IGF-1 is actually produced from both Insulin and growth hormone in the liver and other tissues. IGF-1 is made up of 70 amino acids in a chain. Well, when a clever chemist removes the last 3 amino acids in the IGF-1 chain (the N-terminal tri-peptide) it becomes Des (1-3) IGF-1 and 1000% plus more anabolic. Why?
IGF-1 circulates through our blood stream and tissue 24 hours a day, 7 days a week. Unfortunately, most of the IGF-1 is inactive because it is bound by another protein called (get this) IGF-1 Binding Protein-3, or IGF-1-BP-3 for short. Since bound hormones can not fit into and trigger a receptor-site, the majority of circulating and muscle IGF-1 can not trigger an anabolic stimulus. Like tons of cellulite in a porno movie (who watches those?) there is little good stuff happening. However, when IGF-1 is altered and becomes Des (1-3) IGF-1 the binding protein IGF-1-BP-3 can not bind to it and it is totally active. Another reason Des (1-3) IGF-1 is so potent is its unique ability to fit into lactic acid altered IGF-1 receptor sites. (YUP) When we train we burn carbohydrates as a fuel to make cellular ATP. When cells switch to this ATP pathway, the by-product is Lactic Acid. This is of course the cause of most of the burn we feel during intense or higher rep sets. Well, the lactic acid build-up is called acidosis, and it destroys the shape of some receptor-sites for period of time. Therefore some anabolic/anti-catabolic hormones have difficulty merging with their respective receptorsite and triggering a response (such as even unbound IGF-1). Not so with Des (1-3) IGF- 1, the super growth factor. It fits into the IGF-1 receptor-site even after acidosis. Des (1- 3) IGF-1 is unbound, over 10 times more potent than IGF-1, and it picks receptor-site locks. Too bad it has only a few minute active-life.
Did you know that our body's make Des (1-3) IGF-1 naturally? Most un-informed individuals claim other wise, but it is true. When an athlete trains lactic acid builds up in muscle tissue. As we know, there is always IGF-1 / GH present in the blood stream and tissues (including muscle) from prior work-outs and other metabolic factors. That lactic acid burn triggers IGF-1/GH secretion from both prior and present work-outs. Unfortunately, lactic acid destroys some of the IGF-1 present in muscles being trained. But wait, this is good too!
Lactic acid also cuts (truncates) the last 3 amino acids off the 70 amino acid chain of "some" of the surviving IGF-1 and creates Des (I-3) IGF-1. So acidosis increases GH/IGF-1 production in the liver, "unbinds" IGF-1 locally in the muscle being trained (burned), destroys some of the IGF-1, and converts some IGF-1 into Des (I-3) IGF-1. Huh, good deal. And the synthetic form of this super anabolic stuff is beginning to show up on the black market more frequently.
L. Rea (2002) - Chemical Muscle Enhancement Bodybuilders Desk Reference