Seasonal characteristics of the circadian rhythm of peripheral blood leukocyte content in Wistar rats]

In Wistar rats, the seasonal variability of acrophase position, mesor value and circadian rhythm amplitudes of total leukocyte count, as well as of percentage and absolute lymphocyte count was revealed. The leukocyte count and absolute lymphocyte content were found highest in spring, while eosinophils--in autumn, neutrophils and monocytes--in winter.     

Postnatal development of the circadian rhythm of circulating blood cells in rats

In the present study the variations in the leukocyte and erythrocyte counts were investigated in the peripheral blood within the light and darkness periods during the postnatal development of rats. The animals were kept under an artificial illumination regime (12 hours light, 12 hours darkness), and examined at the ages of 7, 14, 21, 28, 35 and 45 days, and in maturity (56 days). Erythrocyte counts exhibited no light-dark rhythm. The circadian rhythm of leukocyte counts developed in male and female laboratory rats in the fourth week of age.     

Rat liver cholesterol 7 alpha-hydroxylase. Pretranslational regulation for circadian rhythm.

A complete cDNA encoding cholesterol 7 alpha-monooxygenase (EC 1.14.13.17) which had been isolated from rat liver cDNA libraries by using specific antibodies to the enzyme (Noshiro, M., Nishimoto, M., and Okuda, K. (1989) FEBS Lett. 257, 97-100) was totally sequenced. The cDNA contained a 1,509-base pair open reading frame encoding 503 amino acid residues (Mr = 56,880) and an unusually long 3'-untranslated region rich in AT sequence in the total length of 3,545 base pairs. The predicted amino acid sequence displays less than 30% similarity to other sequenced cytochrome P-450s indicating that the 7 alpha-hydroxylase constitutes a novel family of cytochrome P-450. The AT-rich region often contained ATTTA motifs, 5'-AAT-3' or 5'-TAA-3' trinucleotides which were reported to be involved in rapidly degrading mRNA. Employing the specific antibodies and the cDNA as probes, a diurnal variation of the levels of the three factors, i.e. enzyme protein, mRNA, and enzyme activity, was studied on rat livers prepared at various times of the day. In normal animals, all three factors exhibited maximum level at 10:00 p.m. and minimum at 10:00 a.m. No significant sexual difference was observed. Cholestyramine feeding increased all three factors at 10:00 a.m. close to the maximum levels of the normal rats, but did not show a significant increase at 10:00 p.m. On the contrary, starvation markedly decreased all three factors either at 10:00 a.m. or at 10:00 p.m., while maintaining still the diurnal variation. A good correlation of the levels of mRNA to the enzyme activities and the protein levels demonstrates that pretranslational regulation is most likely a mechanism for the circadian rhythm of 7 alpha-hydroxylase. The marked diurnal fluctuation of the amount of protein and the level of mRNA also indicates their rapid turnover. The short half-life of mRNA could be correlated with the structure of the 3'-untranslated region of the mRNA characteristic of rapidly degrading mRNA, i.e. abundance of motif, AUUUA, and existence of 5'-AAU-3' or 5'-UAA-3' trinucleotides in single-stranded regions of the secondary structure.     

Brain monoamines and circadian rhythm of spontaneous motor activity of rats]

The effect of three drugs, parachlorophenylalanine, nialamide and disulfiram, drugs known by their action on the two sleep phases, slow wave sleep and I-REM-sleep, have been studied and tested by their effect on the motor circadian rhythm : PCPA and disulfiram reduce the amplitude of the rhythm by two opposed mechanisms : PCPA increases the motor activity, especially the day-time activity, disulfiram reduces the motor activity, especially the night-time activity. The former reduces the serotonine content, the latter the noradrenaline content of the central nervous system. Nialamide (5 or 10 mg/1000 g) is without any action of the rhythm. Both doses increase very much the motor activity ; but the central excitatory state undergoes the normal circadian rhythm. This monoaminoxydase inhibitor is without any action on the circadian rhythm.     

