Role of gonadal and adrenal steroids and thyroid hormones in the regulation of molting in domestic goose.

Plasma levels of testosterone (T), 17-ß-estradiol (E2), progesterone (P4), dehydroepiandrosterone (DHEA), corticosterone (B), thyroxine (T4) and triiodothyronine (T3) were monitored during postnuptial and the prenuptial molt in domestic goose (Anser anser domesticus) in both sexes. 1. At the beginning of postnuptial molt (when the old, worn dawny-, and cover feathers' loss starts) in ganders, the levels of T, E2, P4 decrease while DHEA and B significantly increase. The elevated levels of T4 and low T3 concentrations characteristic of the last phase of the reproduction, remain unchanged. In layers, similar changes were observed, however, B decreases. 2. In the early phase of outgrowth of wing and cover feathers, plasma levels of T, E2 and P4 are low. Elevated B, DHEA and T4 concentrations decrease in ganders, while in layers DHEA increases and B and T4 levels remain unchanged. T3 increases in both sexes. 3. The subsequent intensive outgrowth period of wing- and cover feathers both in ganders and in layers is characterized by very low levels of T, E2, DHEA and T4, but P4 increased, and T3 concentration remain high. 4. At the end of postnuptial molt - when the outgrowth of dawny, cover-, and wing feathers stops - very low T, E2, P4, DHEA and T4 levels and and high T3 plasma levels were found in both sexes. Fast increase of plasma B was detected in ganders, while in geese, B concentration remain high. 5. During prenuptial molting (outgrowth of contour and tail feathers) low E2, P4 and T4, increasing T and DHEA, but very high T3 and B plasma concentration were measured in ganders. In layers, very low T, E2, P4, DHEA and T4 levels, and very high B and T3 levels were found. 6. At the beginning of the fall-winter sexual repose (postmolting stage) T, E2, P4, DHEA and T4 levels increase, T3 and B declines in both sexes. 7. In the subsequent phase of fall-winter period (preparatory stage) there is a further increase in T, P4 and T4, a fast increase of B and a decrease of E2, DHEA and T3 in ganders. In layers, T, P4 and DHEA decrease, B increases and the T4 and T3 do not change. 8. At the beginning of reproduction high T level, unchanged DHEA, slightly declined P4, and decreased E2, T4, T3 and a strong decline of B concentrations occur in ganders. In layers, T is further increased, E2 and P4 shows high levels, and, at the same time DHEA and T3 remain unchanged, while B and T4 decrease.

Seasonal changes in hypothalamic gonadotropin-releasing hormone-I immunoreactivity in relation with testicular volume in adult male free-living European starlings (Sturnus vulgaris).

Birds from the temperate and cold zones show annual sexual activity accompanied by gonadal changes and fluctuation in their brain gonadotropin-releasing hormone (GnRH) levels. However, most of the studies were done on captive birds where the constant environment can profoundly modify periodical changes. Therefore our aim was to reveal annual variations of hypothalamic and gonadal changes in male, free-living European starlings (Sturnus vulgaris) captured directly from their natural environment. We analyzed hypothalamic GnRH-I immunoreactivity and testes volume. Four key time points of the active reproductive cycle and the photorefractory phase were studied. GnRH-I immunoreactivity was analyzed in the preoptic area (POA) and the median eminence (ME). Photorefractory birds (August) with regressed gonads had the lowest level of GnRH-I immunoreactivity compared to other birds from the active reproductive phases. These results suggest that parallel with the gonadal volume GnRH-I undergoes seasonal changes in adult male free-living European starlings.

Display activity and seasonality of faecal sexual steroids in male great bustard (Otis tarda L.).

