Significant Time Of Day Effect Research Articles

OR34-05 Second Phase Insulin Secretion Varies By Time Of Day And Body Mass Index

Abstract Disclosure: S. Naaman: None. S. Sintetas: None. E. Van Cauter: None. E.C. Hanlon: None. Diurnal variation in insulin secretion (ISR) is documented in healthy adults with and without obesity. However, in previous studies, the caloric content of meals varied across the day or the analysis focused solely on morning versus evening differences. It remains unclear if dietary intake timing is associated with metabolic response differences to the same dietary challenge if presented across a full day in individuals categorized as lean (L), with overweight (OW) or obesity (OB). Thus, we examined ISR following consumption of identical meals, equally spaced across the day, in a lab setting with controlled sleep and energy expenditure. Our study included 74 individuals; 41 lean (19 women), 14 overweight (4 women), and 19 obese (14 women). Obstructive sleep apnea (OSA), a known confounder of glucose metabolism, was an exclusion criterion. Mean age between groups was similar (L, 25.2 ± 5.3yrs vs OW, 27.0 ± 6.6yrs vs OB, 32.2 ± 7.6yrs). BMI was 38 ± 5.9 kg/m2 in the OB, 27 ± 1.2 kg/m2 in the OW, vs 22 ± 1.8 kg/m2 in the L groups, respectively (p < 0.0001). We collected blood samples continuously at regular intervals over a 24hr period in which participants ate isocaloric identical high carbohydrate meals (20% fat, 68% carbohydrate, 12% protein) at 0900, 1400, and 1900; each meal was 33% of total caloric intake. Serum C-peptide was measured using high-sensitivity chemiluminescence assays (Immulite). ISR was derived from plasma C-peptide levels by mathematical deconvolution using a two-compartment model for C-peptide clearance. Each profile was expressed as a percentage of individual 24hr mean ISR to examine the profile wave shape independently of individual differences in mean ISR. We examined 2 phases of ISR following meal ingestion; 1st phase (AUC, 0 - 1.5hrs) and 2nd phase (AUC, 1.5hrs - 3.5hrs). The profiles were analyzed with ANOVA for repeated measures with participants as a random factor and mealtime, group (L, OW, OB), and interaction “mealtime by group” as fixed effects. Despite 3 equally spaced identical meals, significant differences emerged. Irrespective of BMI, 1st phase relative ISR was similar across breakfast, lunch and dinner. Second phase relative ISR, however, revealed significant time of day effects; with midday eliciting the highest relative ISR for all groups (p = 0.0002). Significant time x group effects emerged in the 2nd phase such that relative ISR varied across the day, differently for each group (p < 0.0001). Specifically, 2nd phase relative ISR was lowest following dinner in those with obesity. This is the first study to compare 24hr profiles of ISR in healthy individuals at multiple BMI ranges, without OSA, in an experimental setting of 3 equally spaced identical meals. These findings imply that the midday meal elicits the highest ISRs, irrespective of BMI. Further, BMI impacts ISR across the day in response to identical meals. These findings have implications for obesity management. Presentation: Sunday, June 18, 2023

Abstract 096: Adrenal-specific KO Of The Circadian Clock Protein Bmal1 Alters Blood Pressure Rhythm

