Neuropeptide B promotes differentiation of rodent white preadipocytes into mature adipocytes.

Neuropeptide B (NPB) modulates energy homeostasis and metabolism through activation of NPBWR1 and NPBWR2 in humans and NPBWR1 in rodents. Recently, we reported that NPB promotes adipogenesis in rat brown preadipocytes. In the present study, we evaluated the effects of NPB on proliferation and differentiation into mature adipocytes of white rat preadipocytes and 3T3-L1 cells. We found the expression of NPBWR1 and NPB on mRNA and protein level in rat white preadipocytes and 3T3-L1 cells. NPB increased expression of mRNA and protein production of adipogenic genes (PPARγ, C/EBPß, CEBPα and FABP4) in rat preadipocytes and 3T3-L1 cells during the differentiation process. Furthermore, NPB stimulated lipid accumulation in rat preadipocytes and 3T3-L1 cells. In addition, we found that NPB promotes phosphorylation of p38 kinase in rat preadipocytes and 3T3-L1 cells. NPB failed to stimulate expression of proadipogenic genes in the presence of p38 inhibitor. NPB failed to modulate viability and proliferation of rat preadipocytes and 3T3-L1 cells. Taken together, we report that NPB promotes differentiation of rodent preadipocytes via p38-dependent mechanism. NPB does not modulate viability and proliferation of rat preadipocytes and 3T3-L1 cells.

Obesity is associated with increased level of kisspeptin in mothers' blood and umbilical cord blood - a pilot study.

OBJECTIVE: Kisspeptin (KP) is a major regulator of reproductive functions. It has also been shown to be involved in the metabolic changes associated with obesity. According to the well-established concept of prenatal programming, environmental factors can influence physiological and behavioral systems at the early stages of development. Thus, we hypothesized that in pregnant women, obesity can be associated with alterations in the levels of KP. We also assumed that the observed changes in obese mothers' blood (MB) would be reflected in the umbilical cord blood (CB). MATERIALS AND METHODS: We collected MB and CB from obese and nonobese women and analyzed the differences in metabolic and hormonal profiles, including KP concentration, using commercially available assays. RESULTS: We found that the level of KP was increased in the MB and CB of obese patients compared to nonobese subjects (p<0.05). A strong correlation was observed between the concentration of KP in MB and CB (r=0.8343; p<0.01). Moreover, we detected that the differences in the adipokine profile observed in the MB were not reflected in CB. CONCLUSIONS: Our results indicate that blood KP concentration can serve as a valuable marker in pregnant women. However, further studies are needed to understand the alterations of this peptide in obese pregnant woman and their potential effects on offspring.

Orexin A but not orexin B regulates lipid metabolism and leptin secretion in isolated porcine adipocytes.

It is well known that orexins are involved in the metabolism and endocrine function of rodent adipocytes, but there are no data on other animal species, including pigs. Therefore, in this study, we tested the hypothesis that orexin A (OxA) and orexin B (OxB) modulate the metabolism and endocrine functions of isolated porcine adipocytes and adipose tissue explants. Moreover, we characterized the possible mechanism of OxA action in porcine adipocytes. According to the results, both orexin receptor 1 and orexin receptor 2 were expressed in the porcine adipose tissue. We found that OxA suppressed the release of glycerol from porcine adipocytes both in the absence (basal lipolysis; P < 0.05) and in the presence (stimulated lipolysis; P < 0.05) of isoproterenol. Orexin A increased basal and insulin-stimulated glucose uptake (P < 0.05), as well as it enhanced the rate of glucose incorporation into lipids with insulin (stimulated lipogenesis; P < 0.01) or without insulin (basal; P < 0.05). We have also shown that OxA stimulated the mRNA expression of glucose transporter 4 (P < 0.05) and its translocation into the plasma membrane (P < 0.01). Moreover, OxA upregulated the mRNA expression of leptin in isolated porcine adipocytes (P < 0.05) and increased the secretion of leptin (P < 0.05). We have also demonstrated one of the possible mechanisms of OxA action in adipocytes. In the presence of extracellular-signal-regulated kinase 1 and 2 (ERK1/2) inhibitor, the effect of OxA was not detectable in porcine adipocytes, which indicates that this peptide increased cell viability via ERK1/2 pathway (P < 0.05). However, OxB did not show any effect on the metabolism and endocrine functions of porcine adipocytes. In summary, we have shown for the first time that OxA has a significant impact on the intensity of lipolysis, glucose uptake, lipogenesis, as well as on the expression and secretion of leptin. Therefore, we conclude that OxA but not OxB regulates lipid metabolism in porcine adipose tissue and that this regulation is partly mediated via ERK1/2 pathway. The action of orexins should be further explored to better understand their role in the regulation of adiposity in pigs.

