| 1. |
- Gibney, James, et al.
(författare)
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Comparison of the metabolic effects of raloxifene and oral estrogen in postmenopausal and growth hormone-deficient women.
- 2005
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Ingår i: The Journal of clinical endocrinology and metabolism. - : The Endocrine Society. - 0021-972X .- 1945-7197. ; 90:7, s. 3897-903
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Tidskriftsartikel (refereegranskat)abstract
- CONTEXT: The endocrine and metabolic functions of the liver are affected by estrogen. Oral estrogen reduces IGF-I and suppresses fat oxidation despite augmenting GH secretion. The aim of this study was to determine whether selective estrogen receptor modulators display similar effects and whether these effects are magnified in GH-deficient (GHD) women because of the loss of GH feedback. DESIGN: This was an open-label, randomized, two-period, crossover study comparing treatment (raloxifene vs. estradiol) and group (normal vs. GHD). SETTING: The setting of this study was a clinical research unit. PARTICIPANTS: Twelve postmenopausal women and 12 women with hypopituitarism participated in this study. INTERVENTION: Two 4-wk treatments with 17beta-estradiol (E2; 2 mg, followed by 4 mg) or raloxifene (60 mg, followed by 120 mg) were given, crossing over to the alternate treatment after a 4-wk washout period. OUTCOME MEASURES: Endocrine [GH, IGF-I, IGF-binding protein-3 (IGFBP-3), GH-binding protein, and SHBG] and metabolic (fat oxidation) end points were used as outcome measures. RESULTS: E2 reduced serum IGF-I levels in a dose-dependent manner in both groups, with effects greater (P < 0.05) than raloxifene. Raloxifene reduced IGF-I levels in the GHD group (P < 0.001), but not in the postmenopausal group. E2 reduced (P < 0.05), and raloxifene increased (P < 0.05), IGFBP-3 levels in both groups. E2, but not raloxifene, increased GH (P < 0.05) in postmenopausal women. The effects of E2 and raloxifene on IGF-I, IGFBP-3, IGF-I/IGFBP-3 molar ratio, GH-binding protein, and SHBG were significantly different (P < 0.05). E2 and raloxifene reduced (P < 0.05) fat oxidation equally in GHD, whereas the decrease in postmenopausal women was not significant. CONCLUSION: E2 and raloxifene exert different hepatic endocrine, but not lipid oxidative, effects. The greater effects seen in GHD women may be explained by the loss of endogenous GH feedback.
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| 2. |
- Johannsson, Gudmundur, 1960, et al.
(författare)
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Independent and combined effects of testosterone and growth hormone on extracellular water in hypopituitary men.
- 2005
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Ingår i: The Journal of clinical endocrinology and metabolism. - : The Endocrine Society. - 0021-972X .- 1945-7197. ; 90:7, s. 3989-94
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Tidskriftsartikel (refereegranskat)abstract
- CONTEXT: Symptoms of fluid retention in GH-deficient patients during GH replacement are greater in men than in women, suggesting that testosterone may augment or estradiol may attenuate the antinatriuretic actions of GH. The mechanisms underlying the sodium-retaining effects of GH are poorly understood. AIM: The aim of this study was to investigate the effects of GH and testosterone, alone and in combination, on extracellular water (ECW) and the hormonal mechanisms involved. DESIGN: Two separate, open-label, randomized, two-period, crossover studies were performed; the first compared the effects of GH alone with those of GH and testosterone, and the second compared the effects of testosterone alone with those of GH and testosterone. PARTICIPANTS: Twelve hypopituitary men with GH deficiency and hypogonadism were studied. INTERVENTION: During the weeks of intervention, GH (0.5 mg/d) and testosterone enanthate (250 mg) were administered by im injection. OUTCOME MEASURES: The outcome measures were ECW, IGF-I, plasma renin activity (PRA), aldosterone (Aldo), and atrial natriuretic peptide (ANP). RESULTS: GH treatment significantly increased (P < 0.05) both IGF-I and ECW, and these changes were enhanced by cotreatment with testosterone (P = 0.07 for both). PRA, Aldo, and ANP levels did not change. Testosterone treatment alone did not change the IGF-I concentration, whereas cotreatment with GH induced a marked increase. Testosterone alone increased (P < 0.05) ECW, and the effect was augmented (P < 0.01) by cotreatment with GH. Although PRA and ANP did not change, plasma Aldo decreased after single and combined treatments. CONCLUSION: GH and testosterone exerted independent and additive effects on ECW. The mechanisms of fluid retention for both hormones are likely to be exerted on the renal tubules. This is the first direct evidence that testosterone increases ECW.