BMAL1 is a core circadian clock protein that regulates most physiological functions, including blood pressure (BP). Global BMAL1 knockout (KO) male mice exhibit reduced, non-dipping BP and loss of diurnal rhythm of renal sodium (Na) excretion. Although, BP and renal Na excretion rhythm remained intact in kidney-specific BMAL1 KO male mice. The adrenal gland synthesizes hormones which influence BP rhythm and renal electrolyte handling. The role of adrenal BMAL1 in the regulation of BP and renal function remains unknown. The goal was to test the hypothesis that adrenal BMAL1 is required for normal circadian rhythms of BP and renal Na excretion. Adrenal-specific aldosterone synthase Cre positive (AS)-BMAL1 KO male mice ( n =5) and littermate Cre negative, floxed control (CNTL) male mice ( n =6) underwent a telemetry study to measure BP. Cosinor analysis was performed to assess BP rhythms. During telemetry recordings, mice were placed in metabolic cages for 5 days on a normal salt diet. The latter 3 days, 12 h urine samples were collected before each light-dark Zeitgeber (6AM and 6PM/ Zeitgeber Time (ZT)0 and ZT12) to measure night/day patterns in renal Na excretion. Kidneys were collected from a separate cohort of mice ( n =7-8/genotype) at ZT0 and ZT12 for gene expression analysis of key Na transporters. No BMAL1-dependent changes in the 24 h averages for BP were observed. Cosinor analysis revealed significant differences in BP rhythm, however. The period (time taken for a full circadian cycle, ~24 h) was significantly shortened for BP in AS-BMAL1 KO mice vs. CNTL (23 h 31 vs 24 h 16, p =0.01). Acrophase (the time at which BP peaks) was shifted ~2 hours later in KO mice (KO ZT17 h 38 vs CNTL ZT15 h 45, p =0.002). The MESOR (midline estimating statistic of rhythm) of BP remained similar between groups (KO 133.5 mmHg vs CNTL 132.7 mmHg, p =0.904). Day/night Na excretion was not different in AS-BMAL1 KO mice vs. CNTL (ANOVA interaction p =0.168). This was consistent with a lack of genotype effects on gene expression for NCC, α, β, or γ ENaC. Significant time of day effects were observed for all 4 genes (all with p <0.001). In conclusion, BMAL1 KO in the adrenal gland altered BP rhythm, with no changes in renal Na excretion. This work is the first to investigate the role of adrenal BMAL1 on BP regulation.

Dissociated resting-state functional networks between the dream recall frequency and REM sleep percentage

Rapid eye movement (REM) sleep has been frequently associated with dreaming. However, mounting evidence obtained from behavioral, pharmacological, and brain imaging studies suggests that REM sleep is not indicative of the dream report and may originate from diverse neural substrates in brain functionality. The aim of the current study was to investigate the functional systems associated with inter-individual differences in dream recall and REM sleep through assessments of the resting-state functional connectivity. We collected resting-state functional magnetic resonance imaging (fMRI) data for functional connectivity evaluations from 43 healthy adult volunteers (23 men) before and after sleep. For assessment of the dream recall frequency, a 2-week sleep diary was maintained by all volunteers. In addition, whole-night polysomnography was performed for measuring the REM sleep percentage. Voxel-wise correlation analyses of 12 functional connectivity networks of interest with the dream recall frequency and REM sleep percentage were conducted using general linear model analysis. Both the dream recall frequency and REM sleep percentage showed negative associations with multiple brain functional networks. However, the dream recall frequency was mainly related to functional connectivity within the lateral visual network and thalamus, whereas the REM sleep percentage was mainly associated with connectivity within the frontoparietal networks and cerebellum. In addition, the dream recall frequency showed stronger coupling with the lateral visual network connectivity at night, whereas the coupling between the REM sleep percentage and cerebellum was higher in the morning. This indicated a significant time of day effect. Our results provide neuroimaging evidence that the functional system associated with the dream recall frequency is different from that associated with the REM sleep percentage.

Group creativity and the time of the day

ABSTRACTIn today’s knowledge-based economies, creativity in higher education has become a central focus for policy-makers. However, developing student creativity is still a challenge for higher education institutions. This paper seeks to contribute to our understanding of the creative processes at play in educational environments by using an experimental design to explore the time-of-day effect on group creativity. Examining 36 groups of university students, Experiment 1 explored differences in creative performance between morning and afternoon, and the optimal time of day for group creative exercises. Experiment 2 comprised 18 groups, and further studied the effect of chronotype on group creativity in the morning versus the afternoon. In both experiments a significant relationship was found between the timing of the group task and creative performance, with a peak in creative fluency around midday. This research thus points to a significant time of day effect in the creative process in groups.

Truck crash severity in New York city: An investigation of the spatial and the time of day effects

This paper investigates the differences between single-vehicle and multi-vehicle truck crashes in New York City. The random parameter models take into account the time of day effect, the heterogeneous truck weight effect and other influencing factors such as crash characteristics, driver and vehicle characteristics, built environment factors and traffic volume attributes. Based on the results from the co-location quotient analysis, a spatial generalized ordered probit model is further developed to investigate the potential spatial dependency among single-vehicle truck crashes. The sample is drawn from the state maintained incident data, the publicly available Smart Location Data, and the BEST Practices Model (BPM) data from 2008 to 2012. The result shows that there exists a substantial difference between factors influencing single-vehicle and multi-vehicle truck crash severity. It also suggests that heterogeneity does exist in the truck weight, and it behaves differently in single-vehicle and multi-vehicle truck crashes. Furthermore, individual truck crashes are proved to be spatially dependent events for both single and multi-vehicle crashes. Last but not least, significant time of day effects were found for PM and night time slots, crashes that occurred in the afternoons and at nights were less severe in single-vehicle crashes, but more severe in multi-vehicle crashes.

