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.     

Association of ischemic stroke onset time with presenting severity,acute progression,and long-term outcome: A cohort study

BackgroundPreclinical data suggest circadian variation in ischemic stroke progression, with more active cell death and infarct growth in rodent models with inactive phase (daytime) than active phase (nighttime) stroke onset. We aimed to examine the association of stroke onset time with presenting severity, early neurological deterioration (END), and long-term functional outcome in human ischemic stroke.Methods and findingsIn a Korean nationwide multicenter observational cohort study from May 2011 to July 2020, we assessed circadian effects on initial stroke severity (National Institutes of Health Stroke Scale [NIHSS] score at admission), END, and favorable functional outcome (3-month modified Rankin Scale [mRS] score 0 to 2 versus 3 to 6). We included 17,461 consecutive patients with witnessed ischemic stroke within 6 hours of onset. Stroke onset time was divided into 2 groups (day-onset [06:00 to 18:00] versus night-onset [18:00 to 06:00]) and into 6 groups by 4-hour intervals. We used mixed-effects ordered or logistic regression models while accounting for clustering by hospitals. Mean age was 66.9 (SD 13.4) years, and 6,900 (39.5%) were women. END occurred in 2,219 (12.7%) patients. After adjusting for covariates including age, sex, previous stroke, prestroke mRS score, admission NIHSS score, hypertension, diabetes, hyperlipidemia, smoking, atrial fibrillation, prestroke antiplatelet use, prestroke statin use, revascularization, season of stroke onset, and time from onset to hospital arrival, night-onset stroke was more prone to END (adjusted incidence 14.4% versus 12.8%, p = 0.006) and had a lower likelihood of favorable outcome (adjusted odds ratio, 0.88 [95% CI, 0.79 to 0.98]; p = 0.03) compared with day-onset stroke. When stroke onset times were grouped by 4-hour intervals, a monotonic gradient in presenting NIHSS score was noted, rising from a nadir in 06:00 to 10:00 to a peak in 02:00 to 06:00. The 18:00 to 22:00 and 22:00 to 02:00 onset stroke patients were more likely to experience END than the 06:00 to 10:00 onset stroke patients. At 3 months, there was a monotonic gradient in the rate of favorable functional outcome, falling from a peak at 06:00 to 10:00 to a nadir at 22:00 to 02:00. Study limitations include the lack of information on sleep disorders and patient work/activity schedules.ConclusionsNight-onset strokes, compared with day-onset strokes, are associated with higher presenting neurologic severity, more frequent END, and worse 3-month functional outcome. These findings suggest that circadian time of onset is an important additional variable for inclusion in epidemiologic natural history studies and in treatment trials of neuroprotective and reperfusion agents for acute ischemic stroke.

Wi-Sun Ryu and colleagues investigate the association of stroke onset time with presenting severity, early neurological deterioration (END), and long-term functional outcome in ischemic stroke.     

Circadian rhythms may not influence the outcomes of thrombolysis in patients with ischemic stroke: A study from China

ABSTRACT

Circadian rhythms can affect physical or mental activities as well as the time of stroke onset. The impact of circadian rhythms on acute ischemic stroke (AIS) patients treated by recombinant alteplase (rt-PA) is still incongruent. This study aims to consider whether the outcomes of thrombolysis differ depending on stroke onset time and rt-PA infusion time in patients with AIS. A total of 447 AIS patients, who underwent rt-PA intravenous infusion within 4.5 hours after stroke onset, were enrolled in this study consecutively from June 2010 through December 2016. All of the patients were grouped based on the stroke onset time and rt-PA infusion time into two exact 12-hour intervals as daytime (06:01–18:00) and nighttime (18:01–06:00) and further divided into four subgroups at 6-hour time intervals (00:01–06:00, 06:01–12:00, 12:01–18:00 and 18:01–24:00). Major neurological improvement at 1 hour, 24 hours and 7 days, 7-day mortality rate and 24-hour hemorrhage transformation was recorded. The results showed that a total of 295 patients (66.4%) appeared with AIS and 252 (56.4%) were treated during daytime. Higher NIHSS at admission was observed when stroke occurred in nighttime, especially during 00:01–06:00. Patients with stroke onset in nighttime especially during 18:01–24:00 had a significant shorter onset-door time and onset-needle time. No differences of the major neurological improvement at 1 hour, 24 hours and 7 days, 24-hour hemorrhagic transformation and 7-day fatality rate were found among either 12-hour time frames or 6-hour time frames according to the time of stroke onset or rt-PA infusion. In conclusion, there was no evidence to predict that circadian rhythms could influence the outcomes of AIS patients treated with rt-PA in China, although stroke onset during nighttime might aggravate neurological impairment before treatment. Further, multicenter and prospective clinical trials with larger number of subjects are still needed to draw more reliable conclusions.     

