I’ve read that serum (blood) binding proteins, mainly IGF-bp3 (insulin-like growth factor, binding protein-3) with the acid labile unit, act as carriers to greatly increase the half-life of the IGF-1 molecule in the blood.
I know that if injected subcutaneous, IGF-1 is cleared from the blood in minutes. If bound to binding proteins, IGF-1 can freely dissociate, acting as a reservoir when needed. I do understand completely that only free drug can interact with receptors, but what is, in your expert opinion, the best form of IGF-1 to take?
The problem is, how do you we know how much IGF-1 (if any) will dissociate from the proposed binding protein (bp3) to actually act to cause growth? At least when you inject free IGF-1, we know that there will be some binding (despite the short half-life) to open IGF-1 receptors. (I suggest individuals try taking their IGF-1 right after training, since damaged muscle tissue will display the greatest density of IGF-1 receptors).
Additionally, long-R3 IGF-1 (an IGF-1 analog that’s manufactured by the Australian company GroPep), can avoid being bound to IGF-1 binding proteins and thus being inactivated. This unique ability enables long-R3 IGF-1 to prolong its serum half-life from 20 minutes to about eight hours.
