Hormonal changes during forced moult induced by progesterone in domestic hen

Forced moulting has been induced in domestic hens by progesterone treatment (5 mg/day) for 25 days. Moult happened between the 11th and 19th day after the first treatment. Endocrine changes were followed during the moult by blood sampling in one week intervals. At the time of the last sampling, new egg laying cycle was initiated in all birds. Plasma progesterone concentration increased significantly in response to the treatment then tended to decrease. Oestrone and testosterone levels were the lowest during the period when feather loss was most intensive and increased in the course of feathering. This increase was significant in the case of oestrone. The level of 17-beta-oestradiol did not vary during moult induced by progesterone treatment. Plasma concentration of thyroxine significantly increased during feather loss, showing a maximum in the second and/or third week after the beginning of the treatment, while it decreased when feather growth had begun. Plasma triiodothyronine as well as corticosterone levels were the highest during the latest phase of moult, at the time of feather outgrowing. It has been supposed that moulting would be initiated in response to the synergistic effect on feather follicles of progesterone and thyroxine, which was stimulated by the progesterone treatment. The atrophic stage of the ovary suggested that progesterone was probably of adrenal origin. It was assumed that triiodothyronine and oestrone were responsible for controlling feather outgrowth.     

Changes in plasma testosterone, thyroxine and triiodothyronine in relation to sperm production and remex moult in domestic ganders

Changes in plasma testosterone (T), thyroxine (T4), triiodothyronine (T3), semen output and remex moult were studied in domestic ganders. A bimodal pattern in both plasma T and sperm concentration was observed during the annual cycle. Ganders started to produce semen at the end of January; maximum semen volume (0.32 +/- 0.04 ml) and sperm concentration (148 +/- 38 x 10(3)/mm3) were reached in March and a marked decrease was observed after mid-April, when the moult of the remiges began. Plasma T3 levels peaked in February (9.7 +/- 0.6 nmol.l-1) and this peak coincided with maximum T concentrations (9.8-10.4 nmol.l-1). Elevated levels of T4 were found from late February until mid-April (31.0-33.6 nmol.l-1). Plasma T concentration was low at all stages of remex moult and regrowth. Decreased T4 levels were found in ganders during remex regrowth from the "brush" to half of the full primary growth stage. Higher plasma T4 levels were found before and after this stage of the moult. A reverse pattern was observed for T3 concentrations.     

Role of environmental temperature and photoperiod in regulation of seasonal testicular activity in the frog, Rana perezi.

To analyze the role of environmental temperature and photoperiod in the regulation of the annual testicular cycle in Rana perezi, we performed experiments combining high (25 +/- 1 degrees C) or low (6 +/- 1 degrees C) temperature and different photoperiod regimens (18L:6D, 12L:12D, and 6L:18D (hours light:hours dark)) during three phases of the reproductive cycle: winter stage (December) and prebreeding (February) and postbreeding (May, June) periods. Low temperature and short photoperiod in winter induced the arrest of the maturation phase of spermatogenesis and the activation of primary spermatogonia proliferation and spermiohistogenesis. Rana perezi testis responded to long days stimulus in winter, even at low temperature, with induction of the maturation phase of the cycle. Exposure of male frogs to either high temperature or long photoperiod induced a decrease in testosterone levels in winter. During the prebreeding period, an increase in environmental temperature caused a reduction in testosterone, and a lengthening in photoperiod produced the opposite effect. Photoperiod had no effect on testosterone levels during the postbreeding period, but low temperature increased testosterone plasma levels. These results suggest that both temperature and photoperiod effects can vary seasonally, depending on the phase of the annual reproductive cycle in R. perezi.     