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.     

Depressive Symptoms and the Risk of Ischemic Stroke in the Elderly—Influence of Age and Sex

Although a relationship between depression and cardiovascular events has been suggested, past study results regarding the risk of stroke in relation to depression by subgroups are ambiguous. The aim of this study was to investigate the influence of depressive symptoms on risk of incident ischemic stroke in elderly according to age and sex. This prospective cohort study followed up 3852 subjects older than 55 years. Baseline depressive symptoms were defined by a score ≥5 on the Geriatric Depression Scale or antidepressant intake. The outcome measure was incident ischemic stroke within 6 years of follow-up. Multivariate Cox-proportional hazard models as well as cumulative survival analyses were computed. A total of 156 ischemic strokes occurred during the study period (24 strokes in the age-group<65 years and 132 strokes in the age-group≥65 years). The distribution of strokes in sex-subgroups was 4.5% in men and 3.7% in women. The multivariate analysis showed an elevated stroke risk (Hazard Ratio (HR): 2.84, 95% CI 1.11–7.29, p = 0.030) in subjects from 55 to 64 years with depressive symptoms at baseline but not in subjects older than 65 years. In the multivariate analysis according to sex the risk was increased in women (HR: 1.62, 95% CI 1.02–2.57, P = 0.043) but not in men. The Cox-regression model for interaction showed a significant interaction between age and sex (HR: 3.24, 95% CI 1.21–8.69, P = 0.020). This study corroborates that depressive symptoms pose an important risk for ischemic stroke, which is particularly remarkable in women and patients younger than 65 years.     

Delay of behavioral estrus in hamsters and phenobarbital

The onset of behavioral estrus was used as a phase marker of the hamster timing system in SLD 16:8 (dark 20:00-04:00). TZ was injected between 11:00 of cycle day 3 and noon of cycle day 4 when onset of estrus was determined. At no time did injection of TZ cause a phase advance in SLD 16:8. Small delays of estrus resulted from 11:00-16:00 injections but marked delays began with the 17:00 injection. Phenobarbital was injected between noon and 19:30 on cycle day 3. Injections between noon and 16:00 had no effect but all later injections beginning at 17:00 delayed estrus, the 17:30 injection causing the greatest delay. Diazepam also markedly delayed estrus when tested at 17:30. These results with three drugs support results with light pulses that 18:00 in SLD 16:8 marks the same phase of the 24-h hamster timing system as the onset of wheel running does in DD, LL, and WLD. These findings with three GABA potentiators extend to SLD previous evidence based on the onset of wheel running in DD, LL and WLD that GABA may be involved in hamster timekeeping and its responses to light and drugs.     

