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S Yang, X Xu, P Björntorp, and S Edén


The effects of growth hormone (GH) and testosterone, alone or in combination, on the regulation of lipolysis in isolated adipocytes from hypophysectomized rats were investigated. Male Sprague-Dawley rats were hypophysectomized at 50 days of age. One week after operation, hormonal replacement therapy with l-thyroxine and hydrocortisone acetate was given to hypophysectomized rats. Groups of rats were treated with GH (1·33 mg/kg, daily), testosterone (10 mg/kg, once) alone or in combination. After one week of hormonal treatment, adipocytes were isolated from the pooled epididymal and perirenal fat pads and glycerol release after isoproterenol stimulation and 125I-cyanopindolol binding was measured. Hypophysectomy caused a marked decrease in basal and isoproterenol-stimulated lipolysis. There was no effect of testosterone treatment alone on lipolysis, but GH treatment resulted in an increase in isoproterenol-induced lipolysis but not to the levels observed in cells from control rats. Testosterone and GH in combination restored the lipolytic response to isoproterenol. Also 125I-cyanopindolol binding was decreased after hypophysectomy. Testosterone treatment alone and GH treatment alone increased the binding, while in combination the treatment had an additive effect. Affinity was not changed, but the effects seemed to be on receptor number, as determined by Scatchard analysis.

Forskolin-stimulated cAMP accumulation in adipocytes was markedly reduced after hypophysectomy. Testosterone treatment alone had no effect. GH treatment alone increased forskolin-stimulated cAMP accumulation, although the level was lower than that found in control rats. The combined treatment resulted in a further increase to levels observed in adipocytes from control rats.

These results demonstrate that GH and testosterone have additive effects in the regulation of lipolysis. Both hormones increase the β-adrenergic receptor density, partly explaining this additive effect. Moreover, GH may contribute to the lipolytic response by affecting steps distal to the receptor in the lipolytic cascade.

Journal of Endocrinology (1995) 147, 147–152

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Chanika Phornphutkul, Ke-Ying Wu, Xu Yang, Qian Chen, and Philip A Gruppuso

Insulin-like growth factor-I (IGF-I) is a critical regulator of skeletal growth. While IGF-I has been shown to be a potent chondrocyte mitogen in vitro, its role in chondrocyte differentiation is less well characterized. We chose to study the action of IGF-I on an accepted model of chondrocyte differentiation, the ATDC5 cell line. Insulin concentrations sufficiently high to interact with the IGF-I receptor are routinely used to induce ATDC5 cells to differentiate. Therefore, we first examined the ability of IGF-I to promote chondrocyte differentiation at physiological concentrations. IGF-I could induce differentiation of these cells at concentrations below 10 nM. However, increasing IGF-I concentrations were less potent at inducing differentiation. We hypothesized that mitogenic effects of IGF-I might inhibit its differentiating effects. Indeed, the extracellular-signal-regulated kinase (ERK)-pathway inhibitor PD98059 inhibited ATDC5 cell DNA synthesis while enhancing differentiation. This suggested that the ability of IGF-I to promote both proliferation and differentiation might require that its signaling be modulated through the differentiation process. We therefore compared IGF-I-mediated ERK activation in proliferating and hypertrophic chondrocytes. IGF-I potently induced ERK activation in proliferating cells, but minimal ERK response was seen in hypertrophic cells. In contrast, IGF-I-mediated Akt activation was unchanged by differentiation, indicating intact upstream IGF-I receptor signaling. Similar findings were observed in the RCJ3.1C5.18 chondrogenic cell line and in primary chick chondrocytes. We conclude that IGF-I promotes both proliferation and differentiation of chondrocytes and that the differentiation effects of IGF-I may require uncoupling of signaling to the ERK pathway.