Subacute ruminal acidosis affects fermentation and endotoxin concentration in the rumen and relative expression of the CD14/TLR4/MD2 genes involved in lipopolysaccharide systemic immune response in dairy cows.

The first objective of this study was to investigate the effects of subacute ruminal acidosis (SARA) on fermentation, ruminal free lipopolysaccharides (LPS), and expression of the cluster of differentiation 14 (CD14), toll-like receptor 4 (TLR4), and myeloid differentiation protein 2 (MD2) complex in white blood cells involved in the systemic immune response in dairy cows. The second objective was a study of whether increased expression of the LPS receptor complex led to increases in the concentrations of plasma high-density lipoprotein (HDL) and serum Ca. Three hundred five dairy cows located in 13 Polish high-yielding dairy commercial farms were selected according to their days in milk (40-150 d; average = 75), 305-d milk yield (10,070-12,041 kg; average = 10,940), and number of lactations (primiparous, n = 139 and multiparous, n = 166). Next, the herds were segregated into 3 groups based on the percentages of cows with an assigned value of ruminal fluid pH: SARA-positive, SARA-risk, and SARA-negative herds. Moreover, 305 selected dairy cows were divided according to the classification based on ruminal fluid pH into 3 groups as healthy (pH >5.81), risk (pH 5.8-5.6) and acidotic cows (pH <5.6). Rumen fluid samples were collected via rumenocentesis. In the AC group, we recorded higher concentrations of ruminal free LPS [4.57 Log10 endotoxin units (EU)/mL; 42,206 EU/mL] compared with the healthy group (4.48 Log10 EU/mL; 34,179 EU/mL). Similarly, the concentration of ruminal free LPS was higher in SARA-positive herds (4.60 Log10 EU/mL; 43,000 EU/mL) compared with SARA-negative herds (4.47 Log10 EU/mL; 32,225 EU/mL). The relative mRNA abundance of genes associated with the function of LPS receptors, such as CD14, TLR4, and MD2, in white blood cells differed between all experimental groups on both cow and herd levels. In the acidotic group, we recorded higher concentrations of HDL (78.16 vs. 68.32 mg/dL) and serum amyloid A (10.80 vs. 9.16 µg/mL) and lower concentrations of Ca (8.26 vs. 10.16 mg/dL) and haptoglobin (470.19 vs. 516.85 ng/mL) compared with the healthy group. Similar results were obtained in the SARA herd status analysis, but the concentration of lipopolysaccharide-binding protein differed statistically. Moreover, the pH of ruminal fluid was negatively correlated with relative mRNA abundance of genes such as CD14, TLR4, MD2, and concentrations of serum HDL and serum amyloid A, although positively correlated with serum Ca. The results indicated that decreases in ruminal fluid pH increased the release of free LPS into the rumen and stimulated the expression of the LPS receptor complex and immune response. Moreover, an increase in the expression of the LPS receptor led to higher concentrations of plasma HDL and lower serum Ca, which may be a protective mechanism against endotoxemia. However, the biological significance of these results needs to be investigated further in larger field trials.

Serum levels of spexin and kisspeptin negatively correlate with obesity and insulin resistance in women.

