The role of ghrelin and some intracellular mechanisms in controlling the secretory activity of chicken ovarian cells

Expressions of ghrelin and GHSR-1a in the corpus luteum and the stimulatory effect of ghrelin on luteal function of pregnant sows

Studies have shown that ghrelin played direct actions in ovarian function, but the direct role of ghrelin in corpus luteum (CL) of pregnant sows has remained obscure. The study aimed to examine the expressions of ghrelin and its functional receptor (GHSR-1a) in the CL of sows during pregnancy, and evaluate the role of ghrelin in CL function of pregnant sows. Immunohistochemistry analysis showed that ghrelin and GHSR-1a are both predominantly localized in the luteal cells of pregnant sows CL. Strong immunoreactivity for ghrelin and GHSR-1a is detected at days 20 (early) and 50 (middle), but weak immunoreactivity is observed at days 90 (late) post mating. Similarly, there is a significant effect of pregnant phase on the expression (mRNA and protein) of ghrelin and GHSR-1a in the CL, with higher levels at days 20 (early) and 50 (middle), and lower values at 90 (late) post mating. In vitro, treatments of luteal cells with ghrelin (from 0.01 to 10 ng/mL) are promoted cell viability and P4 secretion in a dose-dependent manner. Ghrelin is also accelerated the LH-induced P4 secretion in luteal cells. Moreover, ghrelin is induced the release and mRNA expression of LH, and increased the release of prostaglandin (PG)E₂, but reduced the secretion of PGF_2α in luteal cells. In conclusion, the presences of ghrelin and GHSR-1a in the porcine CL during pregnancy, and the stimulatory effect of ghrelin on luteal cells suggest positive regulation by ghrelin in CL function of pregnant sows.

The Role of the Gastric Hormones Ghrelin and Nesfatin-1 in Reproduction

Ghrelin and nesfatin-1 are enteroendocrine peptide hormones expressed in rat X/A-like and human P/D1cells of the gastric mucosa. Besides their effect on food intake, both peptides are also implicated in various other physiological systems. One of these is the reproductive system. This present review illustrates the distribution of ghrelin and nesfatin-1 along the hypothalamus–pituitary–gonadal (HPG) axis, their modulation by reproductive hormones, and effects on reproductive functions as well as highlighting gaps in current knowledge to foster further research.

The Role of the Gastric Hormones Ghrelin and Nesfatin-1 in Reproduction

Ghrelin and nesfatin-1 are enteroendocrine peptide hormones expressed in rat X/A-like and human P/D1cells of the gastric mucosa. Besides their effect on food intake, both peptides are also implicated in various other physiological systems. One of these is the reproductive system. This present review illustrates the distribution of ghrelin and nesfatin-1 along the hypothalamus-pituitary-gonadal (HPG) axis, their modulation by reproductive hormones, and effects on reproductive functions as well as highlighting gaps in current knowledge to foster further research.

The Role of the Gastric Hormones Ghrelin and Nesfatin-1 in Reproduction

Ghrelin and nesfatin-1 are enteroendocrine peptide hormones expressed in rat X/A-like and human P/D1cells of the gastric mucosa. Besides their effect on food intake, both peptides are also implicated in various other physiological systems. One of these is the reproductive system. This present review illustrates the distribution of ghrelin and nesfatin-1 along the hypothalamus–pituitary–gonadal (HPG) axis, their modulation by reproductive hormones, and effects on reproductive functions as well as highlighting gaps in current knowledge to foster further research.

