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H. S. YU, S. F. PANG, and P. L. TANG

To study the short- and long-term effects of pinealectomy on the level of retinal melatonin, male rats adapted to a photoperiod of 12 h light: 12 h darkness (with lights on at 06.00 h) were pinealectomized. In the short-term experiment, the rats were decapitated 1 week after pinealectomy. In the long-term experiment, 1 month was allowed for recovery. Melatonin was extracted from retinae and quantified by radioimmunoassay. A diurnal rhythm of retinal melatonin was found to persist after pinealectomy in both experiments. An increase in retinal melatonin was demonstrated 1 month after pinealectomy, indicating a compensatory effect on melatonin in the retinae of pinealectomized rats. Thus, biosynthesis of melatonin in the retina may be modulated through a negative feedback system.

Free access

H Stangl, GA Graf, L Yu, G Cao, and K Wyne

High-dose 17alpha-ethinyl estradiol treatment is associated with increased adrenal and decreased hepatic levels of scavenger receptor class B type 1 (SR-BI) in rats. In this paper we explored the mechanisms responsible for the differential regulation of SR-BI by estrogen in these two tIssues. Previously it was shown that estrogen-treated rats are profoundly hypolipidemic due to increased hepatic low density lipoprotein receptor (LDLR) activity, and that this effect is not maintained with hypophysectomy. To determine if the reduction in hepatic SR-BI was a direct or indirect effect of estrogen, we treated hypophysectomized rats with high-dose estrogen; the levels of SR-BI expression did not change in the livers or adrenals of these animals. To determine if the absence of response to estrogen in the adrenals of hypophysectomized animals was due to the absence of adrenocorticotropic hormone (ACTH), we examined the effect of estrogen treatment on SR-BI expression in animals treated with dexamethasone, which inhibits endogenous ACTH production. The administration of dexamethasone completely inhibited the increase in SR-BI expression in the adrenals of estrogen-treated rats. From these studies we conclude that estrogen does not have a direct effect on SR-BI expression in either the liver or the adrenals. In the liver, the decrease in SR-BI is dependent on the estrogen-induced increase in LDLR activity, and in the adrenal glands, ACTH is required for the estrogen-associated increase in expression of SR-BI.

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Yu-Chyu Chen, Madan L Nagpal, Douglas M Stocco, and Tu Lin

This study was performed to compare the effects of three well-known phytoestrogens such as genistein, resveratrol, and quercetin on steroidogenesis in MA-10 mouse tumor Leydig cells. Addition of genistein or resveratrol to MA-10 cells resulted in decreases in the cAMP-stimulated progesterone secretion, but quercetin had an opposite response. Steroidogenic acute regulatory (StAR) mRNA expression and StAR promoter activity in transiently transfected MA-10 cells were significantly reduced by genistein or resveratrol, but increased by quercetin. Genistein was found to inhibit MA-10 cell proliferation, while resveratrol and quercetin had no effect. Quercetin-induced increase in cAMP-stimulated progesterone secretion was reversed by ICI 182,780, an estrogen receptor (ER) antagonist. However, ICI 182,780 had no effect on cAMP plus quercetin-stimulated StAR promoter activity. To examine whether non-ER factors are associated with quercetin-stimulated progesterone production, we treated MA-10 cells with EGTA to deprive them of extracellular Ca2+. We found that EGTA inhibited quercetin-plus cAMP-stimulated progesterone secretion and StAR promoter activity. Blocking of Ca2+ influx through L- or T-type voltage-gated Ca2+ channels with verapamil or mibefradil respectively, attenuated quercetin-stimulated progesterone secretion, while they had no effect on quercetin-plus cAMP-stimulated StAR promoter activity. Blocking of intracellular Ca2+ efflux by sodium orthovanadate, a Ca2+-pump inhibitor, blocked quercetin- plus cAMP-stimulated progesterone secretion and StAR promoter activity in MA-10 cells. Finally, EGTA or vanadate reduced quercetin and cAMP-increased in StAR mRNA expression in MA-10 cells, while ICI 182,780 had no effect. Taken together, these results indicate that phytoestrogens have differential effects on steroidogenesis in MA-10 cells.

