Melatonin and adjustment to phase shift

SUMMARY  The pineal hormone melatonin has clear circadian phase-shifting effects in humans which have recently been formalized as a phase response curve. Its potential use in circadian rhythm disorders has been investigated in field studies of jet lag and shift work and in simulated phase shift. A substantial amount of information indicates that in the majority of subjects it hastens adaptation of both subjective and objective measures to forced shifts in time cues with few reported side-effects. Field studies of its use in adaptation to shift work are sparse and preliminary but the first indications are positive. In some blind subjects with sleep disturbance it can stabilize sleep onset time without necessarily entraining all circadian rhythms and it can advance sleep timing in delayed sleep-phase insomnia. Acute suppression of core body tempera-ture may be an integral part of the phase-shifting mechanism.     

不同光暗循环下小鼠自发活动生物节律周期的频率分析

目的 探讨不同光-暗循环条件下小鼠的自发性活动是否存在3．5d节律、7d节律以及10d节律。方法 以小鼠为动物模型，排除社会活动因素对生物节律的影响，采用红外线检测系统检测小鼠自发性活动，对不同光-暗循环作用下小鼠自发活动的多频率生物节律进行了研究。结果 用余弦法的频谱分析发现：在10h光照（L）／10h黑暗（D）环境下，小鼠的自发活动存在明显的τ=20h的近日节律和τ=10h的近半日节律（P〈0．001），以及较弱的近7d节律和近3．5d节律，P〈0．01；在12h（L）／12h（D）环境下，存在很强的24h为周期的近日节律和12h为周期的近半日节律，P〈0．001，未见近7d节律存在；在14h（L）／14h（D）环境下，以τ=28h为周期的近日节律和τ=14h的近半日节律表现明显（P〈0．001），同时亦有较弱的近7d节律。上述情况下，小鼠均未发现10日节律。结论 生物体存在多种频率的生物节律，其节律的特征受到光-暗循环的影响。     

Effect of x-ray irradiation on circadian rhythm of microsomal hemoprotein levels in rat liver

Research Institute of Biology and Biophysics, V. V. Kuibyshev Tomsk State University. (Presented by Academician of the Academy of Medical Sciences of the USSR N. V. Vasil'ev.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 110, No. 12, pp. 653–655, December, 1990.     

Postoperative deep body temperature rhythm

The postoperative deep body temperature rhythms of fifteen patients who received aorto-coronary bypass surgery (group I), and of seven patients who received non-cardiac major surgery (group II), were studied. Postoperative patients, especially those who received aortocoronary bypass surgery, showed greatly disturbed deep body temperature rhythm. There existed infradian and ultradian rhythm in both groups, and there existed two patients in group I who did not show sinusoidal rhythm. The patients of group I also showed a longer period of rhythm than did those of group II. The mesor and amplitude of the patients in group I showed a greater individual variation than did those in group II. The acrophase of both groups deviated widely. The patients who underwent cardiac surgery needed a longer time for temperature rhythm recovery than did those who underwent general surgery.     

用卡托普利治疗肾性高血压山羊模型的血压近日节律分析

作者用计算机辅助自动采样控制贮存的测压系统,对正常山羊及Goldblatt高血压山羊作48小时连续测定动脉血压。用群体均值余弦法分析,发现两者呈相似的血压近日节律波动式样,山羊血压昼低夜高。用卡托普利常规和择时给药两种方式治疗高血压,结果两种给药方式均能降低全天血压,两者降压程度无统计学差异,而择时疗法的药物剂量和给药次数均较少,提示于血压峰值时相前给予半衰期短的药物 对高血压山羊能有效地降低全天动脉血压。     

