GHRH (growth-hormone-releasing hormone)

GHRH (growth-hormone-releasing hormone) is a peptide hormone produced by neurons in the hypothalamus, at the base of the brain. It’s released into a small, dedicated blood supply called the hypophyseal portal system, which carries it directly to the anterior pituitary gland.

What GHRH does

Once it arrives at the pituitary, GHRH binds the GHRH receptor on cells called somatotrophs. That binding signals the somatotrophs to synthesize and release growth hormone (somatotropin) in pulses. GHRH’s release, and therefore growth hormone release, is opposed by a separate hormone called somatostatin — the two work as a push-pull pair that shapes the pulsatile pattern of growth hormone in the blood.

GHRH as a secretagogue

Because its role is to trigger release of another hormone, GHRH is classified as a secretagogue — specifically, a growth-hormone secretagogue. It functions as a receptor agonist at the GHRH receptor, meaning it activates the receptor the way a native signaling molecule is meant to.

GHRH analogs

Several lab-made peptides are described as GHRH analogs because their sequence is modeled on GHRH’s own structure closely enough to bind the same receptor. Sermorelin, for instance, corresponds to the first 29 amino acids of the natural 44-amino-acid GHRH sequence — the fragment that retains the ability to bind and activate the receptor.