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Anybody know of any studies that show how testosterone affects muscle protein synthesis?
I'm not sure if any exist.
I'm talking about actual [B]biochemical mechanisms[/B], not the results and rate of protein synthesis. I've found plenty showing that it DID increase it, but not HOW.
Thanks for your help guys.
Hi Blast, this may help you. I have also provided the scientific references. In a nutshell and in simple terms, all anabolic factors including Insulin, HGH, IGF and Androgens, ie: Testosterone contribute to blocking the effects of Myostatin and related negative growth factors. All anabolic genetic pathways lead to this gene to block its effects. Satellite cell and stem cell maturation are affected by this pathway. Block myostatin and you will increase protein synthesis.
Mechanisms of androgen action;
The key cellular vector for androgen-associated muscle hypertrophy appears to be the satellite cell (Chen et al. 2005). Immuno-histochemical examination has demonstrated the expression of androgen receptors (ARs) in CD34C cells,
fibroblasts, smoothmuscle cells and satellite cells (Sinha- Hikim et al. 2004). Murine pluripotent C3H10T1/2 cells have been used to demonstrate increased MyoDC and MHCC myotubes following androgen administration, with dynamic effects of an AR antagonist (Artaza et al. 2005). The role of the androgen receptor has been studied using C2C12 myoblast satellite cells transfected with a flagged AR?accelerated myoblast cell differentiation was seen via enhanced myogenin expression (Lee 2002).Using C2C12myoblasts transfected with wild-type or mutant ARs, testosterone induced a variable rate of cell
differentiation or proliferation (Benjamin et al. 2004), androgen action using a gonadotrophin-releasing hormone agonist in young men resulted in a dose?response increase in satellite cell number in muscle biopsy samples (Sinha-Hikim et al. 2003).
Functionally important ARpolymorphisms, including effects on body omposition, have been recently associated with the cytosine adenine guanine (CAG) riplet repeatmotif (Walsh et al. 2005). A pathological lengthening of CAG repeat is seen in Kennedy disease, an X-linked spinobulbar muscular atrophy (Merry 2005). When a cohort of patients with Kennedy disease were analysed in detail, a correlation was found between CAG repeat length and clinical manifestations with O60% subjects showing evidence of androgen insensitivity (Dejager et al. 2002).
There is increasing evidence of androgen action in muscle
interacting with IGF-I. In rat diaphragmatic muscle, a dose dependent increase in IGF-I mRNA expression occurred following exposure to androgen (Lewis et al. 2002). When harvested bovine male satellite cells were treated with various androgen concentrations (using trenbolone), a dose-dependent
increase in IGF-I mRNA expression occurred (Kamanga-Sollo et al. 2004). As yet no data have been generated demonstrating a distinction in dynamics of specific IGF-I isoforms upon androgen administration. Androgenic activity may be directly linked to the IGF-I signalling system with p70s6kinase, found downstream of the Akt/mTOR pathway, a candidate for early evidence is emerging (Xu et al. 2004). A proportion of the anabolic effects of androgens may also be anti-catabolic via an anti-glucocorticoid action (Danhaive & Rousseau 1988, Zhao et al. 2004).
Thanks for that. It's something for me to look at.
Anyone else?
Bump
Does none exist?
Last damn bump...
Would be interesting to see. I'm by no means an expert on what is out there as far as studies, but I haven't seen anything in my reading that I recall as being what you are looking for. :o
I've read that for years the 'establishment' denied testosterone even contributed to increased muscle mass.
That and the anti-steroid propaganda probably made it hard to get funding, so I'd not be surprised if there weren't many studies, or the ones that are out there are in some way disguised.
Kind of like studies on ******* or heroin - not a lot considering its (fairly) widespread use.
Also not a lot of money to be made.