Effect of luteinising hormone releasing hormone and its analogues on plasma luteinising hormone concentrations in incubating bantam hens

Welfare issues associated with moulting of laying hens

A practice that is used to extend the period of lay of hens is induced moulting. It involves restriction of nutrients, and sometimes manipulation of lighting, with the consequent loss of bodyweight and feathers, regression of the reproductive tract and cessation of egg lay. When the period of moulting is completed, the reproductive tract will regenerate and egg production will resume, thereby extending the overall period of lay. Towards the end of the laying cycle of hens, the production and quality of eggs decline. At this point, some egg farmers will induce a moult in the flocks to reduce bird-replacement costs and improve profitability. In the Australian egg industry, less than 10% of layers are moulted. There are implications for the welfare of hens that are induced to moult, particularly due to loss of bodyweight and feathers. Histopathological studies have shown the extent to which loss of feathers may affect welfare from a physical perspective, and it terms of pain. It is apparent that induced moulting can lead to an increase in aggression and injurious pecking, and birds with poor feather cover are vulnerable to damage from this pecking. Induced moulting can increase stress, although the implications of this for the welfare of hens is not well understood. The endocrine events associated with induced moulting are reasonably well known and it is possible to manipulate the endocrine system to extend the lay of hens without the need to moult. Nevertheless, these approaches are unlikely to be adopted into practice. More importantly, hens should always have feed and water available and are in good condition before undergoing a moult. This is essential from the perspective of ensuring adequate standards of welfare of birds.

Regulation of Pituitary Cocaine- and Amphetamine-Regulated Transcript Expression and Secretion by Hypothalamic Gonadotropin-Releasing Hormone in Chickens

There is increasing evidence that cocaine- and amphetamine-regulated transcript (CART) peptide is abundantly expressed in the anterior pituitary of birds and mammals, suggesting that CART peptide may be a novel pituitary hormone and its expression and secretion is likely controlled by the hypothalamic factor(s). To substantiate this hypothesis, using chicken as an animal model, we examined the effects of gonadotropin-releasing hormone (GnRH) on pituitary CART secretion and expression and investigated whether GnRH could modulate plasma CART levels. The results showed that: (1) chicken GnRH (GnRH1 and GnRH2) could potently stimulate CART peptide secretion in intact pituitaries incubated in vitro, as detected by Western blot; (2) GnRH could also stimulate CART mRNA expression in cultured pituitary cells, as revealed by quantitative real-time polymerase chain reaction (qPCR) assay; (3) GnRH actions on pituitary CART expression and secretion are likely mediated by GnRH receptor coupled to the intracellular Ca²⁺, MEK/ERK, and cAMP/PKA signaling pathways; and (4) plasma CART levels are high in chickens at various developmental stages (1.2–3.5 ng/ml) and show an increasing trend towards sexual maturity, as detected by enzyme-linked immunosorbent assay (ELISA). Moreover, plasma CART levels could be significantly induced by intraperitoneal administration of GnRH in chicks. Taken together, our data provide the first collective evidence that CART peptide is a novel pituitary hormone and its expression and secretion are tightly controlled by hypothalamic GnRH, thus likely being an active player in the hypothalamic-pituitary-gonadal (HPG) axis.

The chicken type III GnRH receptor homologue is predominantly expressed in the pituitary, and exhibits similar ligand selectivity to the type I receptor

Two GnRH isoforms (cGnRH-I and GnRH-II) and two GnRH receptor subtypes (cGnRH-R-I and cGnRH-R-III) occur in chickens. Differential roles for these molecules in regulating gonadotrophin secretion or other functions are unclear. To investigate this we cloned cGnRH-R-III from a broiler chicken and compared its structure, expression and pharmacological properties with cGnRH-R-I. The broiler cGnRH-R-III cDNA was 100% identical to the sequence reported in the red jungle fowl and white leghorn breed. Pituitary cGnRH-R-III mRNA was approximately 1400-fold more abundant than cGnRH-R-I mRNA. Northern analysis indicated a single cGnRH-R-III transcript. A pronounced sex and age difference existed, with higher pituitary transcript levels in sexually mature females versus juvenile females. In contrast, higher expression levels occurred in juvenile males versus sexually mature males. Functional studies in COS-7 cells indicated that cGnRH-R-III has a higher binding affinity for GnRH-II than cGnRH-I (K(d): 0.57 vs 19.8 nM) with more potent stimulation of inositol phosphate production (ED(50): 0.8 vs 4.38 nM). Similar results were found for cGnRH-R-I, (K(d): 0.51 vs 10.8 nM) and (ED(50): 0.7 vs 2.8 nM). The initial rate of internalisation was faster for cGnRH-R-III than cGnRH-R-I (26 vs 15.8%/min). Effects of GnRH antagonists were compared at the two receptors. Antagonist #27 distinguished between cGnRH-R-I and cGnRH-R-III (IC(50): 2.3 vs 351 nM). These results suggest that cGnRH-R-III is probably the major mediator of pituitary gonadotroph function, that antagonist #27 may allow delineation of receptor subtype function in vitro and in vivo and that tissue-specific recruitment of cGnRH-R isoforms has occurred during evolution.

