Effect of time of day on aerobic contribution to the 30-s Wingate test performance

The purpose of this study was to evaluate the effects of time of day on aerobic contribution during high-intensity exercise. A group of 11 male physical education students performed a Wingate test against a resistance of 0.087 kg . kg(-1) body mass. Two different times of day were chosen, corresponding to the minimum (06:00 h) and the maximum (18:00 h) levels of power. Oxygen uptake (.VO(2)) was recorded breath by breath during the test (30 sec). Blood lactate concentrations were measured at rest, just after the Wingate test, and again 5 min later. Oral temperature was measured before each test and on six separate occasions at 02:00, 06:00, 10:00, 14:00, 18:00, and 22:00 h. A significant circadian rhythm was found in body temperature with a circadian acrophase at 18:16+/-00:25 h as determined by cosinor analysis. Peak power (P(peak)), mean power (P(mean)), total work done, and .VO(2) increased significantly from morning to afternoon during the Wingate Test. As a consequence, aerobic contribution recorded during the test increased from morning to afternoon. However, no difference in blood lactate concentrations was observed from morning to afternoon. Furthermore, power decrease was greater in the morning than afternoon. Altogether, these results indicate that the time-of-day effect on performances during the Wingate test is mainly due to better aerobic participation in energy production during the test in the afternoon than in the morning.     

Effect of Ca2+ diffusion on the time course of neurotransmitter release.

The three-dimensional (3D) diffusion model of Fogelson, A. L., and R. S. Zucker (1985. Biophys. J. 48: 1003-1017) has been employed as the basis of a refined version of the "Ca theory" for neurotransmitter release. As such, it has been studied here as to its ability to predict the time course of release under various conditions. In particular, conditions were chosen in which the temporal variations in intracellular Ca2+ concentration, the sole factor controlling the release according to the Ca theory, were modified and tested experimentally. The predictions of this model were compared with the experimental results. It is shown that the 3D diffusion model, similarly to earlier simpler versions of the Ca theory, predicts that the time course of release is highly sensitive to both the level of depolarization and the level of the resting concentration of intracellular Ca2+ Moreover, the 3D diffusion model predicts that the time course of release is insensitive to changes in temperature. In contrast, the experimental results show that the time course of release is invariant to the level of depolarization and to the resting level in intracellular Ca2+, but highly sensitive to variations in temperature.     

Effect of PACAP on LH release studied by cell immunoblot assay depends on the gender, on the time of day and in female rats on the day of the estrous cycle

We have previously demonstrated that pituitary adenylate cyclase activating polypeptide (PACAP) can be released from cultured rat anterior pituitary cells and when added to the medium in physiological concentration it releases LH from individual gonadotropes. In the present work, we studied whether the release of PACAP and the responsiveness of LH cells to PACAP depend on the gender, on the time of day when the animals were sacrificed, and in females on the stage of the estrous cycle. Anterior pituitary cells were cultured on nitrocellulose membrane. We found that the number of PACAP releasing cells was higher in proestrous than in diestrous female or in male rats and their number was always higher in the evening than at the other times. The effect of PACAP on LH cells was stimulatory in the morning of proestrus and diestrus. In proestrous rats, PACAP did not influence LH release in the afternoon or the evening, but in diestrous rats it decreased it in the afternoon and the evening. In males, there was a decrease of LH due to PACAP treatment at 10 and 20 h; however, PACAP did not influence LH at 16 h. It was concluded that in vivo PACAP might be involved in the circadian and episodic release of LH at pituitary level.     

Effect of age and time of day on sex attraction and mating of the face fly, Musca autumnalis

A well-defined sexual attraction exists between mature virgin female and mature unmated male face flies, Musca autumnalis, tested in a Y-tube olfactometer. Attraction seems to be maximum when females are 5 to 6 days old and males are 4 to 8 days old post emergence. Gonadotrophic cycles probably play a rôle in the periodicity of the sexual attraction. Attraction as well as insemination reach a peak during the noon hours, gradually decline through the afternoon, and reach a minimum level in the evening. A daily rhythm of sex pheromone release and/or production is most probably present in virgin female flies.     

Effect of age and day time on the adenosine modulation of basal and insulin-stimulated glucose transport in rat adipocytes

1. The relationship between the activity of adenosine metabolizing enzymes 5'nucleotidase (5'N), adenosine kinase (A.K.) and adenosine deaminase (A.D.) with basal and insulin-stimulated glucose transport in isolated fat cells from young and old animals was studied at 08:00 and 16:00 hr. 2. In cells from young animals a larger insulin-stimulation of glucose transport was observed at 16:00 hr than at 08:00 hr. Also at 16:00 hr small changes in 5'N, A.K. and A.D. activities suggest a decrease in adenosine formation. 3. In the cells from old animals no effect of insulin was observed at any time, while a 3-5-fold increase in 5'N indicated a predominance of adenosine formation at both times studied. 4. An inverse relationship was observed in the changes of adenosine metabolism and insulin action.     

