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1.
Gao FY Lu MX Ye X Huang ZH Wang H Zhu HP Yang LP 《Fish physiology and biochemistry》2011,37(3):553-565
Growth hormone plays important roles in various physiological processes such as growth, metabolism, and reproduction. In this
study, two cDNAs encoding growth hormone receptor (GHR) were isolated from the liver of zanzibar tilapia (Oreochromis hornornum). The two cDNAs were 2,831 and 2,044 bp in length and named GHR1 and GHR2, respectively. GHR1 and GHR2 shared 57.4% similarity
in nucleotide sequences and 33.5% similarity in deduced amino acid sequences. Consequently, it was presumed that they were
two different genes. Conserved regions of GHR1 and GHR2 in zanzibar tilapia were different from those of other vertebrates.
For example, conserved box2 regions of GHR1 and GHR2 in zanzibar tilapia were, respectively, WVELM and WVEFT, while it was
WVEFI for GHRs in other vertebrates. Similar to other fish species, GHR1 and GHR2 were expressed in brain, gill, liver, muscle,
spleen, gonad, stomach, kidney, and pituitary in zanzibar tilapia. The expression levels were the highest in liver. Unlike
fathead minnow (Pimephales promelas) and mossambique tilapia (O. mossambicus), the expression levels of GHR1 in most female fish tissues were higher than those in male fish. No significant difference
in GHR2 expression was found in all the tissues in male and female of zanzibar tilapia. Under fasting condition, the expressions
of GHRs and IGF-II were significantly up-regulated (P < 0.05) in liver, while the expression of IGF-I remained stable. This observation would contribute to understanding the evolution
of the GHR family in further investigation of growth regulation of zanzibar tilapia. 相似文献
2.
Cichlasoma dimerus responds to refeeding with a partial compensatory growth associated with an increment of the feed conversion efficiency and a rapid recovery of GH/IGFs axis 
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下载免费PDF全文 T.H. Delgadin I. Simó D.I. Pérez Sirkin M.P. Di Yorio S.E. Arranz P.G. Vissio 《Aquaculture Nutrition》2018,24(4):1234-1243
Many fish species display compensatory growth (CG), a phenomenon by which fasted fish grow faster during refeeding. However, most studies use a group‐housed fish approach that could be problematic in social fish when interaction between individuals is not considered or eliminated. Additionally, the growth hormone (GH)/insulin‐like growth factors’ (IGF‐1 and IGF‐2) axis is implicated in postnatal growth in vertebrates, but its relevance in CG is not fully understood. Thus, the aim of this work was to determine whether CG occurs in a social fish, Cichlasoma dimerus, using an individually held fish approach and secondly, to evaluate the GH/IGFs expression profile during refeeding by 3 days and 3 weeks. C. dimerus showed partial CG. The feed conversion efficiency (FCE) was higher in three‐day‐refed fish, which presented higher GH plasma and mRNA levels than controls but shown no differences in liver and muscle GH receptors (GHR1 and GHR2) and IGFs mRNA levels. Surprisingly, three‐week‐refed fish exhibited GHR1 and IGF‐2 increments, but a reduction in GHR2 expression in muscle. These results show a strong association between GH levels, growth rate and FCE during refeeding, and a long‐lasting effect of refeeding on muscular expression of GHRs and IGF‐2. 相似文献
3.
