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PubMed1992

The role of the adrenal glands in regulating onset of winter fur growth in mink (Mustela vison).

The role of the adrenal glands in regulating onset of winter fur growth in mink was investigated in long-term adrenalectomized animals. Bilateral adrenalectomy of adult female standard dark mink between June 23 and July 11, 1990, initiated onset of winter fur growth approximately 6 weeks earlier than controls. One month following completion of the winter fur growth in adrenalectomized mink, molting and growth of a new coat was observed. The type of pelage that grew as a result of the second growth wave was less dense than the normal summer or winter fur. However, this renewed hair growth suggests that adrenal hormones not only inhibit the onset of winter fur growth but also influence the duration of inactivity following each period of hair growth. Administration of deoxycorticosterone as a mineralocorticoid supplement had no effect on initiation of fur growth. It would appear that adrenal hormones are part of the mechanism through which photoperiod regulates fur growth in the mink. The identity of the adrenal hormones and their site of action is unknown.

Adrenal Glands↗
PubMed1997

Sex-related differences in habitat selection in wintering American kestrels, Falco sparverius

The American kestrel, Falco sparveriushas sex-related differences in habitat use during the non-breeding season, with females occupying more open habitats than males. Two competing hypotheses have been proposed to explain this phenomenon: (1) males and females prefer different habitats, and (2) males and females prefer similar habitats, but larger females exclude smaller males from preferred areas. This study experimentally investigated habitat selection in wintering kestrels by temporarily removing kestrels from areas, and then observing the numbers and sex of the kestrels that occupied vacated areas. The home ranges of 20 birds (10 males and 10 females) were mapped and their occupants removed. Areas vacated in early winter (November 1994) were filled more quickly than those vacated in late winter (February 1995). Areas previously held by females were reoccupied more frequently than were those previously occupied by males. Female kestrels reoccupied vacated female areas more than vacated male areas. Male kestrels reoccupied vacated female and male areas equally. The results demonstrate that (1) high-quality kestrel habitat may be limited in the non-breeding season, (2) vacated areas are more likely to be reoccupied in the early winter than in late winter, (3) female kestrels appear at an advantage relative to males in occupying scarce and competed-for areas, and (4) male kestrels will use female areas when female occupants have been removed. It is hypothesized that open habitats are preferred over less open habitats because the former offer reduced risk of predation from bird-eating hawks.

Journal Article↗
PubMed1999

Travel distance and mass gain in wintering blackbirds.

Birds that range over a large area will have a greater mass-dependent risk of predation than more sedentary birds. Birds that travel more may then reduce winter mass gain to compensate for the increased predation risk that greater travelling entails. I tested whether European blackbirds, Turdus merula, that travelled more in winter had a lower mass than more sedentary birds, independently of any confounding effects of food supply on both ranging behaviour and mass gain. I measured change in winter mass and amount of food eaten in conjunction with the distance that blackbirds travelled to a randomly sited mobile feeder. Blackbirds that travelled shorter distances (per trip and in total) and less often to the feeder had the highest mass midwinter relative to their spring mass. Blackbirds with a higher mean mass midwinter also travelled, on average, shorter distances to the feeder. The distance an individual blackbird travelled to the feeder at any one time was probably independent of the state of its daily energy reserves (how much of its daily total mass gain it had achieved at that point). The relationship between distance travelled and mass was probably independent of food supply because distances actually increased at the end of the winter and the amount of food eaten per individual changed little. More mobile blackbirds were therefore likely to have compensated for any increases in predation risk associated with their greater ranges by decreasing winter mass gain, but will have had an increased risk of starvation because of their lower mass. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed2003

Effect of vitamins D2 and D3 supplement use on serum 25OHD concentration in elderly women in summer and winter.