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A L Markel, O E Redina, M A Gilinsky, G M Dymshits, E V Kalashnikova, Yu V Khvorostova, L A Fedoseeva, and G S Jacobson

The functions of the hypothalamic adrenal cortical and sympathetic adrenal medullary systems were studied in rats with inherited stress-induced arterial hypertension (ISIAH strain). A characteristic feature of the ISIAH strain is an increase in arterial blood pressure measured both under basal conditions and after restraint stress in particular. In the control ISIAH rats, the basal plasma ACTH concentration was slightly lower than that in the normotensive Wistar albino Glaxo (WAG) rats, and no differences were found in plasma corticosterone. However, the 0.5-h restraint stress produced higher activation of the adrenal cortex in the ISIAH rats. Gluco- and mineralocorticoid responses to the blood volume reduction stresses and ACTH and corticosterone responses to social stress were stronger in the ISIAH than in the control WAG rats. An increase in epinephrine content in adrenals in the basal state and enhanced response of the sympathetic adrenal medullary system to handling stress were observed in the ISIAH rats. Restraint stress produced significantly higher expression of genes encoding corticotropin-releasing hormone-mRNA in hypothalamus and proopiomelanocortin-mRNA in pituitary in the ISIAH than in the WAG rats. Restraint stress produced a decrease in glucocorticoid receptor (GR) gene expression (GR-mRNA) in hippocampus in the ISIAH, but not in the WAG rats. A persistent increase in tyrosine hydroxylase-mRNA in adrenals of the ISIAH rats was found. It is concluded that the ISIAH rat strain is an appropriate model of stress-sensitive hypertension with the predominant involvement of the hypothalamic adrenal cortical and sympathetic adrenal medullary systems in its pathogenesis.

Open access

Sandra Pereira, Wen Qin Yu, María E Frigolet, Jacqueline L Beaudry, Yaniv Shpilberg, Edward Park, Cristina Dirlea, B L Grégoire Nyomba, Michael C Riddell, I George Fantus, and Adria Giacca

We have shown in rats that sodium salicylate (SS), which inhibits IkBa kinase B (IKKB), prevents hepatic and peripheral insulin resistance caused by short-term (7 h) i.v. administration of Intralipid and heparin (IH). We wished to further determine whether this beneficial effect of SS persisted after prolonged (48 h) IH infusion, which better mimics the chronic free fatty acid (FFA) elevation of obesity. Hence, we performed hyperinsulinemic euglycemic clamps with tritiated glucose methodology to determine hepatic and peripheral insulin sensitivity in rats infused with saline, IH, IH and SS, or SS alone. SS prevented peripheral insulin resistance (P<0.05) caused by prolonged plasma FFA elevation; however, it did not prevent hepatic insulin resistance. In skeletal muscle, protein levels of phospho-IkBa were augmented by prolonged IH administration and this was prevented by SS, suggesting that IH activates while SS prevents the activation of IKKB. Markers of IKKB activation, namely protein levels of phospho-IkBa and IkBa, indicated that IKKB is not activated in the liver after prolonged FFA elevation. Phosphorylation of serine 307 at insulin receptor substrate (IRS)-1, which is a marker of proximal insulin resistance, was not altered by IH administration in the liver, suggesting that this is not a site of hepatic insulin resistance in the prolonged lipid infusion model. Our results suggest that the role of IKKB in fat-induced insulin resistance is time and tissue dependent and that hepatic insulin resistance induced by prolonged lipid elevation is not due to an IRS-1 serine 307 kinase.

Free access

M Candolfi, G Jaita, D Pisera, L Ferrari, C Barcia, C Liu, J Yu, G Liu, M G Castro, and A Seilicovich

