Regulation of the growth hormone and luteinizing hormone response to endotoxin in sheep

The Effect of Endotoxin-Induced Inflammation on the Activity of the Somatotropic Axis in Sheep

The hypothalamic-pituitary-somatotropic (HPS) axis controls many physiological and pathophysiological processes. The phenomenon of insensitivity to growth hormone resistance (GHres) was previously reported to be due to the development of inflammation. Therefore, the primary aim of the study was to determine the impact of inflammation caused by lipopolysaccharides (LPS) on the secretory activity of the HPS axis in sheep. The further goal was to determine the effect of inflammatory factors on individual components involved in intracellular signal transduction to GH via the GH receptor (GHR). The research was carried out on 24 seasonal sheep kept under a short-day photoperiod, randomly divided into two groups. Before the experiment, the sheep estrous cycles were synchronized. The results of the current study in a sheep model showed that inflammation impairs the activity of the somatotropic axis. On the one hand, LPS injection stimulated (p < 0.01) GH secretion, and on the other hand, it reduced the liver's sensitivity to this hormone by directly reducing (p < 0.01) GHR expression and activating the GHR inhibitory signal transduction mechanism. A symptom of such an inhibitory postreceptor signaling pathway may be due to an increase in SOCS3 expression (p < 0.01). The effect of various inhibition pathways is a significant reduction in the expression of the main transcription activator IGF1-STAT5B (p < 0.05). The action of GHres in the liver resulted in the inhibition of IGF1 secretion, which in the long term may have negative consequences for growth and development. Our study suggests that disruption of the GH cell signaling pathway may be one of the important elements of the pathophysiology of inflammation. It can suppress growth and hepatic metabolism to spare energy expenditure.

Pro-inflammatory cytokines and reproductive hormone responses in bucks post-challenge with Mannheimia haemolytica A2 and its outer membrane protein

The lipopolysaccharide (LPS) endotoxin and outer membrane protein (OMP) are among the virulence factors of Gram-negative bacteria responsible for inducing pathogenicity in the infected host. OMP and LPS occur on the outer membrane of M. haemolytica A2, the primary aetiological agent of pneumonic mannheimiosis in small ruminants. While the LPS is known to mediate Gram-negative bacterial infection by activating downstream inflammatory pathways, the potential role of OMP during inflammatory responses remained unclear. Hence, this study determined the effect of the OMP of M. haemolytica A2 on the serum concentration of pro-inflammatory cytokines and the male reproductive hormones (testosterone and Luteinizing Hormone). We randomly assigned twelve bucks to three groups (n = 4 bucks each): Group 1 was challenged with 2 mL PBS buffer (pH 7.0) intranasally; Group 2 received 2 mL of 1.2 X 109 CFU/mL whole M. haemolytica A2 intranasally; and Group 3 received 2 mL of OMP extract obtained from 1.2 X 109 CFU/mL M. haemolytica A2 intramuscularly. Serum samples collected at pre-determined intervals were used for the quantitative determination of the pro-inflammatory cytokines (IL-1β, IL-6, and TNFα) and reproductive hormones (testosterone and LH) using commercial sandwich enzyme-linked immunosorbent assay (ELISA). The serum concentration of IL1β was initially increased within the first-hour post-challenge in Groups 2 and 3, followed by a significant decrease in concentration at 21d and 35d (p < 0.05) in Group 3. Only mild fluctuations in IL-6 occurred in group 2, as opposed to the 1.7-fold rapid increase in TNFα within 2 h post-challenge before decreasing at 6 h. An increase in pro-inflammatory cytokines was accompanied by an acute febrile response of 39.5 ± 0.38 °C (p < 0.05) at 2 h and 40.1 ± 0.29 °C (p < 0.05) at 4 h in Group 2 and Group 3, respectively. Serum testosterone decreased significantly (p < 0.05) in both treatment groups but remained significantly (p > 0.05) lower than in Group 1 throughout the study. There was a moderate negative association between testosterone and IL1β (r = -0.473; p > 0.05) or TNFα (r = -0.527; p < 0.05) in Group 2. Serum LH also showed moderate negative associations with TNFα in Group 2 (r = -0.63; p < 0.05) and Group 3 (r = -0.54; p > 0.05). The results of this study demonstrated that M. haemolytica A2 and its OMP produced marked alterations in serum levels of pro-inflammatory cytokines and male reproductive hormones. The negative correlations between serum testosterone and inflammatory cytokines would suggest the potential role of OMP in causing male infertility by mediating innate inflammatory responses to suppress testosterone production in bucks.

