Somatotropin response in vitro to corticosterone and triiodothyronine during chick embryonic development: Involvement of type I and type II glucocorticoid receptors

Corticosterone (CORT) can stimulate growth hormone (GH) secretion on embryonic day (e) 12 in the chicken. However, CORT failed to induce GH secretion on e20 in a single report, suggesting that regulation of GH production changes during embryonic development. Secretion in response to CORT during embryonic development is modulated by the thyroid hormones triiodothyronine (T(3)) and thyroxine (T(4)). Growth hormone responses on e12 involve both glucocorticoid (GR) and mineralocorticoid receptors (MR); however, involvement of MR has not been evaluated past e12. To further define changes in somatotroph responsiveness to CORT, pituitary cells obtained on e12-e20 were cultured with CORT alone and in combination with T(3) and GH-releasing hormone (GHRH). Growth hormone mRNA levels and protein secretion were quantified by quantitative real-time polymerase chain reaction (qRT-PCR) and radioimmunoassay (RIA), respectively. Corticosterone significantly increased GH mRNA and protein secretion on e12; however, mRNA concentration and protein secretion were unaffected on e20. Contributions of GR and MR in CORT responses were evaluated using GR and MR antagonists. Treatment with a GR-specific antagonist effectively blocked the CORT-induced increase in GH secretion on e12. The same treatment on e20 had no effect on GH secretion. These findings demonstrate that GR is directly involved in glucocorticoid stimulation of GH secretion at the time of somatotroph differentiation but is not regulatory at the end of embryonic development. We conclude that positive somatotroph responses to CORT are lost during chicken embryonic development and that GR is the primary regulator of CORT-induced GH secretion.

Exposure duration to long day lengths associated with the expression of photorefractoriness in turkey breeder hens

In addition to inducing egg production, exposure to long days concomitantly activates processes that eventually result in photorefractoriness (PR) and cessation of egg production. Experiments were conducted to evaluate the duration of exposure to long days that result in these processes. In each of 3 experiments, we subjected Large White turkey breeder hens to long days (16 or 18 h per day) for differing lengths of time from initial photostimulation and then returned them to a photoperiod (12L:12D) that provided sufficient, but decreased, photoperiodic drive to support egg production but not induce PR. Photoresponsiveness was then evaluated by egg production after a return to a longer day length (20 h per day) late in the lay period and beyond the mean onset of PR typical for these turkey hens. Hens that have undergone any reduction in photoresponsiveness should not increase egg production in response to the increased photoperiod. From experiments 1 and 2, exposure to long days for as little as 1 d and as much as 9 wk from initial photostimulation did not result in an alteration in subsequent photoresponsiveness. This was based on an increased egg production response to a change in photoperiod from 12L:12D to 20L:4D after 20 wk of photostimulation that was similar to controls held continuously on 12L:12D and opposite to the response of controls held continuously on 18L:6D. It was clear that PR had been fully programmed by 20 wk of exposure to long days. Exposure to long days for 12 wk (experiment 3) resulted in a partial alteration of subsequent photoresponsiveness. It was concluded that programming of PR during late spring-summer season occurs after 9 wk of long day exposure, is not fully expressed by 12 wk of long days, and can be fully expressed by 20 wk of photostimulation.

Gonadotrophin-inhibitory hormone receptor expression in the chicken pituitary gland: potential influence of sexual maturation and ovarian steroids

Gonadotrophin-inhibitory hormone (GnIH), a hypothalamic RFamide, has been found to inhibit gonadotrophin secretion from the anterior pituitary gland originally in birds and, subsequently, in mammalian species. The gene encoding a transmembrane receptor for GnIH (GnIHR) was recently identified in the brain, pituitary gland and gonads of song bird, chicken and Japanese quail. The objectives of the present study are to characterise the expression of GnIHR mRNA and protein in the chicken pituitary gland, and to determine whether sexual maturation and gonadal steroids influence pituitary GnIHR mRNA abundance. GnIHR mRNA quantity was found to be significantly higher in diencephalon compared to either anterior pituitary gland or ovaries. GnIHR mRNA quantity was significantly higher in the pituitaries of sexually immature chickens relative to sexually mature chickens. Oestradiol or a combination of oestradiol and progesterone treatment caused a significant decrease in pituitary GnIHR mRNA quantity relative to vehicle controls. GnIHR-immunoreactive (ir) cells were identified in the chicken pituitary gland cephalic and caudal lobes. Furthermore, GnIHR-ir cells were found to be colocalised with luteinising hormone (LH)beta mRNA-, or follicle-stimulating hormone (FSH)beta mRNA-containing cells. GnIH treatment significantly decreased LH release from anterior pituitary gland slices collected from sexually immature, but not from sexually mature chickens. Taken together, GnIHR gene expression is possibly down regulated in response to a surge in circulating oestradiol and progesterone levels as the chicken undergoes sexual maturation to allow gonadotrophin secretion. Furthermore, GnIHR protein expressed in FSHbeta or LHbeta mRNA-containing cells is likely to mediate the inhibitory effect of GnIH on LH and FSH secretion.

The effect of heat stress on ovarian function of laying hens

Reproductive failure associated with heat stress is a well-known phenomenon. The mechanism involved in this failure is not clearly understood. In order to test a possible direct effect of heat stress on ovarian function, 36 White Leghorn laying hens were housed in individual cages in 2 temperature- and light-controlled rooms (n = 18). At 31 wk of age, one group was exposed daily for 12 h to high temperature (42 +/- 3 degrees C), and the second group was maintained under thermoneutral conditions (24 to 26 degrees C) and served as control. Body temperature, feed intake, egg production, and egg weight were recorded daily; heparinized blood samples were drawn every 3 d for plasma hormonal level of luteinizing hormone, follicular stimulating hormone, progesterone, 17beta-estradiol, and testosterone. Six days after exposure half of the birds in each group were killed, and the ovary and oviduct were weighed and preovulatory follicles removed and extracted for mRNA of Cytochrome P 450 aromatase, 17-alpha hydroxylase. The same procedure was repeated 9 d later with the rest of the birds. Short and long heat exposure caused significant hyperthermia and reduction of egg production, egg weight, ovarian weight, and the number of large follicles. In addition, a significant reduction in plasma progesterone and testosterone was detected 2 d after exposing the birds to heat stress, and plasma 17beta-estradiol was significantly reduced 14 d after initiation of heat stress. Short exposure to heat stress caused significant reduction in mRNA expression of cytochrome P450 17-alpha hydroxylase, exposing the birds to long-term heat stress caused significant reduction in expression of mRNA of both steroidogenic enzymes. No significant change was found in plasma luteinizing hormone and follicular stimulating hormone levels during the entire experimental period. We suggest a possible direct effect of heat stress on ovarian function.

Seasonal and photoperiodic regulation of secretion of hormones associated with reproduction in Magang goose ganders

This study examined the reproductive endocrine profile under natural and artificial photoperiods in Magang goose ganders. Group 1 ganders (n=8) served as non-treated controls and were exposed to natural photoperiod throughout the experiment from 13th January to 17th December 2004. Group 2 ganders (n=8) were exposed to 18 h long daily photoperiod for 60 days from 13 January till 15 March 2004 and again to 16 h photoperiod for 75 days till 10th October 2004, and the 11h short photoperiod in the remainder periods of the experiment. In control ganders, plasma LH concentrations were high in normal breeding seasons (August-March) and decreased to low levels in non-breeding season from April to July. Testosterone concentrations changed similarly to that of LH throughout the seasons. Seasonal pattern of PRL concentrations was opposite to those of LH and testosterone, with low values in breeding season and high values in non-breeding season. In artificial photoperiod treated ganders, increasing photoperiod increased PRL and decreased LH and testosterone concentrations, while decreasing photoperiod reversed these changes. There were no seasonal or photoperiod caused changes in plasma T3 concentrations in both control ganders and artificial photoperiod treated ganders. These results demonstrated that in Magang goose ganders that long photoperiod stimulates PRL secretion and decreases LH secretion, which terminates reproductive season in spring and early summer, and short photoperiod stimulates LH secretion and inhibits PRL secretion rendering ganders enter into reproductive season.

