Lack of diurnal variation in plasma levels of androstenedione, testosterone, estrone and estradiol in postmenopausal women

Plasma 4-en-androstenedione, testosterone, estradiol and estrone were measured during the day in six healthy postmenopausal women and in six breast cancer patients, three of whom received treatment with glucocorticoids. Blood samples were obtained at 8 a.m., 10 a.m., 12 noon, 4 p.m., 8 p.m. and 12 midnight. There was a considerable variation in plasma levels of all steroids during the day; for 4-en-androstenedione the mean within patient coefficient variation was 61.4%, for testosterone it was 28.9%, for estrone it was 17.8% and for estradiol it was 29.2%. While the plasma levels for all steroids tended to be higher in the morning than in the evening, the changes were not statistically significant (Friedman's test: P greater than 0.10). We conclude that although a moderate diurnal variation in the plasma level of these steroids may occur, it is of a moderate magnitude compared to variations due to other causes.     

Circadian Dependence of Infarct Size and Acute Heart Failure in ST Elevation Myocardial Infarction

Objectives

There are conflicting data on the relationship between the time of symptom onset during the 24-hour cycle (circadian dependence) and infarct size in ST-elevation myocardial infarction (STEMI). Moreover, the impact of this circadian pattern of infarct size on clinical outcomes is unknown. We sought to study the circadian dependence of infarct size and its impact on clinical outcomes in STEMI.

Methods

We studied 6,710 consecutive patients hospitalized for STEMI from 2006 to 2009 in a tropical climate with non-varying day-night cycles. We categorized the time of symptom onset into four 6-hour intervals: midnight–6:00 A.M., 6:00 A.M.–noon, noon–6:00 P.M. and 6:00 P.M.–midnight. We used peak creatine kinase as a surrogate marker of infarct size.

Results

Midnight–6:00 A.M patients had the highest prevalence of diabetes mellitus (P = 0.03), more commonly presented with anterior MI (P = 0.03) and received percutaneous coronary intervention less frequently, as compared with other time intervals (P = 0.03). Adjusted mean peak creatine kinase was highest among midnight–6:00 A.M. patients and lowest among 6:00 A.M.–noon patients (2,590.8±2,839.1 IU/L and 2,336.3±2,386.6 IU/L, respectively, P = 0.04). Midnight–6:00 A.M patients were at greatest risk of acute heart failure (P<0.001), 30-day mortality (P = 0.03) and 1-year mortality (P = 0.03), while the converse was observed in 6:00 A.M.–noon patients. After adjusting for diabetes, infarct location and performance of percutaneous coronary intervention, circadian variations in acute heart failure incidence remained strongly significant (P = 0.001).

Conclusion

We observed a circadian peak and nadir in infarct size during STEMI onset from midnight–6:00A.M and 6:00A.M.–noon respectively. The peak and nadir incidence of acute heart failure paralleled this circadian pattern. Differences in diabetes prevalence, infarct location and mechanical reperfusion may account partly for the observed circadian pattern of infarct size and acute heart failure.     

Adipokine levels are altered by shiftwork: a preliminary study

Shiftwork is often associated with metabolic diseases, and in the past few years, several cytokines have been postulated to contribute to various diseases, including insulin resistance. The aim of this study was to compare the concentrations of adiponectin, tumor necrosis factor-α (TNF-α), and interleukin-6 (IL-6) in samples of young adult men exposed to a fixed (i) night shift (n = 9), working from 22:00 to 06:00 h; (ii) early morning shift (n = 6), working from 06:00 to 14:00 h; and (iii) day shift (n = 7), working from 08:00 to 17:00 h. The fixed night-shift and early-morning-shift samples were considered collectively as a shiftworker group given their work times. Blood samples were collected during the regular working day at 4-h intervals over the course of 24 h, thus totaling six samples. Morphological and physical activity parameters did not differ between the three groups. Total energy intake was lowest on the early morning shifts (p 相似文献   

