Diurnal variation in the release of alpha-MSH from rat hypothalamus and pituitary

Release of alpha-MSH from rat hypothalamic slices was characterized with respect to ionic requirements and possible diurnal variations using a sensitive radioimmunoassay. Addition of 47 mM KCl to the superfusion medium resulted in a twofold increase in alpha-MSH functions as a neurotransmitter or neuromodulator in the hypothalamus. Both spontaneous and potassium-induced alpha-MSH release compared to spontaneous release. Removal of calcium from the superfusion medium abolished the potassium-evoked release of alpha-MSH. This supports the concept that alpha-MSH release were related to diurnal variation. Marked release from the slices was observed at 10.10 h, corresponding to a peak in the alpha-MSH concentration in the hypothalamus [18] and to a lower levels of alpha-MSH in the blood. Contrarily, no significant release from the hypothalamus was obtained at 17.00 h when hypothalamic alpha-MSH content was low, but blood levels exhibited a peak. These findings suggest that there are differences in the regulation of the alpha-MSH from the pituitary and that in the hypothalamus.

Release of plasma atrial natriuretic peptide after volume expansion is not related to pituitary-adrenal axis diurnal variation in normal subjects

The existence of a circadian rhythm of atrial natriuretic peptide (ANP) in humans is controversial. We studied the plasma ANP response to isotonic blood volume expansion in the morning and in the afternoon and its relationship with adrenocorticotropic hormone (ACTH)-cortisol diurnal variation in seven normal subjects. Basal plasma ANP level was similar in the morning (19.6 ± 2.4 pg/ml) and in the afternoon (21.8 ± 4.8 pg/ml). The ANP peak obtained with saline infusion (0.9% NaCl, 12 ml/kg) in the morning (49.4 ± 8 pg/ml) did not differ from that obtained in the afternoon (60.3 ± 10.1 pg/ml). There was no correlation between the individual mean cortisol and ACTH levels and the ANP peak obtained with saline infusion. These data indicate no diurnal variation in plasma ANP secretion induced by blood volume expansion and no relationship between plasma ANP peak and ACTH-cortisol diurnal variation

Diurnal variation of vascular diameter and reactivity in healthy young men

The higher incidence of cardiovascular events in the morning is accompanied by an increased vascular tone. However, there are few published studies designed to evaluate the diurnal variation of vascular and endothelial parameters in healthy subjects. In the present investigation, we evaluated the diurnal variation in brachial artery diameter (BAD), flow-mediated dilation (FMD) and endothelium-independent dilation (NFMD) in a homogeneous sample of healthy non-smoker young men. Fifty subjects aged 20.8 ± 0.3 years (range: 18 to 25 years) were investigated by brachial artery ultrasound. Exclusion criteria were female gender and evidence of clinically significant health problems, including obesity. Volunteers were asked to rest and avoid fat meals as well as alcoholic beverages 48 h before and until completion of the evaluations. BAD, FMD and NFMD were measured at 7 am, 5 pm, and 10 pm and tested by repeated measures ANOVA. BAD was smaller at 7 am (mean ± SEM, 3.8 ± 0.1 mm) in comparison with 5 pm (3.9 ± 0.1) and 10 pm (4.0 ± 0.1 mm; P < 0.001). FMD values did not change significantly during the day, while NFMD increased more at 7 am (18.5 ± 1.1%), when compared to 15.5 ± 0.9% at 10 pm and 15.5 ± 0.9% at 5 pm (P = 0.04). The physiological state of vasoconstriction after awakening, with preserved capability to dilate in the morning, should be considered to be part of the healthy cardiovascular adaptation before considering later life risk factors and endothelial dysfunction.

Diurnal variation in transect counts of birds in a cerrado landscape in the state of São Paulo, Brazil

The general statement that birds are recorded more often on morning than on afternoon counts is quite common and widespread among ornithologists. Although many investigators have reported temporal variations in bird detections using Point Counts in temperate regions, few researches regarding the same objectives have been conducted in Neotropical habitats or used transect counts as field method. We used transect counts to test the hypothesis that birds are evenly recorded between times of day in a predominantly open Cerrado landscape in southeastern Brazil. Although not always significantly, the number of species and individuals were consistently greater during the morning counts, which corroborates the fact that birds can be more detectable during this time of day. However, a few families as well as a small percentage of species were more likely to be recorded during either one of the two periods we analyzed. Our results suggest that morning counts should detect higher number of both species and individuals in our study area, but specific taxa show distinct patterns of detection which should be acknowledged prior to sampling.

Diurnal variation in oral temperature, sleepiness and performance of high school girls

Evaluation of rhythmic fluctuations cf 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 cn 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.

