Wrist Skin Temperature,Motor Activity,and Body Position as Determinants of the Circadian Pattern of Blood Pressure

Although the circadian blood pressure (BP) pattern has been extensively studied, the determinants of this rhythm are not fully understood. Peripheral vasodilatation is a regulatory mechanism for BP maintenance. However, it remains to be established whether the increase of nocturnal distal skin temperature associated with heat loss could also reflect the dipping status. For the first time, this paper investigates the relationship between BP and skin wrist temperature (WT), to evaluate whether the WT circadian rhythm can serve as screening procedure to detect dipping/non-dipping BP patterns. In addition, the authors compare the relationship between WT and other variables previously described as determinants of the BP pattern, such as physical activity and body position. Measurements of WT, motor activity, and body position for 5 d, plus ambulatory BP for 24-h during that span, were obtained from 28 diurnally active normotensive volunteers. WT was negatively correlated, whereas activity and body position were positively correlated, with systolic and diastolic BPs. However, these relationships were stronger during the rest than activity phase. In addition, a 78.6% concordance was detected between the observed dips in BP and the predicted BP pattern calculated based on the WT rhythm. Thus, these results suggest that the increase in WT produced by heat loss during the rest phase through peripheral skin blood vessels is the result of blood vessel vasodilatation reflexes in response to a shift from a standing to a supine position, together with shift in the circadian sympathetic/parasympathetic balance (nocturnal parasympathetic activation). In conclusion, WT could be considered as a potential new screening procedure to implement the diagnosis of non-dipping BP pattern. (Author correspondence: angerol@um.es)     

Uncovering Different Masking Factors on Wrist Skin Temperature Rhythm in Free-Living Subjects

Most circadian rhythms are controlled by a major pacemaker located in the hypothalamic suprachiasmatic nucleus. Some of these rhythms, called marker rhythms, serve to characterize the timing of the internal temporal order. However, these variables are susceptible to masking effects as the result of activity, body position, light exposure, environmental temperature and sleep. Recently, wrist skin temperature (WT) has been proposed as a new index for evaluating circadian system status. In light of previous evidence suggesting the important relationship between WT and core body temperature regulation, the aim of this work was to purify the WT pattern in order to obtain its endogenous rhythm with the application of multiple demasking procedures. To this end, 103 subjects (18–24 years old) were recruited and their WT, activity, body position, light exposure, environmental temperature and sleep were recorded under free-living conditions for 1 week. WT demasking by categories or intercepts was applied to simulate a “constant routine” protocol (awakening, dim light, recumbent position, low activity and warm environmental temperature). Although the overall circadian pattern of WT was similar regardless of the masking effects, its amplitude was the rhythmic parameter most affected by environmental conditions. The acrophase and mesor were determined to be the most robust parameters for characterizing this rhythm. In addition, a circadian modulation of the masking effect was found for each masking variable. WT rhythm exhibits a strong endogenous component, despite the existence of multiple external influences. This was evidenced by simultaneously eliminating the influence of activity, body position, light exposure, environmental temperature and sleep. We therefore propose that it could be considered a valuable and minimally-invasive means of recording circadian physiology in ambulatory conditions.     

The benefits of four weeks of melatonin treatment on circadian patterns in resistance-trained athletes

Exercise can induce circadian phase shifts depending on the duration, intensity and frequency. These modifications are of special meaning in athletes during training and competition. Melatonin, which is produced by the pineal gland in a circadian manner, behaves as an endogenous rhythms synchronizer, and it is used as a supplement to promote resynchronization of altered circadian rhythms. In this study, we tested the effect of melatonin administration on the circadian system in athletes. Two groups of athletes were treated with 100?mg?day^?1 of melatonin or placebo 30?min before bed for four weeks. Daily rhythm of salivary melatonin was measured before and after melatonin administration. Moreover, circadian variables, including wrist temperature (WT), motor activity and body position rhythmicity, were recorded during seven days before and seven days after melatonin or placebo treatment with the aid of specific sensors placed in the wrist and arm of each athlete. Before treatment, the athletes showed a phase-shift delay of the melatonin circadian rhythm, with an acrophase at 05:00?h. Exercise induced a phase advance of the melatonin rhythm, restoring its acrophase accordingly to the chronotype of the athletes. Melatonin, but not placebo treatment, changed daily waveforms of WT, activity and position. These changes included a one-hour phase advance in the WT rhythm before bedtime, with a longer nocturnal steady state and a smaller reduction when arising at morning than the placebo group. Melatonin, but not placebo, also reduced the nocturnal activity and the activity and position during lunch/nap time. Together, these data reflect the beneficial effect of melatonin to modulate the circadian components of the sleep–wake cycle, improving sleep efficiency.     

