Higher Plasma Levels Of Testosterone Research Articles

The number of life-history stages does not influence the androgen responsiveness to male–male interactions: Sedentary and migratory black redstarts (Phoenicurus ochruros) do not elevate testosterone in response to simulated territorial intrusions

High plasma levels of testosterone at the beginning of the breeding season adjust male physiology for mating and promote territorial behavior in birds. Conversely intra-sexual competition may elicit a temporary increase in circulating testosterone. Male black redstarts (Phoenicurus ochruros) from migratory populations show the expected increase in baseline testosterone during early breeding, but circulating testosterone levels do not change in response to male–male interactions. Because sedentary populations express fewer life-history stages they may be more flexible in timing of life-history stages and more responsive to environmental modulation of hormone concentrations. Therefore, we tested whether the androgen responsiveness to male–male interactions differs between migratory (6 life-history stages) and sedentary black redstarts (3 life-history stages) during early breeding, predicting that in contrast to migratory birds, sedentary birds would modulate testosterone in response to simulated territorial intrusions (STI). In contrast to our prediction, sedentary males did not modulate post-capture testosterone levels in response to simulated territorial intrusions. Males of both populations increased testosterone after an injection of gonadotropin releasing hormone (GnRH), demonstrating that they were capable of increasing testosterone. Interestingly, in sedentary males the GnRH injection elicited a higher testosterone response in STI males than in control males. The two populations did not differ in their behavioral response to the STIs, except that sedentary males spent less time close to the decoy. In combination with previous data from black redstarts and other socially monogamous and biparental birds our current study adds to the growing evidence that current theory regarding hormone-behavior relationship needs to be refined.

Inter-sexual differences in T-cell-mediated immunity of black-headed gull chicks ( Larus ridibundus ) depend on the hatching order

Hatching asynchrony in avian species leads to age and size differences between nestlings within a brood, handicapping last-hatched chicks in the sibling rivalry. Starvation due to this competitive disadvantage has been regarded as the primary cause of an increase in mortality with hatching order. However, for gulls it has also been suggested that disease is the cause of mortality for last-hatched chicks, possibly through reduced immunocompetence and thereby an enhanced susceptibility to infection. In addition, the male-biased mortality reported for several gull species may be related to a higher vulnerability to diseases in males compared to females. To determine the potential influence of the immune system on these mortality patterns, we investigated the T-cell-mediated immunity (CMI) of black-headed gull chicks in relation to hatching order and sex. We found a significant decrease in the CMI with hatching order. This result may be causally related to systematic changes in maternal yolk steroids and carotenoids within the laying sequence. For second-laid eggs, male CMI was significantly lower than female CMI. This is possibly linked to higher plasma levels of testosterone in male embryos which might have an immunosuppressive effect. If so, this effect is masked in eggs of either high (first egg) or low (last egg) quality. Chicks with low CMI showed enhanced mortality rates. Thus the differences in immune response are likely to contribute to the observed mortality patterns. However, hatching order significantly affected mortality independently of CMI, suggesting that competitive disadvantage due to hatching asynchrony is also important.

Effects of Time of Sampling on Oocyst Detection and Effects of Age and Experimentally Elevated Testosterone on Prevalence of Coccidia in Male Dark-eyed Juncos

The hormone testosterone (T) has been linked to enhanced expression of secondary sexual traits and acquisition of mates (Ligon et al. 1990, Alatalo et al. 1996, Raouf et al. 1997). However, high plasma levels of testosterone also have been suggested to suppress immune function (Folstad and Karter 1992, Zuk et al. 1995, Hillgarth and Wingfield 1997; but see Ros et al. 1997, Hasselquist et al. 1999). Thus, an obvious question is whether testosterone enhances reproductive success while simultaneously affecting susceptibility to disease. In the Dark-eyed Junco (Junco hyemalis), experimental maintenance of plasma testosterone levels at their natural early season peak for the entire breeding season causes males to sing more frequently, and testosterone-treated males (T-males) in captivity are more attractive to females than are control males (Cmales; Enstrom et al. 1997, Hill et al. 1999). However, T-males also have elevated plasma levels of the steroid hormone corticosterone (Ketterson et al. 1991, Klukowski et al. 1997) and show a greater response to handling stress than do C-males (Schoech et al. 1999), which can translate into suppressed immune function (Sapolsky 1992, Besedovsky and del Rey 1996, J. Casto pers. comm.). To investigate possible effects of elevated levels of plasma testosterone on the junco’s susceptibility to disease, we asked whether free-living males treated with testosterone would be more likely than controls to be infected by coccidia (Isospora spp.), a protozoan gut parasite belonging to the Eimeria complex. We also asked whether yearling juncos were more likely than older adults to be infected and whether our ability to detect infection was affected by the time of day when fecal samples were collected. Methods.—This research was conducted at the University of Virginia’s Mountain Lake Biological Station (378229N, 808329W; see Chandler et al. [1994] for description of study area). We captured male juncos in mist nets and Potter traps during the early spring of 1995 and 1996 and classified them as second year (younger) and after second year (older) based on