Gonadotrophin inhibitory hormone depresses gonadotrophin alpha and follicle-stimulating hormone beta subunit expression in the pituitary of the domestic chicken

Studies performed in vitro suggest that a novel 12 amino acid RF amide peptide, isolated from the quail hypothalamus, is a gonadotrophin inhibitory hormone (GnIH). The aim of the present study was to investigate this hypothesis in the domestic chicken. Injections of GnIH into nest-deprived incubating hens failed to depress the concentration of plasma luteinizing hormone (LH). Addition of GnIH to short-term (120 min) cultures of diced pituitary glands from adult cockerels depressed follicle-stimulating hormone (FSH) and LH release and depressed common alpha and FSHbeta gonadotrophin subunit mRNAs, with no effect on LHbeta subunit mRNA. Hypothalamic GnIH mRNA was higher in incubating (out-of-lay) than in laying hens, but there was no significant difference in the amount of hypothalamic GnIH mRNA in out-of-lay and laying broiler breeder hens at the end of a laying year. It is concluded that avian GnIH may play a role in controlling gonadotrophin synthesis and associated constitutive release in the domestic chicken.

LH responses to chicken luteinizing hormone-releasing hormone I and II in laying, incubating, and out of lay turkey hens

An experiment was conducted to assess the relative in vivo and in vitro activities of chicken LH-RH-I and -II in laying, incubating and out-of-lay turkey hens. The highest plasma concentrations of LH were measured in laying turkey hens, whereas hypophyseal concentrations were highest in incubating hens (I) and lowest in the laying hens at the end of the laying period (EL). Hypophyseal and plasma concentrations of LH decreased with aging in laying hens (L) and the greater decrease occurred in the hypophyses. An in vitro hypophyseal acute challenge with 2-min pulses of cLHRH I or II (10(-7) M) using a perifusion technique resulted in an increase in the release of LH in out-of-lay (OL) and incubating (I) hens, but not in laying (L) hens. Although both peptides elicited comparable responses in I hens, cLHRH II was more effective in OL hens. This difference was attributable to a greater amplitude of the response, whose duration was unchanged. Hypophyseal desensitization to a subsequent stimulation was observed in OL hens when the interval between stimulations was 30 min, but this did not occur at 60- or 120-min intervals. In vivo, the injection of cLHRH I or II, at doses of 10(-8) and 10(-10) M/kg B.W. stimulated increases in the plasma concentrations of LH, which were initiated within 1 min of injection in OL and I hens but from 5 to 20 min postinjection in L hens. The responses were dose-related and greater immediate responses were measured with cLHRH I than with cLHRH II. Also, after the injection of cLHRH II at the 10(-8) M/kg B.W. dose, the shape of the LH response consisted of an initial increase, followed by a more sustained phase during which LH concentrations were either stable (I hens) or continued to increase (L and OL hens) from 20 to 60 min after injection. In contrast, the injection of cLHRH I at doses of 10(-8) or 10(-10) M/kg or cLHRH II at a dose of 10(-10) M/kg in I and OL hens, produced a peak of LH concentrations in plasma within 5 min and thereafter declined gradually. The difference in the in vivo responses to LHRH I and II could not be attributed to a greater potency of cLHRH II, but to a more prolonged action. In summary, the responses to both forms of chicken LH-RH varies markedly with the stage of the reproductive cycle (L, I, and OL) and differs between the in vivo and in vitro situations. Although cLHRH II may be more active than cLHRH I, controversy still surrounds its precise physiological role.