Ambulatory blood pressure monitoring in the prediction of cardiovascular events and effects of chronotherapy: rationale and design of the MAPEC study

Ambulatory blood pressure (BP) measurements (ABPM) correlate more closely with target organ damage and cardiovascular events than clinical cuff measurements. ABPM reveals the significant circadian variation in BP, which in most individuals presents a morning increase, small post-prandial decline, and more extensive lowering during nocturnal rest. However, under certain pathophysiological conditions, the nocturnal BP decline may be reduced (non-dipper pattern) or even reversed (riser pattern). This is clinically relevant because the non-dipper and riser circadian BP patterns constitute a risk factor for left ventricular hypertrophy, microalbuminuria, cerebrovascular disease, congestive heart failure, vascular dementia, and myocardial infarction. Hence, there is growing interest in how to best tailor and individualize the treatment of hypertension according to the specific circadian BP pattern of each patient. All previous trials that have demonstrated an increased cardiovascular risk in non-dipper as compared to dipper patients have relied on the prognostic significance of a single ABPM baseline profile from each participant without accounting for possible changes in the BP pattern during follow-up. Moreover, the potential benefit (i.e., reduction in cardiovascular risk) associated with the normalization of the circadian BP variability (conversion from non-dipper to dipper pattern) from an appropriately envisioned treatment strategy is still a matter of debate. Accordingly, the MAPEC (Monitorización Ambulatoria de la Presión Arterial y Eventos Cardiovasculares, i.e., Ambulatory Blood Pressure Monitoring and Cardiovascular Events) study was designed to investigate whether the normalization of the circadian BP profile toward more of a dipper pattern by chronotherapeutic strategies (i.e., specific timing during the 24 h of BP-lowering medications according to the 24 h BP pattern) reduces cardiovascular risk. The prospective MAPEC study investigates 3,000 diurnally active men and women >/=18 yrs of age. At inclusion, BP and wrist activity are measured for 48 h. The initial evaluation also includes a detailed medical history, an electrocardiogram, and screening laboratory blood and urine tests. The same evaluation procedure is scheduled yearly or more frequently (quarterly) if treatment adjustment is required for BP control. Cardiovascular morbidity and mortality are thus evaluated on the basis of changes in BP during follow-up. The MAPEC study, now on its fourth year of follow-up, investigates the potential decrease in cardiovascular, cerebrovascular, and renal risk from the proper modeling of the circadian BP profile by the timed administration (chronotherapy) of antihypertensive medication, beyond the reduction of clinic-determined daytime or ABPM-determined 24 h mean BP levels.     

Plasma melatonin concentrations in hypertensive patients with the dipping and non-dipping blood pressure profile

Some patients with hypertension exhibit disturbed circadian organization in the cardiovascular system. Hormone melatonin can synchronize circadian rhythms and its repeated administration can improve synchronization of rhythmicity in blood pressure (BP). In our study we measured endogenous melatonin production in patients with essential hypertension exhibiting a dipping and non-dipping BP profile. Blood pressure was monitored for at least 24-hr with an automatic ambulatory BP monitor and patients with no decline in BP were classified as non-dippers. Plasma melatonin was measured in the middle of the daytime and night-time by radioimmunoassay. As expected night-time systolic (P <0.05), diastolic (P <0.001) and mean arterial (P <0.001) BP was higher in non-dippers than in dippers. No significant difference was found between both groups in BP during the day. Mean melatonin concentrations were higher during the night than during the day in both dippers and non-dippers. When patients were divided into dippers and non-dippers on the basis of mean arterial or diastolic BP a lower ratio of night/day concentration was determined in non-dippers than in dippers. Our study showed a blunted night/day difference in plasma melatonin concentrations in hypertensive patients with the non-dipping profile in diastolic BP indicating disturbances in the circadian system of these patients.     