秦岭川金丝猴的昼间活动时间分配

1999年12月至2004年11月,通过野外直接跟踪观察,采用焦点取样和瞬时记录的方法,对秦岭川金丝猴西梁猴群的昼间活动时间分配进行了研究。将川金丝猴的昼间活动定义为摄食、休息、理毛、移动和其他行为5 种类型,结果发现：川金丝猴昼间活动中有两个摄食高峰,分别在每天的上午和下午,中午有一个较长时间的休息期。川金丝猴昼间的主要行为类型是摄食和休息（约占全部活动时间的62%）,各种行为依所占时间比例依次为：摄食（34.64 ± 1.70%）、休息（26.83 ± 1.69%）、理毛（11.58 ± 0.96%）、移动（18.93 ±1.08%）和其他行为（8.02 ± 0.82%）。在不同季节各种行为类型所占时间比例有明显的变化,表现为摄食和休息行为占昼间活动时间比例在夏（75.00%）、秋季（74.15%） 大于春（52.74%）、冬季（56.64%）;而移动、理毛和其他行为所占时间比例之和在夏（25.00%）、秋季（ 25.85%） 则明显小于冬（ 43.4%）、春季（47.3%）。不同季节间的活动时间分配经非参数检验（ Kruskal Wallis H test,N = 199）,理毛行为（ x² =11.438,df = 3,P < 0.05）有显著差异,摄食（x² = 20.469,df = 3,P < 0.01）、休息（x² = 27.235,df = 3,P < 0.01）、移动（x² = 24.110,df = 3,P < 0.01） 和其他行为（ x² = 60.810,df = 3,P < 0.01） 季节间差异非常显著;除摄食行为外,其余各行为类型的时间分配在不同性别-年龄组间也存在显著差异（P < 0.05）。     

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

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

Circadian variation in the onset of acute cerebral ischemia: ethiopathogenetic correlates in 80 patients given angiography.

In a continuous series of 80 acute ischemic hemispheric strokes, the onset of symptoms was between 6:01 a.m. and noon in 45% of cases, between noon and 6:00 p.m. in 22.5%, between 6:01 p.m. and midnight in 31.25%, and between midnight and 6:00 a.m. in 1.25% (p less than 0.0001). By means of angiography and computerized tomography, and by detection of arterial and cardiac sources of emboli, four stroke subtypes were identified. Embolic and thrombotic strokes had their most frequent onset between 6:01 a.m. and noon (45% and 71%, respectively), whereas strokes of unknown origin and lacunar strokes were randomly distributed between 6:01 p.m. and midnight. The morning activation of the catecholaminergic system can account for this pattern of circadian onset of ischemic stroke.     

Circadian Variation in the Onset of Acute Cerebral Ischemia: Ethiopathogenetic Correlates in 80 Patients Given Angiography

In a continuous series of 80 acute ischemic hemispheric strokes, the onset of symptoms was between 6:01 a.m. and noon in 45% of cases, between noon and 6:00 p.m. in 22.5%, between 6:Ol p.m. and midnight in 31.25%, and between midnight and 6:00 a.m. in 1.25% (p < 0.0001). By means ofangiography and computerized tomography, and by detection of arterial and cardiac sources of emboli, four stroke subtypes were identified. Embolic and thrombotic strokes had their most frequent onset between 6:01 a.m. and noon (45% and 71%, respectively), whereas strokes of unknown origin and lacunar strokes were randomly distributed between 6:01 p.m. and midnight. The morning activation of the catecholaminergic system can account for this pattern of circadian onset of ischemic stroke.     

Diurnal variations of plasma testosterone in men

Plasma testosterone (T) levels were assayed by a Competitive Protein Binding (CPB) technique in a group of 31 healthy males. In 22 subjects a single blood sample was taken between 8:00 and 9:00 A.M. and the mean T concentration was 6.84 ± 2.11 ng/ml. In the other 9 normal men, blood samples were taken every 4 hours. The existence of temporal variations for testosterone was confirmed by finding the highest mean plasma levels at 4:00 A.M. (9.28 ± 1.17 ng/ml) and lowest mean levels at 8:00 P.M. (2.66 ± 0.52 ng/ml).     