Territorial behaviour and hormones of pied flycatchers in optimal and suboptimal habitats

Since pied flycatchers,Ficedula hypoleuca, breed at higher densities in deciduous forests than in coniferous forests, competition for territories is likely to be greater in the former, optimal habitat. I tested the hypotheses that males in a deciduous forest defend their newly established territories more intensely and have higher plasma levels of testosterone than males in a suboptimal coniferous forest. In the deciduous forest, breeding density was higher, egg laying started earlier and more fledglings were produced. Morphological characters such as wing length, plumage colour and the size of the white forehead patch did not differ consistently between males establishing territories in deciduous and coniferous forests. Before the nest-building period, males in the deciduous forest were heavier, and had significantly larger furcula fat depots. I tested territorial aggressiveness by exposing unmated territorial males to simulated territorial intrusions. A significantly higher proportion of territorial males in the deciduous forest physically attacked the intruder; those that did attack also attacked more frequently than did males in the coniferous forest. Furthermore, males in the deciduous forest stayed closer to the decoy, and were more restless during the simulated territorial intrusion. Males in the deciduous forest had higher plasma levels of testosterone and corticosterone than did males in the coniferous forest, but there was no difference in dihydrotestosterone levels. These hormonal differences are most likely to be the result of a higher intrusion rate and a higher population density in the deciduous forest. I conclude that prior ownership is a crucial factor in maintaining a territory, and that differences in aggressive motivation between unmated males in the deciduous and coniferous forests reflect the value of the nestboxes defended. The high testosterone levels observed in males from the deciduous forest are likely to be the physiological factor increasing their aggressive motivation and persistency.

Changes in lymphoid tissue after treatment with a gonadotropin releasing hormone antagonist in the neonatal marmoset (Callithrix jacchus).

The effect of neonatal treatment with a gonadotropin releasing hormone (GnRH) antagonist on the morphology and distribution of lymphocytes in lymphoid tissue of the infant marmoset was examined. From a screened panel of antihuman antibodies for specific immune cells, antibodies for the CD20 and CD3 antigens showed excellent reactivity with marmoset tissue. Five sets of marmoset twins were treated with either the GnRH antagonist or a vehicle from birth, and were euthanized at 7 to 9 (3 sets) or 16 to 20 weeks (2 sets) of age. The spleen, thymus, and inguinal lymph nodes from each animal were processed for immunocytochemistry, and the number of cells expressing the CD20 and CD3 antigens were quantified. Control twins exhibited high plasma levels of testosterone, characteristic of the neonatal period, whereas testosterone concentrations were reduced (P = 0.001) to detection limits in the GnRH antagonist-treated twins. Microscopic evaluation suggested that treatment reduced the volume and cellularity of the thymic cortex, resulting in a decrease in the cortical-to-medullary ratio. Treatment reduced (P = 0.046) the number of thymocytes expressing the B-cell antigen (CD20) and marginally lowered (P = 0.067) the number expressing the T-cell antigen (CD3) in the thymic medulla. In the spleens of treated animals, periarterial lymphatic sheaths were less prominent on microscopic examination, and there were marginally fewer (P = 0.064) CD3+ cells. Numbers of CD20+ lymphocytes in the peripheral white pulp of the spleen and in the germinal centers of the lymph nodes, or CD3+ cells in the paracortex and germinal centers of the lymph nodes, were not altered by treatment. Neonatal treatment with a GnRH antagonist may alter maturational processes for B and T cells in the thymus and spleen of the marmoset and may deprive the immune system of its normal sensitivity to GnRH at a potentially critical time in development.

