A phase-dependent delay of the chick pineal rhythm in rate of thymidine incorporation by brief exposure to ouabain

Cultured chick pineal glands show a persistent rhythm in the rate of cumulative incorporation of thymidine into DNA [Wainwright and Wainwright, 1989]. In this study we have examined the effects of a pulse-exposure to ouabain in the dark on the first day of culture upon thymidine incorporation during the second and third days of culture in the dark with ouabain-free medium. The phase of the rhythm in rate of thymidine incorporation was delayed by a 4-hr exposure to 100 microM ouabain commencing in the final hour of the photoperiod, but not by a 2-hr exposure or by 10 microM ouabain. This effect was phase-dependent and not seen when exposure to ouabain began earlier in the photoperiod. The phase delay caused by ouabain was not due to a persistent direct inhibition of the process of thymidine incorporation. The phase-shift due to exposure to ouabain was superimposed on a phase delay caused by renewal of culture medium 4 hr after explanting the glands into culture.     

A phase-dependent delay of the chick pineal rhythm in rate of thymidine incorporation by brief exposure to aphidicolin

Cultured chick pineal glands show a persistent rhythm in the rate of cumulative incorporation of thymidine into DNA. In this study we have examined the effects of pulse-exposure to aphidicolin in the dark on the first day of culture on thymidine incorporation during the second and third days of culture in the dark with aphidicolin-free medium. The phase of the rhythm in the rate of thymidine incorporation was delayed in a concentration-dependent manner by a 4-hr exposure to aphidicolin, commencing in the final hour of the photoperiod. This effect was phase-dependent and not seen when exposure to aphidicolin began earlier in the photoperiod.     

Thymidine kinase activity of the chick pineal gland

Pineal thymidine kinase activity of 1-week-old chicks in situ varied significantly throughout the day. However, the circadian rhythm of thymidine incorporation seen with cultured chick pineal glands was not accompanied by variations in level of thymidine kinase activity in vitro. Thus the circadian rhythm in rate of cumulative incorporation of thymidine by cultured chick pineal glands is not determined by a rhythm in rate of the first reaction of the complex series of reactions by which thymidine is incorporated into DNA.     

Entrainment of the circadian rhythm in the rat pineal N-acetyltransferase activity by melatonin is photoperiod dependent

Entraining effect of melatonin on the circadian rhythm in rat pineal N-acetyltransferase (NAT) activity was studied under various photoperiods. Melatonin administration prior to dark onset for 5 successive days phase-advanced the evening NAT rise under the light:dark (LD) cycle of either LD 10:14 or LD 8:16, but not under LD 12:12. It is assumed that under the latter regime, the end of a light period exhibited a phase-delaying effect on the NAT rise. The light exposure appeared to be a stronger Zeitgeber than melatonin itself. Data show that melatonin applied in the late light period advances the evening NAT rise under a short photoperiod only; under a longer photoperiod, the phase-advancing effect of melatonin may conflict with a phase-delaying effect of the end of a light period, and the effect of light exposure overrides that of melatonin.     

Phototransduction-related circadian changes in indoleamine metabolism in the chick pineal gland in vivo

Abstract: The purpose of this study was to examine the day/night levels of pineal melatonin and its rate limiting enzyme N-acetyltransferase (NAT) in relationship to the ratio of 11-cis-to all-trans-retinal. Three-week-old chicks were placed in 12:12 light: dark (LD 12:12) cycle for one week, pineals were collected during the light phase at 1500 (i.e., after 10 hr light), during the dark phase at 1900 (i.e., 2 hr after dark), at 2100 (i.e., 4 hr after dark), and at 2300 (i.e., 6 hr after dark) and after light extension to 1900. The results show that light-sensitive 11-cis-retinal in the chick pineal has the same diurnal rhythm as NAT and melatonin; all constituents increased within 2 hr of darkness onset (at 1900) and reached their peak after 4 hr of dark. All values were lowest during the light phase at 1500. Low values for 11-cis-retinal, NAT, and melatonin were also seen in the group of chicks which experienced light extension to 1900. The data indicate that in vivo light plays a major role in triggering rhodopsin-bound 11-cis-retinal production within 2–4 hr after darkness onset; this change likely serves as the signal for the subsequent formation of the hormonal product of the pineal gland, melatonin.     