Spexin (SPX) and kisspeptin (KISS) are novel peptides relevant in the context of regulation of metabolism, food intake, puberty and reproduction. Here, we studied changes of serum SPX and KISS levels in female non-obese volunteers (BMI<25 kg/m(2)) and obese patients (BMI>35 kg/m(2)). Correlations between SPX or KISS with BMI, McAuley index, QUICKI, HOMA IR, serum levels of insulin, glucagon, leptin, adiponectin, orexin-A, obestatin, ghrelin and GLP-1 were assessed. Obese patients had lower SPX and KISS levels as compared to non-obese volunteers (SPX: 4.48+/-0.19 ng/ml vs. 6.63+/-0.29 ng/ml; p<0.001, KISS: 1.357+/-0.15 nmol/l vs. 2.165+/-0.174 nmol/l; p<0.01). SPX negatively correlated with BMI, HOMA-IR, insulin, glucagon, active ghrelin and leptin. Positive correlations were found between SPX and QUICKI index, McAuley index, serum levels of obestatin, GLP-1 and adiponectin and orexin-A Serum KISS negatively correlated with BMI, HOMA-IR, serum levels of insulin, glucagon, active ghrelin and leptin. KISS positively correlated with QUICKI index, McAuley index and adiponectin. In summary, SPX and KISS show negative correlations with obesity, insulin resistance indices, and hormones known to affect insulin sensitivity in females. Both, SPX and KISS could be therefore relevant in the pathophysiology of obesity and insulin resistance.

Relationship between pH of ruminal fluid during subacute ruminal acidosis and physiological response of the Polish Holstein-Friesian dairy cows.

The aim of the study was to investigate the effect of ruminal fluid pH depression on biochemical indices of blood, urine, feces, and milk, and to determine which of them may be helpful as a marker for the diagnosis of subacute ruminal acidosis (SARA). Ruminal fluid samples were obtained by rumenocentesis from 305 cows representing 13 commercial dairy herds. The herds were selected based on percentages of cows with an assigned value of ruminal fluid pH segregated into three groups as: SARA-positive herd, if at least 25% of the ruminal fluid samples indicated a pH < 5.6; SARA-risk herd, if less than 25% of ruminal fluid samples indicated a pH < 5.6, but at least 33% showed a pH ≤ 5.8; and SARA-negative herd, if less than 25% of the ruminal fluid samples indicated a pH < 5.6, but less than 33% exhibited a pH = 5.8. Moreover, the dairy cows were divided according to the ruminal fluid pH into three groups as follows: healthy cows (HC, pH>5.80, n = 196), risk cows (RC, pH 5.8 - 5.6, n = 51), and acidotic cows (AC, pH < 5.6, n = 58). Almost 19% (58/305) of the cows were classified as acidotic (pH < 5.6) and 46.2% of the herds as SARA-positive. In the AC group, higher concentrations of insulin-like growth factor-I (IGF-I), non-esterified fatty acids (NEFA), rectal temperature and lower blood pH, compared with those of the HC group, were recorded. Moreover, in the SARA-positive herds, higher concentrations of IGF-I and the lowest blood pH, compared with SARA-negative herds, were observed. The lowering of ruminal fluid pH increased the blood IGF-I and NEFA concentrations and the rectal temperature and decreased the blood pH. These measures are indicators of the physiological changes that occur as part of the pathogenesis of the condition and may be helpful for the diagnosis of the SARA syndrome when serial measurements are conducted.

TRPV4 regulates insulin mRNA expression and INS-1E cell death via ERK1/2 and NO-dependent mechanisms.