Ventricular Parasystole: A Chronobiologic Study

Previous works have reported circadian rhythms for several cardiovascular parameters. A chronobiologic rhythm is characterized by: mesor (a rhythm-determined average), amplitude (half difference between the highest and lowest values), and acrophase (timing of high point in degrees and/or in hours) along with 95% confidence limits. We performed 24-hour ECG Holler monitoring in seven patients (mean age, 50.6 years) with ventricular parasystole (VP) in order to determine whether the chronotropic activity of parasystolic foci has a circadian rhythm similar to that of the sinus node. For each Holter recording parasystolic rates (PRs) and heart rates (HRs) were calculated every hour. Furthermore, a mean hourly PR and a mean hourly HR were calculated from the hourly PRs and HRs of the patients. The statistic chronobiologic analysis was done by single and mean cosinor methods. Correlation between mean hourly PR and HR was evaluated by Pearson's V coefficient. A statistically significant rhythm (P < 0.05) was found for the single and mean rhythms both of HR and PR. In our patients, HR had acrophase at 1.27 P.M., mesor at 73.28 beats/min, and amplitude at 9.53 beats/min, whereas PR had acrophase at 1.42 P.M., mesor al 38.31 beats/min, and amplitude at 3.64 beats/ min. Chronobiological data and the high direct correlation between mean hourly HRs and mean hourly PRs (r = 0.96, P < 0.001) indicate a similar circadian variability of the chronotropic activity of sinus nodes and parasystolic foci. Although several hypotheses can be made, responsiveness of parasystolic foci to circadian variations of the autonomic nervous system tone (sympathetic and/or vagal) and/or circulating substances (particularly catecholamines) seems the more probable one for explaining our findings.     

Physiology: Description of circadian rhythm in uterine artery blood flow during the peri-ovulatory period

Uterine artery blood flow was assessed by transvaginal colourand pulsed Doppler ultrasound prospectively in six women duringthe peri-ovulatory period. All patients had regular ovulatorymenstrual cycles and a mid-luteal serum progesterone consistentwith spontaneous ovulation in the preceding cycle. Each patientunderwent serial transvaginal ultrasound examination and Dopplerassessment of blood flow in the uterine arteries. When the meanfollicular diameter was >16 mm or day –2 from the estimatedday of ovulation was reached, patients were scanned at 6 hourlyintervals at 0600, 1200, 1800 and 2400 h until follicular rupture.The pulsatility index (PI) and time averaged maximum velocity(TAMX) were calculated as Doppler indices of impedance to bloodflow and velocity respectively. A venous blood sample was takenat each visit for subsequent hormonal analysis. The mean uterineartery PI showed a marked daily fluctuation with a nadir occurringmost commonly at 0600 h. A comparison between the mean PI valuesat 0600 and 1800 h showed significantly lower results at 0600h in both dominant (P < 0.05) and non-dominant (P < 0.02)uterine arteries. Furthermore, mean uterine artery TAMX showeddaily fluctuations with peak values most commonly occurringat 0600 h with the nadir occurring during the afternoon andlate evening. There was no temporal relationship between thefluctuations in PI and changes in luteinizing hormone, folliclestimulating hormone, oestradiol or progesterone concentrations.These observations suggest that there is a circadian rhythmin uterine artery blood flow during the peri-ovulatory periodwhich appears to be independent from the hormonal changes.     

Photic control of nitric oxide synthase activity in the hamster suprachiasmatic nuclei

Circadian rhythms are controlled by an endogenous clock, which in mammals is located in the hypothalamic suprachiasmatic nuclei (SCN). A role for nitric oxide in circadian responses to light has been indicated. To test the role of nitric oxide synthase (NOS) in the SCN and in circadian responses to light, we examined NOS specific activity at different time points and photic conditions. NOS activity was determined by the conversion of -arginine to -citrulline. NOS enzymatic activity in the SCN was significantly higher during the dark phase than during the day, without any changes in the levels of the NOS protein. However, this difference disappeared when animals were placed under constant darkness, and NOS activity was similar at CT 8 and CT 18 (with CT 12 defined as the onset of the subjective night). When 5-min light pulses were administered at these time points (when light would induce no phase shift or a phase advance, respectively), NOS activity was significantly increased almost equally. A spectrophotometric assay was used to determine NO content in the SCN, showing relatively high constitutive levels enhanced by 100 μM glutamate. These results suggest that NOS activity is not controlled by the circadian clock, although it might mediate some of the effects of light on biological rhythms.     

African trypanosomiasis in the rat alters melatonin secretion and melatonin receptor binding in the suprachiasmatic nucleus

Rats infected with Trypanosoma brucei brucei, a subspecies of the extracellular parasites that cause African sleeping sickness, were examined for disturbances in the circadian rhythms of melatonin secretion (evaluated by determination of the excretion of melatonin in the urine) and the binding of melatonin to its receptor in the suprachiasmatic nuclei of the anterior hypothalamus. In normal and infected rats, Cosinor analysis showed a significant nocturnal peak. The amplitude of this peak was, however, significantly decreased in the infected rats. The peak of melatonin receptor binding in the suprachiasmatic nuclei showed a 4-h phase advance in the infected rats, compared with the controls (0400 and 0800, respectively). These data point to a disturbance in the circadian rhythm of the melatonin-generating systems in the pathogenesis of African sleeping sickness.