Vitamin D2 and D3 are generally considered equipotent in humans. A few studies have reported that serum 25OHD levels are higher in vitamin D3- compared with vitamin D2-supplemented subjects. As both vitamin D2 and D3 supplements are commonly used by elderly in United States, in the present study we determined the effect of self-reported vitamin D2 and vitamin D3 supplement use on serum total 25OHD levels according to season in elderly women aged 65-77 years. Serum total 25OHD levels were determined in winter and summer in unsupplemented women ( N = 307) and in women who reported taking vitamin D2 ( N = 56) and vitamin D3 ( N = 55) supplements by competitive protein binding assay. In vitamin D2-supplemented women, the contribution of vitamin D2 and D3 to the mean serum total 25OHD level was assessed by HPLC. In summer, there were no significant differences in the mean total serum 25OHD levels (ng/ml) among the vitamin D2 (32 +/- 2.1), vitamin D3 (36.7 +/- 1.95), and unsupplemented (32.2 +/- 0.95) groups. In winter, the mean serum total 25OHD levels were higher in women on vitamin D2 (33.6 +/- 2.34, P < 0.05) and vitamin D3 (29.7 +/- 1.76, NS) supplements compared with unsupplemented women (27.3 +/- 0.72). In vitamin D2-supplemented women, about 25% of the mean serum total 25OHD was 25OHD2, in both summer and winter. Twelve percent of unsupplemented women and 3.6% of vitamin D-supplemented women had a mean serum total 25OHD level below 15 ng/ml in winter. In elderly subjects, both vitamin D2 and Vitamin D3 supplements may contribute equally to circulating 25OHD levels, with the role of vitamin D supplement use being more predominant during winter.

Aged↗
PubMed2000

Peripheral bone mass is not affected by winter vitamin D deficiency in children and young adults from Ushuaia.

Low vitamin D levels in elderly people are associated with reduced bone mass, secondary hyperparathyroidism, and increased fracture risk. Its effect on the growing skeleton is not well known. The aim of this study was to evaluate the possible influence of chronic winter vitamin D deficiency and higher winter parathyroid hormone (PTH) levels on bone mass in prepubertal children and young adults. The study was carried out in male and female Caucasian subjects. A total of 163 prepubertal children (X age +/- 1 SD: 8.9 +/- 0.7 years) and 234 young adults (22.9 +/- 3.6 years) who had never received vitamin D supplementation were recruited from two areas in Argentina: (1)Ushuaia (55 degrees South latitude), where the population is known to have low winter 25OHD levels and higher levels of PTH in winter than in summer, and (2)Buenos Aires (34 degrees S), where ultraviolet (UV) radiation and vitamin D nutritional status in the population are adequate all year round. Bone mineral content (BMC) and bone mineral density (BMD) of the ultradistal and distal radius were measured in the young adults. Only distal radius measurements were taken in the children. Similar results were obtained in age-sex matched groups from both areas. The only results showing significant difference corresponded to comparison among the Ushuaian women: those whose calcium (Ca) intake was below 800 mg/day presented lower BMD and BMC values than those whose Ca intake was above that level (0.469 +/- 0.046 versus 0.498 +/- 0.041 g/cm(2), P < 0.02; 3.131 +/- 0.367 versus 3.339 +/- 0.386 g, P < 0.05, respectively). In conclusion, peripheral BMD and BMC were similar in children and young adults from Ushuaia and Buenos Aires in spite of the previously documented difference between both areas regarding UV radiation and winter vitamin D status. BMD of axial skeletal areas as well the concomitant effect of a low Ca diet and vitamin D deficiency on the growing skeleton should be studied further.

Absorptiometry, Photon↗
PubMed2004

Effects of the Norwegian winter environment on Giardia cysts and Cryptosporidium oocysts.

