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PubMed1990

Effect of season on physical activity score, back extensor muscle strength, and lumbar bone mineral density.

Seasonal variation in physical activity, back extensor muscle strength (BES), and bone mineral density (BMD) of the lumbar spine was studied in 65 healthy postmenopausal women. Physical activity score (PAS) was assessed with an ordinal scale (0-18); this score and the BES were obtained monthly for 2 years (25 readings). BMD values were obtained semiannually (5 readings). A periodic (cosine) regression model was fit to each subject's PAS and BES data to obtain individual estimates of the annual peak day d and the average annual range due to seasonality. There was a strong (P less than 0.001) seasonal pattern in physical activity; August 3 was the average peak day, and the seasonal range was 2.0 PAS units. There was modest (P = 0.047) seasonality in BES; June 6 was the estimated peak day, and the seasonal range was 8.22 pounds (about 7% of the 0.002), and the highest monthly average BMD was in August. This seasonal range of 1.4% is larger than the average annual decline with age in BMD observed in longitudinal studies of postmenopausal women. The results of this study have important implications for the planning of longitudinal studies involving changes in physical activity or bone mass in geographic areas with diverse seasons.

Aged↗
PubMed2001

Seasonal variation in bone lead contribution to blood lead during pregnancy.

Population blood lead level (PbB) often shows seasonal variation, frequently being higher in summer and lower in winter. As vitamin D metabolites also show seasonal variability, and the metabolites are associated with bone metabolism, some authors have posited a role for bone lead release in seasonal PbB changes. We made third trimester and postdelivery PbB measurements on 414 immigrant women (98% Latina) in Los Angeles. We measured in vivo tibia and calcaneus (heel) lead concentration postdelivery via K-shell X-ray fluorescence. We saw evidence of seasonal variation in prenatal PbB, but not postnatal PbB. PbB was highest in spring and lowest in autumn. Tibia lead concentration was associated with prenatal PbB, as reported before. The contribution of tibia lead to prenatal PbB varied seasonally, with the greatest contribution occurring in the winter quarter and the least in the summer quarter. The temporal pattern of bone lead contribution to PbB follows the seasonal alteration of insolation. There was no seasonal component in prenatal PbB associated with calcaneus lead, nor were there seasonal variations in either calcaneus or tibia lead contributions to postnatal PbB. Bone turnover in the third trimester of pregnancy may be higher in winter months than in summer months, resulting in greater fetal lead exposure in spring than at other times of the year.

Bone and Bones↗
PubMed1994

Seasonal changes in body mass, insulin, and glucocorticoids of free-living golden-mantled ground squirrels.

The aim of the present study was to determine the relationship between seasonal variation in levels of insulin, cortisol, and corticosterone and body mass in a natural population of golden-mantled ground squirrels (Spermophilus saturatus) over the active season, from April to August. The body mass of females is at an active season minimum on emergence from hibernation, increases during pregnancy and lactation, and shows a further rise during fattening, reaching a peak in August. Males are heavier than females on emergence from hibernation, lose mass during the mating period, then gradually increase to a maximum in August. Plasma insulin titers generally reflected these patterns of change in body mass. Levels in males were almost double those of females on emergence, then decreased as body mass was lost during mating. Male values increased in July and peaked in August, coincident with the body mass maximum. Females, in contrast, showed very low insulin levels in April on emergence and increased levels during lactation, continuing high into the fattening period. Corticosterone levels were low in both sexes at the beginning of the season and rose throughout most of the active season; female levels exceeded those of males during the lactation phase. Cortisol titers gradually decreased over the first half of the active season in both sexes, but later increased to a seasonal maximum at the end of the season, coincident with the peak in body mass.(ABSTRACT TRUNCATED AT 250 WORDS)

11-Hydroxycorticosteroids↗
PubMed1998

Seasonal fluctuations in the secretory response of neuroendocrine cells of Aplysia californica to inhibitors of protein kinase A and protein kinase C.