The non-invasive faecal sampling and RIA was used to measure faecal equivalents of testosterone (T), dehydroepiandrosterone (DHEA), oestradiol-17beta (E2) and progesterone (P4) in juvenile and adult great bustard males. Possible connections of diurnal and seasonal changes of sexual steroid levels and display activity were studied. Correlations were found between sexual steroid equivalent levels of faeces and display activity and agonistic behaviour in the different phases of annual cycle of adult males. In early display period increasing levels of androgens were measured, during main display period very high androgen dominance was observable against E2 and P4. During postnuptial moult strong T decrease and DHEA and P4 increase were detected. Elevation of E2 was measured during wintering. In juveniles level of DHEA was higher than level of T suggesting its importance in immature males. Decrease of T was detected between reproductive period and postnuptial moult and DHEA between reproduction and wintering, accompanying with E2 elevation. The inhibiting effect of inclement weather on gonad functions also was detected in our study. We suppose that the unexpected cold weather with strong wind depressed the levels of androgens both in juveniles and adults and the increase of faecal E2 was also detected.

Effect of testosterone loading on the kinetic of faecal testosterone excretion in mallards.

Intestinal passage time of coloured fodder and testosterone turnover were examined by faecal steroid analysis in mallards in the reproductive and postrefractory period. In the latter, the discharge of coloured fodder began 36 minutes after ingestion in males, and 56 minutes in females. During reproduction the discharge began 93 minutes and 112 minutes after ingestion in males and females, respectively. Total passage time was similar in the reproductive and postrefractory period in both sexes. After intraperitoneal testosterone injection, faecal samples were collected for 8 hours and testosterone levels were measured using RIA. In the postrefractory period, 1-2 hours after testosterone loading a strong increase of faecal testosterone content developed in males, meanwhile a slighter testosterone peak appeared in females. During reproduction testosterone excretion began 1.5-2 hours after injection in both sexes but in females its increase was smaller. The duration of response to testosterone loading was 5 hours in both periods and both sexes. Intensive excretion after T loading appeared earlier in males than in females, but total passage time finished at the same time: 5 hours after loading. The character of testosterone excretion was corresponding to the passage of fodder-chimus-faeces in the reproductive and postrefractory period in both sexes.

Seasonal changes in plasma dehydro-epiandrosterone (DHEA) levels of domestic geese.

Changes in plasma DHEA, testosterone (T) and 17-B-oestradiol (E2) levels were examined in domestic geese of both sexes in the fall and winter. The levels of steroid hormones were determined in blood plasma by means of radio-immunoassay (RIA). A so-called second (autumn) cycle was induced in geese via a dark-room preparation and natural keeping conditions. The plasma levels of DHEA showed a minor peak at onset of the autumn breeding and a major one prior to the more intense spring reproduction in both sexes. The seasonal curves of plasma DHEA appeared fairly similar in ganders and layers and without considerable differences between the absolute values. In ganders, plasma DHEA peaks preceded the elevations in T levels in the fall and spring alike. With layers, in turn, the autumn and spring peaks of plasma DHEA appeared after the peaks in E2 levels. With ganders, the concentration of plasma T seemed to predominate between the two androgens throughout the experimental period. With layers, in turn, the concentration of DHEA surpassed the level of plasma E2 at the time of the peak periods and other times during the study, as well. In domestic geese, DHEA is probably involved in the autumn physiological processes and the induction of reproduction during fall and early spring periods, alike.

A comparative methodical study of the faecal steroid analysis on birds: looking for a valid method of testosterone determination.

In a comparative study, a relatively simple and high sensitivity method was developed for analysis of testosterone-equivalent(s) in the faeces of different bird species. To determine the recovery of extractions and purifications, tritium-labelled testosterone was added to the wet samples. Then the samples were treated with sodium dodecil sulphate (SDS), an emulsificator to "open-up" the complex, lipid-coated particles of faecal samples. This emulsification resulted in the decrease of the quantity of interfering substances after diethyl-ether extraction and the linearity of the measured testosterone equivalents from aliquots in the range of 2 and 10 mg of faeces. In the RIA, we applied a group specific polyclonal testosterone antibody which cross-reacted with reduced metabolites and at a certain level with sulphate conjugates as well. The use of Helix enzymes did not modified significantly the results of the analysis relating to a low level of conjugated androgens in the faecal extracts. The biological validity of the method was tested on domestic cockerels, where between the plasma and faecal testosterone values a four hours phase shift was observed, with a correlation of 0.6355. This method is suitable for "non invasive", behavioural-ethological studies.

