Peak-trough Differences Research Articles

Diel pattern of soil respiration in N-amended soil under maize cultivation

To understand maize- and N-induced diel variations in CO 2 emission, we examined hourly CO 2 emissions during the three typical growth stages of maize in sandy loam soil. There was a distinct diel pattern in soil CO 2 emissions, with the peak occurring between 14:00 and 18:00 and the trough occurring between 0:00 and 4:00. Maize presence delayed the time of the peak. The absolute amount and diel fluctuation of CO 2 emissions tended to diminish with time in the bare soil fertilized with 150 kg N ha −1 (BS). In contrast, N-fertilized maize (N150) significantly enhanced the total amount of CO 2 emissions and the peak-trough differences in CO 2 emissions, which reached a maximum at the pollination stage and then decreased. Control soil (CK) containing maize but no N fertilizer had highest overall CO 2 emissions but reduced diel fluctuation because rhizosphere respiration was elevated in the nighttime. Soil temperature accounted for 61–71% of diel variation in the BS treatment but for only 44–59% and 38–58% in the N150 and CK treatments, respectively. Photosynthesis rates affected diel variation at the seedling and pollination stages. Both temperature and photosynthesis rates together explained up to 67–84% of diel variation at the seedling and pollination stages in the N150 treatment, but only 61% at the seedling stage in the CK treatment due to more CO 2 released in the nighttime. The increased nighttime CO 2 release, in turn, decreased the effect of temperature and even reduced the influence of photosynthesis rate on diel variations in CO 2 release. Based on the present results, the best time for obtaining a representative daily CO 2 measurement was found to be approximately 8:00 at the seedling stage and 9:00–11:00 at the other growth stages. The current findings indicate that N addition reduces soil CO 2 emissions and its diel fluctuation.

A systems and neurobiological model of nucleus angularis and nucleus laminaris in the barn owl

The representation of binaural sound localization cues was investigated in a model of the barn owl’s auditory nerve, nucleus angularis (NA), nucleus magnocellularis (NM), nucleus laminaris (NL), and superior olivary nucleus (SON) using spiking leaky integrate and fire neurons. A phenomenological model of the barn owl’s auditory-nerve spike response was created to reproduce responses to tonal stimuli and exhibit two-tone rate suppression effects. The representation of stimulus level by NA was investigated by decoding the envelope of the input signal from populations of NA model neurons where the envelope was defined as in a previous computational model of sound localization in the barn owl [B.J. Fischer and C.H. Anderson, Adv. NIPS 16 (2004)]. Simulations demonstrated that inclusion of NA neurons with type IV responses increased the accuracy of the representation of the stimulus envelope. The effect of inhibition on the output of the population of NL model neurons was investigated and compared to a cross-correlation model. The output of the model SON provides inhibitory feedback to ipsilateral NA, NM, and NL model neurons. Simulations demonstrated that inclusion of inhibition of NL neurons by SON output increased peak–trough differences in ITD tuning curves.

Serum thymidine kinase levels are elevated and exhibit diurnal variations in patients with advanced ovarian cancer

Deoxythymidine kinase (TK) is an enzyme involved in DNA synthesis whose serum activity reflects the proliferative activity of tumors and correlates with prognosis in various malignancies. In ovarian cancer, the value of s-TK has not been studied so far. Therefore the serum levels of TK were investigated in patients with advanced ovarian cancer. Because considerable diurnal fluctuations of s-TK levels were reported previously, repeated determinations were performed over a 48-h time span. Fourteen patients (mean age±S.D., 56.1±8.0 years) with advanced ovarian cancer and five healthy volunteers (30.2±3.5 years) were studied. Serial determinations of s-TK and serum CA 125 (s-CA 125) levels were performed over a 48-h time period. S-TK and s-CA 125 were elevated (>4.7 U/l and >35 U/ml) in 10 patients at least once over the 48-h period, respectively. Linear regression analysis showed a strong correlation between s-TK and s-CA 125. However, three patients with consistently normal s-CA 125 values (≤35 U/ml) had elevated s-TK levels, indicating that these two parameters may be independent in some patients. Both s-TK and s-CA 125 levels showed considerable diurnal changes over the 24-h period in individual patients, in marked contrast to normal subjects. Individual peak-trough differences ranged from 0.1–8.5 U/l or 5–268% for s-TK, and from 4–75 U/ml or 15–100% for s-CA 125. Peak-trough differences of s-TK≥100% were found in five patients. The circadian fluctuations of s-TK and CA 125 did not show a regular circadian pattern nor any temporal covariation. This study demonstrates for the first time that s-TK levels may be elevated in ovarian cancer. In some patients, s-TK levels may exhibit considerable, irregular diurnal fluctuations. Repeated determinations should therefore be performed in situations where this marker is relevant for patient monitoring.