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| 3. |
- Leong, Gary M, et al.
(författare)
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Estrogen up-regulates hepatic expression of suppressors of cytokine signaling-2 and -3 in vivo and in vitro.
- 2004
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Ingår i: Endocrinology. - : The Endocrine Society. - 0013-7227 .- 1945-7170. ; 145:12, s. 5525-31
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Tidskriftsartikel (refereegranskat)abstract
- Suppressors of cytokine signaling (SOCS) are important negative regulators of cytokine action. We recently reported that estrogen stimulates SOCS-2 expression and inhibits GH signaling in kidney cells. The effects of estrogen on SOCS expression in other tissues are unclear. The aim of this study was to investigate in vivo and in vitro whether estrogen affected SOCS expression in the liver, a major target organ of GH. The in vivo hepatic effects of estrogen on ovariectomized mice lacking estrogen receptor (ER)-alpha, ERbeta, or both and their wild-type littermates were examined by DNA microarray analysis. In vitro, the effects of estrogen on SOCS expression in human hepatoma cells were examined by reverse transcription quantitative PCR. Long-term (3 wk) estrogen treatment induced a 2- to 3-fold increase in hepatic expression of SOCS-2 and -3 in wild-type and ERbeta knockout mice but not in those lacking ERalpha or both ER subtypes. Short-term treatment (at 24 h) increased the mRNA level of SOCS-3 but not SOCS-2. In cultured hepatoma cells, estrogen increased SOCS-2 and -3 mRNA levels by 2-fold in a time- and dose-dependent manner (P < 0.05). Estrogen induced murine SOCS-3 promoter activity by 2-fold (P < 0.05) in constructs containing a region between nucleotides -1862 and -855. Moreover, estrogen and GH had additive effects on the SOCS-3 promoter activity. In summary, estrogen, via ERalpha, up-regulated hepatic expression of SOCS-2 and -3, probably through transcriptional activation. This indicates a novel mechanism of estrogen regulation of cytokine action.
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| 4. |
- Leung, Kin-Chuen, et al.
(författare)
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Estrogen regulation of growth hormone action.
- 2004
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Ingår i: Endocrine reviews. - : The Endocrine Society. - 0163-769X .- 1945-7189. ; 25:5, s. 693-721
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Tidskriftsartikel (refereegranskat)abstract
- GH plays a pivotal role in regulating body growth and development, which is modulated by sex steroids. A close interplay between estrogen and GH leads to attainment of gender-specific body composition during puberty. The physiological basis of the interaction is not well understood. Most previous studies have focused on the effects of estrogen on GH secretion. There is also strong evidence that estrogen modulates GH action independent of secretion. Oral but not transdermal administration of estrogen impairs the metabolic action of GH in the liver, causing a fall in IGF-I production and fat oxidation. This results in a loss of lean tissue and a gain of body fat in postmenopausal women and an impairment of GH effect in hypopituitary women on GH replacement. The negative metabolic sequelae are potentially important because of the widespread use of oral estrogen and estrogen-related compounds. Estrogen affects GH action at the level of receptor expression and signaling. More recently, estrogen has been shown to inhibit Janus kinase/signal transducer and activator of transcription signaling by GH via the induction of suppressor of cytokine signaling-2, a protein inhibitor for cytokine signaling. This represents a novel paradigm of steroid regulation of cytokine receptors and is likely to have significance for a diverse range of cytokine function.
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| 5. |
- Leung, Kin-Chuen, et al.
