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Results for “Chronobiology Phenomena”

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At least 19 recordsLinked to original sources
PubMed1991

Olfactory bulbectomy increases basal suprachiasmatic cyclic AMP levels in male rats.

For further characterization of the olfactory bulb's role in the medication of chronobiological phenomena, we examined basal cyclic- 3',5'-adenosine monophosphate (cAMP) levels in the suprachiasmatic nuclei (SCN) and lateral hippocampus (LHIP) following bilateral olfactory bulbectomy (OBX) to assess the effects of olfactory bulb removal on the biological clock. Two groups of adult Long-Evans rats underwent OBX or sham control surgery (SHAM). Eight weeks postoperative, the animals were decapitated at the time of maximal cAMP accumulation (circadian time 9-11 h), brains were removed, frozen in liquid nitrogen, and sectioned on a cryostat. Individual brain nuclei (SCN and LHIP) were microdissected using the Palkovits punch technique and analyzed by scintillation proximity assay for cAMP. We report a 83.6% increase in basal cAMP levels in the SCN following OBX (OBX = 63.7 pmol cAMP/mg protein, SHAM = 34.7 pmol cAMP/mg protein, p less than 0.01). No significant differences in LHIP cAMP levels were found. This specific increase in SCN cAMP, at the time of maximum cAMP accumulation, may give insight into the biochemical basis for altered activity levels following OBX.

Animals↗
PubMed1999

Chronopharmacology and its impact on antihypertensive treatment.

Circadian rhythms have been documented throughout the plant and animal kingdom at every level of eukariotic organization. Circadian rhythms are endogenous in nature, driven by oscillators or clocks, and persist under free-running (e.g. constant darkness) conditions. The genes expressing the biological clock have been identified in various species. The important feature of endogeneous biological rhythms is their anticipatory character. Rhythmicity inherent to all living systems, allows them to adapt more easily and to better survive under changing environmental conditions during the 24 hours of a day as well as during changing seasons. Having this in mind it is easy to conceive that not only must the right amount of the right substance be at the right place, but also this must occur at the right time. Also in man nearly all functions of the body including those influencing pharmacokinetic parameters such as drug absorption and distribution, drug metabolism and renal elimination display significant daily variations. Also the onset and symptoms of diseases such as coronary infarction, angina pectoris, stroke, ventricular tachycardia are circadian phase dependent. Myocardial infarction and angina attacks as well as silent ischemias (ST-segment depression) in stable angina pectoris have an early morning peak between 8-12 h. In contrast, ECG abnormalities and angina attacks in variant angina mainly occur at night. Blood pressure and heart rate in normotensives and essential (primary) hypertensive patients display highest values during daytime followed by a nightly drop and an early morning rise. In about 70% of forms of secondary hypertension (e.g. renal disease, hyperthyroidisms, hormonal diseases, gestational hypertension), however, this rhythmic pattern is abolished or even reversed exhibiting nightly peaks in blood pressure. This form of hypertension is accompanied by increased end organ damages. Thus, different subtypes of a disease (angina pectoris, hypertension) can display different circadian patterns in symptoms. These observations are a challenge for basic and clinical research to get a better understanding on the underlying mechanisms of regulation. Moreover, they call for a circadian time-specified drug treatment. From above it is evident that pharmacokinetics may also not be constant within a day. Chronopharmacokinetics have been shown for several cardiovascular active drugs (propranolol, nifedipine, verapamil, enalapril, isosorbide-5-mononitrate, digoxin, etc.). Far more drugs were shown to display significant daily variations in their effects (chronopharmacodynamics, chronotoxicology) even after chronic application or constant infusion. In conclusion, there is clear evidence that the dose/concentration-response relationship of drugs can be significantly dependent on the time of day. Thus, circadian time has to be taken into account as an important variable influencing a drug's pharmacokinetics and/or its effects or side effects.

Animals↗
PubMedDate not supplied

Relevance of circadian cell kinetics in the timing of chemotherapy in animal tumors.

Circadian rhythmicity in cell division has been proved in the actively proliferating healthy tissues of rodents (cornea, G.I.-tract, bone marrow, gonads, epidermis) as well as in most spontaneous or transplanted tumors growing in solid or ascites fluid phases. This circadian division accounts in part for the circadian varying sensitivity of healthy target tissues to oncolytic agents (chronotoxicity/chronotolerance). Similarly, antitumor activity as gauged from analysis of impact on cell kinetics and/or tumor shrinkage or cure was also shown to depend upon the dose and doing time of anticancer drug administration. Variations in the timing of internal cell kinetics after initial drug administration were also shown to depend on the type of drug (alkylating agent, antimitotic, or antimetabolite agent). Interestingly, internal desynchronization may occur in both healthy and tumor tissues, it may allow the selection of given circadian stages for the administration of a second drug at the point of highest tumor sensitivity and healthy tissue resistance (time of least sensitivity). These observations have been utilized to test strategies in sequential drug scheduling aimed at improving the overall therapeutic index. Observations indicate that in some instances these approaches could be translated to human beings.

Animals↗
PubMed1992

Chronobiological aspects of epileptic phenomena: a literature review, implications for nursing and suggestions for research.

Every physiologic and psychologic variable studied heretofore demonstrates rhythmic fluctuations. Chronobiology is the field of study which examines these fluctuations. Chronobiology is highly significant to nursing practice, since human responses are affected by these rhythmic fluctuations. A review of the literature produced little information on epilepsy chronobiology. The status of research in epilepsy chronobiology remains at the basic science level. Continued research is a priority before nursing can use epilepsy chronobiology knowledge in the clinical setting.

Chronobiology Phenomena↗
PubMedDate not supplied

Cross-spectral coherence between geomagnetic disturbance and human cardiovascular variables at non-societal frequencies.

