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PubMed1999

Seasonal variation in hospital admissions for community-acquired pneumonia: a 5-year study.

OBJECTIVES: We conducted a retrospective analysis of computerized hospitalization and regional meteorological and geophysical data in a university hospital in southern Israel. The aim of the study was to determine and depict the seasonal variation in hospitalization for community-acquired pneumonia (CAP-H) and the factors affecting it, for all age groups combined and by age group, over a 5-year period. METHODS: All cases of CAP-H over the period from January 1, 1990 to December 31, 1994 were studied by season of the year and age group. The rates of CAP-H for the four seasons were compared by t-tests. Mathematical models based on quasi-Fourier generalized linear models were developed and used to evaluate potential variables and their relative contributions to CAP-H. RESULTS: A total of 4101 CAP-H were analysed in the study. Throughout the study period the prevalence of CAP-H was significantly higher in the winter and spring than in the summer and fall for all age groups combined and within each age group (P<0.00001). When CAP-H was compared between the winter and the spring, we found that in the 0-16 age group CAP-H was higher in the winter (P<.0.00001), in the 17-64 age group it was higher in the spring (P<0.002), and in the 65+ age group as well as for all age groups combined there were no significant differences between these two seasons. The most important factor explaining the variance in CAP-H in the 0-16 age group were direct and indirect effects of minimum daily temperature (31%), in the 17-64 age group direct and indirect effects of the difference between minimum and maximum daily temperatures (19%), and in the 65+ age group it was geophysical factors (13%). CONCLUSIONS: There is a significant seasonal variation in CAP-H with higher rates for all age groups in the winter and spring. The extent to which the prevalence of CAP-H is dominant in the winter and spring seasons differs among the age groups, as does the principal variable explaining these differences. The most important factor is the direct and indirect effects of meteorological variables in the 0-16 and 17-64 age groups, and a geophysical one among the more elderly patients.

Adolescent↗
PubMed2001

Comparison of consultation rates in primary care attenders with and without seasonal affective disorder.

BACKGROUND: There is a lack of published information about the consultation patterns of patients with seasonal affective disorder (SAD) in primary care, when compared with non-seasonal controls (NSCs). METHODS: Interview-confirmed SAD cases (n=90) were age- and sex-matched to two controls without significant seasonal morbidity on the Seasonal Pattern Assessment Questionnaire (SPAQ) (non-seasonal controls, NSCs). A comparison of their consultation rates was made using data abstracted from primary care records over 4 years. RESULTS: The monthly rate of general practice consultations for SAD cases was significantly higher than that for NSCs. There was a significant difference in the median number of consultations in winter and autumn between the two groups. The matched multivariate analysis revealed that February and April were the independent months in which cases of SAD had significantly more consultations than NSCs. LIMITATIONS: Optimal diagnostic criteria for SAD have not been determined and our criteria may have been over-inclusive. CONCLUSION: In addition to a marked difference in monthly consultation rates between SAD cases and NSCs, the data demonstrate a difference in the pattern of seasonality of these rates. It is possible that increased frequency of consultation, in particular during the winter months (in patients who score as a case SPAQ), could be used as an indication of SAD in primary care.

Adolescent↗
PubMed2002

Seasonal variation of mixed and pure episodes of bipolar disorder.

BACKGROUND: Although seasonal patterns of manic episodes have been reported, the seasonal variation of mixed states of bipolar disorder has received little attention. In the current report we address that concern as well as the overall seasonality of manic episodes. METHODS: The seasonal pattern of 304 psychiatric hospital admissions for treatment of mixed or manic bipolar episodes over a 3-year period were analyzed employing two definitions of mixed manic states: DSM-III-R and an ROC derived definition. RESULTS: The frequency of all manic episodes combined peaked in early spring, with a nadir in late fall. Pure manic admissions showed a similar pattern. Mixed manic admissions had a significantly different pattern, with a peak in late summer and a nadir in November. The differences between pure and mixed manic admissions were demonstrated with the use of the ROC definition for mixed states. LIMITATIONS: Effects of medications and medication non-compliance may dampen natural seasonal patterns of episodes. CONCLUSIONS: The different seasonal pattern of mixed and pure manic episodes support the separation of mixed episodes as a distinct clinical subtype.

