The role of the GH-IGF-I axis in the regulation of myocardial growth: from experimental models to human evidence.

A large body of evidence has accumulated to support the concept that the GH–IGF-I axis targets the heart (5–9). In particular, it has been demonstrated that GHRs are largely expressed in the myocardium (9) and that, by interacting with GH, they stimulate the local biosynthesis of IGF-I, which may act in an autocrine or paracrine manner by binding specifically to its high-affinity membrane-associated receptor (Fig. 1). In this regard, it has been shown that myocardial IGF-I expression and content strictly parallel circulating GH levels (5–8). Studies in both animals and humans have provided consistent evidence that the GH–IGF-I axis is involved in the regulation of myocardial structure and function. In particular, a large number of studies have consistently shown that GH and IGF-I are critically involved in the regulation of cardiomyocyte growth.