HPLC validation of a circadian melatonin rhythm in the pineal gland of inbred mice

Abstract: Production of melatonin in the pineal gland of inbred mice such as C57B1/6J, B ALB/c and AKR strains is still a matter of debate. In previous studies, we and other authors showed that these strains of inbred mice have a clear-cut circadian rhythm of serum melatonin and urinary 6-hydroxy-melatonin-sulphate. In contrast, other groups claimed these mice are unable to synthesize melatonin. These studies were based on RIA measurements and/or estimates of N-acetyltransferase (NAT) and hydroxyindole-O-methyltransferase (HIOMT) activities. In the present study we validate the presence of melatonin in the pineal gland of C57B1/6, BALB/c, and AKR mice by HPLC determinations. We found a short-term melatonin peak in the middle of the dark period with a pattern which mirrors that found previously in the serum. The possibility remains, although it seems unlikely, that the pineal melatonin rhythm measured here represents melatonin produced elsewhere which then was subsequently taken up by the pineal gland.     

Adenosine A2 receptor-mediated stimulation of cyclic AMP in cultured chicken pineal cells

Abstract: The pineal gland of vertebrates produces the time-keeping hormone melatonin in a rhythmic manner. Regulation of melatonin production is a multifactorial process. In the chicken, light, perceived through the skull, and norepinephrine, acting through α2-adrenergic receptors, synergistically inhibit day time melatonin production. In addition, adenosine exerts autocrine/paracrine modulatory effects on melatonin secretion. In an attempt to elucidate how these effects of adenosine are mediated, chicken pineal cells were cultured, in the dark during day time, in the presence of different analogs of adenosine. When the adenosine transmembranous carrier was inhibited, chloroadenosine stimulated cyclic AMP (cAMP) accumulation in a time- and dose-dependent manner. The effects were antagonized by 8-phenyltheophylline, an antagonist at the A1/A2 adenosine receptors. A dose-dependent stimulation of cAMP accumulation was also obtained with other adenosine agonists, with the following order of potency: N-ethylcarboxamidoadenosine > cyclopentyladenosine > R-phenyl-isopropylade-nosine. The stimulatory effect of the latter compound was still observed when basal cAMP levels were increased in the presence of forskolin. Under our experimental conditions no inhibition of cAMP content was observed. Our results are consistent with the idea that stimulation of melatonin secretion by adenosine analogs is mediated through A2 receptors.     

Control of skin cancer by the circadian rhythm

Skin cancer is the most common form of cancer in the United States. The main cause of this cancer is DNA damage induced by the UV component of sunlight. In humans and mice, UV damage is removed by the nucleotide excision repair system. Here, we report that a rate-limiting subunit of excision repair, the xeroderma pigmentosum group A (XPA) protein, and the excision repair rate exhibit daily rhythmicity in mouse skin, with a minimum in the morning and a maximum in the afternoon/evening. In parallel with the rhythmicity of repair rate, we find that mice exposed to UV radiation (UVR) at 4:00 AM display a decreased latency and about a fivefold increased multiplicity of skin cancer (invasive squamous cell carcinoma) than mice exposed to UVR at 4:00 PM. We conclude that time of day of exposure to UVR is a contributing factor to its carcinogenicity in mice, and possibly in humans.     

Phase-shifting effects of light on the circadian rhythms of 5-methoxytryptophol and melatonin in the chick pineal gland

In the chick pineal gland, 5-methoxytryptophol and melatonin concentrations fluctuate in a rhythmic manner. These rhythms are circadian in nature persisting in constant darkness and have opposite phases. Acute exposure of chicks to white light (30 lux for 5, 10, 20, and 30 min) at night increased the amount of pineal 5-methoxytryptophol and decreased pineal melatonin content. A 6 hr pulse of light (100 lux) applied early in the subjective night (CT12-CT18) caused a delay in the phase of the circadian rhythms of 5-methoxytryptophol and melatonin by 3.7 and 4.5 h, respectively, compared to untreated controls. When the 6 hr light pulse was given during the late subjective night (C18 CT24) it advanced the phase of the 5-methoxytryptophol and melatonin rhythms by 8.1 and 11.9 h, respectively. In the chick pineal the phase-advancing effects of light on the circadian rhythms of 5-methoxytryptophol and melatonin were more pronounced than the phase-delaying effects. Our results provide the first evidence that light is capable of phase shifting the 5-methoxytryptophol rhythm in a manner similar to its action on the melatonin rhythm.     

