The hormonal activities associated with the cephalic and caudal regions of the cockerel pars distalis

Avian somatotrophs: differentiation, morphology, distribution, and regulation

Growth hormone (GH) is primarily synthesized, stored, and released by pituitary somatotrophs. These cells comprise a highly labile population that continuously undergoes proliferation, differentiation, and morphogenesis in response to changing physiological stimuli. They are also functionally and morphologically heterogeneous with distinct spatial and temporal distribution within the pituitary gland. The characteristics of these cells are discussed in this brief review.Key words: somatotroph, aves, growth hormone, adenohypophysis.

Evaluation of a sensitive, in vitro bioassay for chicken thyroid stimulating hormone using FRTL-5 cells, a rat thyroid cell line

An in vitro bioassay for mammalian thyroid stimulating hormone (TSH) based on TSH-induced cyclic adenosine 3',5'-monophosphate (cAMP) production in FRTL-5 cells, a rat thyroid cell line, was used to measure chicken TSH. The addition of chicken pituitary homogenate equivalent to > or = 25% of a chicken pituitary gland to cultured FRTL-5 cells increased cAMP within these cells in a dose-dependent manner. The glycoprotein fraction derived from the pituitary homogenate was further fractionated by isoelectric focusing within a pH range of 5 to 11. Analysis of the focused fractions by the bioassay detected three major components with isoelectric points of 9.30, 7.12, and 3.82, in addition to several minor ones distributed over a wide range of pH, from alkaline to acidic. The isoelectric focusing profile obtained by the bioassay was clearly different from those obtained by radioimmunoassay for chicken LH and radioreceptor assay for chicken FSH, indicating that fractions contained chicken TSH. The homogenate of the cephalic portion of the chicken anterior pituitary gland was 4.46 times more active than that of the caudal portion in the bioassay, which is consistent with previous findings on localization of TSH in the chicken pituitary. We conclude that the bioassay using FRTL-5 rat thyroid cells is a sensitive, specific, and time-saving method of measuring chicken TSH.

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.

Ontogenesis of immunocytochemically demonstrable somatotrophs in the adenohypophyseal pars distalis of the developing chick embryo

Growth hormone (GH)-containing cells in the hypophyseal pars distalis of the chick embryo were identified immunohistochemically using anti-chicken GH sera. GH cells are first demonstrable in Rathke's Pouch as early as Day 4.5 of incubation. By Day 9.5, when the two lobes (rostral and caudal) of the pars distalis are easily recognized, GH cells are confined exclusively to the caudal lobe. Although the number of GH cells increases gradually during embryonic development, there is a statistically significant difference between Days 10.5 and 12.5 in both the cellular density and the percentage of somatotrophs. GH cells, which contain coarse granules evenly distributed throughout the cytoplasm, varied in diameter from 9.3 micron on Day 4.5 to 11.8 micron on Day 20.5, while the nuclear diameter of these cells increased from 2.8 micron on Day 4.5 to 4.9 micron on Day 20.5. There was a statistically significant difference in the nuclear/cytoplasmic ratio between Days 4.5 and 13.5 and between Days 13.5 and 20.5 of incubation. Aspects of the regulation of growth hormone synthesis and secretion in the chick embryo are discussed.

Hypothalamo-adenohypophyseal-thyroid interrelationships in the developing chick embryo. VII. Immunocytochemical demonstration of thyrotrophin-releasing hormone

Thyrotrophin-releasing hormone (TRH) was demonstrated immunocytochemically in the infundibulum of the chick embryo as early as Day 4.5 of incubation. From Days 4.5 through 19.5 of embryonic development there is a gradual increase within the developing hypothalamus in the number of TRH-positive perikarya as well as the amount of immunoreactive-TRH (IR-TRH) per cell. There are no abrupt changes in either parameter during the critical time period (Days 10.5-13.5 of incubation) in the maturation of the pituitary-thyroid axis. Thus, although TRH is probably not directly responsible for the dramatic increase in the number of thyrotrophin-producing cells which occurs in the pars distalis of 10.5- to 11.5-day-old embryos (R. C. Thommes, J. B. Martens, W. E. Hopkins, J. Caliendo, M. J. Sorrentino, and J. E. Woods (1983). Gen. Comp. Endocrinol. 51, 434-443) the marked change in the activity of the pituitary-thyroid unit at this time may well reflect the response of these newly differentiated thyrothrophs to low levels of plasma TRH. This hypothesis is supported by the observations that between Days 10.5 and 11.5 the hypothalamic-adenohypophyseal-thyroid (HAT) axis is first responsive to cold (R. C. Thommes, J. B. Martens, J. B. Hopkins, D. A. Griesbach, D. J. Williams, M. J. Sorrentino, P. Wernke, and J. E. Woods. In "Proceedings, Ninth International Symposium on Comparative Endocrinology Hong Kong, 7-11 December 1981" (B. Lofts, ed.). Hong Kong Univ. Press, Hong Kong, in press) and also that the pituitary-thyroid unit exhibits a marked increase in its sensitivity to exogenous TRH (R. C. Thommes, D. J. Williams, and J. E. Woods (1984). Gen. Comp. Endocrinol. 55, 275-279).

