A comparison of the suitabilities of rectal,gut, and insulated axilla temperatures for measurement of the circadian rhythm of core temperature in field studies

Eight healthy males were studied for a total of 13 subject-days to assess if gut (from an ingested pill) and axilla (from a thermally insulated skin probe) temperatures would act as a substitute for rectal temperature in field studies of the circadian rhythm of core temperature. Subjects slept and went about their activities, indoors and outdoors, normally. Regular recordings (at 6min intervals) were made of temperatures from the three sites. In addition, activity was measured (by a sensor on the nondominant wrist) so that the raw temperature data could be “purified,” that is, corrected for the direct effects of sleep and activity. Inspection of the raw data indicated that there was a close parallelism between rectal and gut temperatures, but that the parallelism between rectal and insulated axilla temperatures was less reliable. This parallelism was supported by initial calculations of the correlations between rectal and gut temperatures (high and positive) and between rectal and insulated axilla (lower, though still positive) temperatures. Calculation of the limits of agreement between the parameters of the cosine curves fitted to the raw data confirmed that the rectal and gut temperatures were far closer with regard to acrophase and amplitude than were rectal and insulated axilla temperatures (?0.31±0.89 vs. +0.75±6.03 h and +0.002±0.116 vs. +0.083±0.625°C, respectively). After purification of the temperature data, the limits of agreement for the cosine parameters acrophase and amplitude still indicated that there was a closer agreement between rectal and gut temperatures than between rectal and insulated axilla temperatures (?0.30±1.12 vs. +0.58±6.69 h, and +0.007±0.116 vs. +0.104±0.620°C, respectively). Part of the explanation of this difference was the unreliable relationships between temperature changes in insulated axilla temperature and bursts of activity and going to bed. It is concluded that, whereas gut temperature is a viable alternative to rectal temperature (from the viewpoints of both user acceptability and the reliability of data obtained), insulated axilla temperature, though acceptable to subjects, is unreliable from an experimental viewpoint.     

24-hour, weekly, and annual patterns in traumatic and non-traumatic surgical pediatric emergencies

24 h patterns with high frequency components in the incidence of pediatric trauma were validated and quantified in one of our earlier studies. Herein, we further explored the temporal—high frequency, 24 h, weekly (7 d), hemi-weekly (3.5 d), and annual - patterns in traumatic (1990-1997; n=15,110 events) and non-traumatic pediatric surgical emergencies (PSE) (1992-2001; n=5,593 events) as well as automobile accidents (AA) (1990-1997; n=67,712) in the County of Vaud, Switzerland. The latter served as a reference system of human adult activity and risk. Two-way ANOVA, χ2, correlation, and cosinor analyses were used as statistical tools. A 24 h pattern, reproducible from year to year, was validated in traumatic and non-traumatic PSE and AA. The 24 h patterns were not correlated and differed from one another in terms of their acrophase (peak time) and amplitude. A gender-related difference was found only in the non-traumatic time series for weekly (7 d) and hemi-weekly (3.5 d) patterns. The latter were detected in boys but not girls. No statistically significant difference was found in the acrophase and amplitude between boys and girls in the temporal patterns of other periods. An annual pattern was validated in automobile accidents (acrophase: 4th of September ±37 d (SD)) and pediatric trauma (acrophase: 14th of June ±10 d), but not in non-traumatic PSE. These results suggest that environmental modulations differ between the incidence of traumatic and non-traumatic PSE. Presumably, the two phenomena involve different aspects of the temporal organization and/or different levels of susceptibility of a set of biological rhythms to environmental factors.     

Daily rhythm of body and auricle temperature in goats kept at two different ambient temperatures

In fluctuating environmental temperature, homeotherms are able to maintain stable their body temperature, which however reveals a rhythmic daily pattern as described in literature. Because of the importance of body temperature rhythmicity in the knowledge of thermal homeostasis and as a means to facilitate the study of biological rhythmicity in general, the aim of our study was to assess the influence of two different ambient temperature on the daily rhythmicity of body and auricle temperature in goat (Capra hircus). For our study 6 female adult Maltese goats (18 month old), not pregnant and clinically healthy were used. On each subject body and auricle temperature was recorded during two different periods, of 7 days each, every 3 hours for 24 hours from 07.00 to 04.00, at different environmental temperature (1^st period 18.25 ± 1.48°C, 2^nd period 28.25 ± 2.05°C). The analysis of the obtained result under two ambient temperature indicates the existence of a daily periodicity, with small differences in amplitude and acrophase between the two studied period, both in body and auricle temperature in Maltese breed goat so we can assume that environmental temperature can influence in a significant way the daily pattern of body and auricle temperature.     

