Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “SEASONS”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 901 records · Page 50Linked to original sources
PubMed1995

Seasonal and photoperiod-induced changes in the secretion of alpha-melanocyte-stimulating hormone in Soay sheep: temporal relationships with changes in beta-endorphin, prolactin, follicle-stimulating hormone, activity of the gonads and growth of wool and horns.

Blood plasma concentrations of alpha-melanocyte-stimulating hormone (alpha-MSH), beta-endorphin (beta-END), prolactin and follicle-stimulating hormone (FSH), and associated changes in the size of the testes, and growth of the horns and pelage were measured in male (n = 8), castrated male (n = 5) and female (n = 9) Soay sheep. The animals were born in April and kept outdoors near Edinburgh (56 degrees N) during the first two years of life. In all groups there was a close association between the weekly changes in the plasma concentrations of alpha-MSH and beta-END; the molar ratio in mean concentrations was close to 1:1. The blood plasma concentrations of both hormones varied markedly with season with a 3- to 10-fold increase in concentrations from the minimum in winter to the maximum in autumn. The seasonal peak occurred in September in the first year of life as juveniles, and between July (males) and September (females) in the second year when the animals were sexually mature. The plasma concentrations of ACTH did not vary in parallel with the seasonal changes in the concentrations of alpha-MSH (measured only in males); the molar ratio for the concentrations of alpha-MSH:ACTH was 1:0.12. The seasonal increase in the concentrations of alpha-MSH occurred 1-3 months after the seasonal increase in the concentrations of prolactin and the associated growth in horns and pelage, and slightly before, or coincident with the seasonal increase in the concentrations of FSH and the growth in the testes. In a second experiment, the same parameters were measured in a group of adult male Soay sheep (n = 8) housed indoors under an artificial lighting regimen of alternating 16-week periods of long (16 h light: 8 h darkness) and short days (8 h light: 16 h darkness). In this situation, there was a clearly defined photoperiod-induced cycle in the plasma concentrations of alpha-MSH with a 25-fold increase from a minimum under long days to a maximum under short days. The concentrations of beta-END varied in close parallel with the changes in alpha-MSH, and the temporal associations with the changes in the other pituitary hormones were similar to those observed in animals housed outdoors. Overall, the results support the view that alpha-MSH is co-secreted with beta-END from the melanotrophs in the pars intermedia of the pituitary gland, and that the secretory activity of the melanotrophs changes markedly with season, increasing in summer and autumn, and decreasing in winter and spring.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1995

The role of neuropeptide Y (NPY) in the control of LH secretion in the ewe with respect to season, NPY receptor subtype and the site of action in the hypothalamus.