Responses of testosterone hormone and important inflammatory cytokines in bucks after challenge with Mannheimia haemolytica A2 and its LPS endotoxin

Previous studies have shown that Mannheimia haemolytica A2 is the principal microorganism causing pneumonic mannheimiosis, a major bacterial respiratory disease among sheep and goats. The effect of this bacteria on the respiratory system is well-established. However, its effect on the reproductive physiology remains unclear. Therefore, this study aimed to determine the alterations in the level of pro-inflammatory cytokines and testosterone hormone post-inoculation with M. haemolytica serotype A2 and its lipopolysaccharide (LPS) endotoxin which were hypothesized to affect the reproductive functions of bucks. Twelve clinically healthy adult male goats were divided equally into three groups. Goats in group 1 were treated with 2 ml of sterile phosphate-buffered saline (PBS) pH 7.0 intranasally (negative control), group 2 with 2 ml of 10⁹ colony-forming unit (CFU) of M. haemolytica serotype A2 intranasally (positive control), and group 3 were treated with 2 ml of lipopolysaccharide extracted from 10⁹ CFU of M. haemolytica serotype A2 intravenously. Following inoculation, blood samples were collected via jugular venipuncture into plain tubes at pre-determined intervals for serum collection to determine the concentration of interleukin (IL)-1β, IL6, tumor necrosis factor (TNF)-α, and testosterone hormone by using commercial ELISA test kits. Results from this study demonstrated that the inoculation of M. haemolytica A2 and its LPS increases the concentration of pro-inflammatory cytokines but decreases the concentration of testosterone hormone in challenged animals at most time points throughout the 56 days experimental period (p < 0.05). This study suggests that the M. haemolytica A2 and its LPS could alter the concentration of pro-inflammatory cytokines and testosterone hormone, which in turn, may negatively affect the reproductive functions of bucks.

PPARG regulates gonadotropin-releasing hormone signaling in LbetaT2 cells in vitro and pituitary gonadotroph function in vivo in mice

Peroxisome proliferators-activated receptor gamma (PPARG) ligands improve insulin sensitivity in type 2 diabetes and polycystic ovarian syndrome (PCOS). Despite clinical studies showing normalization of pituitary responsiveness to gonadotropin-releasing hormone (GnRH) in patients with PCOS, the precise role of PPARG in regulating the hypothalamic-pituitary-gonadal axis remains unclear. In the present study, we tested the hypothesis that the PPARG agonist rosiglitazone has a direct effect on the pituitary. In mouse LbetaT2 immortalized gonadotrophs, rosiglitazone treatment inhibited GnRH stimulation of the stress kinases p38MAPK and MAPKs/JNKs, but did not alter activation of ERKs, both in the presence and absence of activin. Furthermore, p38MAPK signaling was critical for both Lhb and Fshb promoter activity, and rosiglitazone suppressed the GnRH-mediated induction of Lhb and Fshb mRNA. Depletion of PPARG using a lentivirally encoded short hairpin RNA abolishes the effect of rosiglitazone to suppress activation of JNKs and induction of the transcription factors EGR1 and FOS as well as the gonadotropin genes Lhb and Fshb. Lastly, we show conditional knockout of Pparg in pituitary gonadotrophs caused an increase in luteinizing hormone levels in female mice, a decrease in follicle-stimulating hormone in male mice, and a fertility defect characterized by reduced litter size. Taken together, our data support a direct role for PPARG in modulating pituitary function in vitro and in vivo.

