A role of pituitary adenylate cyclase activating polypeptide (PACAP) as a regulator of paracrine interactions between folliculo-stellate cells and gonadotropes through the control of activin-follistatin interactions

Pituitary folliculo-stellate (FS) cells were able to modify the effect of activin-A on gonadotropes through the paracrine factor, follistatin. The present study was aimed to examine whether a hypothalamic peptide, pituitary adenylate cyclase activating polypeptide (PACAP), could be a regulator of this paracrine interaction. Co-culture of FS cell-originated cell line TtT/GF cells with rat anterior pituitary cells showed faint inhibitory effect on the stimulatory action of activin-A on FSH secretion. When PACAP was added to the culture during the co-culture period, however, the presence of TtT/GF cells caused significant suppression of the effect of activin-A on FSH secretion. Conditioned-media (CM) from TtT/GF cells, obtained by incubation of TtT/GF cells in the presence or absence of PACAP, were next added to the cultures of anterior pituitary cells alone. CM from TtT/GF cells without PACAP treatment revealed slight, but not significant, suppressive effect on activin-induced increases in FSH secretion and the percentage of FSH cells. Meanwhile, CM from PACAP-treated TtT/GF cells attenuated both effects of activin-A. Furthermore, the inhibitory effect of the CM was neutralized when follistatin antibody was present in the culture. These results suggest that PACAP is able to regulate the paracrine action of FS cells on pituitary gonadotropes. Besides expressing direct actions on pituitary endocrine cells, PACAP may have roles as a regulator of cell-to-cell interactions within the pituitary gland.     

Pituitary function in the acute phase response in domestic farm animals: cytokines,prostaglandins, and secretion of ACTH

Contained in this report is a review of available data on pituitary cytokines in domestic species of agricultural importance. The concept is advanced that the pituitary gland is essential to appropriate generation of host defense mechanisms and thus should be considered among other tissues contributing to innate immunity. The functions of these intrapituitary cytokines, principally IL-6, are discussed in the context of potential regulation of the pituitary-adrenal axis (ACTH secretion) via intrapituitary PGE₂ generation during the acute-phase response to infectious/inflammatory stimuli. Data from other species are cited as appropriate for comparative purposes and elaboration of proposed mechanisms. However, the scope of the review is not intended to comprehensively cover the vast literature on proinflammatory cytokines and prostaglandins generated peripherally and centrally during host responses to inflammatory stimuli.     

Expression of inflammatory-related factors in porcine anterior pituitary-derived cell line

Recent studies have shown that undifferentiated stem cells act as immunomodulators. To investigate the immunomodulatory function of the progenitor cells of the anterior pituitary gland, we attempted to establish a stem/progenitor cell line from the porcine anterior pituitary gland, and to detail its inflammatory cytokine expression. A cloned cell line from the porcine anterior pituitary gland was established and was designated as the porcine anterior pituitary-derived cell line (PAPC). PAPC expressed the mRNA of Nanog and Oct-4, and showed positive immunoreactivity for beta-catenin and Hes1 in its nucleus. PAPC grew stably by repeated passage and rapidly in the EGF and bFGF containing medium. RT-PCR showed that PAPC expressed mRNA of IL-1alpha, IL-6, IL-12, IL-15, IL-18 and TLR4. PAPC expressed S100alpha and IL-18 protein, which was localized in the marginal epithelial cells of Rathke's pouch. These results suggest that PAPC is a stem/progenitor cell and may regulate anterior pituitary cell function through an immuno-endocrine pathway.     

Colloid in the anterior pituitary of helmet guinea fowl (<Emphasis Type="Italic">Numida meleagris galeata</Emphasis>): Morphometric analysis and pattern of occurrence in relation to apoptosis

Colloidal accumulations in the pars distalis of helmet guinea fowls at various ages from 1 to 450 days were examined by Periodic acid-Schiff reaction, immunohistochemistry and electron microscopy. Round, ovoid and elongated colloids were observed. Colloids (69.5 ± 2.997) with 0.169 ± 0.014 μm mean diameter were already present in a 1-day-old bird. Numerous colloids were encountered in 450 days old birds (2931.333 ± 29.847) with 2.263 ±  0.078 μm mean diameter of round colloids. A significant difference in the mean colloidal number and diameter between young and adult birds was observed. In young birds (aged 1–30 days) both Periodic acid-Schiff reaction positive colloids and S-100 positive folliculostellate (FS) cells were found to appear first on or near the posterolateral region. In adult birds, FS cells were found to completely surround the colloids. We examined the biochemical components of colloids and the relationship with apoptosis by immunohistochemistry. Results showed that the colloids are composed of clusterin protein. Apoptotic cells detected by single stranded DNA (ssDNA) were abundant and localized preferentially near colloids. To define clearly the type of cells undergoing apoptosis in the anterior pituitary, we performed electron microscopy. Numerous endocrine cells at different stages of apoptosis were found engulfed by FS cells that were in close association with the colloidal accumulations. The occurrence of extremely large number of colloids in relation to apoptotic profiles in anterior pituitary of helmet guinea fowl is discussed.     

