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At least 1,153 records · Page 64Linked to original sources
PubMed2003

Differential changes in expression of a and b FGF, IGF-1 and -2, and TGF-alpha during seasonal growth and involution of roe deer testis.

Growth factors are involved in the regulation of testicular growth and involution of seasonal breeders. Therefore, we studied the seasonal expression of several growth factors in roe deer: aFGF, bFGF, IGF-1, IGF-2, and TGF-alpha. Total RNA from testis tissue was extracted monthly and analyzed using quantitative RT-PCR. Localization of mRNAs was examined by in situ-hybridization. Levels of expression differed by more than three orders of magnitude. Expression also showed different seasonal patterns. IGF-1, IGF-2 and bFGF were maximally transcribed during testis recrudescence in spring. In contrast, the mRNA amount of aFGF reached its maximum between July (breeding season) and January. TGF-alpha mRNA-levels were very low and showed poor seasonal variation. Each growth factor showed its own typical expression localization in testicular tissues and cell types. The results suggest the specific role of different growth factors in the paracrine control of spermatogenesis and its seasonal regulation.

Animals↗
PubMed2003

The regionality of campylobacteriosis seasonality in New Zealand.

New Zealand has one of the highest incidences of campylobacteriosis in the developed world, which leads a global trend of increasing notifications of Campylobacter infections over the last decade. Foodborne and waterborne transmission have been implicated as significant mechanisms in the complex ecology of the disease in New Zealand. We examined both regional and temporal variation in notification rates to gain some insight into the role of the New Zealand environments in modifying disease incidence. Firstly, there is a marked difference in the seasonality of campylobacteriosis between the North and South Islands of New Zealand. The Far North and much of the rural North Island were found to display relatively low summer incidence and small inter-seasonal variation. Secondly, there appears to be a dispersed grouping of North Island urban areas, including Auckland, Hamilton, Napier and their hinterlands as well as a few areas on the South Island that exhibit higher summer incidence and more seasonality than the first group. Thirdly, Christchurch, Dunedin, much of the South Island and the lower North Island cities of Wellington and Upper Hutt appear to experience the highest summer incidence and strongest inter-seasonal variation in New Zealand. These three broad groupings of campylobacteriosis seasonality, constructed using a principal components analysis, suggest that the importance of transmission routes may vary regionally in New Zealand. The observed variation in seasonal incidence indicates a complex ecology that is unlikely to be explained by a single dominant transmission route across these three groupings.

Campylobacter Infections↗
PubMed2001

Seasonal variations of T-cell cytokine pattern in peripheral blood from atopic subjects.

Previous studies on the effect of seasonal exposure to the sensitizing antigen on T-cell cytokine pattern from atopic subjects evaluated T-cell cytokine production by titration in the serum or culture supernatants. The purpose of this study was to determine the seasonal variations of T-cell cytokine pattern from atopic subjects at the single-cell level. We examined the interleukin-4 (IL-4) and interferon-gamma expression in peripheral blood CD4 + and CD8 + T cells from 11 subjects with grass-pollen-sensitive allergy before and during the 1999 grass pollen season using a flow cytometric method of intracellular cytokine detection. Eight healthy volunteers served as the control group. Flow cytometric analysis of peripheral blood lymphocytes showed no seasonal variations of IL-4- and interferon-gamma-producing T cells in atopic subjects. However, there was a decreased percentage of IL-4-producing cells among peripheral blood CD4+ and CD8+ T cells from the atopic subjects both during and outside the pollen season in comparison to the controLs. We did not find seasonal variations of T-cell cytokine pattern in peripheral blood from atopic subjects. However, we observed a decreased percentage of IL-4-producing T cells in peripheral blood from these subjects in comparison to healthy controls. These data add to the view of a continuous migration of T helper 2 (TH2) cells from the blood to the tissues of primary allergen exposure.

Adult↗
PubMed2002

Seasonal variations in hospital admissions for asthma in Malta.

