The effect of recombinant human growth hormone and resistance training on IGF‐I mRNA expression in the muscles of elderly men

Abstract

The expression of two isoforms of insulin-like growth factor-I (IGF-I): mechano growth factor (MGF) and IGF-IEa were studied in muscle in response to growth hormone (GH) administration with and without resistance training in healthy elderly men. A third isoform, IGF-IEb was also investigated in response to resistance training only. The subjects (age 74 ± 1 years, mean ± S.E.M) were assigned to either resistance training with placebo, resistance training combined with GH administration or GH administration alone. Real-time quantitative RT-PCR was used to determine mRNA levels in biopsies from the vastus lateralis muscle at baseline, after 5 and 12 weeks in the three groups. GH administration did not change MGF mRNA at 5 weeks, but significantly increased IGF-IEa mRNA (237%). After 12 weeks, MGF mRNA was significantly increased (80%) compared to baseline. Five weeks of resistance training significantly increased the mRNA expression of MGF (163%), IGF-IEa (68%) and IGF-IEb (75%). No further changes were observed after 12 weeks. However, after 5 weeks of training combined with GH treatment, MGF mRNA increased significantly (456%) and IGF-IEa mRNA by (167%). No further significant changes were noted at 12 weeks. The data suggest that when mechanical loading in the form of resistance training is combined with GH, MGF mRNA levels are enhanced. This may reflect an overall up-regulation of transcription of the IGF-I gene prior to splicing.

Physiological elevation of endogenous hormones results in superior strength training adaptation

“…It has been suggested that GH and cortisol are involved in the regulation of the mRNA expression of IGF-I and myostatin (Rennie et al 2004). This is in line with the findings of increased IGF-IEa and mechano growth factor expression after GH treatment in older subjects (Hameed et al 2004) and myostatin has been shown to be up regulated in response to elevated serum glucocorticoids (Lang et al 2001;Ma et al 2003). However, reviews of the metabolic effects of GH on human skeletal muscle concludes that the balance of evidence suggests there are no major anabolic effects of exogenous recombinant human GH in stimulating muscle protein accretion, muscle size, muscle strength, or muscle fiber characteristics in normal, healthy adult men or women, including the elderly (Rennie 2003;Liu et al 2007;.…”

Modifying muscle mass – the endocrine perspective

“…In studies combining GH and exercise on muscle strength, a trend towards an increase in fat free mass and myosin heavy chain (MHC) isoforms has been demonstrated (Taaffe et al 1996, Lange et al 2002. Recent work focussing on the molecular adaptations to a 12-week training regime in older men found that GH and exercise together increased the IGF-I isoform MGF gene expression more than each individually (Hameed et al 2004). The mechanisms of GH action and intracellular signalling are not fully understood.…”

Effect of administration of oral contraceptives in vivo on collagen synthesis in tendon and muscle connective tissue in young women

“…However, the difference in free IGF-I concentrations within the tissues is novel. IGF-I is expressed in muscle and tendons (1,11,19,51) and has been shown to stimulate tendon collagen synthesis in rabbit fibroblasts (1). The specific roles of the individual IGFBPs are still discussed (13,14).…”