The structural integrity of Cryptosporidium oocysts and Giardia cysts in the Norwegian winter environment was investigated. During winter 2001/2002, Cryptosporidium oocysts and Giardia cysts were placed in the upper layers of soil in different matrices contained in chambers and exposed to the Norwegian climate. Morphological characteristics and inclusion/exclusion of vital dyes were monitored and compared to refrigerated controls. Reduction in parasite numbers was recorded for all parasites, geographical locations, and matrices. Shear forces generated during freeze-thaw cycles are postulated to have disintegrated the parasites exposed to the Norwegian winter and retrospective laboratory studies support this theory. Increased dye inclusion, possibly indicative of viability loss, was also noted. The refrigerated control parasites exhibited no decline in numbers, and alteration in dye inclusion characteristics for refrigerated parasites was slower. Cryptosporidium oocysts were apparently more robust than Giardia cysts; differences between isolates were also noted. These results suggest Cryptosporidium oocysts and Giardia cysts do not persist in the Norwegian terrestrial environment over winter, and when detected, will have been excreted since the previous winter. Differences in the morphological characteristics, matrix effects, and the possible relationship of the dye data to parasite survival are discussed in relation to further studies.

Animals↗
PubMed2004

Cold temperature increases winter fruit removal rate of a bird-dispersed shrub.

We tested the hypothesis that winter removal rates of fruits of wax myrtle, Myrica cerifera, are higher in colder winters. Over a 9-year period, we monitored M. cerifera fruit crops in 13 0.1-ha study plots in South Carolina, U.S.A. Peak ripeness occurred in November, whereas peak removal occurred in the coldest months, December and January. Mean time to fruit removal within study plots was positively correlated with mean winter temperatures, thereby supporting our hypothesis. This result, combined with the generally low availability of winter arthropods, suggests that fruit abundance may play a role in determining winter survivorship and distribution of permanent resident and short-distance migrant birds. From the plant's perspective, it demonstrates inter-annual variation in the temporal component of seed dispersal, with possible consequences for post-dispersal seed and seedling ecology.

Animals↗
PubMed2002

Nitrate sequestration by corticolous macrolichens during winter precipitation events.

Nitrogen is an essential nutrient in the biogeochemistry of forested ecosystems. The influence of canopy lichens on the winter biogeochemistry of nitrate in broadleaved deciduous forests is examined and it is hypothesized that nitrate sequestration will not differ between winter precipitation events. Rejection of this hypothesis would mean that meteorological conditions of winter precipitation events have a detectable influence on nitrate sequestration by canopy lichens and nitrate input to the forest floor. Canopy lichens of the genus Parmelia were found to influence winter nitrate stemflow inputs to forest soils differentially. Epiphytic lichens on an individual Carya glabra Mill. (pignut hickory) canopy tree, centrally located within the stand of an open deciduous forest, actively sequestered nitrate leached from the tree's woody frame, lowering aqueous stemflow inputs at the tree base. The quantities of nitrate sequestered by corticolous lichens during the 2 February 1999 mixed-precipitation event were significantly greater than those during all other precipitation events examined. Greater rates of nitrate uptake during the 2 February 1999 event may be attributed to (1) its intermediate rain intensity, which would have soaked the lichen thalli in a nutrient-rich bath, and (2) an air temperature range between -2 degrees C and 8 degrees C that would have increased viscosity and surface tension of stemflow drainage, thereby decreasing stemflow velocity and increasing the contact time of stemflow water on the lichen thalli. Other precipitation events were either too cold to promote metabolic activity by canopy lichens or too warm and intense for an optimal contact time of stemflow with lichen thalli, resulting in lower quantities of nitrate sequestered. Meteorological conditions of winter precipitation events have been documented to influence sequestration of nitrate by corticolous lichens and decrease aqueous stemflow inputs to the forest floor of broadleaved deciduous forests.

Ecosystem↗
PubMed1990

Natural summer and winter sunlight exposure patterns in seasonal affective disorder.