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

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

Response of broiler breeder hens to forced molting by hormonal and dietary manipulations

Experiments were conducted to compare dietary and hormonal techniques for molting broiler breeder hens. In the first experiment, production dropped to 5% 3 wk after hens were restricted to an intake of one half of their calculated energy requirement (FR). Egg production levels of hens given a single i.m. injection of the Lupron Depot formulation of leuprolide acetate (LA) in a dose intended to provide 10 micrograms/kg BW per d for 30 d dropped to 9.5% whereas production dropped to 33% in hens receiving 5 micrograms and was unchanged by 2.5 micrograms. Postmolting fertility and hatchability of eggs from the FR and the 10-micrograms LA groups were not different. In the second experiment, postinjection egg production, oviduct weight, and uterus weight were depressed, in a dose-related manner, when hens received 0, 10, or 22 micrograms LA/kg per d. In a third experiment, egg production dropped to zero within 2 wk when hens were deprived of feed (FD) or deprived of feed and light (FD+LR), whereas it reached zero in 4 wk in hens fed only 30 g of wheat shorts per d (FR). Lupron Depot at a dose intended to deliver 30 micrograms/kg BW per d, reduced egg production to 9.5% by the 3rd wk. Twenty-eight weeks postmolting, egg production ranged from 84 to 98 eggs per hen in the molted groups and 56 eggs per hen in the unmolted controls. Fertility ranged from 82.1% in the FD+LR groups to 69.8% in the unmolted controls, whereas chick production averaged 36, 50, 59, 60, and 68 chicks per hen in the unmolted controls and in hens molted by LA, FR, FD, or FD+LR, respectively.

Chicken gonadotropin-releasing hormones enhance soluble and insoluble fibronectin production by granulosa cells of the domestic fowl in vitro

Experiments were conducted in vitro to examine the effect of two chicken gonadotropin-releasing hormones, cGnRH-I ([Gln8]-GnRH) and cGnRH-II ([His5,Trp7,Tyr8]-GnRH), on fibronectin (soluble and insoluble) production by chicken granulosa cells isolated from the largest (F1; about 35 mm in diameter), and third largest (F3; 15 to 20 mm in diameter) preovulatory follicles as well as from a pool of immature small yellow follicles (SYF; 6 to 8 mm in diameter). The amounts of soluble fibronectin (fibronectin secreted into the incubation medium) and insoluble fibronectin (fibronectin associated with cells plus fibronectin attached to culture substratum) were quantified with a specific ELISA. Fibronectin secreted into the incubation medium (soluble fibronectin) by unstimulated cells increased with advanced stages of follicular maturation. Addition of both cGnRH-I and -II increased the amount of fibronectin secreted into the incubation medium by all follicular cell types. The amount of insoluble fibronectin in culture wells that contained unstimulated cells also increased with advanced stages of follicle development. Both cGnRH-I and -II increased the quantity of insoluble fibronectin by granulosa cells from all follicle types. Total (soluble plus insoluble) fibronectin production was elevated when cGnRH-I or -II was added to F1, F3, and SYF granulosa cells. The magnitude of cGnRH-I or -II stimulation (percentage increase) of soluble, insoluble, or total fibronectin production was calculated as a multiple of the unstimulated (control) value for each follicle type, and they were greatest in cells derived from developing and immature follicles. These results indicate that homologous cGnRH-I and -II are capable of directly modulating the physiology of the avian ovary.

Short-term reduction in egg production in laying hens treated with an agonist of GnRH

1. In two experiments laying hens were treated with an agonist of gonadotrophin releasing hormone (GnRH) to induce a reduction in the secretion of luteinising hormone (LH) and a pause in egg production. 2. In experiment 1, 70-week-old laying hens were either given daily subcutaneous injections of saline for 7 d, offered whole oats for 7 d (nutrient restriction), given daily injections of the GnRH agonist [D-Trp6-Pro9 N-ethyl amide]GnRH for 7 d at 50 micrograms/kg or 100 micrograms/kg or administered 4 biocompatible implants each containing 120 micrograms of the GnRH agonist. 3. Weekly egg production was monitored for 7 weeks and blood samples were taken at weekly intervals and assayed for plasma LH and oestradiol. Egg production was reduced in the birds treated with the agonist (28 to 46% reduction) but not to the same extent as in the birds offered whole oats (92.3% reduction). 4. The treatments also reduced plasma LH and oestradiol in treated hens but again to a greater extent in the birds offered whole oats than the birds treated with the agonist. Egg production and plasma LH and oestradiol increased following the termination of the treatments. 5. The birds fed whole oats suffered a reduction in weight of 16.7% over the treatment period whereas there were increases in the weights of the birds treated with saline, 50 micrograms of GnRH agonist and the implants of GnRH agonist, but no change in birds treated with 100 micrograms of GnRH agonist. 6. The birds fed oats lost feathers over the treatment period but the birds in the other treatment groups suffered no loss. 7. In experiment 2 laying hens were either injected daily with saline or 200 micrograms GnRH agonist and weekly egg production and plasma LH and oestradiol were measured. As egg production was reduced by almost 60% in the birds treated with the agonist but did not completely cease. Reductions in plasma LH and oestradiol were also observed. All variables increased to pretreatment levels once treatment ceased. 8. These data confirm the effects of severely depriving hens of nutrients on egg production and the secretion of LH and oestradiol.(ABSTRACT TRUNCATED AT 400 WORDS)