Sleep length as a function of morning shift-start time in irregular shift schedules for train drivers: self-rated health and individual differences

Forty-six male train drivers (mean age = 46.5, SD = 5.1) were recruited to participate in a diary study for 14 consecutive days with questions about their sleep and working hours. A polynomial mixed-effect regression model showed a curvilinear relation ( p < .001) between shift-start time and sleep duration for shifts starting at 03:00-12:00 hand with a near linear increase for ones starting between 04:30 and 09:00 h of approximately 0.7 h for every 1 h the shift was delayed. The longest sleeps were estimated at approximately 8 h before shifts that started at approximately 10:00 h. The shortest sleeps were found for shifts that started before 04:30 h and were estimated at approximately 5 h. Individual differences were estimated with a random-effect standard deviation of 0.51 h, independent of shift start time ( p = .005). One-half of the between-subject variance was explained by subjective health. A one-step decrease in health was associated with a 26 min increase in sleep length. The results have practical implications for constructing shift schedules. Early morning shifts reduced sleep length substantially and should be mixed with later start hours to avoid the accumulation of sleep dept. Delaying the shift-start past 10:00 h had little effect on sleep opportunity; however, delaying shift-start to between 04:30 and 9:00 h had a strong impact on sleep length, with 70% of the extra time used for sleep, suggesting large positive effects for this range of shift-start times.     

A method to evaluate dynamics and periodicity of hormone secretion

Spontaneous hormone secretory dynamics include tonic and pulsatile components and a number of periodic processes. Circadian variations are usually found for melatonin, TSH and GH, with peak secretions at night, and in cortisol secretion, which peaks in the morning. Free thyroxine (FT4) and insulin-like growth factor (IGF)1 levels do not always change with circadian rhythmicity or show only minor fluctuations. Fractional variations explore the dynamics of secretion related to time intervals, and the rate of change in serum levels represents a signal for the receptorial system and the target organ. We evaluated time-related variations and change dynamics for melatonin, cortisol, TSH, FT4, GH and IGF1 levels in blood samples obtained every 4 h for 24 h from eleven healthy males, ages 35-53 years (mean ? SE 43.6 ± 1.7). Nyctohemeral (i.e., day-night) patterns of hormone secretion levels and the fractional rate of variation between consecutive 4-hourly time-qualified hormone serum levels (calculated as percent change from time 1 to time 2) were evaluated for circadian periodicity using a 24 and 12-h cosine model. A circadian rhythm was validated for serum level changes in cortisol with peaks of the 24-h cosine model at 07:48 h, and melatonin, TSH and GH, with phases at 01:35 h, 23:32 h, and 00:00 h, respectively. A weak, but significant, 12-h periodicity was found for FT4 serum levels, with minor peaks in the morning (10:00 h) and evening (22:00 h), and for IGF1, with minor peaks in the morning (07:40 h) and evening (19:40 h). Circadian rhythmicity was found in the 4-hourly fractional variations with phases of increase or surge at 02:00 h for cortisol, 22:29 h for melatonin, 05:14 h for FT4, and 21:19 h for GH. A significant 12-h periodicity was found for the 4-hourly fractional variations of TSH with two peaks in the morning (decrease or drop at 04:42 h) and afternoon (surge at 16:28 h), whereas IGF1 fractional variation changes did not show a significant rhythmic pattern. In conclusion, the calculation of the time-qualified fractional rate of variation allows evaluation of the dynamics of secretion and the specification of the timepoint(s) of maximal change of secretion, not only for hormones whose secretion is characterized by a circadian pattern of variation, but also for hormones that show no circadian or only weak ultradian (12 h) variations (i.e., FT4).     

不同形状城市湿地对周边环境温湿度的影响

2015年春、夏、秋季选择大庆市区5种不同形状特征的城市湿地及周边环境作为研究对象,利用小尺度定量测定的方法,分析城市湿地形状特征对周边环境温、湿效益的影响.结果表明: 不同形状特征的城市湿地均具有增湿降温效应.其中,夏季的增湿降温效应最强,春季其次,秋节最差.形状特征对湿地的降温增湿能力具有显著影响,不规则形状湿地>规则形状湿地(近圆形湿地、近矩形湿地)>长条形状湿地;增湿降温日变化受环境温度影响较大,即早晚弱、中午强,春、秋季增湿降温幅度最大的时段为12:00—14:00,夏季增湿降温幅度最大的时段为14:00—16:00.     