Behavioural and hormonal responses to capture stress in the male red-sided garter snake, Thamnophis sirtalis parietalis

We measured the behavioural and hormonal responses to capture stress in male red-sided garter snakes. Four hours of capture stress resulted in no suppression of mating behaviour relative to control individuals. In contrast, the same stress resulted in a significant increase in plasma levels of corticosterone and a significant decrease in plasma levels of testosterone. There was a significant negative correlation between plasma levels of corticosterone and testosterone in both control and capture-stress groups, suggesting that the increase in corticosterone directly drives the decrease in testosterone. While there was no relation between body size and initial plasma levels of the two steroids, longer individuals had a significantly greater increase in corticosterone following capture stress than did shorter individuals. Snakes display indeterminate growth, suggesting that older individuals have decreased sensitivity to negative feedback in the hypothalamic-pituitary-adrenal axis and thus hypersecrete glucocorticoids. These results suggest that male red-sided garter snakes have uncoupled their behavioural stress response from their hormonal stress response to maximize reproductive opportunities. Copyright 2000 The Association for the Study of Animal Behaviour.     

Relation between the Adrenals and Thyroid and their Hormones and the Testicular cycle of a Subtropical Avian Species

In order to understand the hormonal interactions throughout the reproductive phases (non-breeding, progressive, breeding and regressive) of a sub-tropical avian species, the male common myna (Acriodotheres tristis), hormones like epinephrine (E), norepinephrine (NE), corticosterone, tri-iodothyronine (T 3), thyroxine (T 4) and testosterone (along with testicular sialic acid) were quantitated. Histometry and histology of the testis and adrenal glands were also performed. It became evident that a parallel relationship exists between the reproductive phases of the common myna and levels of the hormones E, NE, corticosterone, T 3, T 4 and testosterone. Considering the ambient climatological conditions, it is suggested that primarily daylength and secondarily humidity control the gonadal cycle of this species.     

Relation between the Adrenals and Thyroid and their Hormones and the Testicular cycle of a Subtropical Avian Species

In order to understand the hormonal interactions throughout the reproductive phases (non-breeding, progressive, breeding and regressive) of a sub-tropical avian species, the male common myna ( Acriodotheres tristis ), hormones like epinephrine (E), norepinephrine (NE), corticosterone, tri-iodothyronine (T 3 ), thyroxine (T 4 ) and testosterone (along with testicular sialic acid) were quantitated. Histometry and histology of the testis and adrenal glands were also performed. It became evident that a parallel relationship exists between the reproductive phases of the common myna and levels of the hormones E, NE, corticosterone, T 3 , T 4 and testosterone. Considering the ambient climatological conditions, it is suggested that primarily daylength and secondarily humidity control the gonadal cycle of this species.     

Effects of fasting and exogenous melatonin on annual rhythms in the blue fox (Alopex lagopus)

The arctic fox (Alopex lagopus) is a winter-active inhabitant of the high arctic with extreme fluctuations in photoperiod and food availability. The blue fox is a semi-domesticated variant of the wild arctic fox reared for the fur industry. In this study, 48 blue foxes were followed for a year in order to determine the effects of exogenous melatonin and wintertime food deprivation on their reproductive and thyroid axes. Half of the animals were treated with continuous-release melatonin capsules in July 2002, and in November-January, the animals were divided into three groups and either fed continuously or fasted for one or two 22-day periods. Food deprivation decreased the plasma triiodothyronine and thyroxine concentrations probably in order to preserve energy due to a decreased metabolic rate. The same was observed in the plasma testosterone levels of the males but not in the plasma estradiol concentrations of the females. Exogenous melatonin advanced the autumn moult and seasonal changes in the voluntary food intake. It also advanced the onset of the testosterone peak in the males. The plasma estradiol levels of the females were unaffected, but the progesterone levels peaked more steeply in the sham-operated females. Melatonin exerted a strong influence not only on the reproductive axis of the males but also on the seasonal food intake. The species seemed quite resistant to periodic involuntary food deprivation.     

