Diurnal Variation in Glucose Tolerance: Associated Changes in Plasma Insulin,Growth Hormone,and Non-esterified

Oral glucose tolerance tests were performed in the morning and afternoon of separate days on 31 people derived from a normal population sample. Blood sugar levels were higher in the afternoon test from and including 60 minutes after the glucose load. The degree of diurnal variation was similar in men and women, but greater in the older half of the group. It was negatively correlated with the degree of obesity. The plasma insulin response was less at the 30 minute time point in the afternoon, but significantly exceeded the morning values at 120 and 150 minutes after the glucose load. Growth hormone levels were similar in morning and afternoon tests. Fasting non-esterified fatty acid levels were significantly higher before the afternoon test.The relatively impaired glucose tolerance in the afternoon is associated with a delayed insulin response to the glucose load. This seems unlikely to be the sole explanation, however, and increased non-esterified fatty acid metabolism with a consequent decrease in glucose disposal may also contribute.     

Diurnal Variation in Response to Intravenous Glucose

Intravenous glucose tolerance tests (25 g) were performed in the morning and afternoon on 13 apparently normal persons. The individual K values (rate of decline of blood sugar) were all higher in the morning tests, and the mean values were significantly higher in the morning. Fasting blood sugar levels were slightly lower in the afternoon. There was no difference between the fasting morning and afternoon plasma insulin levels, but the levels after glucose were lower in the afternoon. Growth hormone levels were low at all times in non-apprehensive subjects and unaffected by glucose. The results suggest that the impaired afternoon intravenous glucose tolerance, like oral glucose tolerance, is associated with impaired insulin release and insulin resistance.     

Adrenal and plasma corticosterone levels in the pregnant, foetal and neonatal rat, in the perinatal period.

A group of pregnant control rats was sacrificed before parturition, in the morning, afternoon and evening of day 20 and 21 and in the morning of day 22. Another group was sacrificed during parturition, when 2 to 8 foetuses had been expelled. The onset of parturition occurred for the first rat in the afternoon of day 21 and for the last rat in the afternoon of day 22. Corticosterone was extracted from maternal, foetal and neonatal adrenals and plasma, and was assayed by a fluorometric procedure. The maternal adrenal and plasma corticosterone levels, before parturition, were lower in the morning than in the afternoon excepting day 22 when morning values were as high as those in the afternoon of day 21. Adrenal and plasma corticosterone concentrations were elevated during parturition in the mother but not the foetus. Plasma corticosterone values were raised in the newborn compared to their littermates in utero.     

Diurnal Variation of Oral Glucose Tolerance: a Possible Pointer to the Evolution of Diabetes Mellitus

Possible diurnal variation in the blood sugar response to oral glucose was studied by comparing, in the same individuals, the results of oral glucose tolerance tests performed in the morning and the afternoon. In a group of normal individuals the blood sugar levels were significantly higher in the afternoon. In hyperglycaemic individuals the diurnal variation decreased as the blood sugar levels reached during the morning test increased, so that in a group of grossly hyperglycaemic men the mean morning and afternoon tests were almost identical. The causes of this diurnal variation are not known.     

Might cardiac catheterization influence diurnal rhythm of the steroid stress hormones secretion?

Glucocorticoids (GCs) are steroid hormones produced by the adrenal cortex in reaction to stress stimuli. GCs production is not stable over a 24-hour period; the plasma concentration peaks in the morning (approximately upon awakening) and then the plasma levels decrease, reaching the nadir in the evening. In our experiments, the levels of cortisol, cortisone, DHEA and DHEAS were tested in young female pigs (n=23) during heart catheterization at two different day times (in the morning and in the afternoon). The non-parametric Mann-Whitney test for statistical analysis was used. We found only minimal statistical differences in studied markers between the morning and afternoon group (p>0.05). The absence of circadian variation in GCs levels could originate either at an early age of our experimental pigs, or in stressful conditions on the experiment day, or most likely the day before (e.g. social isolation, fasting, transport, and catheterization), respectively. We can conclude there is no difference in the stress load between morning and afternoon experiments, and therefore we can assume the stress load is not a limiting factor for the timing when catheterization should be preferably performed.     