Interrelation of the avian immune and neuroendocrine systems

Our understanding of immunology and endocrinology has been enriched by studies with different avian species. Numerous experiments have identified the role of the avian thymus and bursa of Fabricius in the immune response and the interrelation of these glands and their cellular products with the neural endocrine system. The growth pattern of the thymus and bursa are influenced by steroids. Increases in thymi growth appear to be controlled, in part, by fluctuations in thyroid activity. Sex-linked dwarf (SLD) chicks have lower T3 levels than normal chicks, but normal levels of growth hormone. The poor agglutinin response of SLD chickens to low concentrations of sheep red blood cells (0.1-1.0%) may be overcome by increasing the percentage of sheep erythrocytes to 5 or injecting growth hormone, which may enhance the conversion of T4 to T3. Castration impaired cell-mediated immunity but surgical removal of the thyroid did not significantly influence the humoral response to sheep erythrocytes or Brucella. Embryonic hypophysectomy reduced the number of B cells in the late embryo. Lesioning the anterior pituitary in 9-day-old chicks markedly reduced several parameters of cell-mediated immunity. In ovo bursectomy at 68 hr markedly increased the size of the adrenals and testes, numbers of Leydig cells, and levels of circulating testosterone but not corticosterone. On the basis of identification of lymphokines or cytoplasmic granules, lymphocytes and other cells of the lymphomyeloid complex are candidates for an endocrine role. A circuitry between the lymphocyte and neuroendocrine system has been identified in mammals and should be extended to Aves.

Hypothalamo-adenohypophyseal-thyroid and gonadal interrelationship in the chick embryo. I. Differential effect of ectopic pituitary grafts on plasma total T4 and testosterone levels

Plasma total thyroxine (T4) and testosterone concentrations of Day 15.5 intact, surgically partially decapitated (hypothalamo-hypophyseoprivic) and partially decapitated chick embryos with adenohypophyseal transplants were determined by radioimmunoassay of the same plasma sample. Decapitation in both male and female chick embryos at 33-38 h of incubation results in plasma thyroxine and testosterone levels which are statistically significantly lower than those of intact embryos. The addition of a single adenohypophyseal transplant to the chorioallantoic membrane (CAM) of male and female decapitated embryos only partially restores plasma thyroxine levels to intact levels. However, the same procedure results in plasma testosterone levels which are higher than those of both decapitated and intact individuals. The data suggest that in the developing chick embryo there are differences in dependence of the thyroid and the gonads upon a functional hypothalamo-adenohypophyseal unit. The possible differential regulatory effects of the hypothalamus on the adenohypophyseal-thyroid and adenohypophyseal-gonadal components of the hypothalamic-adenohypophyseal-thyroid and hypothalamic-adenohypophyseal-gonadal axes are discussed.

Influence of an early grafted adenohypophysis on the thyroid of the chick embryo

A hypophyseal pars distalis from an 11-day-old chick embryonic donor was implanted in the extraembryonic coelom of a 3-day-old recipient in order to evaluate the reactions of the thyroid of the host embryo and thus the functional capabilities of the grafted pituitary related to the thyroid. The graft did not modify the general growth of the embryo, but strongly influenced thyroidal development. The volume, colloid content, and radioiodide uptake of the thyroid gland were significantly increased, from Day 10 of incubation, compared with controls, as was the development of cytological structures, studied with the electron microscope. However, all these characteristics progressively returned to normal values between Days 14 and 17, in spite of the presence of this additional hypophysis. The grafted hypophysis thus acted autonomously during a first period resulting in increased stimulation of the thyroid. However, from Day 14, the influence of the graft decreased progressively and disappeared after Day 16. This signified the loss of its autonomy, and the mechanism of this loss, particularly the possible role of the hypothalamus, is discussed.

Appearance of LH-immunoreactive cells in the Rathke's pouch of the chicken embryo

The differentiation of the pituitary of the chicken embryo was studied by means of an immunohistochemical technique using antisera to turkey and chicken pituitary hormones. Immunoreactive LH-cells are detected in 4-day embryos (stage 23 of Hamburger and Hamilton) when the primordium of the anterior pituitary, the Rathke's pouch is only composed of a single-layer epithelium lined with an undifferentiated mesenchyme. A few immunoreactive cells are observed grouped on the posterior aspect of the pouch. As development proceeds, a strip of positive cells is detected encircling the Rathke's pouch. Prolactin-, growth hormone-, and ACTH-immunoreactive cells are detected in 6- and 7-day embryos, only after the pituitary has acquired its characteristic structure with cords in which different cell types become progressively recognizable. The early appearance of immunoreactive LH-cells following a precise distribution shows that secretory properties and differentiation capacities are acquired simultaneously in the epithelium of the Rathke's pouch and may be induced by the same stimulus.