Adolescent↗
PubMed2002

Seasonal and nonseasonal depression: how do they differ? Symptom profile, clinical and family history in a general population sample.

BACKGROUND: A small number of studies have previously compared the symptom profiles and clinical and family history patterns of patients with seasonal and nonseasonal depression. However, previous research has tended to be conducted in secondary and tertiary care populations. Little comparative data is available for seasonal and nonseasonal depression in general population samples. METHODS: Patients aged 18-64 registered on a primary care database in North Wales were screened via post for the presence of SAD via the Seasonal Patterns Assessment Questionnaire (SPAQ) and depression via the Beck Depression Inventory (BDI). Interview-confirmed cases of SAD (n=25) and major depression (n=43) were compared in terms of symptom profile, clinical history and family history of psychiatric disorder. RESULTS: Seasonal depression was found to be associated with lower occupational and cognitive impairment and psychiatric intervention than nonseasonal depression. The symptoms of hopelessness and weight loss were particularly predictive for nonseasonal depression. LIMITATIONS: The study was conducted at only one geography. CLINICAL RELEVANCE: Seasonal depression's discrete symptom profile may be used to distinguish cases of seasonal and nonseasonal depression in primary care patients. CONCLUSIONS: SAD appears to be a relatively mild variant of depression, but this finding should not detract from the need for improved identification and treatment of SAD in primary care populations.

Adult↗
PubMed2002

Seasonal variation in specific methods of suicide: a national register study of 20,234 Finnish people.

BACKGROUND: Previous studies have suggested differences in seasonal variation of violent and non-violent suicides, but seasonal distribution of the specific methods of suicide is less clear. METHOD: We investigated the seasonal distribution of the specific suicide methods for both genders during a 16-year period. The seasonal effect was explored by monthly ratio statistics from the large population-based data including all suicides in Finland during years 1980-1995 (n=20,234). RESULTS: Hanging peaked in spring among both genders. In summer, the significant peaks were occurred in suicides by drowning, jumping and gassing among males. The bimodality in female suicides with autumn peaks was explained by poisoning and drowning. Traffic suicides showed substantial winter-troughs for both genders. CONCLUSIONS: The results suggested that specific violent and nonviolent methods of suicides grouped into their traditional clusters on the basis of their seasonality, except suicides by gassing and shooting. The seasonal distribution in specific suicide methods should take into account in suicide prevention at clinical work and also it should be considered while determining which methods of suicides are regarded as violent or non-violent methods in research.

Cause of Death↗
PubMed2004

The reliability and validity of the Seasonal Pattern Assessment Questionnaire: a comparison between patient groups.

BACKGROUND: The Seasonal Pattern Assessment Questionnaire (SPAQ) is a frequently used screening instrument in the research on Seasonal Affective Disorder (SAD). Nevertheless, studies on its reliability and validity are relatively scarce. In the present study the reliability and the contrast validity of the SPAQ are investigated. METHODS: SAD patients, selected by means of a clinical interview, non-seasonal depressed out-patients, non-depressed out-patients, and a control group, are contrasted to estimate the discriminating power of the SPAQ. Also, the reliability and factor structure of the seasonality and the climate subscales are investigated. To study food intake the Seasonal Food Preference Questionnaire (SFPQ) was developed. RESULTS: The SAD criterion of the SPAQ shows good specificity (94%), but a low sensitivity (44%). Discriminant analysis shows sufficient ability to classify subjects (81% correctly classified). The Global Seasonality Scale has a good internal consistency. It consists of two factors, a psychological factor and a food factor. The SFPQ is sensitive for carbohydrate intake by SAD patients. LIMITATIONS: Most SAD patients had received treatment and completed the SPAQ while they were not depressed, which may have influenced the sensitivity. CONCLUSIONS: The SPAQ is not sensitive enough to be considered a diagnostic instrument for SAD. Nevertheless, it is accurate enough to be used as a screenings instrument. The only false positives were found in the depressive group. The accuracy of prevalence Figs. can be improved by completion of the SPAQ in the summer months, combined with the completion of a depression scale.