The impact of time of day on the gait and balance control of Alzheimer’s patients

Alzheimer’s patients suffer from circadian dysregulation. The aim of this study was to examine the evolution of balance control and gait at different times of the day (11:00, 14:00, 18:00) in order to identify whether Alzheimer’s patients were more likely to fall at certain periods of the day. Spatio-temporal parameters of centre of foot pressure displacements were measured with a force platform and spatio-temporal parameters of walking were evaluated with a gait analysis device. The results highlighted that balance control was worse in the evening and the afternoon than in the morning. Furthermore, the walking speed was faster and support duration, swing duration and cycle duration were shorter in the evening than in the morning and afternoon. The combined analysis of balance control and gait parameters revealed that balance control and walking are concomitantly altered in the evening which increases the fall risk in the evening, in comparison with the morning, for Alzheimer’s patients.     

Phloem Translocation and Heat-induced Callose Formation in Field-grown Gossypium hirsutum L

Phloem translocation rates in field-grown cotton (Gossypium hirsutum L.) dropped from morning to afternoon and continued to decline toward evening, except that recovery occurred following the hottest afternoon when the maximum temperature was 44 C. Water deficits increased from morning to evening, and severity of deficits generally were proportional to daytime heating. Water stress contributed toward reducing translocation but was not always the governing factor. Callose breakdown appeared to be slower than heat-induced synthesis, and in the evening callose still reflected the influence of high afternoon temperatures. Translocation was considerably reduced when about 50% or more of the hypocotyl sieve plates had large amounts of callose. While heat-induced callose may have reduced translocation because of sieve plate pore constriction, temperatures of 39 to 44 C appeared to inhibit an additional component of translocation as well, possibly in the leaf blade.     

Effects of Waking Time and Breakfast Intake Prior to Evaluation of Psychomotor Performance in the Early Morning

Many studies conducted in the field of chronobiology report diurnal fluctuation in cognitive and physical performance that occurs in phase with the body temperature circadian rhythm. Waking time and whether or not breakfast is consumed are currently considered to influence the diurnal fluctuation in data collected in the morning at 06∶00 h and evening at 18∶00 h. Nineteen male subjects participated in four test sessions to examine if wake‐up time (04∶00 h or 05∶00 h) and eating or not eating breakfast influence psychomotor performance capacity at 06∶00 h. All four sessions were separated by ≥36 h and were completed in a counterbalanced order. Each test session comprised sign cancellation, Epworth Sleepiness Scale, simple reaction time, and manual dexterity tests. Most of the results indicate that psychomotor performance when evaluated at 06∶00 h under each of the four different study situations (two waking times and two breakfast conditions) is not statistically significantly different. Consequently, previous results that documented diurnal fluctuations in morning and evening performance capacities, with test sessions at 06∶00 h, are confirmed. Being less efficient in the early morning than in the afternoon potentially exposes people to elevated risk of accident and injury at this time of the day. Prior waking time and/or consumption of a light meal, plus other countermeasures mentioned in the literature, are insufficient to prevent this risk.     

Diurnal variation and response to food withdrawal of lactose synthesis in lactating rats.

1. The incorporation of radiolabelled plasma glucose into mammary lactose was used to measure the rate of lactose synthesis in lightly anaesthetized lactating rats. 2. Lactose synthesis showed a diurnal variation with a minimum at 18:00h 3. Food withdrawal for 6h did not affect lactose synthesis in the early morning but greatly decreased it in the afternoon or evening. 4. Plasma glucose, milk sugars and total galactosyltransferase activity (EC 2.4.1.22) did not show the above changes. 5. Measurements of plasma insulin, which varies diurnally, and experiments with injected insulin suggested that variations of insulin within the physiological range do not account for the changes in lactose synthesis described.     