Neuropeptide Y1-36 (NPY1-36) acts through Y1 and Y2 receptors while the C-terminal NPY fragments NPY18-36 and N-acetyl[Leu28,31]pNPY24-36 act only through the Y2 receptor. We have investigated the effects of intracerebroventricular (i.c.v.) administration of NPY1-36, NPY18-36 and N-acetyl[Leu28,31]pNPY24-36 on LH secretion in the ovariectomised (OVX) ewe. These peptides were administered into a lateral ventricle (LV) or the third ventricle (3V) of OVX ewes during the non-breeding and breeding seasons. Microinjections of NPY were also made into the preoptic area (POA) during both seasons to investigate the effects of NPY at the level of the GnRH cell bodies. Tamed sheep were fitted with 19 gauge guide tubes into the LV, 3V or the septo-preoptic area (POA). Jugular venous blood samples were taken every 10 min for 3 h. Sheep were then given NPY1-36 (10 micrograms), NPY18-36 (100 micrograms) or saline vehicle into the LV; N-acetyl[Leu28,31]pNPY24-36 (100 micrograms), NPY1-36 (10 micrograms or 100 micrograms), NPY18-36 (10 micrograms or 100 micrograms) or saline vehicle into the 3V, or NPY1-36 (1 microgram, 5 micrograms, 10 micrograms) into the POA. Blood sampling continued for a further 3 h. LH was measured in plasma by radioimmunoassay. LV or 3V injection of 10 micrograms NPY1-36 caused a small but significant (P < 0.025) increase in the interval from the last pre-injection pulse of LH to the first post-injection LH pulse during the breeding season. Other LH pulse parameters were not significantly affected. NPY18-36 did not produce any significant change in LH pulsatility when injected into the LV, and neither peptide had any effect on plasma prolactin or GH levels. There was a significant (P < 0.01) reduction in LH pulse frequency after 3V injection of 10 micrograms and 100 micrograms NPY and 100 micrograms NPY18-36. Pulse amplitude was reduced by 3V administration of the Y2 agonist, N-acetyl[Leu28-31]pNPY24-36 and 100 micrograms NPY18-36. When the amplitude of the first post-injection LH pulse was analysed, 10 micrograms NPY also had a significant (P < 0.05) suppressive effect. During the non-breeding season, 100 micrograms NPY1-36 (but not 10 micrograms) decreased (P < 0.01) LH pulse frequency. LH pulse amplitude was significantly (P < 0.01) decreased by 100 micrograms NPY18-36. Doses of 10 micrograms NPY1-36 and 100 micrograms NPY18-36 had greater inhibitory effects on pulse frequency during the breeding season but the suppressive effect of 100 micrograms NPY was similar between seasons. Microinjections of NPY into the POA decreased (P < 0.01) average plasma LH levels during the non-breeding season at a dose of 10 micrograms but did not significantly affect pulse frequency or amplitude. We conclude that a substantial component of the inhibitory action of NPY on LH secretion in the absence of steroids is mediated by the Y2 receptor. This inhibition is probably exerted by way of a presynaptic action on GnRH terminals in the median eminence as NPY does not modulate the frequency or amplitude of LH pulses at the level of the GnRH cell bodies in the POA.

Animals↗
PubMed1988

Season of birth of breast cancer patients and its relation to patients' reproductive history in Tokyo, Japan.

Seasonal distribution of the birth dates of 405 pre-menopausal and 285 post-menopausal breast cancer patients was investigated in order to determine whether or not the season of their birth was related to various reproductive risk factors of breast cancer, including nulliparity, late age at first birth, early age at menarche, late age at menopause, and a history of benign breast diseases. The seasonal distributions of births were compared between groups of patients categorized according to whether they possessed each risk factor or not, separately for pre- and post-menopausal patients. Patients with the same menopausal status generally had the same seasonal distribution of births, irrespective of whether or not they possessed a risk factor. Moreover, low-risk patients exhibited more deviation in the seasonal distribution of birth from general births than the high-risk patients. These results suggest that the distinctive seasonal distribution of birth observed in breast cancer patients is basically a phenomenon independent from the effect of the reproductive history on the occurrence of breast cancer, and that specific seasonal factors are involved at the fetal or neonatal stage in the etiology of breast cancer.

Adult↗
PubMed1998

Comparison of the seasonal pattern in the clinical onset of IDDM in Finland and Sardinia.

OBJECTIVE: To examine the seasonal pattern for the clinical onset of IDDM in Finland and Sardinia, two areas where the incidence of IDDM is the highest in the world, and to determine the effect of climate and temperature on the clinical onset of IDDM. RESEARCH DESIGN AND METHODS: Analysis of seasonality for the diagnosis of IDDM was based on 1,405 cases in Finland and 425 cases in Sardinia diagnosed at < or = 14 years of age from 1989 to 1992. The average annual incidence of IDDM was 36.4/100,000 in Finland and 34.4/100,000 in Sardinia. Seasonal patterns were estimated presenting the data as short Fourier series up to three harmonics together with a possible linear trend. Likelihood ratio tests and Akaike's information criterion were used to determine the number of harmonics necessary to model the seasonal pattern. Seasonal patterns in both countries were compared between sexes and between the three 5-year age-groups, each controlling for the other's effect. RESULTS: In both countries, a significant seasonal pattern during a calendar year was found for the sexes combined and for two age-groups (0-9 and 10-14 years). In Sardinia, two distinct cycles were found in the younger age-group, with a decreased incidence during May through August and an increased incidence during the autumn months. Two cycles were apparent in the older age-group, with the nadir occurring during June through September. In Finland, one cycle was found in the younger age-group, with a decreased incidence in June. In the older age-group, there were two distinct cycles, with a decreased incidence in June and in the September through December period. CONCLUSIONS: Differences between Finland and Sardinia in the seasonal pattern for the incidence of newly diagnosed IDDM cannot be explained by differences in climate, temperature, a longer warm period in Sardinia, or other climatic phenomena. The results do not provide evidence in favor of a specific viral etiology of IDDM. It may be suggested that there are triggering events at certain times, but they are likely to be unspecific. Nevertheless, why the incidence of IDDM in these two populations is equally high despite differences in climate, environment, and genetic background remains an unsolved question.