The neuroendocrine bag cells of Aplysia provide an excellent model system for exploring the roles of second-messenger pathways regulating peptide hormone secretion. Both the cAMP and diacylglycerol second-messenger systems and their associated protein kinases (PKA and PKC) are involved in regulating membrane excitability in bag-cell neurons of Aplysia. The purpose of the present set of experiments was to determine if PKA and PKC also play roles in regulating egg laying hormone (ELH) secretion from bag-cell neurons. Abdominal ganglia with attached bag-cell clusters and connective nerves were dissected from reproductively mature Aplysia, and ELH secretion in response to electrically stimulated afterdischarges was measured by RIA. ELH secretion from bag cells treated with protein-kinase inhibitors (Rp-cAMPS to inhibit PKA; H-7 to inhibit PKC) was compared to that from untreated controls. Our experiments showed that 100 microM Rp-cAMPS significantly attenuated ELH secretion during the nonbreeding seasons (winter and spring) of 2 consecutive years. This suggested a role for PKA in regulating ELH secretion. However, Rp-cAMPS had no effect on ELH secretion during the breeding seasons (summer and fall) of 2 consecutive years, even when the dose of Rp-cAMPS was increased to 200 microM. These findings indicate that there is a seasonal fluctuation in responsiveness to PKA inhibition. We also investigated if there was a seasonal fluctuation in the ability of the PKC inhibitor H-7 to suppress ELH secretion. During the nonbreeding season, 10-100 microM H-7 significantly inhibited ELH secretion, but during the breeding season, only the highest dose (100 microM) of H-7 inhibited ELH release. These results confirm that PKC plays a role in regulating ELH secretion and indicate that there is a seasonal fluctuation in responsiveness to PKC inhibition. Overall, our findings suggest that both the cAMP and diacylglycerol second-messenger pathways are regulated on a seasonal basis.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1999

Seasonal and social correlates of fecal testosterone and cortisol levels in wild male muriquis (Brachyteles arachnoides).

Fecal testosterone and cortisol levels were analyzed from six wild male muriquis (Brachyteles arachnoides) over a 19-month period at the Estação Biológica de Caratinga in Minas Gerais, Brazil, to investigate the hormonal correlates of seasonal sexual behavior and environmental conditions. Group mean testosterone levels based on weekly samples from the six males did not differ between copulatory and noncopulatory periods or between rainy and dry seasons. Cortisol levels did change with copulatory periods, and were significantly higher during the second dry season, when mating continued following an exceptionally heavy rainy season, than during the first dry season, when mating ceased. Males exhibited individual variation in the timing of their hormone shifts relative to their sexual activity, but neither hormone levels nor sexual activity were related to male age. Despite individual differences in the timing of testosterone fluctuations around the onset and offset of the copulatory season, all males exhibited elevated cortisol concentrations following a slight increase in testosterone at the beginning of the copulatory season. Both the lack of significant changes in testosterone levels with the onset of the rainy and copulatory season and the lack of prebreeding increases in cortisol may be related to the low levels of overt aggression displayed by male muriquis over access to mates.

Aggression↗
PubMed1986

Elevated testosterone levels during nonbreeding-season territoriality in a fall-breeding lizard, Sceloporus jarrovi.

In many vertebrates, seasonal activation of sexual and territorial behaviors coincides with seasonal gonadal activation and is caused by the increase in sex steroid hormones. Both male and female Sceloporus jarrovi are territorial, but in this species territorial behavior is seasonally activated in late April, months before seasonal gonadal maturation, which occurs in August prior to the fall mating season. Measurements of seasonal changes in circulating levels of the sex steroid hormones testosterone, progesterone, and estradiol indicated that testosterone levels in both sexes are elevated when territorial behavior is expressed, even during the period of nonbreeding-season territoriality during the summer. This suggests that a nonbreeding season behavior is activated by a sex steroid hormone in this species.