Yun Li Xiaochun Liu Yong Zhang Xilan Ma Haoran Lin 《Fish physiology and biochemistry》2013,39(3):605-613
Effects of cysteamine (CS) on growth hormone (GH) mRNA, two types of growth hormone receptor (GHR) mRNAs and growth rate in orange-spotted grouper (Epinephelus coioides) were investigated. CS could cause a modification in the structure of somatostatin, which is the most important neuroendocrine inhibitor of basal and stimulated growth hormone synthesis and release, and renders it nonimmunoreactive probably through interaction with the disulfide bonds. In the present study, cysteamine hydrochloride (CSH) enhanced the level of pituitary GH mRNA in a dose-dependent manner through attenuating or deleting the inhibiting action of somatostatin on GH mRNA expression. CSH at relatively low doses (from 1 to 3 mg/g diet) enhanced the levels of two types of GHR mRNAs in dose-dependent manner, whereas the stimulation induced by CSH declined from the peak at higher dose of CSH (4 mg/g diet). It might be attributed to the variation in GH-induced up-regulation of GHRs at different doses of GH. Feeding of CSH could induce remarkable enhancement of growth rate in orange-spotted grouper. In addition, the stimulatory effect of CSH could be potentiated by the additive effect of luteinizing hormone-releasing hormone analog (LHRH-A). Compared with individual treatments, combined feeding of CSH and LHRH-A caused more efficient elevation of growth rate after 8 weeks of feeding. CSH and LHRH-A individually and in combination remarkably increased the levels of GH and GHR mRNAs compared with the control. The combined administration of CSH and LHRH-A in diet was most effective to enhance the level of GH and GHR1 mRNA. The morphological characteristics of the experimental fish were evaluated. Compared with control, the ratios of muscle RNA/DNA, condition factors (CF) and feed conversion efficiency (FCE) were significantly enhanced in the treated groups, while the highest values were observed in the combined treatment. All the results suggested that CSH (1–3 mg/g diet) is an effective, economical and feasible feed additive in orange-spotted grouper culture. 相似文献
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生长激素/胰岛素样生长因子-轴(growth hormone/insulin-like growth-axis,GH/IGF-轴)是调控鱼类生长的主要内分泌轴线。为探讨生长相关基因GHR、IGF-2对河川沙塘鳢(Odontobutis potamophila)生长发育的调控机制,采用cDNA末端快速扩增(RACE)和实时荧光定量PCR等技术,对河川沙塘鳢的GHR、IGF-2基因进行了克隆和表达模式分析。研究结果显示:河川沙塘鳢GHR基因的cDNA全长序列为2 179 bp,开放阅读框为1 830 bp,共编码609个氨基酸,IGF-2基因的cDNA全长序列为1 586 bp,开放阅读框642 bp,共编码213个氨基酸。采用qRT-PCR方法检测了GHR、IGF-2基因在9个不同组织(脑、肝、心、肌肉、脾、肠、性腺、鳃、肾)和8个胚胎不同发育时期(受精卵期、桑椹胚期、原肠胚期、神经胚期、体节期、口裂期、出膜后1 d、出膜后3 d)的表达情况。结果表明:IGF-2和GHR基因在所检测的9种组织中均有表达,其中以肝脏、肌肉、性腺、脑中的表达量较高,在胚胎发育阶段GHR和IGF-2基因表达呈先上升后下降的趋势,在原肠胚期表达量较高,表明其在胚胎发育过程中发挥重要作用。qRT-PCR进一步比较了雌、雄河川沙塘鳢GHR和IGF-2基因在不同生长发育阶段(90、150、210、270、330 d)脑、肝、肌肉mRNA的表达量,结果表明:各时期雄鱼GHR和IGF-2基因在肝组织中表达量均显著高于雌鱼,肌肉和脑GHR基因mRNA的表达量则无显著差异。而IGF-2基因则仅在雌、雄鱼210 d的脑和150、210 d的肌肉存在显著性差异,推测肝GHR和IGF-2基因mRNA表达的雌雄差异是河川沙塘鳢雌雄生长差异的主要原因之一。 相似文献
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J. Pérez-Sánchez J.A. Calduch-Giner M. Mingarro S. Vega-Rubín de Celis P. Gómez-Requeni A. Saera-Vila A. Astola M.M. Valdivia 《Fish physiology and biochemistry》2002,27(3-4):243-258
Growth hormone (GH), prolactin (PRL) and somatolactin (SL) are single chain proteins structurally and functionally related. Fish PRL and GH receptors (PRLR, GHR) have been characterized in several fish species. There is limited evidence of fish PRLR isoforms, but emerging data support the existence of different GHR variants. In gilthead sea bream, black sea bream, turbot and fugu, but not in zebrafish, GHR has retained an exclusive fish intron (10/10A). In gilthead sea bream and turbot, this intron is not alternatively spliced, but the black sea bream intron is either removed or retained during mRNA processing, resulting in a long GHR isoform with a 31 amino acid insertion that does not alter the open reading frame. This or any other GHR variant are not found in gilthead sea bream, but a truncated anchored form has been reported in turbot. The latter GHR isoform comprises extracellular and trans-membrane domains, the first 28 amino acids of the intracellular domain and 21 divergent amino acids before a stop codon. This GHR variant is the result of alternative splicing, being the 3′ UTR and the divergent sequence identical to the sequence of the 5′ end of the 9/10 intron. The physiological significance of different fish GHR isoforms remains unclear, but emerging data provide suitable evidence for season and nutrition related changes in the somatototropic axis activity. The up-regulation of circulating GH together with the decrease of plasma titres of insulin-like growth factor-I (IGF-I), an altered pattern of serum IGF binding proteins and a reduced expression of hepatic IGF-I and GHRs represent a mechanism conserved through vertebrate evolution. It secures the preferential utilization of mobilized substrates to maintain energy homeostasis rather than tissue growth. Somatolactin also changes as a function of season, ration size, dietary amino acid profile and dietary protein source creating opposite plasma GH and SL profiles. There is now direct evidence for a lipolytic effect of fish SL, acting at the same time as an inhibitory factor of voluntary food intake. Indeed, long-term feeding restriction results in the enlargement of the summer GH peak, whereas the SL rise coincident with shortened day length is delayed in juvenile fish until late autumn. These findings agree with the idea that SL may act as a marker of energy surplus, priming some particular process such as puberty onset. However, it remains unclear whether SL works through specific receptors and/or dimers or heterodimers of GH and PRL receptors. 相似文献
7.