柠条主根液流测定中ΔTmax与气象因子间的关系及时间步长的确定

上下两探针间温差的最大值(ΔTmax)是运用Granier方法计算树木液流速率的重要参数,确定这一参数的关键是选择合适的时间步长。运用TDP(Thermal Dissipation Probe)技术在对柠条(Caragana korshinskii)主根部液流速率(Fs)及主要环境要素进行实时、连续监测的基础上,比较分析了2008年4—10月间30d典型晴天日柠条根部液流的变化特征,结果表明,柠条根部液流测定中ΔTmax值的频率分布于夜间22:00—6:00的整个时间段,并主要集中在午夜前后的4h(占52.63%),其中ΔTmax在0:00频率最高。ΔTmax分布时刻与环境要素的相关性不明显,夜间液流的主要驱动力是体内与根系间的水势差而非大气因子。午间柠条主根液流最为旺盛,上下两探针间最小温差(ΔTmin)的频率分布峰值主要集中于10:00—16:00时段,其中以14:00的分布频率最高。ΔTmin频率的分布在13:00有一低谷,而此刻又是主要环境变量太阳辐射最高值(PYmax)与潜在蒸发散最大值(ET0max)分布频率最高的时刻,反映了午间气孔行为对液流的调控。太阳辐射是启动午间气孔行为的主要环境因子。Granier公式计算液流速率时适宜的时间步长为1周。     

Importance of 6 p.m. in Hamster Timekeeping Evidenced by Computer Analysis of Wheel-Running Activity

We addressed the question whether the clock signal for hamsters to become active occurs at sundown throughout summer or at some constant time after noon (p.m. time). Ten female golden hamsters housed in wheel cages in a windowless room were exposed to 24-h light/dark (LD) cycles simulating the equinoxes (LD 12: 12), when the sun sets at 6 p.m. and rises at 6 a.m., and summer (LD 14: 10, 16: 8, and 18: 6), when the sun sets after 6 p.m. and rises before 6 a.m. The onset of behavioral estrus, a mask-free phase marker of the same clock that controls wheel-running, was observed every 4 days, and wheel revolutions were recorded every 5 min for 52 days. Computer analysis of the 5-min values averaged for all 10 hamsters revealed a clear onset of running for each LD exposure. Time in the windowless room is referenced to mid-L (room “noon”) of the LD cycles. Although L-off ranged from 6 p.m. in LD 12: 12 (6 h after mid-L) to 9 p.m. in LD 18: 6, estrus began close to 4 p.m. and running close to 6 p.m. in every LD cycle. In a second study, 13 females not tested for estrus began running closer to 7 p.m. in LD 16: 8 (L-off, 8 p.m.), but when L-off was advanced to 4 p.m. they also began running on that day at 6 p.m. Testing for estrus may have made the first group of hamsters less fearful of light and therefore more responsive to a 6 p.m. clock signal to become active. It is conceivable that these nocturnal rodents voluntarily suppress, to varying degrees, overt activity from 6 p.m. standard time to sundown to avoid predators. It is noteworthy that 6 p.m. room time also marks the onset of the clock's 12-h light-sensitive period underlying hamster timekeeping.     

Circadian Variation of Myocardial Ischemia in Patients with Stable Coronary Artery Disease

The circadian variation of myocardial ischemia detected during 24-h ambulatory electrocardiographic monitoring (AEM) was analyzed in 123 patients with stable angina pectoris, positive exercise test, and angiographically proven coronary artery disease. A total of 437 ischemic episodes (ST-segment depression ≥ 1 mm and duration ≥ 1 min) were observed; 333 (76%) episodes remained asymptomatic, and only 104 (24%) episodes were accompanied by anginal pain. Ischemic episodes predominantly occurred during the morning hours, between 6 a.m. and noon, and another smaller peak was observed in the afternoon, between 4 and 5 p.m.; this diurnal pattern was influenced neither by the extent of coronary artery disease nor the degree of left ventricular dysfunction. The circadian variation was restricted to the 345 (78%) ischemic episodes preceded by increases in heart rate; the 92 (22%) episodes without prior heart rate changes occurred randomly throughout the day. The morning peak in ischemic episodes was not associated with less myocardial oxygen supply; in contrast, heart rate profile showed parallel increases during the morning and afternoon hours, indicating elevated myocardial demand during these periods. Ischemia-related ventricular arrhythmias were concentrated during the morning hours, but their overall prevalence was low-28 (6%) of 437 ischemic episodes. These findings may provide further insight into the pathomechanisms of acute clinical events in patients with coronary artery disease, since the circadian variation of myocardial ischemia is very similar to that observed for the onset of myocardial infarction and sudden cardiac death.     