Effect of heat exposure on the activity of monoamine oxidase in the rat brain and interscapular brown adipose tissue

The exposure of Wistar male rats (200±20 g) to high ambient temperature (38°C) for 20 and 60 min induced an equal decrease in hypothalamic, brain stem and hippocampal monoamine oxidase activity when compared to controls. The interscapular brown adipose tissue monoamine oxidase activity, as well as oxygen consumption and rectal temperature were increased only after a 60 min heat exposure. The adrenal function, assessed by dopamine-beta-hydroxylase activity and cholesterol concentration, was enhanced both after 20 and 60 min. In conclusion, heat induced the increase in adrenal function and interscapular brown adipose tissue monoamine oxidase activity, but the decrease in that of the brain.     

Determination of the thermodynamics of carbonic anhydrase acid-unfolding by titration calorimetry

The enthalpy of unfolding (Δ_uH) of carbonic anhydrase II was determined by titrating the protein with acid and measuring the heat using isothermal titration calorimetry (ITC) in the temperature range of 5 to 59 °C. By combining the ITC results with our previous findings by differential scanning calorimetry (DSC) in the temperature range of 39 to 72 °C, the Δ_uH dependence over a wide temperature range was obtained. The temperature dependence of the enthalpy displays significant curvature indicating that the heat capacity of unfolding (Δ_uC_p) is dependent on temperature. The T-derivative of Δ_uC_p was equal to 100 ± 30 J/(mol × K²), with the result that the Δ_uC_p is equal to 15.8 kJ/(mol × K) at 5 °C, 19.0 kJ/(mol × K) at 37 °C and 21.8 kJ/(mol × K) at 64 °C. The enthalpy of unfolding is zero at 17 °C. At lower temperatures, the Δ_uH becomes exothermic.

This method of determining protein unfolding thermodynamics using acid-ITC, significantly widens the accessible T-range, provides direct estimate of the thermodynamic parameters at physiological temperature, and gives further insight into the third T-derivative of the Gibbs free energy of unfolding.     

Continuous-flow complete-mixing system for assessing the effects of environmental factors on colony-level coral metabolism

A small-scale chamber experimental system was designed to study the effects of temperature on colony-level coral metabolism. The system continuously supplies fresh seawater to the chamber, where it is mixed immediately and completely with the seawater already present. This continuous-flow complete-mixing system (CFCM system), in conjunction with theoretical equations, allows quantitative determination of chemical uptake and release rates by coral under controlled environmental conditions. We used the massive hermatypic coral Goniastrea aspera to examine variations in pH, total alkalinity, and total inorganic carbon for 16 days at 27 °C under controlled light intensities (300 and 0 µmol m^− 2 s^− 1). We confirmed the stability of the CFCM system with respect to coral photosynthetic and calcification fluxes. In addition, we obtained daily photosynthetic and calcification rates at different temperatures (27 °C, 29 °C, 31 °C, and 33 °C). When seawater temperature was raised from 31 °C to 33 °C, the gross primary production rate (P_gross) decreased 29.5%, and the calcification rate (G) decreased 85.7% within 2 days. The CFCM system allows quantitative evaluation of coral colony chemical release and uptake rates, and metabolism.     

