Figure 5. Potential selective modulation of local GH action in IGF-1R-expression GH target tissues.
A) In IGF-1R-negative tissues (such as liver), GH induces STAT5 signaling and other GH actions, culminating with IGF-1 secretion and endocrine actions, but not local IGF-1 effects. B) In IGF-1R-positive tissues (designated as extrahepatic) the presence of IGF-1R augments GH signaling (as above) and local IGF-1 production, which exerts further local effects via the IGF-1R, thereby augmenting the dynamic range of GH/IGF-1 action without necessarily changing the circulating GH or IGF-1 levels. See the text for discussion.