Infection, immunity and the neuroendocrine response

The Central Nervous (CNS) and Immune Systems (IS) are the two major adaptive systems which respond rapidly to numerous challenges that are able to compromise health. The defensive response strictly linking innate to acquired immunity, works continuously to limit pathogen invasion and damage. The efficiency of the innate response is crucial for survival and for an optimum priming of acquired immunity. During infection, the immune response is modulated by an integrated neuro-immune network which potentiates innate immunity, controls potential harmful effects and also addresses metabolic and nutritional modifications supporting immune function. In the last decade much knowledge has been gained on the molecular signals that orchestrate this integrated adaptive response, with focus on the systemic mediators which have a crucial role in driving and controlling an efficient protective response. These mediators are also able to signal alterations and control pathway dysfunctions which may be involved in the persistence and/or overexpression of inflammation that may lead to tissue damage and to a negative metabolic impact, causing retarded growth. This review aims to describe some important signalling pathways which drive bidirectional communication between the Immune and Nervous Systems during infection. Particular emphasis is placed on pro-inflammatory cytokines, immunomodulator hormones such as Glucocorticoids (GCs), Growth hormone (GH), Insulin-like Growth Factor-1 (IGF-1), and Leptin, as well as nutritional factors such as Zinc (Zn). Finally, the review includes up-to-date information on this neuroimmune cross-talk in domestic animals. Data in domestic animal species are still limited, but there are several exciting areas of research, like the potential interaction pathways between mediators (i.e. cytokine-HPA regulation, IL-6-GCS-Zn, cytokines-GH/IGF-1, IL-6-GH-Leptin and thymus activity) that are or could be promising topics of future research in veterinary medicine.

Cortisol reduces gonadotropin-releasing hormone pulse frequency in follicular phase ewes: influence of ovarian steroids

Stress-like elevations in plasma glucocorticoids suppress gonadotropin secretion and can disrupt ovarian cyclicity. In sheep, cortisol acts at the pituitary to reduce responsiveness to GnRH but does not affect GnRH pulse frequency in the absence of ovarian hormones. However, in ewes during the follicular phase of the estrous cycle, cortisol reduces LH pulse frequency. To test the hypothesis that cortisol reduces GnRH pulse frequency in the presence of ovarian steroids, the effect of cortisol on GnRH secretion was monitored directly in pituitary portal blood of follicular phase sheep in the presence and absence of a cortisol treatment that elevated plasma cortisol to a level observed during stress. An acute (6 h) cortisol increase in the midfollicular phase did not lower GnRH pulse frequency. However, a more prolonged (27 h) increase in cortisol beginning just before the decrease in progesterone reduced GnRH pulse frequency by 45% and delayed the preovulatory LH surge by 10 h. To determine whether the gonadal steroid milieu of the follicular phase enables cortisol to reduce GnRH pulse frequency, GnRH was monitored in ovariectomized ewes treated with estradiol and progesterone to create an artificial follicular phase. A sustained increment in plasma cortisol reduced GnRH pulse frequency by 70% in this artificial follicular phase, in contrast to the lack of an effect in untreated ovariectomized ewes as seen previously. Thus, a sustained stress-like level of cortisol suppresses GnRH pulse frequency in follicular phase ewes, and this appears to be dependent upon the presence of ovarian steroids.

Comparative aspects of the endotoxin- and cytokine-induced endocrine cascade influencing neuroendocrine control of growth and reproduction in farm animals

Disease in animals is a well-known inhibitor of growth and reproduction. Earlier studies were initiated to determine the effects of endotoxin on pituitary hormone secretion. These studies found that in sheep, growth hormone (GH) concentration was elevated, whereas insulin-like growth factor-I (IGF-I) was inhibited, as was luteinizing hormone (LH). Examination of the site of action of endotoxin in sheep determined that somatotropes expressed the endotoxin receptor (CD14) and that both endotoxin and interleukin-I beta activated GH secretion directly from the pituitary. In the face of elevated GH, there is a reduction of IGF-I in all species examined. As GH cannot activate IGF-I release during disease, there appears to be a downregulation of GH signalling at the liver, perhaps related to altered nitration of Janus kinase (JAK). In contrast to GH downregulation, LH release is inhibited at the level of the hypothalamus. New insights have been gained in determining the mechanisms by which disease perturbs growth and reproduction, particularly with regard to nitration of critical control pathways, with this perhaps serving as a novel mechanism central to lipopolysaccharide suppression of all signalling pathways. This pathway-based analysis is critical to the developing novel strategies to reverse the detrimental effect of disease on animal production.