Oxidative stress implication in a new phenotype of amyotrophic quadricipital syndrome with cardiac involvement due to lamin A/C mutation

This study aimed at evaluating OS in an amyotrophic quadricipital syndrome with cardiac impairment in a family of 80 members with a mutation in lamin A/C gene. Twelve patients had cardiac involvement (5 cardiac and skeletal muscles impairment). OS was evaluated in blood samples (thiobarbituric acid-reactive substances (TBARS), carbonylated proteins (PCO)) 6 “affected patients” with phenotypic and genotypic abnormalities without heart failure and 3 “healthy carrier” patients. OS was higher in affected patients than in healthy, as shown by the higher TBARS and PCO values. Patients with cardiac and peripheral myopathy exhibited a higher OS than patients with only cardiac disease (TBARS: 1.73 ± 0.05 vs. 1.51 ± 0.04 mmol/l (p = 0.051), PCO: 2.73 ± 0.34 vs. 0.90 ± 0.10 nmol/mg protein (p = 0.47)), and with healthy carriers patients (TBARS: 1.73 ± 0.05 vs. 1.16 ± 0.14 mmol/l (p = 0.05), PCO: 2.73 ± 0.34 vs. 0.90 ± 0.20 nmol/mg protein (p = 0.47)).

OS may thus contribute to the degenerative process of this laminopathy. ROS production occurs, prior to heart failure symptoms. We suggest that the extent activation may also promote the variable phenotypic expression of the disease.     

Comparative study of the activity/rest rhythms in young and old ringdove (Streptopelia risoria): correlation with serum levels of melatonin and serotonin

Aging is characterized by changes in the circadian rhythms of melatonin, serotonin, and sleep/wakefulness, alterations that affect sleep quality. The authors studied the circadian rhythms of serotonin and melatonin in young and old ringdoves (Streptopelia risoria) (2-3 and 10-12 yrs old, respectively), animals that are characterized by being monophasic and active by day, like humans. The aim was to correlate the indole rhythms with the animals' activity/rest periods. The animals were kept under a 12:12 h light/dark cycle, fed ad libitum, and housed in separate cages equipped for activity recording. Activity pulses were recorded with one actometer per animal (two perpendicular infrared transmitters) and were logged every 15 min by a computer program (DAS 16) throughout the experiment. Melatonin was measured by radioimmunoassay and serotonin by ELISA at intervals of 3 h (from 09:00 to 18:00 h) and 1 h (from 21:00 to 06:00 h), respectively. The results showed a reduction in nocturnal vs. diurnal activity of 89% and 61% in the young and old animals, respectively, with 100% considered to be the diurnal activity of each group. The amplitude of a cosine function fit to the melatonin concentrations of the old animals was half that of the young birds. The acrophase and nadir were at 02:00 and 14:00 h in the young and 01:00 and 13:00 h in the old animals, respectively. The amplitude of the corresponding cosine function fit to the serotonin concentrations in the old birds was one-third that of the young animals. The acrophase and nadir were at 15:00 and 03:00 h in the young and 16:00 and 04:00 h in the old animals, respectively. For both melatonin and serotonin, the concentrations in the young animals were significantly higher than in the old at most of the measurement times. There was a clear negative correlation between the circadian rhythms of activity and the serum melatonin levels in both young and old animals. The equivalent correlation for serotonin was positive, and stronger in the case of the young animals. The results suggest a possible relationship between the observed decline in the amplitude of the old animals' melatonin and serotonin rhythms and the lower percentage reduction in their nocturnal relative to diurnal activity pulses compared to the young animals. In conclusion, the circadian rhythms of melatonin and serotonin undergo alterations with age that could be involved in the changes in age-associated sleep.     

Effects of a five-hour exposure of arm and leg to a slightly cool thermal environment in the afternoon on the body temperature rhythm