Adolescent↗
PubMed2001

Seasonal changes in serum calcium, phosphorus, and vitamin D concentrations in llamas and alpacas.

OBJECTIVE: To evaluate the interaction of season and age on serum calcium, phosphorus, and vitamin D3 concentrations in llamas and alpacas. ANIMALS: 23 clinically normal llamas and 7 alpacas. PROCEDURES: Animals were assigned to 1 of the 3 following groups on the basis of age at the start of the study: adult (age, > or = 24 months; n = 8), yearling (> 12 but < 20 months; 5), and neonate (< 6 months; 17). Twelve serum samples were obtained at monthly intervals. Calcium, phosphorus, and vitamin D3 concentrations were measured, and the calcium-to-phosphorus concentration (Ca:P) ratio calculated. Effect of season and age on each of these variables was determined. RESULTS: Vitamin D3 concentrations varied significantly as a function of season; the highest and lowest concentrations were detected September through October and February through March, respectively. The seasonal decrease in vitamin D3 concentration was significantly greater in neonates and yearlings, compared with adults. Serum phosphorus concentration decreased as a function of age, with the most significant seasonal change detected in the neonate group. The Ca:P ratio in neonates varied between 1.1 and 1.3 except during winter months when it increased to > or = 2.0. CONCLUSIONS AND CLINICAL RELEVANCE: Mean vitamin D3 concentration varied by > 6 fold in neonatal and yearling llamas and alpacas and > 3 fold in adult animals as a function of season. These results support the hypothesis that seasonal alterations in vitamin D3 concentrations are a key factor in the development of hypophosphatemic rickets in llamas and alpacas.

Age Factors↗
PubMed1998

Diurnal and seasonal variations in vervet monkeys' activity.

This paper analyzed seasonal and diurnal differences in feeding, locomotion, inactivity, and social grooming of adult and subadult free-ranging vervet monkeys in Natal (38 degrees 35'S and 31 degrees 46'E). Breaking down hourly activity budgets from the perspective of reproductive seasons (birth, premating, and mating seasons) which correspond to environmental conditions in Natal, we obtained several results. First, there were diurnal variations for all the behaviours in all seasons studied, except for inactivity during the mating season when days were shorter and there was greater food shortage and sexual competition. Second, the seasonal influence on the hourly periods of increased activity could not be explained solely by the photoperiod or by the other climatic factors analyzed. Finally, over-all seasonal differences in activity were mainly reflected by the hourly distribution of feeding in the morning and the pattern of inactivity throughout the day. Therefore, rhythms in activity should be understood in terms of adaptation to both climatic constraints and other unrelated metabolic requirements.

Animals↗
PubMed1991

Maintenance requirements of beef cattle as affected by season on different planes of nutrition.

Eight Hereford steers with an initial weight of 344 kg and a final weight of 476 kg were allotted randomly to two groups that were alternated between low (120 x maintenance) and high (2.27 x maintenance) intakes during five consecutive seasons in order to measure effects of season (cold stress) and intake on thermoneutral energy requirements. The steers were housed outdoors with neither shelter nor bedding and adapted to the specified intake levels for 21 to 31 d before each season's measurement of maintenance. Maintenance energy requirements were estimated as fasting heat production (FHP) and maintenance metabolized energy (MEm) by respiration calorimetry at thermoneutral temperatures. The high plane of nutrition caused a consistent increase of about 7% in FHP and 14% in MEm averaged across seasons (P less than .05). Within plane of nutrition, season had no effect on FHP or MEm, with the exception that values recorded in fall were lower than those recorded during the first summer (P less than .05). Nevertheless, daily gain during the winter acclimatization period was lower (P less than .05). We conclude that season had no effect on thermoneutral maintenance energy requirements (FHP, MEm) even though cold increased requirements for weight maintenance or gain. No interactions were found between season and plane of nutrition for the parameters measured. Acute cold stress, rather than chronically elevated metabolic rate, likely was responsible for poorer feedlot performance during the cold months of the year.