Elevated plasma corticosterone decreases yolk testosterone and progesterone in chickens: linking maternal stress and hormone-mediated maternal effects

Despite considerable research on hormone-mediated maternal effects in birds, the underlying physiology remains poorly understood. This study investigated a potential regulation mechanism for differential accumulation of gonadal hormones in bird eggs. Across vertebrates, glucocorticoids can suppress reproduction by downregulating gonadal hormones. Using the chicken as a model species, we therefore tested whether elevated levels of plasma corticosterone in female birds influence the production of gonadal steroids by the ovarian follicles and thus the amount of reproductive hormones in the egg yolk. Adult laying hens of two different strains (ISA brown and white Leghorn) were implanted subcutaneously with corticosterone pellets that elevated plasma corticosterone concentrations over a period of nine days. Steroid hormones were subsequently quantified in plasma and yolk. Corticosterone-implanted hens of both strains had lower plasma progesterone and testosterone levels and their yolks contained less progesterone and testosterone. The treatment also reduced egg and yolk mass. Plasma estrogen concentrations decreased in white Leghorns only whereas in both strains yolk estrogens were unaffected. Our results demonstrate for the first time that maternal plasma corticosterone levels influence reproductive hormone concentrations in the yolk. Maternal corticosterone could therefore mediate environmentally induced changes in yolk gonadal hormone concentrations. In addition, stressful situations experienced by the bird mother might affect the offspring via reduced amounts of reproductive hormones present in the egg as well as available nutrients for the embryo.     

Effects of aggressive encounters on plasma corticosteroid-binding globulin and its ligands in white-crowned sparrows

In birds, corticosteroid-binding globulin (CBG) binds corticosterone, progesterone and testosterone. The concentration of each ligand can alter the binding of the other ligands through competitive interactions. Thus, an increase in corticosterone or progesterone may displace testosterone bound to CBG, leading to an increase in bioactive free testosterone levels without affecting total testosterone levels in the circulation. Aggressive interactions increase plasma total testosterone levels in some birds but not in others. Here, we tested the hypothesis that aggressive encounters in the late breeding season would not increase total testosterone levels in plasma, but would alter CBG, total corticosterone or total progesterone levels in such a way as to modify the number of available binding sites and therefore occupancy by testosterone. A marked decrease in CBG occupancy by testosterone would indirectly suggest an increase in free testosterone levels in plasma. Wild male white-crowned sparrows were exposed to a simulated territorial intrusion (STI) or control for 30 min. Subjects were then caught and bled. We measured CBG using a ligand-binding assay and corticosterone, progesterone and testosterone using highly sensitive radioimmunoassays. STI significantly increased aggressive behaviors but did not affect plasma total testosterone levels. STI significantly increased plasma CBG and total corticosterone levels and decreased plasma total progesterone levels. We predict that CBG occupancy by corticosterone will increase slightly following an aggressive encounter. However, this small change is unlikely to increase free testosterone levels, because of the large number of seemingly unoccupied CBG binding sites in these subjects.     

Hormones, performance and fitness: Natural history and endocrine experiments on a lizard (Sceloporus undulatus)

We used the "morphology-performance-fitness" paradigm (Arnold, 1983) as our framework to investigate endocrine control of performance and fitness in Sceloporus undulatus (Eastern Fence Lizard). Focusing on males, we used the "natural experiments" of seasonal, sexual, and developmental variation in growth and in exercise endurance to identify testosterone and corticosterone as potential modulators of performance and related traits of interest. We followed with experimental manipulations of testosterone to investigate functional relationships, both in the laboratory and in the field. Further, we used focal observations and demographic studies, coupled with genetic determination of paternity, to test associations between performance and fitness, measured as reproductive success. We found that in males, endurance and plasma concentrations of testosterone and corticosterone are at their peaks in the spring breeding season, when lizards are most actively engaged in patrolling home ranges and in reproductive behavior. At that time, plasma concentrations of testosterone are correlated with body size; plasma concentrations of corticosterone and parameters of home range, including area and the number of overlapped females, are correlated with home-range overlap between males and females. During prereproductive development, males (but not females) experience a maturational increase in plasma testosterone. At about the same time, they become more active, expand their home ranges, and grow less quickly than do females, suggesting a trade-off in the allocation of energy, mediated by testosterone. Experimentally, testosterone has positive effects on fitness by stimulating endurance and reproductive activity and increasing home-range area, but it exacts costs in fitness by increasing ectoparasitism, decreasing growth, and decreasing survivorship. We found evidence of selection on body size, endurance, and home-range size (and thus access to potential mates). Despite having positive effects on performance traits, plasma concentrations of testosterone were not correlated with number of offspring sired by males. However, we found a strong correlation between the level of plasma corticosterone and the number of offspring sired. We also found evidence of size-assortative mating, indicating that for males, both the number and the size (and thus, fecundity) of their mates increase with body size. Our studies exemplify the power of natural history combined with experimental endocrine manipulations to identify hormonal regulators of performance and linkages to fitness. Furthermore, our results illustrate ecological and evolutionary significance of individual variation in endocrine traits.     

