somatotropin
Meaning of somatotropin: The pituitary's growth signal, released in bursts through the night and doing much of its work through a messenger from the liver.
Definition of somatotropin
Somatotropin is another name for growth hormone, a protein released by the pituitary gland at the base of the brain. In children it drives the lengthening of bone and the growth of most tissues. In adults it continues to shape how the body handles fat, muscle and sugar, freeing fat from stores and opposing the action of insulin.
How is it released?
The pituitary gland does not release this hormone steadily. It arrives in bursts, largest during deep sleep and after exercise, with long quiet stretches in between. Two signals from the hypothalamus above set the pattern, one prompting release and one suppressing it, and the stomach hormone ghrelin adds a further push. The pulsed pattern is why a single blood measurement says little on its own: a low result may simply have been drawn between pulses, so deficiency and excess are assessed with stimulation and suppression tests instead.
What does it actually do?
| Tissue | Effect |
|---|---|
| Growth plates in bone | Lengthening, mostly through IGF-1 made by the liver |
| Fat tissue | Releases stored fat to be used as fuel |
| Muscle | Supports protein building and muscle mass |
| Liver | Produces IGF-1 and releases glucose |
Much of the growth effect is indirect. The hormone instructs the liver to make insulin-like growth factor 1, and that protein does the work at the growth plate. The same arrangement explains why the hormone opposes insulin, since it pushes sugar into the blood rather than into cells.
What happens when there is too much or too little?
Too little in childhood slows growth, so a child drifts away from the height expected for their age while body proportions stay normal. Too little in adulthood is subtler, showing as more body fat, less muscle, reduced strength and low mood. Too much before the growth plates close produces gigantism, and after they close produces acromegaly, in which hands, feet, jaw and internal organs thicken. Nearly all excess comes from a benign pituitary tumor. Growth hormone is the name in ordinary clinical use today.
Is it used as a medicine?
A manufactured version is prescribed for proven deficiency in children and adults, and for a small number of other conditions affecting growth. It is injected, since it is a protein and would be digested if swallowed. It is also misused in sport and marketed as an anti-aging treatment, neither of which is supported by evidence of benefit, and a sustained excess brings the problems seen in acromegaly. Products sold as growth hormone releasers to be taken by mouth do not contain the hormone at all.
Also known as
Used in a sentence
Somatotropin deficiency was confirmed by stimulation testing before replacement was considered.
Good to know
Growth hormone is released in pulses, so a single blood level is uninformative and assessment relies on stimulation or suppression testing together with an IGF-1 measurement.
Word origin
Where “somatotropin” comes from
From the Greek soma, meaning body, and trope, meaning a turning or influence, so a substance directing the growth of the body.