The seasonality of asthma exacerbations may reflect varying exposure to triggers. This study retrospectively analyzes the seasonality of asthma hospital admissions, at all ages, in a population-based study. Analysis of the seasonality of asthma admissions and correlation with temperature was carried out in the setting of a regional hospital covering all acute asthma admissions in an island population. Admissions were divided into pediatric (1994-8) and adult (1989-8) cases. Both pediatric (0-14 years; n = 2916) and adult (15-59 years; n = 1269) admissions showed a peak in January and a trough in August. The seasonality in pediatric admissions was far more pronounced than in adults. Both cohorts exhibited a second, smaller peak in spring. In school-aged children, the end of school in June was associated with a sharp (91%) drop in admissions, and restarting school in October was associated with an even sharper rise (165%). A negative correlation was found between admissions and mean monthly ambient temperatures, and this was most pronounced in the pediatric age groups. This marked seasonality may indicate that temperature is a proxy for the total time spent indoors. Both the start and end of school had a profound impact on pediatric admission rates. Prospective studies are necessary to establish the role of viral infections and the influence of indoor and outdoor aeroallergens on the seasonality of hospitalization rates for asthma in the local setting.

Adolescent↗
PubMed2005

Thermal acclimation of metabolic rate may be seasonally dependent in the subtropical anuran Latouche's frog (Rana latouchii, Boulenger).

We tested the hypothesis that the lack of metabolic thermal acclimation ability in tropical and subtropical amphibians is dependent on season and investigated the effects of body size, sex, time of day, and season on metabolic rates in Rana latouchii. The males were acclimated at 15 degrees, 20 degrees, and 25 degrees C, and their oxygen consumption was measured at 15 degrees, 20 degrees, 25 degrees, and 30 degrees C in all four seasons, with the exception that we did not measure oxygen consumption at 30 degrees C in winter frogs. We also acclimated the males at 30 degrees C in summer for investigating diel variation of metabolic rate. The females were acclimated at 20 degrees and 25 degrees C, and their oxygen consumption was measured at 15 degrees , 20 degrees , 25 degrees , and 30 degrees C in summer. Our results showed that metabolic rates of R. latouchii differed by time of day, season, and acclimation temperature but did not differ by sex if the results were adjusted for differences in body mass. Summer males exhibited a 26%-48% increase in metabolic rates from the lowest values in the seasons. There was a trend of increased oxygen consumption in cold-acclimated males, but it was significant only at 15 degrees and 25 degrees C in summer, autumn, and winter. These results support the hypothesis that thermal acclimation of metabolism is seasonally dependent, which has not been reported in other tropical and subtropical amphibians.

Acclimatization↗
PubMedDate not supplied

Laboratory-based measurements of swimming performance and related metabolic rates of field-sampled smallmouth buffalo (Ictiobus bubalus): a study of seasonal changes.

Numerous studies have demonstrated how the performance physiology of fish may change when they are acclimated to designated laboratory temperatures, but few researchers have examined naturally occurring seasonal effects on several physiological parameters associated with swimming performance. Using field-acclimatized smallmouth buffalo (Ictiobus bubalus) collected each season, we report significant seasonal effects in the following variables: critical swimming speed (modified), metabolic rate (standard, active, and scope for activity), and swimming efficiency (total and net cost of transport). Underlying seasonal changes in performance was the reproductive cycle of buffalo, particularly the period of fall gonadal recrudescence. Compared with spring, fall buffalo had a significantly lower mean critical swimming speed (72%) and lower active metabolic rate (53%), even when tested at similar temperatures. During spring, buffalo had a high mean critical swimming speed and low net cost of transport in comparison with other seasons. Buffalo are known to participate in a spring migration and spawning that may require the increased performance and efficiency observed during that season. In addition, significant sex effects were detected in winter measurements of standard metabolic rate and net cost of transport, with females the more efficient swimmers.

Animals↗
PubMedDate not supplied

Daily and seasonal rhythms in selected body temperatures in the Australian lizard Tiliqua rugosa (Scincidae): field and laboratory observations.