Photostimulation affects gonadotropin-releasing hormone immunoreactivity and activates a distinct neuron population in the hypothalamus of the mallard.

To reveal central mechanisms that transduce photic stimuli to sexually related neuroendocrine changes, Fra-2-ir, an inducible immediate-early gene marker of neuronal activation has been consecutively localized with that of GnRH-I in the brain of mallards that were triggered by artificial light at the photosensitive phase of the reproductive cycle. Strong neuronal activation was found in the POM and PVN in response to 1x or 4x 20 h light exposure that was accompanied with an increase of GnRH-ir in the hypothalamus and a dramatic depletion of GnRH-ir from terminals in the median eminence. The Fra-2 and GnRH-ir profiles, however, were not co-localized in any region at any phase of photostimulation. These results demonstrate profound changes of GnRH-ir in the hypothalamus and reveal a distinct, photoresponsive cell population in the anterior hypothalamic area of the mallard.

Seasonal relationships between plasma and fecal testosterone in response to GnRH in domestic ganders.

In two groups (eight individuals each) of socially acquainted, outdoor-kept, domestic ganders (male Hungarian white: Anser domesticus), basal and GnRH-stimulated plasma testosterone (T) concentrations were compared with fecal testosterone metabolites (TM) in and between three seasons, spring peak of reproductive activity, summer photorefractoriness, and fall sexual reactivation. Plasma was sampled 90 min following the challenge and T was analyzed by radioimmunoassay following the GnRH challenge. Fecal TM were measured by enzyme immunoassay using two group-specific antibodies against 17beta-OH-androgens or a novel antibody against 17-oxo groups, which was found to react with major testosterone metabolites without prior hydrolytic deconjugation. Baseline plasma T and systemic levels were high in spring and fall but low in summer. Plasma T increases in response to GnRH were followed by significantly elevated fecal TM levels 2 to 6 h following the challenge in spring and fall. In fall, at high plasma T levels, fecal TM levels were disproportionally lower than in spring. Variability of TM levels was two to five times higher in feces than in plasma, which explains why correlations between individual plasma T and fecal TM levels generally remained nonsignificant. This points to a low-level short-term relationship between the excreted TM and the plasma T levels. However, the reliability of the method was demonstrated by standard inter- and intraassay variabilities and by a high correspondence between results obtained by the two assays. It is suggested that, with appropriate sample size, fecal TM reflects plasma T increase. However, fecal TM was more variable than the plasma T, and fecal TM responses to GnRH did not always parallel the plasma T response. In addition, seasonal changes in androgen excretion regimes must be taken into account.

Characteristics of the proopiomelanocortin system in the outdoor-bred domestic gander. I. ACTH and beta-endorphin levels in the brain, pituitary, and plasma.

Immunoreactive (ir-) adrenocorticotropic hormone (ACTH) and beta-endorphin (beta E) levels were determined in seven brain regions, in the three pituitary lobes, and in the plasma of the domestic gander by specific radioimmunoassays. In the brain regions studied the relative concentrations of ir-ACTH and ir-beta E were the highest in the mediobasal hypothalamus and in the paraventricular nucleus. There were lower levels of these peptides in the supraoptic nucleus, in the septum, and in the dorsal thalamus. Very low ir-ACTH and -beta E contents were found in the archistriatum and in the lobus parolfactorius. In the pars distalis of the pituitary gland the cephalic lobe contained about 10 times more ir-ACTH (3596 pmol/lobe) and 4 times more ir-beta E (867 pmol/ lobe) than the caudal lobe (383 pmol/lobe and 189 pmol/lobe, respectively). Sephadex G-50 chromatography of pooled cephalic and caudal lobe extracts resulted in two distinct ir-beta E peaks, with elution volumes corresponding to the mammalian beta-lipotropin and beta E, and three ir-ACTH peaks, the second one coeluting with mammalian ACTH. In the neural lobe the ir-ACTH/-beta E concentrations were similar to those in the hypothalamus. Resting plasma ir-ACTH (12.8 +/- 1.47 pmol/ml) but not ir-beta E (31.4 +/- 1.22 pmol/ml) levels were significantly increased following castration (to 41.4 +/- 1.11 pmol/ml). Serial blood sampling indicated pulsatile ir-beta E secretion (mean, coefficients of variation, and minimum-maximum range: 17.5, 62.78, and 2.9-49.7, respectively, for gander 1 and 23.3, 62.85, and 5.00-61.5, respectively, for gander 2).