Involvement of obestatin, cyclin-dependent kinase and protein kinase C in control of feline ovarian cell viability and hormones release

The aim of our in vitro study was to understand the role of obestatin, cyclin-dependent kinase (CDK) and protein kinase C (PKC) in the control of basic feline ovarian cell functions (viability, ovarian hormones release), as well as the role of protein kinases in mediating the effect of obestatin on these processes. For this purpose, we analyzed the effect of obestatin (0, 10 and 100 ng/mL) alone or in combination with CDK blocker olomoucine (100 ng/mL) or PKC blocker calphostin-c (100 ng/mL) on cultured feline ovarian fragments or granulosa cells. The release of progesterone (P4), testosterone (T) and estradiol (E2) by isolated ovarian follicular fragments were evaluated by ELISA. Granulosa cell viability was analysed using the Trypan blue exclusion test. It was observed that the addition of obestatin alone significantly increased the granulosa cell viability (at dose 100 ng/mL), promoted the release of P4 (at all doses added) and IGF-I (at dose 100 ng/mL) but decreased T (at all doses added). E2 output was below the detection limit in all groups. The addition of either olomoucine or calphostin-c reduced cell viability, P4, T and IGF-I release. Both olomoucine and caplhostin-c inverted the stimulatory effect of obestatin on granulosa cell viability and were able to prevent stimulatory action of obestatin on ovarian cell viability and on hormone and growth factor release and change it to an inhibitory action. These observations show that obestatin can directly regulate (mostly promote) basal feline ovarian cell functions (hormone release and viability). The inhibitory action of CDK and PKC blockers on these functions suggests, that both CDK and PKC can be promoters of ovarian cell viability and steroidogenesis in cats. Furthermore, the ability of both CDK and PKC to prevent olomoucine action demonstrates that obestatin action on the feline ovary could be mediated by these kinases.

Metabolic status and ghrelin regulate plasma levels and release of ovarian hormones in layer chicks

The aim of the present study was to examine the role of nutritional status, the metabolic hormone ghrelin and their interrelationships in the control of chicken hormones involved in the regulation of reproduction. For this purpose, we identified the effect of food deprivation, administration of ghrelin 1-18 and their combination on plasma levels of testosterone (T), estradiol (E), arginine-vasotocin (AVT) and growth hormone (GH) as well as the release of these hormones by isolated and cultured ovarian fragments. It was observed that food deprivation reduces plasma T and E and increases plasma AVT and GH levels. Food restriction also reduced the amount of E produced by isolated ovaries, but it did not affect the ovarian secretion of T and AVT. No ovarian GH secretion was detected. Ghrelin administered to ad libitum fed chickens did not affect plasma T and E levels, but it did increase plasma GH and AVT concentrations. Moreover, it partially prevented the effect of food deprivation on plasma E and AVT levels, but not on T or GH levels. Ghrelin administration to control birds promoted ovarian T, but not E or AVT release and reduced T and no other hormonal outputs in birds subjected to food restriction. Our results (1) confirmed the ovarian origin of the main plasma T and E and the extra-ovarian origin of the main blood AVT and GH; (2) showed that food deprivation-induced suppression of reproduction may be caused by suppression of T and E and the promotion of AVT and GH release; (3) suggest the involvement of ghrelin in control chicken E, AVT and GH output; and (4) indicates that ghrelin can either mimic or modify the effect of the intake of low calories on chicken plasma and ovarian hormones, i.e. it can mediate the effect of metabolic state on hormones involved in the control of reproduction.

Comparison of the effects of human and chicken ghrelin on chicken ovarian hormone release

The aim of the present experiments was to examine the species-specific and cell-specific effects of ghrelin on chicken ovarian hormone release. For this purpose, we compared the effects of chicken and human ghrelin on the release of estradiol (E), testosterone (T), progesterone (P) and arginine-vasotocin (AVT) by cultured fragments of chicken ovarian follicles and on the release of T and AVT by cultured ovarian granulosa cells. In cultured chicken ovarian fragments, both human and chicken ghrelin promoted E release. T output was stimulated by chicken ghrelin but not by human ghrelin. No effect of either human or chicken ghrelin on P release was observed. Human ghrelin promoted but chicken ghrelin suppressed AVT release by chicken ovarian fragments. In cultured ovarian granulosa cells, human ghrelin inhibited while chicken ghrelin stimulated T release. Both human and chicken ghrelin suppressed AVT output by chicken granulosa cells. These data confirm the involvement of ghrelin in the control of ovarian secretory activity and demonstrate that the effect of ghrelin is species-specific. The similarity of avian ghrelin on avian ovarian granulosa cells and ovarian fragments (containing both granulosa and theca cells) suggests that ghrelin can influence chicken ovarian hormones primarily by acting on granulosa cells.