The Development of the Hypothalamic–Pituitary–Gonadal Axis in Juvenile Great Tits

The development of the hypolamic–pituitary–gonadal axis in free-living nestling great tits (Parus major) was studied from the day of hatching until about 40 days of age. The hypothalamic content of GnRH was low during the entire nestling period, although a significant increase was noted between 6 and 9 days of age. Thereafter there was no further increase. The pituitary content of LH was low in 1- to 6-day-old nestlings, but increased significantly at 9 days of age; this increase was only temporary, and levels decreased in 12-day-old nestlings. Injections of chicken GnRH increased plasma levels of LH in newly hatched great tits. The high plasma levels of LH in newly hatched great tits of both sexes decreased to basal by 9 days of age. Circulating levels of testosterone and estradiol showed more or less the same pattern as LH. Both steroids showed very high levels in newly hatched birds of both sexes. Testosterone levels were down to basal in 3-day-old nestlings, and estradiol levels were basal in 2-day-old nestlings. The only sex difference was observed in 1- and 2-day-old nestlings. During this period males had significantly higher plasma levels of testosterone than females. Gonads showed a more or less linear growth during the entire nestling period, and did not increase further after fledging. Histological and ultrastructural examinations of the testis showed that mature Leydig cells appeared for the first time in 6-day-old birds and become common in 9-day-old nestlings. The development of the seminiferous tubules, the interstitial tissue, and the tunica albuginea reached a “plateau” when the nestlings had reached an age of 9 days. At no age had the germinal epithelium developed beyond the stage of spermatogonia. GnRH treatment did not change male testosterone or female estradiol levels until the nestlings were 9 days of age. The response decreased in older nestlings. Castration of 9-day-old male nestlings showed that neither was there a negative feedback of testosterone on LH in older nestlings.

Effect of Dominance Status on Sex Hormone Levels in Laboratory and Wild-Spawning Male Trout

We investigated the relationship between male social status and hormone levels in salmonids spawning under laboratory and field conditions. In small groups of rainbow trout (Onchorhynchus mykiss) spawning in the laboratory, dominant males had higher plasma levels of testosterone (T) and 17α,20β-dihydroxy-4-pregnen-3-one (17,20β-P) compared with subordinates. Steroid levels increased in subordinate males that became dominant after dominant males were experimentally removed; higher steroid levels in dominant males appears to be a result rather than a cause of their social status. In free-ranging brown trout (Salmo trutta) sampled in the field, we found higher levels of 11-ketotestosterone (11KT) but not T in dominant males. No significant differences in levels of either androgen were found between dominant and subordinate male brook trout (Salvelinus fontinalis) sampled at the same field location. Furthermore, in marked contrast with the laboratory fish, there were no significant differences in plasma 17,20β-P between dominant and subordinate males in either species of fish in the wild. The different findings in the laboratory and field may indicate species differences in behavioral endocrinology among brook, brown, and rainbow trout. Alternatively, the greater differential in hormonal profile of dominant and subordinate males in the laboratory may reflect the relative uniformity of the laboratory environment; this simple environment may allow competitively superior males to more completely dominate less competitive tank-mates and to exclude them from female sexual cues. In any case, these results suggest that the relationship between steroid hormones and spawning behavior in male salmonids is likely more complex than suggested by experiments conducted solely on laboratory-held rainbow trout.

Effects of testosterone on a selected neuronal population within the preoptic sexually dimorphic nucleus of the Japanese quail

The effects of testosterone on the volume and cytoarchitecture of the sexually dimorphic nucleus of the preoptic area (POM) were investigated in male and female Japanese quail. It was confirmed that castration decreases the POM volume in males and that, in gonadectomized birds of both sexes, testosterone increases this volume to values similar to those observed in intact sexually mature males. This suggests that the sex difference in POM volume results from a differential activation by T so that this brain morphological characteristic is not truly differentiated in the organizational sense. This conclusion was extended here by demonstrating that males exposed to a photoperiod simulating long days and that are known to have high plasma levels of testosterone have a larger POM than short-day males that have inactive testes. Detailed morphometric studies of POM neurons revealed a structural heterogeneity within the nucleus. A population of large neurons (cross-sectional area larger than 70-80 microns2) was well represented in the dorsolateral but was almost absent in the medial part of POM. This lateral population of neurons was sensitive to variations of testosterone levels in males but not in females. The cross-sectional area, diameter, and perimeter of the dorsolateral neurons were significantly increased in males exposed to high testosterone levels (intact birds exposed to long days or castrated birds treated with the steroid). These changes were not observed in the medial part of the nucleus. Interestingly, the size of the dorsolateral neurons was not affected by testosterone treatments in females. These results suggest that the swelling of neurons in the lateral POM of males might be responsible for the increase in total volume of the nucleus, which is observed in physiological situations associated with a high testosteronemia. In addition, the sensitivity to testosterone of the dorsolateral neurons in the POM appears to be sexually differentiated. This differential response to testosterone might represent a truly dimorphic feature in the organizational sense and additional studies manipulating the early steroid environment should be performed to test this possibility.