Pituitary LH content and plasma LH levels following daily GnRH analogue treatment in male red-winged blackbirds (Agelaius phoeniceus)

1. During the 14-day treatment period, plasma LH levels following GnRH analogue (GnRH-A) injections (10.0 micrograms) were significantly reduced after the 6th and the 14th injection. 2. One day post-treatment, the LH pituitary content was significantly reduced in GnRH-A-treated redwings compared to saline-injected controls. 3. Pituitary LH content was significantly higher in GnRH-A treated birds compared to control birds 14 and 28 days post-treatment and plasma LH levels were similar in both groups. 4. Hypersecretion of LH following GnRH-A injections appears to reduce pituitary LH content, acting as a stimulus for its synthesis. 5. These results suggest a higher LH synthesis and storage in the pituitary gland of the GnRH-A-treated birds compared to the control birds during the post-treatment period.

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.

The ontogeny of luteinizing hormone-releasing hormone (LHRH) producing neurons in the chick embryo: possible evidence for migrating LHRH neurons from the olfactory epithelium expressing a highly polysialylated neural cell adhesion molecule

The development of neurons expressing luteinizing hormone-releasing hormone (LHRH) has been studied immunohistochemically in the chick embryo from the 3.5 embryonic day (ED) to the day of hatching. At ED-3.5, LHRH-immunoreactive neurons were first detected in the medial epithelium of the olfactory pit, but their appearance in the brain was delayed to ED-4.5. On EDs-6-7, cords of the LHRH-immunoreactive cells extended across the nasal septum towards the ventromedial forebrain with the olfactory nerve. By double staining for LHRH and, a highly polysialylated form of neural cell adhesion molecule (NCAM-H), the LHRH-positive neurons in the olfactory-forebrain system were found strongly NCAM-H-positive. At ED-8, a marked decrease in the number of LHRH-positive cells in the olfactory epithelium and a concomitant increase in the LHRH-positive cells in the forebrain area were noted. From ED-11 to the day of hatching, the majority of LHRH-positive neurons tended to move into their usual adult position, whereas the LHRH-positive cells had almost disappeared in the olfactory epithelium. No LHRH-immunoreactive neurons were found strongly positive to NCAM-H. These results suggest that LHRH neurons originate from the olfactory placode, then as they develop they migrate across the nasal septum and enter the forebrain with the olfactory nerve. The close association of NCAM-H with the developing LHRH neurons raises the possibility that NCAM-H plays some role in guiding the migrating LHRH neurons from the olfactory epithelium to the forebrain.

Comparison of in vivo biological activities of luteinizing hormone releasing hormone (LHRH) analogues in 60-day-old cockerels

The in vivo biological activities of various luteinizing hormone releasing hormone (LHRH) analogues in immature 60-day-old cockerels were compared, based on their capacity to increase circulating luteinizing hormone (LH) concentrations. Intravenous injections of 50, 100, or 500 ng of [Gln8]LHRH (cGnRH-I) and [His5,Trp7,Tyr8]LHRH(cGnRH-II) induced significant increases in the plasma LH level. The maximum response was always observed 2 min after the injection. Mammalian LHRH(mGnRH) significantly increased plasma LH, but only at the 500 ng dosage level. [Ile8]LHRH, [D-Ala6]LHRH, [Ala4]LHRH, [Leu8]LHRH, and [Phe5]LHRH increased plasma LH at 50-500 ng. [Ile7]LHRH, [Phe3]LHRH, and [Phe2]LHRH did not significantly increase plasma LH. Relative in vivo biological activities, calculated from dose (30-100 ng)-response curves of mGnRH-I, cGnRH-I, cGnRH-II, [Ile8]LHRH, [D-Ala6]LHRH, [Ala4]LHRH, [Leu8]LHRH, [Ile5]LHRH, [Ile7]LHRH, [Phe3]LHRH, and [Phe2]LHRH were 1.00, 1.40, 1.81, 1.50, 4.59, 1.90, 1.28, 1.56, 0.57, 0.67, and 0.57, respectively. These results demonstrate that avian LHRHs have higher biological activities than mammalian LHRH in the chicken. Furthermore, cGnRH-II is more potent than cGnRH-I, and [D-Ala6]LHRH has a very high activity while [Ile7]LHRH and [Phe2]LHRH have very low activities.

