Phase Angle of Entrainment in Morning‐ and Evening‐Types under Naturalistic Conditions

Differences in morningness‐eveningness among humans are commonly ascribed to circadian parameters, such as circadian period and responsivity to environmental time cues, as well as homeostatic sleep drive. Light is the primary synchronizer of the human biological clock, and if circadian differences exist between morning and evening types, they should have different phase angles of entrainment to the light/dark cycle; that is, morning and evening types should have different patterns of light exposure relative to endogenous circadian phase (ECP). When phase angle of entrainment is strictly defined as the relationship between a marker of ECP and the timing of light exposure, such differences have been demonstrated in the laboratory under controlled light/dark cycles and have recently been shown under conditions of spring and summer light exposure outside the laboratory, taking into account the variable intensity of light. Here, we report similar results from a large (n=66), diverse cohort of morning and evening types across the age span studied at all different times of the year. Differences between morning and evening types in light exposure relative to ECP, indicative of a difference in the phase angle of entrainment to the external light/dark cycle, were found. Specifically, evening types, compared to morning types, had a higher ratio of phase advancing to phase delaying by light. We interpret this as indicating a longer circadian period (τ) in evening types.     

Circadian Rhythms in Hot Flashes in Natural and Surgically-Induced Menopause

The aim of this study was to investigate arcadian and ultradian variations in menopausal hot flash. The number of hot flashes per 2-hr period was collected from 25 diurnally-active, perimenopausal women for 1 week in January or February of each year for 3 consecutive years. Fourteen women were experiencing natural menopause (NM) (mean age 51.9 years) and 11 were experiencing surgically-induced menopause (SIM) (mean age 52.0 years). The difference in the number of hot flashes between the two types of menopause at each clock time was not statistically significant; neither was the mean number of hot flashes per 24 hr different between the two groups (Student's f-test). Data when normalized for each woman and placed end-to-end revealed by cosinor analysis circadian rhythmicity in the SIM group (P =0.02) but not in the NM group. A 12-hr periodicity was detected in both groups (P< 0.001 for both). An 8-hr rhythm was detected only for the NM group (P = 0.04). Both groups combined exhibited statistically significant rhythmicities with periods of 24 hr (p= 0.003), 12 hr (P<0.001) and 8 hr (P= 0.005). Regardless of the type of menopause, the women could be separated into two groups based on the temporal pattern of hot flashes during the day. One group was defined by the occurrence of peak frequency of flashes during the morning (0400–0959), while the second group was defined by the occurrence of the peak in the evening (1600–2159). The difference between the two groups in the number of hot flashes during the morning wasstatistically significant (Student's r-test, P = 0.009) as was the number of hot flashes in the evening (Student's r-test, P= 0.03).     

Circadian rhythms in hot flashes in natural and surgically-induced menopause

The aim of this study was to investigate circadian and ultradian variations in menopausal hot flash. The number of hot flashes per 2-hr period was collected from 25 diurnally-active, perimenopausal women for 1 week in January or February of each year for 3 consecutive years. Fourteen women were experiencing natural menopause (NM) (mean age 51.9 years) and 11 were experiencing surgically-induced menopause (SIM) (mean age 52.0 years). The difference in the number of hot flashes between the two types of menopause at each clock time was not statistically significant; neither was the mean number of hot flashes per 24 hr different between the two groups (Student's t-test). Data when normalized for each woman and placed end-to-end revealed by cosinor analysis circadian rhythmicity in the SIM group (P = 0.02) but not in the NM group. A 12-hr periodicity was detected in both groups (P less than 0.001 for both). An 8-hr rhythm was detected only for the NM group (P = 0.04). Both groups combined exhibited statistically significant rhythmicities with periods of 24 hr (P = 0.003), 12 hr (P less than 0.001) and 8 hr (P = 0.005). Regardless of the type of menopause, the women could be separated into two groups based on the temporal pattern of hot flashes during the day. One group was defined by the occurrence of peak frequency of flashes during the morning (0400-0959), while the second group was defined by the occurrence of the peak in the evening (1600-2159).(ABSTRACT TRUNCATED AT 250 WORDS)     