Animals↗
PubMed2002

Behavioral seasonality in Mahale chimpanzees.

To analyze how the chimpanzees in the Mahale Mountains National Park, Tanzania, change their grouping pattern, activity budget, travel speed, and travel distance within an annual cycle, I divided 1-year data into four periods. The Mahale chimpanzees have the behavioral flexibility to adapt to various climates and exhibited at least three behavioral seasons. In the early wet season, chimpanzees formed a few, large parties, and spent much time feeding on insects and animal meat. In the early and late dry seasons, chimpanzees maintained party sizes as large as in the early wet season, and traveled distances similar to the early wet season, but spent the most time feeding and traveling within the year. By contrast, in the late wet season chimpanzee parties broke up into more numerous, small groups, and traveled slowly over shorter distances. Although time spent feeding and traveling were the same as that in the early wet season, time spent feeding on terrestrial herbaceous vegetation (THV) was the highest in the year. The results suggest that chimpanzees travel longer, faster, and farther in seasons when they form large parties.

Animals↗
PubMed2004

Seasonality in clinical onset of type 1 diabetes in belgian patients above the age of 10 is restricted to HLA-DQ2/DQ8-negative males, which explains the male to female excess in incidence.

AIMS/HYPOTHESIS: Type 1 diabetes arises from an interplay between environmental and genetic factors. The reported seasonality at diagnosis supports the hypothesis that currently unknown external triggers play a role in the onset of the disease. We investigated whether a seasonal pattern is observed at diagnosis in Belgian Type 1 diabetic patients, and if so whether seasonality varies according to age, sex and genetic risk, all known to affect the incidence of Type 1 diabetes. METHODS: The seasonal pattern at clinical diagnosis was assessed in 2176 islet antibody-positive diabetic patients aged 0 to 39 years diagnosed between 1989 and 2000. Additional stratification was performed for age, sex and HLA-DQ genotype. RESULTS: Overall, a significant seasonal pattern at clinical diagnosis of diabetes was observed (p<0.001). More subjects were diagnosed in the period of November to February (n=829) than during the period of June to September (n=619) characterised by higher averages of maximal daily temperature and daily hours of sunshine. However, the seasonal pattern was restricted to patients diagnosed above the age of 10 (0-9 years: p=0.398; 10-19 years: p<0.001; 20-29 years: p=0.003; 30-39 years: p=0.015). Since older age at diagnosis is associated with a male to female excess and a lower prevalence of the genetic accelerator HLA-DQ2/DQ8, we further stratified the patients aged 10 to 39 years (n=1675) according to HLA-DQ genotype and sex, and we found that the seasonal pattern was largely restricted to male subjects lacking DQ2/DQ8 (n=748; p<0.00 vs all others: n=927; p=0.031). CONCLUSIONS/INTERPRETATION: In a subgroup of male patients diagnosed over the age of 10, the later stages of the subclinical disease process may be more driven by sex- and season-dependent external factors than in younger, female and genetically more susceptible subjects. These factors may explain the male to female excess in diabetes diagnosed in early adulthood.

Adolescent↗
PubMed2004

Thyroid hormone-dependent seasonality in American tree sparrows (Spizella arborea): effects of GC-1, a thyroid receptor beta-selective agonist, and of iopanoic acid, a deiodinase inhibitor.

