The insulin-like growth factors (IGFs) are peptides with sequence similarities to insulin. IGF-1 is mainly secreted by the liver via stimulation of GH (growth hormone); this is the primary mechanism of what is known as the IGF/GH axis.. IGF-1 plays a role in both normal, healthy bodily processes as well as other disease states. Because it plays roles in both cell proliferation and inhibition of apoptosis, IGF-1 is important for both normal and abnormal cell growth. Creaney and Hamilton write the following on the topic of IGF-1 and its role in the body, as well as its potential in diagnosing certain disorders:
IGF-1 is a 7.5 kDa polypeptide that is structurally similar to insulin.50 It induces proliferation, differentiation and hypertrophy of multiple cell lines, in particular skeletal muscle, and has an additional role of facilitating glucose entry into skeletal muscle cells... IGF-1 is secreted as the result of a hypothalamic-pituitary liver axis. The hypothalamus secretes growth hormone-releasing hormone (GHRH), which stimulates the pituitary to release growth hormone, which in turn stimulates the liver to release IGF-1. Like most endocrine systems, the system is controlled by negative feedback, thus in normal individuals, exogenous administration of IGF-1 will lead to suppression of the axis. Whereas growth hormone secretion is pulsatile, with greatly varying levels in a 24-hour period, serum IGF-1 levels are relatively stable within a 24-hour period; hence, measurement of the serum IGF-1 level is now the favoured test for acromegaly or growth hormone deficiency.
High IGF-1 levels are correlated with higher levels of lean body mass. Neuroprotective, myelinatory, synaptogenic, and anti-catabolic effects of IGF-1 are well-documented in human and animal study subjects. Serum IGF-1 levels correlate positively to higher IQ in children. 
IGF-1 is also manufactured in skeletal muscle. A form of IGF-1 known as IGF-1 LR3, when applied from an exogenous source, has been shown to circulate longer and bind to more targets in the body than regular IGF-1 as the body manufactures it; further, Dunshea finds that "long arginine (LR3) IGF-I, has been shown to be more potent than IGF-I in the rat."
Exogenous IGF-1 has been shown to "increase muscle mass and promote muscle cell proliferation, differentiation, and survival."  For this reason, IGF-1 is of great interest to current researchers... IGF-1 affects nearly every cell in the human body.
IGF-1 is a candidate for being used as a neurotrophic agent in what is known as gene therapy to effect new nerve growth in victims of severe trauma who experience nerve damage and related symptoms.  Even though microsurgical techniques have improved vastly in the past decade, IGF-1 offers great potential as a concurrent treatment in addition to current microsurgical techniques due to its ability to not only generate new nerve growth (neurotrophy) but also to promote proliferation of muscle cells in damaged areas. IGF-1 also acts as a survival factor for spinal cord motor neurons, increasing its potential further. 
Rabinovsky writes that "nerve sprouting within skeletal muscles is an essential restorative process in response to an injury or a pathological condition. IGF-1 increases intramuscular nerve sprouting 10-fold when administered subcutaneously to normal adult rats" and also that "IGF-1 is also a potent myogenic factor, promoting myoblast proliferation, myogenic differentiation, and myotube hypertrophy."  Rabinovsky's own studies show that "when the sciatic nerve is injured,increased local expression of IGF-1 in muscle hastens motor nerve and muscle repair." 
Upton et al, "assessed the [IGF-1] complexes as a topical agent in wound healing studies conducted in 3-dimensional in vitro human skin equivalent models, as well as in the treatment of deep partial thickness wounds in two different porcine models. This has revealed that the VN:IGF-I:IGFBP complexes hold promise as a wound healing therapy."  Of interest to other researchers is that significant positive results "were obtained with nanogram doses of growth factors."  IGF-1 plays an integral role in the body's own healing process and binds more strongly to damaged tissue. Other researchers have found that without a hypertrophy stimulus, the muscle-building
effects of IGF-1 are unrealized; this is likely for the same reason that Upton et al found injured tissue strongly attracts IGF-1 binding.In fact, IGF-1 is not even released from skeletal tissue in the absence of exercise. 
IGF-1 is well-studied and there is a research consensus on its effectiveness for "healing of tendon and muscle injuries. According to Creaney and Hamilton, "IGF-1 has been used in isolation by a number of investigators. Animal studies have suggested a role for IGF-1 in both the acceleration and enhancement of healing of tendon and muscle injuries" 
Maetsu et al, in a study on IGF-1 levels in bodybuilders in competition condition, found "data [to] indicate that severe energy restriction to extremely low body energy reserves decreases significantly the concentrations of 3 anabolic pathways despite high protein intake." Maetsu concludes that "Monitoring of insulin and IGF-1 concentration is suggested to prevent losses in muscle mass in energy-restricted conditions" and that "other nutritional strategies might be needed to prevent possible catabolic effect during preparation of bodybuilders to competition." 
Yoshida, et al, demonstrate the converse side of the negative correlation between IGF-1 levels and muscle wasting that Maetsu found:
[...]downregulation of IGF-1 signaling in skeletal muscle played an important role in the wasting effect of Angiotension II. However, the signaling pathways and mechanisms whereby IGF-1 prevents Ang II-induced skeletal muscle atrophy are unknown. Yoshida went on to recommend IGF-1 as a treatment for this muscle wasting.