Impact of season and social challenge on testosterone and corticosterone levels in a year-round territorial bird

Plasma testosterone increases during breeding in many male vertebrates and has long been implicated in the promotion of aggressive behaviors relating to territory and mate defense. Males of some species also defend territories outside of the breeding period. For example, the European nuthatch (Sitta europaea) defends an all-purpose territory throughout the year. To contribute to the growing literature regarding the hormonal correlates of non-breeding territoriality, we investigated the seasonal testosterone and corticosterone profile of male (and female) nuthatches and determined how observed hormone patterns relate to expression of territorial aggression. Given that non-breeding territoriality in the nuthatch relates to the reproductive context (i.e., defense of a future breeding site), we predicted that males would exhibit surges in plasma testosterone throughout the year. However, we found that males showed elevated testosterone levels only during breeding. Thus, testosterone of gonadal origin does not appear to be involved in the expression of non-breeding territoriality. Interestingly, territorial behaviors of male nuthatches were stronger in spring than in autumn, suggesting that in year-round territorial species, breeding-related testosterone elevations may upregulate male-male aggression above non-breeding levels. In females, plasma testosterone was largely undetectable. We also examined effects of simulated territorial intrusions (STIs) on testosterone and corticosterone levels of breeding males. We found that STIs did not elicit a testosterone response, but caused a dramatic increase in plasma corticosterone. These data support the hypothesis that corticosterone rather than testosterone may play a role in the support of behavior and/or physiology during acute territorial encounters in single-brooded species.     

Food, stress, and reproduction: Short-term fasting alters endocrine physiology and reproductive behavior in the zebra finch

Stress is thought to be a potent suppressor of reproduction. However, the vast majority of studies focus on the relationship between chronic stress and reproductive suppression, despite the fact that chronic stress is rare in the wild. We investigated the role of fasting in altering acute stress physiology, reproductive physiology, and reproductive behavior of male zebra finches (Taeniopygia guttata) with several goals in mind. First, we wanted to determine if acute fasting could stimulate an increase in plasma corticosterone and a decrease in corticosteroid binding globulin (CBG) and testosterone. We then investigated whether fasting could alter expression of undirected song and courtship behavior. After subjecting males to fasting periods ranging from 1 to 10 h, we collected plasma to measure corticosterone, CBG, and testosterone. We found that plasma corticosterone was elevated, and testosterone was decreased after 4, 6, and 10 h of fasting periods compared with samples collected from the same males during nonfasted (control) periods. CBG was lower than control levels only after 10 h of fasting. We also found that, coincident with these endocrine changes, males sang less and courted females less vigorously following short-term fasting relative to control conditions. Our data demonstrate that acute fasting resulted in rapid changes in endocrine physiology consistent with hypothalamo-pituitary-adrenal axis activation and hypothalamo-pituitary-gonadal axis deactivation. Fasting also inhibited reproductive behavior. We suggest that zebra finches exhibit physiological and behavioral flexibility that makes them an excellent model system for studying interactions of acute stress and reproduction.     

Interrelationship between adrenal cortex and genital apparatus of the male rat]

Interactions between gonadal hormones and adrenocortical function have been studied in the male rat. After injection (im) of testosterone, the accessory reproductive organs are more stimulated in the castrated rats than in the castrated adrenalectomized rats. Gonadectomy increases lipids, cholesterol and corticosterone in adrenal glands and plasma corticosterone levels. Testosterone reverses these effects.     