Diurnal variation and reliability of the urine lactate concentration after maximal exercise

The postexercise urine lactate concentration is a novel valid exercise biomarker, which has exhibited satisfactory reliability in the morning hours under controlled water intake. The aim of the present study was to investigate the diurnal variation of the postexercise urine lactate concentration and its reliability in the afternoon hours. Thirty-two healthy children (11 boys and 21 girls) and 23 adults (13 men and 10 women) participated in the study. All participants performed two identical sessions of eight 25 m bouts of maximal freestyle swimming executed every 2 min with passive recovery in between. These sessions were performed in the morning and afternoon and were separated by 3–4 days. Adults performed an additional afternoon session that was also separated by 3–4 days. All swimmers drank 500 mL of water before and another 500 mL after each test. Capillary blood and urine samples were collected before and after each test for lactate determination. Urine creatinine, urine density and body water content were also measured. The intraclass correlation coefficient was used as a reliability index between the morning and afternoon tests, as well as between the afternoon test and retest. Swimming performance and body water content exhibited excellent reliability in both children and adults. The postexercise blood lactate concentration did not show diurnal variation, showing a good reliability between the morning and afternoon tests, as well as high reliability between the afternoon test and retest. The postexercise urine density and lactate concentration were affected by time of day. However, when lactate was normalized to creatinine, it exhibited excellent reliability in children and good-to-high reliability in adults. The postexercise urine lactate concentration showed high reliability between the afternoon test and retest, independent of creatinine normalization. The postexercise blood and urine lactate concentrations were significantly correlated in all cases, attesting to the validity of urine lactate as an index of anaerobic metabolism. We conclude that urine lactate, after normalization to creatinine, could be used in training practice either in the morning or in the afternoon. Further research is needed to assess the applicability of this novel exercise biomarker.     

Morningness-eveningness scores predict outcomes differentially for depressed patients attending morning vs. afternoon day treatment streams

ABSTRACT

At the Center for Addiction and Mental Health (CAMH) Integrated Day Treatment (IDT) program, each patient attends either a morning stream or an afternoon stream, but not both. We examined whether subjective chronotype, or the time of day an individual prefers to be most active and alert, predicted treatment outcomes differentially in depressed patients attending the morning vs. afternoon IDT streams. The Horne-Östberg Morningness-Eveningness Questionnaire (MEQ) was administered before IDT treatment to 203 consecutive patients experiencing a major depressive episode. Multiple regression was used to predict change in depression and quality of life scores based on treatment stream (morning or afternoon), baseline MEQ scores and the treatment stream by MEQ interaction. The treatment stream by MEQ interaction was a highly significant predictor of both depression and quality of life change scores. Post-hoc analyses based on established MEQ categories revealed that definite evening chronotypes had significantly better responses in the morning stream than did morning chronotypes, and significantly worse responses in the afternoon stream relative to moderate evening or neutral chronotypes. There were insufficient morning chronotypes in the afternoon stream to assess clinical responses for this subgroup. In the morning stream only, there was a significant positive correlation between the change in MEQ scores after four weeks of IDT treatment (i.e. a shift to greater morningness) and the decrease in depression scores (r = .36, p = .003), consistent with a therapeutic phase advance in circadian rhythms. In sum, these preliminary data suggest that definite evening chronotypes may have the greatest relative benefit from attending the morning vs. afternoon IDT stream. As patients currently select which IDT stream they will attend, future work based on randomized treatment assignment and using passive actigraphy to assess circadian phase is currently planned to extend these preliminary findings.     

Effects of prolonged and reduced warm-ups on diurnal variation in body temperature and swim performance

Previous studies have suggested a diurnal variation in the performance of physical tasks. The theoretical basis for the effect of time-of-day on performance centers on the circadian rhythms of many physiological variables and especially the body temperature curve. This investigation had two purposes: (a) to determine if increasing the volume of the warm-up could eliminate diurnal variation in body temperature and swim performance, and (b) to determine if reduction of the warm-up volume in the late afternoon would affect body temperature and swim performance. Participants for this investigation included 6 male and 4 female competitive swimmers (mean age = 15 +/- 1 years). Before the swim performance trials in the morning, participants warmed up with either standard volume (2,011.68 m) or 200% of that volume. Before the afternoon swim performance trials, warm-up volumes were either 33% or 100% of the standard warm-up volume. Before entering the water and immediately after the warm-up, temperature was taken from the ear. After the swim performance, participants were asked to rate their perceived exertion on the basis of Borg's CR-10 rating scale. The order of test administration for time of day and warm-up condition was balanced and with tests carried out over 4 days. Each swimmer completed 1 test condition (warm-up) per day. Results indicated that increased morning warm-up time eliminated diurnal variation in body temperature; however, evening superiority in swimming performance was not eliminated. The results also indicated that reducing the volume of the afternoon warm-up to 33% of the standard warm-up had no effect on body temperature or swim performance.     