贵州习水国家级自然保护区红外相机鸟兽监测及活动节律分析

2015年7月至2017年11月,我们利用红外相机对贵州习水国家级自然保护区的鸟类及兽类进行监测。结果表明:(1)共记录到鸟类5目20科56种、兽类5目12科28种,其中国家Ⅰ级重点保护动物有林麝(Moschus berezovskii),国家Ⅱ级重点保护动物有红腹角雉(Tragopan temminckii)、白鹇(Lophura nycthemera)、鹰雕(Nisaetus nipalensis)、中华鬣羚(Capricornis milneedwardsii)等13种。鹰雕为贵州省新记录,白腹锦鸡(Chrysolophus amherstiae)、白眉鸫(Turdus obscurus)等10种为保护区新记录。(2)从中国动物地理区划来看,保护区物种以东洋型(41.67%)为主,南中国型(29.76%)次之;东北型(2.38%)最少。(3)区内4种主要兽类中,毛冠鹿(Elaphodus cephalophus)主要在傍晚活动;赤腹松鼠(Callosciurus erythraeus)日活动节律呈季节性变化,春秋季集中在午间活动,夏季集中在早上活动,冬季则呈现活动双峰,分别是在8:00–10:00及16:00–18:00之间;豪猪(Hystrix brachyura)主要在20:00–24:00之间活动;藏酋猴(Macaca thibetana)秋冬季集中在14:00–16:00活动,而春季则在早上10:00–12:00之间较活跃,夏季也有2个活动高峰,分别是在12:00–14:00及16:00–18:00。2种主要雉类的活动节律明显不同,红腹锦鸡(Chrysolophus pictus)春夏季都较为集中在午间活动,而秋季主要在6:00–8:00之间;红腹角雉春夏两季活动高峰在早上,秋冬季则是在14:00–16:00之间活动频繁。本监测结果有利于进一步了解和促进此区域的生物多样性及其保护。     

Effect of Sun Light Intensity on the Change of Contents in the Chloroplasts of Tillandsia usneciaes

After the leaves of Tillandsia usneciaes were fixed in 2.5% glutaraldehyde under strong sun light ,some globular objects were found in the chloroplast. These globular objects did not take the ordinary U-Pb double stain but they showed a cyclic change in amount following the change of sum light intensity. At 8 O′clock in the morning,only a few globular objects appeared in the chloroplast, At 10: 00 a. m.,there were several globular objects and they greatly increased at noon and gradually reduced in the afternoon,and finally disappearred at 4: 00 p. m. For detection of periodie acid-reactive complex carbohydrates with silver methenamine staining technique , the globular objects stained black. This result demonstrated that the globular objects may be polymers of intermediat products of the carbon cycle in photosynthesis and C3 compounds in malate decarboxylation.     

Effect of Time of Day on Aerobic Contribution to the 30‐s Wingate Test Performance

The purpose of this study was to evaluate the effects of time of day on aerobic contribution during high‐intensity exercise. A group of 11 male physical education students performed a Wingate test against a resistance of 0.087 kg · kg^?1 body mass. Two different times of day were chosen, corresponding to the minimum (06:00 h) and the maximum (18:00 h) levels of power. Oxygen uptake (V˙O₂) was recorded breath by breath during the test (30 sec). Blood lactate concentrations were measured at rest, just after the Wingate test, and again 5 min later. Oral temperature was measured before each test and on six separate occasions at 02:00, 06:00, 10:00, 14:00, 18:00, and 22:00 h. A significant circadian rhythm was found in body temperature with a circadian acrophase at 18:16±00:25 h as determined by cosinor analysis. Peak power (P_peak), mean power (P_mean), total work done, and V˙O₂ increased significantly from morning to afternoon during the Wingate Test. As a consequence, aerobic contribution recorded during the test increased from morning to afternoon. However, no difference in blood lactate concentrations was observed from morning to afternoon. Furthermore, power decrease was greater in the morning than afternoon. Altogether, these results indicate that the time‐of‐day effect on performances during the Wingate test is mainly due to better aerobic participation in energy production during the test in the afternoon than in the morning.     

Insulin glargine maintains equivalent glycemic control and better lipometabolic control than NPH insulin in type 1 diabetes patients who missed a meal.