VIRILIZING ADRENAL ADENOMA IN AN ADULT WITH THE BECKWITH‐WIEDEMANN SYNDROME: PARADOXICAL RESPONSE TO DEXAMETHASONE

An adult woman with Beckwith-Wiedemann syndrome, hemihypertrophy and an androgen-secreting adrenal adenoma is described. She presented with a 7-year history of progressive virilization and was found to have high plasma levels of testosterone and dehydroepiandrosterone (DHEA) sulphate and elevated levels of urinary metabolites of testosterone and its precursors. Administration of dexamethasone was associated with progressive rises in plasma 17 alpha OH progesterone, 11 beta-desoxycortisol, DHEA sulphate, androstenedione and testosterone, together with increased urinary excretion of androsterone, 11 beta OH androsterone, etiocholanolone, DHEA, and 16 alpha OH DHEA. Hormone levels fell to normal following removal of the tumour.

Hormonal correlates of migration and territorial behavior in juvenile willow tits during autumn

This study compared plasma levels of dihydrotestosterone, testosterone, corticosterone, luteinizing hormone, growth hormone, and prolactin in migrating juvenile willow tits with those in territorial juveniles. Both categories of birds were caught in late September. Migrating juveniles had higher plasma levels of corticosterone than territorial juveniles. Only corticosterone secretion was affected by “handling stress” in both migrating and territorial juveniles. However, territorial birds showed a much stronger relationship between these two variables. It is suggested that high corticosterone levels are involved in the emigration of juveniles out of the coniferous forest. Only juveniles were found among the migrating willow tits, and these birds were not well adapted for migration. Migrating juvenile males had less fat stored than did territorial ones. Furthermore, migrating juvenile males had higher liver/somatic index and higher plasma levels of growth hormone than did territorial males. These results indicate that migrating males had been, or were, exposed to food restrictions. The same proportion of migrating and territorial juveniles, males as well as females, had high plasma levels of testosterone. We suggest that these high levels were caused by recent aggressive interactions. To test the hypothesis that high plasma levels of testosterone are important for a juvenile to become a member of a territorial winter group, we performed a field experiment in which juveniles were given testosterone implants (controls were given empty silastic tubes) at the beginning of the territorial establishment period. The same proportion of testosterone-implanted birds and control birds succeeded in becoming members of territorial winter groups. Thus, testosterone does not seem to play an essential role in autumn territoriality, and it does not prevent autumn migration.

Seasonal Changes in Plasma Levels of LH and Gonadal Steroids in Free-Living Willow Tits Parus montanus

Seasonal variations in plasma levels of luteinizing hormone (LH), dihydrotestosterone (DHT), testosterone and estradiol (only in females) were studied in free-living adult and juvenile Willow Tits from southwest Sweden. All hormones, except DHT, showed pronounced annual cycles. For both sexes, and both age groups, LH titers showed a typical bimodal pattern with transitional peaks during the breeding period and early autumn. Also, LH levels increased significantly in January and remained elevated throughout the winter. Male plasma levels of testosterone also showed a bimodal pattern with peaks occurring concomitant with LH. The August September peak was, however, caused by some juveniles having very high plasma levels of testosterone, whereas the majority of juveniles and all adults showed low testosterone levels at this time. Female testosterone values did not vary significantly during the year, but in junvenile females testosterone levels showed a transitional peak in August. Estradiol showed only one significant annual peak during the breeding period. The winter increase in plasma levels of LH was not accompanied by changes in testosterone, or estradiol, titers. In spring, male LH and testosterone levels started increasing a month earlier than LH and estradiol in females.

