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PubMed2006

Efficacy of montelukast during the allergy season in patients with chronic asthma and seasonal aeroallergen sensitivity.

BACKGROUND: Montelukast has proven efficacy in the treatment of chronic asthma and seasonal allergic rhinitis, but it has not been evaluated in the subpopulation of asthmatic patients with seasonal asthma symptoms. OBJECTIVE: To determine the effectiveness of montelukast treatment in improving the control of asthma symptoms during the allergy season in patients with active asthma and seasonal aeroallergen sensitivity. METHODS: Adults with a history of chronic asthma who are also symptomatic during the allergy season and with skin test sensitivity to seasonal aeroallergens were enrolled in a randomized, parallel-group, multicenter study with a 1-week, single-blind, placebo run-in period followed by 3 weeks of double-blind treatment during the spring of 2004. After the run-in period, eligible patients were randomly assigned to receive either oral montelukast (10 mg) or placebo. Daytime and nighttime asthma symptom scores, beta-agonist use, and morning and evening peak expiratory flow rates were recorded daily using an electronic diary. The primary end point was mean change from baseline to week 3 in the daytime asthma symptom score. RESULTS: Of 455 randomized patients, 433 completed the study. Compared with placebo, treatment with montelukast resulted in a significant improvement from baseline in the daytime asthma symptom score (-0.54 vs -0.34; P = .002) and in beta-agonist use, nighttime symptoms, and peak expiratory flow rates. Few patients in the montelukast and placebo groups discontinued study participation because of asthma (1.3% and 3.0%, respectively). CONCLUSION: In patients with chronic asthma and seasonal aeroallergen sensitivity, montelukast treatment provided significant asthma control during the allergy season compared with placebo.

Acetates↗
PubMed2001

Exhaled nitric oxide in seasonal allergic rhinitis: influence of pollen season and therapy.

Exhaled nitric oxide (eNO) has been proposed as a potential indirect marker of lower airway inflammation in asthma. To investigate the existence of lower airways inflammation in allergic rhinitis eNO measurements were performed in 32 patients with symptomatic and asymptomatic seasonal allergic rhinitis early in and out of pollen seasons and in 80 healthy volunteers. To further define how exhaled NO is modified by therapy, NO levels were detected following 1-month treatment with either inhaled steroids or non-steroids therapy with nedocromil. Exhaled NO (mean +/- SE) was significantly elevated in patients with seasonal allergic rhinitis with and without symptoms (24.2 + 2.5 and 13.9 + 2.9 ppb, respectively) as compared to healthy volunteers (4.5 + 0.3 ppb) both in and out of pollen season (21.2 + 2.1 and 9.0 + 1.4 p.p.b., respectively) with a higher increase during the allergen exposure in season. Higher levels of exhaled NO were detected in patients with symptoms, either from the upper or lower airways, and with bronchial hyperreactivity. The increased exhaled NO in symptomatic patients was reduced only by inhaled steroids and not by nedocromil. These findings possibly suggest the existence of lower airway inflammation in both symptomatic and asymptomatic patients with seasonal allergic rhinitis in and out of pollen season. Thus, exhaled NO may be used as a non-invasive index for early detection of lower airway inflammation and for monitoring the optional treatment in patients with seasonal allergic rhinitis.

Adult↗
PubMed2000

Seasonal changes in the expression of neuropeptide Y and pro-opiomelanocortin mRNA in the arcuate nucleus of the ovariectomized ewe: relationship to the seasonal appetite and breeding cycles.

Sheep experience well-documented seasonal changes in reproductive activity and voluntary food intake (VFI). Within the hypothalamus, neurones that express neuropeptide Y (NPY) and pro-opiomelanocortin (POMC) have been implicated in the regulation of reproduction and appetite. In this study, we aimed to determine the extent to which the expression of these two neuronal systems is linked to the seasonal reproductive cycle and/or the seasonal appetite cycle. VFI in our sheep reaches a nadir in August with no difference occurring between December and February. We examined the brains of ovariectomized (OVX) female sheep (n=5-7) that were killed during the breeding season (February) or during the early or late nonbreeding season (August and December, respectively). The brains of these animals were perfused with paraformaldehyde and processed for in situ hybridization histochemistry, using ribonucleotide probes labelled with 35S. The number of NPY and POMC cells and the number of silver grains per cell were counted using an image analysis system. For NPY, the number of cells counted in the arcuate nucleus/median eminence region and the number of silver grains per cell was significantly lower in animals killed during August than in animals killed in February or December. The number of grains per cell over NPY cells was also significantly lower in animals killed during August. For POMC, the number of cells was lower in February than in August and December. Similarly, the number of grains per cell for POMC were lower in February than in August and December. VFI was significantly lower in animals during August than at other times of the year. We conclude that in OVX ewes: (i) NPY gene expression is lower at the time of the year when VFI is reduced and (ii) POMC gene expression is greater at the time of the nonbreeding season than during the breeding season. Because these results were obtained in OVX animals, the changes appear to be independent of alterations in the secretion and/or action of ovarian steroids. Thus, the activity of NPY neurones appears to relate to changes in appetite whereas changes in POMC expression may be relevant to the seasonal breeding cycle.

