The circadian rhythm of ventricular fibrillation threshold (VFT) and its relation to the heart rate (HR) and the rectal temperature (RT) was studied in female Wistar rats. The animals were exposed to daily light-dark cycles of 12 h of light alternating with 12 h of darkness and were under pentobarbital anaesthesia (40 mg/kg i.p.). The experiments were performed on open chest animals and VFT was measured by direct stimulation of the myocardium. VFT in female rats showed a circadian rhythm with the acrophase -338° (at 22.53 h), with the mesor 2.58 mA and the amplitude 0.33 mA. HR was not significantly changed during the experiments and no dependence was found between VFT and HR during the whole 24-hour period (r=0.08). The acrophase of the circadian rhythm of HR (on -47°, i.e. at 03.08 h) was shifted to the acrophase of VFT. The circadian rhythms of RT before the application of the anaesthetic agent and under general anaesthesia before the operative interventions had a very similar course with the nearly corresponding acrophoses as the circadian rhythm of VFT. It is concluded that the electrical stability of the rat heart measured by VFT shows the significant circadian rhythm in a parallel with the circadian rhythm of RT and probably without dependence on the changes of HR.
Circadian rhythms play an essential role in the adaptation of organisms to the environment and may show species-specific or sex-specific differences even within a closely related taxonomic group. Although spiders (Araneae) are sexually dimorphic in several morphological and behavioural features, there are very few studies on the sex-specific differences in their biological rhythms. This study evaluated the circadian rhythm in the locomotor activity of two agrobiont hunting species of spider, Carrhotus xanthogramma (Latreille, 1819) (Salticidae) and Philodromus cespitum (Walckenaer, 1802) (Philodromidae), under natural photoperiod conditions. Particular attention was paid to possible differences between the sexes in both species. We found that C. xanthogramma is a strictly diurnal species with a mean activity peak in the morning in both sexes and the females are more active than males. The locomotor activity rhythm of males was richer in ultradian (shorter than a day but longer than an hour) components, although the relative power of these components was negligible compared to the main, 24-h period component. In accordance with these results, the diel pattern of locomotor activity of C. xanthogramma can be described by a unimodal cosine curve. In contrast to C. xanthogramma, both sexes of Ph. cespitum showed cathemeral activity (i.e., activity occur within both the light and dark portions of the daily cycle) and females and males follow quite different activity schedules: females were most active at night, shortly before nautical dawn, whereas males were most active early in the morning. Unlike C. xanthogramma, Ph. cespitum has more ultradian components, with higher relative power especially in females, where besides the 24-h circadian component there is a particularly strong 12-h ultradian period. Based on these factors, females of Ph. cespitum show a bimodal and males a unimodal pattern.
The aim of this work was to investigate the effect of 10 weeks of lisinopril treatment to spontaneously hypertensive rats (SHRs) on day/night variations of blood pressure, heart rate and autonomic cardio-regulation parameters. Male SHR with surgically implanted radio-telemetry implant that provided direct measurements of arterial pressure and electrocardiogram wave were used. Animals were allocated to two groups (n=5 each). The first group was treated with lisinopril (20 mg/kg by gavage) daily for 10 weeks (treated group); whereas the second was gavaged daily with tap water (untreated group). Arterial blood pressure, ECG and other telemetry parameters were recorded at the start and at the end of 10-week treatment. Collected data were analyzed using specialized software and were statistically tested. In addition to the expected lowering of blood pressure, spectral analysis of R-R intervals revealed that lisinopril treatment for 10 weeks significantly caused 2-3 fold increase in heart rate variability (HRV) during both active and inactive periods. However, R-R interval durations demonstrated variable distribution patterns during those periods. The cause of observed distribution pattern of R-R intervals during active and inactive periods may be of significance to better understand HRV changes and warrants further investigations., S. Albarwani, S. Al-Siyabi, M. O. Tanira., and Obsahuje seznam literatury
Components of daily and seasonal timing systems in insects are reviewed. Photoperiod indicates seasonal position reliably, but signals can be much modified by habitat, latitude and season. Several receptor features and pigment systems are known, with different daily, seasonal and general functions, including differences between circadian and seasonal reception. Clocks can serve several different purposes, functioning as daily oscillators, interval timers or through successive requirements. The molecular functioning of circadian clocks is best known, but even so there is considerable complexity and diversity and much remains to be discovered. We know relatively little about the internal states that provide information for timed responses (such as the photoperiodic "counter"), about the central controlling mechanism, or about the effectors that transmit output signals. Nevertheless, temporal responses serve a very great range of purposes in insects, and the reported complexity in all of the components of timing systems reflects complex ecological needs across daily and seasonal intervals. The variety of components and the complexity of interactions reported (even within species), as well as the diversity of such elements as photosensitive pigments, molecular clock function and potential neurotransmitters, suggests that - unlike some earlier expectations - there is no single master clock for all timing functions in insects.
Insect photoperiodism and rhythmicity have been studied by both observational or direct approaches (examination of system elements or devices, and qualities such as survival), and by inferential or indirect approaches (such as interpretation of various responses to photoperiod, modelling, and estimating fitness). Many students work with only one approach, but the power of different approaches is not equal, and knowledge at one level may not give answers at another. These difficulties tend to limit our understanding of the linkages among components.
This overview suggests several lessons for the study of photoperiodism and rhythmicity. There are multiple elements, complex integration and a diversity of clocks, showing that different processes serve different purposes. The diversity of findings also results from the fact that different investigative approaches, which depend on the question being asked and on the perspective of the investigator, can influence the outcome of the investigation. Given these complexities, I believe that the key to interpreting photoperiodic and circadian responses is their ecological value. Notwithstanding the interest of timing mechanisms or their parts and of specific responses, daily rhythms and seasonal timing are best understood through the essential context provided by the ecological demands on the actual organisms under study.
In modern society, many people keep working hours different from the standard (9 hours, 5 days a week during conventional time of the day), a regimen leading to sleep deprivation and/or circadian desynchronization, and, consequently, to sleepiness, fatigue, impaired efficiency and ultimately to psychic and somatic complaints. Fortunately, sleepiness-related health and occupational hazards can be kept under control using scientifically tested precautions designed to help maintain wakefulness. Suitable work and rest scheduling and observance of the principles of sleep hygiene are of major importance there. In situations which interfere with sleep, it is possible to use hypnotics or behavioral techniques and melatonin for circadian regimen optimization. In situations when sleep loss is temporarily inevitable, options to be taken into account include work shift shortening, breaks for rest, naps of short duration or administration of vigilance enhancing drugs. In the future, risks associated with sleepiness could be mitigated by means of currently developed technologies for real-time detection of sleepiness.