Characteristics of the proopiomelanocortin system in the outdoor-bred domestic gander. II. Seasonal and circadian rhythmicity; effect of ether stress and lipopolysaccharide administration.

The responsiveness of the POMC system to exogenous stimuli and the diurnal and seasonal rhythmicity of ACTH and beta-endorphin (beta E) in plasma were studied in outdoor-reared domestic ganders. Plasma levels of ACTH- and beta E-like immunoreactivities were determined by direct and specific radioimmunoassays. In the first series of experiments immunoreactive (ir) ACTH and beta E were measured in the plasma of male domestic geese after 5 min of ether stress and after administration of 2 micrograms/kg lipopolysaccharide (LPS). Both ir-ACTH and ir-beta E levels increased 5 and 10 min after ether inhalation, but the increase in the ir-beta E concentration was only half that of the ir-ACTH. The plasma ir-ACTH levels were elevated after 60 and 120 min but not after 90 min of LPS administration: ir-beta E levels were unchanged at all time points. In a second series of experiments blood samples were taken on 30 March. 16 June, 4 August, and 27 October. On these days diurnal samplings were performed at 02:00, 06:00, 10:00, 14:00, 18:00, and 22:00 h. A two-way analysis of variance showed significant diurnal and seasonal changes for both hormones and significant interaction between the diurnal and seasonal levels. The highest daily mean values of the plasma ir-ACTH and ir-beta E concentrations were measured in June. The maximum of the ir-ACTH level was at 10:00 h in March and August, but at 22:00 h in June and October. The changes in ir-beta E concentrations paralleled those of ir-ACTH, but the changes did not reach statistical significance in every case.

Effects of an LH-RH agonist on reproductive responses and endocrinological parameters in landais ganders.

Semen quantitative (sperm production) and qualitative parameters (percentage of live and normal spermatozoa, sperm motility, egg fertility and hatchability), as well as hormonal parameters (LH and testosterone plasma concentrations) were compared for landais ganders, which were treated or not, with an LH-RH agonist prior to being sexually active. Treatment with the LH-RH agonist at this physiological stage delayed the onset of sperm production in some of the treated males. Although, comparable data were obtained during the first half of the reproductive period, treatment with the LH-RH agonist maintained sperm output at higher levels during its second half. Although the percentage of normal and live spermatozoa, sperm motility and true hatchability did not differ, the LH-RH agonist treatment had a positive effect on gosling production because of the higher fertility of the treated birds during the second part of the reproductive period. Treatment induced a large short-term decrease in testosterone levels followed by a rebound, leading to higher levels during the second half of the reproductive period. We conclude that treatment of ganders with an LH-RH agonist partially prevented the naturally occurring decline in sperm production and induced an increase in the rate of fertility rates during the second half of the productive period.

Seasonal and circadian fluctuation of plasma LH level and its change in the domestic goose as an effect of GnRH treatment.

