Growth hormone receptor antagonists
Engineered copies of growth hormone that sit on its receptor without switching it on. They lower IGF-1 in acromegaly.
What they are
Modified growth hormone (GH) proteins that block the GH receptor in the liver and other tissues. They treat acromegaly when surgery, radiotherapy or somatostatin analogues have not controlled the disease. Pegvisomant is the only member in clinical use.
Mechanism of action
GH normally binds its receptor through two sites and brings two receptor chains together in an active shape, which starts JAK-STAT signalling and IGF-1 production. The antagonist carries amino acid changes that weaken the second binding site, so it occupies the receptor but cannot trigger the active change. IGF-1 falls, while GH itself is not suppressed and may rise.
Target: Growth hormone receptor (GHR), a cytokine receptor that signals through JAK2-STAT5
Drugs in this class
Test yourself
Think of the answer, then tap the question to see it.
Why is GH not used to monitor pegvisomant treatment?
Pegvisomant blocks the receptor without lowering GH secretion; GH may even rise. IGF-1 shows whether GH action is controlled.
How does a GH receptor antagonist block signalling?
It binds the receptor through one strong site but its altered second site cannot produce the active receptor shape, so JAK-STAT signalling and IGF-1 production do not start.
Which imaging follow-up do GH receptor antagonists need and why?
Pituitary MRI, because the drug does not shrink the adenoma and loss of feedback could allow it to grow.
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: Pegvisomant for acromegaly (Australian Prescriber (PubMed Central), 2017).
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Representative model, for educational purposes only.