Our goal was to investigate blood glucose and lipometabolism control in type 1 diabetes patients who missed breakfast and the accompanying insulin injection of NPH insulin (NPH) or insulin glargine (glargine) as part of a basal-bolus regimen. This was a multi-center, open-label, controlled study in adults (> or =18 years) with HbA (1c)< or =11.5% on insulin therapy with NPH as basal insulin. Patients were randomized to receive prandial insulin plus either bedtime glargine (n=28) or NPH (n=32). Insulin was titrated to target fasting blood glucose levels 80-130 mg/dl at 06:00-07:00. Patients had no intake of insulin or food between 22:00 and 12:00 the next day. The change in blood glucose levels (07:00-11:00) was similar (27.5 mg/dl vs. 35.4 mg/dl), but the mean blood glucose level was higher with glargine vs. NPH at 22:00 (158.2 mg/dl vs. 130.2 mg/dl). During the period without insulin or food intake, blood glucose decreased with glargine (-25.8 mg/dl) and increased with NPH (+9.1 mg/dl; p=0.0284). Nonesterified fatty acid (07:00 and 09:00-12:00) and beta-hydroxybutyrate (07:00 and 10:00-12:00) levels were lower with glargine vs. NPH (both p<0.05). For patients who miss a morning meal, glargine is associated with maintained glycemic and lipometabolic control compared with NPH insulin.     

Circadian and circannual variations in growth and cold resistance of warm acclimated rats and their relationship with the geomagnetic activity

In winter, summer, spring and fall, groups of 200 g Sprague Dawley male rats were kept for 14 days at constant Ta 28°C±°C and LD 12:12(07:00–19:00 h). They were fed a laboratory chow (P) or a semi-purified diet (H). They were weighed at 0, 7 and 14 days. Cold resistance was determined by the fall in rectal temperature during 4 hours of restrained exposure to +1°C either in the morning (09:00 – 13:00 h) or in the afternoon (14:00 – 18:00 h). Rats fed the H diet could better tolerate cold exposure in the morning than in the afternoon, whereas the chow-fed rats were more vulnerable and became severely hypothermic both in morning and afternoon. The greater morning resistance provided by the H diet was evident in summer and winter but not in spring or fall. With both diets, cold resistance as well as growth decreased during spring and fall. Frozen storage of the diets and the water for use during other seasons showed that the nutrients per se were not a factor in the observed seasonal cycle. Although humidity in the 28°C room varied between a minimum of 26.5% in April to a maximum of 44.3% in August, it was not a statistically significant factor in the growth cycle. Arguments are presented to rule out relative humidity as a significant factor in the seasonal variation in the degree of cold resistance. A significant correlation was found for growth and cold resistance with geomagnetic activity.NRCC # 17310     

Differences in sleep, light, and circadian phase in offshore 18:00-06:00 h and 19:00-07:00 h shift workers

Complaints concerning sleep are high among those who work night shifts; this is in part due to the disturbed relationship between circadian phase and the timing of the sleep-wake cycle. Shift schedule, light exposure, and age are all known to affect adaptation to the night shift. This study investigated circadian phase, sleep, and light exposure in subjects working 18:00-06:00 h and 19:00-07:00 h schedules during summer (May-August). Ten men, aged 46+/-10 yrs (mean+/-SD), worked the 19:00-07:00 h shift schedule for two or three weeks offshore (58 degrees N). Seven men, mean age 41+/-12 yrs, worked the 18:00-06:00 h shift schedule for two weeks offshore (61 degrees N). Circadian phase was assessed by calculating the peak (acrophase) of the 6-sulphatoxymelatonin rhythm measured by radioimmunoassay of sequential urine samples collected for 72 h at the end of the night shift. Objective sleep and light exposure were assessed by actigraphy and subjective sleep diaries. Subjects working 18:00-06:00 h had a 6-sulphatoxymelatonin acrophase of 11.7+/-0.77 h (mean+/-SEM, decimal hours), whereas it was significantly later, 14.6+/-0.55 h (p=0.01), for adapted subjects working 19:00-07:00 h. Two subjects did not adapt to the 19:00-07:00 h night shift (6-sulphatoxymelatonin acrophases being 4.3+/-0.22 and 5.3+/-0.29 h). Actigraphy analysis of sleep duration showed significant differences (p=0.03), with a mean sleep duration for those working 19:00-07:00 h of 5.71+/-0.31 h compared to those working 18:00-06:00 h whose mean sleep duration was 6.64+/-0.33 h. There was a trend to higher morning light exposure (p=0.07) in the 19:00-07:00 h group. Circadian phase was later (delayed on average by 3 h) and objective sleep was shorter with the 19:00-07:00 h than the 18:00-06:00 h shift schedule. In these offshore conditions in summer, the earlier shift start and end time appears to favor daytime sleep.     