Components of biological variation, including seasonality, in blood concentrations of TSH, TT3, FT4, PRL, cortisol and testosterone in healthy volunteers.

There are few detailed studies of annual or seasonal variations in hormone concentrations in man. This study examines the components of biological variation, including seasonality, in plasma TSH, total T3 (TT3), free T4 (FT4), PRL, cortisol and testosterone in healthy volunteers. Monthly blood samplings for the assay of the above hormones were collected during one calendar year. Thirteen normal men and 13 normal women participated in the present study (mean age 38.7 +/- 13.4 years). Assays of TSH, TT3 and FT4 were carried out by means of immunoradiometric assays (IRMA), PRL by ELISA, cortisol by a fluorescence immunoassay, and testosterone with RIA. The time series were analysed by means of (bivariate or multivariate) spectral and cosinor analyses. Significant annual, four-monthly and biannual rhythms were detected in serum TSH; the lowest TSH values were observed in spring. A significant annual rhythm was detected in TT3, with lower values in spring and summer than in the other seasons. The peak-trough differences in the yearly variation expressed as a percentage of the mean were 29.1% and 8.2% for TSH and TT3, respectively. The yearly variation in plasma cortisol was significantly different between men and women: in men, 5.9% of the variation was explained by an annual rhythm, while in women 14.7% was explained by the fourth and seventh harmonical wave. The peak-trough differences in the yearly variation in plasma cortisol were 17.6% and 31.8% in men and women, respectively. There were no significant seasonal rhythms in PRL, FT4 or testosterone. The intraindividual/interindividual CV values were: TSH 29.3/48.4%, TT3 9.4/ 18.5%, FT4 7.1/9.1%, PRL 39.2/65.0%, cortisol 21.7/ 46.2%, and testosterone 12.6/40.8%. The degree of individuality measured in the plasma hormones is such that conventional population-based reference ranges may not correctly identify major alterations in these hormones in individual subjects.

Components of biological variation in serum soluble transferrin receptor: relationships to serum iron, transferrin and ferritin concentrations, and immune and haematological variables

Maes M, Bosmans E, Scharpé S, Hendriks D, Cooremans W, Neels H, De Meyer F, D'Hondt P, Peeters D. Components of biological variation in serum soluble transferrin receptor: relationships to serum iron, transferrin and ferritin concentrations, and immune and haematological variables. Scand J Clin Lab Invest 1997:57:31–41.We investigated the components of biological variation in serum soluble transferrin receptor (TfR) in relation to serum iron, transferrin (Tf), ferritin, soluble interleukin-2 receptor (sIL-2R), sIL-6R, and number of erythrocytes, haemoglobin (Hb), haematocrit (Ht), mean corpuscular volume (MCV), mean cell haemoglobin (MCH), and erythrocyte distribution width (RDW). We took monthly blood samples during 1 calendar year from 26 healthy subjects for assay of the above variables. The estimated CVs for TfR were interindividual CVg=20.8%, and intra-individual CVi=13.6%; for Tf, CVg=14.4% and CVi=6.7%; for iron, CVg=16.8% and CVi=29.2%; and for ferritin, CVg=71.1% and CVi=26.5%. There was a statistically significant seasonal pattern in the four variables with significant annual, biannual and/or trimonthly rhythms, which were expressed as a group phenomenon. The peak-trough differences in the yearly variations, expressed as a percentage of the mean, were: for TfR, 11.7%; for iron, 39.2%; for Tf, 11.7%; and for ferritin, 29.3%. Up to 34.2% of the within-subject variability in TfR (which reflects changes over time) could be explained by the regression on iron, ferritin, Tf, sIL-2R, sIL-6R and MCH values. Up to 67.2% of the between-subject variability in TfR (which reflects differences in the homeostatic setpoint during the study year) could be explained by the regression on gender, iron, Tf, and ferritin values.