Our previous work showed that tumor necrosis factor (TNF)-α and FasL induce apoptosis of anterior pituitary cells. To further analyze the effect of these proapoptotic factors, we infected primary cultures from rat anterior pituitary, GH3 and AtT20 cells with first-generation adenoviral vectors encoding TNF-α, FasL or, as a control, β-galactosidase (β-Gal), under the control of the human cytomegalovirus promoter. Successful expression of the encoded transgenes was determined by immunocytochemistry. Although we observed basal expression of TNF-α and FasL in control cultures of anterior pituitary cells, fluorescence-activated cell sorting (FACS) cell cycle analysis showed that the overexpression of TNF-α or FasL increases the percentage of hypodiploid lactotropes and somatotropes. Nuclear morphology and TUNEL staining revealed that the cells undergo an apoptotic death process. We detected strong immunoreactivity for TNFR1 and Fas in the somatolactotrope cell line GH3. TNF-α, but not FasL, was expressed in control cultures of GH3 cells. The infection of GH3 cells with adenovirus encoding TNF-α or FasL increased the percentages of hypodiploid and TUNEL-positive cells. TNF-α or FasL immunoreactivity was not observed in the corticotrope cell line AtT20. However, adenovirus encoding TNF-α or FasL efficiently transduced these cells and increased the percentages of hypodiploid and TUNEL-positive cells. The expression of β-Gal was detected in all these cultures but did not affect cell viability. In conclusion, these results suggest that death signaling cascades triggered by TNF receptor 1 (TNFR1) and Fas are present in both normal and tumoral pituitary cells. Therefore, overexpression of proapoptotic factors could be a useful tool in the therapy of pituitary adenomas.

Free access

Hui Yu, Zoe Thompson, Sylee Kiran, Graham L Jones, Lakshmi Mundada, Surbhi, Marcelo Rubinstein, and Malcolm J Low

Proopiomelanocortin (POMC) neurons in the hypothalamic arcuate nucleus (ARC) are essential for normal energy homeostasis. Maximal ARC Pomc transcription is dependent on neuronal Pomc enhancer 1 (nPE1), located 12 kb upstream from the promoter. Selective deletion of nPE1 in mice decreases ARC Pomc expression by 70%, sufficient to induce mild obesity. Because nPE1 is located exclusively in the genomes of placental mammals, we questioned whether its hypomorphic mutation would also alter placental Pomc expression and the metabolic adaptations associated with pregnancy and lactation. We assessed placental development, pup growth, circulating leptin and expression of Pomc, Agrp and alternatively spliced leptin receptor (LepR) isoforms in the ARC and placenta of Pomc∆1/∆1 and Pomc+/+ dams. Despite indistinguishable body weights, lean mass, food intake, placental histology and Pomc expression and overall pregnancy outcomes between the genotypes, Pomc ∆1/∆1 females had increased pre-pregnancy fat mass that paradoxically decreased to control levels by parturition. However, Pomc∆1/∆1 dams had exaggerated increases in circulating leptin, up to twice of that of the typically elevated levels in Pomc+/+ mice at the end of pregnancy, despite their equivalent fat mass. Pomc∆1/∆1 dams also had increased placental expression of soluble leptin receptor (LepRe), although the protein levels of LEPRE in circulation were the same as Pomc+/+ controls. Together, these data suggest that the hypomorphic Pomc∆1/∆1 allele is responsible for the perinatal super hyperleptinemia of Pomc∆1/∆1 dams, possibly due to upregulated leptin secretion from individual adipocytes.

Free access

Zhiguo Liu, Chun Yan Lim, Michelle Yu-Fah Su, Stephanie Li Ying Soh, Guanghou Shui, Markus R Wenk, Kevin L Grove, George K Radda, Weiping Han, and Xiaoqiu Xiao

Neonatal overnutrition results in accelerated development of high-fat diet (HFD)-induced metabolic defects in adulthood. To understand whether the increased susceptibility was associated with aggravated inflammation and dysregulated lipid metabolism, we studied metabolic changes and insulin signaling in a chronic postnatal overnutrition (CPO) mouse model. Male Swiss Webster pups were raised with either three pups per litter to induce CPO or ten pups per litter as control (CTR) and weaned to either low-fat diet (LFD) or HFD. All animals were killed on the postnatal day 150 (P150) except for a subset of mice killed on P15 for the measurement of stomach weight and milk composition. CPO mice exhibited accelerated body weight gain and increased body fat mass prior to weaning and the difference persisted into adulthood under conditions of both LFD and HFD. As adults, insulin signaling was more severely impaired in epididymal white adipose tissue (WAT) from HFD-fed CPO (CPO–HFD) mice. In addition, HFD-induced upregulation of pro-inflammatory cytokines was exaggerated in CPO–HFD mice. Consistent with greater inflammation, CPO–HFD mice showed more severe macrophage infiltration than HFD-fed CTR (CTR–HFD) mice. Furthermore, when compared with CTR–HFD mice, CPO–HFD mice exhibited reduced levels of several lipogenic enzymes in WAT and excess intramyocellular lipid accumulation. These data indicate that neonatal overnutrition accelerates the development of insulin resistance and exacerbates HFD-induced metabolic defects, possibly by worsening HFD-induced inflammatory response and impaired lipid metabolism.