This study examined daily and seasonal activity and thermoregulatory behaviour of the sleepy lizard, Tiliqua rugosa, a large, diurnally active temperate-dwelling Australian lizard, in the field and laboratory. Activity temperatures in the field were compared with those selected by lizards in laboratory thermal gradients in order to assess the extent to which endogenous versus exogenous factors contribute to seasonal variations in thermoregulatory behaviour. In the field, lizards are most active in late winter-spring (August-November), during which their activity varies from mostly unimodal on days of mild temperature to bimodal on hot days. In late spring-summer (November-January), activity is largely restricted to early morning, and at all other seasons sleepy lizards are rarely active. The winter-spring activity of sleepy lizards is constrained by low environmental temperatures, as lizards at these seasons have low body temperatures in the field but higher temperatures in laboratory thermal gradients. The lower temperatures selected in the laboratory in the summer-autumn months suggest the avoidance of high ambient temperatures and general inactivity in the field at these times. Thermal selection in the laboratory at the eight times of year tested showed that the phase of the minimum and maximum temperature selected and the amplitude of the rhythm of temperature selected varied continuously with the time of year. These daily and seasonal shifts in thermoregulatory behaviour may be regulated by endogenous physiological mechanisms coupled with seasonal ecological constraints such as food availability.

Animals↗
PubMed2003

Seasonal changes in platelets, fibrinogen and factor VII in elderly people.

BACKGROUND: an increase in mean platelet volume and a decrease in platelet total have been reported following stroke and increased mean platelet volume in acute myocardial infarction has been shown to be predictive of mortality. OBJECTIVE: given the established seasonal variation in morbidity and mortality from cardiovascular disease and various risk factors for the disease, we explored the seasonal variation in mean platelet volume and platelet total. METHODS: we assessed levels of platelet count, platelet volume, fibrinogen, factor VII, core body and ambient temperatures in 54 healthy community dwelling elderly volunteers over a period of 1 year. We used cosinor rhythmometry to quantify and compare the seasonal rhythms. RESULTS: we found significant seasonal variation in fibrinogen, mean platelet volume and core body temperature all of which peaked synchronously in May/June, in a year with an atypically mild winter and hot summer. Platelet total and factor VII did not exhibit a seasonal rhythm. CONCLUSIONS: we conclude that the synchrony between peak size of platelets and peak level of fibrinogen will significantly increase the likelihood of thrombotic events. These results provide further evidence of a seasonal pro-thrombotic state, which has a complex relationship with temperature.

Aged↗
PubMed2005

Seasonal patterns in monthly hemoglobin A1c values.

The purpose of this study was to investigate seasonal variations in population monthly hemoglobin A(1c) (A1c) values over 2 years (from October 1998 to September 2000) among US diabetic veterans. The study cohort included 285,705 veterans with 856,181 A1c tests. The authors calculated the monthly average A1c values for the overall population and for subpopulations defined by age, sex, race, insulin use, and climate regions. A1c values were higher in winter and lower in summer with a difference of 0.22. The proportion of A1c values greater than 9.0% followed a similar seasonal pattern that varied from 17.3% to 25.3%. Seasonal autoregressive models including trigonometric function terms were fit to the monthly average A1c values. There were significant seasonal effects; the seasonal variation was consistent across different subpopulations. Regions with colder winter temperatures had larger winter-summer contrasts than did those with warmer winter temperatures. The seasonal patterns followed trends similar to those of many physiologic markers, cardiovascular and other diabetes outcomes, and mortality. These findings have implications for health-care service research in quality-of-care assessment, epidemiologic studies investigating population trends and risk factors, and clinical trials or program evaluations of treatments or interventions.

Age Distribution↗
PubMed2006

Parameter stability of the functional-structural plant model GREENLAB as affected by variation within populations, among seasons and among growth stages.

