Biology of the prolactin family in bovine placenta. II. Bovine prolactin-related proteins: Their expression, structure and proposed roles

The placenta produces various peptides and steroid hormones that regulate placental function and fetal growth. Prolactin‐related proteins are peptides that are produced by the placenta and belong to the growth hormone/prolactin family, and have structural similarity to prolactin and placental lactogen. Although several prolactin‐related protein genes have been detected in bovine placenta, their expression profiles and functions are not clear. The main difficulties in examining their biological function is the similarity between their genes and the lack of information about their proteins. Recently, molecular biology methods have been used to detect some new bovine prolactin‐related proteins, and elucidate their biological functions. This review focuses on the structures, expression profiles and conceivable functions of prolactin‐related proteins in bovine placenta. With respect to their expression profiles, bovine prolactin‐related proteins fall into four groups: (i) those expressed around the implantation period; (ii) those that reach peak expression in the middle of gestation; (iii) those that increase with the progress of gestation, reaching a peak in late gestation; and (iv) those that reach a plateau in early gestation and are maintained at that level throughout gestation. Data indicate that bovine prolactin‐related proteins have different biological roles in different periods of gestation. In situ monitoring suggests that bovine prolactin‐related protein‐I has a role in the attachment of trophoblast cells to endometrium during the early implantation period.     

Effect of recombinant bovine tumor necrosis factor-α on hormone release in lactating cows

Tumor necrosis factor (TNF)‐α is a powerful macrophage cytokine released during infection, circulating in the blood to produce diverse effects in the organism. We examined the effect of recombinant bovine TNF‐α (rbTNF‐α) administration on hormone release in dairy cows during early lactation. Twelve non‐pregnant Holstein cows were treated subcutaneously with rbTNF‐α (2.5 µg/kg) or saline twice (at 11.00 and 23.00 hours). At 11.00 hours the next day, the cows were given growth hormone‐releasing hormone (GHRH, 0.25 µg/kg), thyrotrophin‐releasing hormone (TRH, 1.0 µg/kg), thyroid‐stimulating hormone (TSH, 10 µg/kg) or adrenocorticotropic hormone (500 µg/head) via the jugular vein. In the growth hormone‐releasing hormone challenge, the plasma growth hormone concentration was lower in the rbTNF‐α group than in the control (saline) group. The growth hormone and TSH responses to TRH were also smaller in the rbTNF‐α group than in the control. The plasma prolactin response to TRH was not affected by the rbTNF‐α treatment. In the TSH challenge, the rbTNF‐α‐treated cows had lower responses, as measured by plasma triiodothyronine and thyroxine, than the control cows. The rbTNF‐α treatment produced an increase in the basal plasma cortisol level, but the cortisol response to adrenocorticotropic hormone was the same level in both groups. The plasma concentrations of TNF‐α and interleukin‐1β in the cows were elevated by the rbTNF‐α treatment. The milk yield was reduced by the rbTNF‐α administration during 4 days. These data demonstrate that TNF‐α alters the secretion of pituitary and thyroid hormones in lactating cows. This effect may contribute to the suppression of the lactogenic function of the mammary gland observed in cases of coliform mastitis with high circulating TNF‐α levels.     

Hypercalcemia and parathyroid hormone‐related peptide expression in a dog with thyroid carcinoma and histiocytic sarcoma

A 9.5‐year‐old, male castrated Walker Hound was presented for evaluation of progressive weakness, anorexia, and weight loss. Imaging revealed multiple abdominal and thoracic masses and ascites; fine‐needle aspirates of mesenteric and splenic masses confirmed malignancy, most likely histiocytic sarcoma. Laboratory analyses revealed increased ionized calcium and parathyroid hormone‐related peptide (PTH‐rP) concentrations, and concurrent low–normal parathyroid hormone concentration, consistent with humoral hypercalcemia of malignancy. Necropsy was performed after euthanasia. The dog had disseminated histiocytic sarcoma, including sarcomatosis, as well as bilateral thyroid carcinoma. PTH‐rP immunostaining was positive in the thyroid carcinoma but negative in the histiocytic neoplasm. These results suggest that thyroid carcinoma‐associated hypercalcemia can be caused by tumor secretion of PTH‐rP.     

