of the circadian system in man. The sleep/wakefulness rhythm, which is very easy to record, was a reliable indicator of the circadian system in the internally-synchronized state.     

Reliability of the circadian rhythm of water and macronutrient-rich diets intake in dietary choice

Rats with ad libitum water and the ability to self-select among three macronutrient-rich diets--carbohydrate (CHO), protein (PRO), and lipid (LIP)--show a circadian rhythmicity in their ingestion. The aim of the present study was to determine whether this circadian rhythmicity is reliable from day to day. Eight rats were offered ad libitum water and a choice of three isoenergetic diet rations providing carbohydrate, protein, and lipid. Water and food intake was recorded every 3 h for 7 days. The reliability of the circadian rhythm of water and food intake was assessed by the Intraclass Correlation Coefficient (ICC) and the test-retest reliability using the Pearson's Correlation Coefficient (r). The results showed that the circadian rhythm of water, CHO, and PRO intake are strongly reliable. However, the circadian rhythm of LIP intake is less reproducible. Among the three reliable parameters-water, CHO, and PRO, the circadian rhythm of water intake was the most reproducible over 7 days. This suggests that water intake may be used as a marker of circadian rhythmicity in ingestive behavior.     

Plasma Corticosterone, Motor Activity and Metabolic Circadian Patterns in Streptozotocin-Induced Diabetic Rats

Experiments were conducted in male rats to study the effects of streptozotocin-induced diabetes on circadian rhythms of (a) plasma corticosterone concentrations; (b) motor activity; and (c) metabolic patterns. Animals were entrained to LD cycles of 12: 12 hr and fed ad libitum.

A daily rhythm of plasma corticosterone concentrations was found in controls animals with peak levels at 2400 hr and low values during the remaining hours. This rhythm was statistically confirmed by the cosinor method and had an amplitude of 3.37μg/100 ml and the acrophase at 100 hr. A loss of the normal circadian variation was observed in diabetic animals, with a nadir at the onset of light period and high values throughout the remaining hours; cosinor analysis of these data showed no circadian rhythm, delete and a higher mean level than controls.

As expected, normal rats presented most of their motor activity during the dark period with 80+ of total daily activity; the cosinor method demonstrated a circadian rhythm with an amplitude of 60+ of the mean level and the acrophase at 0852 hr. Both diabetic and control rats showed a similar activity during the light phase, but diabetic animals had less activity than controls during the night and their percentage of total daily activity was similar in both phases of the LD cycle (50+ for each one). With the cosinor method we were able to show the persistence of a circadian rhythm in the motor activity of diabetic rats, but with a mesor and amplitude lower than in controls (amplitude rested at 60+ of the mean level) and its acrophase advanced to 0148 hr.

The metabolic activity pattern of diabetic rats also changed: whereas controls showed a greater metabolic activity during the night (70+ food; 82+ water; 54+ urine; 67+ faeces), diabetics did not show differences between both phases of the LD cycle. Water ingested and urine excreted by the diabetic group were higher than normal during light and dark periods; food consumed and faeces excreted were higher than controls only in the light phase.

These data suggest that alterations in circadian rhythms of plasma corticosterone and motor activity are consecutive to the loss of the feeding circadian pattern, due to polyphagia and polydipsia showed by these animals, which need to extend intakes during the light and dark phases.     

Differences in circadian time course and level for the plasma concentrations of glucose,free fatty acids and amino acids between ad lib‐eating and fasting rabbits

Abstract

The entrained rhythm in food approaches, representative of the circadian fluctuation in locomotor and food intake activity was recorded from 12 rabbits eating ad libitum during exposure to an LD 12:12 h‐regimen. They were also subjected to 53 h‐sessions with the same LD alternation, in which blood samples were taken at 2 h‐intervals. During these sessions 6 of them were permitted to eat freely whereas the others were food‐deprived. It appeared that in eating rabbits plasma levels are higher for glucose and a‐amino nitrogen but lower for free fatty acids and, further, that eating specimens exhibit marked circadian fluctuations in the levels of glucose and FFA which are closely correlated with, and probably a consequence of, the circadian rhythm in the amounts of food actually taken up in the course of the sessions. In fasting rabbits, however, the same plasma parameters show rhythms with quite another time course, that can be attributed to the circadian fluctuations in (locomotor) activity and endocrine balance.     