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)     

Gentamicin-Induced Chronotoxicity: Use of Body Temperature as a Orcadian Marker Rhythm

Aminoglycoside antibiotics produce varying degrees of ototoxicity, dependent on dosage time, in animals synchronized for rhythm study. Herein, we illustrate the use of an economical and reliable system to telemeter body temperature of laboratory animals as an endogenous marker rhythm for gentamicin-induxed ototoxicity. Two groups of 3 male Sprague-Dawley rats (250–400 gm) were housed in separate cages in a temperature-controlled room programmed with a 12:12 LD schedule and monitored for hearing thresholds at the frequencies of 8kHz, 16kHz, 24kHz and 32kHz at 2-week intervals. Each rat was dosed with 100 mg/kg/day gentamicin subcutaneously for a duration of 28 days. The animals from one group were dosed at their daily temperature maximum, while the animals of the other group were dosed at their daily temperature minimum. Both after 14 and 28 days of gentamicin treatment there was no important changes in auditory thresholds from baseline values when treatment was timed daily to the circadian peak of body temperature. Animals dosed daily at the trough of the circadian temperature rhythm evidenced an auditory threshold shift of between 5 and 25 dB after 14 days of treatment and a total hearing loss (80–90 dB) after 28 days of such treatment. These results document a dramatically greater level of hearing loss induced in those animals dosed with gentamicin at the body temperature trough (diurnal rest span) as compared to those dosed at the acrophase (nocturnal activity span). The findings indicate that the peak and trough of the circadian pattern of body temperature serve as meaningful markers of the resistance and susceptibility, respectively, of gentamicin-induced ototoxicity in rodent models.     

Gentamicin-Induced Chronotoxicity: Use of Body Temperature as a Orcadian Marker Rhythm

Aminoglycoside antibiotics produce varying degrees of ototoxicity, dependent on dosage time, in animals synchronized for rhythm study. Herein, we illustrate the use of an economical and reliable system to telemeter body temperature of laboratory animals as an endogenous marker rhythm for gentamicin-induxed ototoxicity. Two groups of 3 male Sprague-Dawley rats (250-400 gm) were housed in separate cages in a temperature-controlled room programmed with a 12:12 LD schedule and monitored for hearing thresholds at the frequencies of 8kHz, 16kHz, 24kHz and 32kHz at 2-week intervals. Each rat was dosed with 100 mg/kg/day gentamicin subcutaneously for a duration of 28 days. The animals from one group were dosed at their daily temperature maximum, while the animals of the other group were dosed at their daily temperature minimum. Both after 14 and 28 days of gentamicin treatment there was no important changes in auditory thresholds from baseline values when treatment was timed daily to the circadian peak of body temperature. Animals dosed daily at the trough of the circadian temperature rhythm evidenced an auditory threshold shift of between 5 and 25 dB after 14 days of treatment and a total hearing loss (80-90 dB) after 28 days of such treatment. These results document a dramatically greater level of hearing loss induced in those animals dosed with gentamicin at the body temperature trough (diurnal rest span) as compared to those dosed at the acrophase (nocturnal activity span). The findings indicate that the peak and trough of the circadian pattern of body temperature serve as meaningful markers of the resistance and susceptibility, respectively, of gentamicin-induced ototoxicity in rodent models.     

Gentamicin-induced chronotoxicity: use of body temperature as a circadian marker rhythm