Light/dark cycle-dependent metabolic changes in adipose tissue of pinealectomized rats.

We investigated the effects of pinealectomy on adipose tissue metabolism at different times of day. Adult male Wistar rats were divided into two groups: pinealectomized and control (sham-operated). Eight weeks after surgery, the animals were killed at three different times (at 8.00 a.m., at 4.00 p.m. and 11.00 p.m.). We collected blood samples for glucose, insulin, corticosterone, and leptin determinations, and periepididymal adipocytes for in vitro insulin-stimulated glucose uptake, oxidation, and incorporation into lipids. Pinealectomy caused insulin resistance as measured by 2-deoxyglucose uptake (a fall of approximately 40 % in the maximally insulin-stimulated rates) accompanied by hypercorticosteronemia at the three time points investigated without changes in plasma insulin an or leptin levels. Furthermore, pinealectomy increased the insulin-induced glucose incorporation into lipids (77 %) at 4.00 p.m. and insulin-induced glucose oxidation in the morning and in the afternoon, while higher rates were observed in the evening and in the morning in control rats. In conclusion, cell responsiveness to insulin was differentially affected by pineal ablation and time of day, and persistent insulin resistance was obtained in pinealectomized rats. We hypothesize that pinealectomy exposes the animal to an inadequate match between energy requirements and fuel mobilization.     

Day-Night Differences in the Kinetics and Dynamics of Insulin: Diabetic Versus Normal Yucatan Minipigs

Time-dependent variations in the pharmacokinetics and pharmacodynamics of insulin were studied at two times, 10:30 and 20:30 during the same day in normal and streptozotocin (STZ)-induced diabetic minipigs housed in L(06:00):D(18:00) using the intravenous insulin tolerance test. Following intravenous insulin (0.1 IU/kg) administration in normal minipigs, the time for the glucose level to reach nadir (t_nadir) was significantly longer in the evening than the morning [(a.m.: 30.4 (± 2.4) VS. P.M.: 38.5 (± 3.3) min] (p < 0.01), although maximum reduction of glucose level (nadir) in the morning and evening was not significantly different [a.m.: (-70 (± 2) VS. P.M.: -65 (± 5) %]. The rate of glucose decline (K_in) was significantly decreased in the evening [a.m.: 5.33 (± 0.71) VS. P.M.: 4.44 (± 0.54) %dBG/min] (p < 0.01), and the integrated glucose-lowering response (ABCB) was significantly higher in the evening than the morning [a.m.: 3.18 (± 0.38) VS. P.M.: 4.52 (± 0.30) (g/dl) * min] (p < 0.01). The area under the plasma insulin concentration curve was increased significantly in the evening [a.m.: 2.26 (± 0.174) VS. P.M.: 2.74 (± 0.18) (mU/ml) * min], while the morning plasma insulin half-life did not differ significantly from that in the evening [a.m.: 4.79 (± 0.36) VS. P.M.: 5.47 (± 0.47) min]. After induction of diabetes by intravenous STZ injections, minipigs became diabetic, baseline blood glucose was observed to increase from the range of 45–55 to 200–250 mg/dl while plasma insulin levels decreased from 7–12 to 3–5 uU/ml. In the STZ-induced diabetic minipigs, a higher dose (0.2 IU/kg) was used in the intravenous insulin tolerance test in an attempt to normalize the high glucose levels. Following intravenous     

Reduced levels of thyroid hormones, insulin, and glucose, and lower body core temperature in the growth hormone receptor/binding protein knockout mouse