Daytime naps in darkness phase shift the human circadian rhythms of melatonin and thyrotropin secretion

To systematically determine the effects of daytime exposure to sleep in darkness on human circadian phase, four groups of subjects participated in 4-day studies involving either no nap (control), a morning nap (0900-1500), an afternoon nap (1400-2000), or an evening nap (1900-0100) in darkness. Except during the scheduled sleep/dark periods, subjects remained awake under constant conditions, i.e., constant dim light exposure (36 lx), recumbence, and caloric intake. Blood samples were collected at 20-min intervals for 64 h to determine the onsets of nocturnal melatonin and thyrotropin secretion as markers of circadian phase before and after stimulus exposure. Sleep was polygraphically recorded. Exposure to sleep and darkness in the morning resulted in phase delays, whereas exposure in the evening resulted in phase advances relative to controls. Afternoon naps did not change circadian phase. These findings indicate that human circadian phase is dependent on the timing of darkness and/or sleep exposure and that strategies to treat circadian misalignment should consider not only the timing and intensity of light, but also the timing of darkness and/or sleep.     

Effects of constant darkness and constant light on circadian organization and reproductive responses in the ram

The relationship between circadian rhythms in the blood plasma concentrations of melatonin and rhythms in locomotor activity was studied in adult male sheep (Soay rams) exposed to 16-week periods of short days (8 hr of light and 16 hr of darkness; LD 8:16) or long days (LD 16:8) followed by 16-week periods of constant darkness (dim red light; DD) or constant light (LL). Under both LD 8:16 and LD 16:8, there was a clearly defined 24-hr rhythm in plasma concentrations of melatonin, with high levels throughout the dark phase. Periodogram analysis revealed a 24-hr rhythm in locomotor activity under LD 8:16 and LD 16:8. The main bouts of activity occurred during the light phase. A change from LD 8:16 to LD 16:8 resulted in a decrease in the duration of elevated melatonin secretion (melatonin peak) and an increase in the duration of activity corresponding to the changes in the ratio of light to darkness. In all rams, a significant circadian rhythm of activity persisted over the first 2 weeks following transfer from an entraining photoperiod to DD, with a mean period of 23.77 hr. However, the activity rhythms subsequently became disorganized, as did the 24-hr melatonin rhythms. The introduction of a 1-hr light pulse every 24 hr (LD 1:23) for 2 weeks after 8 weeks under DD reinduced a rhythm in both melatonin secretion and activity: the end of the 1-hr light period acted as the dusk signal, producing a normal temporal association of the two rhythms. Under LL, the 24-hr melatonin rhythms were disrupted, though several rams still showed periods of elevated melatonin secretion. Significant activity rhythms were either absent or a weak component occurred with a period of 24 hr. The introduction of a 1-hr dark period every 24 hr for 2 weeks after 8 weeks under LL (LD 23:1) failed to induce or entrain rhythms in either of the parameters. The occurrence of 24-hr activity rhythm in some rams under LL may indicate nonphotoperiodic entrainment signals in our experimental facility. Reproductive responses to the changes in photoperiod were also monitored. After pretreatment with LD 8:16, the rams were sexually active; exposure to LD 16:8, DD, or LL resulted in a decline in all measures of reproductive function. The decline was slower under DD than LD 16:8 or LL.(ABSTRACT TRUNCATED AT 400 WORDS)     

THE STATHMOKINETIC METHOD IN VIVO TIME-RESPONSE WITH SPECIAL REFERENCE TO CIRCADIAN VARIATIONS IN EPIDERMAL CELL PROLIFERATION IN THE HAIRLESS MOUSE

Groups of hairless mice were injected i.p. with a stathmokinetic dose of 0·15 mg colcemid at seven different times of the day and animals killed 0, 15 and 30 min, 1, 2, 3 and 4 hr after the injection. The proportion of cells in metaphase and ana/telophase was determined in histological sections. The results showed a transient accumulation of metaphases about 30 min after the injection, followed by an increase in metaphases from 1 to 4 hr. Therefore, no value before 1 hr after the colcemid injection should be used in calculations of the mitotic rate. The presence of circadian rhythms with high mitotic activity in the morning and low activity in the evening was confirmed. It is shown by regression analyses that the accumulation period of 4 hr is sufficiently short to reflect circadian variations in epidermal cell proliferation and that the 4-hr accumulation value alone is sufficient to estimate the mitotic rate.     