Animals↗
PubMed2004

Seasonality and wildlife disease: how seasonal birth, aggregation and variation in immunity affect the dynamics of Mycoplasma gallisepticum in house finches.

We examine the role of host seasonal breeding, host seasonal social aggregation and partial immunity in affecting wildlife disease dynamics, focusing on the dynamics of house finch conjunctivitis (Mycoplasma gallisepticum (MG) in Carpodacus mexicanus). This case study of an unmanaged emerging infectious disease provides useful insight into the important role of seasonal factors in driving ongoing disease dynamics. Seasonal breeding can force recurrent epidemics through the input of fresh susceptibles, which will clearly affect a wide variety of wildlife disease dynamics. Seasonal patterns of social aggregation and foraging behaviour could change transmission dynamics. We use latitudinal variation in the timing of breeding, and social systems to model seasonal dynamics of house finch conjunctivitis across eastern North America. We quantify the patterns of seasonal breeding, and social aggregation across a latitudinal gradient in the eastern range of the house finch, supplemented with known field and laboratory information on immunity to MG in finches. We then examine the interactions of these factors in a theoretical model of disease dynamics. We find that both forms of seasonality could explain the dynamics of the house finch-MG system, and that these factors could have important effects on the dynamics of wildlife diseases generally. In particular, while either alone is sufficient to create recurrent cycles of prevalence in a population with an endemic disease, both are required to produce the specific semi-annual pattern of disease prevalence seen in the house finch conjunctivitis system.

Animals↗
PubMed2004

Off seasonal and pre-seasonal assessment of circulating energy sources during prolonged running at the anaerobic threshold in competitive triathletes.

OBJECTIVES: To compare changes in circulating energy sources during prolonged exercise in off season (OS) and pre-season (PS) training of triathletes. METHODS: Nine athletes of the Swiss national triathlon team (three female, mean (SD) age 28.7 (4.9) years, height 169.8 (6.0) cm, weight 57.0 (6.2) kg, VO(2)max 66.5 (5.3) ml/min/kg; six male, mean (SD) age 24.0 (4.1) years, height 181.4 (6.9) cm, weight 73.5 (6.0) kg, VO(2)max 75.9 (4.9) ml/min/kg) were tested twice (2.5 months apart) during a 25 km aerobic capacity test run at the end of the OS and just before the season. The average training load during the OS was 9.9 h/week, and this increased to 14.4 h/week in the PS. With heart rates as reference, exercise intensity during the aerobic capacity test was 97.0 (4.9)% of the anaerobic threshold and 91.2 (4.5)% of VO(2)max. Blood samples were collected before, during, and after the aerobic capacity test. Samples were collected every 5 km during three minute rest intervals. RESULTS: Blood was analysed for triglyceride (TG), free fatty acids, cholesterol, high density lipoprotein cholesterol, glucose, insulin, lactate, and changes in plasma volume. A two factor (season by distance) repeated measures analysis of variance revealed an increase in capacity for prolonged exercise in the PS by a decrease in running intensity during the aerobic capacity test (% of speed at 2.0 mmol/l lactate threshold, p = 0.008), an increase in running speed at the anaerobic threshold (p = 0.003) and at 4.0 and 2.0 mmol/l (p<0.001) of the lactate threshold. A significant season by distance interaction was found for TG (p<0.001). TG concentrations peaked at 5 km and decreased logarithmically throughout the OS (1.48 (0.34) to 0.86 (0.20) mmol/l) and PS (1.90 (0.31) to 0.73 (0.18) mmol/l) tests. From the OS to the PS, there was an increase in the difference in TG at 5-15 km with a concomitant increase at 2.0 mmol/l of the lactate threshold. The peak TG concentrations at 5 km followed by a logarithmic decrease suggest that TG may also provide circulating energy. A greater logarithmic decrease in TG occurred in the PS than in the OS, indicating a higher rate of use. There was an increase in the difference in TG at 5-15 km similar to the increase in the speed at 2.0 mmol/l of the lactate threshold between the two seasons. Glucose, insulin, lactate, and free fatty acids were similar in the two seasons. CONCLUSION: Free fatty acid and TG concentrations were much higher than expected, and the two training seasons showed significantly different patterns of TG concentration during prolonged running. These responses may be related to aerobic capacity of prolonged exercise.