Effects of largely different feeding intensities on serum insulin‐like growth factor‐1 concentrations,quantified by enzyme immunoassay,leptin and growth hormone receptor 1 mRNA in rainbow trout (Oncorhynchus mykiss) 下载免费PDF全文
下载免费PDF全文 B. Pfundt B. Mielenz F. Sanver E. Pfeffer H. Sauerwein M. Mielenz 《Aquaculture Nutrition》2016,22(3):586-596
Insulin‐like growth factor‐1 (IGF‐1), somatolactin and leptin are involved in growth regulation and energy metabolism in fish. We herein focused on serum IGF‐1 concentration analysed by enzyme‐linked immunosorbent assay in restrictively fed rainbow trout (Oncorhynchus mykiss). The animals were fed a high‐fat/low‐protein diet at daily feed increases (DFI) ranging from 0.5% to 2% of initial body weight (IBW), starting either at 62 or 176 g IBW. In selected groups, growth hormone receptor 1 (GHR1) and leptin mRNA were quantified in liver, and GHR1 mRNA also in visceral adipose tissue. Serum IGF‐1 concentrations in both IBW groups were highest at 2% and 1% DFI and were nonlinearly decreasing with reduced DFI. The low‐IBW groups had mostly lower IGF‐1 concentrations than the high‐IBW groups. Leptin and GHR1 mRNA decreased with feeding intensity in liver, but GHR1 mRNA increased in adipose tissue. IGF‐1 is related to growth and may help to mitigate oxidative stress in consequence of lipid mobilization during restrictive feeding. IGF‐1 secretion associated with stress response in addition to its function in growth and energy metabolism seemed to reach a point of inflection at DFI 1%. Leptin and GHR1 might be linked to lipid metabolism and free fatty acid partitioning towards liver. 相似文献
8.
Environmental estrogen could mimic natural estrogens thereby disrupting the endocrine systems of human and animals. The actions
of such endocrine disruptors have been studied mainly on reproduction and development. However, estrogen could also affect
the somatotropic axis via multiple targets such as growth hormone (GH). In the present study, two endocrine disruptors were
chosen to investigate their effects on the expression level and signal transduction of growth hormone receptor (GHR) in fish.
Using real-time PCR, it was found that exposure to both the estrogenic (bisphenol A) and anti-estrogenic (malachite green)
compounds could attenuate the expression levels of GHR1 and GHR2 in black seabream (Acanthopagrus schlegeli) hepatocytes. The expression level of IGF-I, the downstream effector of GHR activation in the liver, was decreased by bisphenol
A but not by malachite green. Luciferase reporter assay of the β-casein promoter was used to monitor GHR signaling in transfected
cells. In the fish liver cell line Hepa-T1, both GHR1 and GHR2 signaling were attenuated by bisphenol A and malachite green.
This attenuation could only occur in the presence of estrogen receptor, indicating that these agents probably produce their
actions via the estrogen receptor. Results of the present study demonstrated that estrogenic or anti-estrogenic compounds
could down-regulate the somatotropic axis in fish by affecting both the gene expression and signaling of GHR. In view of the
increasing prevalence of these compounds in the environment, the impact on fish growth and development both in the wild and
in aquaculture would be considerable. 相似文献
9.