Some epidemiologic and clinical problems in ischemic cerebral stroke

The study involved 739 patients with the ischemic cerebral stroke into two groups: with reversible and irreversible ischemic cerebral stroke. General characteristics of patients (incidence, sex, age etc.) was similar to the characteristics of patients from other centres. Morbidity rate for ischemic cerebral strokes was 93.9, including reversible stroke 21.3 and other 72.6; mortality factor 47.2, and mortality rate 29.6%. An increase in morbidity for irreversible stroke in women over 80 years of age is striking. The authors suggest that the classification of cerebral strokes should include reversible strokes whereas progressive stroke should not be considered distinguished entity.     

Clinical Significance of Cerebral Microbleeds Locations in CADASIL with R544C NOTCH3 Mutation

MethodsThis is a cohort study of patients who were diagnosed with genotype-confirmed R544C-mutation CADASIL. Primary neurologic symptoms were recorded. Symptomatic strokes were defined as transient ischemic attack, ischemic strokes and hemorrhagic strokes. CMBs were defined as focal areas of round signal loss on T2*-weighted gradient echo planar images with a diameter of less than 10 mm. The locations of CMBs were divided into lobar, basal ganglia, thalamus, brain stem and cerebellum. Multiple logistic regressions were performed to identify the epidemiologic or vascular risk factors associated with symptomatic stroke in patients with CADASIL.ResultsAmong total of 51 subjects in this cohort, CMBs were present in 20 of 32 patients (64.5%) in the symptomatic stroke-group and in 8 of 19 patients (42.1%) in the non-stroke group (p = 0.16). CMBs were observed more frequently in the basal ganglia (p<0.001) and the cerebellum (p<0.018) in the symptomatic stoke group compared to the non-stroke group. The mean number of CMBs was significantly higher in the symptomatic stroke group (15.4±18.0 lesions per patients with CMBs) versus those without symptomatic stroke (3.3±3.0 lesions per patients with CMBs) (p = 0.003). Hypertension was an independent risk factor for symptomatic stroke in CADASIL (p = 0.014). It was independently associated with CMBs locations as basal ganglia (p = 0.016), thalamus (p = 0.010), brainstem (p = 0.044), and cerebellum (p = 0.049). However, It was not independently associated with CMBs on lobar lesion (p = 0.152).ConclusionsIn this study hypertension was an independent predictor of CMBs presence in specific brain locations, as well as symptomatic stroke in the CADASIL patients. The distribution and burden of CMBs might be a clinically useful marker for the risk of symptomatic stroke. However, further prospective studies on the relationship between CMBs distribution and symptomatic stroke are required in order to support these preliminary findings.     

Circadian Variation of Myocardial Ischemia in Patients with Stable Coronary Artery Disease

The circadian variation of myocardial ischemia detected during 24-h ambulatory electrocardiographic monitoring (AEM) was analyzed in 123 patients with stable angina pectoris, positive exercise test, and angiographically proven coronary artery disease. A total of 437 ischemic episodes (ST-segment depression ≥ 1 mm and duration ≥ 1 min) were observed; 333 (76%) episodes remained asymptomatic, and only 104 (24%) episodes were accompanied by anginal pain. Ischemic episodes predominantly occurred during the morning hours, between 6 a.m. and noon, and another smaller peak was observed in the afternoon, between 4 and 5 p.m.; this diurnal pattern was influenced neither by the extent of coronary artery disease nor the degree of left ventricular dysfunction. The circadian variation was restricted to the 345 (78%) ischemic episodes preceded by increases in heart rate; the 92 (22%) episodes without prior heart rate changes occurred randomly throughout the day. The morning peak in ischemic episodes was not associated with less myocardial oxygen supply; in contrast, heart rate profile showed parallel increases during the morning and afternoon hours, indicating elevated myocardial demand during these periods. Ischemia-related ventricular arrhythmias were concentrated during the morning hours, but their overall prevalence was low–28 (6%) of 437 ischemic episodes. These findings may provide further insight into the pathomechanisms of acute clinical events in patients with coronary artery disease, since the circadian variation of myocardial ischemia is very similar to that observed for the onset of myocardial infarction and sudden cardiac death.     