Animal Nutritional Physiological Phenomena↗
PubMed2006

Effects of growth-promoting agents and season on blood metabolites and body temperature in heifers.

To assess the efficacy of growth-promoting agents among seasons, triiodothyronine (T3), thyroxine (T4), plasma urea nitrogen (PUN), IGF-I, and tympanic temperature (TT) were measured in summer and winter studies. Heifers (n = 9/pen) were allotted to 12 pens in both December and June. Pens were assigned to 1 of 6 growth promotant treatments: control (no growth promotant), estrogenic implant (E), trenbolone acetate implant (TBA), E + TBA (ET), melengestrol acetate (MGA), and ET + MGA (ETM). Blood samples were collected from 4 heifers per pen per study on d 0, 28, 56, and 84 via jugular puncture. Near the midpoint of both studies, TT were obtained from the heifers. There was a season by sample day interaction for all blood metabolites (P < 0.05). During the winter, IGF-I levels peaked on d 28, whereas T3, T4, and PUN peaked on d 56. In the summer, IGF-I levels increased from d 0 to 28 and remained elevated throughout the study. Season by growth promotant interactions (P < 0.05) indicated that in the winter ET increased T3, whereas TBA alone decreased both T3 and T4, compared with control, or ET, and ETM treatment groups. Across seasons, treatments ET and ETM increased (P < 0.05) IGF-I and decreased (P < 0.05) PUN. However, E, TBA, and MGA alone had no effect on IGF-I or PUN concentrations. The maximum TT was greater (P < 0.01) in the summer than in the winter, whereas the minimum TT was lower (P < 0.01) in the summer. Mean TT did not differ among growth-promoting treatments. However, in the summer and over both seasons, the maximum TT was lower (P < 0.05) in E-, MGA-, and ETM-treated heifers. Although limited growth promotant by season interactions existed, changes in blood metabolite levels resulting from the use of growth promotants do not appear to influence seasonal changes in body temperature as measured by TT.

Absorbable Implants↗
PubMed1981

Seasonal variation in urinary excretion of calcium, oxalate, magnesium and phosphate on free and standard mineral diet in men with urolithiasis.

Seasonal variations of urine volume and urinary excretion of calcium, oxalate, magnesium and phosphate were studied in 118 men with urolithiasis on a standard mineral diet and on free diet. The 24-hour urine volume did not vary by season. There was no significant seasonal variation in the excretion of urinary calcium, oxalate, magnesium or phosphate on a standard mineral diet. While on a free diet the patients' urinary excretion of calcium showed statistically significant seasonal differences between age groups. The seasonal variations in the excretion of urinary oxalate and phosphate were statistically significant on free diet, but did not differ by age. The urinary excretion of magnesium was not affected by season nor age. Dietary intake probably best explains seasonal changes in the urinary excretion of calcium, oxalate and phosphate.

Adolescent↗
PubMed1997

Seasonal covariation in physical fitness and blood pressure at rest and during exercise in healthy middle-aged men.

It has been suggested that seasonal changes in cardiovascular risk factors may explain simultaneous seasonal variations in cardiovascular diseases. Since systolic blood pressure (SBP) during an ergometer exercise test adds prognostic information beyond that of BP at rest we aimed to study whether SBP during exercise also demonstrates similar seasonal variation after adjustment for covariates. Blood pressures of 1574 apparently healthy men aged 40-59 years examined throughout two consecutive years showed a seasonal variation, with higher SBP during the period September-December compared with the rest of the year, 2.8 mmHg (p = 0.003) at rest and 4.2 mmHg (p < 0.001) during ergometer exercise at 600 kpm min-1. After adjustment for a parallel marked drop in physical fitness, these differences were no longer significant. Thus, the seasonal variation in SBP at rest and during exercise in apparently healthy middle-aged men may be explained by a parallel seasonal variation in physical fitness. A seasonal covariation in long-term cardiovascular mortality in the same study suggests that the parallel variation of independent risk factors is of clinical significance.