Aminoglycoside antibiotics produce varying degrees of ototoxicity, dependent on dosage time, in animals synchronized for rhythm study. Herein, we illustrate the use of an economical and reliable system to telemeter body temperature of laboratory animals as an endogenous marker rhythm for gentamicin-induced ototoxicity. Two groups of 3 male Sprague-Dawley rats (250-400 gm) were housed in separate cages in a temperature-controlled room programmed with a 12:12 LD schedule and monitored for hearing thresholds at the frequencies of 8kHz, 16 kHz, 24 kHz and 32 kHz at 2-week intervals. Each rat was dosed with 100 mg/kg/day gentamicin subcutaneously for a duration of 28 days. The animals from one group were dosed at their daily temperature maximum, while the animals of the other group were dosed at their daily temperature minimum. Both after 14 and 28 days of gentamicin treatment there was no important changes in auditory thresholds from baseline values when treatment was timed daily to the circadian peak of body temperature. Animals dosed daily at the trough of the circadian temperature rhythm evidenced an auditory threshold shift of between 5 and 25 dB after 14 days of treatment and a total hearing loss (80-90 dB) after 28 days of such treatment. These results document a dramatically greater level of hearing loss induced in those animals dosed with gentamicin at the body temperature trough (diurnal rest span) as compared to those dosed at the acrophase (nocturnal activity span). The findings indicate that the peak and trough of the circadian pattern of body temperature serve as meaningful markers of the resistance and susceptibility, respectively, of gentamicin-induced ototoxicity in rodent models.     

Ambulatory Blood Pressure Monitoring in the Prediction of Cardiovascular Events and Effects of Chronotherapy: Rationale and Design of the MAPEC Study

Ambulatory blood pressure (BP) measurements (ABPM) correlate more closely with target organ damage and cardiovascular events than clinical cuff measurements. ABPM reveals the significant circadian variation in BP, which in most individuals presents a morning increase, small post‐prandial decline, and more extensive lowering during nocturnal rest. However, under certain pathophysiological conditions, the nocturnal BP decline may be reduced (non‐dipper pattern) or even reversed (riser pattern). This is clinically relevant because the non‐dipper and riser circadian BP patterns constitute a risk factor for left ventricular hypertrophy, microalbuminuria, cerebrovascular disease, congestive heart failure, vascular dementia, and myocardial infarction. Hence, there is growing interest in how to best tailor and individualize the treatment of hypertension according to the specific circadian BP pattern of each patient. All previous trials that have demonstrated an increased cardiovascular risk in non‐dipper as compared to dipper patients have relied on the prognostic significance of a single ABPM baseline profile from each participant without accounting for possible changes in the BP pattern during follow‐up. Moreover, the potential benefit (i.e., reduction in cardiovascular risk) associated with the normalization of the circadian BP variability (conversion from non‐dipper to dipper pattern) from an appropriately envisioned treatment strategy is still a matter of debate. Accordingly, the MAPEC (Monitorización Ambulatoria de la Presión Arterial y Eventos Cardiovasculares, i.e., Ambulatory Blood Pressure Monitoring and Cardiovascular Events) study was designed to investigate whether the normalization of the circadian BP profile toward more of a dipper pattern by chronotherapeutic strategies (i.e., specific timing during the 24 h of BP‐lowering medications according to the 24 h BP pattern) reduces cardiovascular risk. The prospective MAPEC study investigates 3,000 diurnally active men and women ≥18 yrs of age. At inclusion, BP and wrist activity are measured for 48 h. The initial evaluation also includes a detailed medical history, an electrocardiogram, and screening laboratory blood and urine tests. The same evaluation procedure is scheduled yearly or more frequently (quarterly) if treatment adjustment is required for BP control. Cardiovascular morbidity and mortality are thus evaluated on the basis of changes in BP during follow‐up. The MAPEC study, now on its fourth year of follow‐up, investigates the potential decrease in cardiovascular, cerebrovascular, and renal risk from the proper modeling of the circadian BP profile by the timed administration (chronotherapy) of antihypertensive medication, beyond the reduction of clinic‐determined daytime or ABPM‐determined 24 h mean BP levels.     

Seasonal variation of temporal niche in wild owl monkeys (Aotus azarai azarai) of the Argentinean Chaco: a matter of masking?