Regulation of Rat Pineal α1-Adrenoceptors

Some aspects of the physiological regulation of the pineal alpha 1-adrenoceptor have been studied using the selective, high-affinity ligand [125I] iodo-2-[beta-(4-hydroxyphenyl)ethylaminomethyl]tetralone ([125I]HEAT). Pineal glands taken from rats housed in a diurnal lighting cycle showed no circadian rhythm in the number of specific [125I]HEAT binding sites, although a characteristic rhythm in pineal melatonin was seen. It was established that the pineal alpha 1-adrenoceptor is under neural control because interruption of neural stimulation of the pineal by bilateral superior cervical ganglionectomy (SCGX) or by exposing rats to constant light for 3 weeks doubled receptor density but did not change affinity for [125I]HEAT. Administration of various alpha 1-adrenoceptor agonists either acutely (i.p. injection) or chronically (s.c. infusion) did not alter the number of specific [125I]HEAT binding sites. Together these results indicate that the pineal alpha 1-adrenoceptor, like the pineal beta-adrenoceptor, is regulated by sympathetic nerve activity, probably through the physiological release of the neurotransmitter norepinephrine. However the absence of a circadian rhythm in alpha 1-adrenoceptor number and lack of down-regulation by adrenergic agonists imply different mechanisms of regulation.     

Digestive Tract Cell Proliferation and Food Consumption Patterns of Ha/Icr Mice

The relationship between the daily pattern of food consumption and the proliferation rate of the qesophagus, stomach, forestomach, small intestine and colon of Ha/ICR mice was examined. Proliferative activity was determined by [³H]TdR incorporation on a wet weight tissue basis, along with selective counting of labelled nuclei. Under conditions of ad libitum feeding with a 12 hr light cycle (lights on at 0600) mice eat most of their food during the dark period. A distinct circadian rhythm was observed in the oesophagus, stomach, forestomach and colon with the peak of [³H]TdR incorporation between 0400 and 0600 and the nadir between 1600 and 1800. Although a circadian fluctuation was observed in the small intestine, its amplitude was much less than in other areas. This rhythmic change in proliferation rate could be phase shifted by allowing the mice to feed only between 0800 and 1600 for 14 days. Under these conditions the peak in proliferative activity occurred between 1800 and 2000. Fasting reduced the daily level of proliferative activity in all of the digestive tract sites studied, and for all areas except the oesophagus greatly reduced or eliminated the circadian fluctuation. the forestomach and colon were the most influenced by fasting with 24 hr [³H]TdR incorporation reduced to 30–40% of the control value. Refeeding following a 48 hr fast produced a rapid increase in proliferative activity peaking at levels well above the control value at 16 hr after the onset of refeeding. the major exception to this was the small intestine which slowly returned to the control value during the first 24 hr. Partial refeeding produced a diminished refeeding response. Once the normal pattern of food consumption was re-established following refeeding the normal proliferative fluctuations were again observed.     

Circadian rhythms of basic fibroblast growth factor (bFGF), epidermal growth factor (EGF), insulin-like growth factor-1 (IGF-1), insulin-like growth factor binding protein-3 (IGFBP-3), cortisol, and melatonin in women with breast cancer

Background: Circadian rhythms in plasma concentrations of many hormones and cytokines determine their effects on target cells. Methods: Circadian variations were studied in cortisol, melatonin, cytokines (basic fibroblast growth factor [bFGF], EGF, insulin-like growth factor-1 [IGF-1]), and a cytokine receptor (insulin-like growth factor binding protein-3 [IGFBP-3]) in the plasma of 28 patients with metastatic breast cancer. All patients followed a diurnal activity pattern. Blood was drawn at 3h intervals during waking hours and once during the night, at 03:00. The plasma levels obtained by enzyme-linked immunoassay (ELISA) or radioimmunoassay (RIA) were evaluated by population mean cosinor (using local midnight as the phase reference and by one-way analysis of variance (ANOVA). Results: Cortisol and melatonin showed a high-amplitude circadian rhythm and a superimposed 12h frequency. bFGF showed a circadian rhythm with an acrophase around 13:00 with a peak-to-trough interval (double amplitude) of 18.2% and a superimposed 12h frequency. EGF showed a circadian rhythm with an acrophase around 14:20, a peak-to-trough interval of 25.8%, and a superimposed 12h frequency. IGF-1 showed a high value in the morning, which is statistically different t test) from the low value at 10:00, but a regular circadian or ultradian rhythm was not recognizable as a group phenomenon. IGFBP-3 showed a low-amplitude (peak-to-trough difference 8.4%) circadian rhythm with the acrophase around 11:00 and low values during the night. Conclusions: (1) Circadian periodicity is maintained in hospitalized patients with metastatic breast cancer. (2) Ultradian (12h) variations were superimposed on the circadian rhythms of the hormones and several of the cytokines measured. (3) Studies of hormones and cytokines in cancer patients have to take their biologic rhythms into consideration. (4) The circadian periodicity of tumor growth stimulating or restraining factors raises questions about circadian and/ or ultradian variations in the pathophysiology of breast cancer. (Chronobiology International, 18(4), 709-727)     