Lack of effects of atrazine on estrogen-responsive organs and circulating hormone concentrations in sexually immature female Japanese quail (Coturnix coturnix japonica)

The widely used herbicide, atrazine, has been reported to exhibit reproductive toxicity in rats and amphibians. The present studies investigate toxicity of atrazine in Japanese quail and its ability to influence reproduction in sexually immature females. Atrazine was administered in the diet at concentrations from 0.001 to 1000 ppm (approximately 109 mg kg-1 per day) or systemically via daily subcutaneous injections (1 and 10 mg kg-1) or Silastic implants. Atrazine did not cause overt toxicity in sexually immature female quail (no effects on change in body weight, feed intake, mortality or on circulating concentrations of the stress hormone, corticosterone). It was hypothesized that if atrazine were to have estrogenic activity or to enhance endogenous estrogen production, there would be marked increases in the weights of estrogen sensitive tissues including the oviduct, the liver and the ovary together with changes in gonadotropin secretion. However, atrazine had no effect on either liver or ovary weights. Atrazine in the diet increased oviduct weights at 0.1 and 1 ppm in some studies. These effects were not consistently observed and were not significant when data from studies were combined. Systemic administration of atrazine had no effect on oviduct weights. Dietary (concentrations from 0.001 to 1000 ppm) and systemically administered atrazine had no effect on circulating concentrations of luteinizing hormone (LH). The present studies provide evidence for a lack of general or reproductive toxicity of atrazine in birds.

Potential role of thyroid hormones and prolactin in the programming of photorefractoriness in turkey hens

The domestic turkey hen is a seasonal breeder, requiring a period of short days to establish photosensitivity and a long day length to initiate egg production. The reproductive season is then limited by the onset of photorefractoriness (PR), which causes a decline, and then termination, of egg laying. In passerine birds, PR is programmed early in the reproductive season by the presence of thyroid hormones and a long photoperiod. High circulating prolactin (PRL) is thought to hasten the onset of PR. In a prior study, we reported that hens destined to have PR exhibited lower levels of thyroxine (T4) and PRL at certain points (weeks) following photostimulation than did hens destined to remain photosensitive (PS), a result opposite to what might be expected. The present study was conducted to further explore the possible relationship between circulating hormone levels and subsequent PR in the commercial turkey hen at times (days) closer to photostimulation than our previous study. Plasma levels of triiodothyronine (T3), T4, and PRL were compared in 2 subpopulations of hens identified retrospectively after 50 wk of egg production: A group of 17 hens that exhibited PR (mean onset = 27 wk of photostimulation) and a group of "good" layers that remained PS (mean production = 210 eggs/50 wk). Results showed no differences between groups in plasma T3 or T4 levels or in the T3:T4 ratio at -6, 0, 1, 3, and 7 d from photostimulation. Plasma PRL levels were significantly higher at 8 and 9 wk after photostimulation in hens that remained PS vs. those that became PR. We conclude that thyroid hormone levels around the time of photostimulation either are not actively related to programming of subsequent PR in turkeys or programming for PR in the turkey hen occurs later in the reproductive cycle than in passerine birds. We further conclude that hens that exhibit PR tend to have lower circulating PRL levels early in the reproductive season than hens that remain PS and lay at a relatively high rate.

Identification of dopamine, gonadotrophin-releasing hormone-I, and vasoactive intestinal peptide neurones activated by electrical stimulation to the medial preoptic area of the turkey hypothalamus: a potential reproductive neuroendocrine circuit

The neural and neurochemical substrates regulating reproduction in birds remain vaguely defined. The findings that electrical stimulation in the medial preoptic area (ES/MPOA) or intracerebroventricular infusion of dopamine (DA) stimulated luteinising hormone (LH) and prolactin (PRL) release in female turkeys, led to the suggestion that ES/MPOA might help to clarify the DA circuitry regulating LH and PRL. We used c-fos mRNA and tyrosine hydroxylase immunoreactivity as measured by double in situ hybridisation/immunocytochemistry (ISH/ICC) to determine which group/subgroup of DA neurones was activated following unilateral ES/MPOA. To establish that the reproductive neuroendocrine system was activated, double ISH/ICC was also conducted on c-fos/gonadotrophin-releasing hormone-I (GnRH-I) and c-fos/vasoactive intestinal peptide (VIP). Changes in circulating LH and PRL were determined by radioimmunoassay. Unilateral ES/MPOA (100 microA, right side) of anaesthetised laying turkeys for 30 min increased circulating LH and PRL levels. It also induced c-fos mRNA expression on the ipsilateral side by all GnRH-I neurones within the septopreoptic region, implying that GnRH-I neurones in this region share similar circuitry. VIP neurones within the nucleus infundibularis were the only VIP group to show c-fos mRNA expression, suggesting their involvement in ES/MPOA induced PRL release. c-fos mRNA expression was also observed in a subgroup of DA neurones in the nucleus mamillaris lateralis (ML). To our knowledge, the present study is the first to show that activation of DAergic cells in the ML is associated with the activation of GnRH-I and VIP neurones and the release of LH and PRL. It is likely that ES/MPOA activated VIP/GnRH-I neurones via activation of DA neurones in the ML, as this was the only DA subgroup that showed c-fos mRNA expression.

Thyroid hormone and prolactin profiles in male and female turkeys following photostimulation

The turkey hen, a photosensitive bird, will become photorefractory (PR) during the reproductive cycle and will cease laying despite a stimulatory day length. This response is thought to be "programmed" by hormonal events early in the reproductive cycle. The turkey tom, in contrast, produces semen for extended periods and has not been shown to exhibit PR. We compared hormone profiles following photostimulation of hens and toms to assess differences that might program one, but not the other, for PR. We photostimulated with 16 h light per day and measured plasma prolactin (PRL), thyroxine (T4), and triiodothyronine (T3) weekly for 12 wk, and again at 16 and 22 wk. Hens were fed ad libitum, and toms were moderately feed-restricted. Results showed increasing PRL levels following photostimulation in hens, with peak levels occurring at about the time of peak egg production, and declining thereafter. Toms maintained significantly lower concentrations of PRL (P < 0.0001) than hens after 2 wk of photostimulation. A highly significant sex by time interaction in plasma T3 levels was observed due to extreme fluctuations in males. Similar, often reciprocal, fluctuations in mean T4 concentrations also occurred in males. We recycled the toms and repeated blood collections under identical conditions, but with ad libitum feeding to determine if feed restriction may have produced these unusual results. This study revealed an initial significant decline in plasma T3 levels and an increase in T4 levels immediately following photostimulation, and then steady (T4) or slowly rising (T3) levels through 12 wk photostimulation. We conclude that PRL profiles of toms and hens differ markedly during the reproductive cycle, lending support to the suggestion that rising PRL may mediate the onset of PR. Further study is needed to determine if the low plasma T3 levels in males may be related to delayed PR. The extreme fluctuations in plasma T3 and T4 levels of toms receiving relatively mild feed restriction suggest a need for further study of the metabolic effects of feed restriction in turkeys.

Effect of a single short-term reduction in photoperiod on photorefractoriness in turkey hens

In a prior study, we reported that a high proportion of hens in a winter-laying flock became relatively photorefractory (rPR) early in the reproductive cyand that successive short-term reductions in photoperiod in such hens each initially depressed egg production but then caused a rebound in rate of lay to briefly exceed that of hens that did not exhibit rPR. The present study was conducted to assess rPR in a summer-laying flock and to determine whether a single short-term reduction in day length early in the reproductive cycle might enhance egg production and delay the onset of absolute photorefractoriness (aPR). Control hens received a photoperiod of 16L:8D throughout the experiment. Experimental hens were photostimulated with 16L:8D, received a reduced (but still stimulatory) photoperiod of 11.5L:12.5D for 2 wk beginning 8 wk after photostimulation, and then were returned to 16L:8D for the remainder of the 23-wk test period. Results showed that a single 2-wk reduction in day length shortly after the hens reached peak egg production did not significantly reduce overall flock egg production, but it also did not improve late-season egg production or retard the onset or incidence of aPR. The incidence of rPR was substantially less in this study than we had observed with a winter-laying flock (32.9 vs. 67.1%), but similar proportions of treated hens exhibited the most severe rPR response (a brief but complete cessation of egg production) in both studies (21.1 vs. 24.0%), and all treated hens that subsequently became aPR had shown this severe rPR response to the test photoperiod. We concluded that a core proportion of hens (approximately one-fifth) exhibited a strong rPR response when presented with a reduced photoperiod early in the reproductive cycle, regardless of season of the year, and that such hens were more likely to subsequently exhibit poor egg production or become aPR than flockmates that did not exhibit rPR. Therefore, some indication of the incidence of rPR early in the lay period may have a predictive value for the overall egg production of the flock.