Influence of long-term exposure to an air-conditioned environment on the diurnal cortisol rhythm

In the present study, the influence of the long-term use of air-conditioning in summer on the cortisol rhythm was examined by measuring the rhythm in subjects who had been exposed to air-conditioning for a short [S] or long [L] time. Investigations were conducted twice in July and September. Atmospheric temperature and relative humidity near the subjects were measured for three days in each season. Saliva samples for cortisol analysis were collected every 2 hours during the daytime beginning at 8:00 h with subsequent sampling times at 10:00, 12:00, 14:00, 16:00, 18:00, 20:00 and 22:00 h. A questionnaire on sleep and duration of air-conditioning use was also undertaken. Ambient mean temperature was higher in the S group (mean+/-SD; 30.8+/-1.2 degrees C in July, 28.0+/-0.8 degrees C in September) than in the L group (28.0+/-1.2 degrees C in July, 27.3+/-1.0 degrees C in September) (p<0.01), while mean relative humidity did not differ. There were no differences in bedtime, waking time and sleeping hours either between groups or months. Diurnal patterns of salivary cortisol rhythm in July and September were similar in the S group, but the L group had a delayed rise of morning cortisol secretion in September compared with July. These results suggest that long-term exposure to an air-conditioned environment might adversely affect the human cortisol rhythm.     

C3和C4植物叶片对光氧化响应的日变化

田间生长的C3植物花生和C4植物玉米分别于晴天上午9：00、中午12：00、下午15：00取样。中午12：00花生叶片的Fv／Fm较早上9：见下降16％,出现了光抑制现象,玉米叶片的Fv／Fm则未下降。不同时间取样的花生和玉米叶片经甲基紫精（MV） 强光的人为光氧化处理,叶绿素和类胡萝卜素出现不同程度的氧化降解,中午12：00降解幅度最大,15时降幅最小。植物叶片的抗氧化能力与其SOD活性相关,而与PEPCase的活性没有明显的相关性。光氧化处理后,花生和玉米的叶绿素荧光参数FV／Fm、qp、pSII都下降,花生在12：00的降幅最小,玉米的降幅最大。光氧化引起花生的qN和热耗散系数（KD）上升,玉米则都下降．结果显示C3植物花生和C4植物玉米对光氧化的响应可能存在不同的机制。     

Fluctuations in peripheral serum testosterone levels within a day, with age and by sexual stimulation in male beagle dogs bred indoors

Fluctuations in serum levels of testosterone (T) within a day, both with age and as a result of sexual stimulation, were examined in male beagle dogs. Eighty male dogs aged between 3 months and 16 years and bred in our laboratory were used under strictly controlled breeding conditions (temperature: 22 +/- 1 degree C, relative humidity: 55 +/- 5%, lighting time: 8:00 a.m.-8:00 p.m.). The level of T was measured by an RIA method. In order to examine the fluctuation in T level within a day, blood samples were obtained at 0:00, 6:00, 12:00 and 18:00 in each of five dogs aged 1.7 and 2.1 years. T levels fluctuated with a regular pattern that was lowest at 12:00, and increased to a peak at 18:00-6:00, thereafter decreasing until 12:00. In order to examine the change in T level with age, blood samples were obtained at 9:00, 12:00 and 16:00 from 70 dogs aged between 3 months and 16 years. The regular diurnal pattern of T level was usually seen, and the levels at 12:00 were always low and did not fluctuate at any age except for 6 months, and 13, 14 and 16 years. The T level at 9:00 increased to reach a peak at 4 years, whereas that at 16:00 did so at 2 years. T levels at 9:00 were significantly higher at 4-12 and 14 years than at 3 months, and were higher at 4 years than at 9 months.(ABSTRACT TRUNCATED AT 250 WORDS)