Among the more than 40 genera of anthropoid primates (monkeys, apes, and humans), only the South American owl monkeys, genus Aotus, are nocturnal. However, the southernmostly distributed species, Aotus azarai azarai, of the Gran Chaco may show considerable amounts of its 24-h activity during bright daylight. Due to seasonal changes in the duration of photophase and climatic parameters in their subtropical habitat, the timing and pattern of their daily activity are expected to show significant seasonal variation. By quantitative long-term activity recordings with Actiwatch AW4 accelerometer data logger devices of 10 wild owl monkeys inhabiting a gallery forest in Formosa, Argentina, the authors analyzed the seasonal variation in the temporal niche and activity pattern resulting from entrainment and masking of the circadian activity rhythm by seasonally and diurnally varying environmental factors. The owl monkeys always displayed a distinct bimodal activity pattern, with prominent activity bouts and peaks during dusk and dawn. Their activity rhythm showed distinct lunar and seasonal variations in the timing and daily pattern. During the summer, the monkeys showed predominantly crepuscular/nocturnal behavior, and a crepuscular/cathemeral activity pattern with similar diurnal and nocturnal activity levels during the cold winter months. The peak times of the evening and morning activity bouts were more closely related to the times of sunset and sunrise, respectively, than activity-onset and -offset. Obviously, they were better circadian markers for the phase position of the entrained activity rhythm than activity-onset and -offset, which were subject to more masking effects of environmental and/or internal factors. Total daily activity was lowest during the two coldest lunar months, and almost twice as high during the warmest months. Nighttime (21:00-06:00 h) and daytime (09:00-18:00 h) activity varied significantly across the year, but in an opposite manner. Highest nighttime activity occurred in summer and maximal daytime activity during the cold winter months. Dusk and dawn activity, which together accounted for 43% of the total daily activity, barely changed. The monkeys tended to terminate their nightly activity period earlier on warm and rainy days, whereas the daily amount of activity showed no significant correlation either with temperature or precipitation. These data are consistent with the dual-oscillator hypothesis of circadian regulation. They suggest the seasonal variations of the timing and pattern of daily activity in wild owl monkeys of the Argentinean Chaco result from a specific interplay of light entrainment of circadian rhythmicity and strong masking effects of various endogenous and environmental factors. Since the phase position of the monkeys' evening and morning activity peaks did not vary considerably over the year, the seasonal change from a crepuscular/nocturnal activity pattern in summer to a more crepuscular/cathemeral one in winter does not depend on a corresponding phase shift of the entrained circadian rhythm, but mainly on masking effects. Thermoregulatory and energetic demands and constraints seem to play a crucial role.     

DO RESTLESS LEGS SYNDROME (RLS) AND PERIODIC LIMB MOVEMENTS OF SLEEP (PLMS) PLAY A ROLE IN NOCTURNAL HYPERTENSION AND INCREASED CARDIOVASCULAR RISK OF RENALLY IMPAIRED PATIENTS?

Hypertension can cause or promote renal failure and is related to cardiovascular mortality, the major cause of death in patients with renal impairment. Changes in the circadian BP pattern, particularly the blunting or reversal of the nocturnal decline in BP, are common in chronic renal failure. These changes in turn are among the major determinants of left ventricular hypertrophy. Using a chronobiological approach, it is possible to obtain better insight into the reciprocal relationship between hypertension, renal disease, and increased cardiovascular risk of renal patients. Disruption of the normal circadian rhythm of rest/activity may be hypothesized to underlie the high cardiovascular morbidity and mortality of such patients. Epidemiological studies reveal that hemodialysis patients experience poor subjective sleep quality and insomnia and, in comparison to healthy persons, are more likely to show shorter sleep duration and lower sleep efficiency. Sleep apnea may be present and is usually investigated in these patients; however, the prevalence of restless legs syndrome (RLS), which is high in dialysis patients and which has been associated with increased risk for cardiovascular disease in the general population, could also play a role in the pathogenesis of sleep-time hypertension in renal patients. Careful assessment of sleep quality, in particular, diagnostic screening for RLS and periodic limb movements (PLM) in renal patients, is highly recommended. In renal failure, attention to sleep quality and related perturbations of the sleep/wake cycle may help prevent the occurrence and progression of cardiovascular disease. (Author correspondence: prf@unife.it)     

Factors associated with severity of daytime sleepiness and indications for initiating treatment in patients with periodic limb movements during sleep