Two isoforms of the full-length cDNA of the growth hormone receptor (GHR) of the Atlantic salmon (Salmo salar; ss) were cloned by a PCR approach using RACE. Respectively, the cDNA sequences of ssGHR isoforms 1 and 2 are 2654 and 2608 nucleotides long, with 1782 and 1773 nucleotide ORFs. The resulting coded proteins
are 594 and 590 aa long, with 19 and 20 aa signal peptides. The two isoforms share 86% protein and 87% cDNA sequence similarity.
Isoform 1 is most similar to other salmonid GHR isoforms 1 while isoform 2 is most similar to salmonid GHR isoforms 2 (93–95%).
Similarity with other teleost species was lower (37–44%). The bioactivity of the cloned ssGHR was tested by transfecting the ssGHR isoform 1 cDNA into CHO-K1 hamster cells, incubating with recombinant salmon GH (sGH) or native ovine prolactin (oPRL),
and measuring cell proliferation by the MTT assay. The ssGHR-transfected cells significantly increased proliferation when stimulated by sGH at all concentrations. oPRL stimulated
ssGHR-transfected cells at higher concentrations due to receptor cross reaction. ssGHR isoforms 1 and 2 contain a single transmembrane domain and the typical conserved motifs found in other teleost GHRs, including
four paired cysteine residues and five potential N-glycosylation sites in the extracellular domain, Box I and Box II, as well as seven potential tyrosine phosphorylation sites
in the intracellular domain. However, in salmonids, these motifs differ from those of other teleosts, and could be responsible
for differentiated hormone binding, signal transduction and response. 相似文献
10.
为探讨急性操作胁迫对银鲳生长的影响,首次克隆了3种生长调控相关基因-生长激素受体1(ghr1)、生长激素受体2(ghr2)和胰岛素样受体1(igfbp1),并对3种基因在银鲳肝脏、心脏、性腺、肌肉和肾脏等不同组织中的表达进行了比较。定量表达结果表明3种基因均广泛分布于所研究的各个组织中,而其中肾脏、性腺和心脏中的表达量较其它组织低。在银鲳受到外界操作胁迫刺激后,3种基因呈现不同的表达模式:其中ghr2和igfbp1的表达下调,而ghr2的表达量与对照组无显著性差异。结果表明,ghr2和igfbp1在银鲳生长调节中起到重要的作用;在胁迫环境中,外界刺激可通过下调生长相关基因表达以影响鱼体的生长。 相似文献
11.
Kouakou Yao Jean-Charles Gabillard Pierre-Yves Le Bail 《Fish physiology and biochemistry》2006,32(2):121-130
In fish, regulation of the growth hormone (GH) receptor has been mainly analyzed by binding studies, with some discrepancies in the results. The present work aims at determining whether circulating GH levels influence the measurement of hepatic GH-binding capacities. To do this, the effectiveness of the dissociation of the GH/GH receptor (GHR) complex by an MgCl2 treatment was assessed in rainbow trout, and data on GH-binding capacities under various physiological conditions were studied using different means of expression. Our results reveal that MgCl2 treatment dissociated the liver GH/GHR complex formed under in vitro conditions (85 ± 23 vs. 361 ± 16 fmol/g of liver; p<0.001) but not in vivo, showing such treatment in trout is not applicable. A comparison of fasted (3 weeks) and fed fish revealed that GH-binding capacities, expressed as femtomoles per milligram protein or femtomoles per gram of liver, were similar in both fed and fasted fish. However, when changes in liver and body size were taken into account, the total GH-binding capacities were lower in the fasted fish (0.026 ± 0.006 vs. 0.062 ± 0.009 fmol/cm3 liver; p<0.05). One day after hypophysectomy or GH injection, changes in the plasma GH levels increased or decreased GH-binding capacities, respectively. Five days later, GH-binding capacities increased in GH-injected fish (527 ± 38 vs. 399 ± 38 fmol/g liver; p<0.01). Our interpretation is that acute treatment modified GH-binding capacities through receptor occupancy and that GH stimulated the synthesis of its own receptor. On the other hand, long-term treatment through successive injections of GH lowered the total binding capacities (approx. 40%), which could result from receptor occupancy. We conclude that circulating GH levels strongly influence the measurement of GH-binding capacities in the liver, thereby limiting interpretation of the binding data and preventing accurate conclusions to be drawn on GHR regulation. 相似文献
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Andrés A Sciara Fabricio A Vigliano Gustavo M Somoza Silvia E Arranz 《Aquaculture Research》2011,42(6):844-857