Twelve subjects with winter depression who lived in the Chicago area recorded their times of going outside during daylight hours for one week during the winter and one week during the summer. These records produced estimates of the duration of daily sunlight exposure and of perceived dawn, dusk and skeleton photoperiod. There was more than twice as much sunlight exposure in summer compared to winter (3.0 vs. 1.2 h/day). The perceived skeleton photoperiod was 4-5 h longer in summer than winter, with a later perceived dusk contributing more to the lengthening than an earlier perceived dawn. The duration of sunlight exposure and perceived skeleton photoperiod in both seasons was much less than what was possible given the available daylight. These results are discussed with reference to the modern urban life style, bright light treatment of winter seasonal affective disorder, and factors which affect the perceived intensity of sunlight.

Adult↗
PubMed1988

Interaction between ozone and winter stress.

In some countries, ozone (O3) is primarily a summer pollutant, but in much of Europe, elevated concentrations occur outside the growing season so perennials and over-wintering annuals may be subjected to the combined stresses of pollution, plus chilling, freezing, and winter desiccation. It is recognised that some air pollutants modify the response of plants to environmental stress, but little is known of interactions involving O3. This paper is part of a programme concerned with the effects of O3 on resistance to chilling, freezing, and winter desiccation. Pea (Pisum sativum L.) was used as a convenient model to confirm that O3 affects freezing resistance. The experiment also served as a further evaluation of the use of induced chlorophyll fluorescence kinetics to detect latent O3 injury. Two cultivars, 'Feltham First' and 'Conquest', were fumigated for 7 days, 7 h day(-1). Diffusive resistance and induced fluorescence were recorded daily during the period, then the plants were hardened at 4 degrees C day/2 degrees C night before exposure to 0, -2, -4, -6 and -8 degrees C. Ozone (0.075 ppm; 150 microg O3 m(-3)) caused stomatal closure in both cultivars, but the response was more rapid in 'Conquest'. There were also rapid effects on fluorescence kinetics, and it was concluded that FR, the rate of rise of induced fluorescence, is a useful parameter for indicating latent injury and for distinguishing between cultivars of different sensitivity. Exposure to O3 increased freezing injury and led to greater electrolyte leakage. The freezing resistance of 'Feltham First' was more affected than that of 'Conquest', probably because of the slower stomatal response to the pollutant leading to greater flux of O3 to the internal tissues. It is concluded that interactions involving pollutants and winter stress have implications for crop loss assessment. Perennials and over-wintering annuals should be exposed to the full range of environmental stresses.

Journal Article↗
PubMed1990

Winter-summer differences in the effects of emotion, posture and place of measurement on blood pressure.

The purpose of this study was to assess whether the effects of emotional state, posture, situation of measurement, and sex on daily blood pressure variation were different in subjects measured during summer months (May-September) and winter months (November-March). The subjects of the study were 157 patients from the Hypertension Center of New York Hospital-Cornell Medical Center in New York, who had ambulatory blood pressure monitoring performed between February 1984 and April 1985. Individual pressures taken with the monitor over the day in each subject were transformed to z-scores using the subject's daily mean pressure and standard deviation in order to assess differences in intraindividual variation. The zeta-scores were examined in separate but identical analyses of variance models (one for the winter months and one for the summer months) which included emotional state (happy, angry, anxious), posture (sitting, standing), situation of measurement (home, work, elsewhere) and sex as factors. The results showed that more factors had greater effects (as reflected in R2) on blood pressure during the winter months than summer months. In particular, the relative effect of anxiety, sitting, and being at work or home on blood pressure was significantly greater (P less than 0.05) in the winter months than summer months. In addition, pressure elevation during happiness was also more accentuated in winter than summer for diastolic pressure (P less than 0.05). These findings may have important implications for the interpretation of population studies examining the relationship between blood pressure and psychosocial stressors.

Adult↗
PubMed1989

Anemia at the onset of winter in the meadow vole (Microtus pennsylvanicus).