Obstructive sleep apnea syndrome (OSAS) is closely associated with hypertension. Activity of angiotensin II (Ang II) and non-dipping nocturnal blood pressure (BP) variability are implicated in hypertension-related target organ damage. We examined the correlation between OSAS with serum Ang II levels and evaluated the risk of non-dipping BP variability in 180 patients with essential hypertension (EHT). Eligible patients were divided into three subgroups based on their apnea-hypopnea index (AHI) evaluated by polysomnography. EHT alone, EHT with mild OSAS, and EHT with moderate/severe OSAS. Ambulatory BP monitoring was used to calculate mean BP over 24 h, as well as diurnal and nocturnal BP variability. Serum Ang II was determined with enzyme-linked immun-osorbent assay. EHT patients with OSAS had significantly higher systolic BP calculated either over 24 h, or by diurnal or nocturnal monitoring (P < 0.05). More EHT patients with OSAS showed non-dipping BP profiles than did EHT patients alone (P < 0.05). The number of patients with non-dipping BP increased with increasing OSAS severity. Surgical treatment alleviated OSAS and reduced AHI (P < 0.05). Preoperative serum Ang II in EHT patients with OSAS was significantly higher than that in those without OSAS (P < 0.05), and showed a rising trend with OSAS severity (P < 0.05). Postoperative serum Ang II, BP and the incidence of non-dipping BP were reduced by surgery to levels lower than preoperative values in patients with OSAS. We therefore conclude that OSAS leads to increased serum Ang II and increased risk of non-dipping BP in patients with EHT.

     

Non-dipping blood pressure in the metabolic syndrome among Arabs of the Oman family study

Objective: The objective was to examine the circadian changes in blood pressure and their relation to the metabolic syndrome and its components in Omani Arabs. Research Methods and Procedures: Ambulatory blood pressure (ABPM) was recorded in 1124 subjects from 5 large, extended, consanguineous, and young Arab pedigrees. According to the International Diabetes Federation's definition, 264 subjects had the metabolic syndrome, a prevalence of 23%. Subjects were defined as non‐dippers when their nocturnal systolic blood pressure (SBP) fell by <10% from daytime SBP. Results: Non‐dippers with the metabolic syndrome were 131 of 264 (50%), compared with 265 of 860 (31%) without the metabolic syndrome. Of the non‐dippers, 99 of 131 (76%) were females and 32 of 131 (24%) were males. Daytime and nighttime SBP and DBP and nighttime pulse pressure were significantly higher in non‐dipper subjects with the metabolic syndrome. The important determinants of a non‐dipping BP in this cohort were high BMI and high serum triglycerides. Discussion: We hypothesize that obesity and nocturnal volume‐dependent hypertension may be involved in the pathophysiology of non‐dipping in the metabolic syndrome. This study showed that non‐dipping BP was common in subjects with the metabolic syndrome. Higher 24‐hour blood pressure load may add to the indices of the overall cardiovascular burden already associated with the metabolic syndrome.     

Differences in daily rhythms of wrist temperature between obese and normal-weight women: associations with metabolic syndrome features

The circadian rhythm of core body temperature is associated with widespread physiological effects. However, studies with other more practical temperature measures, such as wrist (WT) and proximal temperatures, are still scarce. The aim of this study was to investigate whether obesity is associated with differences in mean WT values or in its daily rhythmicity patterns. Daily patterns of cortisol, melatonin, and different metabolic syndrome (MetS) features were also analyzed in an attempt to clarify the potential association between chronodisruption and MetS. The study was conducted on 20 normal-weight women (age: 38 ± 11 yrs and BMI: 22 ± 2.6 kg/m(2)) and 50 obese women (age: 42 ± 10 yrs and BMI: 33.5 ± 3.2 kg/m(2)) (mean ± SEM). Skin temperature was measured over a 3-day period every 10 min with the "Thermochron iButton." Rhythmic parameters were obtained using an integrated package for time-series analysis, "Circadianware." Obese women displayed significantly lower mean WT (34.1°C ± 0.3°C) with a more flattened 24-h pattern, a lower-quality rhythm, and a higher intraday variability (IV). Particularly interesting were the marked differences between obese and normal-weight women in the secondary WT peak in the postprandial period (second-harmonic power [P2]), considered as a marker of chronodisruption and of metabolic alterations. WT rhythmicity characteristics were related to MetS features, obesity-related proteins, and circadian markers, such as melatonin. In summary, obese women displayed a lower-quality WT daily rhythm with a more flattened pattern (particularly in the postprandial period) and increased IV, which suggests a greater fragmentation of the rest/activity rhythm compared to normal-weight women. These 24-h changes were associated with higher MetS risk.     