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Guofeng Zhang, Hiroki Hirai, Tao Cai, Junnosuke Miura, Ping Yu, Hanxia Huang, Martin R Schiller, William D Swaim, Richard D Leapman, and Abner L Notkins

The regulated endocrine-specific protein, RESP18, first found in the rat pituitary, was thought to be regulated by dopaminergic drugs. Bioinformatics studies showed that RESP18 shares sequence homology with the luminal region of IA-2, a dense core vesicle (DCV) transmembrane protein involved in insulin secretion. The present study was initiated to examine the genomic structure and subcellular localization of RESP18 and the effect of glucose on its expression. Human RESP18 was isolated from a pancreas cDNA library and its subcellular localization was determined by immunoelectron microscopy. MIN6 cells and mouse islets were used to study the effect of glucose on RESP18 expression. Bioinformatics analysis revealed that RESP18 and IA-2 are tandemly arranged within a 45 kb region on human chromosome 2 and share common intron–exon boundaries. By confocal microscopy, RESP18 was found in α, β and δ cells in the pancreatic islets. Electron microscopy revealed that RESP18 is present in the lumen of DCVs. The expression of RESP18 in β cells is markedly increased following exposure to high glucose and also elevated in the islets of diabetic, but not non-diabetic, NOD mice. We conclude that RESP18 is a luminal protein of DCVs and its expression is regulated by exposure to glucose.

Free access

Jessica L Pierce, Ke-Hong Ding, Jianrui Xu, Anuj K Sharma, Kanglun Yu, Natalia del Mazo Arbona, Zuleika Rodríguez-Santos, Paul J Bernard, Wendy B Bollag, Maribeth H Johnson, Mark W Hamrick, Dana L Begun, Xing-Ming Shi, Carlos M Isales, and Meghan E McGee-Lawrence

Excess fat within bone marrow is associated with lower bone density. Metabolic stressors such as chronic caloric restriction (CR) can exacerbate marrow adiposity, and increased glucocorticoid signaling and adrenergic signaling are implicated in this phenotype. The current study tested the role of glucocorticoid signaling in CR-induced stress by conditionally deleting the glucocorticoid receptor (Nr3c1; hereafter abbreviated as GR) in bone marrow osteoprogenitors (Osx1-Cre) of mice subjected to CR and ad libitum diets. Conditional knockout of the GR (GR-CKO) reduced cortical and trabecular bone mass as compared to WT mice under both ad libitum feeding and CR conditions. No interaction was detected between genotype and diet, suggesting that the GR is not required for CR-induced skeletal changes. The lower bone mass in GR-CKO mice, and the further decrease in bone by CR, resulted from suppressed bone formation. Interestingly, treatment with the β-adrenergic receptor antagonist propranolol mildly but selectively improved metrics of cortical bone mass in GR-CKO mice during CR, suggesting interaction between adrenergic and glucocorticoid signaling pathways that affects cortical bone. GR-CKO mice dramatically increased marrow fat under both ad libitum and CR-fed conditions, and surprisingly propranolol treatment was unable to rescue CR-induced marrow fat in either WT or GR-CKO mice. Additionally, serum corticosterone levels were selectively elevated in GR-CKO mice with CR, suggesting the possibility of bone–hypothalamus–pituitary–adrenal crosstalk during metabolic stress. This work highlights the complexities of glucocorticoid and β-adrenergic signaling in stress-induced changes in bone mass, and the importance of GR function in suppressing marrow adipogenesis while maintaining healthy bone mass.