Differential Kinetics in Alteration and Recovery of Cognitive Processes from a Chronic Sleep Restriction in Young Healthy Men.

Chronic sleep restriction (CSR) induces neurobehavioral deficits in young and healthy people with a morning failure of sustained attention process. Testing both the kinetic of failure and recovery of different cognitive processes (i.e., attention, executive) under CSR and their potential links with subject’s capacities (stay awake, baseline performance, age) and with some biological markers of stress and anabolism would be useful in order to understand the role of sleep debt on human behavior. Twelve healthy subjects spent 14 days in laboratory with 2 baseline days (B1 and B2, 8 h TIB) followed by 7 days of sleep restriction (SR1-SR7, 4 h TIB), 3 sleep recovery days (R1–R3, 8 h TIB) and two more ones 8 days later (R12–R13). Subjective sleepiness (KSS), maintenance of wakefulness latencies (MWT) were evaluated four times a day (10:00, 12:00 a.m. and 2:00, 4:00 p.m.) and cognitive tests were realized at morning (8:30 a.m.) and evening (6:30 p.m.) sessions during B2, SR1, SR4, SR7, R2, R3 and R13. Saliva (B2, SR7, R2, R13) and blood (B1, SR6, R1, R12) samples were collected in the morning. Cognitive processes were differently impaired and recovered with a more rapid kinetic for sustained attention process. Besides, a significant time of day effect was only evidenced for sustained attention failures that seemed to be related to subject’s age and their morning capacity to stay awake. Executive processes were equally disturbed/recovered during the day and this failure/recovery process seemed to be mainly related to baseline subject’s performance and to their capacity to stay awake. Morning concentrations of testosterone, cortisol and α-amylase were significantly decreased at SR6-SR7, but were either and respectively early (R1), tardily (after R2) and not at all (R13) recovered. All these results suggest a differential deleterious and restorative effect of CSR on cognition through biological changes of the stress pathway and subject’s capacity (ClinicalTrials-NCT01989741).

Time of day and caffeine influence some neuropsychological tests in the elderly.

We report that performance on neuropsychological tests used in the diagnosis of dementia can be influenced by external factors such as time of day (TOD) and caffeine. This study investigates TOD effects on cognitive performance in the elderly. The optimal TOD at which an individual is at his or her maximal arousal alters with age, and in the elderly, typically occurs in the morning. Neuropsychological test scores from healthy elderly participants were analyzed to determine whether TOD affected performance. Interactions between caffeine and TOD were also investigated. Across 2 data sets that were analyzed, significant TOD effects were noted for Pattern-Comparison Speed (PCS), Letter-Comparison Speed (LCS; Salthouse & Babcock, 1991), Trail Making Test Part A (Reitan, 1958), Mini-Mental State Examination (MMSE; Folstein, Folstein, & McHugh, 1975) and the Graded Naming Test (GNT; McKenna & Warrington, 1980), revealing a decline in test scores as TOD increases. Significant interactions between TOD, age, and the PCS, LCS, and Trail Making Part A were noted in Data Set 1. In Data Set 2, caffeine intake had been controlled for, and significant interactions between caffeine, TOD, and scores on the MMSE and GNT were found. The TOD and caffeine effects highlight the need to control for these external factors when scoring the assessments. This conclusion has implications for the clinical procedure of diagnosis and treatment of dementia and Alzheimer's.

Sleep/wake dependent changes in cortical glucose concentrations

Most of the energy in the brain comes from glucose and supports glutamatergic activity. The firing rate of cortical glutamatergic neurons, as well as cortical extracellular glutamate levels, increase with time spent awake and decline throughout non rapid eye movement sleep, raising the question whether glucose levels reflect behavioral state and sleep/wake history. Here chronic (2-3 days) electroencephalographic recordings in the rat cerebral cortex were coupled with fixed-potential amperometry to monitor the extracellular concentration of glucose ([gluc]) on a second-by-second basis across the spontaneous sleep-wake cycle and in response to 3 h of sleep deprivation. [Gluc] progressively increased during non rapid eye movement sleep and declined during rapid eye movement sleep, while during wake an early decline in [gluc] was followed by an increase 8-15 min after awakening. There was a significant time of day effect during the dark phase, when rats are mostly awake, with [gluc] being significantly lower during the last 3-4 h of the night relative to the first 3-4 h. Moreover, the duration of the early phase of [gluc] decline during wake was longer after prolonged wake than after consolidated sleep. Thus, the sleep/wake history may affect the levels of glucose available to the brain upon awakening.