Histological changes in the testis of the domestic fowl after partial adenohypophysectomy

The effects of partial adenohypophysectomy on comb size, testicular weight, and histology 20 or 30 days after the operation are described and discussed in relating these observed changes with the volume of remaining adenohypophyseal tissue. From the present observation, it is concluded that 1) the response of the domestic fowl to partial deficiency of adenohypophyseal tissue may be more sensitive than that of some mammals, 2) the decrease in testicular weight and tubular diameter precedes the histological change in testis and comb regression, and 3) to maintain fully active testicular function, more than 75% of the adenohypophysis is needed. About 40% of the adenohypophyseal tissue including a remnant of cephalic lobe can stimulate spermatogenesis, but the spermatozoa produced were partially abnormal. The critical amount of adenohypophyseal tissue for normal spermiogenesis may exist between 55 and 75%. All histological change is initially observed in the center of testis and then extended toward the periphery. It is suggested that the cephalic lobe contains at least a trace of ICSH in addition to FSH.

Ultrastructural study of the adenohypophysis of the male Chinese quail

The ultrastructural analysis of the adenohypophysis in the male Chinese quail reveals seven different types of granular cells, and agranular folliculo-stellate cells. The cell types are assumed to be endocrine cells and are classified as: Type I cells (presumptive LH-gonadotrophs), with dilated endoplasmic reticulum, perinuclear spaces, and granules of 150--260 nm; Type II cells (presumptive FSH-gonadotrophs), with regularly-shaped cytoplasmic cisterns and small granules (80--150 nm); Type III cells (presumptive thyrotrophs), very close in appearance to the type II cells of normal birds; Type IV cells (presumptive prolactin cells), with very large secretory granules (up to 400 nm), Type V cells (presumptive corticotrophs), with abundant and electron-dense granules (160--300 nm); Type VI cells, with irregularly-shaped granules; Type VII cells (presumptive somatotrophs), with abundant granules (130--220 nm) and less cytoplasmic structures. Cytological characteristics of the nucleus, and more particularly the presence of a Feulgen-postive nucleolus with a very particular ultrastructure are here reported. It is proposed that heterospecific associations of Chinese quail cells with chick cells can be used in embryological work for the study of cellular interactions.

[Ultrastructural study of the cytological changes in the adenohypophysis of the male quail submitted to long daily photoperiods (author's transl)]

The collective data obtained at the ultrastructural level in anterior pituitaries of male Chinese quails submitted to long daily photoperiods, confirm the cytological changes observed earlier in, at least, 2 types of cells of the gland. This cellular types may be the source of avian LH and FSH.

Goblet cells in embryonic intestine: accelerated differentiation in culture

If duodenal tissue from 14-day chick embryos is cultured in chemically defined medium, more than twice as many goblet cells appear within 48 hours as in intact embryos during the same time. The increase in goblet cell number is further accelerated by 10(-9) molar thyroxine but is prevented by 10(-6) molar hydrocortisone. The results suggest that differentiation of intestinal epithelium is regulated in part by a circulating inhibitor.

Precocious development of glucuronidating and hydroxylating enzymes in chick embryos treated with pituitary grafts

1. Initiation of precocious development of UDP-glucuronyltransferase by an endogenous factor is reported for the first time. 2. This development occurs in chick embryo liver and kidney after grafting of the cephalic lobe of chicken pars-distalis pituitary tissue on to the chorioallantoic membrane, and in liver results in a rise in the enzyme activity from virtually zero to ;adult' values. Aniline hydroxylase also precociously develops in the liver of grafted embryos, its activity rising from one-third to the full adult value. Specific activities of glucose 6-phosphatase, cytochrome P-450 and NADPH-cytochrome c reductase did not significantly change. 3. The response of the transferase does not require the presence of host pituitary gland nor, apart from 1 day's necessary initiation, the presence of the graft itself. 4. The host becomes competent to respond on the 14th day of incubation; response continues for at least 3 days after removal of the graft, and for 2 days in the isolated liver. Grafting of embryonic pars distalis younger than 17 days does not evoke a response in the host liver. 5. Secretion of the pituitary factor increases suddenly some 24-48h before the naturally developing surge in liver UDP-glucuronyltransferase activity and may be responsible for initiating this rise in vivo. 6. The factor is probably not a growth or luteinizing hormone; its nature and the likelihood of a secondary hormone acting directly on the liver are discussed.

The effect of hypothalamic lesions on thyroid-stimulating hormone concentration in the chicken pituitary

Studies of thyroid activity following hypothalamic lesions have provided indirect evidence of TSH influence on the pars distalis of birds. The present study examined the influence of hypothalamic lesions on TSH assays of the rostral and caudal lobes of the pars distalis. Lesions of the septomesencephalic tract increased TSH levels in the rostral lobe but had no influence on the caudal lobe. Lesions of the supraoptic or ventrolateral nuclei neither stimulated nor depressed TSH in either lobe of the pars distalis.