Biological variability in serum vitamin E concentrations: relation to serum lipids

The components of biological variation in serum vitamin E in relation to serum cholesterol, triglycerides, high- and low-density lipoprotein cholesterol (HDL-C, LDL-C), apolipoprotein A-I (apo A-I), and apo B were examined in 26 healthy volunteers who had monthly blood samplings during one calendar year. The estimated CVs for vitamin E were: interindividual, 19.9%, and intraindividual, 11.9%; the index of individuality (I-index) was 0.59. The I-indices for all lipid variables were < 0.51. Serum concentrations of vitamin E, cholesterol, triglycerides, HDL-C, LDL-C, and apo B were lower in spring than in the other seasons. The peak-trough differences in the yearly variations, expressed as a percentage of the mean, were for vitamin E 14.5%, cholesterol 16.2%, triglycerides 14.5%, and LDL-C 24.3%. A significant common annual rhythm was expressed in vitamin E or lipid variables and in the changes in ambient temperature the weeks before blood sampling (inverse relations). There were highly significant positive time relations between serum vitamin E and cholesterol, triglycerides, and apo B. Subjects with higher homeostatic setpoints of cholesterol showed higher homeostatic setpoints of vitamin E, triglycerides, LDL-C, and apo B.

Components of biological, including seasonal, variation in hematological measurements and plasma fibrinogen concentrations in normal humans.

This study has been carried out in order to examine the components of biological and, in particular, seasonal variation in hematologic measurements in normal humans. Toward this end, 26 normal volunteers had monthly blood samplings during one calendar year for determination of number of red blood cells (RBC) and platelets, hemoglobin (Hb), hematocrit (Ht), mean corpuscular volume (MCV), MC Hb (MCH), MC Hb concentration (MCHC), RBC distribution width (RDW), mean platelet volume (MPV), platelet distribution width (PDW), plateletcrit (PCT), and plasma fibrinogen concentrations. The data were analyzed by means of spectral analyses of a group of time series or a single time series, and by means of repeated measures analyses of variance. Most of the hematologic variables show seasonal rhythms, such as annual rhythms or harmonics, which are expressed as a group phenomenon. An important part of the variance ( > 15%) in Ht, MCV, MCH, MCHC, RDW, number of platelets, MPV and plasma fibrinogen was explained by a yearly variation. The peak-trough differences (expressed as a percentage of the mean) in the yearly variations in number of RBC, Ht, MCV, MCH, MCHC and RDW were very low (all < 8.5%). Number of platelets (14.4%) and plasma fibrinogen values (28%) showed a high-amplitude yearly variation. All hematological variables, except MCHC, show a high interindividual variability which exceeds by far the intraindividual variability.

Circadian and seasonal variations of electrolytes in aging humans

The circadian and seasonal variations of a set of routinely determined variables (chloride, sodium, potassium, calcium, inorganic phosphorus, magnesium, creatinine, urea and urate) were documented in young men (mean age ± SD: 24.0 ± 3.9 yr) and in healthy elderly men (75.3 ± 6.6) and women (78.2 ± 9.1). The same urinary variables, except magnesium, were studied in young men. The circadian variability of serum variables was between 2 and 11% except for serum inorganic phosphorus (12–22% according to the group). By contrast, urinary chloride, sodium and potassium revealed large peak-trough differences (55–75%) and the variability of urinary creatinine, urate and urea was also not negligible (20–30%). ANOVA validated seasonal variations for most of the plasma variables and for urinary calcium, phosphorus and uric acid. No age or sex difference in either 24 h means or amplitudes could be observed. These data are of interest for the concept of reference values, for the diagnosis of certain bone and renal disease as well as for chronooptimization in treatment of potential electrolytes deficiency states.

Multipotent stem cell (CFU-S) numbers and circadian variations in aging mice.

The multipotent stem cell (CFU-S) numbers were studied in aging female C3H mice (16, 21 and 26 months old, respectively) versus young controls (3 months old). Using the spleen colony technique, the d-8 CFU-S numbers were measured every 3 h during the 24-h period at three different times of the year. Prominent circadian variations were found in young mice. The peak and trough values were significantly different also in aging mice, although the peak-trough differences were declining. When comparing young and old mice at different times of the 24-h period, the CFU-S numbers were sometimes significantly different, but often not. The 24-h mean values were consistently declining during aging. Young mice had different circadian variation patterns and 24-h mean values when examined at different times of the year. It is concluded that the d-8 CFU-S numbers decline in aging mice. Conflicting reports may partly be due to neglect of physiological variations.