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Hong Xu, Yang Zhou, Yongxia Liu, Jian Ping, Qiyang Shou, Fangming Chen, and Ru Ruo

Nonalcoholic fatty liver disease and cirrhosis are strongly associated with insulin resistance and glucose intolerance. To date, the influence of metformin on glycogen synthesis in the liver is controversial. Limited studies have evaluated the effect of metformin on hepatic insulin signaling pathway in vivo. In this study, an insulin-resistant rat model of nonalcoholic steatohepatitis and cirrhosis was developed by high-fat and high-sucrose diet feeding in combination with subcutaneous injection of carbon tetrachloride. Liver tissues of the model rats were featured with severe steatosis and cirrhosis, accompanied by impaired liver function and antioxidant capacity. The glucose tolerance was impaired, and the index of insulin resistance was increased significantly compared with the control. The content of hepatic glycogen was dramatically decreased. The expression of insulin receptor β (IRβ); phosphorylations of IRβ, insulin receptor substrate 2 (IRS2), and Akt; and activities of phosphatidylinositol 3-kinase (PI3K) and glycogen synthase (GS) in the liver were significantly decreased, whereas the activities of glycogen synthase kinase 3α (GSK3α) and glycogen phosphorylase a (GPa) were increased. Metformin treatment remarkably improved liver function, alleviated lipid peroxidation and histological damages of the liver, and ameliorated glucose intolerance and insulin resistance. Metfromin also significantly upregulated the expression of IRβ; increased the phosphorylations of IRβ, IRS2, and Akt; increased the activities of PI3K and GS; and decreased GSK3α and GPa activities. In conclusion, our study suggests that metformin upregulates IRβ expression and the downstream IRS2/PI3K/Akt signaling transduction, therefore, to increase hepatic glycogen storage and improve insulin resistance. These actions may be attributed to the improved liver histological alterations by metformin.

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Yuan Ni, Dan Xu, Feng Lv, Yang Wan, Guanlan Fan, Wen Zou, Yunxi Chen, Linguo Pei, Jing Yang, and Hui Wang

Prenatal ethanol exposure (PEE) adversely affects the offspring reproductive system. We aimed to confirm the susceptibility to premature ovarian insufficiency (POI) in female PEE offspring and elucidate its intrauterine programming mechanism. The pregnant Wistar female rats were intragastrically administered with 4 g/kg × day of ethanol from gestational day (GD) 9 to 20. Offspring reproductive parameters were detected on GD20, postnatal week (PW) 6 and PW12. The PEE foetuses showed a decreased number of oocytes, increased ovarian cell apoptosis and upregulated expression levels of ovarian insulin-like growth factor 1 (IGF1) signalling pathway and steroidogenic enzymes. The proportion of atretic follicles in adult rats was increased, while the number of anti-Müllerian hormone-positive antral follicles was decreased. The serum oestradiol (E2) levels were decreased, but the follicle stimulation hormone levels were elevated. The ovarian Igf1 signalling pathway was transformed from activation during puberty to relative inhibition in adulthood, and the expression levels of ovarian steroidogenic enzymes were inhibited in adulthood. Furthermore, we treated the human granulosa cell line KGN with different ethanol concentrations (15, 30, 60, 120 mM) and found that the expression of IGF1 signalling pathway components, 3β-HSD and P450arom, as well as the production of E2, was increased. After IGF1 siRNA transfection, P450arom expression and E2 production were downregulated. These results suggest that PEE induces POI susceptibility in adult females, which may be caused by over-activation of the foetal ovarian Igf1 signalling pathway and steroidogenesis under PEE, resulting in accelerated early development of folliculogenesis and depletion of primordial follicles.

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Te Du, Liu Yang, Xu Xu, Xiaofan Shi, Xin Xu, Jian Lu, Jianlu Lv, Xi Huang, Jing Chen, Heyao Wang, Jiming Ye, Lihong Hu, and Xu Shen

Vincamine, a monoterpenoid indole alkaloid extracted from the Madagascar periwinkle, is clinically used for the treatment of cardio-cerebrovascular diseases, while also treated as a dietary supplement with nootropic function. Given the neuronal protection of vincamine and the potency of β-cell amelioration in treating type 2 diabetes mellitus (T2DM), we investigated the potential of vincamine in protecting β-cells and ameliorating glucose homeostasis in vitro and in vivo. Interestingly, we found that vincamine could protect INS-832/13 cells function by regulating G-protein-coupled receptor 40 (GPR40)/cAMP/Ca2+/IRS2/PI3K/Akt signaling pathway, while increasing glucose-stimulated insulin secretion (GSIS) by modulating GPR40/cAMP/Ca2+/CaMKII pathway, which reveals a novel mechanism underlying GPR40-mediated cell protection and GSIS in INS-832/13 cells. Moreover, administration of vincamine effectively ameliorated glucose homeostasis in either HFD/STZ or db/db type 2 diabetic mice. To our knowledge, our current work might be the first report on vincamine targeting GPR40 and its potential in the treatment of T2DM.