Short‐term ingestion of deoxynivalenol in naturally contaminated feed alters piglet performance and gut hormone secretion

The mycotoxin deoxynivalenol (DON) generally exists in cereals and affects human and animal health. The aim of this study is to analyze the impacts of DON in naturally contaminated feed on piglet growth performance and intestinal hormone secretion in the short term. We randomly divided 5‐week‐old piglets into four groups: Control, DON 1,000, DON 2,000 and DON 3,000 groups. Piglets received a feed naturally contaminated with DON (approximately 400, 1,000, 2,000 or 3,000 μg/kg) for 21 days. Body weight showed no significant difference following exposure to DON. The balance of anti‐oxidation and oxidation was disrupted by DON after 21 days. The concentration of tumor necrosis factor‐alpha (TNF‐α) and cyclooxgenase‐2 (COX‐2) significantly increased (p < .001) in all DON‐treated groups. Gut anorexigenic hormone secretion of peptide YY (PYY) and cholecystokinin (CCK) had a time‐ and dose‐dependent relationship with DON exposure; however, there was no effect on orexigenic hormone ghrelin secretion. Changes of histomorphology in the jejunum were observed in DON‐treated groups, including villi flattening and fusion, and apical necrosis of villi. These results indicated that DON could suppress piglet growth performance and alter gut hormone secretion in the short term.     

Sex steroid hormones do not enhance the direct stimulatory effect of kisspetin‐10 on the secretion of growth hormone from bovine anterior pituitary cells

The aims of the present study were to clarify the effect of kisspeptin10 (Kp10) on the secretion of growth hormone (GH) from bovine anterior pituitary (AP) cells, and evaluate the ability of sex steroid hormones to enhance the sensitivity of somatotrophic cells to Kp10. AP cells prepared from 8–11‐month‐old castrated calves were incubated for 12 h with estradiol (E₂, 10^?8 mol/L),progesterone (P₄, 10^?8 mol/L), testosterone (T, 10^?8 mol/L), or vehicle only (control), and then for 2 h with Kp10. The amount of GH released in the medium was measured by a time‐resolved fluoroimmunoassay. Kp10 (10^?6 or 10^?5 mol/L) significantly stimulated the secretion of GH from the AP cells regardless of steroid treatments (P < 0.05), and E₂, P₄, and T had no effect on this response. The GH‐releasing response to growth hormone‐releasing hormone (GHRH, 10^?8 mol/L) was significantly greater than that to Kp10 (P < 0.05). The present results suggest that Kp10 directly stimulates the release of GH from somatotrophic cells and sex steroid hormones do not enhance the sensitivity of these cells to Kp10. Furthermore, they suggest that the GH‐releasing effect of Kp10 is less potent than that of GHRH.     

The impact of bisphenol S on bovine granulosa and theca cells

Bisphenol S (BPS) is an endocrine‐disrupting chemical with multiple potential mechanisms of action, including as an oestrogen receptor agonist. BPS is increasingly used in plastics and thermal receipts as a substitute for bisphenol A, which has been phased out due to concerns about human health implications. The ability of BPS to alter female reproductive function in mammals has not been widely studied, despite the importance of normal hormone signalling for female reproduction. The aim of this study was to investigate how BPS (in a wide range of doses, including very low doses) affects granulosa cell and theca cell steroid hormone production and cell viability in the bovine. Granulosa cell oestradiol production was stimulated when cells were exposed to 100 μM BPS under basal conditions, but there was no effect of BPS when cells were stimulated with follicle‐stimulating hormone (FSH). Additionally, there was no effect of BPS on granulosa cell progesterone production or cell viability under basal or FSH‐stimulated conditions. BPS did not affect theca cell androstenedione or progesterone production, or theca cell viability under basal or luteinizing hormone‐stimulated conditions. This study suggests for the first time that BPS may alter oestradiol production by bovine granulosa cells, albeit at a concentration that is unlikely to be physiologically relevant. Further studies are needed to determine the effects of BPS on the bovine oocyte and on other functions of follicular cells.     

