Growth hormone is a protein hormone synthesized and released by the anterior pituitary. It regulates body growth and metabolism, acting on tissues directly and partly through insulin-like growth factor 1 produced by the liver and other tissues. Its release is controlled by signals from the hypothalamus, including inhibition by somatostatin.[ref]
This makes “growth” a coordinated physiological response rather than merely a change in one chemical concentration. Growth hormone can initiate signaling in one tissue, while a second circulating signal influences other tissues. Negative feedback connects the resulting signal levels back to their control pathway.[ref]
Anatomy and Physiology 2e by J. Gordon Betts and others. §17.3, hormonal regulation of growth
A revealing molecular experiment determined the structure of human growth hormone bound to the extracellular portions of the growth hormone receptor. The 2.8-angstrom X-ray crystallography structure contained one hormone molecule and two receptor portions. Two different surfaces of the hormone contacted the receptor partners. This provides a concrete example of a signaling molecule organizing a multi-part complex, rather than simply occupying one isolated pocket. The structure supported a model for receptor association; establishing the full sequence of activation in a living biological cell requires additional functional experiments.[ref]
Human growth hormone and extracellular domain of its receptor: crystal structure of the complex by A. M. de Vos and others. abstract, complex composition, interfaces and proposed dimerization mechanism
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