1. From 1981 to 1986, 6120 meadow voles (Microtus pennsylvanicus) were sampled for hematological indices in southeastern Manitoba, Canada. This survey revealed the sporadic occurrence of anemia in early winter at mean temperatures below about -5 degrees C. 2. Anemia was associated with leukocytosis and circulating normoblasts, suggesting a sudden, large blood loss. Individuals became anemic quickly, with no obvious predisposing factors. 3. Attempts were made to induce anemia by exposing voles in traps to various temperatures. Temperatures characteristic of most trapping sessions failed to induce anemia in both wild and laboratory-born voles. 4. Short-term exposure to more extreme temperatures (-20 to -30 degrees C) induced anemia. Voles lost blood through erosions of the epithelium of the glandular stomach, and developed other pathological lesions characteristic of hypothermia. 5. Although there was a strong association between cold weather and anemia, we could find no clear relationship between winter survival and winter weather. However, in 1984, extraordinarily cold temperatures were associated with anemia and a subsequent population decline. These events suggest a threshold mean daily temperature of about -15 degrees C, below which vole survival is grossly affected. 6. Deteriorating protein levels and energy reserves of small mammals in winter may make them particularly susceptible to cold stress. Hence, sporadic bouts of sustained cold may be responsible for some of the enigmatic winter declines seen in northern small mammals.

Acclimatization↗
PubMed1989

Effects of breed and wintering diet on growth, puberty and plasma concentrations of growth hormone and insulin-like growth factor 1 in heifers.

Twenty-five Brangus (BR) and 15 Angus (AN) heifers were used to study the effects of breed and wintering diet on average daily gain (ADG), onset of puberty and plasma concentrations of growth hormone (GH) and insulin-like growth factor 1 (IGF-1). Wintering diets (fed for 107 days beginning November 15) consisted of the following: 1) native grass hay (NGH), 2) ammoniated NGH, 3) NGH plus cottonseed meal, 4) Diet 3 plus corn and 5) Diet 4 plus monensin. After wintering, heifers were transferred to ryegrass pasture for 70 days. Mean ADG during the wintering phase were -.20, -.10, .17, .29 and .39 kg for heifers fed Diets 1 through 5, respectively (P less than .01). ADG was greater (P less than .05) for BR than for AN heifers. Plasma concentrations of GH were higher (P less than .05) in heifers fed Diets 1 and 2 than in heifers fed Diets 3, 4 or 5. Plasma concentrations of IGF-1 were lowest in heifers fed Diet 1 and highest in heifers fed Diets 4 and 5. During ryegrass grazing, GH concentrations were similar for all groups. However, concentrations of IGF-1 were higher (P less than .05) in heifers fed Diets 3, 4 and 5 than in heifers fed Diets 1 and 2. Age at puberty (onset of cyclic progesterone concentrations) was greatest in heifers fed Diet 1 and lowest in heifers fed Diet 5. Weight at puberty was not affected (P greater than .10) by wintering diet but was greater (P less than .01) in BR than in AN heifers. Therefore, negative ADG appears to be associated with elevated plasma GH concentrations in heifers, and plasma IGF-1 concentration appears to be a more accurate indication of nutritional status than plasma concentrations of GH.

Aging↗
PubMed2006

Down regulation of bisphenol A glucuronidation in carp during the winter pre-breeding season.

Environmental pollution by bisphenol A is prevalent in many rivers. The influence of bisphenol A on the reproductive organs of carp has been demonstrated to be serious, especially in the winter pre-breeding season. Although bisphenol A is detoxified as bisphenol A-glucuronide in carp organs, principally the intestine, the seasonal variation in the efficiency of the detoxification is not known. To estimate the seasonal risk of bisphenol A in carp, we investigated seasonal changes in microsomal UDP-glucuronosyltransferase activity toward bisphenol A in male-carp. Seasonal elimination efficiency of bisphenol A was also examined by organ perfusion in everted intestine. No marked seasonal differences were observed in UDP-glucuronosyltransferase activity toward 1-naphthol, but high activity toward sex steroid hormones (testosterone and estradiol) was observed in the winter pre-breeding season. Low UDP-glucuronosyltransferase activity toward bisphenol A was indicated in winter. The addition of bisphenol A into the mucosal fluid of the everted intestine resulted in excretion of bisphenol A into the mucosal side of the intestine as the metabolite, bisphenol A-glucuronide. Excretion of bisphenol A-glucuronide from carp intestine was highest in summer (proximal intestine: 13.3 nmol; middle intestine: 8.3 nmol; distal intestine: 7.9 nmol) and lowest in winter (proximal intestine: 1.0 nmol; middle intestine: 1.0 nmol; distal intestine: 0.9 nmol). These results suggest that metabolism and excretion of bisphenol A in carp hepatopancreas and intestine are impaired by down regulation of UDP-glucuronosyltransferase activity in the winter pre-breeding season.

