Twenty-four-hour rhythm patterns of plasma melatonin in short-day and long-day breeders maintained under natural environmental conditions

ABSTRACT

Photoperiodic treatments have been of practical interest in controlling seasonal reproduction in sheep, goats and horses. Melatonin is the principal mediator of the environmental photoperiodic message. To investigate the intra- and inter-subject variability of melatonin 24 h rhythm, ten female Italian Saddle horses (8–10 yrs old, mean body weight 525 ± 30 kg), ten female Sarda breed sheep (2–3 yrs old, mean body weight 40.5 ± 2.8 kg) and ten female Sarda breed goats (3–4 yrs old, mean body weight 38.9 ± 4.1 kg), housed individually in a 4 × 4 m soundproof box equipped with 50 × 100 cm opening windows, were subjected to a natural photoperiod of the vernal equinox (sunrise 06:00 h; sunset 18:00 h). Blood samples were collected from each animal, every 3 h over a 48 h period starting at 00:00 h of day 1 and ending at 00:00 h of day 3. Plasma melatonin concentrations were determined by direct radioimmunoassay (MelatoninDirect RIA, Labor Diagnostika Nord GmbH, Nordhorn, Germany). The application of single cosinor method substantiated a circadian rhythm of melatonin with a nocturnal peak in all studied species. The application of two-way ANOVA on the rhythmic parameters indicated statistically significant differences between the three species in all of the cosinor analysis-derived parameters of MESOR, amplitude, acrophase and robustness of rhythm. Analyses of intra- and inter-subject variability indicate that organization of the melatonin 24 h rhythm is characterized by great accuracy of control within and between the individuals of a breed. In conclusion, features of the 24 h rhythm of melatonin among species; however, the 24 h rhythmicity of melatonin each species showed high stability within the various subjects and within the same subject. These findings must be taken into consideration when applying photoperiod and melatonin treatments for breeding purposes.     

REPEATED ASSESSMENT OF THE ENDOGENOUS 24-HOUR PROFILE OF BLOOD PRESSURE UNDER CONSTANT ROUTINE*

The impact of environmental and behavioral factors on the 24-h profile of blood pressure (BP) has been well established. Various attempts have been made to control these exogenous factors, in order to investigate a possible endogenous circadian variation of BP. Recently, we reported the results of the first environmentally and behaviorally controlled laboratory study with 24-h recordings of BP and heart rate (HR) during maintained wakefulness. In this constant-routine study, a pronounced endogenous circadian rhythm of HR was found, but circadian variation of BP was absent. This result suggested that the circadian rhythm of BP observed in earlier controlled studies, with sleep allowed, was evoked by the sleep–wake cycle as opposed to the endogenous circadian pacemaker. In order to verify our previous finding during maintained wakefulness, we repeated the experiment five times with six normotensive, healthy young subjects. Statistical analyses of the hourly measurements of BP and HR confirmed the replicable presence of an endogenous circadian rhythm of HR, as well as the consistent absence of an endogenous circadian variation of BP. Thus, this study provided additional evidence that the 24-h profile of BP—as observed under normal circumstances—is the sole result of environmental and behavioral factors such as the occurrence of sleep, and has no endogenous circadian component. (Chronobiology International, 18(1), 85–98, 2001)     

FEEDING ENTRAINMENT OF DAILY RHYTHMS OF LOCOMOTOR ACTIVITY AND CLOCK GENE EXPRESSION IN ZEBRAFISH BRAIN

Light and feeding cycles strongly synchronize daily rhythms in animals, which may, as a consequence, develop food anticipatory activity (FAA). However, the light/food entraining mechanisms of the central circadian oscillator remain unknown. In this study, we investigate the existence of FAA in seven groups of zebrafish subjected to a light/dark (LD) cycle or constant light (LL) and different feeding regimes (random, fasting, and feeding in the middle of the light phase or dark phase). The aim was to ascertain whether the daily rhythm of behavior and clock gene (per1 and cry1) expression in the zebrafish brain was entrained by the light and feeding regime. The results revealed that FAA developed in zebrafish fed daily at a fixed time, under LD and under LL. Zebrafish displayed locomotor activity mostly during the daytime, although the percentage of activity during the light phase varied depending on feeding time (ranging from 93.2% to 63.1% in the mid-light and mid-dark fed groups, respectively). However, the different feeding regimes failed to modify the daily rhythm of per1 and cry1 expression in the zebrafish brain under LD (approximate acrophases [peak times] at ZT22 and ZT4, respectively; lights-on =?ZT0). Under LL, per1 and cry1 expression did not show significant daily rhythmicity, regardless of the feeding regime. These findings indicate that, although schedule-fed zebrafish developed FAA as regards locomotor activity, feeding had little effect on clock gene expression in whole brain homogenates, suggesting the feeding-entrainable oscillator may be located elsewhere or at specific brain sites. (Author correspondence: jasanchez@um.es)     

