Endocrinology, doi:10.1210/en.2003--0311
Endocrinology Vol. 144, No. 8 3692-3697
Copyright © 2003 by The Endocrine Society
Growth Hormone Receptor Expression in Atrophying Muscle Fibers of Rats
Al Hassan Casse,
Dominique Desplanches,
Marie Hélène Mayet-Sornay,
Mireille Raccurt,
Sylvie Jegou and
Gérard Morel
Centre National de la Recherche Scientifique (A.H.C., D.D., M.H.M.-S., M.R., G.M.), Unité Mixte de Recherche 5123, Claude Bernard-Lyon 1 University, F69622 Villeurbanne, France; and Institute National de la Santé et de la Recherche Médicale (S.J.), Unité U413, University of Rouen, F76821 Mont-Saint-Aignan, France
Address all correspondence and requests for reprints to: Dr. G. Morel, Physiologie Intégrative, Cellulaire et Moléculaire, Centre National de la Recherche Scientifique, Unité Mixte de Recherche 5123, Université Claude Bernard-Lyon 1, Bâtiment R. Dubois, 43 Boulevard du 11 Novembre 1918, F69622 Villeurbanne cedex, France. E-mail: Gerard. Morel{at}univ-lyon1.fr.
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Abstract
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Biological actions of GH on muscle growth and metabolism are mediated through specific trans-membrane receptors. The aim of this study was to determine GH receptor (GHR) mRNA expression in muscle atrophy. GHR gene expression in the rat was investigated by in situ hybridization and RT-PCR in slow-twitch oxidative muscle [soleus (SOL)] and fast-twitch glycolytic muscle [extensor digitorum longus (EDL)] after 7 and 35 d of hindlimb unloading. In control rats, the RT-PCR mRNAs levels of GHR were greater (+34%) in EDL compared with SOL. At single fiber level, relative expression of GHR mRNA increases in the following order: IIb>IIa>I. After hindlimb unloading, GHR expression significantly increased in atrophied SOL muscle after 7 (+170%) and 35 (+220%) d, whereas no significant alterations appeared in the EDL muscle. At the individual fiber level, in situ hybridization demonstrated this increase was accounted for by an increase in type I fiber expression of GHR transcripts. This increase was also seen in the EDL, but the low content of type I fibers in EDL resulted in a nonsignificant increase in GHR transcript content. The present data suggest that muscle atrophy is associated with a muscle fiber type-specific GHR mRNA up-regulation mechanism that helps protect atrophying fibers in EDL but might be part of an attempt to repair in SOL.
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Introduction
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SUSTAINED HYPOKINESIA-HYPODYNAMIA induces a progressive weakness of the antigravity postural skeletal muscles (1, 2). In rat hindlimbs, extensor muscles show greater atrophy than flexor muscles, due to the removal of their function in supporting body weight. In addition to muscle atrophy, a general shift in the contractile and enzymatic profiles of a slow-twitch oxidative muscle toward that of a fast-twitch glycolytic muscle was reported (1). Effective countermeasures known for their anabolic effects on skeletal muscle were defined to minimize muscle atrophy in hindlimb unloaded rats. They involved resistive exercise and/or GH/IGF-I administration (3, 4, 5, 6). Collectively, these studies indicate that only a combination of GH/IGF-I and resistance exercise attenuates atrophy of unloaded fast-twitch skeletal muscles.
GH is known to take direct action on cellular differentiation and proliferation (7, 8, 9, 10), including induction of a number of RNA species in mammalian tissues (11). GH biological actions on growth and metabolism are initiated by binding the hormone to its receptor (GHR), a member of the cytokine receptor superfamily (12, 13) followed by receptor dimerization (14). The GHR lacks intrinsic tyrosine kinase activity, but upon ligand stimulation, receptor phosphorylation is induced by its physical association with the nonreceptor tyrosine kinase Janus kinase 2 (15). Src homology 2 domains of the latent cytoplasmic signal transducer and activator of transcription factors are subsequently recruited to phosphorylated tyrosine residues of the GHR. The mechanism according to which the GHR mediates the general pleiotropic and specific somatic responses to its ligand have only recently begun to be understood (16, 17).
