11th April 2024

Physiology of growth hormone

Released in a pulsatile manner, the production of HGH is controlled in a negative feedback loop, which can be influenced by behavioural factors such as sleep, stress and exercise. Growth hormone-releasing hormone (produced in the hypothalamus) and ghrelin (produced from the stomach when hungry) are the main stimulants that act on the somatotrophs located in the anterior pituitary, resulting in the production/secretion of HGH. Increased HGH levels, in turn, stimulate hepatocytes to produce insulin-like growth factor (IGF-1) which directly reduces the release of HGH and indirectly via somatostatin. HGH also self-regulates its release by inhibiting the production of GHRH.

HGH can directly and indirectly stimulate growth. HGH activates mitogen-activated protein kinases (MAPK), initiating a cascade of protein activations that eventually result in increased gene transcription, replication and cellular division. Indirectly, IGF activates tyrosine kinase-mediated pathways, inhibiting cell apoptosis and increasing cellular division.