TRPV4 is a Ca2+-permeable, nonselective cation channel. Recently, TRPV4 was implicated in controlling peripheral insulin sensitivity, insulin secretion and apoptosis of pancreatic beta cells. Here, we characterize the role and potential mechanisms of TRPV4 in regulating insulin mRNA expression and cell death in insulin producing INS-1E cells and rat pancreatic islets. TRPV4 protein production was downregulated by siRNA. Intracellular calcium level was measured using Fluo-3 AM. Gene expression was studied by real-time PCR. Phosphorylation of extracellular signal-regulated kinase (ERK1 and ERK2) was detected by Western blot. Nitric oxide (NO) production was assessed by chemiluminescent reaction. Reactive oxygen species (ROS) level was analysed using a fluorogenic dye (DCFDA). Cell death was evaluated by determination of cytoplasmic histone-associated DNA fragments. Downregulation of TRPV4 neither affected insulin mRNA expression nor INS-1E cell growth. By contrast, pharmacological TRPV4 activation by 100nmol/l GSK1016790A increased Ca2+ levels in INS-1E cells and enhanced insulin mRNA expression after 1 and 3h, whereas a suppression of insulin mRNA expression was detected after 24h incubation. GSK1016790A increased ERK1/2 phosphorylation and NO production but not ROS production. Pharmacological blockade of ERK1/2 attenuated GSK1016790A-induced insulin mRNA expression. Inhibition of NO synthesis by l-NAME failed to affect insulin mRNA expression in GSK1016790A treated INS-1E cells. Furthermore, inhibition of NO production attenuated GSK1016790A-induced INS-1E cell death. In pancreatic islets, 100nmol/l GSK1016790A increased insulin mRNA levels after 3h without inducing cytotoxicity after 24h. In conclusion, TRPV4 differently regulates insulin mRNA expression in INS-1E cells via ERK1/2 and NO-dependent mechanisms.

Chronic orexin-A (hypocretin-1) treatment of type 2 diabetic rats improves glucose control and beta-cell functions.

Orexin regulates food intake and energy expenditure. Here, we test the ability of orexin-A (OXA, hypocretin-1) at improving metabolic control in type 2 diabetic animals and elaborate potential mechanisms of action. Rats with experimentally induced type 2 diabetes by a combination of streptozotocin injection and high-fat diet feeding were chronically infused with OXA. In vitro experiments were conducted on isolated pancreatic islets, primary adipocytes and insulin secreting INS-1E cells. OXA improved glucose control, enhanced insulin sensitivity and attenuated pancreatic ß-cell loss in type 2 diabetic rats. Ex vivo, apoptotic death of pancreatic islets isolated from OXA-treated type 2 diabetic animals as well as the impairment of glucose-stimulated insulin secretion were attenuated, as compared to islets derived from vehicle-treated rats. OXA reduced plasma tumor necrosis factor-α (TNF-α) and non-esterified fatty acids (NEFA) levels in type 2 diabetic rats. OXA decreased palmitate- and TNF-α-induced apoptosis of INS-1E cells. OXA improves glucose control by enhancing insulin sensitivity and protecting ß-cells from apoptotic cell death in type 2 diabetic animals.

Orexin A modulates INS-1E cell proliferation and insulin secretion via extracellular signal-regulated kinase and transient receptor potential channels.

Orexins A (OXA) and B (OXB) control energy homeostasis by regulating food intake, energy expenditure and sleep-wake cycle. Several studies showed that OXA stimulates insulin secretion and proliferation of beta cells. However, mechanisms of action are still not well understood. Here, we investigated whether ERK and transient receptor potential channels (TRPs) play a role in mediating the effect of OXA on cell growth, insulin production, and secretion using the established INS-1E cell line. Cell proliferation was measured using BrdU assay. Insulin mRNA expression was detected by real-time PCR. Insulin secretion was assessed using ELISA. Intracellular calcium levels were measured using fluorescence calcium imaging (fura-2/AM). Extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation was detected by Western blot. TRP channel activity was blocked by lanthanum (III) chloride (La3+; 100 - 300 µM) or ruthenium red (RuR; 10 µM). OXA (100 nM) stimulated INS-1E cell proliferation, insulin secretion, intracellular Ca2+ concentration and ERK1/2 phosphorylation, without changing insulin mRNA expression. Inhibition of ERK1/2 by 10 µM U0126 attenuated OXA-stimulated INS-1E cell proliferation. Blockade of TRP channel activity by La3+ or RuR rendered OXA ineffective at modulating Ca2+ regulation and insulin release. In contrast, the L-type channel blocker nifedipine (10 µM) failed to affect OXA-stimulated insulin release. Taken together, OXA increases INS-1E cell proliferation via ERK1/2-dependent mechanism. Furthermore, OXA stimulates insulin secretion from INS-1E cells. TRPs are relevant for OXA-stimulated insulin secretion and intracellular calcium regulation.