Reliability of a Single Objective Measure in Assessing Sleepiness

To evaluate reliability of single objective tests in assessing sleepiness. Subjects who completed polysomnography underwent a 4-nap multiple sleep latency test (MSLT) the following day. Prior to each nap opportunity on MSLT, subjects performed the psychomotor vigilance test (PVT) and divided attention driving task (DADT). Results of single versus multiple test administrations were compared using the intraclass correlation coefficient (ICC) and adjusted for test administration order effects to explore time of day effects. Measures were explored as continuous and binary (i.e., impaired or not impaired). Community-based sample evaluated at a tertiary, university-based sleep center. 372 adult commercial vehicle operators oversampled for increased obstructive sleep apnea risk. N/A. AS CONTINUOUS MEASURES, ICC WERE AS FOLLOWS: MSLT 0.45, PVT median response time 0.69, PVT number of lapses 0.51, 10-min DADT tracking error 0.87, 20-min DADT tracking error 0.90. Based on binary outcomes, ICC were: MSLT 0.63, PVT number of lapses 0.85, 10-min DADT 0.95, 20-min DADT 0.96. Statistically significant time of day effects were seen in both the MSLT and PVT but not the DADT. Correlation between ESS and different objective tests was strongest for MSLT, range [-0.270 to -0.195] and persisted across all time points. Single DADT and PVT administrations are reliable measures of sleepiness. A single MSLT administration can reasonably discriminate individuals with MSL < 8 minutes. These results support the use of a single administration of some objective tests of sleepiness when performed under controlled conditions in routine clinical care.

Depression and cortisol responses to psychological stress: A meta-analysis

The purpose of this meta-analysis is to examine the association between depression and cortisol responses to psychological stressors. A total of seven studies comparing plasma or cortisol responses to psychological stressors in clinically depressed (MDD) and non-depressed (ND) individuals (N = 196: 98 MDD, 98 ND; 83 men, 113 women; mean age = 40 years) were included. Sample size-adjusted effect sizes (Cohen's d statistic) were calculated and averaged across baseline (before stressor onset), stress (stressor onset up to 25 min after stressor offset), and recovery (more than 25 min after stressor offset) periods. Overall, MDD and ND individuals exhibited similar baseline and stress cortisol levels, but MDD patients had much higher cortisol levels during the recovery period than their ND counterparts. There was also a significant time of day effect in which afternoon studies were more likely to reveal higher baseline cortisol levels, blunted stress reactivity, and impaired recovery in MDD patients. This blunted reactivity-impaired recovery pattern observed among the afternoon studies was most pronounced in studies with older and more severely depressed patients.

Maritime accident investigation and temporal determinants of maritime accidents: A case study

This paper presents the results of an investigation into temporal determinants of maritime accidents based on a data-set obtained from the proceedings of formal inquiries in the former German Democratic Republic (GDR). The results show that there is no statistically significant outcome between the probability for an accident and the time of watch. Thus the results do not confirm previous studies, which reported significant time of day effects.

Circadian effects on the acute responses of salivary cortisol and IgA in well trained swimmers

Objective: To examine whether time of day significantly affects salivary cortisol and IgA levels before and after submaximal swimming. Methods: Fourteen male competitive swimmers (mean (SD) age 18 (3.2) years)...