A 35-year-old cardiologist monitored himself with an automatic ABPM-630 (Colin Electronics) monitor, mostly at 15-minute intervals around-the-clock for three years with a few interruptions. In this subject with a family history of high blood pressure and stroke, a cross-spectral analysis revealed a statistically significant coherence at 27.7 days between systolic and diastolic blood pressure and heart rate vs. the geomagnetic disturbance index, Kp. A lesser peak in coherence was found for systolic blood pressure with Kp at a trial period of 4.16 days (P = 0.046). These results suggest that changes in geomagnetism may influence the human circulation, at least in the presence of familial cardiovascular disease risk, and they may do so at frequencies that have no precise human-made cyclic worldwide match.

Adult↗
PubMed1985

A chronobiologic study on some cardiovascular parameters.

We studied the chronobiologic pattern of heart rate, R and T wave voltage, QT interval, and ST segment displacement. Premature atrial and ventricular beats obtained by dynamic electrocardiography, as well as arterial blood pressure measurements obtained by autometry, have also been studied in 131 untreated subjects (25 with hypertension, 28 with major risk factors for coronary artery disease, 9 with coronary artery disease, 37 presumably healthy and 11 shift workers). Our results show the existence of circadian rhythms in heart rate, in the duration of the QT interval and also in the voltage of R and T waves. Our data for R and T wave voltages do not completely agree with those from other authors. We demonstrated also that smoking may influence the circadian acrophase of the rhythm in R wave voltage while sleeping does not show any relationship with R and T wave voltages although it seems related to the displacement of the ST segment. We could point out only small differences in the chronobiologic behavior of patients with coronary disease and that of normal subjects, unlike the results previously reported by other authors. Our study demonstrated the existence of circadian and ultradian rhythms in premature atrial and ventricular beats as well as circadian and circaseptan rhythms in arterial blood pressure. Further studies are needed to improve our chronobiologic knowledge in order to optimize dosage and time of administration of the drugs used in the long term management of arrhythmias and hypertension.

Adult↗
PubMed1990

Endpoints of chronobiologic cardiovascular monitoring during pregnancy for planning exercise and assessing effects.

The chronobiologic question is raised whether exercise may be indicated for the pregnant woman as a general prophylactic measure and, if so, whether it should be timed according to rhythms and stage of pregnancy. This question, recently considered by others without chronobiologic focus, is here reviewed against the background of results from ongoing chronobiologic studies of blood pressure (BP) and heart rate (HR) in pregnancy. During pregnancy, the MESORs and circadian amplitudes of systolic (S), mean arterial (MA) and diastolic (D) BP are correlated with a questionnaire-assessed cardiovascular risk score. Such results were found under noisy ordinary conditions of life without accounting for effects of activity. They are group results, and as such require further work before they can contribute to identifying individuals at high risk in particular need of intervention, such as exercise. The dependence of exercise effects upon circadian rhythms should also prompt the use of rhythmometry at all ages for timing exercise, for gauging its effects and eventually for the optimization of fitness training for the population as well as for peak performance.

Blood Pressure↗
PubMed1993

Chronobiology in cardiology.

In these years, circadian periodicity in the onset of myocardial ischemia, myocardial infarction, sudden cardiac death and ischemic stroke has been confirmed by several investigators. There has also been reported that there exists a significant circadian rhythm in ventricular arrhythmias in patients with myocardial infarction. These recent advances in chronocardiology depend on a development of a high quality built-in A/D converter in ambulatory ECG monitoring system and a remarkably developed sophisticated software. One of the most current topics in recent years is heart rate (HR) variability. As an index of HR variability, RR50 is frequently estimated by the cosine fitting technique. Next, we analyzed the so-called Lorenz plot for another index of HR variability, that is preceding R-R intervals and coupling intervals were plotted sequentially every 3 hours on the abscissa and ordinate, respectively. Finally, we investigated HR variability by power spectral analysis of R-R intervals both by the maximum entropy method and the fast Fourier transform. Mainly, in this paper, we introduced current topics in HR variability, but recent advances in ambulatory blood pressure (BP) monitoring system are also strikingly remarkable. Our newly developed monitoring system of physical activity donated quite a few informations evaluating episodic changes of HR and BP. This device was also useful for finding out the difference between the individual life styles, such as the eveningness versus morningness. In conclusion, these very recent advances in ambulatory monitoring system should be really available for the clinical practice from this time onward.

Adult↗
PubMed2003

[Studies of A L. Chizhevskiĭ: Milestones in space biology and biorhythmology].

The authors review the experimental and theoretical studies of eminent Russian scholar A.L. Chizhevsky, and his fruitful collaboration with K.E. Tsiolkovsky, a pioneer of the science of rocket navigation. Highlighted are postulates of the modern space biorhythmology furthering the notions of A.L. Chizhevsky about the harmony in nature, and significance of rhythmic phenomena for living organisms.

Biological Clocks↗
PubMed1992

Two 19th-century chronobiologists: Thomas Laycock and Edward Smith.

This article describes the works of two 19th-century chronobiologists. Thomas Laycock (1812-1876), who held the Chair of Medicine in Edinburgh from 1855-1876, published a series of seven articles in Lancet, all dedicated to periodicities in "vital phenomena." Laycock considered the understanding of periodicities essential for the advancement of the treatment of diseases. Edward Smith (1818-1874) was a pioneer in experimental chronobiology. In his 1861 book entitled: Health and disease as influenced by daily, seasonal and other cyclical changes in the human, Smith summarized a large number of experiments in which he investigated the occurrence of periodicities in pulse rate, urine flow, urea excretion, and respiration. From his experimental results and those of others, Smith drew practical conclusions regarding patients' care, the timing of drug administration, and the design of night work.

Animals↗