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Y Yang, J Cao, W Xiong, J Zhang, Q Zhou, H Wei, C Liang, J Deng, T Li, S Yang, and L Xu

It has been documented that stress or glucocorticoids have conflicting effects on memory under different conditions. However, it is not fully understood why stress can either impair or enhance memory. Here, we have examined the performance of six age groups of Wistar rats in a water maze spatial task to evaluate the effects of stress under different conditions. We found that the impairment or enhancement effect of an 'elevated platform' (EP) stress on memory was dependent on previous stress experience and on age. EP stress impaired memory retrieval in water maze naive animals, but enhanced rather than impaired memory retrieval in young water maze stress-experienced animals. Furthermore, exogenously applied corticosterone or foot shock stress before water maze training prevented the impairment of memory retrieval that should be induced by treatment with corticosterone or foot shock before the 'probe trial'. Again, memory retrieval was enhanced in young animals under these conditions, and this enhancement can be prevented by the glucocorticoid receptor antagonist RU 38486. Thus, glucocorticoid receptor activation not only induced impairment of memory but also increased the capacity of young animals to overcome a later stress. The present findings suggest that the effect of stress on memory can be switched from impairment to enhancement dependent on both stress experience and age.

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Chao Li, Bin Yang, Zhihao Xu, Eric Boivin, Mazzen Black, Wenlong Huang, Baoyou Xu, Ping Wu, Bo Zhang, Xian Li, Kunsong Chen, Yulian Wu, and Gina R Rayat

Oxidative stress is a major cause of islet injury and dysfunction during isolation and transplantation procedures. Cyanidin-3-O-glucoside (C3G), which is present in various fruits and vegetables especially in Chinese bayberry, shows a potent antioxidant property. In this study, we determined whether C3G could protect neonatal porcine islets (NPI) from reactive oxygen species (H2O2)-induced injury in vitro and promote the function of NPI in diabetic mice. We found that C3G had no deleterious effect on NPI and that C3G protected NPI from damage induced by H2O2. Significantly higher hemeoxygenase-1 (HO1) gene expression was detected in C3G-treated NPI compared to untreated islets before and after transplantation (P < 0.05). Western blot analysis showed a significant increase in the levels of phosphorylated extracellular signal-regulated kinase 1/2 (ERK1/2) and phosphatidylinositol 3-kinase (PI3K/Akt) proteins in C3G-treated NPI compared to untreated islets. C3G induced the nuclear translocation of nuclear erythroid 2-related factor 2 (NRF2) and the significant elevation of HO1 protein. Recipients of C3G-treated NPI with or without C3G-supplemented drinking water achieved normoglycemia earlier compared to recipients of untreated islets. Mice that received C3G-treated islets with or without C3G-supplemented water displayed significantly lower blood glucose levels at 5–10 weeks post-transplantation compared to mice that received untreated islets. Mice that received C3G-treated NPI and C3G-supplemented drinking water had significantly (P < 0.05) lower blood glucose levels at 7 and 8 weeks post-transplantation compared to mice that received C3G-treated islets. These findings suggest that C3G has a beneficial effect on NPI through the activation of ERK1/2- and PI3K/AKT-induced NRF2-mediated HO1 signaling pathway.

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L Yang, CB Kuo, Y Liu, D Coss, X Xu, C Chen, ML Oster-Granite, and AM Walker

During rat pregnancy initial high concentrations of prolactin (PRL) decline by about day 9, concomitant with an increase in the ratio of unmodified to phosphorylated PRL. The physiological significance of both the decline in total PRL and the change in ratio of the two PRLs is unknown. To test the importance of each, either unmodified PRL (U-PRL) or a molecular mimic of phosphorylated PRL (PP-PRL) were continuously administered to rats throughout pregnancy. A dose of 6 microg/24 h resulted in circulating concentrations of 50 ng/ml of each administered PRL and had little effect on the pregnancy itself. After birth, pups were killed and various tissues examined. In the pup lungs, exposure to additional PP-PRL caused a reduction in epithelial integrity and an increase in apoptosis, whereas exposure to additional U-PRL had beneficial, anti-apoptotic effects. In the heart, PP-PRL caused an apparent developmental delay, whereas U-PRL promoted tissue compaction. In the blood, U-PRL increased the number of mature red blood cells at the expense of white blood cell production. Within the white blood cell population, myelopoiesis was favored at the expense of lymphopoiesis. PP-PRL, in contrast, had a less dramatic influence on the hematopoietic compartment by promoting red blood cell maturation and granulocyte production. In the thymus, exposure to PP-PRL caused accumulation of apoptotic thymocytes in enlarged glands, whereas exposure to U-PRL resulted in smaller thymi. In the spleen, exposure to U-PRL increased cellularity, with the majority of cells belonging to the erythroid series - a finding consistent with increased red blood cells in the circulation. Exposure to PP-PRL was without discernible effect. In all of these tissues, the contrasting effects of the two PRLs indicate that the absolute concentration of PRL is not crucial, but that the ratio of U-PRL to PP-PRL has a profound effect on tissue development. In brown fat, both PRL preparations decreased the number of lipid droplets. This result is therefore probably a consequence of the increase in total PRL. The results of this study attest to the importance of the U-PRL:PP-PRL ratio normally present during pregnancy and have provided clues as to the possible pathogenesis of a variety of neonatal problems.