Circadian Assessment of Lipids in the Hyperphagic Obese Rat Compared with Lean Litter-Mates

Time and feeding influences on cholesterol, triglyceride, glucose and insulin levels, and serum cholinesterase activity were assessed in a genetically-hyperlipidemic hyperphagic obese rat model, and compared with its lean litter-mate. Following a 28-day acclimation to a 12-hr light/dark cycle, blood samples were obtained every 2 hr from rats via tail bleed for a 24-hr period. Synchronization with other animal studies was established by endogenous serum Cortisol levels [acrophase 18-20 hr after light onset (HALO) in both groups]. Triglycerides cholesterol, insulin and glucose levels were significantly elevated in obese versus lean rats. Obese rats were observed to feed throughout the 24-hr cycle, whereas lean litter-mates ate only during the dark cycle. No circadian rhythmicity was found in glucose levels with either rat group. Insulin levels were not correlated. Although triglyceride levels peaks at 13 HALO in lean rats, no pattern was observed in obese rats. Cholesterol levels were unchanged with time in either group. Cholinesterase activity followed a circadian rhythm in the lean, but not obese, rats with an acrophase estimated at 8 HALO. In contrast to previous reports, enzyme activity was not correlated with triglyceride levels in either rat group. Circadian similarities in insulin levels between rat groups suggest changes in insulin metabolism and/or secretion which are likely to be independent of feeding or activity. Conversely, triglyceride levels remained elevated throughout the 24-hr period in obese rats, whereas significant increases were observed in lean rats during the dark active cycle. These data suggest that triglyceride levels, and not insulin and cholesterol levels, are most likely dependent on feeding patterns.     

Circadian Assessment of Lipids in the Hyperphagic Obese Rat Compared with Lean Litter-Mates

Time and feeding influences on cholesterol, triglyceride, glucose and insulin levels, and serum cholinesterase activity were assessed in a genetically-hyperlipidemic hyperphagic obese rat model, and compared with its lean litter-mate. Following a 28-day acclimation to a 12-hr light/dark cycle, blood samples were obtained every 2 hr from rats via tail bleed for a 24-hr period. Synchronization with other animal studies was established by endogenous serum Cortisol levels [acrophase 18–20 hr after light onset (HALO) in both groups]. Triglycerides cholesterol, insulin and glucose levels were significantly elevated in obese versus lean rats. Obese rats were observed to feed throughout the 24-hr cycle, whereas lean litter-mates ate only during the dark cycle. No circadian rhythmicity was found in glucose levels with either rat group. Insulin levels were not correlated. Although triglyceride levels peaks at 13 HALO in lean rats, no pattern was observed in obese rats. Cholesterol levels were unchanged with time in either group. Cholinesterase activity followed a circadian rhythm in the lean, but not obese, rats with an acrophase estimated at 8 HALO. In contrast to previous reports, enzyme activity was not correlated with triglyceride levels in either rat group. Circadian similarities in insulin levels between rat groups suggest changes in insulin metabolism and/or secretion which are likely to be independent of feeding or activity. Conversely, triglyceride levels remained elevated throughout the 24-hr period in obese rats, whereas significant increases were observed in lean rats during the dark active cycle. These data suggest that triglyceride levels, and not insulin and cholesterol levels, are most likely dependent on feeding patterns.     

