There is plenty of scientific literature to show an additive anabolic effect when GH and IGF1 are combined (which of course indicates that they have multiple different paracrine and autocrine effects). GH and IGF1 has a distinct synergistic effect both on ananbolism (and anati-catabilism) as well as the metabolism,
Here are a couple of examples -
http://www.ncbi.nlm.nih.gov/pubmed/9129466
------------conclusions -
GH and IGF-I combined further enhanced fat oxidation while reducing protein catabolism. Serum insulin concentrations were significantly increased by GH but decreased by IGF-I. GH significantly decreased serum total triiodothyronine concentrations and IGF-I significantly decreased serum corticosterone concentrations.
http://www.ncbi.nlm.nih.gov/pubmed/10571453
-----------results and conclusions
RESULTS:
Administration of IGF-I, but not GH, attenuates dexamethasone-induced protein catabolism and increases insulin sensitivity. Simultaneous treatment with GH and IGF-I additively increases the serum concentration of IGF-I, whole-body anabolism, and lipid oxidation. GH or IGF-I when given alone produces similar increases in the serum concentration of IGF-I. However, GH selectively increases skeletal muscle mass whereas IGF-I selectively attenuates the intestinal atrophy and abnormal intestinal ion transport induced by TPN. These tissue-selective anabolic effects of GH and IGF-I are associated with differential increases in protein synthesis in skeletal muscle and jejunum, respectively.
CONCLUSIONS:
Simultaneous treatment with GH and IGF-I may offer the greatest clinical efficacy because of improved nitrogen retention in association with enhanced lipid oxidation and stimulation of protein synthesis in multiple tissue types.