Modulation of in vitro DNA synthesis in the chicken ovarian granulosa cell follicular hierarchy by follicle-stimulating hormone and luteinizing hormone

Folliculogenesis in domestic hens appears to be controlled by numerous factors, particularly the gonadotropins, luteinizing hormone (LH) and follicle-stimulating hormone (FSH). The involvement of LH in follicular steroidogenesis has been described in some detail; however, the specific role of FSH has remained elusive. In 3 experiments, the effects of ovine (o)- or chicken (c)-derived FSH (oFSH, cFSH) or LH (oLH, cLH) were evaluated on in vitro DNA synthesis [3H-thymidine (3H-TdR) incorporation], indicative of cellular proliferation, of granulosa cells from F1, F3, or F5-6 preovulatory follicles. In experiment 1, oFSH or cFSH stimulated (P < 0.05) and oLH or cLH decreased DNA synthesis by F1 granulosa cells. In experiment 2, oFSH resulted in concentration-related changes in DNA synthesis by F5-6 granulosa cells; however, no significant changes were observed in F1 or F3 granulosa cells. No effect of oLH was observed on granulosa cell proliferation from any of the follicles. Similar to oFSH, cFSH resulted in concentration-related increases in DNA synthesis in granulosa cells from F5-6 follicles with smaller magnitude changes in proliferation of F1 or F3 granulosa cells. Granulosa cells from F5-6 or F3 follicles had small increases in DNA synthesis in response to cLH. These data support the proposed role for FSH in granulosa cell proliferation, possibly contributing to follicle growth, and suggest that in vitro 3H-TdR incorporation by granulosa cells may provide a sensitive and selective bioassay for chicken gonadotropin preparations. Furthermore, data suggest that proliferative responsiveness of granulosa cells to FSH or LH may differ depending on position of follicles in the preovulatory hierarchy.

Sulfamethazine advances puberty in male chicks by effecting a rapid increase in gonadotropins

A sulfonamide, sulfamethazine (SMZ) has been shown to have a robust, progonadal effect. The mechanism of action of SMZ, however, is unknown. Our hypothesis is that the compound may act centrally and/or at the level of the pituitary. Four experiments were completed to test that hypothesis. Chicks exposed to a continuous photoperiod and fed a diet containing 0.2% SMZ showed an exponential increase in testes size. When 6 weeks of age (5 weeks on the SMZ diet), experimentals had testes weight nine times heavier than controls. Profiles for thyroid and gonadotropin plasma hormones suggested that T(3) was transiently lower in experimentals solely during the first week on treatment, while thyroxine levels were not different from controls. In contrast, luteinizing hormone (LH) and follicle stimulating hormone (FSH) were significantly elevated at the initial 1-week sampling point and remained elevated throughout the entire experiment. In a follow-up study, LH was found significantly higher than controls by 48 h after initially consuming the compound. When T(3) was added to the SMZ diet at 0.5 ppm, the progonadal effect of SMZ was attenuated. Importantly, chronic intake of T(3) delayed but did not block the stimulatory effect of SMZ for increasing plasma LH. We conclude that since one of the primary effects of SMZ is to increase rapidly plasma gonadotropins, data suggest the compound is acting at the level of the brain or pituitary to stimulate early gonadal development in chicks.

Immunohistochemical localization of chromogranin A in gonadotrophs and somatotrophs of the turkey and chicken pituitary

In the course of producing monoclonal antibodies to turkey prolactin, three monoclonal antibodies to turkey chromogranin A (CgA) were also produced, apparently arising from minor contamination of the turkey prolactin immunogen with peptide fragments of CgA. The identity of the antigen recognized by these antibodies was established by tandem mass spectrometry de novo sequencing of seven tryptic peptides from a turkey pituitary protein purified by immunoaffinity chromatography. These peptides showed high homology with distinctly separate regions of mammalian and ostrich CgA, and in silico cloned chicken CgA sequences. Chromogranin A immunostaining patterns on Western blots and pituitary tissue sections differed from those of prolactin, growth hormone, or luteinizing hormone (LH). Dual-label fluorescent immunohistochemistry revealed that CgA was co-localized with LH in most avian gonadotrophs in young chickens and turkeys, but not in adult, laying birds. Conversely, CgA was found in a majority of somatotrophs in laying birds but was absent from somatotrophs in young, growing chickens and turkeys. Lactotrophs contained no detectable CgA immunoreactivity in the tissues studied. These results suggest that CgA may modulate hormone secretion by gonadotrophs and somatotrophs in a manner that differs between cell type with age or reproductive state.

Photoresponsiveness of turkey breeder hens changes during the egg-laying season: relative and absolute photorefractoriness

Photosensitive species undergo neuroendocrine changes during a reproductive season that cause them to gradually become unresponsive to a photoperiod that initially stimulated reproduction. They may first become relatively photorefractory (rPR), when they will cease egg laying only if photoperiod is reduced, and then absolutely photorefractory (aPR), when they will cease laying despite long day length. Our objective was to test the photoresponsiveness of breeder turkey hens during egg production at various times following photostimulation and to relate photoresponsiveness to rPR and aPR as well as plasma levels of prolactin (PRL) and luteinizing hormone (LH). Hens were maintained in cages in light-controlled facilities and photostimulated at 31 wk of age (September) with a photoperiod of 16L:8D. At 8, 14, and 20 wk after photostimulation, treated hens received a 2-wk exposure to an 11.5L:12.5D photoperiod and were then returned to 16L:8D. Exposure to the shortened photoperiod at 8 wk of photostimulation resulted in three distinct responses of declining egg production: nonresponders (NR, 32.7% of hens), partial responders (PAR, 43.9%), or full responders (FR, 23.4%). Egg production returned to control levels following return to a 16L:8D photoperiod. This response repeated at the 14- and 20-wk treatment periods but with greater declines in egg production in the NR and PAR groups. The incidence of subsequent aPR in the NR, PAR, and FR groups was 5.7, 8.5 and 24%, respectively, as compared to 23.3% for the controls. Plasma LH and PRL concentrations also declined in response to 11.5L:12.5D and also rebounded following return to 16L:8D. The hormonal responses of NR, PAR, and FR were similar. We conclude that turkey hens exhibit varying degrees of rPR early during the egg laying season and that the incidence and severity of the rPR response increases as the laying season progresses. Further, PRL and LH levels did not reflect the differences in egg production among the responder and nonresponder groups to changes in photoperiod.

Relative and absolute photorefractoriness in turkey hens: profiles of prolactin, thyroxine, and triiodothyronine early in the reproductive cycle

An experiment was conducted to determine whether a commercial strain of turkey hens exhibits relative photorefractoriness (rPR) during a reproductive cycle and to ascertain whether plasma levels of certain hormones early in the reproductive cycle might be associated with subsequent expression of rPR or absolute photorefractoriness (aPR). Twenty-seven percent of hens maintained on a stimulatory photoperiod of 18L:6D for 19 wk and then given a shorter, but still stimulatory, photoperiod (13L:11D) ceased to lay and their ovaries regressed within 4 wk. These hens were considered rPR. Subsequent exposure to the 18L:6D photoperiod resulted in ovarian recrudescence in 41.7% of these PR individuals, confirming the presence of rPR at 19 wk after photostimulation. Absolute PR was observed in 15.1% of hens during a 27-wk reproductive season. Hens that became rPR or aPR exhibited significantly lower plasma prolactin levels at 8 and 14 wk after photostimulation than did hens that remained photosensitive (PS). Plasma levels of thyroxine were lower at 1 and 2 wk following photostimulation in hens that subsequently became PR than in hens that remained PS. We conclude that turkey hens may exhibit rPR and aPR during a reproductive cycle, whereas flockmates may remain PS for at least 27 wk. The presence of long daylengths, thyroid hormones, and PRL did not assure expression of PR. The expression of PR appears to be associated with reduced plasma throxine levels during a period when programming of PR is thought to occur and with reduced levels of prolactin following peak egg production.

FSH- and LH-cells originate as separate cell populations and at different embryonic stages in the chicken embryo

The histological distribution of gonadotrophs containing either LH or FSH, but not both gonadotropins, has been demonstrated before in the juvenile and adult chicken throughout the caudal and cephalic anterior pituitary lobes. In the present investigation, the distribution of FSH- and/or LH-containing gonadotrophs was further investigated in the chicken embryo by use of the same homologous antibodies as used in our earlier study. Fluorescent dual-labeling immunohistochemistry revealed that during embryogenesis LH and FSH reside exclusively in separate gonadotrophs, as has been described before in the post hatch bird. LH-immunoreactive cells were observed for the first time at day 9 of embryogenesis. This is as much as 4 days earlier than the FSH-immunoreactive cells, which appeared at day 13 of embryogenesis. Our results confirm that FSH- and LH-containing gonadotrophs are distributed throughout both lobes of the anterior pituitary. No conspicuous differences were observed between the sexes in any of the aspects investigated. The described situation is unique in that it seems to imply the existence of separate cell lineages for FSH- and LH-producing cells, as opposed to the single gonadotrope lineage described in all other species studied so far, with the exception of bovine. Our data indeed raise the question as to which signaling and/or transcription factors may cause the unique dichotomy observed in the chicken gonadotrophs.