Feline acromegaly

Acromegaly, or hypersomatotropism, results from chronic, excessive secretion of growth hormone in the adult animal. The anabolic effects of growth hormone are exerted through the intermediary hormone, insulin-like growth factor 1, which is produced in the liver under the influence of growth hormone. Feline acromegaly is caused by a pituitary adenoma that secretes excessive amounts of growth hormone. Characteristic effects of excessive growth hormone secretion include the development of diabetes mellitus and growth of the acral segments of the body (jaw, extremities, skull, etc.). Acromegaly occurs in older, predominately male cats and is often associated with diabetes mellitus. Other clinical signs include stridor, enlargement of the jaw and extremities, lean weight gain, and organomegaly (heart, liver, kidney, etc.). Diagnosis is made by documentation of increased levels of growth hormone or insulin-like growth factor (or both) and demonstration of a pituitary mass via magnetic resonance imaging or computed tomography. The most effective treatment to date has been radiation therapy. Prognosis is fair to good with proper treatment.     

Concentration effect of prostaglandin E2 on the growth factor expression and cell proliferation in bovine endometrial explants and their kinetic characteristics

Bovine endometrium undergoes various physiological and histological changes that are necessary for blastocyst implantation during oestrous cycle. From pro‐oestrus to late‐oestrus, endometrium thickens gradually for implantation preparation and exhibits remarkable capacity for self‐repair after uterine lining shedding while implantation does not occur. The prostaglandin E₂ (PGE ₂) secretion pattern is synchronized with endometrial growth during oestrous cycles in bovine endometrium; however, limited information is available regarding the association between PGE ₂ secretion and endometrial growth. In this study, the concentration (10^?9 to 10^?5 M) and time effect (2–36 hr) of PGE ₂ treatment on a series of growth factors are essential for endometrial growth including connective tissue growth factor (CTGF ), fibroblast growth factor‐2 (FGF ‐2), interleukin‐8 (IL ‐8), transforming growth factor‐β1 (TGF ‐β1), matrix metalloproteinase‐2 (MMP ‐2), and vascular endothelial growth factor A (VEGFA ) mRNA and protein expression, and proliferation of epithelial and fibroblast cells was investigated in bovine endometrial explants in vitro. The results indicated that PGE ₂ at concentration about 10^?7 to 10^?5 M could up‐regulate CTGF , FGF ‐2, IL ‐8, MMP ‐2, TGF ‐β1, VEGFA mRNA and protein expression, and could induce the proliferation of epithelial and fibroblast cells and reduce the proapoptotic factor (caspase‐3) expression in bovine endometrial explants in vitro. These results collectively improved the possibility of PGE ₂ functions in endometrial growth during oestrous cycles.     

The control of adenohypophysial hormone secretion by amino acids and peptides in swine

Several different amino acids and peptides control secretion of adenohypophysial hormones and this control may be indirect, via the modulation of hypothalamic hormone secretion. Indeed, classical hypothalamic hormones (e.g., gonadotropin-releasing hormone [GnRH], growth hormone-releasing hormone [GHRH], somatostatin, etc.) may be released into the hypothalamo-hypophysial portal vasculature, travel to the adenohypophysis and there stimulate or inhibit secretion of hormones. Alternatively, some amino acids and peptides exert direct stimulatory or inhibitory effects on the adenohypophysis, thereby impacting hormone secretion. In swine, the most extensively studied modulators of adenohypophysial hormone secretion are the excitatory amino acids (ExAA), namely glutamate and aspartate, and the endogenous opioid peptides (EOP). In general, excitatory amino acids stimulate release of luteinizing hormone (LH), follicle-stimulating hormone (FSH), growth hormone (GH), and prolactin (PRL). Secretion of adenohypophysial hormones induced by ExAA is primarily, but perhaps not exclusively, a consequence of action at the central nervous system. By acting primarily at the level of the central nervous system, EOP inhibit LH secretion, stimulate GH release and depending on the animal model studied, exert either stimulatory or inhibitory influences on PRL secretion. However, the EOP also inhibited LH release by direct action on the adenohypophysis. More recently, peptides such as neuropeptide-Y (NPY), orexin-B, ghrelin, galanin, and substance P have been evaluated for possible roles in controlling adenohypophysial hormone secretion in swine. For example, NPY, orexin-B, and ghrelin increased basal GH secretion and modulated the GH response to GHRH, at least in part, by direct action on the adenohypophysis. Secretion of LH was stimulated by orexin-B, galanin, and substance P from porcine pituitary cells in vitro. Because the ExAA and various peptides modulate secretion of adenohypophysial hormones, these compounds may play an important role in regulating swine growth and reproduction.     

