Expansion
Pulsatile secretion controlled by GHRH and somatostatin, acting largely through IGF-1
Expansion
Control
- GHRH stimulates; somatostatin inhibits; ghrelin stimulates
- Secretion is pulsatile, greatest during deep sleep and after exercise, fasting, hypoglycaemia and stress
- Suppressed by glucose, free fatty acids and cortisol
Actions
- Direct: lipolysis, insulin antagonism (so blood glucose rises), protein anabolism
- Indirect through hepatic IGF-1: linear bone growth at the epiphyses, and organ growth
Testing
- IGF-1 is stable and reflects average secretion
- Excess (acromegaly): fails to suppress during an oral glucose tolerance test
- Deficiency: fails to rise during an insulin tolerance test or glucagon stimulation
Clinical patterns: excess before epiphyseal fusion gives gigantism, after fusion gives acromegaly with acral enlargement, coarse features, sweating, carpal tunnel syndrome, hypertension and diabetes. Deficiency in childhood gives short stature with normal proportions; in adults it causes reduced muscle mass, central adiposity and poor quality of life.