TRPV6 channel modulates proliferation of insulin secreting INS-1E beta cell line.

Transient receptor potential channel vanilloid type 6 (TRPV6) is a non-selective cation channel with high permeability for Ca²âº ions. So far, the role of TRPV6 in pancreatic beta cells is unknown. In the present study, we characterized the role of TRPV6 in controlling calcium signaling, cell proliferation as well as insulin expression, and secretion in experimental INS-1E beta cell model. TRPV6 protein production was downregulated using siRNA by approx. 70%, as detected by Western blot. Intracellular free Ca²âº ([Ca²âº]i) was measured by fluorescence Ca²âº imaging using fura-2. Calcineurin/NFAT signaling was analyzed using a NFAT reporter assay as well as a calcineurin activity assay. TRPV6 downregulation resulted in impaired cellular calcium influx. Its downregulation also reduced cell proliferation and decreased insulin mRNA expression. These changes were companied by the inhibition of the calcineurin/NFAT signaling. In contrast, insulin exocytosis was not affected by TRPV6 downregulation. In conclusion, this study demonstrates for the first time the expression of TRPV6 in INS-1E cells and rat pancreatic beta cells and describes its role in modulating calcium signaling, beta cell proliferation and insulin mRNA expression. In contrast, TRPV6 fails to influence insulin secretion.

Resistin - from gene expression to development of diabetes.

Adipocyte-originated hormonal factors, playing a role of signaling particles, are widely engaged in energy control, feeding behavior and general glucose or lipid metabolism. One of them – resistin – has been suspected to initiate or develop insulin resistance and diabetes. From the moment of discovery of resistin, during last 13 years, numerous investigations put some light on a potential role of this hormone in mammals. In this review knowledge on resistin, including its structure, physiological role related to obesity and diabetes, as well as, gene sequence and phenotypic effects of the identified polymorphisms in human and domestic mammals is discussed.

Activation of TRPV4 channel in pancreatic INS-1E beta cells enhances glucose-stimulated insulin secretion via calcium-dependent mechanisms.

Transient receptor potential channel vanilloid type 4 (TRPV4) is a Ca(2+)- and Mg(2+)-permeable cation channel that influences oxidative metabolism and insulin sensitivity. The role of TRPV4 in pancreatic beta cells is largely unknown. Here, we characterize the role of TRPV4 in controlling intracellular Ca(2+) and insulin secretion in INS-1E beta cells. Osmotic, thermal or pharmacological activation of TRPV4 caused a rapid rise of intracellular Ca(2+) and enhanced glucose-stimulated insulin secretion. In the presence of the TRPV channel blocker ruthenium red (RuR) or after suppression of TRPV4 protein production, TRPV4 activators failed to increase [Ca(2+)]i and insulin secretion in INS-1E cells.

Obestatin inhibits lipogenesis and glucose uptake in isolated primary rat adipocytes.

Ghrelin and obestatin are encoded by the preproghrelin gene and originate from post-translational processing of the preproghrelin peptide. Obestatin is mainly present in the stomach, but its action is focused on appetite inhibition in opposition to ghrelin function. Recently, it has been presented that obestatin may regulate adipocyte metabolism and influence fat content. However, obestatin action is still poorly understood. Therefore, we aimed to investigate obestatin function on adipocyte metabolism in the rat. We studied changes in the mRNA expression of active and inactive isoforms of obestatin receptors. In addition, we analyzed influence of obestatin on lipogenesis, lipolysis and glucose transport in isolated adipocytes. Moreover, we also performed analysis of obestatin action on lipolysis in differentiated rat preadipocytes with silenced obestatin receptor. We found significantly higher expression of the obestatin receptor Gpr39-1a active form at an mRNA level following adipocytes incubation with obestatin. We did not observe expression changes in the inactive form of obestatin receptor Gpr39-1b. Additionally, we found significant changes in Gpr39-1a expression following obestatin receptor silencing in cells incubated with obestatin in comparison to control. Obestatin inhibited both, basal and insulin-stimulated lipogenesis and glucose transport in adipocytes. Furthermore, obestatin potentiated adrenalin-stimulated lipolysis. We also found reduced glycerol release following obestatin incubation in adipocytes with silenced Gpr39 gene. Our results indicate that obestatin acts via the GPR39 receptor in isolated adipocytes, and that through this mechanism obestatin influences lipid accumulation, glucose uptake and lipolysis.