In vitro and in vivo temporal aspects of ACTH secretion: stimulatory actions of corticotropin-releasing hormone and vasopressin in cattle

The objective of the present study was to evaluate the temporal aspects associated with corticotropin-releasing hormone (CRH) and vasopressin (VP) stimulated bovine adrenocorticotropic hormone (ACTH) secretion in vitro and in vivo. For the in vitro studies, bovine anterior pituitary glands were enzymatically dispersed to establish primary cultures. On day 5 of culture, cells were challenged for 3 h with medium alone (Control) or various combinations and concentrations of bovine CRH (bCRH) and VP. Both CRH and VP each increased (P < 0.05) ACTH secretion. Maximal increases in ACTH secretion occurred in response to 0.1 microM CRH (5.5-fold) and 1 microM VP (3.7-fold), relative to Control cells. The in vivo portion of the study examined possible temporal differences in the activation of the pituitary-adrenal axis by CRH and VP. Jersey cows were randomly assigned to one of four groups (n = 8 cows/group): (i) Control (saline); (ii) bCRH (0.3 microg/kg BW); (iii) VP (1 microg/kg BW) and (iv) bCRH (0.3 microg/kg BW) + VP (1 microg/kg BW). Jugular blood samples were collected at 15-min intervals for 4 h pre- and for 6 h post-treatment; samples were also taken at 1, 5 and 10 min post-treatment. Plasma concentration of ACTH did not differ among treatment groups for the 4-h pre-treatment period. At 1 min post-treatment, bCRH + VP, VP and bCRH increased ACTH secretion by 22.4-, 9.6- and 2.2-fold, respectively, relative to Control (32.7 +/- 7.2 pg/ml). Maximal plasma concentration of ACTH occurred at 5, 10 and 15 min post-treatment for the VP (1017.7 +/- 219.9 pg/ml), bCRH + VP (1399.8 +/- 260.1 pg/ml) and bCRH (324.8 +/- 126.2 pg/ml) treatment groups respectively. Both the in vitro and in vivo data demonstrated that while VP acutely activates the bovine pituitary-adrenal axis, CRH-induced ACTH secretion is slower in onset but of longer duration. The present study also provides insight into the dynamics of ACTH and cortisol (CS) responsiveness to CRH and VP in cattle.     

Effects of STX,a Novel Estrogen Membrane Receptor Agonist,on GnRH-Induced Luteinizing Hormone Secretion from Cultured Bovine Anterior Pituitary Cells

STX is an agonist for a recently characterized membrane estrogen receptor whose structure has not been identified. We evaluated whether STX suppresses gonadotropin-releasing hormone (GnRH)–induced luteinizing hormone (LH) release from bovine anterior pituitary (AP) cells. We cultured AP cells (n=12) for 3 days in steroid-free conditions, followed by increasing concentrations (0.001, 0.01, 0.1, 1 and 10 nM) of 17β-estradiol or STX for 5 min before GnRH stimulation until the end of the experiment. Estradiol (0.001 to 0.1 nM) significantly suppressed GnRH-stimulated LH secretion, whereas STX did not affect GnRH-stimulated LH secretion at any of the tested concentrations. In conclusion, STX, unlike estradiol, possesses no suppressive effect on GnRH-induced LH release from bovine AP cells.     