Experimentally Induced Pain Perception in Men and Women in the Morning and Evening

The literature regarding whether or not there are diurnal differences in pain perception in men and women is equivocal. The purpose of this study was to examine the influence of time of day on experimentally induced pain threshold in men and women. A secondary purpose was to measure selected psychological and physiological responses. Pressure (3000 gm force) was applied to the middle digit of the left forefinger for 2-min with the Forgione - Barber pain stimulator. Twenty-nine volunteers (women = 14; men = 15) completed two randomly assigned sessions between 6.00 - 8.00 in the AM and PM. Selected psychological variables (STAI, POMS) and physiological variables (BP, HR, TEMP) were assessed before application of the pressure stimulus. Data were analyzed with a 2 × 2 ANOVA. Results indicated that men had significantly higher (p <. 05) systolic blood pressure and pain thresholds than women however, there was not a significant time of day effect for pain threshold. Significant time of day effects (p <. 05) were found for systolic blood pressure and tympanic temperature. Heart rate, and tympanic temperature were found to be significantly higher (p <. 05) in women in comparison to men. It is concluded that pain threshold did not differ in the AM and PM. Furthermore, men were found to have higher pain thresholds compared to the women.

THE EFFECT OF TIME OF DAY AND GENDER ON PAIN PERCEPTION AND SELECTED PSYCHOBIOLOGICAL RESPONSES

30 The literature regarding whether or not there are gender and diurnal differences in pain perception is equivocal. The purpose of this study was to examine the influence of gender and time of day on pain threshold (PT) and pain ratings (PR). A secondary purpose was to measure selected psychological(STAI, POMS) and physiological (SBP, DBP, HR, TEMP) responses. Pressure (3000 gm force) was applied to the middle digit of the left forefinger for 2-min with the Forgions-Barber pain stimulator. Twenty-nine volunteers (women-14; men=15) completed 2 randomly assigned sessions between 6:00-8:00 in the AM and PM. STAI, POMS and TEMP were assessed before the stimulus, while BP and HR were assessed before and following the pressure stimulus. Data were analyzed with a 2 x 2 ANOVA. Results indicated that men had significantly higher(p<0.05) pain thresholds than women, however there was not a significant time of day effect (p>0.05). PR and HR were found to be significantly higher (p<0.05) in women in comparison to men. Significant time of day effects (p<0.05) were found for TEMP, SBP and vigor. It is concluded that PT did not differ in the AM and PM, and that men had higher PT than women.

Chronobiological effects on exercise performance and selected physiological responses.

Previous studies investigating the impact of circadian rhythms on physiological variables during exercise have yielded conflicting results. The purpose of the present investigation was to examine maximal aerobic exercise performance, as well as the physiological and psychophysiological responses to exercise, at four different intervals (0800 hours, 1200 hours, 1600 hours, and 2000 hours) within the segment of the 24-h day in which strenuous physical activity is typically performed. Ten physically fit, but untrained, male university students served as subjects. The results revealed that exercise performance was unaffected by chronobiological effects. Similarly, oxygen uptake, minute ventilation and heart rate showed no time of day influences under pre-, submaximal, and maximal exercise conditions. Ratings of perceived exertion were unaffected by time of day effects during submaximal and maximal exercise. In contrast, rectal temperature exhibited a significant chronobiological rhythm under all three conditions. Under pre- and submaximal exercise conditions, significant time of day effects were noted for respiratory exchange ratio, while a significant rhythmicity of blood pressure was evident during maximal exercise. However, none of these physiological variables exhibited significant differential responses (percent change from pre-exercise values) to the exercise stimulus at any of the four time points selected for study. Conversely, resting plasma lactate levels and lactate responses to maximal exercise were found to be significantly sensitive to chronobiological influences. Absolute post-exercise plasma norepinephrine values, and norepinephrine responses to exercise (percent change from pre-exercise values), also fluctuated significantly among the time points studied. In summary, these data suggest that aerobic exercise performance does not vary during the time frame within which exercise is normally conducted, despite the fact that some important physiological responses to exercise do fluctuate within that time period.

Circadian rhythms have no effect on cycling performance.

The aim of this research was to determine if circadian rhythms have an effect on time trial cycling performance of 15 min duration. Seven males (Mean+/-SD): age, 22.3+/-4.9 yr; height 179.0+/-7.9 cm, body mass 74.5+/-15.5 kg; VO2max 68.0+/-5.7 ml x kg(-1) x min(-1) who were all competitive cyclists or triathletes with previous experience in laboratory testing procedures volunteered to participate in this study. Each of the seven subjects underwent a series of four tests; one VO2 max test, and three 15 min maximal performance tests, at varying times during a 24 hr period. Testing times were at 08.00-10.00; 14.00-16.00 and 20.00-22.00 hours. Heart rate was recorded during the last 10-15 seconds of each minute and blood lactate levels were taken at 5 and 10 min during exercise and again immediately post-exercise. O2 consumption was measured continuously using open circuit spirometry. RPE was measured using the Borg scale at 5 and 10 min during, and again immediately following the completion of testing. Resting oral temperature was the only variable to show a significant time of day effect (p<0.05). Oral temperature during the afternoon was higher than both morning and evening results by 0.76 degrees C and 0.09 degrees C respectively. Total work (kJ) and average power output (W) were recorded at their highest during the morning session and reached a trough during the afternoon session, but these differences were not significant (p = 0.9997 and 0.9972 respectively). The results obtained in this study indicate that while certain biological rhythms are present, they appear to have no effect on this type of cycling performance. Although athletic performance may be enhanced by training programs that are compatible with an individuals body clock, the ability to perform and train at various times has an adaptive response which appears to over-ride these naturally inherent rhythms.

