GHRH and somatostatin (arcuate and periventricular nuclei)
Hypothalamus · GHRH Somatostatin Ghrelin
Growth hormone output is the balance of GHRH bursts from the arcuate nucleus against somatostatin tone from periventricular neurones, amplified by ghrelin from the stomach. Because of that balance a random GH level means nothing.
Detail
- Raise GH
- Slow-wave sleep, exercise, fasting, hypoglycaemia, arginine, ghrelin, stress
- Lower GH
- Glucose load, free fatty acids, obesity, somatostatin, and IGF-1 and GH themselves
- Testing
- Deficiency needs a stimulation test (insulin tolerance test is the reference, glucagon if that is unsafe); excess needs failure to suppress on oral glucose
- Drugs
- Octreotide and lanreotide are somatostatin analogues used in acromegaly and neuroendocrine tumours
When it goes wrong
Insulin tolerance test proposed in a patient with ischaemic heart disease or epilepsy
Contraindicated because of induced hypoglycaemia; use the glucagon stimulation test instead
Practise this structure
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