Diurnal variation of zooplankton biochemical composition and biomass in plankton production tanks

The nutritional value of zooplankton (lipid and phosphorus contents) was analyzed in outdoor, plankton-culture tanks, to monitor the effects of diurnal variation and fertilization. Total lipid contents were significantly higher (average values of about 14% DW) for the treatment fertilized during the sampling week. A significantly highher total lipid concentrations generally coincided with high biomass of Moina sp. (Cladocera) and Thermocyclops sp. nauplii (Copepoda), which is probably related to zooplankton filtration rates. The values tended to be higher during the afternoon and the night. Phosphorus contents in the zooplanktonic population varied from 0.15 to 0.91% DW, with significant differences among the tanks. The zooplankton nutritional quality was greatly influenced by fertilization, which also determined the species composition in the tanks.

Spurious shifts in the pattern of diurnal variation of sea level pressure of reanalysis datasets

The main purpose of this work is to report the presence of spurious discontinuities in the pattern of diurnal variation of sea level pressure of the three reanalysis datasets from: the National Centers for Environmental Prediction (NCEP) and National Center for Atmospheric Science (R1), the NCEP and Department of Energy (R2), and the European Centre for Medium Range Weather Forecasting (ERA-40). Such discontinuities can be connected to the major changes in the global observing system that have occurred throughout reanalyses years. In the R1, the richest period in discontinuities is 1956-1958, coinciding with the start of modern radiosonde observation network. Rapid increase in the density of surface-based observations from 1967 also had an important impact on both R1 and ERA-40, with larger impact on R1. The reanalyses show discontinuities in the 1970s related to the assimilation of radiances measured by the Vertical Temperature Profile Radiometer and TIROS-N Operational Vertical Sounders onboard satellites. In the ERA-40, which additionally assimilated Special Sensor Microwave/Imager data, there are discontinuities in 1987-1989. The R1 also presents further discontinuities, in 1988-1993 likely connected to replacement/introduction of NOAA-series satellites with different biases, and to the volcanic eruption of Mount Pinatubo in June 1991, which is known to have severely affected measurements of infrared radiances for several years. The discontinuities in 1996-1998 might be partially connected to change in the type of radiosonde, from VIZ-B to VIZ-B2. The R2, which covers only satellite era (1979-on), shows discontinuities mainly in 1992, 1996-1997, and 2001. The discontinuities in 1992 and 2001 might have been caused by change in the satellite measurements and those in 1996-1997 by some changes in land-based observations network. © 2012 Springer-Verlag.

The diurnal variation in stratospheric ozone from the MACC reanalysis, the ERA-Interim reanalysis, WACCM and Earth observations: characteristics and intercomparison

In this study we compare the diurnal variation in stratospheric ozone derived from free-running simulations of the Whole Atmosphere Community Climate Model (WACCM) and from reanalysis data of the atmospheric service MACC (Monitoring Atmospheric Composition and Climate) which both use a similar stratospheric chemistry module. We find good agreement between WACCM and the MACC reanalysis for the diurnal ozone variation in the high-latitude summer stratosphere based on photochemistry. In addition, we consult the ozone data product of the ERA-Interim reanalysis. The ERA-Interim reanalysis ozone system with its long-term ozone parametrization can not capture these diurnal variations in the upper stratosphere that are due to photochemistry. The good dynamics representations, however, reflects well dynamically induced ozone variations in the lower stratosphere. For the high-latitude winter stratosphere we describe a novel feature of diurnal variation in ozone where changes of up to 46.6% (3.3 ppmv) occur in monthly mean data. For this effect good agreement between the ERA-Interim reanalysis and the MACC reanalysis suggest quite similar diurnal advection processes of ozone. The free-running WACCM model seriously underestimates the role of diurnal advection processes at the polar vortex at the two tested resolutions. The intercomparison of the MACC reanalysis and the ERA-Interim reanalysis demonstrates how global reanalyses can benefit from a chemical representation held by a chemical transport model. The MACC reanalysis provides an unprecedented description of the dynamics and photochemistry of the diurnal variation of stratospheric ozone which is of high interest for ozone trend analysis and research on atmospheric tides. We confirm the diurnal variation in ozone at 5 hPa by observations of the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) experiment and selected sites of the Network for Detection of Atmospheric Composition Change (NDACC). The latter give valuable insight even to diurnal variation of ozone in the polar winter stratosphere.

Diurnal variation of the adenylyl cyclase type 1 in the rat pineal gland.