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.     

Effects of photoperiod on secretory patterns of growth hormone in adult male goats

The aim of the present study was to clarify the effect of photoperiod on secretory patterns of growth hormone (GH) in male goats. Adult male goats were kept at 20°C with an 8‐h or 16‐h light photoperiod, and secretory patterns of GH secretion were compared. In addition, plasma profiles of prolactin (PRL), insulin‐like growth factor‐I (IGF‐I) and testosterone (T) were also examined to characterize GH secretion. GH was secreted in a pulsatile manner. There was no significant difference in pulse frequency between the 8‐h and 16‐h photoperiods. However, GH pulse amplitude tended to be greater in the group with the 16‐h photoperiod (P = 0.1), and mean GH concentrations were significantly greater in the 16‐h photoperiod (P < 0.05). The GH‐releasing response to GH releasing hormone was greater in the 16‐h than 8‐h photoperiod (P < 0.05). Plasma PRL and IGF‐I levels were higher in the 16‐h than 8‐h photoperiod (P < 0.05). In contrast, plasma T levels were lower in the 16‐h photoperiod (P < 0.05). These results show that a long light photoperiod enhances the secretion of GH as well as PRL and IGF‐I, but reduces plasma T concentrations in male goats.     

Effects of photoperiod on the secretion of growth hormone in female goats

The aim of the present study was to clarify the effect of photoperiod on the secretion of growth hormone (GH) in goats. Adult female goats were kept at 20°C with an 8‐h or 16‐h photoperiod, and secretory patterns of GH for 4 h (12.00 to 16.00 hours) were compared. In addition, the goats were kept under a 16‐h photoperiod and orally administered saline (controls) or melatonin, and the effects of melatonin on the secretion of GH were examined. GH was secreted in a pulsatile manner. There were no significant differences in pulse frequency between the 8‐ and 16‐h photoperiods; however, GH pulse amplitude tended to be greater in the group with the 16‐h photoperiod (P = 0.1), and mean GH concentrations were significantly greater in the 16‐h photoperiod (P < 0.05). The GH‐releasing response to GH‐releasing hormone (GHRH) was also significantly greater for the 16‐h photoperiod (P < 0.05). There were no significant differences in GH pulse frequency between the saline‐ and melatonin‐treated groups. However, GH pulse amplitude and mean GH concentrations were significantly greater in the saline‐treated group (P < 0.05). The present results show that a long photoperiod enhances the secretion of GH, and melatonin modifies GH secretion in female goats.     

Cytoplasmic kinases downstream of GPR30 suppress gonadotropin-releasing hormone (GnRH)-induced luteinizing hormone secretion from bovine anterior pituitary cells

GPR30 is known as a membrane receptor for picomolar concentrations of estradiol. The GPR30-specific agonist G1 causes a rapid, non-genomic suppression of gonadotropin-releasing hormone (GnRH)-induced luteinizing hormone (LH) secretion from bovine anterior pituitary (AP) cells. A few studies have recently clarified that protein kinase A (PKA) and phosphorylated extracellular signal-regulated kinase (pERK) might be involved in cytoplasmic signaling pathways of GPR30 in other cells. Therefore, we tested the hypothesis that PKA and ERK kinase (MEK) are important cytoplasmic mediators for GPR30-associated non-genomic suppression of GnRH-induced LH secretion from bovine AP cells. Bovine AP cells (n = 8) were cultured for 3 days under steroid-free conditions. The AP cells were previously treated for 30 min with one of the following: 5000 nM of PKA inhibitor (H89), 1000 nM of MEK inhibitor (U0126), or a combination of H89 and U0126. Next, the AP cells were treated with 0.01 nM estradiol for 5 min before GnRH stimulation. Estradiol treatment without inhibitor pretreatment significantly suppressed GnRH-induced LH secretion (P < 0.01). In contrast, estradiol treatment after pretreatment with H89, U0126 or their combination had no suppressive effect on GnRH-induced LH secretion. The inhibitors also inhibited the G1 suppression of GnRH-induced LH secretion. Therefore, these data supported the hypothesis that PKA and MEK (thus, also pERK) are the intracellular mediators downstream of GPR30 that induce the non-genomic suppression of GnRH-induced LH secretion from bovine AP cells by estradiol or G1.     