Reproduction in hens: is testosterone necessary for the ovulatory process?

Avian reproduction entails complex endocrine interactions at the hypothalamic and ovarian levels. The initiation of the reproductive season is due to the reduction in melatonin and GnIH production as day length increases. The decline in GnIH permits GnRH and gonadotropin secretion starting follicle growth. Follicular steroids stimulate sexual activity and have important roles for the induction of ovulation. Progesterone (P4) is an inductor of the preovulatory surge of LH, while estradiol (E2) acts as a hypothalamic primer to allow P4 receptor development, as well as a stimulator of yolk production. Conversely, the role of testosterone (T) has been more controversial; however, there is now enough evidence, which demonstrates an essential action of T in the ovulatory process. For instance, blockage of endogenous T, by passive or active immunization or by the use of a specific antagonist of T, inhibits ovulation and the preovulatory surges of P4 and LH. This information is supported by the fact that there is a positive correlation between the occurrences of the T preovulatory surge and those of P4 and LH, in which the absence of T caused a lack of P4 and LH increase in almost 90% of the cases. Additionally, it has been observed that T has a paracrine action within the ovary, to promote P4 secretion by granulosa cells from the larger follicles. This has been related with an increased mRNA expression of StAR and P450scc enzymes, which are essential for P4 production, as well as with LH-R mRNA expression in granulosa cells of preovulatory follicles, an effect that should enhance the positive feedback between P4 and LH necessary for ovulation. Lastly, endocrine activity of hierarchical follicles occurs as a result of a complex interaction between the larger follicles (F1-F3) and the smaller follicles (F4-F6), which is necessary to achieve an adequate preovulatory milieu.

Structure and physiological actions of ghrelin

Ghrelin is a gastric peptide hormone, discovered as being the endogenous ligand of growth hormone secretagogue receptor. Ghrelin is a 28 amino acid peptide presenting a unique n-octanoylation modification on its serine in position 3, catalyzed by ghrelin O-acyl transferase. Ghrelin is mainly produced by a subset of stomach cells and also by the hypothalamus, the pituitary, and other tissues. Transcriptional, translational, and posttranslational processes generate ghrelin and ghrelin-related peptides. Homo- and heterodimers of growth hormone secretagogue receptor, and as yet unidentified receptors, are assumed to mediate the biological effects of acyl ghrelin and desacyl ghrelin, respectively. Ghrelin exerts wide physiological actions throughout the body, including growth hormone secretion, appetite and food intake, gastric secretion and gastrointestinal motility, glucose homeostasis, cardiovascular functions, anti-inflammatory functions, reproductive functions, and bone formation. This review focuses on presenting the current understanding of ghrelin and growth hormone secretagogue receptor biology, as well as the main physiological effects of ghrelin.

The role of thyroid hormones in regulation of chicken ovarian steroidogenesis

In all vertebrates, including birds, the normal development of the ovary and ovarian follicles is under the regulatory influence of hormones produced by the reproductive axis. In recent years, it has become clear that in birds an adequate level of thyroid hormones (THs), i.e. thyroxine (T4) and triiodothyronine (T3), in blood circulation is of primary importance for normal female reproductive functions. In avian species, characterized by seasonal reproduction, THs are involved in the photoperiodic regulation of reproduction acting at the mediobasal hypothalamus. In domestic fowl, where the seasonality of reproduction has been eliminated, the role of THs in ovarian function is not fully elucidated. Recent studies have revealed that ovarian follicles of the laying hen express mRNAs of TH nuclear receptors (TRα and TRβ0) as well as integrin (αVβ3) plasma membrane receptors, indicating genomic and nongenomic action of THs in the chicken ovary. In vivo experiments carried out on laying hens have showed that the bolus injection of T3 decreases levels of luteinizing hormone (LH) and estradiol (E2) in blood, and a hyperthyroid state evoked by administration of T3 for few days diminishes LH, E2 and progesterone (P4) levels, reduces the weight of the ovary, induces atresia of preovulatory follicles and eventually causes stoppage of egg laying. In vitro studies have demonstrated that T3 decreases E2 secretion from white nonhierarchical follicles and the theca layer of yellow preovulatory follicles, while on the other hand, it elevates P4 production from the granulosa layer of these follicles. These effects have been associated with steroidogenic enzyme expression and cyclic AMP synthesis. This review summarizes the current knowledge concerning the role of THs in regulation of steroidogenesis in chicken ovarian follicles.