Plasma and muscle amino acid and ammonia responses during prolonged exercise in humans

Plasma and muscle amino acid (AA) and ammonia (NH3) responses were measured during prolonged submaximal exercise in humans. Increased NH3 production during submaximal exercise has been attributed to the activity of the purine nucleotide cycle, without consideration of any possible contribution from AA. Six men cycled at 75% of maximal O2 uptake until exhaustion on two occasions after 2.5 days of ingestion of a high-carbohydrate or mixed diet. Plasma samples (antecubital vein) and muscle biopsies (vastus lateralis) were obtained at rest and during exercise and analyzed for plasma and muscle NH3 and AA as well as muscle metabolites. There were no significant diet effects in these parameters, so the majority of results focus on the effects of exercise. Plasma and muscle NH3 increased significantly from the onset and continued to increase throughout exercise. The total and total essential [AA] of muscle were significantly increased at exhaustion, whereas both the plasma and muscle branched-chain AA contents were unchanged. This suggests that protein catabolism was occurring during exercise and the branched-chain AA were used for energy and NH3 production.     

Studies on the circadian rhythm of phosphoenolpyruvate carboxykinase. III. Circadian rhythm in the kidney.

Phosphoenolypyruvate carboxykinase [EC 4.1.1.21] activity in rat kidney shows a circadian rhythm with the highest activity between 0200 h and 0800 h and the lowest activity between 1400 h and 2000 h. The rhythm was observed in both sexes and throughout the year. Actinomycin D and cycloheximide effectively blocked the circadian increase in enzyme activity. These findings suggest that the circadian increase in phosphoenolypyruvate carboxykinase activity is due to net synthesis of enzyme protein through newly synthesized mRNA. In experiments with kidney cortex slices, gluconeogenesis from the radioactive precursor, [14C]malic acid, was considerably higher at 0200 h than at 1400 h, varying in parallel with the change in the enzyme activity.     

Rhythmic cortisol secretion in the equine: Analysis and physiological mechanisms

Abstract

Four Thoroughbred mares (no. 1–4) were maintained under constant temperature (24°C) and controlled light (L/D:12/12 with lights on at 06.00 hr) conditions. They were fed and watered ad libitum with fresh feed and water given at 09.00 hr. After a 45‐day pre‐conditioning period, blood samples were obtained by veinipuncture at 4‐hr intervals for 14 days to determine circadian and day‐to‐day variation. The horses exhibited a circadian rhythm with maximum values attained at about 12.00 hr, however, there are periods of days in which no rhythm is distinguishable. Ultradian rhythms with mean periods of 105 to 128 and 24 to 31 min are superimposed upon the circadian rhythm. The individual rhythms are quite variable from horse to horse and within the same horse. During periods of decline in plasma cortisol with metabolic half‐lives of approximately 70 min, secretion of cortisol was very low or had ceased. During periods of increasing plasma concentration, secretion was occurring at a faster rate than degradation. Rapid decreases in plasma concentration (metabolic half‐life of approximately 30 min) was accompanied by a rise in specific activity indicating cortisol with a high specific activity was entering the plasma pool from other storage pools.     