The mechanisms that are responsible for the extension of lifespan in the mouse with targeted disruption (knockout [KO]) of the growth hormone (GH) receptor/binding protein (GHR-KO) are unknown. However, in the long-living Ames dwarf mouse, blood glucose and body core temperature (Tco) are consistently lower than in normal mice. In addition, insulin levels are reduced and corticosterone levels are elevated in male dwarfs. These functional alterations, similar to those seen in animals under caloric restriction, have not been proven to be causally related to the extension of lifespan, but they do provide some insight into what traits may be necessary for long life. Therefore, to investigate which of these parameters are similarly affected in two genetically unrelated, yet similarly long-living mouse models, we measured Tco, thyroid hormones (triiodothyronine [T3] and thyroxine [T4]), and insulin, in addition to morning and afternoon levels of glucose and corticosterone, in young adult male and/or female GHR-KO mice and their normal siblings. Tco in GHR-KO mice was numerically reduced throughout the 24-hr period; however, these differences were only significant 4 hr prior to lights-off (14:00 hr), immediately after lights-off (18:00 hr), and during the 3 hr preceding lights on (03:00 to 06:00 hr). GHR-KO mice had significantly reduced levels of T3 and T4, while the ratio of these hormones was similar to that in normal mice. Insulin levels in GHR-KO mice were lower than in normal mice; levels in male GHR-KO mice were below the detectable limits of the assay used. Glucose levels in GHR-KO mice (male and females) were lower than in normal mice in measurements taken in both morning and afternoon; however, these differences arose from consistent reductions in males, as morning glucose levels in GHR-KO females were similar to those of normal mice. Corticosterone levels measured in blood plasma collected under basal (nonstressed) conditions showed sex-related alterations. Basal corticosterone levels in female GHR-KO mice were similar to normal females, while those in male GHR-KO mice were higher than in normal males in the afternoon. Corticosterone levels in stressed GHR-KO females were similar to those measured in stressed normal females. These data show that the long-living GHR-KO mouse shares a reduction in glucose, insulin, thyroid hormones, and Tco with the Ames dwarf mouse. Reductions in these parameters may be important to the underlying mechanisms of delayed aging in these animals.     

24-hour assessment of performance on a palmtop computer: validating a self-constructed test battery

A test battery was constructed on a palmtop computer for ambulatory purposes. This study explored whether the test battery could assess circadian rhythmicity under constant routine conditions. Performance, body temperature, and subjective sleepiness of 12 healthy subjects were measured. The test battery consisted of a sleepiness questionnaire and three performance tests: a vigilance detection test, a working memory test, and a choice-reaction time test. The subjects were divided into early-start and late-start groups and were subjected to the constant-routine protocol. All tests showed a trough in performance in the early morning around 07:00h and a peak in the evening between 21:00 and 23:00h. In addition, an afternoon decrement in performance was observed between 15:00 and 17:00h. On average, the circadian (peak-to-trough) variation of the performance variables amounted to 16.9%±1.7 SEM of the maximum across subjects. The late starters showed a larger impairment in performance during the morning than the early starters. This could be attributed to prior wakefulness. The characteristics of the performance rhythms found in this study replicate findings in several other studies carried out under constant routine conditions. In conclusion, the present test battery appeared to be a good tool for future assessment of performance under natural conditions.     

Diurnal variation in heart rate variability before and after maximal exercise testing

As heart-rate variability (HRV) is under evaluation in clinical applications, the authors sought to better define the interdependent impact of age, maximal exercise, and diurnal variation under physiologic conditions. The authors evaluated the diurnal changes in HRV 24-h pre- and post-maximal aerobic exercise testing to exhaustion in young (19-25 yrs, n?=?12) and middle-aged (40-55 yrs, n?=?12) adults. Subjects wore a portable 5-lead electrocardiogram holter for 48?h (24?h prior to and following a maximal aerobic capacity test). Time-, frequency-, time-frequency-, and scale-invariant-domain measures of HRV were computed from RR-interval data analyzed using a 5-min window size and a 2.5-min step size, resulting in a different set of outputs every 2.5?min. Results were averaged (mean?±?SE) over four prespecified time periods during the morning, afternoon, evening, and night on Day 1 and Day 2. Diurnal changes in HRV in young and middle-aged adults were compared using a two-way, repeated-measures analysis of variance (ANOVA). Young adults demonstrated higher HRV compared to middle-aged adults during periods of wakefulness and sleep prior to maximal exercise stress testing (i.e., high-frequency power during Day 1: young adults: morning 1862?±?496?ms(2), afternoon 1797?±?384?ms(2), evening 1908?±?431?ms(2), and night 3202?±?728?ms(2); middle-aged adults: morning 341?±?53?ms(2), afternoon 405?±?68?ms(2), evening 469?±?80?ms(2), and night 836?±?136?ms(2)) (p < .05). Exercise resulted in reductions in HRV such that multiple measures of HRV were not significantly different between age groups during the afternoon and evening periods. All measures of HRV demonstrated between-group differences overnight on Day 2 (p < .05). Young adults are associated with higher baseline HRV during the daytime. Sleep increases variability equally and proportionally to daytime variability. Given the higher baseline awake HRV and equal rise in HRV during sleep, the change in HRV from sleep to morning with exercise is greater in younger subjects. These physiologic results have clinical significance in understanding the pathophysiology of altered variability in ill patients.     