The turkey transcription factor Pit-1/GHF-1 can activate the turkey prolactin and growth hormone gene promoters in vitro but is not detectable in lactotrophs in vivo

The transcription factor Pit-1/GHF-1 plays an important role in regulating the prolactin (Prl) and growth hormone (GH) genes in mammals. In this study, the role that Pit-1 plays in regulating the prolactin and growth hormone genes in avian species was examined by cotransfection assays and immunofluorescence staining of pituitary sections. In cotransfection assays, turkey Pit-1 activated the turkey Prl, turkey GH, and rat Prl promoters 3.8-, 3.7-, and 12.5-fold, respectively. This activation was comparable to rat Pit-1 activation of these same promoters. A point mutation in the turkey Pit-1 cDNA, which changed leu-219 to ser-219, resulted in a 2-, 2-, and 10-fold reduction in the activation of the turkey Prl, turkey GH, and rat Prl promoters, respectively. Unexpectedly, coexpression of tPit-1 (leu-219) and tPit-1(ser-219) activated turkey Prl and rat Prl promoters 9.4- and 35.9-fold, respectively, but had no effect on the turkey GH promoter. Dual-label immunofluorescence analysis of turkey pituitary sections revealed that Pit-1 was not detectable in prolactin-staining cells but was detectable in GH-staining cells. Taken together, these data indicate that in the domestic turkey, Pit-1 can activate the turkey Prl promoter in vitro, but does not appear to play a role in regulating Prl gene expression in vivo. Pit-1, however, still likely plays a role in regulating GH gene expression.

Increased proliferative activity and programmed cellular death in the turkey hen pituitary gland following interruption of incubation behavior

Incubation behavior or broodiness in turkey hens is characterized by ovarian regression, hyperprolactinemia, and persistent nesting. Nest-deprivation of incubating turkey hens results in disruption of broodiness accompanied by a precipitous decline in plasma prolactin (PRL) concentrations. The objective of the present study is to examine cellular changes in the pituitary gland associated with nest-deprivation for 0, 1, 2, 3, 4, or 7 days. Bromodeoxyuridine (BrdU) was administered prior to kill to study proliferative activity. Pituitary tissue sections were immunostained using turkey growth hormone (GH) antibody, and/or chicken PRL peptide antibody, and BrdU antibody. Plasma PRL concentrations declined significantly following nest-deprivation for 1 or more days. The midsagittal pituitary area immunoreactive (ir) to GH was significantly increased while that of PRL was significantly decreased following nest-deprivation for 2 or more days. Terminal deoxy-UTP nick end labeling and PRL-immunostaining revealed an abundance of apoptotic nuclei in both cephalic and caudal lobes of the anterior pituitary gland, suggestive of programmed cellular death of lactotrophs in the pituitary gland of hens nest-deprived for 2 or more days. Mammosomatotrophs were abundant in hens nest-deprived on Day 0 but were absent in hens nest-deprived for 1 or more days. Proliferating (BrdU-ir) cells were significantly abundant in the pituitary cephalic and caudal lobes following nest-deprivation for 1 or more days but were absent on Day 0 or in laying hens. Dual-labeling studies indicated that most of the BrdU-ir nuclei in the caudal lobe were not colocalized in somatotrophs in hens nest-deprived for 1-4 days but did colocalize with GH following 7 days of nest-deprivation. In conclusion, nest-deprivation of incubating turkey hens results in 1) a precipitous decline in plasma PRL concentration, 2) programmed cell death of lactotrophs, 3) disappearance of mammosomatotrophs, 4) increased proliferative activity of pituitary cells, and 5) recruitment of somatotrophs arising primarily from mitosis of nonsomatotrophic cells.

Identification of growth-hormone- and prolactin-containing neurons within the avian brain

Prolactin (PRL)- and growth-hormone (GH)-containing perikarya and fibers independent of the anterior pituitary gland have been reported to exist in the central nervous system of several mammalian species. The specific distributions of PRL- or GH-like neurons in the avian forebrain and midbrain, however, have not been reported. The objective of the study was to identify GH- and PRL-containing neurons in the hypothalamus and a few extrahypothalamic areas of two avian species. Brain and peripheral blood samples were collected from laying and broody turkey hens and ring doves. Broody turkey hens and doves had significantly higher plasma PRL concentrations compared with laying hens. Coronal brain sections were prepared and immunostained using anti-turkey GH and anti-chicken synthetic PRL antibodies. In turkey hens, the most dense GH-immunoreactive (ir) perikarya and fibers were found in hippocampus (Hp), periventricular hypothalamic nucleus, paraventricular nucleus, inferior hypothalamic nucleus, infundibular hypothalamic nucleus, medial and lateral septal area, and external zone of the median eminence (ME). In the ring dove, a similar pattern of distribution of GH-ir neurons was noticed at the brain sites listed above except that GH-ir fibers and granules were found only in the internal zone of ME and not in the external zone. In both turkeys and doves, the most immunoreactive PRL-ir perikarya and fibers were found in the medial and lateral septal area, Hp (turkey only), and bed nucleus of the stria terminalis pars magnocellularis. There were no apparent differences in the staining pattern of GH- or PRL-ir neurons between the laying and broody states in either species. However, the presence of GH-ir- and PRL-ir perikarya and fibers in several hypothalamic nuclei indicates that GH and PRL may influence parental behavior, food intake, autonomic nervous system function, and/or reproduction.

Influence of continuous growth hormone or insulin-like growth factor I administration in adult female chickens

A series of studies was conducted to determine whether growth hormone (GH) exerts effects on adult female chickens. Recombinant chicken GH (rcGH) was administered continuously via osmotic minipumps. No consistent effects of rcGH treatment were observed on reproductive indices. Hens receiving rcGH treatment for 10 days exhibited hepatomegaly and showed a tendency (P < 0.1) for increased spleen and thymus weights. Moreover, there were increases in the circulating concentrations of insulin-like growth factor-I (IGF-I) and IGF-binding proteins (IGF-BPs) (22-kDa IGF-BP after 2, 5, and 10 days; 28-kDa IGF-BP after 5 and 10 days; and 36-kDa IGF-BP after 10 days) with rcGH treatment. To determine whether the changes in IGF-BPs were due directly to GH or indirectly via IGF-I, the effects of the continuous administration of rcGH or recombinant human IGF-I (rhIGF-I) were compared. While rcGH again elevated the circulating levels of 28- and 36-kDa IGF-BPs, no such effect was observed with rhIGF-I treatment. However, both treatments exerted similar effects in depressing pituitary GH mRNA levels and elevating plasma concentrations of IGF-I. It is concluded that GH directly elevates circulating concentrations of IGF-I and IGF-BPs, but the negative feedback effect on GH synthesis is mediated via IGF-I.

Immunohistochemical evidence that follicle-stimulating hormone and luteinizing hormone reside in separate cells in the chicken pituitary

As is the case in other tetrapod species, the chicken gonadotropins LH and FSH consist of a common alpha subunit and a hormone-specific beta subunit. Gonadotrophs containing LH were shown earlier to be distributed throughout both the caudal and cephalic lobes of the chicken anterior pituitary, but the cellular distribution of FSH in avian species is still uncertain. The purpose of this study was to determine the cellular distribution of FSH-containing chicken gonadotrophs by use of FSH-specific monoclonal antibodies (mAbs). Three new mAbs toward chicken FSH were proven hormone specific by immunodetection of purified hormones on dot blots and by dual-label immunohistochemistry (IHC) on sagittal sections of chicken pituitaries. A rabbit antibody was used to detect chicken LH. Results showed that LH-containing gonadotrophs were densely distributed throughout the anterior pituitary, whereas gonadotrophs containing FSH were much less numerous; in addition, while also present in both lobes, FSH-positive cells were largely absent from the outer margin of the gland. Dual-label IHC revealed that LH and FSH reside almost exclusively in separate gonadotrophs. The identity of FSH-containing cells was further confirmed through use of an antibody to the chicken alpha subunit, which showed that FSH immunoreactivity was always colocalized with the alpha subunit. Our results suggest the possibility that production and secretion of LH and FSH may be regulated differently in chickens than in most other species studied to date.

Endocrine patterns during aging in the common tern (Sterna hirundo)

Blood samples were taken from breeding common terns (Sterna hirundo) of known age during two successive breeding seasons to determine if plasma concentrations of estradiol, progesterone, androgen, and luteinizing hormone (LH) reflect the process of aging. Males and females were trapped and sampled once between laying of the first and the second eggs in the clutch. The transient capture and sampling did not disrupt incubation or the timing of the subsequent oviposition. Ages ranged from 2 to 21 years, with most in the range 4-11 years. There was a strong inverse correlation (P < 0.0001) between age and laying date in both females and males, with older birds nesting earlier in the season. Plasma LH levels increased (P < 0.005) among mature (>5 year) females. Plasma progesterone and E2 were positively correlated with each other among mature females, but did not change in an age-dependent manner. In males, plasma progesterone levels showed no age-related changes. However, maturing (3-5 year) males showed increasing plasma androgen levels (P < 0.01); mature males showed no change with age. Plasma LH levels were correlated with androgen levels in both maturing and mature males. Plasma progesterone declined with age in maturing males (P < 0.001). These data provide evidence for changing endocrine status with age, but the patterns differ for younger individuals (</=5 year) and mature birds. It appears that in younger individuals, nesting experience and maturity of the pair affect reproductive performance and endocrine status. Individual variability was high for all hormones, possibly masking age-related changes. Only breeding individuals were sampled at all ages, although the proportion of the population that continues to reproduce may decline as the birds age. In summary, common terns continue to breed successfully until at least age 21 years and these individuals maintain relatively stable endocrine status during aging. Although there was some indication of declines in estradiol and androgens among the oldest birds (16-21 years), these declines were not statistically significant and were manifested in only a small fraction (<4%) of the breeding population.