Dosing schedule-dependent attenuation of dexamethasone-induced muscle atrophy in mice

Many inflammatory and autoimmune diseases are treated using synthetic glucocorticoids. However, excessive glucocorticoid can often cause unpredictable effects including muscle atrophy. Endogenous glucocorticoid levels robustly fluctuate in a circadian manner and peak just before the onset of the active phase in both humans and nocturnal rodents. The present study determines whether muscle atrophy induced by exogenous glucocorticoid can be avoided by optimizing dosing times. We administered single daily doses of the glucocorticoid analog dexamethasone (Dex) to mice for 10 days at the times of day corresponding to peak (early night) or trough (early morning) endogenous glucocorticoid levels. Administration at the acrophase of endogenous glucocorticoids significantly attenuated Dex-induced wasting of the gastrocnemius (Ga) and tibialis anterior (TA) muscles that comprise mostly fast-twitch muscle fibers. Real-time RT-PCR revealed that the Dex-induced mRNA expression of genes encoding the atrophy-related ubiquitin ligases Muscle Atrophy F-box (Fbxo32, also known as MAFbx/Atrogin-1) and Muscle RING finger 1 (Trim63, also known as MuRF1) in the Ga and TA muscles was significantly attenuated by Dex when administered during the early night. Dex negligibly affected the weight of the soleus (So) muscle that mostly comprises slow-twitch muscle fibers, but significantly and similarly decreased the weight of the spleen at both dosing times. These results suggest that glucocorticoid-induced muscle atrophy can be attenuated by optimizing the dosing schedule.     

SIRT1 and circadian gene expression in pancreatic ductal adenocarcinoma: Effect of starvation

Pancreatic cancer (PC), the fourth leading cause of cancer-related deaths, is characterized by high aggressiveness and resistance to chemotherapy. Pancreatic carcinogenesis is kept going by derangement of essential cell processes, such as proliferation, apoptosis, metabolism and autophagy, characterized by rhythmic variations with 24-h periodicity driven by the biological clock. We assessed the expression of the circadian genes ARNLT, ARNLT2, CLOCK, PER1, PER2, PER3, CRY1, CRY2 and the starvation-activated histone/protein deacetylase SIRT1 in 34 matched tumor and non-tumor tissue specimens of PC patients, and evaluated in PC derived cell lines if the modulation of SIRT1 expression through starvation could influence the temporal pattern of expression of the circadian genes. We found a significant down-regulation of ARNLT (p?=?0.015), CRY1 (p?=?0.013), CRY2 (p?=?0.001), PER1 (p?<?0.0001), PER2 (p?<?0.001), PER3 (p?=?0.001) and SIRT1 (p?=?0.017) in PC specimens. PER3 and CRY2 expression levels were lower in patients with jaundice at diagnosis (?<?0.05). Having adjusted for age, adjuvant therapy and tumor stage, we evidenced that patients with higher PER2 and lower SIRT1 expression levels showed lower mortality (p?=?0.028). Levels and temporal patterns of expression of many circadian genes and SIRT1 significantly changed upon serum starvation in vitro, with differences among four different PC cell lines examined (BXPC3, CFPAC, MIA-PaCa-2 and PANC-1). Serum deprivation induced changes of the overall mean level of the wave and amplitude, lengthened or shortened the cycle time and phase-advanced or phase-delayed the rhythmic oscillation depending on the gene and the PC cell line examined. In conclusion, a severe deregulation of expression of SIRT1 and circadian genes was evidenced in the cancer specimens of PC patients, and starvation influenced gene expression in PC cell lines, suggesting that the altered interplay between SIRT1 and the core circadian proteins could represent a crucial player in the process of pancreatic carcinogenesis.     

Role of Corpus Allatum on the Modulation of Feeding Rhythm in the Semilooper Caterpillar,Achaea Janata (L)

A circadian feeding rhythm which may be entrained by photoperiod was found in fifth instarcaterpillars of the lepidopteran, Achaea Janata (L.). AUatectomy reduced the amount of food consumed; this consumption was significantly lower during the fifth instar in both allatectomized and sham-operated insects. An apparent circadian feeding pattern appeared on day 2 in the sham-operated caterpillars. Topical application of the anti-allatin, Precocene-II (50μg/animal) also reduced leaf consumption significantly compared to the respective controls, although these controls maintained the same apparent circadian feeding rhythm on day 2.     