Melatonin: a major regulator of the circadian rhythm of core temperature in humans.

The circadian rhythm of core body temperature (BTc), with maxima during the day and minima at night, is normally coupled with the sleep-wake cycle. Pineal melatonin secretion occurs contemporaneously during the nighttime hours and is mediated by the activation of beta-adrenergic receptors during darkness. The hypothesis that nocturnal melatonin secretion may be involved in the regulation of the human circadian BTc rhythm was examined. The temporal relationship between melatonin and the circadian BTc rhythm was characterized in 12 young women, normally entrained to the light-dark cycle. Melatonin levels were manipulated through the administration of exogenous melatonin (2.5 mg, orally) during the daytime (n = 6) or suppression of endogenous nocturnal melatonin secretion by the beta-adrenergic antagonist atenolol (100 mg; n = 6) in double blind placebo-controlled experiments conducted during 2 consecutive days. Serum melatonin levels and BTc were monitored at 20- and 10-min intervals, respectively. In a nightshift worker the temporal relationship between the circadian rhythm of melatonin and BTc was investigated before and after entrainment to a reversed wake-sleep cycle. Our data show that in normally entrained subjects, the time course and amplitude of nocturnal melatonin secretion were temporally coupled with the decline of BTc (r = 0.97; P less than 0.00001). The same occurred in the nightshift worker, both during the dissociation and after entrainment to the reversed sleep-wake cycle. Compared with placebo, administration of melatonin significantly reduced daytime BTc (P less than 0.01), and the suppression of melatonin (by atenolol) attenuated the nocturnal decline of BTc (P less than 0.01). Cosinor analysis showed that the amplitude of the circadian BTc rhythm was reduced by about 40% in response to both daytime melatonin administration (P less than 0.05) and nocturnal melatonin suppression (P less than 0.02). In conclusion, circadian rhythms of melatonin and BTc are inversely coupled. The demonstrated hypothermic properties of melatonin are accountable for the generation of at least 40% of the amplitude of the circadian BTc rhythm. Manipulation of melatonin levels might be clinically useful to resynchronize the BTc rhythm under conditions of BTc rhythm desynchronization.     

Intracellular Ca2+ signaling pathway is involved in light-induced phase advance, but may not be in phase delay, of the circadian melatonin rhythm in chick pineal cell

Chick pineal cells have photoreceptive, circadian clock and melatonin synthetic capacities, and express circadian oscillation of melatonin release in vitro. Light pulses cause phase-dependent phase shift of the melatonin rhythm. The purpose of this study was to address the questions whether intracellular calcium is involved in both light-induced phase advance and delay. Thapsigargin and cyclopiazonic acid, which deplete the intracellular calcium stores, blocked the light-induced phase advance in a dose-dependent manner. The pulses of ryanodine receptor antagonist (dantrolene sodium or ruthenium red) also blocked the light-induced phase advance. Most agents did not cause a significant phase shift by themselves. On the other hand, all the agents used, failed to block the light-induced phase delay, even if the magnitude of phase delay was decreased using low intensity light. An antagonist of nitric oxide synthase blocked neither light-induced phase advance nor phase delay. These results indicate the following possibilities: (1) the mechanism of light-induced phase advance and delay may be different in chick pineal cells, or (2) if intracellular calcium is involved in both light-induced phase advance and delay, the sensitivity to light and/or agents used in this study may differ according to Zeitgeber time.     

Long-Term follow-up of the circadian rhythm of heart rate and heart rate variability in healthy elderly patients.