Effects of body weight and feed allocation during sexual maturation in broiler breeder hens. 2. Ovarian morphology and plasma hormone profiles

The effects of broiler breeder BW and nutrient intake on ovary morphology and plasma reproductive hormone profiles were examined at photostimulation (PS) (21 wk) and at sexual maturity (SM) in standard (STD) and low (LOW), or high (HIGH) BW birds provided either restricted (RF) or ad libitum (AL) access to feed between PS and SM. At PS, 30 Shaver Starbro pullets at target BW were assigned to the STD treatment, and birds either 20% heavier (HIGH) or lighter (LOW) assigned accordingly. Ten birds of each size group were processed immediately for carcass analysis and 10 birds assigned to each size by feed interaction group. Blood samples were taken at 3-d intervals beginning at PS and profiles constructed for estradiol-17beta, luteinizing hormone (LH), and follicle-stimulating hormone (FSH) to examine the relationship between body size, feeding level, and reproduction. Birds were processed for assessment of reproductive traits following SM. The AL birds reached SM with 11.0 large yellow follicles (LYF) (> 10 mm diameter) compared to 7.1 in RF birds. Small follicle atresia (< 5 mm diameter) was low in AL birds (10.3) compared to RF birds (32.3). The extent of small follicle atresia in RF birds was found to be inversely proportional to LYF number by stepwise regression. Increased small follicle atresia was associated with a longer sexual maturation period in RF birds (r = 0.619; P = 0.0003). Plasma estradiol-17beta concentration was greater in HIGH than in STD or LOW birds at PS, suggesting more advanced ovary development in HIGH birds. Estradiol-17beta profiles were similar in shape in all treatments, with the primary difference being the length of time prior to a substantial estradiol-17beta increase. Following PS, plasma LH and FSH concentrations of AL birds increased to levels nearly double that of RF birds, indicating a role for nutrient intake with rate of reproductive development. Plasma LH and FSH concentrations remained elevated for a greater time period in RF birds, however, possibly relating to the development of processes limiting LYF recruitment. This experiment demonstrated a modulation of reproductive hormone concentrations during sexual maturation by feeding level in conjunction with a sensitivity of the ovary to nutritional effects.

Identification of mammosomatotrophs in the turkey hen pituitary: increased abundance during hyperprolactinemia

We have previously reported that the hyperprolactinemia in incubating turkey hens is associated with recruitment of lactotrophs in the pituitary gland. In this study we have used double immunofluorescence and in situ hybridization histochemistry to 1) identify mammosomatotrophs in the anterior pituitary gland of egg-laying turkey hens and incubating hens, and 2) verify PRL gene expression within mammosomatotrophs by colocalizing PRL messenger RNA in GH-immunoreactive (ir) cells. The pituitaries of laying and incubating turkey hens were collected, and the midsagittal sections were dual labeled for either PRL and GH or PRL messenger RNA and GH. The plasma PRL concentrations were higher in incubating hens (231 +/- 10.6 ng/ml) than in laying hens (43 +/- 7.4 ng/ml; P < 0.01). In the midsagittal pituitary sections, mammosomatotrophs were predominantly found scattered in the caudal lobe of the anterior pituitary gland, in the ventral half of the cephalic lobe, and at the junction of cephalic and caudal lobes. In incubating hens, the proportion of mammosomatotrophs was 7.4 +/- 1.52% (mean +/- SEM) of the total number of GH-ir and/or PRL-ir cells counted, which was significantly higher (P < 0.05) than that found in laying hens (0.6 +/- 0.23%). Furthermore, PRL gene expression was observed in many GH-ir cells in the incubating hen pituitary gland. These data suggest that 1) mammosomatotrophs are present in the turkey pituitary gland, and 2) there is an increased abundance of mammosomatotrophs in the incubating turkey hen that may contribute to hyperprolactinemia.

Circulating prolactin levels at the end of the photophase and the end of the scotophase throughout the reproductive cycle of the turkey hen

Plasma prolactin (PRL) levels rise following long daily photostimulation and increase dramatically at the onset of incubation behavior. Previous work has shown that a daily rhythm in PRL secretion may occur, with the lowest PRL levels found prior to lights out and the highest levels found prior to lights on. It has been suggested that an early event in the onset of incubation behavior may be an increase in nocturnal PRL levels. A retrospective study was conducted to contrast the morning and evening PRL secretion patterns at weekly intervals throughout the reproductive cycle in birds that exhibited: 1) incubation behavior; 2) high egg production and low nesting frequency for the last 16 wk of a 21-wk reproductive cycle; 3) high egg production while nesting frequently; or 4) photorefractoriness (defined by a cessation of egg production without incubation behavior). All hens showed an increase in PRL levels following photostimulation. When day and night PRL levels for each hen were compared over the entire reproductive cycle, more than 50% of those studied had significantly higher PRL levels at the end of the scotophase than at the end of the photophase. Circulating PRL levels increased greatly with the onset of incubation behavior, but morning and evening PRL levels changed in parallel. Good layers had moderate PRL levels throughout egg production, but PRL levels did not differ among laying hens with high or low nesting frequency. Plasma PRL levels declined to low levels in photorefractory hens. These results show that daytime PRL measurements accurately reflect reproductive state, and that moderate PRL levels seem consistent with optimum egg production.

Baculovirus-mediated expression of chicken growth hormone

A full-length chicken growth hormone (cGH) cDNA was placed downstream from the Autograph californica nuclear polyhedron virus, AcNPV, polyhedron gene promoter and expressed in Sf9 insect cells. Secreted recombinant cGH levels averaged 2-10 micrograms/ml from day 5-10 postinfection. The recombinant cGH analyzed by SDS-PAGE gels and Western blotting consisted of a doublet with M(r) of 26.5 and 23.5 kDa. Analysis by 2-D electrophoresis of partially-purified recombinant cGH and purified native cGH revealed similar immunoreactive charge isoforms and M(r) variants. The recombinant hormone was biologically active in a homologous radioreceptor assay. The results show that cGH expressed in insect cells is biologically and immunologically active, and that a variety of isoforms are secreted which exhibit size and charge properties similar to those of pituitary-derived cGH.

Chronic administration of growth hormone (GH) to adult chickens exerts marked effects on circulating concentrations of insulin-like growth factor-I (IGF-I), IGF binding proteins, hepatic GH regulated gene I, and hepatic GH receptor mRNA

In young birds, growth hormone (GH) administration has been found to have only a small or even no effect on circulating concentrations of insulin-like growth factor-I (IGF-I). This is in obvious contrast to the situation in mammals. The present study examines the effect of continuous administration of GH in adult male chickens. Plasma concentrations of IGF-I were markedly elevated (2.5-3.0-fold, p < 0.001) in GH-treated chickens. There were also some transient increases in the circulating levels of IGF binding proteins. Adult chickens showed other manifestations of increased responsiveness to GH, including elevated hepatic expression of GH-regulated gene-I (mRNA) with GH treatment (p < 0.05), and a tendency (p < 0.08) for decreased GH-receptor mRNA. In contrast to the changes in circulating concentrations of GH and IGF-I with GH treatment, no changes in plasma concentrations of thyroid hormones, reproductive hormones, glucose, or nonesterified fatty acids were evident.

Changes in pituitary somatotroph and lactotroph distribution in laying and incubating turkey hens

Turkey hens can rapidly shift from a laying condition to one characterized by ovarian regression, incubation behavior, and hyperprolactinemia. Although remarkable changes occur in hormonal profiles as turkey hens pass from a laying to an incubating state, studies have not been undertaken to examine histochemical alterations of functionally relevant pituicytes in the adenohypophysis. The objective of this study was to compare the immunocytochemical changes in pituitary lactotrophs and somatotrophs in incubating turkey hens with those of egg laying hens. Based upon nest visiting and egg production records, laying and incubating hens were selected for sampling blood, pituitaries, and ovaries. Plasma prolactin (PRL) and growth hormone (GH) concentrations were determined. Sagittal pituitary sections of laying and incubating hens were immunostained using antibodies against turkey growth hormone or synthetic chicken PRL peptide. Somatotrophs were found predominantly in the caudal lobe while lactotrophs occurred only in the cephalic lobe of adenohypophysis in laying hens. In incubating hens, somatotrophs in the ventral half of the caudal lobe were replaced by lactotrophs. The sagittal area which immunostained for PRL was significantly greater while the area that immunostained for GH was less in the adenohypophysis of incubating turkey hens. Some of the lactotrophs were hypertrophied in incubating hens. The lactotrophic recruitment and hypertrophy provide a cellular basis for the hyperprolactinemia in incubating turkey hens.