Environmental and seasonal adaptations of the adrenocortical and gonadal responses to capture stress in two populations of the male garter snake, Thamnophis sirtalis

Stress and reproduction are generally thought to work in opposition to one another. This is often manifested as reciprocal relationships between glucocorticoid stress hormones and sex steroid hormones. However, seasonal differences in how animals respond to stressors have been described in extreme environments. We tested the hypothesis that garter snakes, Thamnophis sirtalis, with limited reproductive opportunities will suppress their hormonal stress response during the breeding season relative to conspecifics with an extended breeding season. The red-sided garter snake, T.s. parietalis, of Manitoba, Canada, has a brief breeding season during which males displayed no change in either plasma levels of testosterone or corticosterone, which were both elevated above basal levels, in response to capture stress. During the summer, capture stress resulted in increased plasma corticosterone and decreased testosterone. During the fall, when mating can also occur, males exhibited a significant decrease in testosterone but no increase in corticosterone in response to capture stress. The red-spotted garter snake, T.s. concinnus, of western Oregon, has an extended breeding season during which males displayed a stress response of increased plasma corticosterone and decreased testosterone levels. The corticosterone response to capture stress was similar during the spring, summer, and fall. In contrast, the testosterone response was suppressed during the summer and fall when gametogenesis was occurring. These data suggest that male garter snakes, in both populations, seasonally adapt their stress response but for different reasons and by potentially different mechanisms. J. Exp. Zool. 289:99-108, 2001.     

Circadian and circannual rhythms of LH, FSH, testosterone (T), prolactin, cortisol, T3 and T4 in plasma of mature, male white-tailed deer

Circadian and circannual rhythm of plasma LH, FSH, testosterone (T), prolactin, cortisol, triiodothyronine (T3) and thyroxine (T4) were investigated in two mature male white-tailed deer. No circadian rhythms were detected. Seasonal levels of LH and FSH were reached in September and October; troughs occur in May and June. Maximal T values were detected in November and December (the time of the rut); minimal levels occur between February and July. Prolactin peaked in May and June; minimal levels were detected between October and February. T3 exhibited two maxima; the first in the May-June period, the second in the September-October period. T4 showed no recognizable circannual rhythm. Cortisol levels were found to be much higher during cold months (December-April) than during the rest of the year. The least variable circadian levels were that of FSH and prolactin, with LH, T4, T3, cortisol and testosterone following in descending order. Cannulation stress might have some effect on the levels of testosterone, LH and cortisol. Correlation between LH and testosterone levels were detected mainly during sexually active periods.     

The reproductive cycle of the Nile crocodile (Crocodylus nilotkus)

The reproductive cycle of the Nile crocodile ( Crocodylus niloticus ) was studied in Zimbabwe. Females attained sexual maturity after they had reached a total length of about 262 to 287 cm and males, 270 to 295 cm. Some adult females did not reproduce every year. Follicle growth and vitellogenesis occurred from April to mid August during the dry winter. During this time reproductive females had elevated levels of plasma oestradiol-17β, testosterone, calcium and magnesium, but lowered levels of iron. The measuring of plasma calcium was an 'early pregnancy' test, reliable up to four months before nesting. Elevated levels of plasma testosterone in reproductive females corresponded to the time of courtship and mating. Ovulation occurred during the latter half of August. Males had viable sperm from mid May to mid September, during the winter. Courtship and mating occurred from late June to mid August, when crocodiles were confined to pools. Females nested on the higher sand ridges in the dry river bed from early September to early October, and eggs hatched during December.     

Requirement of thyroid function for the expression of seasonal reproductive and related changes in red deer (Cervus elaphus) stags.