The anterior pituitary gland: lessons from livestock

There has been extensive research of the anterior pituitary gland of livestock and poultry due to the economic (agricultural) importance of physiological processes controlled by it including reproduction, growth, lactation and stress. Moreover, farm animals can be biomedical models or useful in evolutionary/ecological research. There are for multiple sites of control of the secretion of anterior pituitary hormones. These include the potential for independent control of proliferation, differentiation, de-differentiation and/or inter-conversion cell death, expression and translation, post-translational modification (potentially generating multiple isoforms with potentially different biological activities), release with or without a specific binding protein and intra-cellular catabolism (proteolysis) of pituitary hormones. Multiple hypothalamic hypophysiotropic peptides (which may also be produced peripherally, e.g. ghrelin) influence the secretion of the anterior pituitary hormones. There is also feedback for hormones from the target endocrine glands. These control mechanisms show broadly a consistency across species and life stages; however, there are some marked differences. Examples from growth hormone, prolactin, follicle stimulating hormone and luteinizing hormone will be considered. In addition, attention will be focused on areas that have been neglected including the role of stellate cells, multiple sub-types of the major adenohypophyseal cells, functional zonation within the anterior pituitary and the role of multiple secretagogues for single hormones.     

Differential expression of myostatin and its receptor in the porcine anterior pituitary gland

Myostatin (MSTN), known as growth and differentiation factor 8 (GDF-8), is a member of the transforming growth factor β (TGF-β) superfamily that negatively regulates skeletal muscle mass. Myostatin binds with high affinity to the receptor serine threonine kinase activin receptor type IIB (ActRIIB). Activins that also belong to the TGF-β superfamily, stimulate follicle-stimulating hormone production in gonadotrophs and suppress growth hormone and adrenocorticotropic hormone production in somatotrophs and corticotrophs, respectively. The aim of the present paper was therefore to clarify the endocrine action of MSTN in adenohypophysis. The present study details the expression and cellular localization of MSTN and ActRIIB in porcine anterior pituitary gland. The mRNA of MSTN and ActRIIB was consistently expressed in RT-PCR. Immunohistochemistry of MSTN and specific hormones showed that MSTN localized in thyrotrophs and gonadotrophs, in which most of the MSTN immunoreactive cells were identified as thyrotrophs. The immunostaining of ActRIIB was restricted to corticotrophs. These results indicate that MSTN was mainly produced in thyrotrophs and its receptor, ActRIIB, was restrictively contained in corticotrophs. Interestingly, thyrotrophs immunoreactive for MSTN were frequently close to corticotrophs immunoreactive for ActRIIB. The present study suggests that MSTN from thyrotrophs may regulate corticotroph function as a paracrine mediator among the porcine anterior pituitary cells.     

生长激素自分泌作用机制研究进展

生长激素(growth hormone,GH)是由脑垂体前叶分泌的一种多肽激素,它作为一种特殊的生物活性蛋白促进机体合成代谢和蛋白质合成。GH传统的作用机制是垂体产生GH开始作用于膜受体,然后刺激肝脏胰岛素生长因子(insulin-like growth factor-1,IGF-1)生成,进而影响机体多个器官发育。近年的研究表明,GH除了内分泌作用途径,还可通过自分泌及旁分泌途径产生生物学效应。GH自分泌可以参与调控雄性和雌性动物生殖功能;GH自分泌对肌肉组织的代谢和生长也有重要影响,另外,GH自分泌与肿瘤的发生有密切的关系,其在一定程度上可以促进部分癌细胞的增殖,分化与迁移。通过对GH自分泌作用机制的研究有望发现自分泌GH在动物体内新的生物学作用,也有助于研究并治疗GH自分泌异常引发的相关疾病。     

Expression of genes related to corticotropin production and glucocorticoid feedback in corticotroph adenomas of dogs with Cushing's disease