The suppressive effects of testosterone on growth in young chickens appears to be mediated via a peripheral androgen receptor; studies of the anti-androgen ICI 176,334

ICI 176,334 is a nonsteroidal anti-androgen that has been shown to selectively block peripheral androgen receptors in rats and is presumed to do so in chickens. In chickens, androgens stimulate secondary sexual characteristics (e.g., comb), but inhibit growth and the immune tissues. The present study examined the effect of dietary ICI 176,334 (5 or 25 mg/kg body weight) on growth in chickens in the presence or absence of testosterone treatment (as 1-cm long silastic implants). Treatments began at 2 wk of age and continued through 6 wk of age. Testosterone alone reduced body growth (average daily gain and shank-toe length, together with weights of the body, skeletal muscle, and the bursa of Fabricius, an immune tissue), and stimulated comb development. At the low dose (5 mg/kg), ICI 176,334 alone had no effect on body growth or organ weight with the exception that comb weight was reduced. At the high dose (25 mg/kg), ICI 176,334 decreased growth (body weight, average daily gain, and shank-toe length) and organ weights (breast muscle, bursa of Fabricius, testis, and comb weights). This effect may represent a toxicity. As might be expected with an anti-androgen, ICI 176,334 (at either 5 or 25 mg/kg) completely suppressed the stimulation of comb growth evoked by testosterone. Similarly, ICI 176,334 (5 mg/kg) overcame, albeit partially, the growth-suppressive effects of testosterone (on body weight, average daily gain, shank-toe length, and breast muscle weight) and also had inhibitory effects on the weights of the testis and bursa of Fabricius. The anti-androgen, ICI 176,334, did not influence the reduction in circulating concentrations of luteinizing hormone occurring after testosterone treatment. The present data are consistent with the growth-suppressive effects of testosterone in chickens being mediated via a peripheral androgen receptor. No effects of either testosterone or ICI 176,334 were observed on circulating concentrations of insulin-like growth factor-I despite the marked changes in growth rate.

Vasoactive intestinal peptide stimulates prolactin mRNA expression in turkey pituitary cells: effects of dopaminergic drugs

It is well documented that vasoactive intestinal peptide (VIP) is a prolactin (PRL)-releasing factor and that dopamine (DA) is an inhibitory neurotransmitter in avian species. However, the roles of VIP and DA in the regulation of PRL gene expression are unclear. In this study, primary anterior pituitary cells cultured from laying turkeys were utilized to investigate the influence of VIP and dopaminergic D1 and D2 receptors on PRL secretion, PRL mRNA, and PRL synthesis. Incubation of pituitary cells with VIP increased PRL secretion up to 3.5-fold within 3 hr. Prolactin mRNA was undetectable during the first 2 hr of pituitary cell treatment; thereafter, the PRL mRNA content response to VIP increased with 24-48 h (P < 0.05). Total PRL content (media + cellular) increased over time in the presence of VIP. The response of cells incubated in the presence of a dopaminergic D1 receptor agonist (SKF38393) was variable and inconclusive. However, cells incubated with a dopaminergic D2 receptor agonist (quinpirole) inhibited VIP-induced PRL secretion (P < 0.05) and PRL mRNA levels (P < 0.05) in a dose-related fashion without effect on the basal levels of PRL release and PRL mRNA. These observations suggest that VIP, in addition to acting as a PRL-releasing peptide, also plays a role in the regulation of PRL gene expression. Moreover, the results of this study also indicate that a drug that can selectively stimulate dopamine D2 receptors can also regulate PRL secretion and PRL mRNA in turkey pituitary cells in culture.

Pulsatile secretion of prolactin in laying and incubating turkey hens

Incubation behavior in the turkey hen is associated with a large increase in prolactin secretion. Previous research using hourly sampling of incubating hens has shown that prolactin levels fluctuate widely throughout a 24-hr period, suggestive of pulsatile secretion. This study compared the prolactin secretory patterns of laying and incubating turkeys to determine if prolactin is secreted episodically and if the high prolactin levels characteristic of the incubating hen may result, at least in part, from a change in the amplitude or frequency of secretory pulses. Blood samples were collected from cannulated, unrestrained laying and incubating hens at 10-min intervals for up to 24 hr. Data were analyzed with the PULSAR program to determine baseline prolactin levels and to establish the magnitude, frequency, and duration of episodic secretory peaks. The results revealed tha prolactin is secreted in a pulsatile pattern in both laying and incubating turkey hens. Incubating hens had ninefold higher mean and baseline plasma prolactin levels than laying hens. The prolactin pulses were of approximately 12-fold greater amplitude in incubating hens than in laying hens, but the duration and frequency of pulses were the same in both groups. Therefore, the high prolactin levels required for incubation do not appear to result from an increase in the frequency of lactotroph stimulation, but rather from an increase in the prolactin secretion rate.

Effects of growth hormone injection to embryos on growth and myosin heavy chain isoforms in growing turkeys (Meleagris gallopavo)

Effects of embryonic imprinting with growth hormone (GH) on growth and myosin heavy chain (MyHC) isoforms in pectoralis muscle were determined by injecting turkey embryos with ovine growth hormone (oGH) at a dose of 10 micrograms three times a day. Injections were made on days 20 and 26 (Treatment 1), days 14 and 20 (Treatment 2) or days 14 and 26 (Treatment 3) of incubation. In Treatment 1 poults, plasma GH concentrations were elevated at 3 days posthatch and in Treatment 3 poults, plasma GH concentrations were elevated at 15 days posthatch, as compared to control poults. At 4 weeks of age, in males, body weights, shank length and weights of pectoralis, gastrocnemius and sartorius muscles were increased in Treatment 3, and in females, body weights, shank length and weights of gastrocnemius muscle of female turkeys were increased in Treatment 1. The growth rate of female turkeys from 4 weeks through 16 weeks was increased by Treatment 1. Treatment 1 resulted in a delay in the transition from the embryonic MyHC isoform to the neonatal MyHC isoform and to the adult MyHC isoform. Treatment 3 induced an earlier appearance of the adult MyHC isoform. No effects on body and muscle growth and MyHC isoforms were observed by Treatment 2.

Changes in pituitary somatotrophs and lactotrophs associated with ovarian regression in the turkey hen (Meleagris gallopavo)

Hyperprolactinemia has been associated with incubation behavior and ovarian regression in turkey hens. Preliminary data show that tamoxifen, a partial estradiol receptor antagonist, may effect ovarian regression. The objectives of the study were to induce ovarian regression in egg-laying turkey hens by administration of tamoxifen, to determine whether incubation behavior would be effected by tamoxifen treatment and to examine the distribution of lactotrophs and somatotrophs and their immunocytochemical changes in the adenohypophysis due to a change in reproductive state. Two commercial strains of turkey hens were administered tamoxifen (experimentals) or vehicle (controls) intramuscularly (40 mg/hen/d). Equal numbers of experimental and control hens were killed for sample collection after 5, 9 and 14 days (n = 4 per strain) of treatment. Blood samples were collected for hormone assay and pituitaries prepared for immunocytochemistry. Tamoxifen treatment for 9 and 14 days induced ovarian regression but not incubation behavior. Plasma luteinzing hormone levels were significantly increased after 5 and 9 days of tamoxifen administration, whereas prolactin and growth hormone levels were unchanged. Somatotrophs were found predominantly in the caudal portion and lactotrophs occurred in the cephalic lobe of the pituitary. Relative to controls, the prolactin immunoreactive area was significantly greater in tamoxifen-treated hens, whereas the growth hormone immunoreactive area was reduced.

Ontogeny of pituitary and serum growth hormone in growing turkeys as measured by radioimmunoassay and radioreceptor assay

Some mammalian studies have revealed a wide discrepancy in pituitary and circulating growth hormone (GH) measurements determined by immunological and biological assay methods. Recent studies demonstrating that avian GH exists in numerous isoforms raise concerns that immunological measurement of GH may not accurately reflect the amount of biologically active hormone present. We sampled eight different male turkeys of a commercial strain weekly until 6 wk of age, and then biweekly until 20 wk. Total pituitary GH content and serum GH concentration were measured by avian GH RIA and radioreceptor assay (RRA). The highest mean serum GH concentration occurred at 3 wk, and the ontogeny of serum GH content from 1 to 8 wk was similar whether measured by RIA or RRA. Pituitary GH content was highest at 6 wk, but RIA and RRA estimates differed markedly throughout the study. Pituitary content of biologically active GH, as estimated by RRA, exceeded that of immunologically active GH from 2 to 10 wk, whereas the reverse was true at 14, 18, and 20 wk. We conclude that this avian GH RIA accurately measures bioactive circulating turkey GH, but that the pituitary of the young turkey may contain bioactive GH isoforms that have poor immunological activity in our RIA.