(författare)
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Regulation of growth hormone signaling by selective estrogen receptor modulators occurs through suppression of protein tyrosine phosphatases.
- 2007
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Ingår i: Endocrinology. - : The Endocrine Society. - 0013-7227 .- 1945-7170. ; 148:5, s. 2417-23
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Tidskriftsartikel (refereegranskat)abstract
- Activation of the Janus kinase 2 (JAK2)/signal transducer and activator of transcription 5 (STAT5) pathway by GH is terminated by the suppressors of cytokine signaling (SOCSs) and protein tyrosine phosphatases, Src homology 2 domain-containing protein tyrosine phosphatase (SHP)-1 and SHP-2. Based on our recent report that estrogen inhibits GH signaling by stimulating SOCS-2 expression, we investigated the effects of selective estrogen receptor modulators (SERMs) on GH signaling in human embryonic kidney (HEK293) and breast cancer (MDA-MB-231) cells expressing human GH receptor and estrogen receptor-alpha. 17beta-estradiol (E(2)) suppressed GH activation of a STAT5-responsive luciferase reporter and JAK2 phosphorylation in both cell models. 4-hydroxytamoxifen and raloxifene augmented these actions of GH in HEK293 cells but not breast cancer cells. SOCS-2 expression in both cell types was stimulated by E(2) but unaffected by SERMs. In HEK293 cells, SHP-1 was inhibited by raloxifene and 4-hydroxytamoxifen, whereas the latter additionally inhibited SHP-2. The phosphatases were unaffected by E(2). In breast cancer cells, phosphatase activity was not altered by SERMs or E(2). In summary, estrogen inhibited the JAK2/STAT5 signaling of GH and stimulated SOCS-2 expression in both HEK293 and breast cancer cells. By contrast, SERMs augmented GH signaling by reducing SHP activities in HEK293 cells and had no effect on both in breast cancer cells. We provide the first evidence for a novel mechanism regulating GH signaling, in which SERMs enhance GH activation of the JAK2/STAT5 pathway in a cell-type-dependent manner by attenuating protein tyrosine phosphatase activities.
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| 6. |
- Sjögren, Klara, 1970, et al.
(författare)
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Growth hormone regulation of metabolic gene expression in muscle: a microarray study in hypopituitary men
- 2007
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Ingår i: AMERICAN JOURNAL OF PHYSIOLOGY-ENDOCRINOLOGY AND METABOLISM. - : American Physiological Society. - 0193-1849 .- 1522-1555. ; 293:1
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Tidskriftsartikel (refereegranskat)abstract
- Muscle is a target of growth hormone (GH) action and a major contributor to whole body metabolism. Little is known about how GH regulates metabolic processes in muscle or the extent to which muscle contributes to changes in whole body substrate metabolism during GH treatment. To identify GH-responsive genes that regulate substrate metabolism in muscle, we studied six hypopituitary men who underwent whole body metabolic measurement and skeletal muscle biopsies before and after 2 wk of GH treatment (0.5 mg/day). Transcript profiles of four subjects were analyzed using Affymetrix GeneChips. Serum insulin-like growth factor I (IGF-I) and procollagens I and III were measured by RIA. GH increased serum IGF-I and procollagens I and III, enhanced whole body lipid oxidation, reduced carbohydrate oxidation, and stimulated protein synthesis. It induced gene expression of IGF-I and collagens in muscle. GH reduced expression of several enzymes regulating lipid oxidation and energy production. It reduced calpain 3, increased ribosomal protein L38 expression, and displayed mixed effects on genes encoding myofibrillar proteins. It increased expression of circadian gene CLOCK, and reduced that of PERIOD. In summary, GH exerted concordant effects on muscle expression and blood levels of IGF-I and collagens. It induced changes in genes regulating protein metabolism in parallel with a whole body anabolic effect. The discordance between muscle gene expression profiles and metabolic responses suggests that muscle is unlikely to contribute to GH-induced stimulation of whole body energy and lipid metabolism. GH may regulate circadian function in skeletal muscle by modulating circadian gene expression with possible metabolic consequences.
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