应用植入式遥测技术观察自发性高血压大鼠血压的昼夜波动

目的应用植入式遥测技术观察自发性高血压大鼠在清醒无束缚状态下血压昼夜波动变化。方法取8只SPF级3月龄雄性SHR大鼠,进行C50-PXT植入子植入手术,恢复7 d后,用遥测系统进行24 h连续清醒无束缚的血压监测,并用EMKA分析软件对动态血压心率均值、24 h血压心率趋势等指标进行分析。结果 3月龄的SHR大鼠血压和心律呈昼夜节律性变化,白昼阶段血压明显低于夜间阶段(P<0.01),血压在1∶30～2∶30和20∶30～21∶30时出现两个高峰期,14∶00～14∶30时出现一低谷期。其中夜间阶段平均收缩压为166.02 mmHg,两个收缩压峰值分别为172.13 mmHg和171.38 mmHg;白昼平均收缩压是162.73 mmHg,收缩压谷底值为155.73mmHg。而心率两个高峰期出现在1∶30～2∶00和20∶00～21∶00,高峰值分别为375.00次/分和373.26次/分;心率低谷出现在11∶00左右,谷底值为310.91次/分,白昼和夜间的平均心率分别为328.85次/分和346.05次/分。结论 3月龄的SHR大鼠血压和心律呈昼夜节律性变化,血压和心率在夜间出现两个高峰,白昼出现一个低谷,且夜间的平均血压和心率要高于白昼,SHR大鼠的血压和心率的节律变化与其活动有关。植入式遥测技术可准确反映SHR大鼠血压昼夜的节律性变化,有助于正确评价抗高血压药物的作用和高血压的生理机制研究。     

Analysis of the circadian rhythm in energy metabolism of rat liver

• 1.1. To study the temporal organization of energy metabolism in rat liver the steady state concentrations of key intermediates of carbohydrate and phosphorus metabolism were determined during 24 hr.
• 2.2. The circadian rhythm in energy metabolism of rat liver has been analysed by four different approaches. It was shown that neither apparent PEP synthesis nor crossover theorem were acceptable for the elucidation of the temporal organization of multi-enzyme systems.
• 3.3. Correlations analysis explained the temporal organization of energy metabolism most satisfactorily.
• 4.4. Based on the results of this analysis it was suggested that circadian regulation of energy metabolism in liver was realized at the level of the citric acid cycle.

     

Influence of feeding rhythm on blood insulin in growing rats]

Plasma insulin in ad libitum fed growing rats increases during dark hours and decreases during light hours. In contrast, meal fed growing rats [6 equal meals at regular interval during the day] exhibit a constant plasma insulin level. It may be inferred that improvement of nitrogen retention in meal fed rats is not related to an increase in insulin secretion.     

Influence of the seasons on the circadian rhythm of blood glucose and tissue glycogen in male Wistar rats

Adult, ad libitum fed male Wistar rats were adapted for three weeks to standard laboratory conditions and a 12:12 h light:dark regimen (7 a.m. to 7 p.m., 7 p.m. to 7 a.m.). In January, in April, in July and in October they were decapitated at 3-hour intervals and the glucose level was determined in their blood and the glycogen concentration in their liver, skeletal muscle, heart and white and brown adipose tissue. The influence of the seasons on circadian variation of the given parameters was not the same in all the tissues. Circadian variation of the liver and heart glycogen concentration was the least affected. The liver glycogen curves attained the maximum at the beginning of the light part of the day in all the seasons except the autumn; the rhythm was present everywhere. The rhythm was not demonstrated in the heart in the winter only and except for the summer the curves attained the maximum at the end of the dark part of the day. Pronounced seasonal changes were observed in the blood glucose and skeletal muscle glycogen concentration, whose curves reached the maximum in various parts of the day and where the rhythm was absent in the autumn - and in the case of skeletal muscle in the summer as well. The glycogen concentration in the two adipose tissues displayed the greatest seasonal changes. The shape of the circadian oscillation curves and their maxima in the various seasons were very different, with absence of the rhythm in the autumn. Determination of the influence of the photoperiodic reactions and of changes in hormones and the key enzymes regulating the main metabolic routes might help to explain the basis of circaannual variations in the metabolism of the laboratory rat.     

Role of photoperiodicity and circadian rhythm of glucocorticoids in synchronizing the fluctuations in free-radical oxidation of lipids in rats

A biphasic circadian rhythm in the content of liver lipid peroxidation products has been demonstrated in male Wistar rats housed under the conditions of 12L: 12D, with 3 hours of morning and evening twilight. Maxima of the concentration of the products were observed in the morning and early at night. The rhythm of lipid anti-oxidative activity was found in an anti-phase. Inversion of both the L: D cycle and glucocorticoid circadian rhythms (cortisol injections) led after 14-16 days to the same shifts in the rhythm of anti-oxidative activity. The data indicate that glucocorticoids modulate the diurnal rhythms of lipid anti-oxidative activity and may be responsible for the shifts in the rhythms of free radical oxidation, induced by inversion of the L: D cycle.     