The turkey prolactin-encoding gene and its regulatory region

Overlapping prolactin (Prl) lambda clones were isolated from a turkey genomic library. The 6.7-kb turkey Prl gene consists of five exons. Major transcription start points were located by primer extension 51-53 nucleotides upstream from the Met start codon. No estrogen response element (ERE) was found, but two regions similar to mammalian Pit-1/GHF-1-binding sites were identified by computer analysis. This suggests that transcription of the turkey Prl gene may be regulated by Pit-1/GHF-1, and not by the estrogen receptor.

Endocrine and metabolic responses of intact and hypophysectomized turkey poults given a daily injection of chicken growth hormone

Female turkey poults were hypophysectomized at 4-5 weeks of age. Beginning at 6 weeks of age, 20 hypophysectomized and 20 intact birds received a daily intramuscular injection of natural chicken growth hormone (cGH, 100 micrograms/kg body weight) or vehicle for 12 days. Blood samples were taken from each bird just before injection and 4 hr post-injection at 6 and 12 days of treatment. Hypophysectomy reduced the growth rate of turkey poults to 75% of that of intact controls, significantly reduced carcass protein and ash percentages, and significantly lower plasma concentrations of GH, insulin-like growth factor-I, triiodothyronine, thyroxine, insulin, glucose, triglycerides, and non-esterified fatty acids. Hypophysectomy was without effect on liver GH receptor binding activity, but increased liver 5'-monodeiodinase activity. Daily cGH injection had no effect on the average daily gain of either hypophysectomized or intact poults when compared to vehicle-injected controls over 12 days of treatment. Daily cGH administration increased plasma insulin-like growth factor-I levels in intact and hypophysectomized turkeys, and increased plasma triiodothyronine, insulin, glucose, and triglyceride concentrations in hypophysectomized birds, but not in intact birds. Responses of young turkeys to hypophysectomy and GH replacement were consistent with the known metabolic role of GH in other species, but the influence of GH on growth appears to be of less importance in poultry than in mammals.

Purification and partial characterization of isoforms of luteinizing hormone from the chicken pituitary gland

Isoforms of chicken luteinizing hormone (cLH) were isolated from chicken pituitaries by differential extraction, sequential chromatography on HPLC cation- and anion-exchange columns, and gel-filtration chromatography. Three purified isoforms of the cLH had high biological potency in the chicken granulosa cell LH bioassay (4.21-7.4 x NIH-LH-S1 U/mg). One cLH isoform without detectable biological activity showed substantial immunological activity in a homologous cLH radioimmunoassay. The cLH isoforms contained negligible follicle-stimulating hormone activity, but some contained thyroid-stimulating hormone activity. The apparent molecular weight of cLH was 37,000 Da, and the holoprotein consisted of subunits with a molecular weight of approximately 17,000 Da.

Development of an homologous radioimmunoassay for chicken follicle-stimulating hormone and measurement of plasma FSH during the ovulatory cycle

1. A highly specific and sensitive homologous radioimmunoassay was developed for measurement of chicken follicle stimulating hormone (cFSH). 2. Mammalian gonadotropin releasing hormone (GnRH) significantly stimulated secretion of chicken luteinising hormone (cLH) but not cFSH when administered to 22 week non-laying hens. 3. Chicken GnRH-I did not affect circulating cFSH concentrations but significantly stimulated cLH secretion when administered to 3 week cockerels. 4. The plasma concentration of cFSH was low throughout the ovulatory cycle, but a significant decline in cFSH occurred prior to the pre-ovulatory LH surge and a significant increase occurred during the 3 hr prior to oviposition as LH levels decline.

Effects of reproductive status, ovariectomy, and photoperiod on vasoactive intestinal peptide in the female turkey hypothalamus

Vasoactive intestinal peptide (VIP) appears to be a physiologically relevant prolactin (PRL)-releasing factor during the avian reproductive cycle, yet little is known of the factors involved in modulating the hypothalamic concentrations of this neuropeptide. A heterologous chicken VIP radioimmunoassay was developed to examine the effects of reproductive status, ovariectomy, and photoperiod on hypothalamic VIP immunoreactivity in the female turkey. VIP concentrations were highest in the median eminence/infundibular nuclear complex (ME/INF) relative to other subregions of the hypothalamus and changed only in this region during the reproductive cycle. Quiescent, nonphotostimulated hens subjected to stimulatory photoperiod exhibited a 1.6-fold increase in VIP in the ME/INF (quiescent 59.9 +/- 6.0 vs photostimulated 95.8 +/- 7.1 pg/microgram protein). An additional 2-fold increase in ME/INF VIP concentrations was observed in laying hens (183.0 +/- 28.5 pg/microgram protein). Coincident increases in plasma PRL were also observed. In contrast, during incubation and the photorefractory stage, a dissociation between hypothalamic VIP and plasma PRL occurred. No changes were observed in VIP in incubating hens, yet a 6-fold increase in PRL was noted, compared to layers. In addition, ME/INF VIP concentrations exhibited no change during the photorefractory stage, whereas a 28-fold decrease in plasma PRL occurred. VIP concentrations in the ME/INF of laying hens were unaffected by ovariectomy, whereas exposure to short photoperiod reduced VIP by 44%. The inhibitory effects of short photoperiod could not be reversed by administration of exogenous steroids, while steroid treatment reduced VIP concentrations by 45% in the ovariectomized hens. These results provide additional correlative evidence for a modulatory role of VIP in PRL secretion and suggest that the expression of this neuropeptide in the INF may serve as a neural link between photoperiodic mechanisms and PRL release during the avian reproductive cycle.

Phosphorylation of prolactin and growth hormone

To determine whether GH and prolactin could be phosphorylated, turkey GH, chicken GH, chicken prolactin and turkey prolactin were incubated in vitro with the catalytic subunit of protein kinase A and [gamma-32P]ATP. Phosphorylation was assessed after sodium dodecyl sulphate-polyacrylamide gel electrophoresis, Western blotting and autoradiography. Polyacrylamide electrophoresis showed that both purified native chicken GH and turkey GH were phosphorylated under the conditions employed. However, the glycosylated variant of chicken GH did not appear to be labelled. Chicken prolactin, turkey prolactin and the glycosylated variant of turkey prolactin were all intensely phosphorylated by protein kinase A. Ovine and rat prolactins could also be phosphorylated by protein kinase A. The phosphate content of different native prolactin (turkey, ovine and rat) and GH (ovine and chicken) preparations was also determined and found to be significant. Chicken pituitary cells in primary culture incorporated 32P in GH- and prolactin-like bands isolated by non-denaturing polyacrylamide gel electrophoresis, and this was stimulated by phorbol myristate acetate. Phosphorylation of GH and prolactin may thus explain some of the charge heterogeneity of these hormones.

Purification and characterization of chicken follicle-stimulating hormone

1. Highly purified chicken follicle-stimulating hormone (cFSH) was isolated from chicken pituitaries by differential extraction, sequential chromatography on HPLC cation and anion exchange columns, and gel filtration chromatography. 2. Purified cFSH (USDA-cFSH-K-1) had a potency of 77.44 units/mg in a chicken testes radioreceptor assay, and was biologically active in stimulating the secretion of progesterone by chicken granulosa cells. 3. Purified cFSH contained negligible luteinizing hormone and thyroid stimulating hormone activity. 4. The apparent molecular weight of cFSH was 38,000 Da and a single band on isoelectric focusing had a pI of 4.65.

Immunocytochemistry and immunoblotting of avian prolactins using polyclonal and monoclonal antibodies toward a synthetic fragment of chicken prolactin

A major obstacle in the production of specific antibodies toward chicken prolactin (PRL) has been overcome by mimicking a putative epitope of the molecule using the synthetic decapeptide Lys-chPRL 59-67. This peptide represents the highest hydrophilicity peak of the amino acid sequence of chPRL that was recently derived from the nucleotide sequence. Polyclonal mouse antisera against the fragment specifically recognized the lactotropes in the cephalic lobe of the chicken pars distalis as illustrated by immunocytochemical double staining experiments. Monoclonal antibody production yielded antibodies that specifically labeled purified turkey PRL upon SDS-PAGE separation and immunoblotting. Turkey and chicken PRL showed a very similar polymorphism with respect to their apparent molecular weights, including the occurrence of a glycosylated variant of chicken PRL. The monoclonal antibodies were finally used to demonstrate the presence of PRL-like immunoreactivity both in the pituitary gland and in the brain of the quail. In the brain, immunoreactive neurons were in the nucleus accumbens and in the lateral parts of the ventro-medial hypothalamus, partly similar to those described in the rat.