Adult↗
PubMed1999

Prospective decrease in progesterone concentrations in female lightweight rowers during the competition season compared with the off season: a controlled study examining weight loss and intensive exercise.

The purpose of this study was to monitor ovarian hormone function response to intense exercise and body weight changes in female athletes. Ovarian hormone function was evaluated in 12 female lightweight rowers and 10 age-height-weight matched sedentary controls. Ovarian hormone function was assessed during consecutive competition season and off season, by measurement of peak and average alternative day overnight urinary oestrone glucuronide (E1G) and pregnanediol glucuronide (PdG) excretion. Competition season was associated with a 5.8 kg (9.3%) body weight loss in the lightweight rowers. Significantly lower competition season peak and average urinary excretion of PdG were found in the lightweight rowers compared with the controls. Lower competition season peak and average urinary excretion of E1G were also found in the lightweight rowers compared with the controls, but the difference did not reach significance. The number of rowing training hours was a significant determinant of peak PdG excretion in the rowers (R2 = 0.40; p<0.02). The seasonal suppression of PdG excretion was associated with degree of weight loss (R2 = 0.46; p<0.01). The competition related decrease in E1G and PdG excretion for the lightweight rowers was predominantly restored during the off season when exercise intensity and duration were decreased and body weight increased. These results showed a significant (p<0.05) reduction in progesterone metabolite excretion and a non-significant decrease in oestrone metabolite excretion associated with intensive competition season training loads and body weight reduction in female lightweight rowers.

Adolescent↗
PubMed1981

THe changing seasonality of infant deaths in England and Wales 1912-78 and its relation to seasonal temperature.

Seasonal variation in the rates of stillbirth, and of deaths under the age of one year, were studied for England and Wales in order to examine (a) changes in the seasonal variation over the years and (b) the correlation between seasonal rates and seasonal temperatures. The quarterly rates of stillbirths were studied for the period 1928-78; and of deaths under the age of one year, in six different age groups, for the period 1912-78. A disappearance of seasonal variation in rates ('deseasonality') occurrred from stillbirths in about 1950, and for neonatal deaths in about 1965. For deaths at 1-2 months a trend towards deseasonality has been apparent since 1955, but there has been no such trends for deaths at 3-11 months of age. In the period before deseasonality, and for the first quarter of the year, there was a high negative correlation between the neonatal death rate and the mean temperature in England and Wales but this correlation fell as the seasonal variation in rates fell. The findings suggest that seasonal variation in the neonatal death rate was closely related to winter temperatures during the period 1921-60. For deaths at 1-11 months old, there has been and still is a relation between temperature and seasonal variation in rates, but the relation was less close than for the neonatal death rate.

England↗
PubMed2000

[Effect of land management in winter crop season on seasonal variations of CH4 emissions from rice paddy soils].

A pot experiment in greenhouse was carried out to study seasonal variations of CH4 fluxes from rice paddy soils and the effect of land management in winter crop season on the seasonal variations. The results showed that four emission peaks occurred respectively 13 days after flooding and 7, 40, 91 days after rice transplanting, and CH4 emission amounts during the first 30 days after flooding accounted for as high as 67.5%, 35.5% and 33.3% of the total emission amounts during the observing period of 133 days for treatments with dry fallow but rice straw being applied just before flooding, alfalfa, and flooded fallow in winter crop season. However, for treatments with dry fallow but rice straw being applied before winter crop cultivating and winter wheat in winter crop season, CH4 emission amounts during the first 50 days after flooding just accounted for 0.27% and 6.74 of the total emission amounts during the observing period, and CH4 fluxes thereafter were also very small. Difference in the seasonal variation patterns of soil Eh due to land management in winter crop season was the main reason why seasonal variation patterns of CH4 fluxes from different treatments were different.