Influence of oral glucose load upon blood glucose level in relation to the time of day

Blood glucose levels were estimated at different times of day in fasted rats and after 30, 60,90 and 120 min, since oral glucose load. Circadian variations in basal glucose levels and in the levels after glucose load were observed with the highest values noted between 11 a.m. and 7 p.m., and the lowest ones about midnight. These variations were most prominent when the measurements were performed 60 min after glucose load. Circadian variation in glucose tolerance was also revealed with the best tolerance at about midnight while the worst one was noted at noon and in the afternoon.     

Diffuse optical detection of global cerebral ischemia in an adult porcine model

Rapid screening for ischemic strokes in prehospital settings may improve patient outcomes by allowing early deployment of vascular recanalization therapies. However, there are no low-cost and convenient methods that can assess ischemic strokes in such a setting. Diffuse correlation spectroscopy (DCS) is a promising method for continuous, noninvasive transcranial monitoring of cerebral blood flow. In this study, we used a DCS system to detect cerebral hemodynamics before and after acute ischemic stroke in pigs. Seven adult porcines were chosen to establish ischemic stroke models via bilateral common carotid artery ligation (n = 5) or air emboli (n = 2). The results showed a significant difference in blood flow index (BFI) between the normal and ischemic groups. Relative blood flow index (rBFI) exhibited excellent results. Therefore, the diffuse optical method can assess the hemodynamic changes in acute cerebral ischemic stroke onset in pigs, and rBFI may be a promising biomarker for identifying cerebral ischemic stroke.     

Plasma-free homovanillic acid: within- and across-day stability in children and adults with Tourette's syndrome

Within- and across-day stability of plasma-free homovanillic acid (pHVA) was assessed in children and adults with Tourette's syndrome. A diurnal fall in pHVA was observed in 13 of 15 subjects. There was a small but significant (p less than .0001) decrease (8%) in mean morning pHVA levels obtained just 20 minutes apart (8:30 A.M. and 8:50 A.M.). A substantial and significant (p less than .001) mean decrease in pHVA (25%) was observed when samples obtained between 8:00 and 8:30 A.M. were compared with samples obtained at 12:00 noon. Changes in pHVA levels observed during the afternoon (between 12:00 noon and 4:00 P.M.) were small, nondirectional, and nonsignificant. Repeated measurement of morning pHVA in the same individual after 24 or more hours revealed marked increases or decreases in many individuals, suggesting that morning pHVA is not a stable measure. The results of this and previous studies suggest that pHVA obtained at 12:00 noon or later in the day may be a more reliable measure of centrally produced HVA. Further studies are needed regarding the stability of pHVA over time.     

The daily variations of airborne fungal spores in Mexico City

The daily and seasonal distribution of airborne fungal particles was recorded in a high altitude tropical zone. Sampling was carried out in the southern part of Mexico City. An Andersen air sampler was used over a period of six months. Ten minutes sampling for each set of plates was done at fixed schedule: 07:30, 14:00 and 19:00 hours. The sampler was placed 10 m above the ground. Daily variation was found to be associated with the season, weather and atmospheric stability. The highest value of mold counts (3195 CFU m⁻³) was recorded in the evening on October, a transitional month between the rainy and the dry seasons, the lowest (45 CFU m⁻³) at noon during the rainy season. Mold counts were significantly correlated with temperature, having negative signs both in the morning and at noon, and being positive in the evening. The abundance of only three genera was recorded.Cladosporium, was isolated more frequently, and its abundance at 14:00 h was of 38%;Alternaria represented 4.0%, at 14:00 h, andAspergillus 3.0% at 7:30 h. Fifteen species belonging to the latter genera were identified and most of them are considered as opportunistic molds of clinical significance.     