BACKGROUND AND AIMS: It is increasingly accepted that crop models, if they are to simulate genotype-specific behaviour accurately, should simulate the morphogenetic process generating plant architecture. A functional-structural plant model, GREENLAB, was previously presented and validated for maize. The model is based on a recursive mathematical process, with parameters whose values cannot be measured directly and need to be optimized statistically. This study aims at evaluating the stability of GREENLAB parameters in response to three types of phenotype variability: (1) among individuals from a common population; (2) among populations subjected to different environments (seasons); and (3) among different development stages of the same plants. METHODS: Five field experiments were conducted in the course of 4 years on irrigated fields near Beijing, China. Detailed observations were conducted throughout the seasons on the dimensions and fresh biomass of all above-ground plant organs for each metamer. Growth stage-specific target files were assembled from the data for GREENLAB parameter optimization. Optimization was conducted for specific developmental stages or the entire growth cycle, for individual plants (replicates), and for different seasons. Parameter stability was evaluated by comparing their CV with that of phenotype observation for the different sources of variability. A reduced data set was developed for easier model parameterization using one season, and validated for the four other seasons. KEY RESULTS AND CONCLUSIONS: The analysis of parameter stability among plants sharing the same environment and among populations grown in different environments indicated that the model explains some of the inter-seasonal variability of phenotype (parameters varied less than the phenotype itself), but not inter-plant variability (parameter and phenotype variability were similar). Parameter variability among developmental stages was small, indicating that parameter values were largely development-stage independent. The authors suggest that the high level of parameter stability observed in GREENLAB can be used to conduct comparisons among genotypes and, ultimately, genetic analyses.

Agriculture↗
PubMed2006

Dietary diversity scores and nutritional status of women change during the seasonal food shortage in rural Burkina Faso.

In developing countries, dietary diversity is usually assessed during a single yearly period and the effects of seasonal variations remain unknown. We studied these variations in women living in a Sahelian rural area (Burkina Faso). A representative sample of 550 women was surveyed at the beginning and at the end of the seasonal cereal shortage in April and September 2003, respectively. For each season, a dietary diversity score (DDS) representing the number of food groups consumed over a 24-h period, was computed and nutritional status was assessed by the BMI. The DDS increased from 3.4 +/- 1.1 to 3.8 +/- 1.5 food groups between the beginning and the end of the shortage season (P < 0.0001), and the proportion of women exhibiting low DDS decreased from 31.6 to 8.1%. This was due to the consumption of foods available during the cereal shortage season and despite the decrease in the consumption of some purchased foods. The increase in DDS was lower in women for whom DDS was already high in April and vice versa. Over the same period, the percentage of underweight women (BMI <18.5 kg/m(2)) increased from 11.1 to 17.1%. The relation between DDS and the women's socioeconomic characteristics or nutritional status was weakened in September. Thus, in April, fewer women were underweight when their DDS was high than when it was medium or low [odds ratio = 0.3 (0.2; 0.6)], but not in September [odds ratio = 0.6 (0.3; 1.0)]. In such a context, it would be useful to measure dietary diversity at the beginning of the cereal shortage season, when many women exhibit low DDS.

Adult↗
PubMed1987

Seasonal variation in the incidence of cutaneous malignant melanoma: an analysis by body site and histologic type.

A seasonal analysis of the incidence of cutaneous malignant melanoma was conducted to investigate the degree to which the increased frequency of cases diagnosed in the summer may be due to an artifact of increased ascertainment. The monthly incidence of 13,151 microscopically-confirmed cases of cutaneous malignant melanoma diagnosed between 1973 and 1982 among white residents of nine regions in the United States served by population-based cancer registries participating in the Surveillance, Epidemiology, and End Results (SEER) program was evaluated for the presence of seasonal trends. Except for nodular melanoma, there was substantial seasonal variation in the incidence of all histologic types. For the two most common categories, superficial spreading melanoma and melanoma not further classified as to histology (of which the majority are likely to be superficial spreading melanoma), the peaks in incidence at body sites which are likely to experience seasonal changes in clothing (upper limbs, trunk, legs) occurred in the summer and were of similar relative size to the peaks, located in the spring, at sites which are likely to experience little variation in clothing during the year (head, face, and neck). A summer peak was also observed for Hutchinson's melanotic freckle melanoma of the head, face, and neck. The presence of seasonal variation in the incidence of superficial spreading melanoma of the head, face, and neck suggests that increased ascertainment cannot by itself account for seasonal variation in the incidence of superficial spreading melanoma of other parts of the body.

Female↗
PubMed1989

Fetal loss associated with two seasonal sources of electromagnetic field exposure.

