IGF1 and endothelial dysfunction: While results from both preclinical and clinical studies clearly indicate that GH plays a key role in the prevention or recovery of endothelial dysfunction, it is not clear at all which of the effects of GH are due to a direct action of the hormone and which are mediated by IGF-I, because this peptide and its receptors (IGF-IR) are widely expressed in endothelial cells [131].