To explore the role of TH in the control of seasonality [i.e., photoperiodic testicular growth, photorefractoriness, and postnuptial (prebasic) molt] in American tree sparrows (Spizella arborea), we performed experiments in which THX males were simultaneously photostimulated and given TH replacement therapy. In the first experiment, equimolar concentrations (1X = 1.3 nmol) of T4, T3, or GC-1, an iodine-free TRbeta agonist, were administered s.c. daily during the first 21 days of photostimulation. Two additional THX groups received GC-1 at 0.1X or 10X, and THX and THI control groups received vehicle. In the second experiment, T4 or T3, alone or in combination with the deiodinase inhibitor IOP, was injected i.m. twice daily during the first 14 days of photostimulation. In both experiments, end points were testis length and molt score. In the first experiment, THI birds given vehicle and THX birds given T4 replacement therapy exhibited all three components of seasonality. THX birds given T3 or GC-1 (1X or 10X) showed a subdued photoperiodic testicular response, but they did not become photorefractory or initiate molt. THX birds that received 0.1X GC-1 or vehicle exhibited none of the components of seasonality. These data are consistent with the hypothesis that photoperiodic testicular growth, a vernal component of seasonality, is a TRbeta-mediated response and suggest that T4 may activate TRbeta more efficiently than does T3 or GC-1. By contrast, the failure both of T3 and of GC-1, but not of T4, to program photostimulated THX males for photorefractoriness and postnuptial molt suggests that autumnal components of seasonality may be TRalpha-mediated responses solely to T4. In the second experiment, IOP administered alone had no significant impact on seasonality. THX birds that received T4 with or without IOP showed all components of seasonality, whereas birds that received T3 with or without IOP showed only photoperiodic testicular growth. These results challenge the widely held view that T4 is merely a prohormone for T3 and support the emerging view that T4 has intrinsic hormonal activity. Because IOP augmented the photoperiodic testicular response in T3-treated THX birds, T3 may act either independently or co-dependently with T4 in programming vernal seasonal events.

Acclimatization↗
PubMed2001

A test of the hypothesis that T3 is the "seasonality" thyroid hormone in American tree sparrows (Spizella arborea): intracerebroventricular infusion of iopanoic acid, an inhibitor of T3 synthesis and degradation.

This study tested the hypothesis that L-3,5,3'-triiodothyronine (T3) is the bioactive "seasonality" thyroid hormone in American tree sparrows (Spizella (arborea). The experimental approach coupled thyroid hormone replacement therapy after radiothyroidectomy with photostimulation and intracerebroventricular infusion of iopanoic acid, an inhibitor of L-3,5,3'-triiodothyronine synthesis and degradation. Endpoints were testis length, molt score, and hypothalamic content of chicken gonadotropin-releasing hormone 1. The hypothesis predicts that thyroidectomized male tree sparrows moved to long days and given thyroxine in combination with iopanoic acid will lack L-3,5,3'-triiodothyronine and so will not express thyroid hormone-dependent photoperiodic testicular growth (a vernal component of seasonality) and photorefractoriness or postnuptial molt (autumnal components of seasonality). It further predicts that iopanoic acid will enhance the efficacy of L-3,5,3'-triiodothyronine and so will facilitate the expression of seasonality in thyroidectomized males given L-3,5,3'-triiodothyronine replacement therapy. Iopanoic acid had no significant effect on any component of seasonality in thyroid-intact males given vehicle, or in thyroidectomized males given thyroxine or L-3,5,3'-triiodothyronine. Thyroid-intact males, as well as thyroidectomized males infused with thyroxine alone, commonly expressed all components of seasonality. Thyroidectomized males given L-3,5,3'-triiodothyronine alone exhibited photoperiodic testicular growth, but did not become photorefractory or initiate molt. While these results confirm that thyroid hormone acts centrally to program American tree sparrows for seasonality, they do not support the hypothesis that L-3,5,3'-triiodothyronine is the bioactive "seasonality" thyroid hormone, and they challenge the view that thyroxine is merely a prohormone.

Animals↗
PubMed2003

Seasonal variation in top-down and bottom-up processes in a grassland arthropod community.