The effect of pedal rate and time of day on the time to exhaustion from high-intensity exercise

The aim of this study was to examine the supposed influence of pedal rate on the diurnal fluctuation of the time to exhaustion from high-intensity exercise. Eleven male cyclists performed three tests at 06:00 h and three at 18:00 h at a free pedal rate (FPR) and two imposed pedal rates (80% and 120% of the FPR). They performed the tests until exhaustion using a power output corresponding to 95% maximal power (Pmax). Time to exhaustion, rectal temperature, oxygen consumption (.VO2), M. quadriceps, vastus medialis, M. biceps femoris electromyographic Root Mean Square activity rise (RMS slope), and blood lactate concentration were measured. The mean time to exhaustion recorded at 18:00 h (270.6+/-104.8 sec) was greater than at 06:00 h (233.9+/-84.9 sec). The time to exhaustion was significantly greater when the pedal rate was imposed at 80% versus 120% FPR. The blood lactate concentration and absolute core temperature at the point of exhaustion were significantly higher during tests done at 18:00 h. There was no diurnal variation in core temperature increase, .VO2, and RMS slope. The time-of-day effect for every variable did not depend on pedal rate. Diurnal variations in maximal aerobic endurance cannot be explained by a change in aerobic metabolism or in muscular fatigue. The origin of the diurnal variation in the time to exhaustion is likely to lie in greater participation in anaerobic metabolism. Also, the influence of temperature on neuromuscular functioning as an explanation for the diurnal variation in performance cannot be excluded in this study. The hypothesis on the basis of which pedal rate would influence diurnal variations in time to exhaustion in cycling was not validated by this research.     

Space-time characteristics of DNA synthesis in mesothelial cells of the rat after surgery at different times of the day

Differences in the DNA synthesis dynamics (according to the label index-LI) and those of mitotic activity (MA) in the mesothelium of the rat parietal peritoneum have been studied after burn performed at 9 AM, or at 9 PM. A number of peculiarities in the regeneration character are dependent on the day time of the operation. Immediately after the PM operation inhibition of both DNA synthesis and MA is manifected more distinctly and lasts longer, but then activation of the processes occurs more intensively the LI and MA values are greater than after the AM operation. Drop in the LI and MA takes place also with a greater rate after the PM operation, but their absolute values are kept higher up to the 7th day. Despite the fact that the reaction after the AM operation is comparatively weak, it is more rhythmical: against the background of general dynamics the fluctuations are more distinctly manifested, their period is nearly similar to the circadian. Increase in the proliferative activity is accompanied with a widening of the zone, where the dividing cells are situated. After the PM operation the wavy character of the process is expressed only in the pattern of the spatial organization of the regenerating mesothelium: nearly at regular intervals the area of the MA distribution becomes widen or narrow in turn. Thus, the LI and MA dynamics in the regenerating mesothelium depend on the circadian phase of the organism's state at the moment of the operation.     

Variations in body height within the course of a working day

Variation of body height during the day has been analyzed considering the influence of various occupations (standing, sitting, mixed) on the posture. In addition to this the following variables have been recorded on the 302 individuals under study: Sex, age, working time, time of getting up in the morning, kind of occupation, physique, sporting activities in the leisure-time, presence of defects of the spinal column, possibility of changes of the carriage at the working place and extensibility of the spinal column. The statistical analysis showed that with the exception of pathological alterations of the spinal column all these variables are influencing the variation of body height during the day. It could also be shown that the extensibility of the spinal column does not vary during the day. The author is discussing also ergonomical rules concerning the organization of working places for standing and sitting occupations. Finally some recommendations for the future organization of such places are given.     

Effect of genotype and day or night time of testing on mice behavior in the light-dark box and the open-field tests

The light-dark box (LDB) and the open-field (OF) tests are widespread experimental models for studying locomotion and anxiety in laboratory rats and mice. The fact that rodents are nocturnal animals and more active at night raises a critical question of whether behavioral experiments carried out in the light phase are methodologically correct. Parameters of behavior of four mouse strains (C57BL/6J, DBA2/J, AKR/J and CBA/LacJ) in the light-dark box and open-field tests in the light and dark phases were compared. No significant influence of the phase of testing on anxiety in LDB and OF tests was revealed. In the OF test CBA mice showed increased locomotor activity, whereas AKR and C57BL/6 mice showed increased defecation in the dark phase. It was concluded that: 1) the phase of testing is not crucial for the expression of anxiety in LDB and OF; 2) the sensitivity to the phase of testing depends on the genotype; 3) the indices of behavior in the genotypes sensitive to the phase of testing (locomotion in the CBA and defecation in the AKR and C57BL/6 mouse strains) are increased in the dark phase.     