The involvement of SIRT1 and transcription factor NF-κB (p50/p65) in regulation of porcine ovarian cell function

The role of either mTOR system/enzyme sirtuin1 (SIRT1) or transcription factor NF-κB in the direct control of ovarian function has not been estabished. The aim of our in vitro experiments was to examine the involvement of SIRT1 and the p65 and p50 subunits of NFκB in control of porcine ovarian granulosa cell functions and the interrelationships between SIRT1, NFκB (p65, p50) 30 and FSH in the ovary. Monolayers of primary granulosa cells were transfected with gene constructs encoding either SIRT1 or p65 and p50, and thereafter cultured with, or without, addition of FSH. The accumulation of markers of proliferation (cyclin B1 and cyclin-dependent protein kinase Cdc2/p34) and proteins p50, p65 and SIRT1 in the cells was detected by using SDS-PAGE/Western immunoblotting and immunocytochemistry. The secretion of progesterone (P4) and insulin-like growth factor I (IGF-I) was measured by using radioimmunoassay. It was observed that transfection of cells with a SIRT1 gene construct promoted accumulation of proliferation markers, Cdc2/p34, cyclin B1, decreased accumulation of p50 and p65 and stimulated release of P4 and IGF-I. Co-transfection of cells with cDNA p50 and cDNA p65 enhanced the accumulation of SIRT1 and the release of P4 but did not influence the release of IGF-I. Adding FSH to the culture medium stimulated accumulation of both subunits of NF-κB, as well as accumulation of Cdc2/p34, cyclin B1 and release of both P4 and IGF-I. The ability of FSH to promote NF-κB accumulation, the similarity of the main effects of FSH, SIRT1 and NF-κB, as well as the inability of NF-κB to substantially modify the the majority of FSH effects suggest that SIRT1/NF-κB system could be a mediator of FSH action on ovarian cell functions. On the other hand, SIRT1 was able to inhibit NF-κB and to change stimulatory the effect of FSH on NF-κB from stimulatory to inhibitory. This could suggest the existence of negative feedback control of FSH/NF-κB system by high amounts of SIRT1. Our observations (1) confirm the previous data on proliferation, P4 and IGF-I release in ovarian cells and their up-regulation by FSH, (2) demonstrate the presence of SIRT1, NF-κB/p50 and NF-κB/p65 in these cells, (3) show for the first time the involvement of SIRT1 and NF-κB in direct control of proliferation and secretory activity of ovarian cells, (4) represent the first data on interrelationships between FSH, SIRT1 and NF-κB within the ovary.

Role of ghrelin on estrogen and progesterone secretion in the adult rat ovary during estrous cycle

The objective of the present study was to evaluate the effects of ghrelin on the concentrations of estrogen (E(2)) and progesterone (P(4)) in serum and the mRNA expression of estrogen receptor beta (ER(β)) and progesterone receptor (PR(A+B)) in ovary in rats during estrous cycle. Adult female Sprague Dawley rats were intracerebroventricularly (i.c.v.) injected with 3 nmol ghrelin during the estrous cycle, and sacrificed 15 min later. Blood samples and ovaries were collected. The concentrations of serum E(2) and P(4) were measured by radioimmunoassay, while the amount of ER(β) and PR(A+B) mRNA was assessed by real-time quantitative PCR. Our studies showed that ghrelin could significantly reduce the serum concentration of E(2) throughout the estrous cycle (P < 0.05), the serum level of P(4) (P < 0.05), and the amount of ER(β) mRNA during metestrus (P < 0.05). Meanwhile, the amount of PR(A+B) mRNA was only reduced during diestrus (P < 0.05). Overall, our present findings provide the first evidence that i.c.v. injection of ghrelin could reduce the serum concentration of E(2) and P(4) and the level of ER(β) and PR(A+B) mRNA expression, supporting the role of ghrelin in reproduction.