Animals↗
PubMed2005

Effects of waterborne iron overload and simulated winter conditions on acute physiological stress response of whitefish, Coregonus lavaretus.

Two-year-old whitefish (Coregonus lavaretus) were exposed for 30 days to episodic iron overload in iron-rich humic water (5%) supplemented with inorganic iron (5 mg FeL(-1)). Two parallel laboratory exposures were performed, one under conditions simulating winter and the other under conditions simulating spring. After exposure, some of the fish were subjected to acute handling stress in the form of a short air challenge to reveal possible modification of the primary and secondary stress responses. In whitefish sampled without additional handling, iron accumulated in the liver (under spring conditions) and gills (under winter and spring conditions); plasma catecholamine and beta-estradiol (both winter and spring groups) as well as blood hematocrit (winter group only) levels were depressed; blood glucose (winter group only) and red blood cell (RBC) Na+ levels (spring group only) were increased. In handled whitefish, liver glycogen phosphorylase (GPase), RBC, and blood glucose stress responses were impaired by the applied exposure conditions, which reflected natural iron-rich humic water. Exposure also removed some physiological effects of the applied ambient conditions: plasma catecholamines and beta-estradiol, gill Na+/K+ -ATPase, and RBC K+ concentration were not different in two iron-exposed fish groups, whereas there was a difference in reference fish. Thus, the physiological effects of this type of subchronic exposure, together with alterations in the acute stress response, can lead to incorrect conclusions being drawn from the results, if the effects of time-dependent stress response are ignored. In conclusion, waterborne iron overload may impair the optimal capacity of whitefish to carry out their normal physiological functions such as responding to external threats.

Adaptation, Physiological↗
PubMed2006

The epidemiology of illness and injury at the alpine venues during the Salt Lake City 2002 Winter Olympic Games.

The Emergency Medicine literature has described levels of medical care for mass gatherings in the United States, including for the Los Angeles 1984 Summer and Calgary 1988 Winter Olympic Games. However, there are limited data to describe the type and number of illness or injury that may occur during mass gatherings in an alpine winter environment. To describe the epidemiology of illness and injury seen among spectators at the alpine and snowboarding venues during the Salt Lake City 2002 Winter Olympic Games, we conducted a retrospective review of the Salt Lake City 2002 Olympic Medical Care database for all patient encounters during the operational period of the Games at the alpine and snowboarding venues. The three venues included were: Deer Valley Resort (DVR), Park City Mountain Resort (PCM), and Snowbasin Resort (SBA). Each venue had a medical clinic located on site for spectators and another for athletes. Physicians, nurses, emergency medical technicians, and therapists staffed the clinics. The database was created by Inter-mountain Health Care (IHC) in conjunction with Salt Lake City 2002 Winter Olympic staff and consisted of descriptive reports of all patient encounters from all venues including demographic, epidemiology, and outcome information. IHC maintains the database, and was the sole medical provider for the Games. Each venue had at least 6 days of competition events. Over the 19 days of the Olympiad, a total of 410,160 spectators and 3,961 competitive athletes attended the three venues. There were 841 spectators evaluated and treated at the venue clinics, and mobile medical staff treated 262 spectators. The top five spectator clinic diagnostic categories were: sprain/strain (n=108), miscellaneous trauma (n=103), respiratory (n=88), miscellaneous medical (n=69), and digestive (n=52). Fifty spectators required transport to a hospital for additional care: 27 required transfer by ground ambulance and the remainder were transported by private vehicle. The overall spectator medical utilization rate was 26.9. In conclusion, the rate and acuity of patients seen at the alpine venues during the 2002 Winter Olympic Games was low. Nevertheless, we recommend full on-site physician and nurse staffing with advanced trauma and cardiac life support available during similar events.