We have defined the seasonal and circadian changes of the LH level of plasma of 2 years old male and female Hungarian domestic geese by means of the LH antigen-antibody of chickens in the heterologous RIA system. The LH level of plasma in geese living in conditions of natural light does not show any variation resulting from sexual differences, but the application of GnRH analogue (Ovurelin) causes higher peaks in ganders than in females. Since the LH level of plasma at the end of November in sexually inactive birds is high at night and lower during the day; the fluctuation in females can be considered as having a circadian rhythm. Five minutes after the intravenous application of GnRH analogue the LH level reaches its peak in the plasma and this high LH level returns to pre-injection values in 3 hours. The LH level shows a characteristic seasonal cycle in both sexes. The spring peak (reproduction cycle) is followed by a definite decrease at the beginning of the photorefractoriness (mid-June) with a slight automnal increase in female geese.

The photorefractoriness in domestic goose: effect of gonads and thyroid on the development of postbreeding prolactinemia.

Blood samples were taken from adult male and female geese, and from gonadectomized (GX), thyroidectomized (TX) and gonadectomized+thyroidectomized (GX+TX) ones during the reproduction peak period (March 16), at the beginning of photorefractoriness (June 14), in the second half of the photorefractory period (August 14), and at the beginning of the postrefractory period (October 2). Surgeries were carried out at the age of 10-13 weeks. The birds were kept under natural light conditions. From the blood plasma prolactin (PRL), luteinizing hormone (LH), testosterone (T), progesterone (P4), 17 beta-oestradiol (E2) as well as thyroxine (T4) and triiodo-tironine (T3) were determined by RIA methods. At the beginning of photorefractoriness in intact geese the LH and E2 levels significantly decrease, relative to sexually active period, whereas the P4 remains at a high level. In ganders the LH shows only a slight decrease but the T level is significantly lower than in spring. The PRL, T4 and T3 levels increase after reproduction and give a peak value in both sexes. In both GX ganders and geese decreased T, P4 and T3 levels are observable and the PRL is decreased in females, and the LH is increased in both sexes. Gonadectomy does not influence the E2 in females, the PRL in males and the T4 in both sexes. In TX birds the PRL is higher in March and lower in June than the control level, but these changes are significant only in females. In TX females the P4 level is lower during reproduction and at the beginning of photorefractoriness. The T and E2 levels do not change during the photorefractoriness. In the second half of photorefractoriness a low PRL and P4 level, an increasing LH, T and medium high T4 and T3 levels characterized the intact male and female geese. In GX animals an increase of LH levels is occurred in both sexes. The T4 is higher in castrated-, and lower in ovarectomized geese. In TX birds the P4 is higher than in controls, but the difference is significant only in males. The levels of PRL, LH, T and E2 remain unchanged in TX animals. At the beginning of the postrefractory phase the T (in males) and the P4 and the T4 level increase in both sexes. The PRL and LH show a low value. In GX animals the high LH level refer to the increased sensitivity of hypothalamo-gonadotropic system, because of the absence of negative feed-back of sexual steroids.4+ in both sexes and a high thyroid hormone level and a transitional slight reactivation of gonadotropic-gonadal system occur then.

The fine structure of the follicular cells in growing and atretic ovarian follicles of the domestic goose.

The structure of follicular layer of growing and atretic follicles in the ovary of the domestic goose, was studied by electron microscopy. In small follicles, the wall is lined with a narrow layer of tightly packed small, cuboidal cells separated from the thecal tissue by the basal lamina. During growth, they transform into tall, columnar cells arranged in a single row. The cells display several peculiar ultrastructural features. First, annulate lamellae are commonly observed. Second, cytoplasmic dense-cored granules accumulate in close association with fenestrated cisternae and networks of tubuli derived from the RER. They consist of spheres and strands of amorphous substance of unknown origin. Third, the cells contain many transosomes, a unique organelle of the avian follicle cell consisting of a dense plaque associated with ribosome-like particles. The mature forms of transosomes are located at the tips of lateral and apical cell projections, while bodies thought to be their precursors, are found in the apical cytoplasm. In follicles larger than 8 mm in diameter, most of the transosomes and their precursors have disappeared. Follicular atresia occurs in all of the size-classes of follicles investigated. A loss of transosomes (in follicles up to 8 mm in diameter) and an accumulation of lipid droplets, are the first atretic events detectable by electron microscopy. Morphologic features, including deep nuclear indentations, accumulation of lipid droplets frequently encircled by membrane whorls, dilation and disintegration of RER cisterns, swelling of mitochondria and accumulation of dense irregular masses of unknown origin in the cytoplasm, are taken as evidence for advanced degradation.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma adrenocorticotropin in domestic geese: effects of ether stress and endocrine manipulations.

