Growth Hormone acts on a number of target tissues and organs, including bones and muscles, adipose (fat) tissue, and the liver, which produces a hormone called Insulin-like Growth Factor I (IGF-1), to further modulate bone and muscle growth.
IGF-1 provides negative feedback to the pituitary to limit GH secretion. Other sources of negative feedback and GH suppression occur through a hormone called Somatostatin, which is produced by both the pancreas and hypothalamus. Somatostatin also directly suppresses GH release by producing Somatotropin Release-inhibitory factor (SRIF).
Stimulation of GH production and secretion occurs through hypothalamic production of Growth Hormone-Releasing Hormone (GH-RH). Positive feedback for GH secretion is also known to occur from a hormone produced in the stomach called Ghrelin. Ghrelin stimulates the appetite leading to increased food intake.