The effect of thyroid function on regulation of seasonal reproduction was investigated in three red deer stags thyroidectomized (THX) in summer (January 1988) in comparison with five thyroid-intact controls. Responses of luteinizing hormone (LH) and testosterone to a bolus injection of 10 micrograms gonadotrophin-releasing hormone (GnRH) were tested in July, October, December, February and April. Blood samples were collected at weekly intervals from December 1987 to June 1989 for measurement of testosterone, triiodothyronine (T3) and prolactin concentrations. Testis diameters were measured every 2 weeks. In October 1988 (spring), plasma LH concentrations of control stags were less responsive (P less than 0.01) to stimulation by GnRH than those of THX stags; plasma testosterone concentrations and testis diameters were low and there was no increase in plasma testosterone concentrations after injection of GnRH in control stags during October or December (spring, early-summer). In contrast, THX stags maintained a testosterone response (P less than 0.01) in these 2 months and did not exhibit any signs of a seasonal lack of reproductive activity at this time of year. Control stags cast antlers in spring whereas THX stags maintained hard antlers throughout the study. Concentrations of plasma T3 were not detected in THX stags from June 1988 onwards, but exhibited a seasonal pattern in control stags, with low concentrations during autumn and winter (April to July) and high concentrations in spring and summer (August to February). There was no effect of thyroidectomy on the seasonal pattern of prolactin secretion.(ABSTRACT TRUNCATED AT 250 WORDS)     

Reproductive phase dependent circadian variations of plasma melatonin, testosterone, thyroxine and corticosterone in Indian palm squirrel, Funambulus pennanti

To explain the complex mechanism of environmental influence along with internal hormonal (factors) milieu on daily variations in the circulating levels of melatonin, testosterone, thyroxine and corticosterone were analyzed with the help of inferential statistics (Cosinor rhythmometry) in a seasonally breeding tropical rodent, F. pennanti during the reproductively active (RAP) and inactive phases (RIP). Plasma melatonin, thyroxine and corticosterone levels exhibited a significant circadian oscillation during both the active and inactive phases of the annual reproductive cycle. Melatonin showed higher amplitude during RIP in the circulating plasma. Testosterone presented a peak level during evening hours (16:00 - 18:00 h) during RAP only. The phase of thyroxine was noted ∼09:76 h and ∼10.35 h during active and inactive phases, respectively. Corticosterone showed a peak level at ∼12.00 h during both phases of the reproductive cycle. Further, in this tropical rodent, the minimum difference in photoperiod (∼3 - 4 hours) and maximum variation in temperature (max. 18°C - min. 10°C during RIP and max. 45°C - min. 32°C during RAP) and humidity (85% during RIP and 35% during RAP) regulated the diurnal rhythm of circulating melatonin circadian rhythm by ∼1 hour phase advance during RIP. In conclusion, the studied hormonal rhythms may be part of an integrative system to coordinate reproduction and physiological processes successfully with environmental factors.     

Evidence of a sex related difference of transcortin level in adult ducks

Corticosteroid binding globulin (CBG) serum level as evaluated by either equilibrium dialysis or gel filtration was found to be higher in male than in female adult ducks during the reproductive period. Castration did not modify CBG concentrations in females,whereas in males it induced a significant decrease in CBG, to the level observed in intact or castrated females. Testosterone injections administrated to castrated females increased CBG to the level of adult intact males. Finally it was found that testosterone stimulated CBG production in ducks without altering thyroxine levels.     

Seasonal evolution of blood levels of thyroxine and triiodothyronine in the post-pubertal bull in France and Iraq. Concomitant variations of LH and testosterone

An inquiry was conducted in 2 performance testing stations, A and B located in France and Iraq, respectively. In both stations, at solstice and equinox, thirty 15 month-old Holstein bulls were blood sampled for plasma LH, testosterone, thyroxine and triiodothyronine determination. For LH, no coherent seasonal effect was found. As regards testosterone, maximal mean values were obtained in December in both stations (3.4 ng/ml). In A as well as in B, thyroxine peaked in December reaching 64.6 ng/ml and 77.8 ng/ml, respectively, and falling down to 49.4 ng/ml and 65.6 ng/ml, respectively in June. The difference was significant for A (P less than 0.001). For T3, the fall from December (1.42 ng/ml in A and 1.68 ng/ml in B) to June (1.09 ng/ml in A and 1.26 ng/ml in B) resulted in about the same relative value and was significant (P less than 0.005) in both stations. The detrimental effect of high temperatures on semen quality does not seem to be mediated by an alternation of thyroid function.