Methane↗
PubMed2005

[Correlation of serum concentration of tumor necrosis factor alpha, clinical course, ventilation and nonspecific bronchial hyperresponsiveness in patients with isolated seasonal rhinitis and seasonal asthma].

UNLABELLED: Tumor necrosis factor alpha (TNF-alpha) plays a central role in pathogenesis of many inflammatory diseases including asthma and allergic rhinitis. Its capability for cell activation, chemotaxis and upregulation of adhesion molecule expression on surface of inflammatory cells suggests that TNF-alpha may be responsible for bronchial hyperresponsiveness (BHR) and clinical symptoms of atopic diseases. THE AIM: Relationships between serum concentration of TNF-alpha and clinical course as well as nonspecific BHR in patients with isolated seasonal rhinitis (SR) and seasonal bronchial asthma (SA) were assessed. MATERIAL AND METHODS: The study was performed in 19 subjects with SR and 26 subjects with asthma sensitized to pollens, with measurable BHR during symptomatic phase of disease. Control group consists of 16 healthy volunteers. Serum concentration of TNF-alpha, ventilatory parameters, BHR to methacholine, asthma and seasonal rhinitis score were assessed two times--during and outside pollen season. RESULTS: Nonspecific BHR was find in 10 (21%) patients with SR and 18 (69%) patients with asthma symptoms out of season. In both groups postseasonal mean geometric values of PC20M were significant higher than during season. There were no marked changes in ventilatory parameters accompanied the increase in BHR. TNF-alpha concentration in serum in both groups of patients was significant higher than in healthy subjects. Further increase of its activity about 50-70% compared to baseline values was observed during pollen season. There was no correlation between serum concentration of TNF-alpha, BHR and symptom score. There is increased serum concentration of TNF-alpha in patients with seasonal airway allergy even in asymptomatic period of disease. CONCLUSIONS: Natural exposure to allergens causes significant increase of TNF-alpha concentration in patients with rhinitis and asthma. Although level of BHR and intensification of clinical symptoms coexist with changes in TNF-alpha concentration there is no correlation between them.

Adolescent↗
PubMed1999

The effect of first season chemoprophylaxis in calves on second season pasture contamination and acquired resistance and resilience to gastrointestinal nematodes.

Two groups of second grazing season cattle, which had been treated with an ivermectin-sustained-release bolus (ISRB) in their first grazing season, were monitored during consecutive years (1995 and 1996) on the same second grazing season pasture. In the preceding year (1994), this pasture had been grazed by yearlings that had not received chemoprophylaxis in their first grazing season. The objectives of the study were, firstly, to investigate whether the chemoprophylactic-treated yearlings were less resistant to gastrointestinal nematodes upon subsequent exposure, and hence excreted more strongyle eggs compared to the control yearlings; secondly, whether an increased susceptibility of the previously treated animals resulted in a yearly increase of the pasture infestation on the second grazing season pasture; and finally, whether this affected the second year weight gain of the animals. In 1996, the yearlings that had been chemoprophylactic-treated in 1995 excreted higher numbers of nematode eggs, compared to the previously 'untreated' yearlings. In addition, the proportion of Cooperia larvae was markedly higher in the faecal cultures from the chemoprophylactic treated-animals, suggesting a negative effect of preventive treatment with an ISRB on the acquired resistance of the animals. However, there was no evidence that the slightly higher egg output in the previously treated yearlings had an effect on the larval contamination of the second grazing season pasture. A significant yearly decrease in the second season average daily weight gains was observed, but it could not be inferred from the results of the parasitological parameters that the differences in second year growth were caused by different levels of resilience between chemoprophylactic-treated and -untreated animals. As the study covered three consecutive second grazing seasons, an effect of differences between years (e.g. in weather conditions or grass growth) on the results cannot be excluded.

Animal Husbandry↗
PubMed2000

Allergen induced mRNA expression of interleukin-5, but not of interleukin-4 and interferon-gamma, in peripheral blood mononuclear cells obtained before the pollen season predicts the clinical efficacy of immunotherapy for seasonal allergic rhinitis.