Both top-down and bottom-up processes are common in terrestrial ecosystems, but how these opposing forces interact and vary over time is poorly understood. We tested the variation of these processes over seasonal time in a natural temperate zone grassland, a field site characterized by strong seasonal changes in abiotic and biotic conditions. Separate factorial experiments manipulating nutrients and cursorial spiders were performed in the wet and dry seasons. We also performed a water-addition experiment during the summer (dry season) to determine the degree of water limitation during this time. In the spring, nutrient addition increased plant growth and carnivore abundance, indicating a bottom-up control process. Among herbivores, sap-feeders were significantly enhanced while grazers significantly declined resulting in no net change in herbivore abundance. In the summer, water limitation was predominant increasing plants and all herbivores while nutrient (N) effects were non-significant. Top-down processes were present only in the spring season and only impacted the guild of grazing herbivores. These results show that bottom-up limitation is present throughout the season in this grassland, although the specific limiting resource changes as the season progresses. Bottom-up processes affected all trophic levels and many different guilds, while top-down effects were limited to a select group of herbivores and did not extend to the plant trophic level. Our results show that the relative strengths of top-down and bottom-up processes can shift over relatively short periods of time in habitats with a strong seasonal component.

Animals↗
PubMed2004

Seasonality of alcohol-related phenomena in Estonia.

We studied alcohol consumption and its consequences as a seasonal phenomenon in Estonia and analysed the social and environmental factors that may cause its seasonal rhythm. There are two important questions when researching the seasonality of human activities: (1) whether it is caused by natural or social factors, and (2) whether the impact of the factors is direct or indirect. Often the seasonality of social phenomena is caused by social factors, but the triggering mechanisms are related to environmental factors like temperature, precipitation, and radiation via the circannual calendar. The indicators of alcohol consumption in the current paper are grouped as: (1) pre-consumption phenomena, i.e. production, tax and excise, sales (beer, wine and vodka are analysed separately), and (2) post-consumption phenomena, i.e. alcohol-related crime and traffic accidents and the number of people detained in lockups and admitted to alcohol treatment clinics. In addition, seasonal variability in the amount of alcohol advertising has been studied, and a survey has been carried out among 87 students of Tartu University. The analysis shows that different phenomena related to alcohol have a clear seasonal rhythm in Estonia. The peak period of phenomena related to beer is in the summer, from June to August and the low point is during the first months of the year. Beer consumption correlates well with air temperature. The consumption of vodka increases sharply at the end of the year and in June; the production of vodka does not have a significant correlation with negative temperatures. The consumption of wine increases during summer and in December. The consequences of alcohol consumption, expressed as the rate of traffic accidents or the frequency of medical treatment, also show seasonal variability. Seasonal variability of alcohol consumption in Estonia is influenced by natural factors (temperature, humidity, etc.) and by social factors (celebrations, vacations, etc.). However, distinguishing between impacts of direct and indirect relationships is complicated, as they are interlinked.

Accidents, Traffic↗
PubMed2005

The use of discriminant analysis and neural networks to forecast the severity of the Poaceae pollen season in a region with a typical Mediterranean climate.

Biological particles in the air such as pollen grains can cause environmental problems in the allergic population. Medical studies report that a prior knowledge of pollen season severity can be useful in the management of pollen-related diseases. The aim of this work was to forecast the severity of the Poaceae pollen season by using weather parameters prior to the pollen season. To carry out the study a historical database of 21 years of pollen and meteorological data was used. First, the years were grouped into classes by using cluster analysis. As a result of the grouping, the 21 years were divided into 3 classes according to their potential allergenic load. Pre-season meteorological variables were used, as well as a series of characteristics related to the pollen season. When considering pre-season meteorological variables, winter variables were separated from early spring variables due to the nature of the Mediterranean climate. Second, a neural network model as well as a discriminant linear analysis were built to forecast Poaceae pollen season severity, according to the three classes previously defined. The neural network yielded better results than linear models. In conclusion, neural network models could have a high applicability in the area of prevention, as the allergenic potential of a year can be determined with a high degree of reliability, based on a series of meteorological values accumulated prior to the pollen season.