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Shibin Ding, Ying Fan, Nana Zhao, Huiqin Yang, Xiaolei Ye, Dongliang He, Xin Jin, Jian Liu, Chong Tian, Hongyu Li, Shunqing Xu, and Chenjiang Ying

Epidemiological findings on the association between bisphenol A (BPA, 2,2-bis-(4-hydroxyphenyl)propane) exposure and type 2 diabetes mellitus (T2DM) are paradoxical. In animal studies, BPA has been shown to disrupt pancreatic function and blood glucose homeostasis even at a reference ‘safe’ level during perinatal period. In this study, we explored the effects of long-term paternal exposure to a ‘safe’ level of BPA on parents themselves and their offspring. Adult male genitor rats fed with either standard chow diet (STD) or high-fat diet (HFD) were treated respectively with either vehicle or BPA (50 μg/kg per day) for 35 weeks. The male rats treated with vehicle or BPA for 21 weeks were then used as sires, and the adult female rats were fed with STD during the gestation and lactation. Offspring rats were weaned on postnatal day 21 and fed with STD in later life. Metabolic parameters were recorded on the adult male rats and their adult offspring. BPA exposure disrupted glucose homeostasis and pancreatic function, and HFD aggravated these adverse effects. However, BPA exposure did not alter body weight, body fat percentage, or serum lipid. In addition, the paternal BPA exposure did not cause adverse reproductive consequence or metabolic disorder in the adult offspring. Our findings indicate that chronic exposure to a predicted ‘safe’ dose of BPA contributes to glucose metabolic disorders, and that HFD aggravates these adverse effects in paternal rats.

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Tong Sun, Wen-Bo Deng, Hong-Lu Diao, Hua Ni, Yu-Yan Bai, Xing-Hong Ma, Li-Bin Xu, and Zeng-Ming Yang

Prostaglandin (PGE) 2 is the most common prostanoid and plays an important role in female reproduction. The aim of this study was to examine the expression and regulation of microsomal (m) PGE synthase (PGES)-1 and cytosolic (c) PGES in the mouse ovary during sexual maturation, gonadotropin treatment and luteal development by in situ hybridization and immunohistochemistry. Both mPGES-1 mRNA signals and immunostaining were localized in the granulosa cells, but not in the thecal cells and oocytes. cPGES mRNA signals were localized in both granulosa cells and oocytes, whereas cPGES immunostaining was exclusively localized in the oocytes. In our superovulated model of immature mice, there was a basal level of mPGES-1 mRNA signals in the granulosa cells at 48 h after equine chorionic gonadotropin (eCG) treatment. mPGES-1 mRNA level was induced by human chorionic gonadotropin (hCG) treatment for 0.5 h, whereas mPGES-1 immunostaining was slightly induced at 0.5 h after hCG treatment and reached a maximal level at 3 h after hCG treatment. eCG treatment had no obvious effects on either cPGES mRNA signals or immunostaining. A strong level of cPGES immunostaining was present in both unstimulated and eCG-treated groups. Both mPGES-1 mRNA signals and immunostaining were highly detected in the corpus luteum 2 days post-hCG injection and declined from days 3 to 7 post-hCG injection. cPGES immunostaining was at a basal level or not detectable from days 1 to 7 after hCG injection and was highly expressed in the corpus luteum from days 9 to 15 post-hCG injection. PGE2 biosynthesized through the mPGES-1 pathway may be important for follicular development, ovulation and luteal formation.