The primary aim of this study was to investigate whether the allergen-induced synthesis of cytokines by peripheral blood mononuclear cells (PBMCs) obtained immediately before the pollen season could predict the clinical efficacy of immunotherapy during the following pollen season. PBMCs (1.0 x 106 cells/ml) were obtained from 17 nonatopic subjects and from 60 patients receiving immunotherapy for seasonal allergic rhinitis (caused by Japanese cedar pollens) immediately before the pollen season of 1998, and were cultured for 24 h in the presence of 10 mg/ml of Cry j 1, a major allergen of Japanese cedar pollens, at 37 degrees C in a fully humidified 5% CO2 atmosphere. Total cellular RNA was extracted from the PBMCs, and the allergen-induced interleukin (IL)-4, IL-5 and interferon-gamma (IFN-gamma) mRNA expression was determined using a reverse transcription-polymerase chain reaction. According to the nasal symptoms during the pollen season of 1998, the 60 patients on immunotherapy were divided into 36 good responders (who had no nasal symptoms and no requirement for rescue medications) and 24 poor responders who needed rescue medications to control nasal symptoms. Neither IL-4 mRNA nor IL-5 mRNA was expressed in any of the 17 nonatopic individuals. By contrast, IL-4 mRNA was expressed in 26 good responders and in 22 poor responders, and IL-5 mRNA was expressed in eight good responders (22.2%) and in 23 poor responders (95.8%). IFN-gamma mRNA was expressed in four nonatopic subjects, in nine good responders and in seven poor responders. The expression of IFN-gamma did not differ significantly among the nonatopic subjects, the good responders and the poor responders. The mRNA expression of IL-5 (P < 0.0001), but not of IL-4 (P = 0.0999) and IFN-gamma (P = 0. 7713), differed significantly between the good and poor responders. Therefore, our study has highlighted that positive expression of IL-5 mRNA in PBMCs sampled immediately before the pollen season could be predictive of a poor clinical outcome of immunotherapy during the following pollen season and that the down-regulation of IL-5 mRNA expression in PBMCs could be an important mechanism of pollen immunotherapy related to the clinical efficacy.

Actins↗
PubMed1996

Winter seasonal affective disorder: a follow-up study of the first 59 patients of the National Institute of Mental Health Seasonal Studies Program.

OBJECTIVE: The purpose of this study was to characterize the long-term course of patients with seasonal affective disorder. METHOD: The first 59 patients with winter seasonal affective disorder who had entered winter protocols were retrospectively followed up after a mean interval of 8.8 years. Detailed life charts were constructed through use of a semistructured interview and collateral records. RESULTS: The disorder of 25 patients (42%) remained purely seasonal, with regular recurrences of winter depression and no depression or treatment through any summer. The course of illness was complicated by varying degrees of nonseasonal depression in 26 patients (44%). The disorders of eight patients (14%) had fully remitted. Certain features of the group with complicated seasonal affective disorder suggested that they were more severely ill. Twenty-four patients (41%) continued to use light treatment regularly throughout the follow-up period. Light treatment was preferred to medication for winter recurrences, although antidepressants had been used in the winter by most (63%) of the patients who still used lights at follow-up. CONCLUSIONS: The pattern of winter depressions and summer remissions remained fairly persistent over time in this group of patients. The temporal distribution of depressive episodes both within and across individual patients was consistent with the results of several recent follow-up studies of seasonal affective disorder, providing support for the predictive and construct validity of the Rosenthal et al. diagnosis of winter seasonal affective disorder. Light treatment, while remaining a safe and satisfactory treatment for many, may be insufficient for more severely ill patients. The appearance of nonseasonal depressions in patients with winter seasonal affective disorder may be associated with greater severity of illness and less responsiveness to light treatment.

Antidepressive Agents↗
PubMed1996

Seasonal changes in pituitary function: amplification of midfollicular luteinizing hormone secretion during the dark season.