Cushing's disease caused by pituitary corticotroph adenoma is a common endocrine disease in dogs. A characteristic biochemical feature of corticotroph adenomas is their relative resistance to negative feedback by glucocorticoids. In this study, we examined gene expression related to adrenocorticotropic hormone (ACTH) production and secretion, and the negative feedback by glucocorticoids in canine corticotroph adenoma. We used resected corticotroph adenomas from 10 dogs with Cushing's disease. In order to investigate the alteration of gene expression between corticotroph adenoma and normal corticotrophic cells, ACTH-positive cells in the anterior lobe were microdissected using a laser-capture microdissection system, and mRNA levels of proopiomelanocortin (POMC), corticotropin releasing hormone receptor 1 (CRHR1), glucocorticoid receptor (GR), mineralocorticoid receptor (MR), and 11 beta hydroxysteroid dehydrogenase (11HSD) type 1 and type 2 were determined using real-time RT-PCR. POMC, CRHR1, and 11HSD2 mRNA levels in corticotroph adenoma were greater than those in normal corticotrophic cells (POMC, 5.5-fold; CRHR1, 4.9-fold; 11HSD2, 4.2-fold, P<0.01, respectively). MR and 11HSD1 mRNA levels in corticotroph adenoma were lower than those in normal corticotrophic cells (MR, 2.2-fold; 11HSD1, 2.9-fold, P<0.01, respectively). GR mRNA levels did not differ between corticotroph adenoma and normal corticotrophic cells. Our results may help to understand the increased ACTH production and the resistance to negative feedback suppression by glucocorticoids in canine corticotroph adenomas. These changes in gene expression may have a role in the growth of canine corticotroph adenoma, and help elucidate the pathophysiology of dogs with Cushing's disease.     

Pituitary effects of steroid hormones on secretion of follicle-stimulating hormone and luteinizing hormone

Steroid hormones have a profound influence on the secretion of the gonadotropins, follicle-stimulating hormone (FSH) and luteinizing hormone (LH). These effects can occur as a result of steroid hormones modifying the secretion of gonadotropin-releasing hormone (GnRH) from the hypothalamus, or a direct effect of steroid hormones on gonadotropin secreting cells in the anterior pituitary gland. With respect to the latter, we have shown that estradiol increases pituitary sensitivity to GnRH by stimulating an increase in expression of the gene encoding the GnRH receptor. Since an estrogen response element (ERE) has not been identified in the GnRH receptor gene, this effect appears to be mediated by estradiol stimulating production of a yet to be identified factor that in turn enhances expression of the GnRH receptor gene. However, the importance of estradiol for enhancing pituitary sensitivity to GnRH during the periovulatory period is questioned because an increase in mRNA for the GnRH receptor precedes the pre-ovulatory rise in circulating concentrations of estradiol. In fact, it appears that the enhanced pituitary sensitivity during the periovulatory period may occur as a result of a decrease in concentrations of progesterone rather than due to an increase in concentrations of estradiol. Estradiol also is capable of altering secretion of FSH and LH in the absence of GnRH. In a recent study utilizing cultured pituitary cells from anestrous ewes, we demonstrated that estradiol induced a dose-dependent increase in secretion of LH, but resulted in a dose-dependent decrease in the secretion of FSH. We hypothesized that the discordant effects on secretion of LH and FSH might arise from estradiol altering the production of some of the intrapituitary factors involved in synthesis and secretion of FSH. To examine this hypothesis, we measured amounts of mRNA for activin B (a factor known to stimulate synthesis of FSH) and follistatin (an activin-binding protein). We found no change in the mRNA for follistatin after treatment of pituitary cells with estradiol, but noted a decrease in the amount of mRNA for activin B. Thus, the inhibitory effect of estradiol on secretion of FSH appears to be mediated by its ability to suppress the expression of the gene encoding activin.     

Ovine luteinizing hormone: isoforms in the pituitary during the follicular and luteal phases of the estrous cycle and during anestrus.

