Mechanical load increases muscle IGF-I and androgen receptor mRNA concentrations in humans

Abstract

The mechanism(s) of load-induced muscle hypertrophy is as yet unclear, but increasing evidence suggests a role for locally expressed insulin-like growth factor I (IGF-I). We investigated the effects of concentric (CON) vs. eccentric (ECC) loading on muscle IGF-I mRNA concentration. We hypothesized a greater IGF-I response after ECC compared with CON. Ten healthy subjects (24.4 +/- 0.7 yr, 174.5 +/- 2.6 cm, 70.9 +/- 4.3 kg) completed eight sets of eight CON or ECC squats separated by 6-10 days. IGF-I, IGF binding protein-4 (IGFBP-4), and androgen receptor (AR) mRNA concentrations were determined in vastus lateralis muscle by RT-PCR before and 48 h after ECC and CON. Serum total testosterone (TT) and IGF-I were measured serially across 48 h, and serum creatine kinase activity (CK), isometric maximum voluntary contraction (MVC), and soreness were determined at 48 h. IGF-I mRNA concentration increased 62% and IGFBP-4 mRNA concentration decreased 57% after ECC (P < 0.05). Changes after CON were similar but not significant (P = 0.06-0.12). AR mRNA concentration increased (P < 0.05) after ECC (63%) and CON (102%). Serum TT and IGF-I showed little change. MVC fell 10% and CK rose 183% after ECC (P < 0.05). Perceived soreness was higher (P < 0.01) after ECC compared with CON. Results indicate that a single bout of mechanical loading in humans alters activity of the muscle IGF-I system, and the enhanced response to ECC suggests that IGF-I may somehow modulate tissue regeneration after mechanical damage.

β-Hydroxy-β-Methylbutyrate Did Not Enhance High Intensity Resistance Training-Induced Improvements in Myofiber Dimensions and Myogenic Capacity in Aged Female Rats

“…However, we also observed a strong trend for increased IGF-I mRNA in the non-HMB group (+30%, p = 0.056). Because of this, we could surmise that IGF-I mRNA increased similarly in both experimental groups primarily from the RT stimulus itself, which agrees with numerous investigations demonstrating the induction of muscle IGF-I by high tension loading (Bamman et al, 2001;Kim et al, 2005;Petrella et al, 2006;Sun et al, 2006). For MGF mRNA levels, significant increases were observed in soleus muscles of both the HMB (+32%) and non-HMB (+40%) groups compared to control (p < 0.05).…”

Physiological elevation of endogenous hormones results in superior strength training adaptation

“…Androgen receptor mRNA and protein have been observed to increase after 1-3 strength training sessions where levels of serum testosterone was acutely elevated (Bamman et al 2001;Willoughby and Taylor 2004;Hulmi et al 2008;Spiering et al 2009). Furthermore, administration of testosterone (without strength training) increases the content of androgen receptors in animal muscles (Carson et al 2002;Lee et al 2003) and humans (Ferrando et al 2002).…”

Cellular mechanisms and local progenitor activation to regulate skeletal muscle mass

“…These are IGF-1Ea, which is the liver type or systemic form and IGF-1Ec, also called Mecano Growth Factor (MGF), an autocrine/paracrine form that is particularly interesting as it is expressed in response to mechanical stimuli and cellular damage. Increased muscle loading results in augmented expression of the IGF-1 encoding gene both in humans and animal models (DeVol et al 1990;Bamman et al 2001). MGF expression peaks earlier than IGF-1Ea and after damage or mechanical stress is produced as a pulse lasting only 2 days, then replaced by a longerlasting expression of IGF1Ea (Haddad and Adams 2002;Hill and Goldspink 2003;Haddad and Adams 2004).…”