The purpose of this study was to determine whether the different thermal conditions of the arm and leg due to wearing different types of clothing during the afternoon could modulate the circadian rhythm of body temperature and subjective sleep quality. Six healthy female volunteers were studied twice with two types of clothing, leaving the arm and leg covered or uncovered. The environmental chamber was controlled at 24 ± 0.5°C and 50 ± 5% RH during wakefulness and 28 ± 0.5°C and 50 ± 5% RH during night sleep. One type of clothing consisted of long-sleeved shirts and full-length trousers (Type L, 989 g, 0.991 clo); the other type was of half-sleeved shirts and knee-length trousers (Type H, 750 g, 0.747 clo). One testing session lasted for 16 h from 14:00 to 06:00 h the next morning. Subjects wore Type L or Type H clothing during the afternoon exposure (14:00 - 19:00), and Type L clothing during the evening (19:00 - 22:30 h) and the night sleep (22:30 - 06:00 h). Results were as follows. (1) When wearing Type H rather than Type L clothing, skin temperatures of the arm and leg were significantly lower during the time of exposure, and increased more after the evening. (2) Rectal temperature was not significantly different between the two types of clothing except during the early part of the exposure period, but it decreased during the evening by a significantly greater amount when wearing Type H clothing. (3) Subjective sleep quality was not significantly different between the two clothing types. These results suggest that afternoon exposure of the arm and leg to a slightly cool environment does not have a strong after-effect on the body temperature and subjective sleep quality.     

Effect of Ramadan on the diurnal variation in short-term high power output

This study examined the effects of Ramadan fasting on anaerobic performances and their diurnal fluctuations. In a balanced and randomized study design, 12 subjects were measured for maximal power (P_max; force-velocity test), peak power (P_peak), and mean power (P_mean) with the Wingate test at 07:00, 17:00, and 21:00 h on four different occasions: one week before Ramadan (BR), the second week of Ramadan (SWR), the fourth week of Ramadan (ER), and two weeks after Ramadan (AR). There was an interval of 28 h between any two successive tests. Oral temperature was measured before each test. Under each condition, the results showed a time-of-day effect on oral temperature. Analysis of variance revealed a significant (Ramadan×time-of-day of test) interaction effect on P_max. This variable improved significantly from morning to evening before Ramadan (1.1±0.2 W · kg^-1), during the second week of Ramadan (0.6±0.2 W · kg^-1), and two weeks after the end of Ramadan (0.9±0.2 W · kg^-1). However, daily fluctuations disappeared during the fourth week of Ramadan. For P_peak and P_mean, there was no significant Ramadan×test-time interaction. These variables improved significantly from morning to evening before Ramadan ([1±0.3 W · kg^-1] for P_peak and [1.7±1.6 W · kg^-1] for P_mean) and in the second week of Ramadan ([0.9±0.6 W · kg^-1] for P_peak and [1.7±1.5 W · kg^-1] for P_mean). However, they were not affected by time-of-day in the fourth week of Ramadan. Considering the effect of Ramadan on anaerobic performances, in comparison with before Ramadan, no significant difference was observed during Ramadan at 07:00 h. The variables were significantly lower in the second week of Ramadan and in the fourth week of Ramadan at 17:00 h and 21:00 h. P_mean was not affected during the second week of Ramadan. In conclusion, the time-of-day effect on anaerobic power variables tends to disappear during Ramadan. In comparison with the period before Ramadan, anaerobic performances were unaffected in the morning but impaired in the evening during Ramadan.     

Thermal inactivation, denaturation and aggregation of mitochondrial aspartate aminotransferase

A comparative study of thermal denaturation and inactivation of aspartate aminotransferase from pig heart mitochondria (mAAT) has been carried out (10 mM Na phosphate buffer, pH 7.5). Analysis of the data on differential scanning calorimetry shows that thermal denaturation of mAAT follows the kinetics of irreversible reaction of the first order. The kinetics of thermal inactivation of mAAT follows the exponential law. It has been shown that the inactivation rate constant (k_in) is higher than the denaturation rate constant (k_den). The k_in/k_den ratio decreases from 28.8 ± 0.1 to 1.30 ± 0.09 as the temperature increases from 57.5 to 77 °C. The kinetic model explaining the discrepancy between the inactivation and denaturation rates has been proposed. The size of the protein aggregates formed at heating of mAAT at a constant rate (1 °C min^{− 1}) has been characterized by dynamic light scattering.     

The effect of temperature on caecal fermentation processes in a poikilothermic mammal, Heterocephalus glaber

1. 1.|The effect of temperature on caecal function was examined in the naked mole-rat Heterocephalus glaber, a poikilothermic mammal, which consumes a high proportion of fibre in its natural diet.

2. 2.|The temperature of optimal caecal function was determined from fermentation data measure at three specifically chosen temperatures (28, 33 and 40°C).