Adult↗
PubMed2004

Seasonal distribution of acute myocardial infarction and its relation to acute infections in a mild climate.

BACKGROUND: There is evidence that acute myocardial infraction (aMI) occurs more frequently in certain seasons and months of the year. Recently various infectious agents have been implicated in atherogenesis. In the present study we recorded the seasonal distribution of aMI and evaluated its relation to acute systemic infections (AIs). METHODS: The study included 1196 patients with aMI hospitalized during the years 1988-1998 in the General Hospital of the island of Rhodes and 2976 patients with AI during the years 1993-1998. Foreigners or visitors in the island were excluded to avoid their influence in the annual distribution. We corrected the absolute number of the aMI and AI cases by month and season in such a way that all months and seasons would have standard 30 and 90 days, respectively. RESULTS: During the entire period of the study, more patients with aMI were hospitalized in winter [30.7%, 95% confidence limits (CL) 28.1 to 33.3%]. In spring the percentage of aMI cases hospitalized was 24.5% (CL 22.1-27%), in summer 23.2% (CL 20.1-25.6%) and in autumn 21.6% (CL 19.2 -24%). There were 42.35% more cases hospitalized in winter than in autumn. The monthly distribution showed that March was the month with the most aMI cases (10.83%, CL 9.06-12.6% ) and October with the fewest (6%, CL 4.65-7.35%). The percentage of patients with AI hospitalized in winter was 30.5% (CL 28.8-32.2%), in spring 25.2% (23.6-26.7), in summer 23.5% (CL 22-25%) and in autumn 20.8% (CL 19.4-22.3%). The correlation coefficient (r) between the distribution of aMI and AI was 0.73 (P<0.01). CONCLUSIONS: Our results indicate that (1) there is a seasonal distribution in aMI with the winter being the season of the highest incidence of aMI and autumn of the lowest and (2) there is a significant correlation of the distribution of aMI to AI cases, which is of interest in the understanding of the pathogenesis of acute coronary syndromes.

Acute Disease↗
PubMed2000

Seasonal variations of blood pressure and overhydration in patients on chronic hemodialysis.

Blood pressure (BP) has a seasonal cycle in the general population and in patients undergoing maintenance dialysis, but the causes remain unclear. We studied the BP measurements recorded at fixed hours three times weekly from 1994 to 1997 in 102 hemodialysis patients. We obtained monthly averages of the following variables: predialysis mean BP, greatest overhydration (OH) estimated by predialysis body weight excess over dry weight, chronic OH estimated by the remaining postdialysis weight excess over dry weight, urea reduction ratio (URR) in dialysis, and monthly means for daylight span and outdoor temperature over the study period. Average BP in the population diminished over the 48-month period, associated with a decrease in chronic OH (r = 0.66; P < 0.0005) but independent of greatest OH. BP and chronic OH presented synchronous seasonal variations, with peaks in late autumn and early winter and troughs in summer. These biological rhythms were inversely related to the seasonal daylight span and outdoor temperature. Both BP and chronic OH periods were synchronous with the daylight annual cycle and preceded the seasonal variations of temperature by 1 month. Multiple regression analysis showed that chronic OH and daylight, but not URR or temperature, had a significant independent association with BP changes. These results show the existence of seasonal variations of BP in dialysis patients that are associated and synchronous with seasonal changes in chronic OH status. Both cycles depend on conditions influenced by the annual daylight span more than by external temperature.

Blood Pressure↗
PubMed2003

Are seasonalities in suicide dependent on suicide methods? A reappraisal.