Plasma levels of luteinizing hormone and steroid hormones in free-living winter groups of willow tits ( Parus montanus)

Plasma levels of LH, DHT, testosterone, and corticosterone were measured for all members in free-living winter flocks of willow tits, Parus montanus. Hormonal data were related to (1) flock size and (2) age/sex differences. The winter flock defends a large winter territory and shows a well-established social hierarchy in which adults consistently dominate first-year birds. One winter group normally consists of four individuals, two adults and two juveniles. In flocks containing four or five members juvenile willow tits had significantly higher corticosterone values than adults. In small-sized groups, containing three members, all individuals had high plasma levels of corticosterone. No other effects of flock size was found. When data were treated on an age/sex basis, i.e., flock size was not considered, juvenile females were found to have significantly higher plasma levels of testosterone than adult birds, and also significantly higher levels of DHT than juvenile males and adult females. Also, juvenile willow tits had significantly higher plasma levels of corticosterone than adult birds.

Effect of the presence of females on the pituitary-testicular activity in male Japanese quail ( Coturnix coturnix japonica)

Five experiments were carried out to study the role of the presence of a female on the reproductive endocrinology of male Japanese quail. In the first three experiments, exposure of an adult male raised in long days to a female for 10 min or 1 week failed to increase plasma testosterone and LH levels; in fact a significant transitory decrease in plasma testosterone was observed, associated with a preceding increase in plasma corticosterone. These changes are interpreted as a result of the stress caused by repeated bleeding or by the continuous presence of a female in a limited space. In the last two experiments, an increase in the maturation rate of immature males could be observed in birds maintained in the continuous presence of females by comparison with birds kept in isolation. The paired males had larger cloacal glands and testes and higher plasma levels of testosterone and LH than the isolated ones. This effect of the female was observed in long days (16L:8D) as well as in marginally stimulating short days (12L:12D).

9 Androgen receptors

Testosterone and its active metabolite dihydrotestosterone exert their influence on target cells through a specific intracellular protein receptor. Structural abnormalities of this receptor lead to a diminished androgen action within the cell and result in the syndrome of androgen insensitivity. Androgen insensitivity is classified on the basis of whether the insensitivity is complete or partial and whether the androgen receptor is normally present (AR(+)), absent (AR(-)) or diminished (AR(+/-)). All patients with androgen insensitivity have normal or high plasma levels of testosterone and elevated serum LH. Patients with complete androgen insensitivity are phenotypically female. The clinical presentation of partial androgen insensitivity is variable, ranging from a minimal amount of virilization to a completely masculine appearance. All patients described with a syndrome of androgen insensitivity are infertile. The influence of androgen receptor function in the pathogenesis of benign prostatic hypertrophy is being investigated. Androgen receptor content is also being studied as a possible marker of responsiveness to hormonal therapy in prostatic carcinoma.

Effect of female sexual displays on the endocrine physiology and behaviour of male white‐crowned sparrows, Zonotrichia leucophrys

In photoperiodic birds, endocrine responses to behavioural interactions between males and females may be involved in temporally “fine‐tuning” the onset of reproduction to yearly variations in the environment. This study examined the endocrine and behavioural responses of male White‐crowned sparrows (Zonotrichia leucophrys) to changes in the endocrine state of the female, as signalled by changes in her behaviour. Males on different photoperiodic regimes were paired with oestrogen‐treated, sexually receptive females. Males exposed to gonadostimulatory long days mounted and copulated with oestrogen‐treated females even before gonadal development was complete. These males had higher plasma levels of testosterone and luteinizing hormone and maintained enlarged testes longer than control males paired with untreated, nonreceptive females. Males maintained on nonstimulatory short days also mounted oestrogen‐treated females; however, testes of these males remained nonfunctional and their plasma levels of testosterone and luteinizing hormone were basal. Thus, reproductive function of photostimulated males is profoundly affected by changes in the endocrine state and behaviour of the female. However, male sexual behaviours are expressed in response to visual and auditory stimuli from the female regardless of male hormonal condition or photoperiodic treatment.