3. 3.|There was no significant difference between gas production at 33 and 40°C, however, gas production was significantly lower at 28°C.

4. 4.|The relative proportions of the gases produced were markedly different at 33 and 40°C (P ≤ 0.01). More methane and hydrogen were produced at 33°C than at 40°C.

5. 5.|These data suggest that microbial organisms within the caecum were active and functioning more effectively at 33°C (the preferred body temperature of the naked mole-rat) than at the other two temperatures.

Nitrotyrosine formation and apoptosis in rat models of ocular injury

This study was performed to examine inducible nitric oxide synthase (NOS-2) expression, nitrotyrosine formation and apoptosis in rats with elevated intraocular pressure (IOP) and/or ocular inflammation. Ocular inflammation was induced via injection of intra-vitreal lipopolysaccharide (LPS) while IOP was elevated by episcleral vessel cauterization. Animals were randomized to one of the following conditions: elevated IOP, LPS, elevated IOP+LPS, and control. Immunohistochemical staining and western blot analysis of retinal lysates revealed NOS-2 and nitrotyrosine immunoreactivity in all disease groups. NOS-2 expression and protein nitration was significantly greater in rats with elevated IOP+LPS compared to elevated IOP, LPS, and control groups. Nitrite levels in the retina affirmed significantly increased levels of nitric oxide generation in LPS-treated rats with elevated IOP (346 ± 23.8 μM) vs LPS-treated, elevated IOP and control groups (195.6 ± 12.6, 130 ± 2.5 and 76.6 ± 15.6 μM, respectively). Retinal TUNEL staining showed apoptosis in all diseased groups. Percent of apoptotic cells was significantly greater in the elevated IOP+LPS group compared to LPS-treated or elevated IOP groups. Presented data illustrates that both elevated IOP and ocular inflammation augment NOS-2 expression, retinal protein nitration and apoptosis in rats.     

Validation of a new telemetric core temperature monitor

The purpose of this study was to validate the accuracy and acceptability of the new VitalSense^® telemetric physiological monitoring system (Mini Mitter Co., Inc., Bend, OR). It consists of a receiver/monitor and a thermistor-based ingestible capsule for core body temperature measurement. For comparison, each subject was also monitored with a standard thermistor probe inserted 11 cm beyond the anal sphincter (Mini-Logger^® Series 2000). Both the measurement systems have specified accuracy of ±0.1 °C.

Ten volunteers, four females, six males, mean age 51.1±11.8 years, gave informed consent to wear the two systems for the duration of the passage of the temperature capsule through their digestive tracts. Minute-by-minute comparisons were made between the temperatures recorded by the two systems. Parameters reported include: average transit time of the capsule; temperature at each minute of the experiment; mean difference in temperature at each time point; correlation coefficient for the two temperature measurements; and number of missed data points for each system.

Mean capsule transit time was 48.6±35.5 h with a range of 12.4–136.2 h. The mean temperature for all subjects was 36.93 °C±0.15 °C and 36.96 °C±0.16 °C for the capsule and rectal probe respectively, with no significant difference between the means. The mean difference between readings (capsule–rectal probe) was 0.04 °C±0.03 °C. There was a significant correlation between the capsule and rectal probe temperatures, R²=0.80,p<0.05 and R²=0.90,p<0.05 for all data points and quiescent periods respectively. Of the average 2916±2132 data points per subject, there was a significant (p<0.05) difference in data points lost, 105±120 with VitalSense vs. 449±697 with the rectal probe. The percentage of missing data points was 3.1%±2.5% for the capsule (monitor out of the one-meter range of the capsule) and 11.4%±15.9% for the rectal probe (primarily due to probe slippage, but also due to removal for personal hygiene). The data support the finding that the VitalSense core body temperature monitoring system is at least as accurate as rectal probe monitors and the subjects found it to be much more acceptable.     