Plasma LH and androgen levels in the red-winged blackbird (Agelaius phoeniceus) treated with a potent GnRH analogue

1. Low doses of GnRH-A (0.01-0.10-1.0 micrograms) given during the annual testes growth period did not clearly affect plasma LH and androgen levels 10 min following the injection. 2. The first injection of high doses of GnRH-A (2.0-10.0-20.0 micrograms) markedly increased plasma LH and androgen levels measured 10 min following the injection. The increase in plasma LH level was dose-dependent and the maximal LH level was obtained with 10.0 micrograms of GnRH-A. 3. Impairment of the LH response to GnRH-A was assessed by comparing the first and the fourteenth injection of high doses of GnRH-A. Evidences of pituitary gland desensitization are reported since plasma LH levels were reduced following the fourteenth injection in all groups. 4. Plasma androgen levels following high doses of GnRH-A were not clearly affected in red-winged blackbirds.

Localization of avian LHRH-immunoreactive neurons in the hypothalamus of the domestic fowl, Gallus domesticus, and the Japanese quail, Coturnix coturnix

The localization of LHRH-containing perikarya and nerve fibers in the hypothalami of the domestic fowl and Japanese quail was investigated by means of the specific immunoperoxidase ABC method, using antisera against chicken LHRH-I ([Gln8]-LHRH), chicken GnRH-II ([His5-Trp7-Tyr8]-LHRH[2-10]) and mammalian LHRH ([Arg8]-LHRH). Chicken LHRH-I-immunoreactive perikarya were sparsely scattered in the nucleus preopticus periventricularis (POP), nucleus filiformis (FIL) and nucleus septalis medialis (SM), and in bilateral bands extending from these nuclei into the septal area in both species. A few reactive perikarya were also observed in the nucleus accumbens (Ac) and lobus parolfactorius (LPO). Numerous cLHRH-I-immunoreactive fibers were widely scattered in the preoptic, septal and tuberal areas, and were densely concentrated in the external layer of the median eminence and in organum vasculosum of the lamina terminalis (OVLT) in both species. Anti-mammalian LHRH serum cross-reacted weakly with perikarya and fibers immunoreactive to anti-cLHRH-I serum in normal chicken and quail. Anti-cGnRH-II[2-10] serum immunoreacted with magnocellular neurons distributed in the rostral end of the mesencephalon along the midline close to the nervus oculomotorius (N III). These perikarya were apparently different from cLHRH-I immunoreactive neurons. No immunoreactive cells and fibers against anti-cGnRH-II[2-10] were observed in the hypothalamus and median eminence of the chicken or quail. Anti-cGnRH-II[2-10] bound specifically with cGnRH-II.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of two kinds of chicken luteinizing hormone-releasing hormone (LH-RH), mammalian LH-RH and its analogs on the release of LH and FSH in Japanese quail and chicken

A newly isolated and characterized chicken luteinizing hormone-releasing hormone-II (chicken LH-RH-II, Miyamoto et al., 1984) had luteinizing hormone (LH) and follicle-stimulating hormone (FSH) releasing activity in vitro and in vivo in Japanese quail: the activity was almost equal to chicken LH-RH-I and mammalian LH-RH. These three LH-RHs induced the release of LH several times higher than that of FSH in vitro and also in vivo. No significant difference between chicken LH-RH-I and LH-RH-II was observed in LH releasing activity in vitro using chicken pituitary gland in the same incubating condition as in quail. Another experiment indicated that no synergism existed between chicken LH-RH-I and -II and that there was neither LH nor FSH releasing activity in [D-Phe2, Pro3, D-Phe6]-LH-RH or in mesotocin. However, the same potency as in the chicken LH-RH-II was observed in [D-Ala6, des-Gly10]-LH-RH ethylamide, a superactive analog in mammals. The results indicate that an avian adenohypophysis differs from a mammalian adenohypophysis in its responsiveness to LH-RH suggesting that an avian LH-RH receptor may have a lower specificity in "recognition" of LH-RH molecules than a mammalian LH-RH receptor has.