Association between Diurnal Variation of Ozone Concentration and Stroke Occurrence: 24-Hour Time Series Study

Background and Purpose

Increasing ozone concentrations have been known to damage human health and ecosystems. Although ozone tends to display diurnal variation, most studies have reported only on the association between daily ozone concentrations and ischemic stroke occurrence on the same day, or with a 1-day lag. We investigated the effect of the diurnal variation of ozone on ischemic stroke occurrence during the same day.

Methods

We included a consecutive series of 1,734 patients from January 1, 2008, to December 31, 2014, at a single tertiary hospital in Seoul, South Korea. We evaluated differences between temperature and pollutants at the time of stroke onset for each time interval and averaged those parameters across the 7-year study period.

Results

During the interval from 13:00 to 16:59, we found a positive association between ischemic stroke occurrence and ozone concentration relative to other time periods. Upper median ozone levels from 13:00 to 16:59 were positively correlated with ischemic stroke (odds ratio, 1.550; 95% confidence intervals, 1.220 to 1.970; P = <0.001) when compared with lower median levels.

Conclusions

The results show diurnal patterns of ischemic stroke occurrence based on upper and lower median ozone levels for a 24-hour period, which extends understanding of the association between stroke occurrence and environmental influences.     

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.     

Diurnal pattern of rat pancreatic acinar cell replication

Fully differentiated pancreatic acinar cells can enter the cell cycle under appropriate conditions in the rat. The aim of this study was to analyse the diurnal pattern of acinar cell proliferation as a function of food intake and the release of cholecystokinin (CCK), because the peptide hormone CCK is a major physiological regulator of rat pancreatic acinar cell replication. Pancreatic acinar cell replication was quantitated using an antibody against the S-phase marker proliferating cell nuclear antigen (PCNA). In addition, acinar cells in S-phase were detected after injecting bromodeoxyuridine (BrdU) and subsequent immunohistochemical staining of BrdU-positive nuclei. Rat pancreata were analysed during the day under standard diet conditions, as well as after various schedules of fasting and refeeding and after the application of the CCK receptor antagonist L-364,718. Between 6 a.m. and 6 p.m., the PCNA labeling index was 4.4±0.9%, while between 9 p.m. and 3 a.m. the PCNA labeling index was elevated and reached peak values of 11.4% (mean value: 7.8±2.5%) around midnight. BrdU-positive cells also doubled around midnight, compared to the 9:00 a.m. value. In fasted rats, acinar cell proliferation was completely suppressed and this suppression could be overcome by injection of the CCK analog cerulein. In addition, the CCK antagonist L-364,718 led to the same results as fasting. Here we show for the first time that there is a diurnal pattern of pancreatic acinar cell proliferation in rats, which is dependent on food intake and is mediated by CCK.     

DIURNAL ACID METABOLISM IN ISOETES HOWELLII FROM A TEMPORARY POOL AND A PERMANENT LAKE

Water chemistry and titratable acidity and malic acid levels in Isoetes howellii leaves were sampled every 6 hr from plants in a seasonal pool and an oligotrophic lake. Plants in the seasonal pool showed a diurnal fluctuation of ~ 300 μequivalents titratable acidity g⁻¹ fresh wt; daytime deacidification was 75% complete by noon and nighttime acidification was 45% complete by midnight. Late in the season after the pool had dried, emergent leaves showed only a very weak tendency to accumulate acid at night. Plants from the oligotrophic lake had a diurnal change of ~100 μeq g⁻¹ fresh wt, daytime deacidification was only 45% complete by noon but nighttime acidification was 80% complete by midnight. Water characteristics were distinctly different between these two systems. In the seasonal pool there were marked diurnal changes in temperature, pH, oxygen and carbon dioxide. Free-CO₂ levels were an order of magnitude greater in the early morning than in the late afternoon. In contrast, the conditions in the oligotrophic lake showed no marked diurnal fluctuation, though total inorganic carbon levels were extremely low relative to other aquatic systems.