The aim of our study was to determine the GHR mRNA expression in different single muscle fibers and then to investigate the physiological consequences of atrophy on this expression in a slow-twitch oxidative [soleus, SOL] and a fast-twitch glycolytic muscle [extensor digitorum longus (EDL)] after 1 and 5 wk of hindlimb unloading. Relative expression of GHR on whole muscles was assessed by macroautoradiography along with a specific RT-PCR. As muscle atrophy is fiber type specific (1), in situ hybridization was performed on muscle sections to further identify the GHR mRNA expression per single fiber type, i.e. slow-twitch, oxidative (type I), fast-twitch oxidative-glycolytic (type IIa), and fast-twitch glycolytic (type IIb).
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Materials and Methods
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Experimental animals
The experiments were performed on 30 female pathogen-free Wistar rats, weighing 240–270 g (IFFA Creddo, St. Germain sur l’Arbresle, France). The rats were housed in a temperature-controlled room (22 ± 2 C) with a 12-h light, 12-h dark cycle and were fed with water and Purina laboratory chow ad libitum. One week later, these animals were divided into three groups. Two groups were hindlimb suspended for 7 and 35 d in individual cages using Morey’s tail-suspension model (18). The other rats were used as controls. The animal care and experiments were carried out in the animal facilities of the Faculté de Médecine (Université Lyon I, Lyon, France), according to the NIH guidelines for the care and use of laboratory animals. All the rats were anesthetized through inhalation of halothane. The SOL and the EDL muscles were removed from the hindlimbs for histochemical in situ hybridization and RT-PCR analyses.
Histochemical analysis
Muscle samples were frozen in isopentane chilled with liquid nitrogen and were stored at –80 C. A 5-mm-thick block from the midportion of each muscle was mounted in an embedding medium (TEK O.C.T. compound, Labonord, Paris, France) and stored at –80 C. Serial transverse sections (10 µm) were cut on a microtome at –30 C and stained by myosin ATPase activity (19). After preincubation at pH 4.4 in acid buffer (50 mM acetic acid) with 25 mM CaCl2 for 4 min at 25 C, the ATPase reaction was carried out in a buffer (pH 9.4) with 18 mM CaCl2 and 2.7 mM ATP at 37 C for 20 min. Based on observed differences in pH lability of the myosin ATPase activity of the isomyosins in the different fibers, the muscle fibers were classified into three major types, type I (slow-twitch, oxidative), type IIa (fast-twitch, oxidative-glycolytic) and type IIb (fast-twitch, glycolytic) and intermediate fiber types (int I or IIc and int II or IIab). Distribution of fiber types was expressed as the number of fibers of each type relative to the total number of fibers. Measurements were made on a minimum of 600 fibers on each section. The cross-sectional areas of fiber types were calculated with a computerized planimetry system coupled with a digitizer (Visioscan software, Biocom, Paris, France).
In situ hybridization (ISH)
Probes.
To detect GHR mRNA, two 30-mer oligodeoxyribonucleotide sense and antisense probes were synthesized (Eurobio, Les Ulis, France). The probes were complementary to nucleotides 6–35 localized in the exon 3, and 46–75 in the exon 4, according to the reported GHR cDNA sequence (20). The probes were 3' end-labeled with [35S]deoxy-ATP (Amersham Bioscience, Les Ulis, France) and were purified as previously described (21). The mean of the probes’ specific activity was 1000 ± 108 Ci/mM. Random priming was performed for the cDNA labeling using a multiprime DNA labeling system kit (Amersham Bioscience). The specific activity of the 18S probe was 1132 Ci/mM.
Hybridization and detection procedures.