Bovine anterior pituitary progenitor cell line expresses interleukin (IL)-18 and IL-18 receptor

In the anterior pituitary gland, inflammatory mediators regulate cell function through an immuno-endocrine pathway. Recent studies have shown that undifferentiated stem cells act as immunomodulators. These studies prompted us to establish a progenitor cell line from the bovine anterior pituitary gland and to detail its function. First, we localised interleukin (IL)-18 by immunohistochemistry to the marginal cell layer of Rathke's pouch that is assumed to embody a stem/progenitor cell compartment of the postnatal pituitary gland. A cloned anterior pituitary-derived cell line from the bovine anterior pituitary gland was established from single cell clone by the limiting dilution method and was designated as bovine anterior pituitary-derived cell line (BAPC)-1. BAPC-1 cells constantly expressed mRNAs for IL-18 and IL-18 receptor, and grew steadily and rapidly in the medium containing epidermal growth factor and basic fibroblast growth factor. The cell line also expressed the mRNAs for the stem/progenitor cell- related factors such as Nanog, Oct-4, Ptch1, Nestin, Notch1, Hes1, Lrp and Fzd4, and the mRNAs for embryonic pituitary-related factors, such as Lhx3, PitX1 and Pit-1. The nuclei of BAPC-1 were immunostained positively for Pit-1, Hes1 and beta-catenin antibodies. Furthermore, BAPC-1 cells expressed mRNAs for cytokine such as IL-1alpha, IL-6, IL-7, IL-12 and IL-15. Stimulation of BAPC-1 cells with IL-18 increased expression of mRNAs for IL-1alpha, IL-6, IL-1beta and IL-8. At day 6 in culture, BAPC-1 cells also express growth hormone mRNA. These results strongly suggest that BAPC-1 is a stem/progenitor cell line and modulates the immuno-endocrine function of the anterior pituitary cells through its cytokine production.

Bidirectional communication: Growth and immunity in domestic livestock1,2,3,4

Evidence continues to mount supporting the existence of a bidirectional communication network between the immune system and the somatotropic axis in a variety of species. For more than 4 decades, researchers have sought and identified linkages between the growth axis and the immune system. Although significant advances have been made with regard to elucidation of various bidirectional communication pathways between the immune system and growth axis in humans and rodents, the current paper focuses on the relationships between the immune system and somatotropic axis in sheep, cattle, and swine. Aspects from historical and current research associated with changes in somatotropic function following immune challenges with endotoxin, parasites, viruses, and bacteria have been provided. Collectively, these studies demonstrate that a bidirectional communication network, similar to that described in humans and rodents, also exists in a variety of domestic livestock. Identifying and understanding this bidirectional communication network could have significant economic benefits if it leads to intervention strategies to prevent production losses associated with sickness and disease.

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.

Participation of the endocannabinoid system in the effect of TNF-alpha on hypothalamic release of gonadotropin-releasing hormone

It is known that Delta(9)-tetrahydrocannabinol (THC), the major active ingredient of marijuana, can suppress reproductive function. Also, we reported previously that the endocannabinoid, anandamide (AEA), inhibited gonadotropin-releasing hormone (LHRH) release from medial basal hypothalamus (MBH) of male rats incubated in vitro as well as reduced plasma LH levels after i.c.v. AEA injections into the cerebral lateral ventricle. On the other hand, it is known that during endotoxemia the hypothalamic gonadotropin axis is inhibited. Therefore, the aim of the present study was to determine whether the effect of TNF-alpha, a proinflammatory cytokine induced by lipopolysaccharide (LPS) that inhibits LHRH release, is mediated by the activation of the endocannabinoid system. The intraperitoneal injection of LPS (5 mg/kg) as well as the i.c.v. injection of tumor necrosis factor-alpha (TNF-alpha) (100 ng/rat) increased significantly the AEA synthesis measured ex vivo in MBHs removed 3 h after the treatments. To examine the possibility that TNF-alpha also acted by increasing the synthesis of AEA that was released and activated the CB1-r followed by inhibition of LHRH release, we measured the effect of TNF-alpha on the AEA synthase activity in MBHs incubated in vitro. As expected, we found that TNF-alpha (2.9 x 10(-9) M) increased the AEA synthesis. Second, we showed that TNF-alpha reduced significantly the forskolin-stimulated LHRH release and that the CB1-r antagonist AM251 (10(-5) M) blocked that inhibition, supporting the hypothesis that TNF-alpha inhibits LHRH release, acting at least in part by activating the endocannabinoid system. Therefore, our data demonstrate a key role for the endocannabinoid system in the response of the reproductive system to inflammatory signals.