Yang, et al, corroborate the potential of IGF-1 as an anti-wasting agent:
It was found that H(2)O(2) diminishes muscle cell viability and induces a case-independent apoptotic cell death. Pretreatment with IGF-I protects muscle cells from H(2)O(2)-induced cell death and enhances muscle cells survival.  Protecting muscle cells from oxidative damage presents a potential application in the treatment of the muscle wasting, which appears in many muscle pathologies including Duchenne muscle dystrophy and sarcopenia [age-related muscle loss]. 
As noted previously, IGF-1 acts in nearly every cell in the body, which makes it widely applicable to treat wounds of various types. Results of a study by Kim, et al, "suggest that IGF-1 gene therapy may be applied to corpus cavernosum regeneration. Insulin-like growth factor-1 (IGF-1) promotes the proliferation of penile cavernous smooth muscle cells in the rats. ..." 
It is very important to note that not only do the tissue type (and cell type), as well as type of IGF and dosage, matter greatly in outcome, but also the particular environment in which the ligand is
administered or released. As demonstrated above, the ligand binds preferentially to injured tissue and plays very different roles in different situations; Shavlakadze, et al, drive home this point with a study demonstrating that rats with transgenically altered IGF-1 production levels have greatly increased hypertrophy but only with proper growth stimulus:
"...transgenic mice have increased muscle levels of IGF-1 (approximately 13-26 fold) and show striking muscle hypertrophy (approximately 24-56% increase in mass). ...data demonstrate that
elevated IGF-1 has a hypertrophic effect on skeletal muscle only in growth situations." 
 Targeted Expression of IGF-1 Transgene to Skeletal Muscle Accelerates Muscle and Motor Neuron Regeneration, Eric D. Rabinovsky, The FASEB Journal Express Article doi:10.1096/fj.02-0183fje
 Lecture: A novel IGF:IGFBP:vitronectin complex for treatments of wounds, Z. Upton, Institute of Health and Biomedical Innovation, Queensland University of Technology, Kelvin Grove, Brisbane, Queensland, Australia
 Growth factor delivery methods in the management of sports injuries: the state of play, L Creaney and B Hamilton, Br J Sports Med
 - Hameed, M., Lange, K.H., Andersen, J.L., Schjerling, P., Kjaer, M., Harridge, S.D., Goldspink, G., 2004. The effect of recombinant human growth hormone and resistance training on IGF-I mRNA expression in the muscles of elderly men. J. Physiol. 555, 231-240.
 - Iida, K., Itoh, E., Kim, D.S., del Rincon, J.P., Coschigano,K.T., Kopchick, J.J., Thorner, M.O., 2004. Muscle mechano growth factor is preferentially induced by growth hormone in growth hormone-deficient lit/lit mice. J. Physiol. 560, 341-349.
 Mäestu J, Eliakim A, Jürimäe J, Valter I, Jürimäe T. Anabolic and
Catabolic Hormones and Energy Balance of the Male Bodybuilders During the Preparation for the Competition. J Strength Cond Res. 2010 Mar 17.
Yoshida T, Semprun-Prieto L, Sukhanov S, Delafontaine P. IGF-1 prevents Ang II-induced skeletal muscle atrophy via Akt- and Foxo-dependent inhibition of the ubiquitin ligase Atrogin-1 expression. Am J Physiol Heart Circ Physiol. 2010 Mar 12.
 Kim M, Hwang EC, Park IK, Park K. Insulin-like Growth Factor-1 Gene Delivery May Enhance the Proliferation of Human Corpus Cavernosal Smooth Muscle Cells. Urology. 2010 Mar 4.
 Shavlakadze T, Chai J, Maley K, Cozens G, Grounds G, Winn N, Rosenthal N, Grounds MD. A growth stimulus is needed for IGF-1 to induce skeletal muscle hypertrophy in vivo. J Cell Sci. 2010 Mar 15.
Yang SY, Hoy M, Fuller B, Sales KM, Seifalian AM, Winslet MC. Pretreatment with insulin-like growth factor I protects skeletal muscle cells against oxidative damage via PI3K/Akt and ERK1/2 MAPK pathways. Lab Invest. 2010 Mar;90(3):391-401.
Dunshea FR, Chung CS, Owens PC, Ballard JF, Walton PE. Insulin-like growth factor-I and analogues increase growth in artificially-reared neonatal pigs. Br J Nutr. 2002 Jun;87(6):587-93.
Gunnell D, Miller LL, Rogers I, Holly JM; ALSPAC Study Team. (2005). Association of insulin-like growth factor I and insulin-like growth factor-binding protein-3 with intelligence quotient among 8- to 9-year-old children in the Avon Longitudinal Study of Parents and Children. Pediatrics. Nov;116(5):e681-6.
*The latter article is intended for educational / informational purposes only. THIS PRODUCT IS INTENDED AS A RESEARCH CHEMICAL ONLY. This designation allows the use of research chemicals strictly for in vitro testing and laboratory experimentation only. Bodily introduction of any kind into humans or animals is strictly forbidden by law.