Pattern of secretion of luteinizing hormone and testosterone in the sexually mature male turkey

Whether luteinizing hormone (LH) and testosterone (T) are secreted in pulsatile patterns was determined in sexually mature male turkeys. Turkeys were chronically cannulated and serially bled for three 8-hr periods covering the 24-hr day (14L:10D, n = 7, series B), or for two 12-hr periods covering the 24-hr day (14L:10D, n = 4, series C). Pulses of both LH and T occurred during both the light and dark portions of the 24-hr day. A portion of the secretory episodes of T, where the baseline level of LH was relatively low, was associated with prior peaks of LH secretion. Secretory episodes of T also occurred, where baseline levels of LH and T were both relatively high, without detection of prior peaks of LH. No differences were found between the photophase and scotophase portions of the photoperiod for either LH or T concentration. It is concluded that T is secreted in a pulsatile pattern in sexually mature male turkeys. However, LH is secreted in a pulsatile pattern only when baseline levels of both LH and T are relatively low. Neither LH nor T secretion is entrained by the photoperiod. Corticosterone was measured in hourly samples, but no changes in concentration occurred in association with the photoperiod.

Turkey and chicken prolactins stimulate the proliferation of rat Nb2 lymphoma cells

The purpose of this investigation was to assess the actions of two avian prolactins (PRL) on rat Nb2 lymphoma cell proliferation. Various turkey and chicken PRL preparations stimulated the proliferation of rat Nb2 cells. The ability of avian PRL preparations to influence the behavior of rat Nb2 lymphoma cells provides a useful method for monitoring the PRL-like actions of native and recombinant avian PRL and suggests a potential role of PRL in modulating the avian immune system.

Daily rhythm of prolactin and corticosterone in unrestrained, incubating turkey hens

Plasma concentrations of prolactin and corticosterone were determined in hourly samples collected over a 25-hr period from unrestrained turkey hens exhibiting incubation (broody) behavior. Hens were maintained in cages on a 14 hr light: 10 hr dark photoperiod. Mean plasma prolactin concentration increased significantly late in the dark period to reach maximum daily levels of 496 ng/ml at the start of the photophase. However, a well-defined daily rhythm in prolactin secretion was not evident. Plasma corticosterone concentration showed a significant daily rhythm characterized by a major secretory peak (7.14 ng/ml) in the middle of the light period and a smaller, less well-defined peak (4.11 ng/ml) during the dark period. Both prolactin and corticosterone secretion ranged widely throughout the day in individual hens in a manner suggestive of pulsatile hormone secretion. This study demonstrates that the extremely high prolactin concentrations characteristic of the incubating turkey hen reflect large, dynamic changes in plasma prolactin concentrations occurring throughout the photoperiod, rather than a constantly high level of prolactin secretion.

Isoforms of turkey prolactin: evidence for differences in glycosylation and in tryptic peptide mapping

1. Three isoforms of turkey pituitary prolactin have been isolated, including a nonglycosylated isoform of 22,500 mol. wt and two glycosylated isoforms of 24,500 mol. wt. 2. The glycosylated turkey prolactins differed in carbohydrate composition, with one isoform apparently containing only O-linked carbohydrate. 3. Tryptic peptide maps showed a few peptides distinctly different among the three prolactin isoforms. 4. Amino acid sequencing of the first 40 residues of the three prolactin isoforms showed arginine at position 24 and histidine at position 27, for the nonglycosylated form, but no identifiable amino acids were detected at this position for the glycosylated isoforms.

Radioligand receptor assay for prolactin using chicken and turkey kidney membranes

1. A sensitive and specific radioreceptor assay for measuring prolactin in tissue extracts, culture media and serum has been developed utilizing membrane fractions prepared from either chicken or turkey kidney, and an ovine prolactin standard and tracer. 2. Assay sensitivity was 1.0 +/- 0.1 ng per tube, 50% inhibition of binding occurred with 12.8 +/- 1.2 ng of unlabeled ovine prolactin standard, and intra- and interassay coefficients of variation were 3.9% and 8.8%, respectively. 3. The 47,800 g kidney membrane preparation, which yielded maximum specific binding of 20-40%, offered advantages over current methods including use of an easily available and inexpensive tissue, no need for pretreatment of the donor animal, a high yield of receptor protein, and a simplified method of membrane preparation.

Half-life and metabolic clearance rate of recombinant-derived chicken growth hormone and purified turkey growth hormone in intact and hypophysectomized turkeys

The half-life and metabolic clearance rate (MCR) of natural turkey growth hormone (tGH) were compared with those of recombinant-derived chicken growth hormone (rcGH) in intact and hypophysectomized (hypox) turkey poults at 8 and 13 wk of age. The hypox poults used were all hypophysectomized at 8 wk of age. The purpose of the experiment was to determine whether the source of growth hormone (GH) or the physiological changes associated with hypophysectomy might affect the disappearance of the hormone from the circulation and, hence, alter the biological response of the bird to exogenous GH. The mean half-life of GH in the growing turkey was 12.88 +/- .54 (SE) min. The source of GH had no effect on half-life, and GH half-life did not vary significantly between poults sampled at 8 and 13 wk. Hypophysectomy significantly (P less than .01) increased the half-life of administered GH from 11.21 +/- .50 min in intact poults to 14.70 +/- .84 min in hypox poults. The MCR of GH in hypox poults 2 days following hypophysectomy was markedly lower than that of intact birds (1.08 versus 2.95 mL/min; P less than .001). The GH clearance in hypox birds increased during the 5 wk following hypophysectomy but still remained somewhat lower than that of intact birds (2.55 versus 3.00 mL/min; P = .06). The MCR of GH did not change in intact birds between 8 and 13 wk of age, and the MCR of rcGH and tGH did not differ.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of peptide histidine isoleucine on in vitro and in vivo prolactin secretion in the turkey

Studies were conducted both in vitro, using monolayer cultures of turkey pituitary cells, and in vivo, using ovariectomized turkey hens, steroid-primed ovariectomized hens, and immature toms to compared the effectiveness of peptide histidine isoleucine (PHI) with that of vasoactive intestinal peptide (VIP) in stimulating prolactin (PRL) secretion. Vasoactive intestinal peptide, a putative PRL-releasing factor (PRF) in the turkey, was approximately 1000-fold more effective than PHI in stimulating PRL secretion in vitro. Prolactin secretion was significantly enhanced by the exposure of pituitary cells to 10(-7) M PHI and a similar stimulation was observed with 10(-10) M VIP. Injection of cannulated, unrestrained turkeys with PHI at doses up to 100 micrograms per kg of BW caused no significant change in circulating PRL concentrations, but injection of 10 micrograms of VIP per kg resulted in a 7 to 22-fold increase in plasma PRL concentration within 10 to 30 min following injection. These results demonstrate a marked difference between the turkey and the rat in their response to a PRL-stimulating neuropeptide. In contrast to what was observed in the turkey, PHI is a strong PRF in the rat, with a potency equal to or greater than that of VIP. Earlier studies have shown that thyrotropin-releasing hormone, another strong PRF in mammals, has little consistent PRF activity in the turkey. Thus, the present studies add additional evidence of major differences between mammals and birds in the control of PRL secretion by hypothalamic neuropeptides.

Avian growth hormone receptor assay: use of chicken and turkey liver membranes

A sensitive avian growth hormone (GH) radioreceptor assay (RRA) was developed using recombinant chicken growth hormone (rcGH) and a membrane receptor preparation of chicken or turkey livers. The specific binding of 125I-labeled rcGH to a 47,800 X g pellet was 33-36% in a 16-20 h incubation period at 4 degrees C. Binding was time, temperature and pH dependent. Scatchard analysis indicated a single class of high affinity GH binding sites in chicken and turkey livers, with binding affinities of 1.03 X 10(10) liter/M and 1.11 X 10(10) liter/M, respectively, and corresponding binding capacities of 10.7 fmol and 21 fmol per mg protein. The sensitivity of the assay was 0.41 ng of rcGH. Intra- and inter-assay coefficients of variation were 5.3% and 9.7%, respectively. Bovine GH, ovine GH, and porcine GH competed effectively for the GH binding sites in chicken and turkey livers. Turkey prolactin (PRL) and porcine PRL showed little cross-reaction (less than 0.07%), while cross-reaction of ovine and bovine PRL was greater (less than 10%). Standard rcGH (0.5-30 ng) was added to sera from hypophysectomized chickens and turkeys (hypox sera) and to tissue culture medium and was measured quantitatively. Untreated medium (10-100 microliters) and hypox sera (5-40 microliters) did not inhibit rcGH binding. These studies report the existence of specific binding sites for avian GH in chicken and turkey liver and validate a sensitive RRA for measurement of bioactive GH in sera and tissue culture medium.