Endocannabinoids in TNF-alpha and ethanol actions

During marijuana and alcohol consumption as well as during inflammation the reproductive axis is inhibited, mainly through the inhibition of luteinizing hormone-releasing hormone release. In male rats, this inhibitory effect is mediated, at least in part, by the activation of hypothalamic cannabinoid type 1 receptors (CB1). During inflammation, this activation of the endocannabinoid system seems to be mediated by an increase in TNF-alpha production followed by anandamide augmentations, similarly the effect of intragastric administration of ethanol (3 g/kg) seems to be due to an increase in anandamide. On the other hand, a number of different actions mediated by the endocannabinoid system in various organs and tissues have been described. Both cannabinoid receptors, CB1 and CB2, are localized in the submandibular gland where they mediate the inhibitory effect of intrasubmandibular injections of the endocannabinoid anandamide (6 x 10(-5)M) on salivary secretion. Lipopolysaccharide (5 mg/kg/3 h) injected intraperitoneally and ethanol (3 g/kg/1 h) injected intragastrically inhibited the salivary secretion induced by the sialogogue metacholine; this inhibitory effect was blocked by CB1 and/or CB2 receptor antagonists. Similar to the hypothalamus, these effects seem to be mediated by increased anandamide. In summary, similar mechanisms mediate the inhibitory actions of endocannabinoids and cannabinoids in both hypothalamus and submandibular gland during drug consumption and inflammation.

Bacterial complications of postpartum uterine involution in cattle

The bacterial contamination of the postpartum uterus is a frequent finding which by itself does not disturb the anatomical and histological restoration of tubular genital tract. The improper balance between uterine infection and the intrauterine antimicrobial self-defence mechanisms, however, often results in complications, such as puerperal metritis, clinical endometritis, pyometra and subclinical endometritis. After reviewing the bacteriology of uterine involution, and the predisposing factors for its bacterial complications, this paper defines the different clinical forms, and summarizes their pathology, furthermore, the recent progress in diagnostic considerations and principles of current treatments for these diseases of bovine genitals.

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.

Interleukin-1beta and tumor necrosis factor-alpha mediation of endotoxin action on growth hormone

In humans and sheep, endotoxin (LPS) administration results in increased growth hormone (GH) concentrations. To determine the role of cytokines in the effect of LPS on GH, sheep were challenged with IL-1beta or TNF-alpha. GH data were compared with results with LH, where the major effects of LPS are known to act via the hypothalamus. Intracerebroventricular (icv) administration of IL-1beta or TNF-alpha did not alter plasma concentrations of GH. Endotoxin was then administered intravenously (iv) in combination with icv injection of IL-1 receptor antagonist (IL-1RA), TNF antagonist (sTNF-R1), or saline. Administration of LPS increased GH (P < 0.0001), although coadministration of IL-1ra or sTNF-R1 icv did not alter GH response to LPS. In contrast, plasma concentrations of LH were profoundly inhibited by icv administration of either cytokine (P < 0.03), but the LH response to LPS was not altered by cytokine antagonists. Intravenous administration of either IL-1beta or TNF-alpha increased plasma concentrations of GH (P < 0.0001). Administration of IL-1RA and sTNF-R1 iv prevented LPS-induced increases in GH. Although LH was suppressed by high iv doses of IL-1beta (P = 0.0063), the antagonists did not alter the LH response to LPS. To determine whether LPS might directly activate GH release, confocal microscopy revealed colocalization of CD14, the LPS receptor, with GH and, to a lesser extent, LH and some prolactin (PRL)-containing cells, but not ACTH or TSH. These data are consistent with the effects of LPS on GH secretion originating through peripheral cytokine presentation to the pituitary, as well as a potential to act directly on selective populations of pituitary cells via CD14.