In general, suicide frequencies peak in spring and early summer and depict a low in autumn and winter months. Suicide seasonality is a ubiquitous phenomenon; however, recent studies have indicated that it is related particularly to violent suicide methods. We investigated differences in suicide seasonalities by suicide methods using Swiss mortality data. The suicide data were extracted from the Swiss cause of death statistics and cover the period 1969-1994. In this period 37,518 suicides (ICD-8 codes 950-959) were registered in the mortality statistics. The data were analysed by the Edwards' method, which examines unimodal sinusoidal patterns in aggregated monthly data, and by spectral analysis with disaggregated monthly data. Overall, Swiss suicide data in 1969-1994 depict the expected pattern with a peak in May and June and a low in December. However, analyses by suicide methods show that there is no common pattern. Suicide seasonalities are absent or weak in some violent as well as non-violent methods (firearms, cutting, crashing, poisoning). Even if clearly present (hanging, drowning, jumping from high places, unspecified/other), the seasonalities show distinct patterns and cycles. Apart from sinusoidal patterns, there are also outliers: in overall data as well as in most method-specific data, the December frequencies fall more than 10% below the neighbouring months. The decrease of the frequencies culminates at Christmas/New Year and then returns to average levels. Hence, the seasonality of the overall Swiss suicide frequencies is but a compound seasonality. It largely depends on specific suicide methods and different cyclical dynamics.

Accidents, Traffic↗
PubMed1999

Seasonal variation in plasma prolactin response to D-fenfluramine in healthy subjects.

To assess dynamically a seasonal variation in the functioning of the central serotonin (5-HT) system, we investigated the prolactin (PRL) response to the specific serotonergic agent D-fenfluramine (D-FEN) in the different seasons of the year. Thirteen healthy women and 11 healthy men (six for each season), aged 20-50 years, received PO 30 mg D-FEN and placebo, according to a randomized double-blind design. As compared to placebo, D-FEN induced a clear-cut increase in plasma PRL levels in all the seasons; this response was higher in fall than in spring and summer (p < .01 and < .05, respectively). In all the subjects, as a group, the hormone response to the 5-HT probe was inversely correlated with the body weight and age. These results document a seasonal variability in the PRL response to D-FEN, which suggests a seasonal fluctuation in central 5-HT transmission in healthy humans.

Adult↗
PubMed2001

Morphological and functional changes of stallion spermatozoa after cryopreservation during breeding and non-breeding season.

The study compared quality and freezability of stallion semen during breeding and non-breeding seasons. Ejaculates were collected twice per week from four stallions during May (n = 24) and December (n = 24). The semen was mixed with skim milk extender, centrifuged and resuspended in fresh extender. Aliquots of this sperm suspension were separated from extender and diluted in TALP medium for sperm evaluation or with cryoextender (type "Gent" or a combination of Triladyl and skim milk). Samples of 0.5ml were cryopreserved in straws using a programmed freezer. Parameters of sperm quality were evaluated before and after freezing/thawing. These included percentages of motile spermatozoa and of morphological intact sperm. Typical injuries were demonstrated by scanning electron microscopy (S.E.M.). The acrosomal status was visualised using FITC-conjugated peanut agglutinin, and the acrosome reaction was induced by calcium ionophore A 23187. The chromatin stability was estimated by acridine orange test. In winter, the average percentages of motile and morphologically normal sperm (67 and 74.3%, respectively) were higher than during the breeding season in May (59 and 65.9%; P < 0.05). After freezing/thawing the proportions of vital and intact sperm decreased significantly. The number of motile sperm declined to 15 and 18% in May and December (range 5-40%), and of morphologically intact sperm to 51% in both seasons. Results of S.E.M. showed typical membrane ruptures in the acrosomal region and some sperm with abnormal necks. The proportion of frozen sperm with spontaneous acrosome reaction was higher during winter (86.5 versus 77.0%), suggesting a higher degree of membrane reactivity. Percentages of spermatozoa with denaturated chromatin were minimal and showed minimal differences between fresh and frozen state, stallions or seasons. An additional decondensation treatment with papain and DTE revealed a slightly enhanced number of spermatozoa with denaturable DNA after cryopreservation, especially in December (5.4 +/- 1.3%). The influence of cryoextenders was not significant for most sperm parameters, but there was a high variability between the stallions. Altogether, the influence of factors on the quality of spermatozoa has the following rank order: cryopreservation > stallion > season. Different cellular structures seem to have different susceptibilities to physicochemical stress. The cryopreservation of sperm during December results in survival rates similar to those measured during the breeding season, even more important for successful preservation is the selection of suitable semen donors.