As previously described (21), frozen sections were first fixed for 10 min in paraformaldehyde 4% before pretreatment. Sections were digested with 1 µg/ml proteinase K (Roche Diagnostics, Meylan, France) in a Tris (20 mM)-CaCl2 (2 mM) buffer for 30 min at 37 C. The slides were dehydrated in a graded ethanol series and were then air-dried. Following this, sections were covered with hybridization buffer containing 50% deionized formamide, 10% dextran sulfate, 4x standard saline citrate (SSC) (1x SSC; 0.15 M NaCl; 0.03 M sodium citrate, pH 7.0), 1x Denhardt’s solution (50x Denhardt’s solution, 1% BSA, 1% Ficoll 400, 1% polyvinylpyrrolidone), 100 µg/ml yeast tRNA, 10 mM dithiothreitol, and labeled probes (2.5 pM/ml of hybridization cDNA buffer). An ISH was performed overnight at 40 C. The sections were then washed sequentially in 2x SSC for 1 h at room temperature, 2x SSC for 45 min at 48 C and 1x and 0.5x SSC for 30 min each at room temperature. To obtain a semiquantitative estimation of gene expression in each muscle, the ISH signals were analyzed directly on macroautoradiographic film. Dehydrated sections were apposed under autoradiographic film (Hyperfilm [3H], Amersham Bioscience) for 14–15 d at room temperature. For microautoradiographical purposes, the slides were dipped in NTB2 nuclear emulsion (Kodak, Paris, France), exposed at 4 C for 7–15 d, and then developed in D19 (Kodak) diluted (1:1) and counterstained with Hemalun eosin (Labonord). Controls of the specificity of the ISH were done with a labeled sense oligonucleotide probe specifically for GHR mRNA and a heterologous probe (chicken uncoupling protein 3 cDNA) for 18S rRNA.
Semiquantification of the ISH.
A semiquantitative analysis of gene expression was performed on more than 50 macroautoradiograms from 10 samples of muscle for each group. Detection of GHR and 18S mRNAs was run through the same hybridization, washing and detection assays to render the signal levels comparable. The levels of mRNA in each sample were determined in at least four separate experiments. Autoradiograms were analyzed under constant parameters, using a densitometric computer imaging system (Qwin software, Leica, Lyon, France). Optical densities for each sample were measured on autoradiograms and on homogenous areas excluding artifacts and were then averaged. The nonspecific signal in each sample was measured using the sense or the heterologous probe and was subtracted from each measurement. A linear relationship (standard curve) with a slope depending on exposure time was found by single regression between OD values of the standards and their corresponding radioactivity. It was then possible to compare the different radioactivity values, which were expressed in arbitrary units, by inserting the OD value of each sample into the standard curve equation.
The density of autoradiographic silver grains was assessed using the Visioscan computerized program (Biocom) interfaced with an Eclipse E-600 microscope (Nikon, Rollay, France) equipped with a charge-coupled device Sony DXC950 camera (Clichy, France). Three sections from each muscle were analyzed for GHR mRNA and 18S rRNA quantification and a total of 600 fibers were considered for each animal. Once the area corresponding to the cellular surface was delimited under bright-field illumination (x20 objective), the computer measured the surface of the area. The grain density per surface unit was measured under a x60 epipolarization objective.
RT-PCR.
Total RNA was extracted using the guanidinium thiocyanate method (22). The amount of RNA was determined by absorbance at 260 nm. One microgram of total RNA was primed using polyT and Moloney murine leukemia virus reverse transcriptase. Reverse transcriptase reaction products were amplified with 30 cycles of PCR on a thermal cycler (Perkin-Elmer Life Science, Courtaboeuf, France) using 1 U/µl Taq DNA Polymerase. PCR was then performed using specific primers of the GHR sequence for the sense (5'-GAG GAG GTG AAC ACC ATC TTG GGC-3') and for the antisense (5'-ACC ACC TGC TGG TGT AAT GTC-3'). A fixed amount of nonhomologous DNA fragment (mimic) containing the GHR primer-templates was coamplified with the target cDNA to normalize tube-to-tube variations in amplification efficiency. The hot start method was employed and each cycle consisted of denaturing at 94 C for 45 sec, annealing at 69 C for 45 sec, and extension at 72 C for 1 min, following with 10 min at 72 C. Amplified products and mimic (691 bp and 533 bp, respectively) were separated and analyzed on a 2% agarose gel stained with ethidium bromide. The relative intensity of the bands was acquired and quantitated by Kodak Digital Science1D Image Analysis Software using a Kodak Digital Science camera (DC 120). The target cDNA-to-mimic ratio was used as a relative estimate of mRNA abundance on account of the linear relationship between the increased amount of target mRNA in the assay and target cDNA-to-mimic ratios.