Effects of irradiance, temperature, and nutrients on growth dynamics of seagrasses: A review

Productivity of seagrasses can be controlled by physiological processes, as well as various biotic and abiotic factors that influence plant metabolism. Light, temperature, and inorganic nutrients affect biochemical processes of organisms, and are considered as major factors controlling seagrass growth. Minimum light requirements for seagrass growth vary among species due to unique physiological and morphological adaptations of each species, and within species due to photo-acclimation to local light regimes. Seagrasses can enhance light harvesting efficiencies through photo-acclimation during low light conditions, and thus plants growing near their depth limit may have higher photosynthetic efficiencies. Annual temperatures, which are highly predictable in aquatic systems, play an important role in controlling site specific seasonal seagrass growth. Furthermore, both thermal adaptation and thermal tolerance contribute greatly to seagrass global distributions. The optimal growth temperature for temperate species range between 11.5 °C and 26 °C, whereas the optimal growth temperature for tropical/subtropical species is between 23 °C and 32 °C. However, productivity in persistent seagrasses is likely controlled by nutrient availability, including both water column and sediment nutrients. It has been demonstrated that seagrasses can assimilate nutrients through both leaf and root tissues, often with equal uptake contributions from water column and sediment nutrients. Seagrasses use HCO₃⁻ inefficiently as a carbon source, thus photosynthesis is not always saturated with respect to DIC at natural seawater concentrations leading to carbon limitation for seagrass growth. Our understanding of growth dynamics in seagrasses, as it relates to main environmental factors such as light, temperature, and nutrient availability, is critical for effective conservation and management of seagrass habitats.     

Change of serum mitochondrial uncoupling protein 1 (UCP1) levels and daily rhythm of rectal and cutaneous temperatures in Equus caballus and Capra hyrcus

The aim of the present study was to monitor the daily rhythm of rectal and cutaneous temperatures together with the changes in the serum levels of mitochondrial uncoupling protein 1 (UCP1) in equine and goat species. On five gelding horses and five female goat rectal and cutaneous temperatures were recorded at 4 h intervals for a 48 h period. At the same time points blood samples were collected from each animal. Daily rhythms of rectal and cutaneous temperatures were observed in both species, in both day of monitoring. Mesor value of rectal temperature was statistically higher of about 4 °C than cutaneous temperature, and acrophase was postponed of about 2 h in both day of monitoring and in both species. UCP1 did not show daily rhythmicity in horses and goats. We can speculate that the thermogenesis due to thermal system is auxiliary to keeping the body temperature daily rhythm.     

Effects of temperature, photoperiod, and light intensity on the eclosion rhythm of the high-altitude Himalayan strain of Drosophila ananassae

Eclosion rhythm of the high-altitude Himalayan strain of Drosophila ananassae from Badrinath (altitude 5123 m) was temperature-dependent and at 21°C, it was entrained by cycles of 12 h light: 12 h darkness (LD 12:12) and free-ran in constant darkness, however, it was arrhythmic at 13°C or 17°C under identical experimental conditions (Khare, P. V., Barnabas, R. J., Kanojiya, M., Kulkarni, A. D., Joshi, D. S. (2002). Temperature dependent eclosion rhythmicity in the high altitude Himalayan strains of Drosophila ananassae. Chronobiol. Int. 19:1041-1052). The present studies were designed to see whether or not these strains could be entrained at 13°C, 17°C, and 21°C by two types of LD cycles in which the photoperiod at 100 lux intensity varied from 6 h to 18 h, and the light intensity of LD 14:10 cycles varied from 0.001 lux to 1000 lux. All LD cycles entrained this strain at 21°C but not at 13°C or 17°C. These results demonstrate that the entrainment of eclosion rhythm depends on the ambient temperature and not on the photoperiod or light intensity of LD cycles. Thus the temperature has taken precedence over the light in the entrainment process of eclosion rhythm of the high altitude Himalayan strain of D. ananassae. This may be the result of natural selection in response to the environmental temperature at Badrinath that resembles that of the sub-Arctic region but the photoperiod or light intensity are of the subtropical region.     