Effect of epidermal growth factor on rat pleural mesothelial cell growth

We recently reported that the growth of normal rat pleural mesothelial cells (RPMCs) is inhibited by conditioned media from either in vivo or in vitro transformed RPMCs. In this study we report that the growth of normal RPMCs is inhibited by epidermal growth factor (EGF). This was demonstrated by using three methods of investigation. Two types of studies were carried out with growing cells. First, cell counts indicated that the number of cells was reduced in EGF-treated cultures when compared with untreated cultures. Second, the percentage of S cells detected by flow cytometry following treatment with EGF was lower than without EGF. In other experiments, incorporation of tritiated thymidine in confluent cells was decreased by EGF treatment, either in the presence or absence of fetal calf serum; these effects were dose dependent and were observed from 2 ng/ml EGF. Lower EGF concentrations did not significantly modify thymidine incorporation when compared with untreated cells. Analysis of 125I EGF binding experiments by the Scatchard method indicated that RPMCs posses EGF receptors (about 10(5) per cell) with low ligand binding affinity (Kd = 1.7 +/- 0.4 nM). These results indicate that EGF might modulate the growth of RPMCs.     

Effects of time of day on chlorpyrifos-induced alterations in body temperature

Chlorpyrifos (CPF) is an organophosphate (OP) insecticide and is among the most common and widely used commercial insecticides. Human intoxication is reported to result in a typical set of responses, which include an immediate and long lasting hyperthermic response (fever). Rodents exposed to similar doses exhibit a biphasic body temperature response: short-term hypothermia followed by subtle hyperthermia several days after administration. Time of day of administration has been suggested to alter the body temperature effect of CPF. In the present study, it is shown that adult male Sprague-Dawley rats exposed to CPF via (oral) gavage at four different times of the day demonstrate a hypothermic response, the timing and magnitude of which is independent of time of exposure and that is blocked by atropine pretreatment. However, a delayed (hyperthermic) response seems to be exhibited only when dosing occurs during the light phase. Our findings support existing theories that the hypothermic and hyperthermic effects of CPF work through independent mechanisms. It is also suggested that humans may indeed exhibit a biphasic temperature response to CPF intoxication, but that it is not typically detected.     

Effects of time of day and sleep deprivation on motorcycle-driving performance

The aim of this study was to investigate whether motorcycle handling capabilities--measured by means of the efficiency of emergency manoeuvres--were dependent on prior sleep deprivation and time of day. Twelve male participants voluntarily took part in four test sessions, starting at 6 a.m., 10 a.m., 2 p.m., and 6 p.m., following a night either with or without sleep. Each test session comprised temperature and sleepiness measurements, before three different types of motorcycling tests were initiated: (1) stability in straight ahead riding at low speed (in "slow motion" mode and in "brakes and clutch" mode), (2) emergency braking and (3) crash avoidance tasks performed at 20 kph and 40 kph. The results indicate that motorcycle control at low speed depends on time of day, with an improvement in performance throughout the day. Emergency braking performance is affected at both speeds by time of day, with poorer performance (longer total stopping distance, reaction time and braking distance) in the morning, and also by sleep deprivation, from measurements obtained at 40 kph (incorrect initial speed). Except for a tendency observed after the sleepless night to deviate from the initial speed, it seems that crash avoidance capabilities are quite unaffected by the two disturbance factors. Consequently, some motorcycle handling capabilities (stability at low speed and emergency braking) change in the same way as the diurnal fluctuation observed in body temperature and sleepiness, whereas for others (crash avoidance) the participants were able to maintain their initial performance level despite the high levels of sleepiness recorded after a sleepless night. Motorcycle riders have to be aware that their handling capabilities are limited in the early morning and/or after sleep deprivation. Both these situations can increase the risk of falls and of being involved in a road accident.     

Core temperature response to cycling exercise: Effect of time of day and measurement site

This study evaluated the effect of time of day and temperature measurement site on core temperature response to exercise. Six trained cyclists performed a 1 h cycling exercise at a fixed power-output of 160 W in a controlled environment (ambient temperature of 21.5±1.6 °C and relative humidity of 31±6%) at batyphase +2 h (08:00 h) and acrophase +2 h (20:00 h) of their estimated circadian temperature rhythm; corresponding respectively to the heat gain and heat loss mode phases. Throughout the exercise, rectal and gastro-intestinal temperature data were collected. A two-way ANOVA was applied and a common nonlinear logistic-type function dependant on three parameters (asymptote, xmid and scale) was used to fit collected data. ANOVA only indicated a time of day effect without interaction with exercise duration. A nonlinear mixed-effect model allowed further analysis of temperature kinetics. The model indicated a higher theoretical increase in temperature at the end of morning exercise compared to the evening session. However, the circadian difference observed at rest persists throughout the exercise. Theoretical asymptotic temperature values at the end of the exercise and scale values (inversely proportional to the slope) are higher for the rectal measurement site than for the gastro-intestinal measurement. The model proposed offers a solution for refining the study of individual core temperature response to prolonged exercise. The main advantage is that it takes into consideration intra- and inter-individual variability in temperature kinetics.