Growth hormone (GH) can be orally administrated to fish in order to increase growth rates. Fish growth is characterized by the hyperplasia and hypertrophy of muscle fibre throughout adult life. In this respect, GH could affect directly and indirectly (by growth and metabolic factors) the development and growth of muscle fibres. Recombinant pejerrey GH (r‐pjGH) was expressed in Escherichia coli and refolded in a highly efficient batch dilution system, obtaining 0.1 g L?1 of hormone without protein precipitation during the refolding procedure. Orally administered hormone to pejerrey produced a 30% increase in mean weight and stimulated liver insulin‐like growth factor type I (IGF‐I) mRNA expression after 1 month of treatment. Histological analyses showed that muscle growth was generated mainly by hypertrophy of the fibres. A higher r‐pjGH dose increased muscle fibre hypertrophy but somatic growth was negatively affected probably due to a reduced capacity of generating new fibres. 相似文献
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The Effects of Brackish Water on Growth Hormone/Insulin‐like Growth Factor‐1 Gene Expression of the Caspian Trout,Salmo trutta caspius (Kessler, 1877), During the Early Stage of Smoltification 下载免费PDF全文
下载免费PDF全文 Sepideh Sharif Alireza Shoae Bagher Mojazi Amiri Hamid Farahmand 《Journal of the World Aquaculture Society》2015,46(2):201-209
16.
Shunsuke Moriyama Kiyoko Yamaguchi Tomomi Takasawa Hiroaki Chiba Hiroshi Kawauchi 《Fish physiology and biochemistry》2006,32(3):189-201
In an attempt to understand growth regulation in the Japanese eel, Anguilla japonica, we cloned insulin-like growth factor-I (IGF-I) cDNAs and examined their mRNA expression in several tissues. Two eel IGF-I (eIGF-I) cDNAs encoding preprohormones, eIGF-I-Ea1and eIGF-I-Ea2, were cloned from the liver by polymerase chain reaction (PCR). The preproIGF-Is were identical in signal peptide and mature IGF-I, but different in the E domain—eIGF-I-Ea2 mRNA was 36 bp longer than eIGF-I-Ea1 mRNA. Eel IGF-I was 83–94% identical with that of teleosts, 71% identical with that of dogfish, 87% identical with that of bullfrog and chicken, and 83% identical with that of humans. In both males and females the highest eIGF-I-Ea1 mRNA levels were observed in the liver, with detectable levels also found in the gills, heart, stomach, spleen, kidney, intestine, swim-bladder, muscle, and gonads. eIGF-I-Ea1 mRNA levels in the liver were higher in females than in males whereas in the intestine they were lower than in males. eIGF-I-Ea2 mRNA was detected in all the tissues examined and at similar levels in males and females. In this experiment higher eIGF-I-Ea1 mRNA levels were observed in the liver of larger glass eels than in those of smaller fish. eIGF-I-Ea2 mRNA levels were also higher in larger eels, although they were lower than IGF-I-Ea1 mRNA levels. Both eIGF-I mRNA levels in liver were positively correlated with the body size of the␣glass eels. Intraperitoneal injection of recombinant eel GH (reGH), 0.25 μg g−1 body weight, into glass eels resulted in a significant increase in both eIGF-I mRNAs in the liver 1 day after injection compared with control fish, but no elevation was observed 2 days after injection. Incubation of liver slices with reGH at concentrations of 10, 100, and 1,000 ng mL−1 for 24 h resulted in a significant concentration-dependent increase in the levels of both eIGF-I mRNAs. Higher levels of eIGF-I-Ea1 and Ea2 mRNA were observed in the gills ofseawater-reared eels than in those of freshwater-reared fish, but no differenceswere observed in the whole kidney. These results suggest that IGF-I is involved in the regulation of somatic growth and also in adaptation of the Japanese eel to seawater. 相似文献
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The analysis of the tench growth hormone gene structure revealed a comparable organization of coding and non-coding regions than other from cyprinid species. Based on the performed mRNA and amino acid sequence alignments, gh tench is related to Asian than to European representatives of Cyprinidae family. Second aim of the work was to characterize and predict protein structure of the tench growth hormone. Tinca tinca GH share many common features with human GH molecule. The Tench GH protein binds to the growth hormone receptor (GHR) using two regions I and II that are situated at opposite sites of molecule. Binding site I is placed in the central part of T. tinca GH and H 189 amino acid in the middle region of the IV helix is crucial for GH–GHR interactions. 相似文献
19.