Duration of activity and period of circadian activity–rest rhythm in a photoperiod-dependent primate,Microcebus murinus

Under free-running conditions, the grey lesser mouse lemur expresses a circadian activity–rest rhythm with a period particularly short (22.50 ± 0.6 h) for a mammal. Light exerts a strong suppressive effect upon activity. After transfer from nycthemeral to free-running conditions the duration of activity was systematically increased. This extension took place in the first cycle and was characterized by both a phase advance in activity onset and an even larger phase delay in activity offset. This phenomenon was more pronounced after long day entrainment. Any shift of the light–dark cycle was followed the next day by a corresponding shift in activity onset. The phase response curve pattern was similar to that already described for nocturnal mammals. Due to the strength of light as a zeitgeber and the plasticity of the response to photic conditions, the mouse lemur appears as a convenient species for chronobiological studies on non-human primates.     

Seasonal Variation of Temporal Niche in Wild Owl Monkeys (Aotus azarai azarai) of the Argentinean Chaco: A Matter of Masking?

Among the more than 40 genera of anthropoid primates (monkeys, apes, and humans), only the South American owl monkeys, genus Aotus, are nocturnal. However, the southernmostly distributed species, Aotus azarai azarai, of the Gran Chaco may show considerable amounts of its 24-h activity during bright daylight. Due to seasonal changes in the duration of photophase and climatic parameters in their subtropical habitat, the timing and pattern of their daily activity are expected to show significant seasonal variation. By quantitative long-term activity recordings with Actiwatch AW4 accelerometer data logger devices of 10 wild owl monkeys inhabiting a gallery forest in Formosa, Argentina, the authors analyzed the seasonal variation in the temporal niche and activity pattern resulting from entrainment and masking of the circadian activity rhythm by seasonally and diurnally varying environmental factors. The owl monkeys always displayed a distinct bimodal activity pattern, with prominent activity bouts and peaks during dusk and dawn. Their activity rhythm showed distinct lunar and seasonal variations in the timing and daily pattern. During the summer, the monkeys showed predominantly crepuscular/nocturnal behavior, and a crepuscular/cathemeral activity pattern with similar diurnal and nocturnal activity levels during the cold winter months. The peak times of the evening and morning activity bouts were more closely related to the times of sunset and sunrise, respectively, than activity-onset and -offset. Obviously, they were better circadian markers for the phase position of the entrained activity rhythm than activity-onset and -offset, which were subject to more masking effects of environmental and/or internal factors. Total daily activity was lowest during the two coldest lunar months, and almost twice as high during the warmest months. Nighttime (21:00–06:00?h) and daytime (09:00–18:00?h) activity varied significantly across the year, but in an opposite manner. Highest nighttime activity occurred in summer and maximal daytime activity during the cold winter months. Dusk and dawn activity, which together accounted for 43% of the total daily activity, barely changed. The monkeys tended to terminate their nightly activity period earlier on warm and rainy days, whereas the daily amount of activity showed no significant correlation either with temperature or precipitation. These data are consistent with the dual-oscillator hypothesis of circadian regulation. They suggest the seasonal variations of the timing and pattern of daily activity in wild owl monkeys of the Argentinean Chaco result from a specific interplay of light entrainment of circadian rhythmicity and strong masking effects of various endogenous and environmental factors. Since the phase position of the monkeys' evening and morning activity peaks did not vary considerably over the year, the seasonal change from a crepuscular/nocturnal activity pattern in summer to a more crepuscular/cathemeral one in winter does not depend on a corresponding phase shift of the entrained circadian rhythm, but mainly on masking effects. Thermoregulatory and energetic demands and constraints seem to play a crucial role. (Author correspondence: hans.erkert@t-online.de)     

Atrial Natriuretic Peptide and Circadian Blood Pressure Regulation: Clues from a Chronobiological Approach