Hormonal response of free-living male white-crowned sparrows to experimental manipulation of female sexual behavior

In free-living male white-crowned sparrows ( Zonotrichia leucophrys), plasma levels of testosterone, 5α-dihydrotestosterone (DHT), and luteinizing hormone (LH) decrease precipitously at onset of incubation. The hypothesis that this decrease is a response to the simultaneous cessation of estradiol-dependent solicitation displays by females was tested in an experiment on free-living pairs. Solicitation displays were prolonged by implanting females with subcutaneous estradiol capsules and releasing them. Subsequent capture and blood sampling of the mates of these females showed that they had significantly higher plasma levels of testosterone and DHT than did control males, but results for LH were equivocal. Nevertheless, these results support the above hypothesis and suggest that hormone-behavior interactions are important even in free-living animals exposed to the entire spectrum of environmental information.

Is 3α-Androstanediol a Marker of Peripheral Hirsutism?

The behaviour of 5 alpha-reduced metabolites of testosterone, dihydrotestosterone1, 3 alpha-androstanediol and 3 beta-androstanediol, was studied in 36 hirsute women: Group I: 24 patients with high plasma levels of testosterone, androstenedione and/or dehydroepiandrosterone sulphate and Group II: 12 patients with normal plasma concentrations of these steroids. Testosterone and its 5 alpha-reduced metabolites were determined by radioimmunoassay after chromatographic separation on celite 535 microcolumns. Plasma 3 alpha-androstanediol was found to be elevated both in Group I (26.9 +/- 10.8 SD ng/100 ml) and in Group II patients (23.2 +/- 10.5 SD ng/100 ml). 3 beta-Androstanediol and dihydrotestosterone, on the contrary, were elevated in only a few cases: in 6 cases in Group I and in 2 and in 1 case, respectively, in Group II. The finding of high plasma 3 alpha-androstanediol levels in hirsute women, with normal values of the other androgens, may be an index of hirsutism of peripheral origin, since this steroid is produced almost exclusively in the extraglandular compartment.

Is 3 alpha-androstanediol a marker of peripheral hirsutism?

The behaviour of 5 alpha-reduced metabolites of testosterone, dihydrotestosterone1, 3 alpha-androstanediol and 3 beta-androstanediol, was studied in 36 hirsute women: Group I: 24 patients with high plasma levels of testosterone, androstenedione and/or dehydroepiandrosterone sulphate and Group II: 12 patients with normal plasma concentrations of these steroids. Testosterone and its 5 alpha-reduced metabolites were determined by radioimmunoassay after chromatographic separation on celite 535 microcolumns. Plasma 3 alpha-androstanediol was found to be elevated both in Group I (26.9 +/- 10.8 SD ng/100 ml) and in Group II patients (23.2 +/- 10.5 SD ng/100 ml). 3 beta-Androstanediol and dihydrotestosterone, on the contrary, were elevated in only a few cases: in 6 cases in Group I and in 2 and in 1 case, respectively, in Group II. The finding of high plasma 3 alpha-androstanediol levels in hirsute women, with normal values of the other androgens, may be an index of hirsutism of peripheral origin, since this steroid is produced almost exclusively in the extraglandular compartment.

Photoperiodic control of thyroid function and wool and horn growth in rams and the effect of cranial sympathectomy.

Eight adult Soay rams (four control and four superior cervical ganglionectomized) were housed in an artificial lighting regimen of alternating 16-week periods of long days [16 h of light, 8 h of darkness (16 L:8D)] and short days (8L:16D) for nearly 3 yr, and the long term variations in growth of the wool and horns were recorded along with measurements of the plasma concentration of T4, T3, and testosterone. In the control rams all of the parameters varied in relation to the imposed lighting regimen. An increase in the growth of the wool and horns occurred during each period of long days at a time when the circulating concentrations of T4 and T3 were high; at this time the animals were reproductively quiescent, with low plasma levels of testosterone. During each period of short days the rate of wool and horn growth declined, as did the plasma concentrations of T4 and T3, while the rams became sexually active with high plasma levels of testosterone. Moulting of the old coat occurred during the periods of long days, coinciding with the phase of increasing wool growth. The variations in the ganglionectomized rams were quite different from those in the controls, bearing no clear relationship to the imposed lighting regimen. In these operated animals there were long term changes in all of the parameters, but these were generally less pronounced than those in the controls. The unusual pattern in the growth of horns and wool was correlated with long term changes in the plasma levels of T4, T3, and testosterone. Moulting of the old coat did not occur in the normal manner in the animals after the first year.