Regulation of protein and energy metabolism by the somatotropic axis.

The somatotropic axis plays a key role in the co-ordination of protein and energy metabolism during postnatal growth. This review discusses the complexity of the regulation of protein and energy metabolism by the somatotropic axis using three main examples: reduced nutrition, growth hormone (GH) treatment and insulin-like growth factor-1 (IGF-1) treatment. Decreased nutrition leads to elevated GH secretion, but it reduces hepatic GH receptor (GHR) number and plasma levels of IGF-1; it also changes the relative concentrations of IGF binding proteins (IGFBPs) in plasma. GH treatment improves the partitioning of nutrients by increasing protein synthesis and decreasing protein degradation and by modifying carbohydrate and lipid metabolism. However, these well-established metabolic responses to GH can change markedly in conditions of reduced nutritional supply or metabolic stress. Short-term infusion of IGF-1 in lambs reduces protein breakdown and increases protein synthesis. However, long-term IGF-1 administration in yearling sheep does not alter body weight gain or carcass composition. The lack of effect of IGF-1 treatment can be explained by activation of feedback mechanisms within the somatotropic axis, which lead to a reduction in GH secretion and hepatic GHR levels. The somatotropic axis has multiple levels of hormone action, with complex feedback and control mechanisms, from gene expression to regulation of mature peptide action. Given that GH has a much wider range of biologic functions than previously recognized, advances in research of the somatotropic axis will improve our understanding of the normal growth process and metabolic disorders.     

Clinical evaluation of growth hormone secretion in cattle using insulin tolerance test

Growth hormone secretion was evaluated in cattle. Clinically healthy bovine growth hormone (bGH) concentrations were 10.7 +/- 1.6 ng/ml in Holstein and 7.8 +/- 3.9 ng/ml in Japanese black cattle. The bGH concentration alternated at three-hour intervals, and tended to be higher at midnight and lower in the morning and before feeding. Insulin tolerance test (ITT) at an insulin dosage of 0.25 U/kg showed a significant increase of bGH concentration to 331 +/- 153% at 60 to 90 min after injection. In ITT applied to five under-growth calves of Japanese black cattle, the basal bGH concentrations were lower and peak values after insulin injection were shown to be significantly low. The ITT is useful for the clinical examination of bGH secretion in cattle.     

Analysis of differential strategies to enhance detection of low‐abundance proteins in the bovine serum proteome

Serum‐based biomarkers hold propitious applications for addressing livestock health, and management. However, discovery of protein biomarkers in complex biological fluids like serum is wholly intractable due to the large dynamic range of protein concentrations; that is, ?10–12 high abundance proteins constitute >90% of the total protein content and effectively mask proteomic detection of low‐abundance biomarkers. Toward addressing this limitation, we test a continuous elution size‐based fractionation method, and two approaches that use affinity interaction‐based separation of proteins in preparing bovine serum, and compare liquid chromatography tandem mass spectrometry protein identification to neat serum. Our results identify the high‐abundance proteins in bovine serum, and demonstrate dynamic range compression and improved protein identification with the different enrichment methods. Although these findings indicate the highest protein number identified in bovine serum (445 proteins, all methods combined), and by any single sample processing method (312 proteins) to date, they still remain lower than levels deemed necessary for biomarker discovery. As such, this investigation revealed limitations to resolving the bovine serum proteome, and the need for species‐specific tools for immunodepleting high‐abundance proteins. In concert, this study represents a step toward advancing sample preparation methods for bovine serum biomarker identification.