Pharmacokinetics of extracellular melatonin in Siberian hamster forebrain

In vivo brain microdialysis was used to characterize the pharmacokinetics of subcutaneously injected melatonin in the anterior hypothalamic-preoptic area (AH-POA) of the male Siberian hamster. Animals with a microdialysis probe implanted in the AH-POA were treated with a subcutaneous melatonin injection at 0900 h (3 h after lights-on) or 2000 h (2 h prior to lights-off). Treatment with 2.5 or 0.25 mg/kg dosages of melatonin in saline vehicle induced peak concentrations of melatonin in AH-POA microdialysates within 20 min of injection (165 ± 34 and 18 ± 8 pg/20 min, respectively). For the 2.5 and 0.25 mg/kg dosages, the half-life of the absorbed melatonin ( t 1 2 elimination) was less than 20 min, and the concentrations fell to baseline within 60 min after injection. There were no significant time of day effects on the kinetic profile of extracellular melatonin associated with either of these dosages. These results confirm the rapid accumulation and clearance of extracellular melatonin in the vicinity of its putative target tissues.

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.

Influence of the time of day on physical performance in patients with coronary artery disease

The exercise training workload for cardiac patients is determined from the peak heart rate achieved safely during a stress test. Circadian rhythms may play a key role in changing physiological responses to the stress test. Therefore, the purpose of this study was to evaluate the influence of the time of day on cardiopulmonary and metabolic responses in highly trained men with coronary artery disease. A group of 15 patients with coronary artery disease [53.5 (SD 6) years] performed two sessions of graded tests to exhaustion: one session was performed at 10 a.m. and the second at 5 p.m. in randomized order. Treadmill velocity was kept constant at a speed of 4.8 km h-1 starting with an elevation of 0% which was increased thereafter by 2.5% every 3 min. At rest the results revealed that only oxygen uptake was significantly lower (P < 0.05) in the morning compared to that observed in the evening [2.9 (SD 0.4) compared to 3.5 (SD 0.5) ml O2.kg-1.min-1, respectively]. During exercise, differences due to time of day were found in the variables of maximal oxygen uptake which were significantly higher (P < 0.05) in the evening than in the morning [34.2 (SD 2.6) and 40.8 (SD 2.5) ml O2.kg-1.min-1, respectively]. These data indicated that in these well-trained coronary artery disease patients there was a significant time of day effect associated with metabolic responses following stress-testing.

Activity-stress ulcers in rats: The role of preentrainment to meal time

Rats housed in activity wheels (A-W) or hanging cages (HC) received food restriction to 4 h/day for 15 days. Food was given at fixed times to entrain the feeding entrainable oscillator or at irregular times to prevent entrainment. One half of the rats received food in the light phase, the other half in the dark phase of the light-dark cycle. Food was then reduced to 6 g/day for 4 days for A-W rats of 7 days for HC rats. Stomachs were removed 24 h after the last meal and the ulcerated area was quantified. Twenty one of 32 A-W rats and 19 of 32 HC rats had ulcers in the glandular stomach. Ulcers were significantly larger in A-W rats ( p < 0.01). Activity levels (in A-W rats), % body weight loss and terminal body weight (in both groups) were significantly correlated with the area of ulcers. There was no significant time of day effect on the ulcer severity. However, an unexpected finding was that for A-W rats, those fed at fixed times had larger ulcers than those fed at irregular times ( p < 0.01) while HC rats showed an expected trend in the opposite direction. One possible explanation for this result is that for A-W rats, the reduced food supply at an expected time of day generated a greater stress response than in rats whose feeding time was unpredictable.