Growth Hormone (GH) and IGF-1

What stimulates GH secretion from the anterior pituitary?

GHRH (Growth hormone-releasing hormone)
Ghrelin
Stress, sleep, fasting, exercise

What inhibits GH secretion?

Somatostatin (from hypothalamus)
High IGF-1 levels (negative feedback)

What are the two main actions of GH?

1. Direct metabolic effects
   on muscle, liver, fat

2. Indirect growth effects
   via IGF-1 (cell proliferation, differentiation)

GH is the only pituitary hormone that…

Acts
directly
on peripheral tissues (besides acting via IGF-1)

What is the anabolic effect of GH?

Stimulates growth of soft tissue and bones
Increases cell size and number via IGF-1
Increases protein synthesis
Promotes mineral retention (Ca²⁺, Mg²⁺, phosphate)

What is the paradoxical catabolic effect of GH?

Hyperglycaemic effect
(insulin antagonism)
Increases gluconeogenesis
Inhibits glucose uptake
Increases lipolysis and ketogenesis

What are the indirect growth effects of GH?

Via
IGF-I and IGF-II (somatomedins)
Proliferation of osteoblasts, chondrocytes, bone remodeling

What is the cause of dwarfism in African pygmies?

Congenital deficiency of
IGF-I
and underexpression of GH receptors