Food and a sustained release theophylline tablet on chronic dosing: bioavailability, peak-trough and trough-trough differences.

The bioavailability of theophylline and the serum concentration fluctuations after administration of a sustained release tablet (Theograd 250 mg, one tablet twice daily) were studied in the steady state in six volunteers. On postprandial administration of the 250 mg tablets the bioavailability was 89 +/- 16%. Good sustained release properties were obtained provided that the tablets were taken after a meal; Cmax was 7.9 +/- 2.0 mg X 1(-1), tmax was 5.3 +/- 1.6 h, the peak-trough difference was 2.3 +/- 0.6 mg X 1(-1) and the serum concentration fluctuation was accounted for 42.8 +/- 11.2%. It was shown that on postprandial administration the mean serum concentration-time profile could be successfully calculated by means of multiple dose projection from single dose data. However, when the a.m. dose was given on an empty stomach and the p.m. dose 3 h after a meal, it appeared not to be possible to use the single diurnal dose data for calculation of the steady state serum concentration-time profile: the experimentally observed a.m. trough levels were significantly higher than the p.m. trough values and also the observed mean serum concentration was significantly higher than the calculated level. The possible causes for this discrepancy are extensively discussed.

Evaluation of a sustained-release theophylline tablet in young asthmatics.

A sustained-release theophylline (SRT) tablet was evaluated in 15 children with moderately severe asthma between the ages of 3 and 5 years (4.2 +/- 0.83 years). They received a mean daily dose of 20.4 mg/kg given q12h for 3 or more weeks with daily symptom scores and twice daily peak flow rates (PFR) measured. Serum theophylline levels (STL) were then obtained at 0, 1, 2, 4, 6, 8, 10, and 12 hr (eight children had 24-hr samples obtained), along with PFRs every 3 hr. The mean peak STL (x +/- SD) was 16.6 +/- 4.4 and the trough was 5.9 +/- 2.8, with a peak-trough difference of 10.6 +/- 3.9. The average time to peak level was 3.9 hr. The mean +/- SD clearance was 1.42 +/- 0.63 ml/kg per min and the apparent T1/2 was 5.11 +/- 1.34 hr. The average weekly morning PFR for the 3-week period ranged from 116.8 +/- 41.2 to 127.4 +/- 37.4 L/min, and the evening PFT ranged from 126.5 +/- 38.4 to 137.0 +/- 40.9 L/min. In conclusion, the SRT tablet is effective in treating many young asthmatics on a 12-hr dosage schedule. For some children who experience excessive peak-trough differences, an 8-hr dosage schedule may be indicated.

Pharmacokinetic consequences of drug displacement from blood and tissue proteins.

Displacement of one drug by another from blood and/or tissue protein will alter the pharmacokinetic behaviour of the displaced drug. For restrictively cleared drugs, displacement from blood proteins will cause only a transient change in free drug concentration and hence in pharmacodynamic response, so that dosage adjustments are rarely necessary. Total drug concentrations, however, are decreased and must be appropriately interpreted. Binding displacement from blood and/or tissue will also shorten the half-lives of these drugs, thus magnifying peak-trough differences during a dosage interval. These theoretical expectations are supported by examples of drug displacement interactions involving warfarin and phenytoin. Although total drug concentrations in blood will be unchanged, free drug concentrations will be increased and drug response enhanced for non-restrictively cleared drugs as a result of displacement from blood protein, possibly necessitating a dosage reduction.

The hemoprotein content of Chromatium sp. strain D

1. The hemoprotein content of autotrophic Chromatium strain D has been measured from difference spectra, using solvent-extracted and intact cells. 2. The quantities of the individual cytochromes were estimated by absorbance differences at single wavelengths and by peak-trough differences in spectra obtained from reduced versus oxidized, and CO-treated reduced versus reduced preparations. The concentrations found in intact cells weer 1.15, 0.49 and 0.56 nmoles heme per mg protein for cytochromes c 553, cc′ and c 555 ∗∗ ∗∗ The components of the cytochrome system in Chromatium were named according to the recommendations of the International Union of Biochemistry on Nomenclature and Classification of Enzymes 1. , respectively. In intact cells, the corresponding values were 1.33, 0.47 and 0.67 nmoles heme per mg protein. 3. The mesoheme content of the cells, estimated as pyridine hemochromogen, was 2.08 nmoles heme per mg protein, while the amount of protoheme was negligible.