Climate↗
PubMed2006

A comparison of growing season indices for the Greater Baltic Area.

Predictions of the effects of global warming suggest that climate change may have large impacts on ecosystems. The length of the growing season is predicted to increase in response to increasing global temperatures. The object of this study was to evaluate different indices used for calculating the thermal growing season for the Greater Baltic Area (GBA). We included established indices of growing season start, end and length, as well as new and modified indices. Based on the results, the GBA can be divided into a maritime western part and a more continental eastern part, with the western part reacting more sensitively to the use of different indices. The eastern part is more stable, but even here the index-to-index differences are large. It was found that including or excluding a frost criterion had a significant influence on the initiation of the growing season in the western, maritime, parts of the GBA. Frost has not the same importance for the end of the growing season. However, some end indices can result in a "never ending" growing season. When looking at twentieth century trends in growing season parameters, it was found that, when averaged over the whole GBA, there was little difference in trends depending on the indices used. The general mean trend in the GBA for the twentieth century discloses an earlier onset of c. 12 days, a delayed end of c. 8 days and consequently a lengthening of the growing season of about 20 days.

Europe↗
PubMed2000

Sun avoidance in the yellow baboons (Papio cynocephalus cynocephalus) of Ruaha National Park, Tanzania. Variations with season, behavior and weather.

Do free-ranging baboons avoid traveling towards the sun? Sun avoidance, in addition to resource and predator locations, may influence troop movement and non-random use of the home range. This paper investigates how sun avoidance, as measured by facial exposure to sunlight, influences directional choices. It hypothesizes that baboons should avoid the sun in the hot, dry season and show indifference to it in the cool, lush season. This paper also hypothesizes that baboons employ sun-avoidance behaviors more while they forage or travel to resting sites than when they travel to foraging sites or engage in active social behaviors; lastly this paper hypothesizes that sun altitude, temperature, humidity, and cloud cover influence sun-avoidance behavior. Using focal-animal techniques on 21 males from free-ranging baboon troops, I collected locational data, accurate to within 1.6 m, over 15 months. I calculated the difference between baboon bearings and the sun's azimuth in angular degrees. Both linear and circular statistics indicate that baboons put significantly (P<0.01) more than 90 degrees between their bearing and the sun's azimuth under certain conditions. Contrary to hypotheses based on the detrimental effects of insolation, baboons in the cool, lush season avoid the sun, while baboons in the hot, dry season do not. In the lush season, the extent to which baboons avoid the sun does not depend on their other behaviors. Dry-season baboons demonstrate stronger sun avoidance while resting than when engaged in other behaviors. Finally, in the dry season, temperature drives sun avoidance; humidity drives it in the lush season.

Animals↗
PubMed2006

Effect of seasonal variation on the clinical course of chronic hepatitis B.

BACKGROUND: Seasonal variation in immunity has been found in healthy individuals and in association with some diseases. It is still unknown whether seasonal variation affects the clinical course of chronic hepatitis B. Our aim in this study was to explore the effect of seasonal variation on the clinical course of chronic hepatitis B. METHODS: The flare and remission time of chronic hepatitis B were observed in patients with hepatitis B virus (HBV) infection. All patients enrolled were followed up at least every 3 months for a mean follow-up time of 24.0 (range, 12-60) months. Seasonal decomposition was employed to analyze the relationship between seasonal variation and flares, remission, and hepatitis B e antigen (HBeAg) seroconversion in chronic hepatitis B patients during follow-up. RESULTS: A total of 2238 patients were observed in our study. Flare and HBeAg seroconversion were seldom seen in 1076 patients (48.08%) with alanine aminotransferase (ALT) levels of less than 2.0 x upper limit of normal (ULN) during follow-up (mean, 36 months). The remaining 1162 patients (51.92%) (766, HBeAg positive; 387 anti-HBeAg positive; 9 negative for both HBeAg and anti-HBeAg) with ALT levels >or=2.0 x ULN were followed longitudinally for 12 months to judge flare, remission, and HBeAg seroconversion. Flare, remission, and HBeAg seroconversion in patients with ALT levels >or=2.0 x ULN showed clear seasonal patterns (P < 0.001), with high peaks during spring, summer, and summer, respectively. An autocorrelation correlogram showed that flares, remission, and HBeAg seroconversion occurred with distinct periodicity in winter, spring, summer, and autumn. CONCLUSIONS: Seasonal variation might affect the clinical course of chronic hepatitis B. The role of seasonal triggering factors should be further investigated.