Glucagon increases circulating fibroblast growth factor 21 independently of endogenous insulin levels: a novel mechanism of glucagon-stimulated lipolysis?

AIMS/HYPOTHESIS: Glucagon reduces body weight by modifying food intake, glucose/lipid metabolism and energy expenditure. All these physiological processes are also controlled by fibroblast growth factor 21 (FGF-21), a circulating hepatokine that improves the metabolic profile in obesity and type 2 diabetes. Animal experiments have suggested a possible interaction between glucagon and FGF-21 however, the metabolic consequences of this crosstalk are not understood. METHODS: The effects of exogenous glucagon on plasma FGF-21 levels and lipolysis were evaluated in healthy volunteers and humans with type 1 diabetes, as well as in rodents with streptozotocin (STZ)-induced insulinopenic diabetes. In vitro, the role of glucagon on FGF-21 secretion and lipolysis was studied using isolated primary rat hepatocytes and adipocytes. Fgf-21 expression in differentiated rat pre-adipocytes was suppressed by small interfering RNA and released FGF-21 was immunoneutralised by polyclonal antibodies. RESULTS: Glucagon induced lipolysis in healthy human volunteers, patients with type 1 diabetes, mice and rats with STZ-induced insulinopenic diabetes, and in adipocytes isolated from diabetic and non-diabetic animals. In addition, glucagon increased circulating FGF-21 in healthy humans and rodents, as well as in patients with type 1 diabetes, and insulinopenic rodents. Glucagon stimulated FGF-21 secretion from isolated primary hepatocytes and adipocytes derived from animals with insulinopenic diabetes. Furthermore, FGF-21 stimulated lipolysis in primary adipocytes isolated from non-diabetic and diabetic rats. Reduction of Fgf-21 expression (by approximately 66%) or immunoneutralisation of released FGF-21 markedly attenuated glucagon-stimulated lipolysis in adipocytes. CONCLUSIONS/INTERPRETATION: These results indicate that glucagon increases circulating FGF-21 independently of endogenous insulin levels. FGF-21 participates in glucagon-induced stimulation of lipolysis.

Effects of orexin A on proliferation, survival, apoptosis and differentiation of 3T3-L1 preadipocytes into mature adipocytes.

Metabolic activities of orexin A (OXA) in mature adipocytes are mediated via PI3K/PKB and PPARγ. However, the effects of OXA on preadipocytes are largely unknown. We report here that OXA stimulates the proliferation and viability of 3T3-L1 preadipocytes and protects them from apoptosis via ERK1/2, but not through PKB. OXA reduces proapoptotic activity of caspase-3 via ERK1/2. Inhibition of ERK1/2 prevents the differentiation of preadipocytes into adipocytes. Unlike insulin, neither short-term nor prolonged exposure of 3T3-L1 preadipocytes to OXA induces preadipocyte differentiation to adipocytes, despite increased ERK1/2 phosphorylation. Unlike insulin, OXA fails to activate PKB, which explains its inability to induce the differentiation of preadipocytes.

Orexin A stimulates glucose uptake, lipid accumulation and adiponectin secretion from 3T3-L1 adipocytes and isolated primary rat adipocytes.