The Effects of Various Lighting Schedules Upon the Orcadian Rhythms of 23 Liver or Brain Enzymes of C57Bl/6J Mice

The activities of 23 brain or liver enzymes were studied in 5–6 week old C57BL/6JNctr male and female mice that had been fed ad libitum and standardized for 2 weeks to either (1) 12 hr of light (0600-1800) alternating with 12 hr of darkness (1800-0600) (LD 12:12), (2) staggered sequences of 12 hr of light and 12 hr of dark (SLD 12:12) or (3) continuous illumination (LL 12:12) for 2 weeks. Mice in the LD 12:12 and LL 12:12 experiments were killed at 4 hr intervals along a 24-hr span in order to sample at six different circadian stages. Lighting schedules for mice in the SLD 12:12 experiment were organized such that six different circadian stages were sampled when all mice were killed at one time of day.

All 23 enzymes demonstrated a prominent circadian rhythm in at least one of the experiments. Moreover, about two-thirds of the enzymes in LD and SLD 12:12 had a statistically significant fit to a 24-hr cosine curve, while only one-third of the enzymes in LL 12:12 had significant fits to cosine curves. Peak activities of enzymes from mice in LD 12:12 were clustered at the time of transition from light to dark. This was also the trend for the activities of enzymes from mice in SLD 12:12, but resynchronization did not appear completed within the 2-week span. This, along with the observation that mesors (mean 24-hr activity) were reduced and amplitudes altered, indicated that the 2-week standardization period was not sufficient for some enzymes. Times of peak activities, mesors and amplitudes were affected for most enzymes from mice in the LL 12:12 environment. This suggests that individual mice became desynchronized from one another with respect to the original light-dark schedule and that rhythms were altered or lost because individual mice were free running with frequencies different from 24 hr.     

The Effects of Various Lighting Schedules Upon the Orcadian Rhythms of 23 Liver or Brain Enzymes of C57Bl/6J Mice

The activities of 23 brain or liver enzymes were studied in 5-6 week old C57BL/6JNctr male and female mice that had been fed ad libitum and standardized for 2 weeks to either (1) 12 hr of light (0600-1800) alternating with 12 hr of darkness (1800-0600) (LD 12:12), (2) staggered sequences of 12 hr of light and 12 hr of dark (SLD 12:12) or (3) continuous illumination (LL 12:12) for 2 weeks. Mice in the LD 12:12 and LL 12:12 experiments were killed at 4 hr intervals along a 24-hr span in order to sample at six different circadian stages. Lighting schedules for mice in the SLD 12:12 experiment were organized such that six different circadian stages were sampled when all mice were killed at one time of day.

All 23 enzymes demonstrated a prominent circadian rhythm in at least one of the experiments. Moreover, about two-thirds of the enzymes in LD and SLD 12:12 had a statistically significant fit to a 24-hr cosine curve, while only one-third of the enzymes in LL 12:12 had significant fits to cosine curves. Peak activities of enzymes from mice in LD 12:12 were clustered at the time of transition from light to dark. This was also the trend for the activities of enzymes from mice in SLD 12:12, but resynchronization did not appear completed within the 2-week span. This, along with the observation that mesors (mean 24-hr activity) were reduced and amplitudes altered, indicated that the 2-week standardization period was not sufficient for some enzymes. Times of peak activities, mesors and amplitudes were affected for most enzymes from mice in the LL 12:12 environment. This suggests that individual mice became desynchronized from one another with respect to the original light-dark schedule and that rhythms were altered or lost because individual mice were free running with frequencies different from 24 hr.     

Therapeutic advantage of unequal dosing of theophylline in patients with nocturnal asthma

Two theophylline treatments were compared in a randomized, multiple-dose, crossover study on 20 patients present with nonallergic bronchial asthma. Both products (E = Euphyllin CR, A = Afonilum Retard) were capsules containing micropellets. They were administered according to the recommendations of the manufactures and differed in the total daily theophylline dose (642 mg versus 500 mg), the partition of this dose (1/3 in the morning and 2/3 in the evening versus equal amounts in the morning and evening) and the timing of the evening dose (2200 hr versus 2000 hr). The patients were off oral theophyllines at least 2 days prior to study onset and no other drugs were allowed to be administered during the testing periods. On the 4th day of each study period, serum theophylline concentrations (STC) and peak expiratory flow rate (PEF) were determined every 2 hr. Compared with the 24-hr PEF reference profile taken prior to study onset, both theophylline treatments produced a significantly higher 24-hr PEF average (mesor). Treatment E resulted in significantly higher mesor than A; in addition, the PEF amplitude relative to the mesor was reduced by treatment E when compared with placebo.     