The Effect of Activity on the Waking Temperature Rhythm in Humans

Nine healthy female subjects were studied when exposed to the natural light-dark cycle, but living for 17 “days” on a 27h day (9h sleep, 18h wake). Since the circadian endogenous oscillator cannot entrain to this imposed period, forced desynchronization between the sleep/activity cycle and the endogenous circadian temperature rhythm took place. This enabled the effects of activity on core temperature to be assessed at different endogenous circadian phases and at different stages of the sleep/activity cycle. Rectal temperature was measured at 6-minute intervals, and the activity of the nondominant wrist was summed at 1-minute intervals. Each waking span was divided into overlapping 3h sections, and each section was submitted to linear regression analysis between the rectal temperatures and the total activity in the previous 30 minutes. From this analysis were obtained the gradient (of the change in rectal temperature produced by a unit change in activity) and the intercept (the rectal temperature predicted when activity was zero). The gradients were subjected to a two-factor analysis of variance (ANOVA) (circadian phase/ time awake). There was no significant effect of time awake, but circadian phase was highly significant statistically. Post hoc tests (Newman-Keuls) indicated that gradients around the temperature peak were significantly less than those around its trough. The intercepts formed a sinusoid that, for the group, showed a mesor (±SE) of 36.97 (±0.12) and amplitude (95% confidence interval) of 0.22°C (0.12°C, 0.32°C). We conclude that this is a further method for removing masking effects from circadian temperature rhythm data in order to assess its endogenous component, a method that can be used when subjects are able to live normally. We suggest also that the decreased effect of activity on temperature when the endogenous circadian rhythm and activity are at their peak will reduce the possibility of hyperthermia.     

Mg2+ ion effect on conformational equilibrium of poly A . 2 poly U and poly A poly U in aqueous solutions

Differential UV spectroscopy and thermal denaturation were used to study the Mg²⁺ ion effect on the conformational equilibrium in poly A · 2 poly U (A2U) and poly A · poly U (AU) solutions at low (0.01 M Na⁺) and high (0.1 M Na⁺) ionic strengths. Four complete phase diagrams were obtained for Mg²⁺–polynucleotide complexes in ranges of temperatures 20–96 °C and concentrations (10⁻⁵–10⁻²) M Mg²⁺. Three of them have a ‘critical’ point at which the type of the conformational transition changes. The value of the ‘critical’ concentration ([Mg_t²⁺]_cr=(4.5±1.0)×10⁻⁵ M) is nearly independent of the initial conformation of polynucleotides (AU, A2U) and of Na⁺ contents in the solution. Such a value is observed for Ni²⁺ ions too. The phase diagram of the (A2U+Mg²⁺) complex with 0.01 M Na⁺ has no ‘critical’ point: temperatures of (3→2) and (2→1) transitions increase in the whole Mg²⁺ range. In (AU+Mg²⁺) phase diagram at 0.01 M Na⁺ the temperature interval in which triple helices are formed and destroyed is several times larger than at 0.1 M Na⁺. Using the ligand theory, a qualitative thermodynamic analysis of the phase diagrams was performed.     

The circadian rhythm of core temperature: origin and some implications for exercise performance

This review first examines reliable and convenient ways of measuring core temperature for studying the circadian rhythm, concluding that measurements of rectal and gut temperature fulfil these requirements, but that insulated axilla temperature does not. The origin of the circadian rhythm of core temperature is mainly due to circadian changes in the rate of loss of heat through the extremities, mediated by vasodilatation of the cutaneous vasculature. Difficulties arise when the rhythm of core temperature is used as a marker of the body clock, since it is also affected by the sleep-wake cycle. This masking effect can be overcome directly by constant routines and indirectly by “purification” methods, several of which are described. Evidence supports the value of purification methods to act as a substitute when constant routines cannot be performed. Since many of the mechanisms that rise to the circadian rhythm of core temperature are the same as those that occur during thermoregulation in exercise, there is an interaction between the two. This interaction is manifest in the initial response to spontaneous activity and to mild exercise, body temperature rising more quickly and thermoregulatory reflexes being recruited less quickly around the trough and rising phase of the resting temperature rhythm, in comparison with the peak and falling phase. There are also implications for athletes, who need to exercise maximally and with minimal risk of muscle injury or heat exhaustion in a variety of ambient temperatures and at different times of the day. Understanding the circadian rhythm of core temperature may reduce potential hazards due to the time of day when exercise is performed.