Statistical analysis
Statistical analysis was performed using one-way ANOVA, followed by Student’s t test. Differences were considered significant at P < 0.05. The levels of the signals obtained after hybridization were expressed as the mean ± SEM.
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Results
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Muscle atrophy and fiber type percentage distribution
Atrophy of the SOL muscle was greater than for the EDL muscle. Compared with control SOL (119.1 ± 5.8 mg), SOL wet weight was significantly lower after 7 (70.8 ± 1.4 mg) and 35 (38.1 ± 5.3 mg) d of unloading. In EDL, only a slight decrease occurred in muscle mass after 7 (109.7 ± 7.6 vs. 130.7 ± 8.2 mg in control rats) and 35 (111.5 ± 9.4 mg) d of hindlimb unloading.
In the control SOL, a slow-twitch muscle, 89.9% of muscle fibers were type I, 1.5% type IIc, and 8.6% type IIa (Table 1
). As previously described (1), structural changes occurred depending on the duration of hindlimb unloading. A decrease in the percentage distribution of type I fibers (–19 and –36% after 7 and 35 d, respectively) was observed with a concomitant increase of type IIc and IIa fibers. In the control EDL muscle, a fast-twitch muscle, 66.9% of muscle fibers were type IIb (Table 1). No significant differences were observed after unloading (Table 1).
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TABLE 1. Influence of 1 and 5 wk of hindlimb unloading (HU) on percentage distribution of fiber types in SOL and EDL muscles
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GHR expression in SOL and EDL muscles
On macroautoradiograms obtained from whole muscle sections of control rats, the ISH signal (GHR mRNA expression) was higher in EDL compared with SOL muscle (Fig. 1). An apparent discrepancy in fiber GHR mRNA expression was due to the different reference area used for the analysis. In single muscle fiber, no significant difference in the ISH signal, i.e. silver grains measured on adjacent sections, was observed among fiber types if the GHR mRNA expression was expressed per fiber cross-sectional area (histochemically characterized by myosin ATPase staining) (Fig. 2, A and B). We should point out that GHR mRNA is not randomly distributed in single fiber sections because GHR mRNA is mainly localized in the cytoplasmic matrix but is not found in the myofibrillar lattice. Consequently, sections of single muscle fibers were hybridized against 18S rRNA as a marker for RNA content according to Habets et al. (23). If the intensity of ISH was estimated per single fiber type 18 S rRNA expression, significant differences in GHR mRNA expression could be observed among different fiber types in SOL and EDL muscles (Fig 3). Type IIa fibers showed a higher GHR mRNA expression than type I, both in SOL (+150%) and EDL (+200%) muscles (Fig. 3). In EDL muscles, the highest GHR mRNA expression was observed in type IIb muscle fibers (Fig. 3).
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FIG. 1. Gene expression of the GHR in SOL and EDL muscle sections detected on macroautoradiograms after 7 and 35 d of hindlimb unloading. *, Significantly different from control, P < 0.05.
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FIG. 2. GHR mRNA expression in different soleus fiber types. A, Cross-sections of rat SOL muscle stained for myosin ATPase after preincubation at pH 4.4, showing slow (type I, colored in black) and fast (type IIa, colored in white) fibers. B, GHR mRNA expression through the ISH on adjacent muscle sections.
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FIG. 3. Semiquantification of GHR mRNA expression per fiber type in SOL and EDL muscles after 7 and 35 d of hindlimb unloading. ISH signal for GHR is reported to 18S rRNA. *, Significantly different from control, P < 0.05.