Pituitaries were collected from late follicular phase (n = 5), mid-luteal phase (n = 5), and anestrous ewes (n = 4) to assess changes in intrapituitary LH heterogeneity at selected reproductive states. After homogenization, an aliquot of each pituitary extract was desalted by flow dialysis against water and chromtofocused on a pH 10.5 to 4.0 gradient. Concentrations of LH in pituitary extracts and chromatofocusing fractions were determined by RIA. The LH in pituitary extracts resolved into 13 isoforms during chromatofocusing, which were coded with letters beginning with the most basic isoform. Follicular and mid-luteal phase ewes exhibited similar distributions of intrapituitary LH among its isoforms. Relative to follicular and luteal phase ewes, anestrous ewes had lower percentages of isoforms D and E as well as higher percentages of isoforms G, H, J and K. Isoform F, the predominant molecular form of LH, constituted a similar percentage in all treatment groups (P > .05). Thus, the distribution of intrapituitary LH among its isoforms did not change significantly between the mid-luteal and follicular phases of the estrous cycle, but higher percentages of the weakly basic and acidic forms of LH were present during anestrus. These observations suggest that intrapituitary LH heterogeneity changes minimally throughout the estrous cycle of ewes during the breeding season.     

Avian reproductive endocrinology.

Hypothalamic-releasing factors regulate the secretion of anterior pituitary hormones. The anterior pituitary gland secretes the same six hormones as found in mammals: FSH, LH, prolactin, GH (somatotropic hormone), ACTH, and TSH, plus the melanotropic hormone. The endocrine hormones of the avian posterior pituitary gland concerned with reproduction are mesotocin and AVT. The pineal gland, through the secretion of the hormone melatonin, modulates the periodic autonomic functions of the central nervous system. The ovary produces estrogens, progestogens, and androgenic compounds. The testes produce testosterones and progesterone. The thyroid glands produce two hormones, T4 and T3. The avian adrenal glands produce corticosterone and aldosterone. The bursa of Fabricius is considered an endocrine organ since it is involved in the production of humoral factors. The male reproductive system undergoes hormonal changes associated with puberty, the breeding season, and molt. Some avian species undergo a type of disintegration and seasonal reconstruction of the testis and epididymis. The relationship of the ovarian follicular hormones and the plasma hormones varies depending on the stage of the reproductive cycle and the seasonal photostimulation. Female birds may conceive in the absence of a mate as a result of the fertile period phenomena. The blood chemistry of laying birds is different from that seen in nonlaying hens. Domestication has had a definite influence on the hormone cycles of some avian species. This may lead to certain reproductive problems.     

Cellular localization of IL-18 and IL-18 receptor in pig anterior pituitary gland

Pro-inflammatory cytokine interleukin 18 (IL-18) has been proposed to have a role in modulating immuno-endocrine functions. Our previous study showed that IL-18 and IL-18 receptor (IL-18R) colocalized in somatotrophs of the bovine anterior pituitary gland, and the possibility that IL-18 acts on somatotrophs as an autocrine factor. In the present study, we investigated the localization of IL-18 and IL-18R in the pig anterior pituitary gland. RT-PCR analysis showed the expression of IL-18 and IL-18R mRNAin the pig anterior pituitary gland. Immunohistochemistry of IL-18 and specific hormones revealed the presence of IL-18 in somatotrophs, mammotrophs, thyrotrophs and gonadotrophs. IL-18R was localized in somatotrophs and thyrotrophs. Furthermore, the somatotrophs immunoreactive for IL-18 did not contain IL-18R. Thus, IL-18R and IL-18 were not colocalized in an identical somatotroph. These findings suggest that the localization of IL-18 in pig somatotrophs is different from that in bovine somatotrophs, although IL-18 closely associates with somatotrophs in the anterior pituitary glands in both species.     

Ghrelin的免疫调节作用

Ghrelin是1999年发现的一种含28个氨基酸残基的脑肠肽,主要由胃黏膜的内分泌细胞分泌,与特异性受体结合后,会产生一系列生物学效应,如刺激垂体前叶释放生长激素、增加采食等。该文就Ghrelin在免疫调节方面的作用进行简要综述,为以后Ghrelin应用于抗炎症与免疫调节方面提供相关资料。     

脑肠肽激素Ghrelin及其在动物生产中的应用展望

Ghrelin是一种的由28个氨基酸组成的脑肠肽激素,是生长激素促泌素受体的内源性配体,主要由胃的一种内分泌细胞分泌,也分布于其他许多组织中,如下丘脑、垂体和胰腺等。Ghrelin与其特异性受体结合后,会产生一系列生物学效应,如刺激垂体前叶释放生长激素,增加采食,调节能量平衡,促进胃酸分泌和胃肠蠕动等作用。Ghrelin可能是新发现的下丘脑、垂体、胃之间内分泌调节的联系纽带,在动物生产中将起到重要的作用。     