We have studied two sources of electromagnetic fields where exposure is highly seasonal (ceiling cable electric heat and electrically heated beds). Because many potential confounders could not be addressed, we can make no valid statement about overall differences in abortion rates between those exposed and those not exposed to these seasonal sources. However, by analyzing seasonal trends, we have minimized the problem of unaddressed confounders because we did not look at a difference between the user and nonuser groups, but rather at a difference within the user group during months of higher exposure compared with months of lower exposure. Thus, each user group provides its own control. The function of the nonuser control group is simply to assure that any seasonal trend found in the user group is not just a general seasonal variation in reported fetal loss that can be found equally well in the nonuser population. Using this technique, we found that each user group reported fetal loss disproportionately often during the season when electromagnetic field exposure was increasing.

Abortion, Spontaneous↗
PubMed2000

The relationship between elevated fibrinogen and markers of infection: a comparison of seasonal cycles.

To test the hypothesis that higher levels of fibrinogen in winter are related to infections via the acute phase response, we assessed seasonal variation in fibrinogen and C-reactive protein, together with three other responses to infection: white cell count, human herpesvirus-6 IgG antibody and interleukin-6. Monthly blood samples from 24 subjects aged 75+ years were assessed for fibrinogen, C-reactive protein, white cell count, and human herpesvirus-6 IgG antibody. Interleukin-6 was measured in seven. Seasonal variation of these measures was determined by the population-mean cosinor procedure. Fibrinogen had a significant seasonal variation with a winter peak (mid-February) 1.26 g/l above the corresponding summer trough. C-reactive protein had a late-February peak, 3.71 mg/l above the summer trough. No seasonal rhythm was found in any other response to infection investigated. This study provides no evidence that winter infections are responsible for the seasonal variation in fibrinogen or C-reactive protein. The explanation for the seasonal changes in these proteins remains unknown.

Aged↗
PubMed2003

Changes in seasonal deaths from myocardial infarction.

BACKGROUND: Cardiovascular disease is the major contributor to excess morbidity and mortality in winter. With the rise in temperatures through global warming, and the use of central heating and air conditioning, this seasonal variation may be declining. AIM: To study possible changes in seasonal variation in case-fatality rates of myocardial infarction (MI), in men and women, over a 20-year period and compare this with possible environmental influences. DESIGN: Retrospective analysis of death certificate and climatological data. METHODS: We analysed all monthly death certificate data from Northern Ireland, for death caused by MI from 1979 through 1998 (n=68 683). Mortality data were standardized to a single reference group for the whole period. Seasonal variation in mortality and in environmental variables was described using the cosinor model. RESULTS: A total of 29 875 women and 38 808 men died from MI during the 20-year period. A significant decrease in mortality from MI was observed in both sexes, accompanied by a non-significant decline in the amplitude of the seasonal rhythm over the study period. Low temperature was associated with higher mortality rates from MI. DISCUSSION: We have documented an overall decline in cardiovascular mortality from 1979 to 1998, together with a small but non-significant decrease in seasonal variation. While improvements in medical care, lifestyle, housing and diet may have contributed to the observed decline in mortality rate, seasonal fluctuations remain a significant problem.

Female↗
PubMed2002

Contrasting distribution and seasonal dynamics of carbohydrate reserves in stem wood of adult ring-porous sessile oak and diffuse-porous beech trees.

We tested the hypothesis that broad-leaved forest species with contrasting wood anatomy and hydraulic system (ring-porous versus diffuse-porous) also differ in distribution and seasonal dynamics of carbohydrate reserves in stem wood. Total nonstructural carbohydrate (TNC) reserves (starch and sugars) were measured enzymatically in the 10 youngest stem xylem rings of adult oak (Quercus petraea (Matt.) Liebl.) and beech (Fagus sylvatica L.) trees during an annual cycle. Radial distribution of carbohydrates was investigated according to ring age. On all dates, oak trees had twofold higher TNC concentration than beech trees (41 versus 23 mg g(DM)(-1)), with starch accounting for the high TNC concentration in oak. Seasonal dynamics of TNC concentration were significantly (P < 0.05) more pronounced in oak (20-64 mg TNC g(DM)(-1)) than in beech (17-34 mg TNC g(DM)(-1)). A marked decrease in TNC concentration was observed in oak trees during bud burst and early wood growth, whereas seasonal fluctuations in TNC concentrations in beech trees were small. The radial distribution of TNC based on ring age differed between species: TNC was restricted to the sapwood rings in oak, whereas in beech, it was distributed throughout the wood from the outermost sapwood ring to the pith. Although the high TNC concentrations in the outermost rings accounted for most of the observed seasonal pattern, all of the 10 youngest xylem rings analyzed participated in the seasonal dynamics of TNC in beech trees. The innermost sapwood rings of oak trees had low TNC concentrations. Stem growth and accumulation of carbon reserves occurred concomitantly during the first part of the season, when there was no soil water deficit. When soil water content was depleted, stem growth ceased in both species, whereas TNC accumulation was negligibly affected and continued until leaf fall. The contrasting dynamics and distribution of carbohydrate reserves in oak and beech are discussed with reference to differences in phenology, early spring growth and hydraulic properties between ring-porous trees and diffuse-porous trees.

