Intact Insulin and Insulin-Like Growth Factor-I Receptor Signaling Is Required for Growth Hormone Effects on Skeletal Muscle Growth and Functionin Vivo

Abstract Exogenous sex steroids have altered growth hormone secretion in some domestic species. This study examined whether different physiological concentrations of testosterone alter muscle growth in sheep through modification of the somatotropic axis. The effects of testosterone on growth hormone (GH), insulin-like growth factor-I (IGF-I), estradiol (E2) and cortisol concentrations in growing lambs were evaluated in 20 rams, 20 wethers and 20 wethers receiving subcutaneous testosterone replacement therapy. Two animals from each of the three testosterone status groups were slaughtered at 14-day intervals from 49 to 133 days of age, and then at 28-day intervals until 217 days of age for a total of 10 slaughter ages. Animals were sampled every 10 min for an 8-h period 1 day prior to slaughter to characterize the episodic patterns of GH and testosterone. Immediately after slaughter, the semitendinosus, splenius and triceps brachii muscles were removed, trimmed of adhering fat and connective tissue, and weighed. Testosterone increased the combined muscle weight. GH concentrations decreased during the course of the experiment. However, there was no effect of testosterone on GH mean, baseline, amplitude or GH pulse frequency measured by PULSAR. IGF-I concentrations increased in response to testosterone treatment. Testosterone had no effect on cortisol levels while E2 levels were increased after 133 days. Increased muscle growth due to testosterone appeared to be caused either by a direct effect or by increased levels of IGF-I independent of circulating GH concentrations. Journal of Endocrinology (1996) 150, 391–399

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Regulation of Components of the Ubiquitin System by Insulin-Like Growth Factor I and Growth Hormone in Skeletal Muscle of Rats Made Catabolic with Dexamethasone

Endocrinology ◽

10.1210/endo.140.12.7217 ◽

1999 ◽

Vol 140 (12) ◽

pp. 5635-5641 ◽

Cited By ~ 40

Author(s):

Dionisios Chrysis ◽

Louis E. Underwood

Keyword(s):

Skeletal Muscle ◽

Growth Hormone ◽

Growth Factor ◽

Insulin Like Growth Factor ◽

Factor I ◽

Ubiquitin System ◽

Growth Factor I

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The Effect of Anabolic Steroid Administration on Passive Stretching-Induced Expression of Mechano-Growth Factor in Skeletal Muscle

The Scientific World JOURNAL ◽

10.1155/2013/313605 ◽

2013 ◽

Vol 2013 ◽

pp. 1-5 ◽

Cited By ~ 2

Author(s):

Satoshi Ikeda ◽

Yurie Kamikawa ◽

Akihiko Ohwatashi ◽

Katsuhiro Harada ◽

Akira Yoshida

Keyword(s):

Skeletal Muscle ◽

Growth Factor ◽

Mrna Expression ◽

Anabolic Steroid ◽

Anabolic Steroids ◽

Muscle Growth ◽

Insulin Like Growth Factor ◽

Factor I ◽

Passive Stretching ◽

Growth Factor I

Background. Stretching of skeletal muscle induces expression of the genes which encode myogenic transcription factors or muscle contractile proteins and results in muscle growth. Anabolic steroids are reported to strengthen muscles. We have previously studied the effects of muscle stretching on gene expression. Here, we studied the effect of a combination of passive stretching and the administration of an anabolic steroid on mRNA expression of a muscle growth factor, insulin-like growth factor-I autocrine variant, or mechano-growth factor (MGF).Methods. Twelve 8-week-old male Wistar rats were used. Metenolone was administered and passive repetitive dorsiflexion and plantar flexion of the ankle joint performed under deep anesthesia. After 24 h, the gastrocnemius muscles were removed and the mRNA expression of insulin-like growth factor-I autocrine variant was measured using quantitative real-time polymerase chain reaction.Results. Repetitive stretching in combination with metenolone, but not stretching alone, significantly increased MGF mRNA expression.Conclusion. Anabolic steroids enhance the effect of passive stretching on MGF expression in skeletal muscle.

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