Anniversaries and Special Events↗
PubMed2005

Tea (Camellia sinensis (L.) O. Kuntze) clone with lower period of winter dormancy exhibits lesser cellular damage in response to low temperature.

There is no literature available on the response of tea plant to low temperature. We studied the effect of low temperature on two clones of tea with contrasting periods of winter dormancy, a phenomenon in which the growth of apical shoots of tea is diminished during winter months. Clone 'Teenali 17/154' (TNL) showed shorter periods of winter dormancy than clone 'Kangra Jat' (KNJ). Low temperature (5 degrees C) resulted in increase of metabolic superoxide (O2*-) content and cellular damage (as measured by tetrazolium chloride reduction test) in both the clones, however, the increase was lesser in the case of TNL compared to KNJ. Activities of superoxide dismutase (SOD; EC 1.15.1.1), ascorbate peroxidase (APX; EC 1.11.1.11) and glutathione reductase (GR; EC 1.6.4.2) increased in both the clones in response to low temperature however, GR activity exhibited significant differences (P < 0.05) between the two clones. Low temperature caused increase in the intensity of various isozymes of SOD, APX and GR. A new isozyme of SOD (Cu/Zn type) was induced in both the clones at low temperature. Significantly higher GR activity in both the clones suggested a role of this enzyme in imparting better protection to tea at low temperature. Also, clonal variation for GR isozyme was observed between the clones. Based on these results it appears that TNL, a clone with relatively lesser period of winter dormancy experiences lesser oxidative stress in response to low temperature compared to KNJ, a clone with relatively higher period of winter dormancy.

Ascorbate Peroxidases↗
PubMed2004

Diurnal patterns of cortisol and thyroid hormones in the Harbor seal (Phoca vitulina) during summer and winter seasons.

A leading hypothesis for the dramatic population decline of the Alaskan harbor seal over the last 2-3 decades have related environmental changes to a decrease in the quality or quantity of available prey. If harbor seals are experiencing some sort of nutritional stress, it is important to understand the physiological and endocrine mechanisms controlling metabolic homeostasis in this species. The purpose of this research project was to determine whether circadian patterns of cortisol and total and free thyroxine (T(4)) and triiodothyronine (T(3)) are present in the harbor seal during the summer and winter seasons, and identify how they might alter metabolic rate and maintenance of body reserves. This study was carried out at the Alaska SeaLife Center in Seward, Alaska in June 2000 and January 2001. Blood samples were obtained every 2-3 h over a 24-h period through in-dwelling catheters inserted the day before sampling. The presence of a diurnal rhythm was determined by comparing levels between ante meridian (12 am to noon) and post meridian (noon to 12 midnight) time periods. Mean daily cortisol concentrations were not significantly different between seasons, but cortisol displayed a circadian rhythm only during the summer. Mean concentrations of cortisol (51.5 ng/ml+/-20.3) in the summer hours of ante meridian differed significantly from levels in the hours of post meridian (28.5 ng/ml+/-17.4). Neither total and free T(4), nor T(3), displayed a diurnal rhythm in either season. However, tT(4), tT(3), and fT(3) levels were significantly higher in the winter than in the summer. There was no seasonal effect on fT(4) levels. The absence of a circadian rhythm of cortisol during the winter may have been a result of the limited amount of daylight as well as the continual need to produce metabolic heat as a by-product of gluconeogenesis. Higher levels of thyroid hormones in the winter indicate an adaptive mechanism to cope with the low temperatures of winter.

Aging↗