Acrosome↗
PubMed1996

Oestrous behaviour of Holstein cows during cooler and hotter tropical seasons.

Seasonal effects on post-partum ovarian activity, duration and intensity of sexual behaviour were determined for Holstein dairy cattle imported from a temperate climate into a tropical region. Animals were observed continuously during the cooler (temperature-humidity index (THI) < 25) and hotter (THI > 25) seasons for 2 years. They were restricted to a cement footing in the hotter season observation period in Year 1, but had access to both concrete and dirt footing during all other seasons. Sequential milk progesterone profiles provided an indication of when follicular phases occurred, and recorded sexual behaviour was compared with these to determine if oestrous signs accompanied ovulations. Most cows had normal ovarian cycles and ovulated regularly during both seasons, but quiet ovulations occurred with greater frequency during the hotter times of the year (P < 0.05). Demonstrations of sexual behaviour were affected by choice of footing rather than season. The actual time when cows stood passively and allowed herdmates to complete mounting ranged from 5.1 +/- 0.7 to 5.8 +/- 1 h with access to exercise yards and cement or dirt footing, but declined to only 1.3 +/- 1.1 h when animals were confined to cement (P < 0.05). Similarly, the total duration of oestrus and mean number of interactions were significantly (P < 0.05) reduced during the observation period conducted with cows confined to concrete footing. These findings further emphasize that the duration of oestrus in dairy cows in considerably shorter than the commonly quoted 18 h.

Animals↗
PubMed1997

Seasonal fluctuations in plasma concentrations of luteinizing hormone and progesterone in Brahman (Bos indicus) and Hereford-Shorthorn (Bos taurus) cows grazing pastures at two stocking rates in a subtropical environment.

The effects of day length and grazing intensity on seasonal fluctuations in plasma concentrations of luteinizing hormone (LH) and cyclic ovarian activity were determined in Brahman (Bos indicus) and Hereford-Shorthorn (Bos taurus) cows maintained at two stocking rates in a subtropical environment. Contemporary groups of ovariectomised cows were monitored for fluctuations in plasma concentrations of LH. Equal numbers (n = 5) of entire and ovariectomised Brahman and Hereford-Shorthorn cows were assigned to a pasture with a greater or lesser stocking rate. Over a 15-month period, live weight was recorded weekly, and a blood sample was taken at the same time for measurement of plasma LH in entire and ovariectomised cows, and plasma progesterone in entire cows. Plasma concentrations of progesterone were used as an index of cyclic luteal function (time of cessation or onset of oestrous cycles). Regression coefficients were calculated to determine the least-order regression coefficient (LORC; range 1st to 10 order) for which time of year explained at least 50% (r2 > 0.05) of changes in live weight, plasma LH, or plasma progesterone; regression coefficients of 4th and 5th order indicated seasonally-related changes in these variables. For all cows, live weight was greatest in late summer to early autumn and lowest in winter. Changes in live weight were more closely related to seasonal changes in pasture availability for cows on pastures at a greater stocking rate (LORC 4th-5th) than for cows on pastures at a lesser stocking rate (LORC 1st-3rd). Cyclic ovarian activity ceased in four Hereford-Shorthorn cows on pastures at a greater stocking rate in late autumn to early winter, and onset of oestrous cycles did not occur in all of these cows until late spring. Oestrous cycles were not detected in one of five cows in the other groups during different periods of the study; however, there were no apparent patterns to cessation of oestrous cycles in these groups. There were no seasonally-related changes in plasma LH in entire cows, at either stocking rate (LORC 10th; r2 = 0.16 to 0.41). In contrast, distinct seasonal fluctuations in plasma LH occurred in ovariectomised cows, with increases in spring and winter. Environmental cues induced greater fluctuations in plasma LH in ovariectomised cows at a greater stocking rate (LORC 3rd-5th; r2 = 0.71 to 0.72) compared with ovariectomised cows at a lesser stocking rate (LORC 3rd-5th; r2 = 0.53 to 0.58). The findings demonstrated that marked seasonal changes in reproductive activity of the hypothalamic pituitary axis can occur in cows with B. indicus and B. taurus genotypes in a subtropical environment; however, changes in plasma concentrations of LH are only apparent in ovariectomised cows. Concentrations of plasma LH in ovariectomised Brahman and Hereford-Shorthorn cows increased during winter, when pasture availability was limiting and cyclic luteal function ceased in four of five Hereford-Shorthorn cows.