Digestive tract cell proliferation and food consumption patterns of Ha/ICR mice

The relationship between the daily pattern of food consumption and the proliferation rate of the oesophagus, stomach, forestomach, small intestine and colon of Ha/ICR mice was examined. Proliferative activity was determined by [3H]TdR incorporation on a wet weight tissue basis, along with selective counting of labelled nuclei. Under conditions of ad libitum feeding with a 12 hr light cycle (lights on at 0600) mice eat most of their food during the dark period. A distinct circadian rhythm was observed in the oesophagus, stomach, forestomach and colon with the peak of [3H]TdR incorporation between 0400 and 0600 and the nadir between 1600 and 1800. Although a circadian fluctuation was observed in the small intestine, its amplitude was much less than in other areas. This rhythmic change in proliferation rate could be phase shifted by allowing the mice to feed only between 0800 and 1600 for 14 days. Under these conditions the peak in proliferative activity occurred between 1800 and 2000. Fasting reduced the daily level of proliferative activity in all of the digestive tract sites studied, and for all areas except the oesophagus greatly reduced or eliminated the circadian fluctuation. The forestomach and colon were the most influenced by fasting with 24 hr [3H]TdR incorporation reduced to 30-40% of the control value. Refeeding following a 48 hr fast produced a rapid increase in proliferative activity peaking at levels well above the control value at 16 hr after the onset of refeeding. The major exception to this was the small intestine which slowly returned to the control value during the first 24 hr. Partial refeeding produced a diminished refeeding response. Once the normal pattern of food consumption was re-established following refeeding the normal proliferative fluctuations were again observed.     

AMPK regulates circadian rhythms in a tissue- and isoform-specific manner

Background

AMP protein kinase (AMPK) plays an important role in food intake and energy metabolism, which are synchronized to the light-dark cycle. In vitro, AMPK affects the circadian rhythm by regulating at least two clock components, CKIα and CRY1, via direct phosphorylation. However, it is not known whether the catalytic activity of AMPK actually regulates circadian rhythm in vivo.

Methodology/Principal Finding

The catalytic subunit of AMPK has two isoforms: α1 and α2. We investigate the circadian rhythm of behavior, physiology and gene expression in AMPKα1−/− and AMPKα2−/− mice. We found that both α1−/− and α2−/− mice are able to maintain a circadian rhythm of activity in dark-dark (DD) cycle, but α1−/− mice have a shorter circadian period whereas α2−/− mice showed a tendency toward a slightly longer circadian period. Furthermore, the circadian rhythm of body temperature was dampened in α1−/− mice, but not in α2−/− mice. The circadian pattern of core clock gene expression was severely disrupted in fat in α1−/− mice, but it was severely disrupted in the heart and skeletal muscle of α2−/− mice. Interestingly, other genes that showed circadian pattern of expression were dysreguated in both α1−/− and α2−/− mice. The circadian rhythm of nicotinamide phosphoryl-transferase (NAMPT) activity, which converts nicotinamide (NAM) to NAD⁺, is an important regulator of the circadian clock. We found that the NAMPT rhythm was absent in AMPK-deficient tissues and cells.

Conclusion/Significance

This study demonstrates that the catalytic activity of AMPK regulates circadian rhythm of behavior, energy metabolism and gene expression in isoform- and tissue-specific manners.     

Acinar cell proliferation in the parotid and submandibular salivary glands of the neonatal rat

Abstract. Although the rat salivary glands are deficient in acini at birth, acinar cells proliferate rapidly during the early post-natal period. The pattern of acinar cell proliferation was analysed in the parotid and submandibular glands of neonatal rats from day of birth until day 34. Mitotic and [³H]thymidine ([³H]TdR) labelling indices of the two glands show distinctly different patterns. Analysis of cell division in the rat parotid gland demonstrated a peak of mitotic index at 14 days (2.9 ± 0.4%) and labelling index at 16 days (25.2 ± 2.1%). Submandibular gland acinar cell proliferation reaches a zenith between 7–8 days; labelling index (14.2 ± 1.1%) and mitotic index (2.3 ± 0.3%). Cell proliferation decreases rapidly in both glands after reaching a peak in activity. Gland size increases more rapidly in the submandibular gland which correlates with the earlier shift from cell proliferation to differentiation which occurs in this organ. Circadian rhythms of [³H]TdR incorporation were also investigated in this study. A circadian rhythm of [³H]TdR incorporation into DNA occurs at 15 days after birth with a peak at 06.00 hours in both glands and a trough occurring at 15.00 hours in parotid gland and 18.00 hours in the submandibular gland. Determination of specific activity of DNA (ct/min per μg DNA) on days 8, 10, 12, 13, 14, 15, and 16 after birth at 06.00 and 15.00 hours indicated that a circadian rhythm in [³H]TdR incorporation into DNA began on day 14. The developmental switch from suckling to solid food may be an initiating factor in the sychronization of the circadian rhythm in cell proliferation.     