Treatment of Asthma by a Controlled-Release Theophylline Tablet Formulation: A Review of the North American Experience with Nocturnal Dosing

As many as 80 percent of asthmatics experience nighttime or early-morning episodes, which are difficult to treat and potentially fatal. The greater-than-normal amplitude of circadian airflow variation in many asthmatics contributes heavily to the genesis of the early ‘morning dip’. Beta-agonists and corticosteroids are of limited usefulness in nocturnal asthma, and slow-release theophylline drugs, while potentially effective, vary in 24-hr blood profile and hence their influence on nocturnal episodes. Traditional 12-hr ‘symmetric’ theophylline regimens, instead of meeting increased nocturnal demands, may actually produce lower night- than daytime blood levels. On the other hand, appropriately timed administration of a once-daily theophylline drug might provide maximum blood levels when needed and help stabilize 24-hr airflow.

Accumulated data, summarized in this review, demonstrate the chronotherapeutic potential of single-daily evening doses of a controlled-release theophylline preparation (Uniphyl® 400-mg tablets*) in nocturnal and early morning asthma. Nighttime blood concentrations with this regimen were higher than were those with Theo-Dur® tablets, ? B.I.D., in the same total daily doses, or with once-daily morning Uniphyl administration. In fed and fasted subjects, evening administration of Uniphyl 400-mg tablets was well tolerated and did not lead to ‘dose dumping.’ Clinically, this treatment demonstrated advantages over B.I.D. theophylline, over single-daily morning regimens, and over prior theophylline therapy. Advantages of the evening regimen included better early-morning airflow (without significant decline later in the day), more effective symptom control, better patient acceptance, fewer night awakenings, and the obvious convenience of once-daily dosing. In addition, lung function showed greater stability, throughout the day, with once-daily evening therapy than with traditional 12 hr dosing.

Uniphyl 400-mg tablets may be administered once daily to provide maximum blood levels at the time of peak bronchoconstriction, whether at night or during the day.     

Administration-time-dependency of the pharmacokinetic behavior and therapeutic effect of a once-a-day theophylline in asthmatic children

Using a double-blind, placebo-control, crossover study design, 8 asthmatic children (8-15 years) were evaluated for temporal patterns in airways function throughout separate study periods when treatment was placebo or Theo-24 once-daily on separate occasions at 0600, 1500 or 2100 hr. During 39-hr in-hospital observations, pulmonary function and serum theophylline concentrations (STC) were assessed every 3 hr under all treatments. The pharmacokinetics of Theo-24 varied greatly depending on the dosing time. For the afternoon and evening dosings, the Cmax, Tmax, AUC, % swing, % fluctuation, % AUC fluctuation, % nocturnal excess and Cav(2-6 hr) were all statistically significantly greater than for the morning dosing. Compared with the placebo regimen, dosing patients with Theo-24 at 1500 hr disrupted circadian patterns of airways function, especially airways patency, while dosing at 2100 hr, reduced the amplitude and shifted the acrophase of several spirometric measures to a slightly earlier time. Theo-24 treatment irrespective of dosing time resulted in comparable enhancement of the group 24-hr mean, minimum and maximum values of airways patency with reference to placebo baselines. Theo-24 dosing at 1500 or 2100 hr, however, resulted in the best effect on the airways as assessed by the 24-hr mean FEV 1.0 level in 7 of the 8 asthmatic children. When the drug was given at 1500 hr, the time of lowest FEV 1.0 was shifted from the nighttime hours in 5 of 8 patients. These findings suggest that clinicians need to individualize the theophylline dosing schedule of patients to best control the symptoms of asthma.     