Adult↗
PubMed1996

Relation of 24-hour ambulatory blood pressure and short-term blood pressure variability to seasonal changes in environmental temperature in stage I hypertensive subjects. Results of the Harvest Trial.

We investigated the seasonal changes in blood pressure (BP) and in short-term BP variability determined using ambulatory blood pressure monitoring (ABPM). 1000 white subjects, who took part in the multicenter HARVEST study, underwent ABPM with the A&D TM-2420 or the Spacelabs 90207. Standard deviation of the mean daytime and nighttime BP was taken as an index of short-term BP variability (v). Maximal outdoor temperature (Tmax) during each ABPM was obtained from local Meteorological Centers. Subjects were divided according to season and to quartiles of Tmax. A subgroup of 46 persons who repeated ABPM in Winter and Summer was also studied. We observed evident seasonal differences in office and ambulatory systolic BP (SBP) with a peak during Winter. Diastolic BP (DBP) and heart rate did not vary throughout the four seasons. Office SBP (p < 0.01), 24-hour (p < 0.002), daytime SBP (p < 0.0001), both daytime SBPv (p < 0.0001), DBPv (p < 0.02), and nighttime SBPv (p < 0.05), DBPv (p < 0.02) as well as norepinephrine (p < 0.005) were significantly higher during Winter than Summer. Similar differences were observed in subjects grouped in quartiles of Tmax. In the subgroup daytime but not nighttime SBP was higher in the cold season. Average 24-hour SBP (p < 0.05), daytime SBP (p < 0.02), daytime SBPv (p < 0.001) and DBPv (p < 0.05) and norepinephrine (p < 0.0001) were significantly negatively correlated with Tmax in the whole population. BP is higher and subjected to wider oscillations during the cold season in patients with mild hypertension probably due to sympathetic activation. The assessment of a hypertensive subject may give different results according to the season.

Adolescent↗
PubMed2002

Day and night seasonal temperature differences for a naturally ventilated freestall barn with different stocking densities.

Temperature data were collected during three 28-d periods. Cold-season one-side-occupied (CSOO), warm-season two-sides-occupied (WSTO), and cold-season two-sides-occupied (CSTO) were used to determine day and night freestall barn temperature differences between north-side and south-side, east-end and west-end, and inside to outside of a naturally ventilated, curtain sided, noninsulated barn. Five sensors measured temperature every 15 min for 28-d periods beginning November 30, 2000, July 9, 2001, and December 23, 2001. Stocking densities were 90 to 100% for CSOO south-side and 0% for CSOO north-side; 92 to 108% for WSTO south-side and 46 to 74% for WSTO north-side; and 102 to 116% for CSTO south-side and 64 to 86% for CSTO north-side. Mean day temperatures (MDT) and mean night temperatures (MNT) were different for all within barn comparisons. Inside and outside MDT were different for cold-season periods. MDT differences between inside and outside were CSTO (6.27 degrees F) > CSOO (5.64 degrees F) > WSTO (-0.03 degrees F). MNT differences between inside and outside were CSTO (7.14 degrees F) > CSOO (5.76 degrees F) > WSTO (1.32 degrees F). Absence of animals on one side of the barn during cold seasons decreased the average temperature difference between inside and outside approximately 1 degree F (day 0.63 degrees F, night 1.38 degrees F). South-side MDT and MNT were higher than the north-side for CSOO. MDT differences between north-side and south-side were CSOO (-2.71 degrees F) > CSTO (-1.22 degrees F) > WSTO (-0.36 degrees F). MNT differences between north-side and south-side were CSOO (-2.46 degrees F) > CSTO (-1.06 degrees F) > WSTO (-0.49 degrees F). The average temperature difference for the unoccupied side during cold seasons was almost 1.5 degrees F lower throughout the day than the fully stocked side (day 1.49 degrees F, night 1.40 degrees F). Stocking density was thought to be the major cause of differences between north-side and south-side. East-end and west-end mean temperatures were not different across seasons, therefore, future barn-temperature research with barns of similar characteristics may require only one sensor per side.

Animals↗
PubMed1998

Seasonal pattern of spontaneous cervical artery dissection.