A direct radioimmunoassay for the determination of avian adrenocorticotropin (ACTH) in a small volume of plasma was developed using an antiserum specific for N-terminal region of the ACTH molecule. The sensitivity of the two stage assay is 0.1 fmol ACTH/tube. The specificity of the antiserum was tested by its cross reactions with synthetic ACTH fragments and by comparing curves obtained by dilution of different plasma specimens to that of ACTH reference standard. Adrenocorticotropin responses of chronically cannulated geese to ether stress were evaluated and compared to changes of plasma corticosterone (B) concentration over a 2-hr period. ACTH showed a maximum between 5 and 10 min after ether exposure, while B peak appeared 10-15 min later. Thirty minutes after ether inhalation plasma ACTH returned to the baseline, while B response was longer-lasting and decreased to the resting level between 60 and 120 min. Basal and stress-induced ACTH plasma levels were also investigated in male and female gonadectomized and thyroidectomized geese. Castration increased, while thyroidectomy decreased the basal ACTH concentration. These endocrine manipulations did not, however, markedly affect the stress-induced ACTH hypersecretion except in thyroidectomized ganders, where the increment of plasma ACTH 10 min after ether inhalation was significantly lower than in sham operated control geese.

Distribution of glucocorticoid receptor-like immunoreactivity in the brain, and its relation to CRF and ACTH immunoreactivity in the hypothalamus of the japanese quail, Coturnix coturnix japonica.

Monoclonal antibody (MAb49) against the rat liver glucocorticoid receptor was used to evaluate glucocorticoid receptor (GR) immunoreactive structures in the brain of the japanese quail, Coturnix coturnix japonica. Using the avidin-biotin technique, the immunoreaction was present in the nerve cell nuclei in intact male birds. High density of glucocorticoid receptor-like immunoreactivity was found in the tubero-infundibular area, nucleus paraventricularis, posteromedialis and lateralis hypothalami, lateral septum and in some brainstem nuclei. Cerebellar cortex was also immunopositive. In contrast to mammals, no immunoreactive cell nuclei were found in the hippocampal region. The glucocorticoid receptors were colocalized with adrenocorticotropin (ACTH) immunoreactivity in the tubero-infundibular region, while corticotropin releasing factor (CRF) positive cells in the paraventricular nucleus did not contain glucocorticoid receptor-like immunoreactivity in their cell nuclei.

The role of gonadotropin releasing hormone (Gn-RH) in the regulation of gonadal functions of birds. Review article.

Gonadotrop hormone secretion is regulated by the central nervous system through the hypothalamus. This neuro-hormonal regulation was first verified in birds by Follett /21/ who was able to increase the LH secretion of hypophysis in vitro by crude extract of quail hypothalamus. His results supported the indirect statements of earlier neuroendocrine studies and emphasized the importance of bird hypothalamus in the regulation of gonadal function /1, 62/. A neurohormone fundamental in the central regulation of gonadic function, luteinizing hormone releasing hormone (abbreviated earlier as LH-RH, but recently, and, thus, hereinafter as Gn-RH) has first been isolated from porcine hypothalamus in Schally's Laboratory /41/, and, following the determination of its amino-acid sequence, it has been synthesized in the same year /42/. It has been stated that this peptide, consisting of 10 amino acids (p Glu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH2), increases the LH and FSH secretion of the hypophysis both in vitro and in vivo. One year later, a decapeptide, similar in its structure to porcine Gn-RH was produced from sheep hypothalamus. Investigations of the two teams suggested that decapeptide containing arginine on place 8 was the physiological Gn-RH of mammals.

