Figure 1 Physiology of the GH-IGF-I Axis. Release of GHRH from the hypothalamus is under the control of somatostatin (inhibitory) and Ghrelin (stimulatory). Alterations in GHRH tone lead to pulsatile release of GH from the anterior pituitary. GH has widespread effects on muscle, fat and in the growth plate. IGF-I is produced in liver and in local tissues in response to GH stimulation. Red lines indicate feedback loops.