Translational control of the circadian rhythm of liver sterol carrier protein

Rat liver sterol carrier protein (SCP), a major regulator of lipid metabolism and transport, undergoes a rapid turnover and dramatic circadian variation in amount. The level of SCP was quantitated by a specific immunochemical assay using an antibody to homogeneous liver SCP. During a 12-h dark, 12-h light cycle, liver exhibits a biphasic pattern in SCP level. A 7-fold increase in SCP (i.e. from 1 to 7 mg/g of liver) occurs in the dark period, peaking at the midpoint and returning to basal levels by the beginning of the light period. A similar but smaller pattern of variation in SCP amount occurs in the light cycle. To elucidate the basic mechanism responsible for these changes in SCP level, the relative synthetic rate of SCP and mRNA functional activity for SCP were measured during the dark-light cycle. Alterations in the rate of SCP synthesis can account for the variations in SCP concentration. Although large changes occur in relative synthetic rate, no significant changes were found in the level of mRNA for SCP. Therefore, the circadian rhythm in SCP synthesis and amount does not reflect variations in the concentration of mRNA for SCP, but instead is caused by some mechanism controlling the efficiency of translation of SCP mRNA.     

Generational variability in the patterns of motor activity circadian rhythm in the rats

Motor activity circadian rhythm of 32 rats belonging to three consecutive generations of rats from a laboratory strain, has been studied. This rhythm has been registered from the day of weaning (at 21 days) to at least 30 days after. The pattern of this rhythm has been analyzed by means of a Fourier analysis, by which the daily power spectrum of each rat was obtained. Based on the mean power spectrum of each animal, the variance among the different families and generations has been calculated. Results show that the variance increases in a statistically significant way with the succeeding generations. It can be suggested that in the third generation, the characteristics of the progenitors are dispersed, confirming the genetic character of the rhythm and suggesting a multigenic character for the transmission of the circadian rhythm of motor activity.     

Thermoperiodic regulation of the circadian eclosion rhythm in the flesh fly, Sarcophaga crassipalpis

We recorded the eclosion time of the flesh fly, Sarcophaga crassipalpis, at different depths in the outdoor soil and under temperature cycles with various amplitudes in the laboratory, to examine the timing adjustment of eclosion in response to temperature cycles and their amplitudes in the pupal stage. In the soil, most eclosions occurred in the late morning, which was consistent with the eclosion time under pseudo-sinusoidal temperature cycles in the laboratory. The circadian clock controlling eclosion was reset by temperature cycles and free-ran with a period close to 24 h. This clock likely helps pupae eclose at an optimal time even when the soil temperature does not show clear daily fluctuations. The eclosion phase of the circadian clock progressively advanced as the amplitude of the pseudo-sinusoidal temperature cycle decreased. This response allows pupae located at any depth in the soil to eclose at the appropriate time despite the depth-dependent phase delay of the temperature change. In contrast, the abrupt temperature increase in square-wave temperature cycles reset the phase of the circadian clock to the increasing time, regardless of the temperature amplitude. The rapid temperature increase may act as the late-morning signal for the eclosion clock.     

Behavioral feedback regulation of circadian rhythm phase angle in light-dark entrained mice

Induced and spontaneous wheel running can alter the phase and period (tau) of circadian rhythms in rodents. The relationship between spontaneous running and the phase angle (psi) of entrainment to 24-h light-dark (LD) cycles was evaluated in C57BL/6j mice. With a wheel freely available, psi was significantly correlated with the absolute (r = 0.32) and relative (r = 0.44) amount of activity during the first 2 h of the activity period. When wheels were locked during the first half of the night in LD and then unlocked in constant dark (DD), mice exhibited a delayed psi and lengthened tau compared with mice that had wheels locked during the second half of the night. In DD, tau correlated negatively with total daily activity. To evaluate if wheel running modulates the phase-resetting actions of LD, phase shifts to light pulses were measured at two time points in DD, when daily activity levels differed by 40%. Phase delays to light were 56% greater when activity levels were lower. However, in a counterbalanced follow-up experiment, phase advances and delays to light pulses were not affected by the availability of wheels, although an effect of time in DD was replicated. Spontaneous activity can regulate psi and tau without altering the response of the pacemaker to light.