翘嘴鲌两种生长激素受体基因结构及微卫星多态性与生长性状的相关性 总被引：1，自引：0，他引：1
为了更好地研究翘嘴鲌两种生长激素受体(GHR)的结构和功能,实验以翘嘴鲌转录组中获得的mRNA为基础,对其DNA序列进行了克隆。在进行生物信息学分析的同时,对其中的多态性微卫星位点在120尾同批繁殖、同塘养殖的翘嘴鲌个体中进行了分析。GHR1的cDNA序列长度为3 498 bp,开放阅读框(ORF)为1 818 bp,编码605个氨基酸;GHR2的cDNA序列长度为1 743 bp,ORF为1 743 bp,编码580个氨基酸;GHR1和GHR2氨基酸序列均由信号肽、胞外区、跨膜区、胞内区组成,相似度为37.2%。二者在结构上存在较大的差异:GHR1胞外区有7个半胱氨酸残基,而GHR2只有5个,且GHR1比GHR2多3个N-糖基化位点;在胞内区,GHR1存在10个酪氨酸残基而GHR2只有5个,这些差异表明二者可能具有不同的生物学功能。同源氨基酸序列比对发现,GHR与其他鲤科鱼类的同源基因保守性较高。翘嘴鲌2个GHR各包含9个内含子,其中GHR1内含子1和2序列在10 kb以上,本实验没有对其进行扩增。所获得的序列中共发现了6个微卫星位点:GHR1中微卫星位点(CT)_6位于第2外显子中,为信号肽编码序列的一部分,位于第8内含子中的(AC)_5经检测没有多态性;GHR2中具有4个微卫星位点,位于第1内含子中的(TG)_5及第7个内含子中的(TATC)_5(AT)_(15)(AC)_(11)(AT)_(14)(TG)_6和(TA)_(15)属于高度多态性位点(PIC0.5),第6个内含子中的(GAAG)_5属中度多态性位点(PIC=0.463)。第7内含子中的2个微卫星位点检测到基因型数目分别为50和61,具有良好的个体识别潜力。关联分析结果表明这4个多态性微卫星位点与生长性状具有一定相关性。翘嘴鲌GHR基因的克隆以及序列中微卫星的特征分析为深入研究其生物学功能及分子标记辅助育种提供助力与参考。 相似文献
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Björn Thrandur Björnsson Viktoria Johansson Susana Benedet Ingibjörg Eir Einarsdottir Jon Hildahl Thorleifur Agustsson Elisabeth Jönsson 《Fish physiology and biochemistry》2002,27(3-4):227-242
The focus of this review is on the regulatory mechanisms and the mode of action of GH in salmonids. To stimulate further research, it aims at highlighting areas where numerous important breakthroughs have recently been made, as well as where data are currently lacking. The regulation of GH secretion is under complex hypothalamic control, as well as under negative feedback control by GH and IGF-I. Further, the recently characterized ghrelin is a potent GH secretagogue, and may prove to be a link between feed intake and growth regulation. GH plasma profiles show indications of diurnal changes, but whether salmonids have true pulsatile GH secretion remains to be elucidated. The recent cloning and characterization of the salmon GH receptor (GHR) is a major research break-through which will give new insights into the mechanisms of GH action. It should also stimulate research into circulating GH-binding proteins (GHBPs), as they appear to be a soluble form of the GHR. The salmonid GHR sequences show evolutionary divergence from other fish species, but with a high degree of identity within the salmonid group. Radioreceptorassay studies have found GHR present in all tissues examined, which is in line with the highly pleiotropic action of GH. Data are currently scarce on the plasma dynamics of GH in salmonids, and further studies on GHR and GHBPs dynamics coupled to assessments of GH clearance rates and pathways are needed. The direct versus indirect nature of GH action remains to be clarified, but GH appears to act both locally at the target tissue level to stimulate the autocrine/paracrine action of IGF-I, as well as on the liver to increase plasma IGF-I levels. In addition, GH interacts with other hormones such as cortisol, thyroid hormones, insulin, and reproductive hormones, generating a wide range of physiological effects. GH may act both peripherally and directly at the level of the central nervous system to modify behavior, probably by altering the dopaminergic activity in the brain. 相似文献