OBJECT: The etiology of spontaneous cervical artery dissection is poorly understood; however, it may involve genetic and environmental factors. The purpose of this study was to determine whether seasonality of spontaneous cervical artery dissection exists. METHODS: The seasonal pattern of spontaneous cervical artery dissection was analyzed in a group of 200 consecutive patients (104 females and 96 males with a mean age of 44.9 years) who were evaluated using the Rayleigh test during the period from 1970 to 1990. The majority of patients resided in the midwestern section of the United States, where large seasonal fluctuations in climate occur. A circannual periodicity was found in the frequency of spontaneous cervical artery dissections with a peak occurring in October (p < 0.02). The seasonal variation was substantial, with approximately 58% more patients suffering a cervical artery dissection during autumn than during other seasons. CONCLUSIONS: A seasonal pattern of spontaneous cervical artery dissection exists with a peak occurring in October. The cause of the seasonality remains to be explained; however, weather- or infectious disease-related factors may provide etiological leads.

Adolescent↗
PubMed2003

Seasonal evolution of faecal egg output by gastrointestinal worms in goats on communal farms in eastern Namibia.

As a more detailed continuation of a previous study, faecal samples for worm egg counts were collected per rectum from ten marked adult animals in selected flocks of goats, in each of six villages evenly spread out in the communal farming district of Okakarara in eastern Namibia. The study was conducted on a monthly basis from August 1999 to July 2000. Average faecal worm egg counts (FECs) were highest during the warm-wet season, much lower during the cold-dry months and moderate during the hot-dry season. Least square means of FECs were 2140, 430 and 653 per gram of faeces for the three seasons, respectively. Seasonal variation in egg counts was significant (P < 0.0001). Gastrointestinal strongyles, and to a lesser extent Strongyloides species, were the predominant parasite groups identified in goats. Kidding rates peaked in the cold-dry season and mortality rates in the hot-dry season. Results of this study suggest that gastrointestinal parasitism may be a problem that accentuates the effect of poor nutrition on small ruminants during the season of food shortages in the east of Namibia and that the use of FECs per se to assess the severity of gastrointestinal parasitic infection in goats followed by chemoprophylactic strategic and/or tactical treatment, may not be the best approach to addressing the worm problem under resource-poor conditions. The use of the FAMACHA system that identifies severely affected animals for treatment is technically a better option for communal farmers.

Animals↗
PubMed1988

Seasonality of adult black flies and Onchocerca volvulus transmission in Guatemala.

Transmission of Onchocerca volvulus, principally by Simulium ochraceum, was studied over a 14-month period in the Atitlán region of Guatemala. Semimonthly catches of black flies were made on human volunteers at 4 localities with different prevalences of human onchocerciasis. Host-seeking activity of S. ochraceum reached its greatest magnitude in the early dry season (October-January) but then declined rapidly and was lowest during the late dry season (February-May). The frequency of O. volvulus larvae in parous host-seeking S. ochraceum also varied seasonally, and this variation was most pronounced for third stage larvae. At a hyperendemic locality, the highest frequency of this larval stage occurred during the February-March period (0.0142 in 1979 and 0.0095 in 1980). From June-January, the frequency of third stage larvae in S. ochraceum was less than 0.003. The frequency of early first stage larvae exhibited the least seasonal variation, ranging from 0.0354 in August-September to 0.0628 in April-May. The transmission rate of O. volvulus by S. ochraceum also varied seasonally. At the same hyperendemic locality, infective biting density of S. ochraceum attained its greatest magnitude in February-March. The survival rate of female S. ochraceum from one gonotrophic cycle to the next was estimated from the ratio of flies with early first stage larvae to those with infective stage larvae. These rates varied seasonally and ranged from 0.2132 to 0.3974, with the highest rates occurring in the late dry season.

Animals↗
PubMed2000

Season of birth and substance abuse: findings from a large national sample.