AIMS/HYPOTHESIS: Orexin A (OXA) modulates body weight, food intake and energy expenditure. In vitro, OXA increases PPARγ (also known as PPARG) expression and inhibits lipolysis, suggesting direct regulation of lipid metabolism. Here, we characterise the metabolic effects and mechanisms of OXA action in adipocytes. METHODS: Isolated rat adipocytes and differentiated murine 3T3-L1 adipocytes were exposed to OXA in the presence or absence of phosphoinositide 3-kinase (PI3K) inhibitors. Pparγ expression was silenced using small interfering RNA. Glucose uptake, GLUT4 translocation, phosphatidylinositol (3,4,5)-trisphosphate production, lipogenesis, lipolysis, and adiponectin secretion were measured. Adiponectin plasma levels were determined in rats treated with OXA for 4 weeks. RESULTS: OXA PI3K-dependently stimulated active glucose uptake by translocating the glucose transporter GLUT4 from cytoplasm into the plasma membrane. OXA increased cellular triacylglycerol content via PI3K. Cellular triacylglycerol accumulation resulted from increased lipogenesis as well as from a decrease of lipolysis. Adiponectin levels in chow- and high-fat diet-fed rats treated chronically with OXA were increased. OXA stimulated adiponectin expression and secretion in adipocytes. Both pharmacological blockade of peroxisome proliferator-activated receptor γ (PPARγ) activity or silencing Pparγ expression prevented OXA from stimulating triacylglycerol accumulation and adiponectin production. CONCLUSIONS/INTERPRETATION: Our study demonstrates that OXA stimulates glucose uptake in adipocytes and that the evolved energy is stored as lipids. OXA increases lipogenesis, inhibits lipolysis and stimulates the secretion of adiponectin. These effects are conferred via PI3K and PPARγ2. Overall, OXA's effects on lipids and adiponectin secretion resemble that of insulin sensitisers, suggesting a potential relevance of this peptide in metabolic disorders.

Ghrelin but not obestatin regulates insulin secretion from INS1 beta cell line via UCP2-dependent mechanism.

The mitochondrial UCP2 mediates glucose-stimulated insulin secretion by decreasing intracellular ATP/ADP ratio. Insulin secretion is a tightly regulated process. Ghrelin, as well as obestatin, were intensively studied to determine their ability to modify insulin secretion. Ghrelin is considered to be an inhibitor of insulin release from pancreatic islets, however little is known about the effects of obestatin. In our study we demonstrate the stimulating effects of both peptides on insulin secretion in INS1 cells. Furthermore, we investigate the potential role of UCP2 in mediating the effects of both peptides on insulin secretion. UCP2 mRNA expression was down-regulated by ghrelin in the presence of 26.4 mM glucose, however it was unchanged after obestatin treatment. Our results confirm that UCP2 could be involved in the stimulating effect of ghrelin on insulin release from INS1 cells.

Importance of ghrelin in hypothalamus-pituitary axis on growth hormone release during normal pregnancy in the rat.

Ghrelin is a hormone mainly produced in the stomach and its first discovered action was connected with regulating growth hormone secretion. It was found that ghrelin injection increases growth hormone release and that this action is dose-dependent. Ghrelin may influence growth hormone secretion both by central and peripheral action. Ghrelin acts via its receptors named growth hormone secretagogue receptors (GHSR). Ghrelin receptors were found in almost all tissues including the central nervous system. Besides influence on growth hormone secretion, ghrelin also regulates food intake and energy metabolism centrally as well as peripherally. In our study, active ghrelin and growth hormone levels in serum were measured. We also investigated gene expression of proghrelin, growth hormone releasing hormone (GHRH) and growth hormone receptor (GH-R) in the hypothalamus and the active form of ghrelin receptor (GHSR-1a) in hypothalamus and pituitary. Expression of growth hormone and growth hormone releasing hormone receptor (GHRH-R) in the pituitary were also measured. The results of our study indicate that active ghrelin and growth hormone levels in serum increased during pregnancy. Expression of ghrelin in hypothalamus and its receptor also increased in hypothalamus and pituitary during pregnancy. We also observed that growth hormone gene expression rose in pituitary, while its receptor mRNA level in hypothalamus decreased. Additionally, growth hormone expression in placenta decreased during pregnancy. Moreover, GHRH in hypothalamus and its receptor in pituitary showed reduced levels during pregnancy. Our results may indicate that ghrelin is a important factor influencing growth hormone release during pregnancy.