Adaptation, Physiological↗
PubMed1999

Ovarian function in ewes at the onset of the breeding season.

Transrectal ultrasonography of ovaries was performed each day, during the expected transition from anoestrus to the breeding season (mid-August to early October), in six Western white-faced cross-bred ewes, to record ovarian antral follicles > or = 3 mm in size and luteal structures. Jugular blood samples were collected daily for radioimmunoassay (RIA) of follicle-stimulating hormone (FSH), oestradiol and progesterone. The first ovulation of the breeding season was followed by the full-length oestrous cycle in all ewes studied. Prior to the ovulation, all ewes exhibited a distinct increase in circulating concentrations of progesterone, yet no corpora lutea (CL) were detected and luteinized unovulated follicles were detected in only three ewes. Secretion of FSH was not affected by the cessation of anoestrus and peaks of episodic FSH fluctuations were associated with the emergence of ovarian follicular waves (follicles growing from 3 to > or = 5 mm). During the 17 days prior to the first ovulation of the breeding season, there were no apparent changes in the pattern of emergence of follicular waves. Mean daily numbers of small antral follicles (not growing beyond 3 mm in diameter) declined (P < 0.05) after the first ovulation. The ovulation rate, maximal total and mean luteal volumes and maximal serum progesterone concentrations, but not mean diameters of ovulatory follicles, were ostensibly lower during the first oestrous cycle of the breeding season compared with the mid-breeding season of Western white-faced ewes. Oestradiol secretion by ovarian follicles appeared to be fully restored, compared with anoestrous ewes, but it was not synchronized with the growth of the largest antral follicles of waves until after the beginning of the first oestrous cycle. An increase in progesterone secretion preceding the first ovulation of the breeding season does not result, as previously suggested, from the ovulation of immature ovarian follicles and short-lived CL, but progesterone may be produced by luteinized unovulated follicles and/or interstitial tissue of unknown origin. This increase in serum concentrations of progesterone does not alter the pattern of follicular wave development, hence it seems to be important mainly for inducing oestrous behaviour, synchronizing it with the preovulatory surge of luteinizing hormone (LH), and preventing premature luteolysis during the ensuing luteal phase. Progesterone may also enhance ovarian follicular responsiveness to circulating gonadotropins through a local mechanism.

Animals↗
PubMed1994

Seasonal variations of nasal resistance in allergic rhinitis and environmental pollen counts. III: Efficacy of antiallergic agents.

We previously reported that, in a patient with Japanese cedar pollinosis, preseasonal increase in total nasal airway resistance (NAR) possibly caused from circannual endogenous rhythm was suppressed by preseasonal systemic administration of antiallergic agent. In this study, in order to determine the influence of preseasonal use of a topical antiallergic agent and seasonal administration of a peroral antiallergic agent, we made measurement of nasal airway resistance and pollen counts under the previous respective conditions in separated years. Preseasonal high mean values of total NAR for a couple of weeks was not suppressed by the preseasonal topical administration of ketotifen nasal spray in 1992 which was a low pollen season (974/cm2). However, the patient did not complained of severe episodes of hay fever at all throughout the season. Preseasonal increases in mean values of total NAR were observed in 1993 which was a high Japanese cedar pollen season (4,875/cm2) with NAR the same as untreated seasons. This may have been because the patient was not treated with preseasonal use of peroral azelastine. On extremely high Japanese cedar pollen count days further increased NAR occurred in the patient. The patient experienced relatively severe hay fever episodes, but used no other anti-histamine nor topical steroid during the season.