Ghrelin: an emerging player in the regulation of reproduction in non-mammalian vertebrates

The endocrine regulation of vertebrate reproduction is achieved by the coordinated actions of multiple endocrine factors mainly produced from the brain, pituitary, and gonads. In addition to these, several other tissues including the fat and gut produce factors that have reproductive effects. Ghrelin is one such gut/brain hormone with species-specific effects in the regulation of mammalian reproduction. Recent studies have shown that ghrelin and ghrelin receptor mRNAs, and protein are expressed in the ovary and testis of mammals, indicating a direct effect for ghrelin in the control of reproduction. Ghrelin regulates mammalian reproduction by modulating hormone secretion from the brain and pituitary, and by acting directly on the gonads to influence reproductive tissue development and steroid hormone release. Based on the studies reported so far, ghrelin seems to have a predominantly inhibitory role on mammalian reproduction. The presence of ghrelin and ghrelin receptor has been found in the brain, pituitary and gonads of several non-mammalian vertebrates. In contrast to mammals, ghrelin seems to have a stimulatory role in the regulation of non-mammalian reproduction. The main objective of this review is to do a perspective analysis of the comparative aspects of ghrelin regulation of reproduction.

Ghrelin in female and male reproduction

Ghrelin and one of its functional receptors, GHS-R1a (Growth Hormone Secretagogue Receptor 1a), were firstly studied about 15 years. Ghrelin is a multifunctional peptide hormone that affects several biological functions including food intake, glucose release, cell proliferation… Ghrelin and GHS-R1a are expressed in key cells of both male and female reproductive organs in several species including fishes, birds, and mammals suggesting a well-conserved signal through the evolution and a role in the control of fertility. Ghrelin could be a component of the complex series of nutrient sensors such as adipokines, and nuclear receptors, which regulate reproduction in function of the energy stores. The objective of this paper was to report the available information about the ghrelin system and its role at the level of the hypothalamic-pituitary-gonadal axis in both sexes.

The avian proghrelin system

To understand how the proghrelin system functions in regulating growth hormone release and food intake as well as defining its pleiotropic roles in such diverse physiological processes as energy homeostasis, gastrointestinal tract function and reproduction require detailed knowledge of the structure and function of the components that comprise this system. These include the preproghrelin gene that encodes the proghrelin precursor protein from which two peptide hormones, ghrelin and obestatin, are derived and the cognate receptors that bind proghrelin-derived peptides to mediate their physiological actions in different tissues. Also key to the functioning of this system is the posttranslational processing of the proghrelin precursor protein and the individual peptides derived from it. While this system has been intensively studied in a variety of animal species and humans over the last decade, there has been considerably less investigation of the avian proghrelin system which exhibits some unique differences compared to mammals. This review summarizes what is currently known about the proghrelin system in birds and offers new insights into the nature and function of this important endocrine system. Such information facilitates cross-species comparisons and contributes to our understanding of the evolution of the proghrelin system.

Role of ghrelin in regulating rabbit ovarian function and the response to LH and IGF-I