Localization of interleukin-18 and its receptor in somatotrophs of the bovine anterior pituitary gland

A pro-inflammatory cytokine, interleukin 18 (IL-18), induces intracellular expression of IL-1 and the release of IL-6. IL-1 and IL-6 has been detected in anterior pituitary cells, suggesting that IL-18 is produced in anterior pituitary cells and may serve to aid immuno-endocrine regulation. In the present study, we addressed this hypothesis by investigating the intracellular localization of IL-18 and its receptor in bovine anterior pituitary gland. IL-18 mRNA and its protein were detected in the anterior pituitary gland by RT-PCR and Western blotting. In situ hybridization showed that IL-18 mRNA was expressed in the anterior pituitary cells. Immunohistochemistry of IL-18 and specific hormones revealed the presence of IL-18 in somatotrophs. Furthermore, the expression of GH mRNA in IL-18 immunoreactive cells was confirmed by immuno-laser microdissection. These results first demonstrated that somatotrophs produced IL-18. Subsequently, the distribution of the IL-18 receptor alpha (IL-18Ralpha) was investigated in order to understand IL-18 signaling among the anterior pituitary cells. Bovine IL-18Ralpha cDNA was partially sequenced and detected in the anterior pituitary gland by RT-PCR. Immunohistochemistry of IL-18Ralpha, IL-18 and GH showed that IL-18Ralpha was co-localized in IL-18 immunoreactive cells or somatotrophs. These data suggest that IL-18 acts on somatotrophs as an immuno-endocrine mediator through the autocrine pathway.

Stimulatory effect of interleukin-1beta on growth hormone gene expression and growth hormone release from rat GH3 cells

Our previous studies demonstrated that interferon gamma increases the human (h) growth hormone (GH) gene promoter activity in rat pituitary GH3 cells, and its regulatory mechanism may be different from the classical GH-releasing hormone-induced regulatory mechanism. Interleukin-1beta (IL-1beta) is thought to induce the release of GH by pituitary cells, but whether or not and by which mechanisms IL-1beta regulates GH synthesis remains unclear. The purpose of our study was thus to investigate the effect of IL-1beta on the hGH gene expression in GH3 rat pituitary tumor cells using stable transfection of the hGH promoter fused to a luciferase reporter gene. Our results showed that IL-1beta (10-10(4) U/ml) increased GH secretion and synthesis and that 10(2) to 10(4) U/ml IL-1beta promoted the luciferase expression in stable GH3 cells, with a maximal action of 1.61 times over that of controls. Among inhibitors of intracellular signaling transduction pathways, mitogen-activated protein kinase kinase (MAPKK/MEK) inhibitor PD98059 (40 microM) and p38 MAPK inhibitor SB203580 (5 microM)blocked completely the stimulatory effect of IL-1beta, and the phosphoinositide 3-kinase inhibitor LY294002 (10 microM) blocked partially the induction of IL-1beta. Western blot analysis demonstrated that IL-1beta increased the activation of phosphorylated MEK and p38 MAPK in GH3 cells. Neither overexpression of Pit-1 nor inhibiting Pit-1 expression affected IL-1beta induction of hGH promoter activity. To identify the DNA sequence that mediated the effect of IL-1beta, six deletion constructs of hGH promoter were created. The stimulatory effect of IL-1beta was abolished following deletion of the -196- to -132-bp fragment. In conclusion, our data show that IL-1beta promotes GH secretion and synthesis by rat pituitary GH3 cells. The stimulatory effect of IL-1beta on the hGH gene promoter appears to require the activation of MEK, p38 MAPK, and phosphoinositide 3-kinase and a fragment of promoter sequence that spans the -196- to -132-bp fragment of the gene, but is unrelated to the Pit-1 protein.

Endocrine aspects in pathogenesis of mastitis in postpartum dairy cows

In well-managed dairy herds some environmental pathogens including Gram-negative (GN) strains (E. coli and others) have been recognized recently as the predominant causative microbes of mastitis in the peri-parturient period. In early weeks of lactation hyperketonaemia may predispose the high-producing cows for GN mastitis. In GN mastitis cytokines, eicosanoids and oxygen radicals are released, which are responsible for the local and systemic symptoms. Experimental administration of endotoxin induces a complex endocrine cascade. Similar changes in plasma levels of cortisol, insulin, insulin-like growth factor-I and thyroid hormones are seen also in severe cases of GN mastitis. However, leptin is not responsible for the anorexia associated with severe mastitis in ruminants. Mastitis can postpone the resumption of ovarian cyclic activity in dairy cows when its outbreak occurs between days 15 and 28 after calving (at the expected time of first ovulation). In cyclic cows severe cases of GN mastitis can induce premature luteolysis or prolong the follicular phase.