Treatment of asthma by a controlled-release theophylline tablet formulation: a review of the North American experience with nocturnal dosing

As many as 80 percent of asthmatics experience nighttime or early-morning episodes, which are difficult to treat and potentially fatal. The greater-than-normal amplitude of circadian airflow variation in many asthmatics contributes heavily to the genesis of the early 'morning dip'. Beta-agonists and corticosteroids are of limited usefulness in nocturnal asthma, and slow-release theophylline drugs, while potentially effective, vary in 24-hr blood profile and hence their influence on nocturnal episodes. Traditional 12-hr 'symmetric' theophylline regimens, instead of meeting increased nocturnal demands, may actually produce lower night- than daytime blood levels. On the other hand, appropriately timed administration of a once-daily theophylline drug might provide maximum blood levels when needed and help stabilize 24-hr airflow. Accumulated data, summarized in this review, demonstrate the chronotherapeutic potential of single-daily evening doses of a controlled-release theophylline preparation (Uniphyl 400-mg tablets) in nocturnal and early morning asthma. Nighttime blood concentrations with this regimen were higher than were those with Theo-Dur tablets, B.I.D., in the same total daily doses, or with once-daily morning Uniphyl administration. In fed and fasted subjects, evening administration of Uniphyl 400-mg tablets was well tolerated and did not lead to 'dose dumping.' Clinically, this treatment demonstrated advantages over B.I.D. theophylline, over single-daily morning regimens, and over prior theophylline therapy. Advantages of the evening regimen included better early-morning airflow (without significant decline later in the day), more effective symptom control, better patient acceptance, fewer night awakenings, and the obvious convenience of once-daily dosing. In addition, lung function showed greater stability, throughout the day, with once-daily evening therapy than with traditional 12 hr dosing. Uniphyl 400-mg tablets may be administered once daily to provide maximum blood levels at the time of peak bronchoconstriction, whether at night or during the day.     

Evening physical activity alters wrist temperature circadian rhythmicity

The adequate time to perform physical activity (PA) to maintain optimal circadian system health has not been defined. We studied the influence of morning and evening PA on circadian rhythmicity in 16 women with wrist temperature (WT). Participants performed controlled PA (45?min continuous-running) during 7 days in the morning (MPA) and evening (EPA) and results were compared with a no-exercise-week (C). EPA was characterized by a lower amplitude (evening: 0.028?±?0.01?°C versus control: 0.038?±?0.016?°C; p?<?0.05) less pronounced second-harmonic (power) (evening: 0.41?±?0.47 versus morning: 1.04?±?0.59); and achrophase delay (evening: 06:35?±?02:14?h versus morning: 04:51?±?01:11?h; p?<?0.05) as compared to MPA and C. Performing PA in the late evening might not be as beneficial as in the morning.     

Circannual Variation of Cell Proliferation in Lymphoid Organs and Bone Marrow of Dbf1 Male Mice on Three Lighting Regimens

The case of a 40-year-old sighted woman with free-running sleep-wake and melatonin rhythms is presented. The subject was studied for 102 days. During the pre-treatment period, both the sleep-wake and melatonin rhythms had a period of 25.1 hr, similar to the average period of humans living in temporal isolation. Treatment consisted of bright artifical light exposure (2500 lx Vita-Lite) for 2 hr each day upon awakening. Clock time of light exposure was held constant for 6 days and then slowly advanced until the subject was arising at her desired time of day. The subject continued the light treatment at home and was able to live on a 24-hr day for the 30-day follow-up study. While other factors may be operating in this situation, it is possible that the light treatment caused the stabilization of the free-running rhythms, advancement to a normal phase and entrainment to the 24-hr day. We suspect that the tendency to free-run was related to sleep onsets that were abnormally delayed relative to the circadian phase response curve for light. By scheduling a 2-hr pulse of bright light each morning, this tendency to delay would be counteracted by light-induced advances, resulting in normal entrainment.     

Entrainment of A Free-Running Human with Bright Light?