Circadian influences on feeding-induced changes in ACTH and corticosterone secretion in rats.

Food ingestion has a variable influence on pituitary-adrenal hormone secretion depending on the species studied and/or the experimental design. In this study, changes in plasma concentrations of ACTH and corticosterone following 30 min of food ingestion were compared in both 24 h fasted and ad libitum fed rats tested during either the early light cycle or the early dark cycle. In the dark, food ingestion caused significant decreases in both ACTH (to 80% of control) and corticosterone (to 32% of control) in both fasted and ad libitum fed rats. In contrast, in the light, food ingestion by the fasted animal resulted in a doubling of corticosterone concentrations. Such a response was not seen in ad libitum fed animals; however, these animals ate very little during the test. There were no significant changes in ACTH during the light phase. These data indicate that time of day has a significant impact on the responses of the pituitary-adrenal system to food ingestion. This circadian effect may be due to the influence of the endogenous levels of ACTH/corticosterone existing at the time of food ingestion.     

Circadian rhythms in digestive enzymes in the small intestine of rats. I. Patterns of the rhythms in various regions of the small intestine.

The activities of the digestive enzymes, maltase [EC 3.2.1.20], sucrase [EC 3.2.1.26], trehalase [EC 3.2.1.28], Leucine aminopeptidase [EC 3.4.11.1], and alkaline phosphatase [EC 3.1.3.1] were measured in various regions of the small intestine of rats. The activities of all these enzymes were much higher in the jejunum than in the ileum, and in the distal regions of the ileum no sucrase, trehalase or alkaline phosphatase activity was detected. In the jejunum, the activities of all the enzymes tested exhibited clear circadian variations with the highest activity at 0000-0400 h and the lowest at 1200 h when the rats were fed ad libitum. In the ileum, maltase and sucrase also exhibited circadian variations, but the amplitude of the rhythm was smaller than that in the jejenum. Trehalase and alkaline phosphatase did not show any circadian variation in the ileum. Leucine aminopeptidase showed a circadian variation in the ileum with the same amplitude as in the jejunum. The phase of the circadian variations shifted about half a day when the rats were fed in the daytime, but the amplitude of the rhythm did not change.     

Correlation between circadian rhythms of polyamine synthesis and cell proliferation in rat liver.

In rats fed ad libitum, a marked circadian rhythm with a peak at night was observed in the hepatic level of ornithine decarboxylase (ODC) [EC 4.1.1.17], the enzyme for the first step of polyamine synthesis. A similar rhythm was found in the hepatic content of putrescine, but not of spermidine or spermine. The mitotic activity of the liver also exhibited a clear rhythm with a peak in the daytime. The rhythms of both ODC and mitosis were generated by cyclic ingestion of proteinous food, since the peaks shifted when rats were meal-fed and both activities disappeared on starvation or protein deprivation. The close parallel between the rhythms suggested that synthesis of polyamine, especially that of putrescine, was a prerequisite for the rhythmic growth of liver. The dietary induction of hepatic ODC depended on the nutritive value of dietary protein; zein or gelatin was effective only when supplemented with limiting amino acids and there was a good correlation between the hepatic ODC level and the relative growth rate.     

Circadian features of carbohydrate metabolism in domestic fowls exposed to weekly 120 degree-shifts of synchronizer schedule.

Effects of weekly 8 hr advance- or delay-shifts on the circadian rhythm of plasma glucose, liver glycogen and muscle glycogen in male domestic fowls, beginning at about 3 days of age, were examined. Circadian rhythm in the aforesaid indices of carbohydrate metabolism in control birds was also studied. Blood and tissue samples were collected from birds in all the three groups at 4 hr intervals over a single 24 hr time scale both at 6th and 12th week of age. Plasma glucose and glycogen content in the tissues were determined by employing standard techniques. Cosinor rhythmometry was used for analyzing time series data. In general, a statistically significant circadian rhythm was documented for all the three indices in control and advance-schedule birds, irrespective of age. In contrast, in delay-schedule birds, statistically significant circadian rhythm could not be detected, excluding in muscle glycogen at 12th week of age. The poor growth rate in the delay-schedule birds could be imputed to the disappearance of circadian rhythm in the indices of carbohydrate metabolism.