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In hindlimb-suspended rats, the ISH signal on macroautoradiograms was significantly higher in SOL muscle after 7 (+5%) and 35 (+15%) d of suspension respectively, whereas no significant alterations were reported in EDL muscle (Figs. 1
and 4). GHR cDNA-to-mimic ratio (measured by semiquantitative RT-PCR) was higher in EDL than in SOL (+34%) and also increased in unloaded SOL muscle after 7 d (+170%) and 35 d (+220%) (Fig. 5). However, at single fiber level, when the intensity of the ISH signal was estimated per single fiber type 18S rRNA expression (Fig. 3), the difference in type II vs. type I GHR expression decreased after 7 d in SOL muscle and was abolished after 35 d of unloading in SOL muscle.
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FIG. 4. Autoradiographic distribution of GHR mRNA in SOL muscle. A, Control rats; B, 35 d of hindlimb unloading. The signal indicating GHR mRNAs appears as bright silver grains through epipolarization.
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FIG. 5. Quantification of GHR mRNA expression (expressed as cDNA-to-mimic ratio) using semiquantitative RT-PCR after 7 (A) and 35 d (B) of hindlimb unloading in SOL and EDL muscles. *, Significantly different from control, P < 0.05.
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This normalization occurred earlier in EDL muscle, as no difference in GHR transcript expression was seen between types I, IIa, and IIb fibers by 7 d of unloading. In SOL, GHR expression increased by 74% in type I fibers after 35 d of unloading, whereas in EDL, GHR expression increased by 460% in type I and by 90% in type IIa fibers only after 7 d of unloading (Fig. 3), but because 1) these types were responsible for only a minority of fibers and 2) no change occurred in the percent distribution of unloaded fibers, it did not result in a significant overall increase in EDL GHR transcripts (Fig. 5). In contrast, the higher GHR mRNA expression reported in unloaded SOL muscle, was primarily due to the decrease in the percentage of type I fibers (expressing less GHR) with a concomitant increase in type IIa fibers but also due to the up-regulation of GHR in type I fibers.
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Discussion
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For the first time, this study demonstrated GHR mRNA expression in three rat muscle fiber types, one slow-twitch, oxidative (type I), and two fast-twitch (oxidative-glycolytic, type IIa and glycolytic, type IIb). Without consideration for the fiber type, whole muscle macroautoradiograms showed that an EDL expressed more GHR mRNA than a SOL. When GHR transcript content was expressed per 18S rRNA, marked differences were seen between fiber types I, IIa, and IIb, which resulted in a higher expression of GHR transcripts in fast fibers relative to slow fibers. This differential expression of GHR mRNA between a slow-twitch (SOL) and a fast-twitch muscle (EDL) from normal control rats were consistent with the unloading-induced GHR mRNA up-regulation in the SOL muscle. During muscle atrophy, a general shift occurs in the contractile and enzymatic profiles of a slow-twitch oxidative muscle toward that of a fast-twitch glycolytic one. Interestingly, both unloading (1) and hypophysectomy (24) induced a reduction of the proportion of type I fibers counterbalanced by the appearance of hybrid or intermediate fibers (type IIc) in SOL muscle. We would speculate that a possible feed-back mechanism involving GHR mRNA up-regulation might at least partly compensate for the reduction of GH secretion (25) and the reduced protein synthesis (5) induced by muscle unloading and hypokinesia (decreased motor activity).
In control SOL and EDL muscles, the GHR mRNA expression increased in the order type IIb>IIa>I. During muscle atrophy, differences in fiber GHR expression decreased as if all fibers had elevated their GHR expression from a slow-twitch oxidative to a fast-twitch glycolytic fiber type transition.