Short-term temporal dynamics of yeast abundance on the tall fescue phylloplane

Six replicate trials were conducted to determine the short-term temporal dynamics and the effects of foliar applications of nutrients on the phylloplane yeast community of tall fescue (Festuca arundinacea Schreb.). In each trial, 2% sucrose + 0.5% yeast extract solution or sterile deionized water (control) was applied to the experiment plots. Twelve hours post-treatment (at 0600 hours), leaf samples were collected and yeast colony-forming units (cfu) were enumerated by dilution plating. This process was repeated at 1200, 1800, and 2400 hours in each trial. Significant differences were observed between the number of yeast cfu and the time at which the samples were collected. On average, the number of yeast cfu recovered was significantly less at 1800 hours and significantly greatest at 2400 hours when compared with all other sampling times. Averaged over all time intervals, we observed a trend of increased yeast abundance in turf treated with the nutrient solution compared with control treatments. In a separate investigation, atmospheric yeast abundance above the canopy of tall fescue was assessed in the morning (0900) and in the afternoon (1500) using a Thermo Andersen single stage viable particle sampler. In 5 of the 6 trials of this experiment, atmospheric yeast abundance was significantly greater in the morning than in the afternoon. Results suggest the following colonization model: phylloplane yeasts on tall fescue reproduce during the late evening and early morning, stabilize during the late morning and early afternoon through exchange of immigrants and emigrants, and decline during the late afternoon and (or) early evening.     

The effect of training at a specific time of day: a review

This article focuses on physical performances after training at a specific time of day. To date, although the effect of time of day on aerobic performances appears to be equivocal, during anaerobic exercises, the effect of time of day has been well established with early morning nadirs and peak performances in the late afternoon. These diurnal rhythms can be influenced by several factors such as the regular training at a specific time of day. Indeed, regular training in the morning hours may increase the lower morning performances to the same or even higher level as their normal diurnal peak typically observed in the late afternoon by a greater increase of performance in the evening. However, regular training in the evening hours may increase the morning-evening (i.e., amplitude of the rhythm) difference by a greater increase of performance in the late afternoon. Therefore, adaptations to training are greater at the time of day at which training is regularly performed than at other times. Nevertheless, although modifications in resting hormones concentrations could explain this time-of-day specific adaptations, precise information on the underlying mechanisms is lacking.     

Diurnal Variation in Oral Temperature, Sleepiness, and Performance of High School Girls

Evaluation of rhythmic fluctuations of physical and mental variables should be of special significance for the understanding of students' performance and setting the schedules of school activities. The present study investigated the pattern of diurnal variation in oral temperature, sleepiness and performance of a group of adolescents undergoing a daytime school schedule. Eighteen girls (mean age 16 years-old), who attended the same class from 0715h to 1645h, were tested on seven days. They measured their oral temperature, quantified their sleepiness level by means of a visual analogue scale, and completed the following tests: letter cancellation test, addition test, and a simple motor task. One-way ANOVA statistics for repeated measures was used in order to verify the effect of test time on oral temperature, sleepiness and performance. Possible correlations between the level of sleepiness and performance were investigated by means of Spearman rank correlation. The results revealed significant time of day effect on all variables, except for the number of addition errors. Oral temperature values showed an increase from morning to afternoon. Letter cancellation, motor task and addition scores increased from early morning to late afternoon, showing rapid fluctuations throughout the day. Sleepiness level was negatively correlated with letter cancellation scores during the first three tests of the day. In agreement with other work, the diurnal variation of oral temperature, letter cancellation and addition test showed an improvement as the day progressed. Sleepiness, on the other hand, decreased throughout the day, with the highest level associated with the first test of the day, suggesting a circadian pattern of variation rather than a cumulative effect due to school activities.