Administration, Topical↗
PubMed1993

Seasonal variations of nasal resistance in allergic rhinitis and environmental pollen counts.

We made measurements of nasal airway resistance in a patient with Japanese cedar pollinosis and also measured the environmental pollen counts under different exposure conditions. In the season of high Japanese cedar pollen counts in Japan values of mean nasal airway resistance were significantly increased, remained elevated for 2 months after the season, and eventually decreased. In the season of low pollen counts, the mean values of nasal airway resistance measurements were increased during the season but decreased more rapidly after the season. In a year with no exposure to the environmental allergen because the subject lived out of Japan, the mean nasal airway resistances were relatively increased closely in phase with the Japanese cedar pollen season.

Adult↗
PubMed2002

Neuroendocrine interactions and seasonality.

Sheep in temperate latitudes are seasonal breeders. Of the different seasonal cues, photoperiod is the most reliable parameter and is used by animals as an indication of the time of the year to synchronize endogenous annual rhythms of reproduction and physiology. The photoperiodic information is transduced into neuroendocrine changes through variations in melatonin secretion from the pineal gland. Melatonin triggers variations in the secretion of luteinizing hormone-releasing hormone, luteinizing hormone and follicle stimulating hormone (LHRH/LH/FSH) responsible for seasonal changes in reproductive activity. In female sheep, the seasonal changes in the hormonal LH pattern mainly reflect an increase in the negative feedback exerted by estradiol under long days on the frequency of pulsatile LH secretion. The resulting seasonal inhibition of LH secretion involves the activation of monoaminergic and especially dopaminergic systems by estradiol. Other types of physiological regulation subject to seasonal changes such as voluntary food intake (VFI), fat metabolism, body mass and pelage growth also occur in sheep, goats or related wild species. Several neuroendocrine intermediates seem to be shared by these different systems and may participate in their synchronization, providing the advantage that this helps mammalian species to adapt to their environment.

Animal Nutritional Physiological Phenomena↗
PubMed1998

Seasonal changes in adrenal sensitivity alter corticosterone levels in Gambel's white-crowned sparrows (Zonotrichia leucophrys gambelii).

Recent work indicates that Gambel's white-crowned sparrows modulate corticosterone release seasonally in response to capture and restraint. Free-living white-crowned sparrows dramatically elevate both baseline and stress-induced corticosterone levels during the breeding season compared with either wintering or migrating birds. Although corticosteroid binding globulin capacity also rises during breeding, it does not fully compensate for elevated glucocorticoid levels. Consequently, we examined what hypothalamic-pituitary-adrenal axis changes could account for seasonal changes in glucocorticoid levels. During winter and fall migration, exogenous ACTH failed to elevate corticosterone levels beyond the response to capture and handling, suggesting that the adrenal's ability to release corticosterone limits circulating levels during these seasons. In contrast, not only were corticosterone levels higher during breeding, but adrenals further responded to an exogenous ACTH signal, indicating a dramatic enhancement of the adrenal's ability to secrete corticosterone. Furthermore, we inferred the pituitary's ACTH secretory ability by injecting exogenous corticotrophin-releasing factor (CRF), arginine vasotocin (AVT) and mesotocin and measured corticosterone release. Pituitaries in breeding birds appear to respond to exogenous CRF and AVT, suggesting hypothalamic control of corticosterone release during this season. Taken together, these results suggest that seasonal modulation of corticosterone release in this species is controlled primarily at the adrenal.

Adrenal Glands↗