Immune and endocrine regulation of food intake in sick animals

To understand why sick animals do not eat, investigators have studied how the immune system interacts with the central nervous system (CNS), where motivation to eat is ultimately controlled. The focus has been on the cytokines secreted by activated mononuclear myeloid cells, which include interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α). Either central or peripheral injection of recombinant IL-1β, IL-6, and TNF-α reduce food-motivated behavior and food intake in rodents. Moreover, these cytokines and their receptors are present in the endocrine system and brain, and antagonism of this system (i.e., the cytokine network) has been shown to block or abrogate anorexia induced by inflammatory stimuli. Recent studies indicate that the same cytokines act on adipocytes and induce secretion of leptin, a protein whose activity has been neuroanatomically mapped to brain areas involved in regulating food intake and energy expenditure. Therefore, many findings converge to suggest that the reduction of food intake in sick animals is mediated by inflammatory cytokines, which convey a message from the immune system to the endocrine system and CNS. The nature of this interaction is the focus of this short review.     

催乳素基因的研究进展

催乳素是主要由垂体前叶腺体分泌的一种蛋白激素，它可通过进入循环系统或局部地通过近旁分泌、旁分泌和自分泌活动形式，起经典的内分泌调节器作用。作者主要介绍催乳素的结构、功能和调控，催乳素基因的克隆及结构、发育性表达、定位和多态性。还阐述了催乳素基因与生产性能的关系。     

抑制素、活化素和卵泡抑素研究进展

抑制素、卵泡抑素和活化素是3种参与垂体促卵泡素调控过程的糖蛋白激素,随着对促卵泡素调控过程的深入了解,发现这3种蛋白在动物生殖周期中发挥着重要的作用。文章主要就抑制素、卵泡抑素和活化素的结构特征、生理功能以及抑制素和卵泡抑素对活化素生物学活性的抑制机理进行了综述。     

Immunocytochemical identification of Pit-1 containing cells in the anterior pituitary of hens

Our goal was to identify the cells expressing Pit-1 protein in chicken anterior pituitary. The anterior pituitaries were collected from laying hens after perfusion with formalin-PBS, and fixed with Bouin's fixative followed by paraffin embedding. Sections of the anterior pituitaries were immunostained for Pit-1 in the first staining sequence followed by staining for 6 types of pituitary hormones in the second sequence. Pit-1 positive nuclei were observed in the glandular cells in both the cephalic and caudal lobes. Pit-1 immunoreaction products were colocalized in the glandular cells immunopositive for growth hormone, thyroid-stimulating hormone, follicle-stimulating hormone, luteinizing hormone, adrenocorticotropic hormone or prolactin. These results indicate that Pit-1 protein induction occurs in 6 types of glandular cells, suggesting that Pit-1 may regulate hormone synthesis in each glandular cell in the chicken pituitary.     

Immunohistochemical localization of chromogranin A in normal tissues from laboratory animals

To analyze the distribution of Chromogranin A in endocrine cells of various species of laboratory animals (dog, gerbil, guinea pig, hamster, monkey, mouse, and fetal, neonatal, and adult rats), normal tissues were stained immunohistochemically with polyclonal anti-bovine Chromogranin A antiserum (SP-1). Selected tissues (pituitary, adrenal, thyroid, parathyroid, pancreas, brain, peripheral nerve, stomach, small and large intestine, bone marrow, spleen, thymus, lymph node, and liver) from these species and from the rabbit were stained with two monoclonal anti-human Chromogranin A antibodies (LK2H10 and PHE5) to compare the immunoreactivities of the monoclonal antibodies and polyclonal antiserum. Staining with the polyclonal antiserum (SP-1) resulted in a broader spectrum of immunoreactivity but had more nonspecific background staining than either monoclonal antibody. Immunoreactivity and staining intensity with SP-1 varied between species, but most endocrine tissues (pituitary cells in the anterior and intermediate lobes, thyroid "C" cells, adrenal medulla, parathyroid, pancreatic islets, and enterochromaffin cells) from most species stained positively. In some species, pancreatic alpha cells stained more intensely, and two populations of adrenal medullary cells with different staining intensities were observed. Sciatic nerve (axonal area) was immunoreactive with monoclonal antibodies and/or the polyclonal antiserum in several species. The spectrum of immunoreactive tissues from fetal and neonatal rats increased with age. There was good cross-reactivity between species with SP-1, but not with either LK2H10 or PHE5. These results indicate that many endocrine cells with secretory granules in laboratory animals express Chromogranin A and that a polyclonal antiserum, such as SP-1, is more sensitive in detecting this protein in various species than monoclonal antibodies such as LK2H10 or PHE5.