OBJECTIVE: To analyze the effect of season on the pulsatility of gonadotropin secretion in women living in an area with a large annual variability in daylight length. DESIGN: A prospective study. Pulse studies were carried out in each subject during both the dark and light season. SETTING: The gynecologic endocrine research unit of the University Central Hospital of Oulu. PARTICIPANTS: Eleven ovulatory, healthy women volunteering for the study. INTERVENTIONS: Serum samples were collected at 10-minute intervals for 6 hours on days 7 to 9 of the cycle. MAIN OUTCOME MEASURES: Serum LH and FSH concentrations were measured and the data were analyzed with an algorithm computer-based program. RESULTS: The mean area of LH pulses analyzed was significantly higher during the dark season than the light season (49.1 +/- 3.1 versus 38.5 +/- 1.7 mIU/mL; conversion factor to SI unit, 1.00), while in the amplitude (1.9 +/- 0.1 versus 1.8 +/- 0.1 mIU/mL), number of pulses (5.2 +/- 0.3 versus 4.4 +/- 0.6), and the mean level (9.6 +/- 0.5 versus 9.4 +/- 0.9 mIU/mL) the difference did not reach statistical significance. The number (5.2 +/- 0.5 versus 5.2 +/- 0.4,), amplitude (1.0 +/- 0.05 versus 1.1 +/- 0.07 mIU/mL; conversion factor to SI unit, 1.00), area (29.9 +/- 2.4 versus 29.6 +/- 3.1 mIU/mL), and the mean level of FSH (5.4 +/- 0.6 versus 6.0 +/- 0.8 mIU/mL) during the dark and light seasons were identical, showing no seasonal variability. CONCLUSIONS: The results indicate increased pituitary LH secretion in the midfollicular phase during the dark season that may be related to increased melatonin secretion and decreased ovarian activity at this time of the year.

Adult↗
PubMed1995

Are seasonal preferences in pregnancy planning a source of bias in studies of seasonal variation in reproductive outcomes? The European Study Group on Infertility and Subfecundity.

Seasonal variation in reproductive failures is expected, as many of the putative causes change over the seasons. Many studies have documented such seasonal variation in reproductive failures, but none has addressed the potential source of bias related to seasonal planning of pregnancies. Our aim was to quantify this bias under realistic assumptions. We used data from the European Study of Infertility and Subfecundity, which is a study based upon representative samples of women age 25-44 years in different parts of Europe. Data on pregnancy planning stem from personal interviews. Altogether, we analyzed 4,731 pregnancies. Results show that pregnancy planning is not evenly distributed over the seasons, with summer the preferred time for starting pregnancy. The most fecund will conceive within the preferred time, but those who are subfecund may not succeed until later. Since subfecund women have a higher risk of some reproductive failures (spontaneous abortions, for example), the seasonal planning differences could in themselves lead to seasonal variations in reproductive failures. A simulation model shows that bias related to differential pregnancy planning is likely to have only a small impact under the present conditions in Europe.

Abortion, Spontaneous↗
PubMed2002

Cyclic variation in seasonal recruitment and the evolution of the seasonal decline in Ural owl clutch size.

Plastic life-history traits can be viewed as adaptive responses to environmental conditions, described by a reaction norm. In birds, the decline in clutch size with advancing laying date has been viewed as a reaction norm in response to the parent's own (somatic or local environmental) condition and the seasonal decline in its offspring's reproductive value. Theory predicts that differences in the seasonal recruitment are mirrored in the seasonal decrease in clutch size. We tested this prediction in the Ural owl. The owl's main prey, voles, show a cycle of low, increase and peak phases. Recruitment probability had a humped distribution in both increase and peak phases. Average recruitment probability was two to three times higher in the increase phase and declined faster in the latter part of the season when compared with the peak phase. Clutch size decreased twice as steep in the peak (0.1 eggs day-1) as in the increase phase (0.05 eggs day-1). This result appears to refute theoretical predictions of seasonal clutch size declines. However, a re-examination of current theory shows that the predictions of modelling are less robust to details of seasonal condition accumulation in birds than originally thought. The observed pattern can be predicted, assuming specifically shaped seasonal increases in condition across individuals.

Adaptation, Physiological↗
PubMed1991

Role of the thyroid gland in seasonal reproduction: thyroidectomy blocks seasonal suppression of reproductive neuroendocrine activity in ewes.