The aim of these in vivo and in vitro studies was to examine the role of ghrelin in the control of plasma hormone concentrations, the proliferation, apoptosis and secretory activity of ovarian granulosa cells and the response of these cells to hormonal treatments. Female rabbits were injected with ghrelin (10 microg/animal/day for one week before ovulation induced by 25IU PMSG and 0.25IU LHRH). On the day of ovulation, blood samples were collected and analyzed for concentrations of progesterone (P(4)), testosterone (T), estradiol (E(2)), estrone-sulphate (ES), insulin-like growth factor I (IGF-I) and leptin (L) by RIA. Some control and ghrelin-treated animals were killed in the periovulatory period, their ovaries were weighed and granulosa cells were isolated and cultured for 2d. Cell proliferation (expression of PCNA) and apoptosis (expression of TdT) were evaluated by immunocytochemistry and TUNEL respectively. Secretion of P(4), T, E(2), IGF-I, and prostaglandin F (PGF) by granulosa cells cultured with and without LH or IGF-I (1, 10 or 100 ng/ml medium) was assessed by RIA. The remaining control and treated animals were kept until parturition, while the number, viability and body weight of pups were recorded. Ghrelin treatment increased rabbit plasma T and decreased ES concentrations but did not influence P(4), E(2), IGF-I or L. Granulosa cells from ghrelin-treated animals showed higher expression of PCNA and lower expression of TdT, than those from control animals. They also secreted less P(4), T, E(2), IGF-I and PGF than granulosa cells from untreated animals. Treatment of cultured granulosa cells with ghrelin (1, 10 or 100 ng/ml medium) either increased (at 1 ng/ml) or decreased (at 10 ng/ml) P(4) secretion, increased (at 100 ng/ml) or decreased (at 10 ng/ml) IGF-I secretion, decreased T (at 1 and 10 ng/ml) and OT (at 1 ng/ml) secretion, and increased (at 100 ng/ml) PGF secretion. LH treatment of cells from control animals stimulated P(4) (at 1 and 10 ng/ml), E(2), and IGF-I (both at 10 and 100 ng/ml), but not T secretion. IGF-I stimulated P(4) (all concentrations) and PGF (at 100 ng/ml) but suppressed T (all concentrations) and E(2) (at 1 and 10 ng/ml) secretion. Pre-treatment of animals with ghrelin stimulated, suppressed or even reversed subsequent LH and IGF-I effects on hormone secretion by cultured granulosa cells. Ghrelin injections did not affect ovarian weight or the number and body mass of pups born, although pup mortality was significantly lower in ghrelin-treated than in control mothers. These observations suggest that ghrelin is involved in the control of ovarian cell proliferation, apoptosis and secretion of hormones, as well as in the response of these cells to physiological stimulators such as LH and IGF-I.

Morphometrical and intracellular changes in rat ovaries following chronic administration of ghrelin

The aim of our investigation was to examine the influence of chronic administration of ghrelin on the rat ovarian state. Morphometrical and intracellular changes in the ovary of 35-d female Wistar rats after sc injection of 1 nmol of ghrelin for 10 consecutive days were studied. Control animals (n=10) were injected with normal saline using similar method. The ovaries were collected on days 1 and 6 after last injection from each group and subjected to light microscopic morphometric and electron microscopic analysis. It was demonstrated that the number of corpora lutea was significantly lower and the number of ovarian follicles was higher in the treated group on days 1 and 6, than in control (P<0.01). Moreover, the mean diameter of each follicle, corpora lutea, luteal cell, theca layer, oocyte and zona plucida, but not of granulosa layer, as well as the whole ovarian volume were significantly lower in the treated animals at days 1 and 6 (P<0.05). Electron microscopic analysis also indicated some intracellular changes associated with apoptosis and cell death such as presence of secondary lysosome, apoptotic bodies, nuclear chromatin condensation as well as margination, nuclear segmentation and vacuolization of cytoplasm of granulosa and theca cells. Our observations provides novel evidences for inhibitory influence of ghrelin on rat ovarian structures and, therefore, for the role of ghrelin as suppressor of female reproductive system.

The effect of obestatin on porcine ovarian granulosa cells

The aim of our in vitro experiments was to investigate the role of obestatin, a newly discovered metabolic hormone produced in the stomach and other tissues, in the direct control of ovarian cell proliferation, apoptosis and secretion. Porcine granulosa cells were cultured in the presence of obestatin (0, 1, 10 and 100ng/ml medium). The expression of intracellular peptides associated with proliferation (PCNA, cyclin B1, MAP kinase), as well as markers of apoptosis (Bax, p53, Caspase 3), were detected using immunocytochemistry and Western immunoblotting. Secretion of progesterone (P4), testosterone (T) and estradiol (E2) was measured by EIA. Addition of obestatin (1-100ng/ml) to the culture medium significantly stimulated the expression of PCNA and resulted in an increase in expression of cyclin B1 and MAPK. It also significantly increased the percentage of cells containing the apoptotic and anti-proliferating peptides p53, Caspase 3 and Bax. At 10 and 100ng/ml, obestatin promoted the secretion of P4, but not T or E2. Our results are the first demonstration that obestatin directly controls porcine ovarian cell functions: it can stimulate proliferation (accumulation of rPCNA, cyclin B1 and MAPK), apoptosis (expression of p53, Caspase 3 and Bax) and the secretion of progesterone.