Unloading-induced muscle atrophy is associated with an increase in fibers containing double-stranded DNA fragmentation after 14 d of hindlimb unloading (26). A loss of myonuclei occurs, but whole muscle cells are not lost. A recent study shows that muscle atrophy is associated with an activation of an alternative nuclear factor-
B pathway suggesting a mechanism through which atrophying fibers are protected from cell death (27). GH/IGF-I treatment improves the apoptosis associated with hindlimb unloading (28). These observations, combined with the transition from fast (type II) to slow (type I) muscle fibers in hypophysectomized rats after human GH injection (24), suggest a role for GH in countering muscle disuse atrophy. Up-regulation of muscle GHR would lessen fiber apoptosis by initiating a survival signal involving activation of the nuclear factor- B pathway and its targets, Bag-1 and Bcl-2, as reported in Ba/F3 cells (29). The SOL muscle was atrophied to a greater extent than the EDL muscle as reported in previous studies (1, 2). In control SOL muscles, a higher expression of GHR was initially observed in type I fibers, but this obviously did not protect them during unloading. Moreover, GHR mRNA was only up-regulated in type I fibers at 35 d of unloading after most of the soleus atrophy had occurred. In contrast, a rapid (7 d) and greater up-regulation of GHR expression was evidenced in single EDL muscle fibers (types I and IIa), suggesting that protection might have occurred in the unloaded EDL muscle. Thus, the present data suggest that muscle disuse atrophy is associated with a muscle-fiber-type specific GHR mRNA up-regulation mechanism that helps protect atrophying fibers in EDL but might be part of an attempt to repair in SOL muscle.
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Acknowledgments
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The authors acknowledge the help of Prof. C. Duchamp, Dr. J. Lachuer, and Dr. H. Mertani in making available a cDNA encoding 18S rRNA and for stimulating discussions.
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Footnotes
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This work was supported by Grant 02CNES4800000034 from the Centre National d’Etudes Spatiales (to D.D.).
A.H.C. and D.D. contributed equally to this work.
Abbreviations: EDL, Extensor digitorum longus; GHR, GH receptor; ISH, in situ hybridization; SOL, soleus; SSC, standard saline citrate.
Received March 11, 2003.
Accepted for publication May 5, 2003.
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References
|
|---|
- Desplanches D, Mayet MH, Sempore B, Flandrois R 1987 Structural and functional responses to prolonged hindlimb suspension in rat muscle. J Appl Physiol 63:558–563[Abstract/Free Full Text]
- Wittwer M, Fluck M, Hoppeler H, Muller S, Desplanches D, Billeter R 2002 Prolonged unloading of rat soleus muscle causes distinct adaptations of the gene profile. FASEB J 16:884–886[Abstract/Free Full Text]
- Criswell DS, Booth FW, DeMayo F, Schwartz RJ, Gordon SE, Fiorotto ML 1998 Overexpression of IGF-I in skeletal muscle of transgenic mice does not prevent unloading-induced atrophy. Am J Physiol 275:E373–E379
- Grindeland R, Roy RR, Edgerton VR, Grossman EJ, Mukku VR, Jiang B, Pierotti DJ, Rudolph I 1994 Interactive effects of growth hormone and exercise on muscle mass in suspended rats. Am J Physiol 267:R316–R322
- Linderman JK, Gosselink KL, Booth FW, Mukku VR, Grindeland RE 1994 Resistance exercise and growth hormone as countermeasures for skeletal muscle atrophy in hindlimb-suspended rats. Am J Physiol 267:R365–R371
- Roy RR, Tri C, Grossman E J, Talmadge RJ, Grindeland RE, Mukku VR, Edgerton VR 1996 IGF-I, growth hormone, and/or exercise effects on non-weight-bearing soleus of hypophysectomized rats. J Appl Physiol 81:302–311[Abstract/Free Full Text]
- Bichell DP, Kikuchi K, Rotwein P 1992 Growth hormone rapidly activates insulin-like growth factor I gene transcription in vivo. Mol Endocrinol 6:1899–1908[Abstract]