BACKGROUND: The long-term age-related changes in circadian rhythm of heart rate variability (HRV), that is, autonomic nervous activity, remain unknown in elderly people. METHODS AND RESULTS: Holter monitoring was conducted twice at an interval of 15 years in 15 healthy elderly patients (age: 70.0 +/- 4.1 years, at first monitoring, female: 10) and assessed the age-related changes in 24-h mean and hourly mean normal sinus R-R interval (mean NN), HRV (high frequency (HF) component, low frequency (LF) component and LF/HF) and the circadian rhythms. As a result, 24-h mean mean NN (0.976 +/- 0.115 vs 0.903 +/- 0.117 (s), p = 0.0019), LF/HF (1.681 +/- 0.731 vs 0.962 +/- 0.442, p = 0.0022), and LF (278.88 +/- 176.43 vs 179.19 +/- 132.33 (ms2), p = 0.0039) significantly decreased 15 years later, although 24-h mean HF (221.20+/-138.89 vs 310.78+/-296.73 (ms2), p = 0.1102) increased slightly. The hourly mean NN closely correlated with hourly HF and LF/HF throughout circadian rhythms both at first and second monitoring. In the morning hours, amplitude rates of all HRV indices increased significantly 15 years later. CONCLUSION: In elderly people, age-related changes in the 24-h mean heart rate (HR) were conversely dissociated from those of the 24-h mean HRV. However, the close correlation between hourly HR and HRV was preserved, even in very elderly patients. Additionally, the amplitude rates in HRV in the morning increased with age. These age-related changes of HR and HRV might be characteristic of elderly people.     

Demonstration of circadian rhythm in heart rate turbulence using novel application of correlator functions

BACKGROUND: Demonstration of a circadian rhythm in two parameters of heart rate turbulence--turbulence onset (TO) and turbulence slope (TS)--has been difficult. OBJECTIVE: The aim of this study was to devise a new method for detecting circadian rhythm in noisy data and to apply it to selected Holter recordings from two postmyocardial infarction databases: Cardiac Arrhythmia Suppression Trial (CAST, n = 684) and Innovative Stratification of Arrhythmic Risk (ISAR, n = 327). METHODS: For each patient, TS and TO were calculated for each hour with >4 ventricular premature contractions (VPCs). An autocorrelation function Corr(Deltat) = then was calculated and averaged over all patients. Positive Corr(Deltat) indicates that TS at a given hour and Deltat hours later are similar. TO was treated likewise. Simulations and mathematical analysis showed that a circadian rhythm required Corr(Deltat) to have a U-shape consisting of positive values near Deltat = 0 and 23 and negative values for intermediate Deltat. Significant deviation of Corr(Deltat) from the correlator function of pure noise was evaluated as a Chi-square value. RESULTS: Circadian patterns were not apparent in hourly averages of TS and TO plotted against clock time, which had large error bars. However, their correlator functions produced Chi-square values of approximately 10 in CAST (both P <.0001) and approximately 3 in ISAR (both P <.0001), indicating the presence of circadian rhythmicity. CONCLUSION: Correlator functions may be a powerful tool for detecting the presence of circadian rhythms in noisy data, even with recordings limited to 24 hours.     

The influence of thyroid function on the circadian rhythm of heart rate in elderly euthyroid subjects

The influence of thyroid function on the circadian rhythm of heart rate was assessed using 24 hour electrocardiographic recordings in 196 elderly euthyroid subjects (78.4 +/- 8.1 years; male 60, 76.1 +/- 9.1 years; female 136, 79.4 +/- 7.4 years). Serum free T3, free T4 and TSH levels were measured by radioimmunoassay. To determine if heart rate fluctuates rhythmically with a circadian period, mean hourly heart rates in 24 hour electrocardiographic recordings were used to fit cosine curves by the statistical technique of least squares, and the parameters of the rhythm--the mesor, amplitude, acrophase, maximal and minimal hourly heart rates--were estimated. To investigate the factors influencing the diurnal variation of heart rate, we applied multiple regression analysis. The cosine curves were fitted with a P value of 0.01 or less in all subjects. The mesor, maximal and minimal hourly heart rates were inversely proportional to serum TSH concentrations in males. Neither amplitude nor acrophase had relation to the thyroid function in males. The mesor, maximal and minimal hourly heart rates were directly proportional to serum-free T4 concentrations and inversely proportional to serum TSH concentrations in females. The increase in the acrophase correlated with the increase in serum-free T4 levels, and the acrophase increased in proportion to serum-free T3 levels in females.     