Expression and localization of growth hormone and its receptors in the chicken ovary during sexual maturation

Roles of pituitary growth hormone (GH) in female reproduction are well established. Autocrine and/or paracrine actions of GH in the mammalian ovary have additionally been proposed, although whether the ovary is an extra-pituitary site of GH expression in the laying hen is uncertain. This possibility has therefore been assessed in the ovaries of Hy-Line hens before (between 10-16 weeks of age) and after (week 17) the onset of egg laying. Reverse transcription/polymerase chain reaction (RT-PCR) analysis has consistently detected a full-length (690 bp) pituitary GH cDNA in ovarian stroma from 10 weeks of age, although GH expression is far lower than that in the pituitary gland or hypothalamus. GH mRNA is also present in small (>1-4 mm diameter) follicles after their ontogenetic appearance at 14 weeks of age and in all other developing follicles after 16 weeks of age (>4-30 mm diameter). Immunoreactivity for GH is similarly present in the ovarian stroma from 10 weeks of age and in small (<4 mm diameter) and large (>4-30 mm) follicles from 14 and 16 weeks of age, respectively. The relative intensity of GH staining in the ovarian follicles is consistently greater in the granulosa cells than in the thecal cells and is comparable with that in the follicular epithelium. A 321-bp fragment of GH receptor (GHR) cDNA, coding for the intracellular domain of the receptor, has also been detected by RT-PCR in the ovary and is present in stromal tissue by 10 weeks of age, in small follicles (<4 mm diameter) by 14 weeks of age, and in larger follicles (>4-30 mm diameter) from 16 weeks. GHR immunoreactivity has similarly been detected, like GH, in the developing ovary and in all follicles and is more intense in granulosa cells than in the theca interna or externa. The expression and location of the GH gene therefore parallels that of the GHR gene during ovarian development in the laying hen, as does the appearance of GH and GHR immunoreactivity. These results support the possibility that GH has autocrine and/or paracrine actions in ovarian function prior to and after the onset of lay in hens.

Ghrelin ligand-receptor mRNA expression in hypothalamus, proventriculus and liver of chicken (Gallus gallus domesticus): Studies on ontogeny and feeding condition

We report here the ontogenic changes in mRNA expression of chicken ghrelin (cGhrelin) and its receptor (cGHS-R1a) and the effects of fasting and refeeding on cGhrelin and cGHS-R1a mRNAs expression in 30-day-old broiler chickens. The level of cGhrelin mRNA in the proventriculus was low from embryo--day 15 (E15) to E19, but dramatically increased at post-hatching-day 2 (P2), then remained constant until P30 and followed by a significant decrease at P44 when there was a diet transition at P31 and thereafter. The decreased level was reversed at P58. Hypothalamic cGhrelin mRNA and proventriculus and hepatic cGHS-R1a mRNA were significantly increased at P30. The cGhrelin mRNA level in the proventriculus significantly increased in response to either 12-h or 36-h fasting but did not decrease after subsequent 12-h refeeding. The level of cGHS-R1a mRNA in the proventriculus was significantly upregulated in response to a 12-h fast but not to a 36-h fast and returned to the control level upon 12-h refeeding. Interestingly, it was apparent that the mRNA levels of both cGhrelin and cGHS-R1a in the liver were upregulated in response to fasting in a time-dependent manner and returned to the control level with subsequent refeeding. These results suggest that the expression pattern of ghrelin and its receptor mRNAs distinctly change in tissues depending on ontogenic stages and feeding states in poultry.