The case of a 40-year-old sighted woman with free-running sleep-wake and melatonin rhythms is presented. The subject was studied for 102 days. During the pre-treatment period, both the sleep-wake and melatonin rhythms had a period of 25.1 hr, similar to the average period of humans living in temporal isolation. Treatment consisted of bright artifical light exposure (2500 lx Vita-Lite) for 2 hr each day upon awakening. Clock time of light exposure was held constant for 6 days and then slowly advanced until the subject was arising at her desired time of day. The subject continued the light treatment at home and was able to live on a 24-hr day for the 30-day follow-up study. While other factors may be operating in this situation, it is possible that the light treatment caused the stabilization of the free-running rhythms, advancement to a normal phase and entrainment to the 24-hr day. We suspect that the tendency to free-run was related to sleep onsets that were abnormally delayed relative to the circadian phase response curve for light. By scheduling a 2-hr pulse of bright light each morning, this tendency to delay would be counteracted by light-induced advances, resulting in normal entrainment.     

Circadian Preference and Thinking Styles: Implications for School Achievement

Research has shown that thinking styles could have an influence on academic achievement. Previous studies have described that evening types are usually right-thinkers who tend to be creative and intuitive, whereas morning types tend to be left-thinkers who prefer verbal and analytic strategies in processing information. However, these studies have been realized among undergraduates, who have more freedom to choose their time schedules according to their circadian preference than adolescents or adult workers. On other hand, the relationship between thinking styles and circadian preference has not been analyzed considering school achievement. The present study aims (1) to investigate the relationship between circadian preference, that is, behavioral differences in circadian rhythmic expression, and thinking styles, referring to the preference toward information processing typical of the right versus the left cerebral hemisphere; and (2) to test the implications for self-reported school achievement. A sample of 1134 preadolescents and adolescents (581 girls; mean?±?SD age: 12.1?±?1.47, range: 10–14?yrs) completed the Morningness-Eveningness Scale for Children (MESC) as measure of circadian preference (morning, neither, or evening types), the Hemispheric Preference Test (HPT), conceived as a tool to measure thinking styles (right-, balanced-, and left-thinkers), and self-reported school achievement. Results indicated a greater percentage of left-thinkers among morning types and a greater percentage of right-thinkers among evening types. No differences were found among balanced-thinkers and neither types. Morning types and left-thinkers reported the highest subjective level of achievement, followed by evening types and left-thinkers, and morning types and right-thinkers. Evening types and right-thinkers reported the lowest subjective level of achievement. Finally, multivariate regression analysis indicated that age, left hemisphere and morning preferences accounted for 14.2% of total variance on self-reported achievement.     

Circadian Rhythm of Gastric Acid Secretion in Active Duodenal Ulcer: Chronobiological Statistical Characteristics and Comparison of Acid Secretory and Plasma Gastrin Patterns with Healthy Subjects and Post-Vagotomy and Pyloroplasty Patients

Twenty-one male patients with active duodenal ulcer underwent hourly 24-hr gastric acid collections under controlled, calorically deprived conditions. The 24-hr hourly acid secretory output for the group displayed a statistically significant (p < 0.001) rhythm, with peak rates occurring during the evening hours and low rates during the early morning hours, by population-mean cosinor statistical analysis. Population-mean cosinor analysis also verified the occurrence of a significant (p=0.034) circadian rhythm in unstimulated acid secretion in a group (N=14) of healthy male subjects similarly studied and reported previously. In contrast, population-mean cosinor analysis confirmed the absence of any detectable circadian rhythm in unstimulated acid secretion in a group (N=17) of post-vagotomy and pyloroplasty patients studied 2-11 years after surgery. Population-mean cosinor analysis of 4-hr plasma gastrin determinations, obtained in all groups during the 24-hr gastric acid collection, revealed an absence of any detectable circadian rhythm in plasma gastrin. This latter finding is compatible with the interpretation that the circadian rhythm of unstimulated gastric acid secretion, observed in the clinically healthy and active ulcer groups, is unrelated to changes in plasma gastrin levels. The employment of quantitative chronobiological inferential statistical techniques is important to the analysis of any time-dependent measurement in gastrointestinal function, of which gastric acidity is one example.