Seasonal reproductive transitions in ewes are generated endogenously and are synchronized by annual changes in photoperiod. Previous evidence indicates that thyroidectomy prevents the transition to anestrus in ewes maintained in a fixed day length, suggesting that the thyroid is needed for endogenously generated reproductive arrest. Here we tested the hypothesis that the thyroid is required for endogenous seasonal suppression of the neuroendocrine mechanism that regulates pulsatile LH secretion. Ewes were thyroidectomized (n = 6) in summer, 6 weeks before the onset of the breeding season, or they remained thyroid intact (n = 6). They were housed in a simulated natural photoperiod until the winter solstice; thereafter, they remained on that photoperiod (10 h of light, 14 h of darkness). To monitor pulsatile LH secretion, the ewes were ovariectomized and implanted with estradiol, and LH was measured in both frequent (every 6 min for 4 h) and infrequent (twice weekly) blood samples. In this model, high LH indicates low response to estradiol negative feedback and reproductive induction; low LH signifies high response to estradiol negative feedback and reproductive arrest. LH levels (samples twice weekly) rose some 50-fold in both groups concurrently at the start of the breeding season in September. Frequent sampling in midbreeding season (autumn) revealed that both thyroidectomized and thyroid-intact ewes exhibited frequent LH pulses, with no group difference, in either the presence or absence of the estradiol implant. A marked group difference, however, emerged at the end of the breeding season. LH fell to basal values in thyroid-intact ewes (onset of low values Feb 3 +/- 8 days), whereas levels remained elevated in thyroidectomized ewes through the end of the study (April 26). At this time, thyroidectomized ewes had more frequent LH pulses than thyroid-intact ewes both in the presence and absence of estradiol. The circadian pattern of melatonin secretion and the seasonal change in PRL were found to be unaffected by thyroidectomy. These observations support the hypothesis that the thyroid is necessary for endogenous suppression of neuroendocrine mechanisms that generate LH pulses, a suppression crucial for the transition to anestrus.

Animals↗
PubMed2006

Nitrogen and phosphorus leaching from growing season versus year-round application of wastewater on seasonally frozen lands.

Land application of wastewater has become an important disposal option for food-processing plants operating year-round. However, there are concerns about nutrient leaching from winter wastewater application on frozen soils. In this study, P and N leaching were compared between nongrowing season application of tertiary-treated wastewater plus growing season application of partially treated wastewater (NGS) vs. growing season application of partially treated wastewater (GS) containing high levels of soil P. As required by the Minnesota Pollution Control Agency (MPCA), the wastewater applied to the NGS fields during October through March was treated such that it contained < or =6 mg L(-1) total phosphorus (TP), < or =10 mg L(-1) NO3-N, and < or =20 mg L(-1) total Kjeldahl nitrogen (TKN). The only regulation for wastewater application during the growing season (April through September) was that cumulatively it did not exceed the agronomic N requirements of the crop in any sprayfield. Application of tertiary-treated wastewater during the nongrowing season plus partially treated wastewater during the growing season did not significantly increase NO3-N leaching compared with growing season application of nonregulated wastewater. However, median TP concentration in leachate was significantly higher from the NGS (3.56 mg L(-1)) than from the GS sprayfields (0.52 mg L(-1)) or nonirrigated sites (0.52 mg L(-1)). Median TP leaching loss was also significantly higher from the NGS sprayfields (57 kg ha(-1)) than from the GS (7.4 kg ha(-1)) or control sites (6.9 kg ha(-1)). This was mainly due to higher hydraulic loading from winter wastewater application and limited or no crop P uptake during winter. Results from this study indicate that winter application of even low P potato-processing wastewater to high P soils can accelerate P leaching. We conclude that the regulation of winter wastewater application on frozen soils should be based on wastewater P concentration and permissible loading. We also recommend that winter irrigation should take soil P saturation into consideration.

Freezing↗
PubMed1987

Seasonality in glycosylated hemoglobin in normal subjects. Does seasonal incidence in insulin-dependent diabetes suggest specific etiology?

Seasonality in the diagnosis of insulin-dependent diabetes mellitus (IDDM), i.e., increased incidence in winter, was the impetus for this study of seasonality in glycosylated hemoglobin levels in nondiabetics. Glycosylated hemoglobin levels of 35 nondiabetic children and adults were highest at the ends of autumn and winter and lowest at the ends of spring and summer (P less than 10(-4)). This result is consistent with reports of seasonal variation in blood glucose, with the highest levels occurring in winter, as well as reports that suggest an internal milieu of increased counterinsulin action in winter due to seasonality in counterinsulin hormones, dietary factors, body weight, amount of exercise, growth rates in children, and ambient temperature. IDDM is caused by the gradual destruction of the pancreatic insulin-producing cells via lymphocytic infiltration--a process that may occur over years. We conclude that a decreased carbohydrate tolerance associated with winter can explain the seasonal variation in the incidence of IDDM and that this seasonality is caused by the precipitation of overt carbohydrate intolerance in individuals with already seriously compromised insulin secretory capacity. This implies that seasonality is not very formative about the cause of the destruction of pancreatic insulin-producing cells.

Adolescent↗