Nocturnal melatonin production in the pineal gland is under the control of norepinephrine released from superior cervical ganglia afferents in a rhythmic manner, and of cyclic AMP. Cyclic AMP increases the expression of serotonin N-acetyltransferase and of inducible cAMP early repressor that undergo circadian oscillations crucial for the maintenance and regulation of the biological clock. In the present study, we demonstrate a circadian pattern of expression of the calcium/calmodulin activated adenylyl cyclase type 1 (AC1) mRNA in the rat pineal gland. In situ hybridization revealed that maximal AC1 mRNA expression occurred at midday (12:00-15:00), with a very low signal at night (0:00-3:00). We established that this rhythmic pattern was controlled by the noradrenergic innervation of the pineal gland and by the environmental light conditions. Finally, we observed a circadian responsiveness of the pineal AC activity to calcium/calmodulin, with a lag due to the processing of the protein. At midday, AC activity was inhibited by calcium (40%) either in the presence or absence of calmodulin, while at night the enzyme was markedly (3-fold) activated by the calcium-calmodulin complex. These findings suggest (i) the involvement of AC1 acting as the center of a gating mechanism, between cyclic AMP and calcium signals, important for the fine tuning of the pineal circadian rhythm; and (ii) a possible regulation of cyclic AMP on the expression of AC1 in the rat pineal gland.

Atlas of Fourier coefficients of diurnal variation of foF2.

Bibliography: p. 23.

Diurnal evolution of solar radiation at the surface in the city of São Paulo: Seasonal variation and modeling

Seasonal variations in the diurnal evolution of the global, diffuse and direct solar radiation at the surface, the clearness index, diffuse fraction and direct fraction are described in detail for the City of Sao Paulo, Brazil. The description is based on measurements of global and diffuse solar radiation carried out over 5.25 years. The diffuse component was measured with a shadow-band device. The annual evolution of the amplitude of the diurnal cycle of all radiometric parameters indicates a seasonal pattern with two distinct periods: autumn-winter and spring-summer. About 10% of the observed period was characterized by clear sky days. This seasonal variation is determined by a larger incidence of clear sky days in the autumn-winter period. Reductions of up to 10% in hourly and daily values of global radiation were observed in conjunction with an increase in particulate matter concentration on clear sky days. The pollution effect may be responsible for the discrepancy, of 16%, found between local and more regional estimates of global solar radiation in Sao Paulo. The diurnal evolution of hourly values of monthly-averaged global and diffuse solar radiation were successfully estimated by the empirical expressions derived here. Daily values of monthly-averaged global solar radiation were satisfactorily estimated using the Angstrom expression.

Diurnal and exercise-related variability of haemoglobin and reticulocytes in athletes.

Haemoglobin (Hb) and Reticulocytes (Ret) are measured as indirect markers of doping in athletes. We studied the diurnal variation, the impact of exercise, fluid intake and ambient temperature in athletes on these parameters. Hourly venous blood samples were obtained from 36 male athletes of different disciplines (endurance (END) and non-endurance (NON-END)) over 12 h during a typical training day. Seven inactive subjects served as controls (CON). Hb and Ret were determined. A mixed model procedure was used to analyse the data. At baseline, Hb was similar for all groups, END showed lower Ret than NON-END and CON. Exercise showed a significant impact on Hb (+0.46 g/dl, p<0.001), the effect disappeared approximately 2 h after exercise. Hb decreased over the day by approximately 0.55 g/dl (p<0.01). There was no relevant effect on Ret. Fluid intake and ambient temperature had no significant effect. Hb shows significant diurnal- and exercise related variations. In an anti-doping context, most of these variations are in favour of the athlete. Blood samples taken after exercise might therefore provide reliable results and thus be used for the longitudinal monitoring of athletes if a timeframe for the re-equilibration of vascular volumes is respected.

Diurnal Structure of Monsoon Boundary Layer

The characteristics of the monsoon boundary layer are imperative to understand in the perception of the tropical regions. The southwest monsoon is associated with a strong wind in the lower troposphere near 1.5 km and is referred to as Low Level Jet stream (LLJ). The boundary layer structure associated with the LLJ during monsoon can be studied using L-band Ultra High Frequency (UHF) radar. This L-band wind profiler-commonly referred as lower atmospheric wind profiler (LAWP), was installed at NARL, Gadanki. Zonal, meridional and vertical wind components are used to understand the diurnal variation of the wind in the Atmospheric Boundary Layer (ABL) and associated features. From the analysis during non rainy days of the southwest monsoon, it is found that the LLJ has maximum strength during the early morning hours at lower level and the height increases as day progresses. The vertical wind shows the transfer of momentum from the LLJ towards the surface, indicating the sinking motion during the daytime. Vertical gradient of the wind shear shows the intensity of clear air turbulence is moderate and no severe clear air turbulence is noticed during the monsoon period