Adolescent↗
PubMed2004

Seasonal variation of arbuscular mycorrhizal fungi in temperate grasslands along a wide hydrologic gradient.

We studied seasonal variation in population attributes of arbuscular mycorrhizal (AM) fungi over 2 years in four sites of temperate grasslands of the Argentinean Flooding Pampas. The sites represent a wide range of soil conditions, hydrologic gradients, and floristic composition. Lotus glaber, a perennial herbaceous legume naturalised in the Flooding Pampas, was dominant at the four plant community sites. Its roots were highly colonised by AM fungi. Temporal variations in spore density, spore type, AM root colonisation, floristic composition and soil chemical characteristics occurred in each site and were different among sites. The duration of flooding had no effect on spore density but depressed AM root colonisation. Eleven different types of spores were recognized and four were identified. Two species dominated at the four sites: Glomus fasciculatum and Glomus intraradices. Spore density was highest in summer (dry season) and lowest in winter (wet season) with intermediate values in autumn and spring. Colonisation of L. glaber roots was highest in summer or spring and lowest in winter or autumn. The relative density of G. fasciculatum and G. intraradices versus Glomus sp. and Acaulospora sp. had distinctive seasonal peaks. These seasonal peaks occurred at all four sites, suggesting differences among AM fungus species with respect to the seasonality of sporulation. Spore density and AM root colonisation when measured at any one time were poorly related to each other. However, spore density was significantly correlated with root colonisation 3 months before, suggesting that high colonisation in one season precedes high sporulation in the next season.

Argentina↗
PubMed2004

Changes in testicular and nipple volume related to age and seasonality in Japanese macaques (Macaca fuscata), especially in the pre- and post-pubertal periods.

We investigated, longitudinally and cross-sectionally, age and seasonal change in both the testis and nipple volume of Japanese macaques (Macaca fuscata) in relation to concentration profiles of gonadal steroids: testosterone (T) in males and progesterone (P) in females. Testicular volume (TV) and nipple volume (NV) showed rapid growth at puberty, 4.5 and 3.5 years of age in males and females, respectively, but in both sexes there were precocious individuals. The testis as a whole matures at about 10 years of age. TV change is closely related to T concentration profile. The pattern of TV change is composed of maturation and seasonal effects, with individual variation evident mainly in the latter. Some individuals show a simple pattern consisting of one peak in the breeding season (from summer to winter) and one trough in the non-breeding season. Other individuals exhibit a more complicated pattern composed of two or more peaks and troughs before and during the breeding season. The nipple matures at about 7 years but it is difficult to determine the exact maturational age as there are many confounding factors relating to NV. NV shows seasonal fluctuations similar to that of TV. Many animals have periods of substantial growth whereas others do not. The NV in adults from 10 to 25 years does not appear to change much with age, but animals older than 25 years of age have significantly smaller nipples. Seasonal fluctuation in NV mirrors that of the P level. Considered to be controlled by estrogen and P, the NV is a good indicator of the physiological status of reproduction, with its peak about 2 weeks earlier than that of P, that is, at the mid-follicular phase. NV and P level show a similar pattern in pregnancy; from conception, indicated by a P peak, NV and P concentration first decrease, then they increase until peri-parturition and slowly decrease again until the next breeding season.

Aging↗