The Hormone: Insulin-like Growth Factor-1

IGF stands for Insulin-like Growth Factor, named so due to its structure being very similar to the hormone insulin, and is one of a group of hormones call somatomedins. Growth hormone (GH) and IGF-1 share many similarities in their modes of action, and this is in part due to the fact that binding of GH to certain GH receptors results in a signalling cascade that leads to the generation of IGF-1. It is through this route that GH exerts its proliferative (proliferation of cells basically means cell growth) effects1. Like GH, IGF-I enhances protein anabolism. Individuals who are normally fed and are administered both IGF-I and GH see no enhanced protein anabolic effect over either compound alone, however in calorie-deprived subjects, GH and IGF-1 appear to work synergistically to enhance a more positive protein balance2. The current trend of thought and research suggests that IGF-1 mediates the protein-anabolic actions of GH in humans3. IGF-1 also has properties including the transport of amino acids into cells and inhibition of protein degradation.

IGF-1 has been shown both in vitro and in vivo that it does not possess the lipolytic (fat mobilising) effects that GH exhibits, probably because there are no functional type-1 IGF-1 receptors found in adipocytes4. This may come as a surprise to many bodybuilders who seem to swear by the fat-loss properties of IGF-1 use; however it is highly unlikely that this arises through direct IGF-1 mediated lipolysis5.

With regards to carbohydrate metabolism, IGF-1 acts much like insulin (no surprise there), and administration of IGF-1 tends towards a hypoglycaemic (low blood sugar) state. Surprisingly though, this does not appear to be completely via the insulin receptor, but probably in addition by way of its own IGF-1 receptor6. IGF-1 is thought to be extremely important in the overall action of insulin on skeletal muscle7. IGF-1 results in improved insulin sensitivity, which is an important point to bear in mind for the bodybuilder who may already use or wish to use insulin. In other words, if you do use IGF-1 and you have not previously used insulin, don't start using it. If you are experienced with insulin and start to take IGF-1, insulin dosages may wish to be lowered as well as increased carbohydrate intake especially after insulin administration.

Use of IGF-1
IGF-1 is not a substance that inexperienced bodybuilders should consider using. Several years of anabolic steroid use is recommended before starting a course of IGF-1, and of course one must be aware of the hypoglycaemic effects of IGF-1. There are other serious risks that can occur with the use of IGF-I, such as increased risk of cancer, accelerated growth of tumours and enlargement of intestinal organs8, 9. For these reasons, it should be re-emphasised that for the inexperienced and novice bodybuilder, IGF-1 should not be taken lightly.

Due to the very short half-life of normal IGF-1 (<10mins) and its highly sensitive and unstable properties, plain (wild-type) IGF-1 is rarely used. Rather, an analogue of IGF-1 referred to as Long R3IGF-1 (LONG™R3IGF-1) is the preferred substance of choice. This analogue has had a substitution for the amino acid arginine (R) at position 3 (hence 'R3') for glutamine, and has been increased in length (hence 'long') by 13 amino acids. Basically these modifications to IGF-1 result in a peptide with lowered binding affinities for proteins that regulate IGF-1, thus increasing the potency of the IGF-1. The other advantage of Long R3IGF-I is its half-life being increased from minutes to several hours. Thus the user can get away using a much smaller amount of Long R3IGF-1 and administration does not have to be as frequent.