BACKGROUND: Season of birth is a putative etiological factor for several psychiatric illnesses. An excess of late winter and early spring births has been demonstrated repeatedly for schizophrenia, which has usually been interpreted as the result of prenatal or infant exposure to seasonally mediated "harmful effects," such as infectious diseases. This study determined whether the seasonal birth rates of substance abusers differed from those of unaffected control groups. METHODS: The 1992 National Longitudinal Alcohol Epidemiologic Survey, an interview-based study of 42,862 men and women, provided data to assess the association between quarter year of birth and lifetime diagnoses of substance abuse. RESULTS: Logistic regression revealed decreases in winter births in men with histories of alcohol dependence. The significant interaction of sex with season of birth reflected an excess of fall births among male but not female alcoholics. In contrast, there was no evidence of seasonality of birth among alcohol abusers. Men and women with histories of illicit drug use had excesses of fall birth. DISCUSSION: Birth rates of men with past or present alcohol dependence, and of men and women with histories of illicit drug use, implicated seasonal factors in the pathogenesis of substance abuse. The similar birth patterns of illicit drug users and male alcoholics suggest that they may share some common etiological factor, such as seasonal effects on environmental temperature, hormonal function, or susceptibility to viral infection during pregnancy or early infancy.

Adult↗
PubMed2000

Statistical analysis of the seasonal variation in demographic data.

There has been little agreement as to whether reproduction or similar demographic events occur seasonally and, especially, whether there is any universal seasonal pattern. One reason is that the seasonal pattern may vary in different populations and at different times. Another reason is that different statistical methods have been used. Every statistical model is based on certain assumed conditions and hence is designed to identify specific components of the seasonal pattern. Therefore, the statistical method applied should be chosen with due consideration. In this study we present, develop, and compare different statistical methods for the study of seasonal variation. Furthermore, we stress that the methods are applicable for the analysis of many kinds of demographic data. The first approaches in the literature were based on monthly frequencies, on the simple sine curve, and on the approximation that the months are of equal length. Later, "the population at risk" and the fact that the months have different lengths were considered. Under these later assumptions the targets of the statistical analyses are the rates. In this study we present and generalize the earlier models. Furthermore, we use trigonometric regression methods. The trigonometric regression model in its simplest form corresponds to the sine curve. We compare the regression methods with the earlier models and reanalyze some data. Our results show that models for rates eliminate the disturbing effects of the varying length of the months, including the effect of leap years, and of the seasonal pattern of the population at risk. Therefore, they give the purest analysis of the seasonal pattern of the demographic data in question, e.g., rates of general births, twin maternities, neural tube defects, and mortality. Our main finding is that the trigonometric regression methods are more flexible and easier to handle than the earlier methods, particularly when the data differ from the simple sine curve.

Algorithms↗
PubMed2001

Reproductive seasonality in domestic sows kept outdoors without boars.

Plasma progesterone, LH and prolactin concentrations were measured twice a week in mature sows kept outdoors without boars in two experiments to examine whether perception of daylength change underlies seasonal infertility in domestic pigs. In Expt 1, melatonin implants inserted on 12 April or 22 May to block perception of the increasing daylength did not affect the oestrous cycle significantly, since only two untreated control sows became seasonally anoestrous. In Expt 2, all control sows became anoestrous for 131 +/- 42.5 days (n = 11). Melatonin implants inserted at the spring equinox (n = 9) prevented seasonal anoestrus (P < 0.001), but timed daily oral melatonin administration was less effective (P < 0.05): 5 of 11 sows became anoestrous for 132 +/- 45.6 days. In both experiments, there were significant low-amplitude seasonal rhythms in mean plasma prolactin and LH concentrations. Prolactin reached maximum concentrations 2-4 weeks before the summer solstice, whereas LH reached a nadir 4-6 weeks after the summer solstice. Neither anoestrus nor melatonin administration altered these patterns consistently. Endogenous plasma melatonin was higher (P < 0.001) during darkness (12.5 ng l(-1)) than during daytime (8.9 ng l(-1)) in untreated sows, but only clearly so during spring and summer. Melatonin implants increased mean daily plasma melatonin to 146 ng l(-1), whereas melatonin fed at 15:00 h increased values to 40-60 ng l(-1) 2-4 h after administration, but daytime concentrations were unchanged. Melatonin administration, despite decreasing seasonal anoestrus, did not prevent the seasonal increase in plasma prolactin and had no significant effect on plasma LH; therefore, its role in regulating seasonal changes in the reproduction of domestic sows remains uncertain.

Anestrus↗