Carbohydrate Metabolism↗
PubMed2003

Seasonal trends in photosynthetic parameters and stomatal conductance of blue oak (Quercus douglasii) under prolonged summer drought and high temperature.

Understanding seasonal changes in photosynthetic parameters and stomatal conductance is crucial for modeling long-term carbon uptake and energy fluxes of ecosystems. Gas exchange measurements of CO2 and light response curves on blue oak leaves (Quercus douglasii H. & A.) were conducted weekly throughout the growing season to study the seasonality of photosynthetic capacity (Vcmax) and Ball-Berry slope (m) under prolonged summer drought and high temperature. A leaf photosynthetic model was used to determine Vcmax. There was a pronounced seasonal pattern in Vcmax. The maximum value of Vcmax, 127 micromol m(-2) s(-1), was reached shortly after leaf expansion in early summer, when air temperature was moderate and soil water availability was high. Thereafter, Vcmax declined as the soil water profile became depleted and the trees experienced extreme air temperatures, exceeding 40 degrees C. The decline in Vcmax was gradual in midsummer, however, despite extremely low predawn leaf water potentials (Psipd, approximately -4.0 MPa). Overall, temporal changes in Vcmax were well correlated with changes in leaf nitrogen content. During spring leaf development, high rates of leaf dark respiration (Rd, 5-6 micromol m(-2) s(-1)) were observed. Once a leaf reached maturity, Rd remained low, around 0.5 micromol m(-2) s(-1). In contrast to the strong seasonality of Vcmax, m and marginal water cost per unit carbon gain (partial partial differential E/ partial partial differential A) were relatively constant over the season, even when leaf Psipd dropped to -6.8 MPa. The constancy of partial partial differential E/ partial partial differential A suggests that stomata behaved optimally under severe water-stress conditions. We discuss the implications of our findings in the context of modeling carbon and water vapor exchange between ecosystems and the atmosphere.

California↗
PubMed2004

Spatial and seasonal variability of temperature responses of biochemical photosynthesis parameters and leaf nitrogen content within a Pinus densiflora crown.

We measured seasonal variation in area-based nitrogen concentration (N), maximum rate of carboxylation (Vcmax) and maximum rate of electron transport (Jmax) in 1-year-old needles along four first-order branches within a Pinus densiflora Sieb. & Zucc. crown, and analyzed their relationships to growth irradiance and temperature. Each leaf light environment was expressed as a ratio of the monthly mean of daily integrated photosynthetically active irradiance (Iint) for the particular needle to Iint above the canopy (Irel). Needle N decreased in the upper crown during the development of new needles, whereas it remained fairly constant in the lower crown, reflecting differences between upper and lower crown needles in their contribution to the nitrogen of new needles. Gradients of N within the crown were correlated with Irel in all seasons (r2 = 0.40-0.78). Seasonal variation in N was weakly correlated with mean daily air minimum temperatures. Both Vcmax and Jmax showed seasonal variation in all first-order branches, and decreased to their lowest values in winter. The gradients of Vcmax and Jmax within the crown were not correlated with Irel in some seasons, but were correlated with changes in N in most months (r2 = 0.33-0.75), except in the winter. Furthermore, the regression slope of the relationship between N and Vcmax and the temperature response of Vcmax and Jmax exhibited seasonal variation.

Electron Transport↗