CONTRIBUTION OF CIRCADIAN PHYSIOLOGY AND SLEEP HOMEOSTASIS TO AGE-RELATED CHANGES IN HUMAN SLEEP

The circadian pacemaker and sleep homeostasis play pivotal roles in vigilance state control. It has been hypothesized that age-related changes in the human circadian pacemaker, as well as sleep homeostatic mechanisms, contribute to the hallmarks of age-related changes in sleep, that is, earlier wake time and reduced sleep consolidation. Assessments of circadian parameters in healthy young (～20–30 years old) and older people (～65–75 years old)—in the absence of the confounding effects of sleep, changes in posture, and light exposure—have demonstrated that an earlier wake time in older people is accompanied by about a 1h advance of the rhythms of core body temperature and melatonin. In addition, older people wake up at an earlier circadian phase of the body temperature and plasma melatonin rhythm. The amplitude of the endogenous circadian component of the core body temperature rhythm assessed during constant routine and forced desynchrony protocols is reduced by 20–30% in older people. Recent assessments of the intrinsic period of the human circadian pacemaker in the absence of the confounding effects of light revealed no age-related reduction of this parameter in both sighted and blind individuals. Wake maintenance and sleep initiation are not markedly affected by age except that sleep latencies are longer in older people when sleep initiation is attempted in the early morning. In contrast, major age-related reductions in the consolidation and duration of sleep occur at all circadian phases. Sleep of older people is particularly disrupted when scheduled on the rising limb of the temperature rhythm, indicating that the sleep of older people is more susceptible to arousal signals genernpated by the circadian pacemaker. Sleep-homeostatic mechanisms, as assayed by the sleep-deprivation–induced increase of EEG slow-wave activity (SWA), are operative in older people, although during both baseline sleep and recovery sleep SWA in older people remains at lower levels. The internal circadian phase advance of awakening, as well as the age-related reduction in sleep consolidation, appears related to an age-related reduction in the promotion of sleep by the circadian pacemaker during the biological night in combination with a reduced homeostatic pressure for sleep. Early morning light exposure associated with this advance of awakening in older people could reinforce the advanced circadian phase. Quantification of the interaction between sleep homeostasis and circadian rhythmicity contributes to understanding age-related changes in sleep timing and quality. (Chronobiology International, 17(3), 285–311, 2000)     

Chronotherapy in Coronary Heart Disease: Comparison of Two Nitrate Treatments

The purpose of this study was to assess the ischemic burden and the hemodynamic changes during daily activities in patients with coronary heart disease. Three exercise tests were performed during the day (10:00 a.m., 2:00 p.m., 6:00 p.m.), recording ST-segment depression, pulmonary artery pressure, pulmonary wedge pressure, and cardiac output as well as heart rate and systemic blood pressure during placebo and nitrate therapy. With placebo as well as nitrate therapy there was a gradual increase of ischemia and preload and a decrease of cardiac output during the day. High nitrate concentrations led to a significant reduction of both preload and ST depression with a marked circadian phase dependency of cardiovascular effects.     

CIRCADIAN PATTERN OF AMBULATORY BLOOD PRESSURE IN UNTREATED HYPERTENSIVE PATIENTS WITH AND WITHOUT METABOLIC SYNDROME

There is a strong association between metabolic syndrome (MS) and increased risk of end-organ damage, cardiovascular disease, stroke, and cardiovascular mortality. Moreover, non-dipping (<?10% decline in the asleep relative to the awake blood pressure [BP] mean) and elevated ambulatory pulse pressure (PP), among other factors related to the circadian BP pattern, have also been associated with increased cardiovascular morbidity and mortality. This cross-sectional study investigated the circadian BP pattern in 2,045 non-diabetic untreated patients with uncomplicated essential hypertension (941 men/1,099 women), 48.7?±?11.9 yrs of age, classified by the presence or absence of MS. BP was measured by ambulatory monitoring for 48 consecutive hours to substantiate reproducibility of the dipping pattern. Physical activity was simultaneously monitored every min by wrist actigraphy to accurately calculate mean BP when awake and asleep for each subject. MS was present in 40.7% of the patients. Patients with MS were characterized by a significantly higher 24?h mean of systolic BP and a lower diastolic BP compared to patients without MS. Accordingly, ambulatory PP was significantly elevated the entire 24?h in MS patients. The prevalence of an altered non-dipper BP profile was significantly higher in MS patients (48.4 vs. 36.1% in patients without MS, p?<?0.001). MS patients were characterized, among other risk factors, by significantly higher uric acid, fibrinogen, leukocyte count, hemoglobin and globular sedimentation velocity, plus lower estimated glomerular filtration rate. Apart from corroborating the significant increased prevalence of a blunted nocturnal BP decline in MS, this study documents ambulatory PP is higher in MS, without differences between groups in mean arterial pressure. This elevated PP might reflect increased arterial stiffness in MS. MS patients were also characterized by elevated values of relevant markers of cardiovascular risk, including fibrinogen and globular sedimentation velocity. These collective findings indicate that MS should be included among the clinical situations in which ambulatory BP monitoring is recommended. (Author correspondence: rhermida@uvigo.es)