- Isaksson OG, Eden S, Jansson JO 1985 Mode of action of pituitary growth hormone on target cells. Annu Rev Physiol 47:483–499[CrossRef][Medline]
- Kaplan SL 1999 Hormonal regulation of growth and metabolic effects of growth hormone. In: Kosto JL, ed. Handbook of physiology. Oxford: University Press; 129–143
- Scanes CG 1999 Hormones and growth in domestic animals. In: Kosto JL, ed. Handbook of physiology. Oxford: University Press; 99–127
- Flores-Morales A, Stahlberg N, Tollet-Egnell P, Lundeberg J, Malek RL, Quackenbush J, Lee NH, Norstedt G 2001 Microarray analysis of the in vivo effects of hypophysectomy and growth hormone treatment on gene expression in the rat. Endocrinology 142:3163–3176[Abstract/Free Full Text]
- Bazan JF 1990 Structural design and molecular evolution of a cytokine receptor superfamily. Proc Natl Acad Sci USA 87:6934–6938[Abstract/Free Full Text]
- Ihle JN, Witthuhn BA, Quelle FW, Yamamoto K, Silvennoinen O 1995 Signaling through the hematopoietic cytokine receptors. Annu Rev Immunol 13:369–398[CrossRef][Medline]
- Cunningham BC, Ultsch M, DeVos AM, Mulkerrin MG, Clauser KR, Wells JA 1991 Dimerization of the extracellular domain of the human growth hormone receptor by a single hormone molecule. Science 254:821–825[Abstract/Free Full Text]
- Argetsinger LS, Carter-Su C 1996 Mechanism of signaling by growth hormone receptor. Physiol Rev 76:1089–1107[Abstract/Free Full Text]
- Herrington J, Carter-Su C 2001 Signaling pathways activated by the growth hormone receptor. Trends Endocrinol Metab 12:252–257[CrossRef][Medline]
- Zhu T, Goh ELK, Graichen R, Ling L, Lobie PE 2001 Signal transduction via growth hormone receptor. Cell Signal 13:599–616[CrossRef][Medline]
- Morey-Holton ER, Globus RK 2002 Hindlimb unloading rodent model: technical aspects. J Appl Physiol 92:1367–1377[Abstract/Free Full Text]
- Brooke MH, Kaiser KK 1970 Muscle fiber types: how many and what kind? Arch Neurol 23:369–379[Medline]
- Baumbach WR, Horner DL, Logan JS 1989 The growth hormone-binding protein in rat serum is an alternatively spliced form of the rat growth hormone receptor. Genes Dev 3:1199–1205[Abstract/Free Full Text]
- Mertani HC, Morel G 1995 In situ gene expression of growth hormone (GH) receptor and GH binding protein in adult male rat tissues. Mol Cell Endocrinol 109:47–61[CrossRef][Medline]
- Chomczynski P, Sacchi N 1987 Single-step method of RNA isolation by acid guanidium-thiocyanate-phenol-chloroform extraction. Anal Biochem 162:156–159[Medline]
- Habets P, Franco D, Ruijter JM, Sargeant AJ, Sant’Ana Pereira JA, Moorman AF 1999 RNA content differs in slow and fast muscle fibers: implications for interpretation of changes in muscle gene expression. J Histochem Cytochem 47:995–1004[Abstract/Free Full Text]
- Ayling CM, Moreland BH, Zanelli, JM, Schulster D 1989 Human growth hormone treatment of hypophysectomized rats increases the proportion of type-1 fibers in skeletal muscle. J Endocrinol 123:429–435[Abstract]
- Grindeland RE, Grossman EJ, Gosselink KL, Tipton CM, Woodman CR, Mukku VR, Arnaud SB 1993 Endocrine function in the suspended rat. FASEB J 7:3865 (Abstract)
- Allen DL, Linderman JK, Roy RR, Bigbee AJ, Grindeland RE, Mukku V, Edgerton VR 1997 Apoptosis: a mechanism contributing to remodeling of skeletal muscle in response to hindlimb unweighting. Am J Physiol 273:C579–C587
- Hunter RB, Stevenson EJ, Koncarevic A, Mitchell-Felton H, Essig DA, Kandarian S 2002 Activation of an alternative NF-B pathway in skeletal muscle during disuse atrophy. FASEB J 16:529–538[Abstract/Free Full Text]
- Allen DL, Linderman JK, Roy RR, Grindeland RE, Mukku V, Edgerton VR 1997 Growth hormone/IGF-I and/or resistive exercise maintains myonuclear number in hindlimb unweighted muscles. J Appl Physiol 83:1857–1861[Abstract/Free Full Text]
- Jeay S, Sonenshein GE, Postel-Vinay MC, Baixeras E 2001 Growth hormone prevents apoptosis through activation of nuclear factor-B in interleukin-3-dependent Ba/F3 cell line. Mol Endocrinol 14:650–661
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Abstract
Introduction