A direct influence of moonlight intensity on changes in melatonin production by cultured pineal glands of the golden rabbitfish, Siganus guttatus

Rabbitfish are a restricted lunar-synchronized spawner that spawns around a species-specific lunar phase. It is not known how the fish perceive changes in cues from the moon. One possible explanation is that rabbitfish utilize changes in moonlight intensity to establish synchrony. The purpose of the present study was to examine whether or not the pineal gland of the golden rabbitfish can directly perceive changes in moonlight intensity. Isolated pineal glands were statically cultured under natural or artificial light conditions and melatonin secreted into the culture medium was measured using a time-resolved fluoroimmunoassay. Under an artificial light/dark cycle, melatonin secretion significantly increased during the dark phase. Under continuous light conditions, melatonin secretion was suppressed, while culture under continuous dark conditions seemed to duplicate melatonin secretion corresponding to the light/dark cycle in which the fish were acclimated. When cultured pineal glands were kept under natural light conditions on the dates of the full and the new moon, small amounts of melatonin were secreted at night. Moreover, exposure of cultured pineal glands to artificial and natural light conditions resulted in a significant decrease of melatonin secretion within 2 hr. These results suggest that the isolated pineal gland of golden rabbitfish responds to environmental light cycles and that 'brightness' of the night moon has an influence on melatonin secretion from the isolated pineal gland.     

An analysis of the circadian rhythm of the heart rate and arrhythmias in healthy elderly subjects]

The incidence of asymptomatic arrhythmia detected by Holter monitor in the normal aged population is high. Nevertheless, there are few studies in the literature about the existence and characteristics of their circadian rhythm (CR). The aim of this study, is to determine the presence of CR of the heart rate (HR), supraventricular and ventricular extrasystoles (SVE, VE), atrial tachycardias (AT) and ventricular complex tachycardias (VCT) in the normal aged population. We studied 120 subjects, older than 70 years of age, belonging to a pensioner club, without apparent cardiovascular disease by history, physical, ECG, Chest X-Ray and echocardiography. All the patients had a 24 hours Holter monitor. 42 patients whose recording showed more than 50 SVE and/or more than 50 VE were included in the study. To study the CR the cosinor method was used. In the simple analysis, the HR had significant CR in 40 subjects (95.2%), the SVE in 18 out of 29 (62.1%) and the VE in 16 out of 26 (61.5%). The global analysis showed significant CR for the HR, with an acrophase at 15:47 hours (confidence limits at 95% between 14:45 and 15:42 hours) and for the VE, (acrophase: 15:35 hours, confidence limits between 11:53 and 19:05 hours). There was not significant CR for the SVE because the wide dispersion of the acrophases between the subjects. The AT had significant CR but no the VCT. We conclude that the majority of the aged normal subjects with frequent ectopy had significant CR for the HR and extrasystoles. The VE follow a CR similar to the frequency, suggesting a common modulation of the autonomic nervous system. The SVE variation follow a different CR.     

苯那普利对高血压病患者心率变异性及其昼夜节律的影响

目的　观察苯那普利对高血压病患者动态血压、心率变异性及其心率变异性昼夜节律的影响。方法　 3 6例高血压病人 ,服用苯那普利 ( 10～ 2 0 mg/ d) 8周 ,用药前后做动态血压和 2 4h动态心电图分析。结果　治疗后动态血压各指标均下降 ( P<0 .0 5或 <0 .0 1) ;HRV(心率变异性 )时域指标 RMSSD(全部相邻 RR间期之差的均方根值 )升高 ( P<0 .0 5 ) ,其他指标虽均有升高 ,但无统计学意义 ( P>0 .0 5 ) ;频域指标中 HF(高频功率 )增加 ,L F(低频功率 )、L F/ HF下降 ;5分钟 HRV中治疗后白昼段和夜间段 HF均升高 ,L F/ HF均下降 ,且白昼段 L F较夜间段高 ,HF比夜间段低。结论　苯那普利可以很好控制全天血压 ,同时降低交感神经活性 ,提高迷走神经张力 ,且不干扰心率变异性的昼夜节律