A critical review of the data available in the literature today permits a better understanding of the multiple actions of atrial natriuretic peptide (ANP) on the cardiovascular system. Moreover, the results of chronobiological studies suggest a role for this peptide in the determination of the circadian rhythm of blood pressure (BP). ANP can affect BP by several mechanisms, including modification of renal function and vascular tone, counteraction of the renin-angiotensin-al-dosterone system, and action on brain regulatory sites. A series of interrelated events may follow from very small changes in the plasma levels of ANP. The endpoints are blood volume and BP reduction, but they are rapidly offset (mainly by reactive sympathetic activation) as soon as blood volume or pressure is thredtened. The circadian rhythms of BP and ANP are antiphasic under normal conditions and in essential hypertension. The loss in the nocturnal decrease of BP is accompanied by a comparable loss in the nocturnal surge of ANP in hypertensive renal failure and hypotensive heart failure. In the latter condition, BP and ANP variabilities correlate significantly both before and after therapy-induced functional recovery, independently of the mean BP levels. Autonomic function modulates the secretion of ANP, which seems more apt to determine only transient changes in BP levels, as suggested by the short half-life of the peptide and the buffering role of its clearance receptors. There is now sufficient evidence that ANP contributes to short-term control over BP and electrolyte balance, in contrast and in opposition to the renin-angiotensin-aldosterone system, which is involved primarily in long-term BP control. By interfering with other well-established neu-rohormonal factors, ANP appears to be an additional modulator of the circadian rhythm of BP.     

Blunting of circadian rhythms and increased acrophase variability in sleep-time hypertensive subjects

24 h and ultradian rhythms of blood pressure (BP) have been previously shown to be disorganized in nocturnal hypertensive subjects. The present study was undertaken to further analyze the ultradian and circadian BP rhythm structure in sleep-time hypertensive subjects with normal or elevated awake-time BP levels. Fourier analysis was used to fit 24, 12, 8, and 6 h curves to mean BP as well as heart rate (HR) time series data derived from 24 h ambulatory blood pressure monitoring. Awake and sleep periods were defined according to individual sleep diaries. Awake-time hypertension was defined as diurnal systolic (SBP) and/or diastolic BP (DBP) means ≥135/85 mmHg. Sleep-time hypertension was defined as nocturnal SBP and/or DBP means ≥120/70 mmHg. The sample included 240 awake-time normotensive subjects (180 sleep-time normotensives and 60 sleep-time hypertensives) and 138 untreated awake-time hypertensive subjects (31 sleep-time normotensives and 107 sleep-time hypertensives). The amplitude and integrity (i.e., percent rhythm) of the 24 and 12 h BP rhythms were lower in the sleep-time hypertensive subjects and higher in the awake-time hypertensive subjects. However, no differences were detected when the integrity and amplitude of the 6 and 8 h mean BP rhythms were analyzed. The sleep-time hypertensive group showed significantly higher 24 h BP rhythm acrophase variability. No differences could be found in any of the HR rhythm parameters. Altogether, the findings suggest a disorganization of the BP circadian rhythm in sleep-time hypertensives that results in reduced 24 h rhythm amplitude and integrity that could be related to cardiovascular risk.     

The relationship between the golden spiny mouse circadian system and its diurnal activity: an experimental field enclosures and laboratory study

Examples of animals that switch activity times between nocturnality and diurnality in nature are relatively infrequent. Furthermore, the mechanism for switching activity time is not clear: does a complete inversion of the circadian system occur in conjunction with activity pattern? Are there switching centers downstream from the internal clock that interpret the clock differently? Or does the switch reflect a masking effect? Answering these key questions may shed light on the mechanisms regulating activity patterns and their evolution. The golden spiny mouse (Acomys russatus) can switch between nocturnal and diurnal activity. This study investigated the relationship between its internal circadian clock and its diurnal activity pattern observed in the field. The goal is to understand the mechanisms underlying species rhythm shifts in order to gain insight into the evolution of activity patterns. All golden spiny mice had opposite activity patterns in the field than those under controlled continuous dark conditions in the laboratory. Activity and body temperature patterns in the field were diurnal, while in the laboratory all individuals immediately showed a free-running rhythm starting with a nocturnal pattern. No phase transients were found toward the preferred nocturnal activity pattern, as would be expected in the case of true entrainment. Moreover, the fact that the free-running activity patterns began from the individuals' subjective night suggests that golden spiny mice are nocturnal and that their diurnality in their natural habitat in the field results from a change that is downstream to the internal clock or reflects a masking effect.