Immunoreactivity to vasoactive intestinal polypeptide (VIP) and thyreotropin-releasing hormone (TRH) in hypothalamic neurons of the domesticated pigeon (Columba livia). Alterations following lactation and exposure to cold.

The distribution of VIP- and TRH-immunoreactivity in neurons and processes within the hypothalamus of the pigeon was investigated with light-microscopic immunocytochemical techniques. Most of the VIP-containing neurons are concentrated in the middle and caudal parts of the hypothalamus, with the greatest concentration of perikarya occurring in the medial and lateral part of the ventromedial hypothalamic nucleus and the infundibular nucleus. These cells give rise to axons that seem to extend into the median eminence. An extensive network of VIP-immunoreactive fibers and varicosities occupy the external layer of the median eminence. The majority of TRH-containing neurons is found in the anterior hypothalamus with the greatest concentration of cells in the magnocellular preoptic, medial preoptic, suprachiasmatic and paraventricular nuclei. TRH-immunoreactive fibers and varicosities form a dense arborization in the external layer of the median eminence. Lactation seems to induce substantial changes in VIP as well as in TRH-immunostaining in the median eminence and other hypothalamic regions as compared to control, sexually active animals. Furthermore, TRH-immunoreactivity decreased in the median eminence following 60-min exposure to cold. These results suggest that VIP- and TRH-containing pathways in the pigeon hypothalamus are involved in the mediation of neuroendocrine responses.

Structural and hormonal changes during follicular maturation in the ovary of the domestic goose.

Follicle maturation in the ovary of sexually mature domestic geese in the spring reproductive cycle was investigated by histological methods and steroid-RIA. The single-layer granulosa of primary follicles temporarily transformed in the growing white follicles into several layers or a simple membrana granulosa with nuclei at several different levels in the cell. In the yolky follicles the granulosa represents a cuboidal epithelium (F4-F3) and subsequently a high cylindrical epithelium (F1). The originally connective tissue-like cells of the theca interna show a glandular proliferation in the largest white (F7) and the small yolky follicles (F6-F5). Glandular cell nests in the theca externa are typical in the generation of small white follicles and are absent in the wall of yolky follicles. Progesterone-content in the follicular wall (granulosa + theca) is the highest in the F1-F2 and F6-F5 types and is low in small white follicles (F8, F9 and F10). E2 concentration shows only slight variations between F1-F10. TEST content shows a slight increase between F1 and F3 and is high in medium-sized white follicles (F8-F9). The results suggest that in addition to the granulosa, the theca interna is also capable of an intensive progesterone synthesis.

Thyroxin induced moult in domestic hen.

Two identical experiments were carried out in domestic hens treated with a lower (0.2 mg/animal) or a higher (0.4 mg/animal) dose of thyroxin (T4), for 21 consecutive days. The low dose diminished egg production, but did not result in moulting while the higher dose stopped egg laying on the 16th day and caused the loss of contour feathers from the 14th day on. The new plumage was completely developed in this group on about the 42th day. The plasma progesterone concentration showed an increase in both thyroxin treated groups, but is was only continuous and significant in the fowls treated with 0.4 mg T4. In this group the peak value of progesterone was synchronous with the most intensive feather loss. In the other group the tendency for increased levels of progesterone was of shorter duration and not significant. Plasma oestrone levels were depressed by the treatment in both groups and increased significantly only in the moulted fowls after administration of T4 was stopped. This increase may be associated with feather growth and regeneration of the oviduct. Plasma 17-beta oestradiol and testosterone concentrations did not change in the T4 treated groups. Plasma corticosterone concentration increased continuously only in the moulting animals. The results suggest that on one hand thyroxin has a role in the endocrine regulation of moulting and, on the other, that a thyroxin-progesterone synergism is of significance in the process.